阅读说明：本技术 柔性谐振陷波电路 (Flexible resonant trap circuit ) 是由 约瑟夫·拉塞尔·科雷亚 吉利恩·金特里·黑默 于 2020-01-22 设计创作，主要内容包括：提供了一种柔性谐振陷波电路,该柔性谐振陷波电路包括：传输线,传输线被布置成包括螺旋绕组,螺旋绕组具有第一螺旋绕组段和第二螺旋绕组段；以及电容器,电容器耦合在第一螺旋绕组段与第二螺旋绕组段之间。(There is provided a flexible resonance trap circuit, including: a transmission line arranged to include a helical winding having a first helical winding segment and a second helical winding segment; and a capacitor coupled between the first spiral winding segment and the second spiral winding segment.)

1. A resonance trap circuit comprising:

a conductor wire arranged to include a helical winding portion including a first helical winding segment and a second helical winding segment helically twisted together; and

a capacitor arranged to provide a capacitance between the first and second spiral winding segments.

2. The resonance trap circuit of claim 1,

wherein the flexibility of the spiral winding portion is commensurate with the flexibility of the conductor wire.

3. The resonance trap circuit of claim 1,

wherein the resonant trap has a frequency dependent resistance;

wherein the helical winding portion comprises an axis of symmetry extending longitudinally within the helical winding portion equidistant from the first and second helical winding segments; and is

Wherein the spiral winding portion is capable of bending along the axis of symmetry without substantially altering the frequency attenuation response.

4. The resonance trap circuit of claim 3,

wherein the spiral winding portion is capable of bending up to one hundred and eighty degrees along the axis of symmetry without substantially altering the frequency attenuation response.

5. The resonance trap circuit of claim 1,

wherein the resonant trap has a frequency attenuation response;

wherein the helical winding portion comprises an axis of symmetry extending longitudinally within the helical winding portion equidistant from the first and second helical winding segments; and is

Wherein the spiral winding portion is deformable about the axis of symmetry without substantially altering the frequency attenuation response.

6. The resonance trap circuit of claim 3,

wherein the spiral winding portion is capable of being deformed up to three hundred and sixty degrees about the axis of symmetry without substantially altering the frequency attenuation response.

7. The resonance trap circuit of claim 1,

wherein a thickness of the spiral winding is commensurate with a thickness of the conductor wire.

8. The resonance trap circuit of claim 1,

wherein the thickness of the spiral winding is commensurate with the number of winding segments in the spiral winding portion.

9. The resonance trap circuit of claim 1,

wherein the helical winding portion is arranged to comprise a folded portion defining a junction of the first and second helical winding segments.

10. The resonance trap circuit of claim 1, further comprising:

a conductor material deposited on a portion of the folded portion to adjust an inductance of the spiral winding portion.

11. The resonance trap circuit of claim 1,

wherein the conductor wire segment is arranged to include a folded portion having a one-hundred-eighty degree fold at a junction of the first and second helical winding segments.

12. The resonance trap circuit of claim 1,

wherein the helical winding portion comprises a folded portion at a junction of the first and second helical winding segments;

wherein the first spiral winding segment comprises a first base and extends between the first base and the folded portion; and is

Wherein the second spiral winding segment includes a second base and extends between the second base and the folded portion.

13. The resonance trap circuit of claim 1,

wherein the capacitor comprises a self-capacitance between the first and second spiral winding segments.

14. The resonance trap circuit of claim 1,

wherein the capacitor comprises at least one external capacitor electrically coupled between the first base and the second base.

15. The resonant trap as set forth in claim 1,

wherein the first spiral winding segment comprises one or more respective first inner-facing surface portions;

wherein the second spiral winding segment comprises one or more respective second inner-facing surface portions; and is

Wherein the one or more first inwardly facing surface portions face the one or more second inwardly facing surface portions.

16. The resonance trap circuit of claim 1,

wherein oppositely facing surfaces of the first and second helical winding segments are arranged within the helical portion to self-shield magnetic and electric fields caused by current flow within the helical winding portion.

17. The resonance trap circuit of claim 1,

wherein the conductor line comprises a transmission line and the spiral winding portion comprises a continuous portion of the transmission line.

18. The resonance trap circuit of claim 1,

wherein the conductor line comprises a transmission line comprising a first conductor, a second conductor, and a dielectric material between the first conductor and the second conductor; and is

Wherein the capacitor comprises at least one external capacitor coupled between a portion of the second conductor at the first spiral winding section and a portion of the second conductor at the second spiral winding section.

19. The resonance trap circuit of claim 1,

wherein the conductor wire comprises a coaxial cable comprising an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor;

wherein the capacitor comprises at least one external capacitor coupled between a portion of the outer conductor at the first spiral winding section and a portion of the outer conductor at the second spiral winding section.

20. The resonance trap circuit of claim 1,

wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric.

21. The resonance trap circuit of claim 1,

wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment;

wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric; and is

Wherein at least a portion of the at least two conductors are coupled to the at least one capacitor and at least another portion of the at least two conductors are not coupled to the at least one capacitor.

22. The resonance trap circuit of claim 1,

wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric;

wherein at least a portion of the at least two conductors function as a differential signal line; and is

Wherein at least another portion of the at least two conductors is used as a potential reference for the differential signal line.

23. The resonance trap circuit of claim 1,

wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment;

wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric;

wherein the transmission line comprises a differential line and a ground shield; and is

Wherein at least one capacitor is coupled between a portion of the ground shield at the first spiral winding segment and a portion of the ground shield at the second spiral winding segment.

24. The resonance trap circuit of claim 1,

wherein the at least one capacitor comprises a plurality of capacitive elements.

25. The resonance trap circuit of claim 1,

wherein the at least one capacitor comprises a distributed capacitance between the first and second spiral winding segments.

26. The resonance trap circuit of claim 1,

wherein the conductor wire comprises a coaxial cable comprising an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor; and is

Wherein the at least one capacitor comprises a distributed capacitance supplied by one of the two or more shields of the coaxial cable.

27. The resonance trap circuit of claim 1,

wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment;

wherein the at least one capacitor comprises a dielectric layer comprising first and second conductor layers on respective opposite sides thereof, the first and second conductor layers being arranged such that the first conductor layer mechanically and/or electrically contacts the first spiral winding section and the second spiral winding section mechanically and/or electrically contacts the second spiral winding section.

28. The resonance trap circuit of claim 27,

wherein the dielectric material comprises a flexible dielectric material.

29. The resonance trap circuit of claim 1, further comprising:

a flexible cover surrounding at least a portion of the spiral winding portion and preventing unwinding of the spiral winding portion.

30. The resonance trap circuit of claim 1,

wherein the conductor line comprises a multilayer printed circuit.

31. The resonance trap circuit of claim 30,

wherein the multilayer printed circuit includes a layered dielectric substrate and conductor traces coupled to signal conductors and ground conductors located at different layers within the layered dielectric substrate;

wherein both signal conductor lines and ground conductor lines follow parallel helical paths within the substrate.

32. The resonance trap circuit of claim 30, further comprising:

a rigid layered dielectric substrate or a flexible layered dielectric substrate;

wherein the conductor line comprises a first ground conductor and a second ground conductor located at different layers within the substrate and following a spiral path within the substrate; and is

Wherein the conductor line further comprises a signal conductor located between the first and second ground conductors within the substrate and following a helical path within the substrate.

33. The resonant circuit of claim 1 wherein the resonant circuit is,

wherein the helical winding portion further comprises a third helical winding segment;

wherein the first, second, and third helical winding segments are twisted together, and further comprising:

a capacitance between the second spiral winding segment and the first spiral winding segment or the third spiral winding segment.

34. A receive circuit for a magnetic resonance imaging system, comprising:

a receiving coil;

a transmission line coupled to the receive coil; and

a first resonance trap circuit comprising:

a first portion of the transmission line arranged to comprise a first spiral winding portion; and

a first capacitor arranged to provide a capacitance across a portion of the first spiral winding portion.

35. The receive circuit as set forth in claim 34,

wherein the first capacitor comprises a self-capacitance across the first spiral winding portion.

36. The receive circuit as set forth in claim 34,

wherein the first capacitor comprises at least one external capacitor coupled across the first spiral winding portion.

37. The receive circuit of claim 34, further comprising:

two or more resonance trap circuits, each comprising:

a respective second portion of the transmission line arranged to comprise a second spiral winding portion; and

a respective second capacitor arranged to provide a capacitance across a portion of the second spiral winding portion.

38. The receive circuit as set forth in claim 37,

wherein the first resonant trap and the corresponding second resonant trap have matched frequency attenuation;

wherein the first resonance trap and the corresponding second resonance trap are spaced from each other by no more than a quarter wavelength of a resonance frequency.

39. The receive circuit as set forth in claim 37,

wherein the first resonant trap and the corresponding second resonant trap attenuate different frequencies.

40. The receive circuit as set forth in claim 35,

wherein the first resonance trap and the respective second resonance trap are positioned side-by-side.

41. The receive circuit as set forth in claim 35,

wherein at least one of the first resonance trap and the respective second resonance trap is folded at least one hundred and eighty degrees.

42. The receive circuit as set forth in claim 34,

wherein the receive coil is formed of a flexible material.

43. A receive circuit array pad for a magnetic resonance imaging system, comprising:

a plurality of receive coils arranged such that each receive coil overlies at least a portion of another receive coil;

a plurality of transmission lines, each transmission line coupled to a different receiving coil; and is

Wherein each respective transmission line is arranged to provide a respective first resonance trap circuit comprising:

a respective first portion of the respective transmission line arranged to include a respective first spiral winding portion; and

a respective first capacitor arranged to provide a capacitance across a portion of the respective first spiral winding portion.

44. The receive circuit array pad of claim 43,

wherein the respective first capacitor comprises a self-capacitance across the respective first spiral winding portion.

45. The receive circuit array pad of claim 43,

wherein the respective first capacitors comprise respective at least one external capacitor coupled across the respective first spiral winding portions.

46. The receive circuit array pad of claim 43,

wherein each respective transmission line is arranged to provide a respective second resonance trap circuit comprising:

a respective second portion of the transmission line arranged to comprise a respective second spiral winding portion; and

a respective second capacitor arranged to provide a capacitance across a portion of the respective second spiral winding portion.

47. The receive circuit array pad of claim 46,

wherein respective first and second resonant traps formed by respective transmission lines each attenuate a different frequency;

wherein the respective first and second resonance traps formed by the respective transmission lines are spaced from each other by no more than a quarter wavelength of the resonant frequency.

48. The receive circuit array pad of claim 43,

wherein the receive coil is formed of a flexible material.

49. The receive circuit array pad of claim 44, further comprising:

a housing surrounding the plurality of receive coils, the housing being formed of a flexible material.

50. A method for generating a resonance trap circuit, comprising:

twisting a portion of a transmission line to form a helical winding portion comprising first and second helical winding segments helically twisted together and comprising a folded portion at a junction of the first and second helical winding segments; and

at least one capacitor is coupled between the first and second spiral winding segments.

51. In accordance with the method set forth in claim 50,

wherein the coupling comprises: coupling the capacitors between respective ground shield portions of the transmission line at the respective first and second spiral winding segments.

52. In accordance with the method set forth in claim 50,

wherein the coupled capacitive element is made of a flexible dielectric sheet covered on both sides with a flexible conductive coating;

wherein a flexible capacitive element is twist-wound around the spiral of the transmission line in a roll-like manner such that the profile of the circuit is reduced without shorting the capacitor.

53. In accordance with the method set forth in claim 52,

wherein tightening or loosening said roll wrap of said capacitive element adjusts the second order inductance and capacitance of said element.

54. The method of claim 50, further comprising:

adjusting an inductance of the spiral winding.

55. In accordance with the method set forth in claim 54,

wherein adjusting the inductance of the spiral winding includes adjusting an amount of conductor at the folded portion.

56. In accordance with the method set forth in claim 54,

wherein adjusting the inductance of the spiral winding comprises adjusting a radius of the spiral winding portion.

57. In accordance with the method set forth in claim 54,

wherein adjusting the inductance of the spiral winding comprises adjusting an amount of conductive shielding surrounding the spiral winding.

58. In accordance with the method set forth in claim 54,

wherein adjusting the inductance of the spiral winding comprises adjusting a position at which the capacitor is coupled to the spiral winding.

59. The method of claim 50, further comprising:

a flexible cover is placed around the spiral winding.

60. In accordance with the method set forth in claim 50,

wherein a length of transmission line passes through the spiral winding forming an additional leg of the spiral.

61. In accordance with the method set forth in claim 60,

wherein the transmission line forming the additional leg of the spiral is electrically continuous with the transmission line forming one of the first two legs of the spiral winding.

62. In accordance with the method set forth in claim 60,

wherein a transmission line is added to a spiral winding comprising more than two sections.

63. In accordance with the method set forth in claim 60,

wherein a capacitor is coupled between the ground shield of the additional leg of the spiral and one or more of the original spiral windings.

Background

Resonance trap circuit

A resonant trap is a functional resonant circuit that provides a high impedance at one or more specific frequencies. In the most basic sense, the resonant trap filters out currents in a very narrow frequency band. The inductance and capacitance of the trap can be determined, for example, by lumped elements, circuit board design, or wiring. The inductance and capacitance of the trap together determine the resonant frequency to be filtered by the trapFor example, a resonant trap may be coupled to a single conductor to act as a Radio Frequency (RF) filter for a DC line. The resonant trap can be coupled to other transmission lines having two or more conductors (e.g., coaxial cables, triaxial cables, planar transmission lines, etc.).

A typical resonance trap includes a capacitor coupled in parallel with an inductor. The impedance of a typical resonant trap circuit becomes very high at its resonant frequency. By adding more inductors and capacitors to the circuit, multiple resonances can be obtained. Resonant trap circuits are used in a wide range of RF applications. For example, in some applications, a resonant trap is used to prevent a signal at the resonant frequency of the resonant trap from reaching a load. For example, in a radio tuner application, the resonant trap may have a variable capacitor that may be used to tune the radio receiver to select one of a plurality of broadcast stations. For example, in antenna applications, a resonance trap may be used to isolate one portion of an antenna from another. For example, in MRI applications, the resonance trap circuit may be used in a Magnetic Resonance Imaging (MRI) system to prevent RF excitation signals used to deposit energy into the object/structure from coupling to various transmission lines and cables in the system. Transmission lines are used in MRI to transfer signals from a receiving antenna/coil to the MRI system. These signals are released from the object/structure and used to create an image. Other cables in an MRI system carry digital and analog control signals or power from various peripherals to the system.

Resonance trap circuit in MRI system

Magnetic Resonance Imaging (MRI) utilizes the nuclear spins of the nuclei of interest. Typically, the nuclear spin of hydrogen in water molecules is used to image the human body. During MRI, the use is called B₀The strong, uniform static magnetic field polarizes the nuclei. Magnetically polarized nuclear spins produce magnetic moments in the human body. In steady state, magnetic moment and static magnetic field B₀Are aligned parallel and do not produce useful information. To acquire an image, the magnetic moment is perturbed to a steady state by the excitation signal. During excitation, the RF transmission coil produces a signal called B₁The excitation magnetic field and the static magnetic field B₀Aligned vertically and oscillates at a frequency closely matched to the natural precession of the nuclear spins. The precession frequency-B₀Larmor frequency of protons in field-enabling excitation signal B₁Energy is deposited into the nuclear spin system to cause net rotation of the magnetic moment away from the static magnetic field B₀Of the alignment of (a). B is₁The effectiveness of the field is determined by both the precession frequency and the amplitude and duration of the pulses. In MRI, larmor frequency or precession frequency refers to the precession rate of the magnetic moment of protons around an external magnetic field. The frequency of precession being determined by the magnetic field B₀And the nuclei of interest. The amplitude and duration of the RF pulse determine how far the magnetization will tilt or flip, which is commonly referred to as the flip angle. During receive mode, an RF receive coil tuned to the larmor frequency detects precessional magnetization as it returns to steady state. Precessional magnetization induces a current in the receiving coil via electromagnetic induction. The induced electricityThe flow is an MR signal and represents a mixture of the magnetization of all tissue within the field of view (FOV) from the receive coils. In general, a transmitting RF coil may be used as a receiving RF coil, or alternatively, the receiving RF coil may be a separate receive-only RF coil.

The amplitude of the energy transmitted by the transmitting RF coil is much greater than the amplitude of the energy induced in the RF receiving coil. Without intervention, a receiving coil disposed proximate to the patient's body may be excited during excitation with B₁The field strengths couple, which creates the risk of damaging the receiving coils, and possible injury to the patient from the strong local fields generated. A transmission line used to transmit excitation pulses to a transmit coil or to transmit MR signals from a receive coil may exhibit antenna-like behavior within the system. In general, any wire or cable, such as those used to carry electrical power or digital/analog signals, will exhibit similar behavior. Similar to a resonant receive coil, this may result in a transmission line and B₁Coupling between the fields. Transmission or receiving coil and B₁Any coupling of the fields may cause non-uniformity in the transmit flip angle. An uneven flip angle will reduce the information content within the induced MR signal and can be used as an indication of potential safety issues. To prevent undesired antenna-like behavior that may reduce the information content, a resonant trap is usually coupled to the receiving coil and to the transmission line for carrying the induced MR signal.

In MRI, it is desirable that the excitation and reception be spatially uniform over the imaging volume for better image uniformity. During excitation of a typical MRI system, excitation field uniformity is usually obtained by transmission using a whole-body volumetric RF coil. Such a whole-body transmit coil is typically the largest RF coil in the system and is used to create a uniform B₁A field. However, if a large coil is also used for reception, a lower signal-to-noise ratio (SNR) results, mainly because of its greater distance from the tissue being imaged. Thus, dedicated receive coils of smaller size, which can be easily placed closer to the patient's body, are typically used for reception to improve the SNR from the smaller volume of interest. In practice, well-designed professional RF receive coilsIs mechanically configured to fit as close to the volume of interest as possible and helps to promote both patient handling and comfort.

There is an industry need for flexible, appropriately shaped, comfortable RF receive coils. In order to make these coils safe, a compact frequency trap circuit is accordingly required to prevent B₁The coupling between the field and the inductive element of the transmission or receive coil, the frequency trap circuit being mechanically structured to facilitate patient handling and comfort. More specifically, there is a need for frequency notch circuits that are mechanically flexible enough to accommodate the space adjacent to the patient's anatomy so that they can be positioned near compact receive coils disposed near the patient's anatomy. Flexible and comfortable frequency notch circuits are most useful in cases where they can be bent and twisted without affecting their frequency notch behavior, for example when positioned close to a patient for MRI imaging, and it is accordingly desirable that these circuits are not affected by any changes in bending or positioning.

Disclosure of Invention

In one aspect, a resonance trap is provided, the resonance trap comprising: a conductor wire arranged to include a helical winding portion including a first helical winding segment and a second helical winding segment helically twisted together. The capacitor is arranged to provide a capacitance between the first and second spiral winding segments.

In another aspect, the resonance trap circuit is applied to a magnetic resonance imaging system. Wires for delivering analog control signals or digital control signals and analog image information are arranged within the magnetic field for exciting nuclei in the object of interest. Resonant trap circuits electrically coupled to these wires prevent them from coupling with the transmitted magnetic field.

In another aspect, a receive circuit for a magnetic resonance imaging system is provided. The receive circuit includes a receive coil, a transmission line coupled to the receive coil, and a resonance trap circuit. The resonance trap circuit includes: a portion of a transmission line arranged to include a spiral winding portion; and comprising a capacitor arranged to provide a capacitance across a portion of the spiral winding portion.

In another aspect, a receiving array pad for a magnetic resonance imaging system is provided. The receiving circuit includes: a plurality of receive coils arranged such that each receive coil overlies at least a portion of another receive coil; and includes a plurality of transmission lines, each coupled to a different receiving coil. Each respective transmission line is arranged to provide a respective resonance trap circuit. Each respective resonance trap circuit includes: respective portions of respective transmission lines arranged to comprise respective spiral winding portions; and comprising a respective capacitor arranged to provide a capacitance across a portion of the respective spiral winding portion.

In another aspect, a method for generating a resonance trap circuit is provided. The method includes twisting a portion of the transmission line to form a helical winding portion including first and second helical winding segments helically twisted together and including a fold at a junction of the first and second helical winding segments. The method also includes coupling a capacitor between the first spiral winding segment and the second spiral winding segment.

Drawings

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the office upon request and payment of the necessary fee.

Aspects of the disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Additionally, the present disclosure may repeat reference numerals in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Fig. 1A is an explanatory diagram showing an RF transmit coil and an RF receive coil positioned relative to a patient within an MRI system.

Figure 1B is a partially transparent top view of an example array pad including a receive coil array coupled to a transmission line containing a resonant trap.

Fig. 2 is an illustrative schematic diagram showing an example transmit circuit and an example receive circuit.

Fig. 3 is an illustrative diagram showing a perspective view of an example resonance trap circuit coupled to a transmission line.

Fig. 4A is an illustrative side cross-sectional view of portions of the first and second segments of the example coaxial transmission line of fig. 3 coupled to a capacitor element of a resonant circuit.

Fig. 4B is an end cross-sectional view of a portion of the example coaxial transmission line of fig. 3 coupled to a capacitor element of a resonant circuit.

Figure 5A is an illustrative side view of the spiral winding portion of the example resonant trap of figure 3.

Figure 5B is an illustrative diagram showing a simulated magnetic field map resulting from outer surface current flow within the spiral winding portion of the example resonant trap of figure 3.

Figure 5C is an illustrative diagram showing an example simulation of an outer surface current path within the spiral winding portion of the example resonant trap of figure 3.

FIGS. 6A to 6C are explanatory views showing flip angles in an example homogeneous water-filled region to show a pair B of a receiving coil, transmission line wiring, and resonance trap circuit₁The effect of the stimulus.

Fig. 7A is an illustrative diagram showing a cross-sectional end view of the base of the first and second segments comprising the unassembled arrangement of flexible capacitive sheets and the spiral winding.

Fig. 7B is an explanatory diagram showing the flexible capacitor sheet of fig. 7A, in which the first conductor plate is rolled into contact with the base of the first segment and in which the second conductor plate is rolled into contact with the base of the second segment.

Figure 8A is an illustrative diagram showing an example resonant trap extending in a substantially linear arrangement.

Figure 8B is an illustrative diagram showing a corresponding example frequency attenuation response of the resonant trap of figure 8A.

Figure 9A is an illustrative diagram showing the example resonant trap of figure 8A, wherein the spiral winding is bent at an angle of about one hundred and eighty degrees at about the middle along the length of the spiral winding portion thereof.

Figure 9B is an illustrative diagram showing a corresponding example frequency attenuation response of the folded resonant trap of figure 9A.

Figure 10A is an illustration showing two example resonant traps, each identical to the resonant trap of figure 8A arranged side-by-side.

Figure 10B is an illustrative diagram showing example frequency attenuation for the side-by-side trap of figure 10A.

Figure 11A is an illustrative side view showing an example resonant trap that includes a transmission line folded and woven to create three helical winding segments.

Figure 11B is a simplified layout schematic of a resonant trap showing a folded and woven representation of the three spiral winding segments of figure 11A.

Figure 11C is an exemplary electrical schematic representation of the resonant trap of figure 11A.

Figure 11D is an illustrative diagram showing an example frequency attenuation response for the example resonant trap of figure 11A.

FIG. 12A is an illustrative perspective view of an example printed circuit board resonance trap.

Figure 12B is an illustrative side cross-sectional view of an example printed circuit board resonance trap showing multiple stacked flat conductor layers embedded in a substrate such as a dielectric material.

Figure 12C is an illustrative diagram showing individual cross-sectional views of various stacked conductor layers of an example printed circuit board resonance trap.

FIG. 13 is an illustrative schematic diagram showing example signal currents flowing up, down, and through within the example printed circuit board resonant trap circuit of FIGS. 12A-12C.

Detailed Description

Fig. 1A is an explanatory diagram showing the RF transmission coil 110 and the RF reception coil 112 arranged in the receiver array pad 113 with respect to the patient within the MRI system 100. A subject patient 102 is shown lying on a table 104 within an MRI room 106. Main magnet 108 is disposedArranged to generate a static magnetic field B₀. During excitation mode, one or more transmit coils 110 transmit a magnetic field that is generated perpendicular to the static magnetic field B at the frequency of interest₀B of (A)₁Excitation field pulses of the magnetic field. A plurality of receive coils 112 are positioned in close proximity to the patient's body. After RF excitation, the magnetic flux changes resulting from the precession of the net nuclear magnetization within the subject induce MR currents in the receive coils 112, which can be post-processed to extract frequency, phase and amplitude information used to construct MR images. As explained below, safety considerations typically require at least a minimum spacing, typically about 5 millimeters, between the patient anatomy and the receive coils 112 and associated electronics.

Figure 1B is a partially transparent top view of an example receive coil array pad 113 including a receive coil array 112 coupled to a resonant trap 124. The coil arrays 112-1, 112-2 may be placed within a flexible housing 126, indicated by dashed lines, which flexible housing 126 may be formed of a soft, cushioning material, such as fabric or foam, for comfort and to space the coils and associated circuit components from the patient when placed on the patient's body. For example, the receive coil 112 is formed from a flexible conductive material, such as a flexible wire or, for example, a conductive foil. The first transmission line 128-1 and the second transmission line 128-2 extend between the receive coil array pad 113 and the MRI system 100. The example first set of three first receive coils 112-1 is electrically coupled to the first transmission line 128-1, wherein one of the three first coils 112-1 is located between another two of the first coils 112-1 and wherein each of the three first coils 112-1 partially overlaps an adjacent one of the other two first coils 112-1, e.g., 20 to 25 percent. Similarly, the example second set of three second receive coils 112-2 is electrically coupled to the second transmission line 128-2, wherein one of the three second coils 112-2 is located between another two of the second coils 112-2 and wherein each of the three second coils 112-2 partially overlaps, e.g., 20 to 25 percent, with an adjacent one of the other two first coils 112-2. The example first set of receive coils and the example second set of receive coils are positioned side-by-side with each coil in each set overlapping at least one coil in the other set, but may in practice be placed spaced apart or overlapping and offset.

Multiple array pads 113 may be placed at different locations of the patient's anatomy to capture the magnetic flux generated during precession. This captured flux is transmitted back to the MRI system 100 via transmission lines 128-1, 128-2 for reconstruction to create an image. The transmission lines 128-1, 128-2, which are flexible and coupled to the respective receive coils 112-1, 112-2, respectively, transmit the MR currents induced in the coils 112-1, 112-2 back to the MRI system during precession. The diagram of fig. 1B depicts multiple transmission lines 128-1, 128-2 bundled together tightly to save space. In the example array pad 113, the transmission lines 128-1, 128-2 are bundled into triads, one transmission line coupled to each circular coil element. The individual or bundled transmission lines 128-1, 128-2 may exhibit antenna-like behavior. A respective resonant trap 124 is coupled at the output of each coil 112-1, 112-2 and is at B₁The signal excitation frequencies are coupled along the individual transmission lines 128-1, 128-2 at intervals no more than one quarter wavelength apart. The resonant frequency of each trap 124 matches the excitation frequency. The preamplifier circuit 130 is shown coupled to the transmission line between the pair of resonance trap circuits 124, but may be located at any point along the transmission line.

Thus, it will be understood that the receive coil array pads 113 may be compliant and formed to fit the anatomy of the patient. The receive coils 112-1, 112-2 are formed of a flexible material. The transmission lines 128-1, 128-2 are flexible, and the resonance trap circuit 124 is formed by an arrangement of segments of the transmission lines 128-1, 128-2. Thus, the flexibility and thickness of the resonance trap circuit 124 is commensurate with the flexibility and thickness of the transmission lines 128-1, 128-2. Finally, the receive coils 112-1, 112-2, transmission lines 128-1, 128-2, and resonant trap circuit 124 are housed within a flexible housing 126 formed of a soft foam material.

Fig. 2 is an illustrative schematic diagram showing an example MRI system transmit circuit 202 and an example MRI system receive circuit 204. The example transmit circuit 202 includes a transmit coil 206, an RF power amplifier 207, a pulse generation circuit 208, a digital-to-analog converter (DAC)210 circuit, and a computer system 215. An excitation signal transmission line 214 couples the amplifier 207 and pulse generation circuit 208 to the transmit coil 206. The example receive circuit 204 includes a receive coil 212, an RF power amplifier circuit 218, an analog-to-digital converter (ADC) circuit 220, and a computer system 215. A receive signal transmission line 228 couples the receive coil 212 to the amplifier circuit 218. The receive circuit 204 also includes a first example resonant trap 224a and a second example resonant trap 224b, sometimes referred to as baluns, coupled to a receive transmission line 228. As shown within the dashed line with reference to the resonant trap 224a, each of the first and second resonant traps 224a and 224b includes a parallel combination of a capacitor 225 and an inductor 226 coupled between portions of a receive transmission line 228. It will be appreciated that the resonant trap 224b comprises a similar arrangement of capacitors and inductors (not shown). The first resonant trap 224a is positioned to couple to a portion of the receive transmission line 228 adjacent the receive coil 212. The example first resonant trap 224a is typically placed as close to the receive coil as mechanically possible. The example first resonant trap 224a is used to prevent an inductor (not shown) of the receive coil 212 from appearing in the scanner as part of the receive transmission line 228. An example second resonant trap 224b is shown positioned along the receive transmission line between the amplifier 218 and the ADC 220. In practice, for example, there may be a number of additional resonant traps (not shown) placed on the connection between the receive coil 212 and the amplifier 218 and the connection between the amplifier 218 and the ADC 220. Typically, these resonant traps are placed such that the length of the receive transmission line 228 between the traps is less than a quarter wavelength (relative to the resonant frequency of the scanner). This prevents standing wave behavior on the transmission line. Thus, the location of the trap is generally determined by the total length of the cable/transmission line 228.

It will be understood that the receive circuit 204 of figure 2 represents a single receive coil 212, a single transmission line 228 with corresponding resonant traps 224a, 224b and electronic components (e.g., amplifiers and ADCs). However, as shown in the illustrative figures of fig. 1A-1B, the MRI system 100 generally includes a plurality of receive circuits 204 arranged in an array, each receive circuit 204 including a separate coil and transmission line and corresponding resonant traps and electronics. The coils are tightly packed together in an overlapping configuration to ensure adequate coverage of the precession energy and to minimize coupling between the receive coils. Furthermore, the coil arrangement is subject to safety standards. It will therefore be appreciated that the size and flexibility of the resonant trap co-located with the coil is a factor in arranging the coil for effective operation.

During the excitation mode, the DAC 210 converts a digital signal provided by the computer system 215 into an analog signal that is provided to the pulse generator 208. The pulse generator 208 produces a short excitation pulse signal at the larmor frequency of the MRI system, which is then amplified by the RFPA207 and then transmitted to the patient tissue via the transmit coil 206 to cause a change in the net rotation of the magnetic moment of the tissue nuclei 230. During the excitation mode, the first and second resonant traps 224a, 224b coupled to the receive circuit 204 absorb the common mode current induced in the transmission line 228 by the excitation pulse. During the receive mode, a current is induced in the receive coil at the larmor frequency due to the precessional magnetization 232 of the nuclei 230 in the subject tissue as they relax back to steady state. The sense signal passes down the transmission line 228 as a differential signal to the amplifier circuit 218, which amplifier circuit 218 amplifies the sense excitation signal. The second portion of the transmission line 228 then passes the amplified signal to the ADC 220 where it is converted to digital form for processing at the computer system 215. All received signals are transmitted as differential signals. Here they are depicted as being transmitted along transmission line 228. The first and second resonant traps 224a, 224b are coupled to not interfere with differential signal transmission during the receive mode and only block common mode currents.

Fig. 3 is an explanatory diagram showing a perspective view of an example resonance trap circuit 300. The example resonant trap 300 includes a portion of a receive transmission line 302 that is twisted to form a spiral winding portion 304 to function as an inductor, and includes a capacitor 306 coupled between segments of the spiral winding portion 304. An example resonant trap, also known as a resonant tank circuit or balun, provides a maximum resistance at a selected frequency, referred to as its resonant frequency. In the example resonant trap 300, each of the capacitance and inductance can be adjusted to select a resonant frequency. The example resonant circuit has a resonant frequency selected to provide a maximum resistance at a larmor frequency of the MRI system. The receiving transmission line 302 is mechanically flexible and the spiral winding portion comprising the continuous portion of the receiving transmission line 302 is likewise flexible. The portion of the transmission line that forms the spiral winding portion 304 of the resonant trap determines the flexibility of the resonant trap. Each leg of the helical portion 304 retains its flexibility in its original, non-wound form, however the radius of curvature of the entire helical winding portion 304 is limited by the overall helical winding radius. Figure 4A is an illustrative side cross-sectional view of portions of the first segment portion and the second segment portion of the example transmission line 302 of figure 3 coupled to the capacitor 306 of the resonant trap 300. Figure 4B is an end cross-sectional view of a portion of the example transmission line 302 of figure 3 coupled to the capacitor 306 of the resonant trap 300. The example transmission line 302 includes a first conductor 310 and a second conductor 312. The example transmission line of fig. 4A-4B includes a coaxial transmission line including a first conductor 310 positioned as an inner conductor of the transmission line 302 and a second conductor 312 positioned as an outer conductor of the transmission line 302. The example transmission line 302 includes a dielectric material 314 interposed between the first conductor line 310 and the second conductor line 312 to electrically isolate the first (inner) conductor 310 and the second (outer) conductor 312. Due to the skin effect, the inner surface 316 and the outer surface 318 of the outer (second) conductor 312 appear as electrically separate surfaces, although they are continuous portions of the outer conductor 312. The example capacitor 306 is coupled between respective outer surface portions 318 of the second conductor line 312 at the bases 307a, 307b of opposing spiral winding segments 308a, 308b of the spiral winding. As explained below, the resonant trap prevents current from flowing freely at a selected frequency, for example at the larmor frequency, on the outer surface of the second conductor line.

Referring again to figure 3, the example resonant trap 300 includes a transmission line 302 that is folded and twisted to form a continuous length of spiral winding portion 304. The capacitor 306 is electrically coupled between the portions of the transmission line at the respective first and second bases 307a, 307b of the spiral winding 304 opposite the folded portion 320. The spiral winding portion 304 includes a first spiral winding segment 308a extending between a first base portion 307a of the spiral winding 304 and a folded portion 320 at the apex of the spiral winding 304. The spiral winding 304 includes a second spiral winding segment 308b extending between a second base portion 307b of the spiral winding and a folded portion 320 at the apex of the spiral winding 304. When the spiral winding 304 is arranged to extend in a linear layout, the longitudinal axis 322 extends through the folded portion 320 and between the centers of the first and second spiral winding segments 308a, 308b and between the first and second base portions 307a, 307 b.

The first helical winding segment 308a and the second helical winding segment 308b together have the following radii of curvature: the radius of curvature is at least partially dependent on the radius of curvature of the transmission line 302. In the example resonant trap 300, the minimum radius of curvature of the spiral-wound portion 304 is twice the diameter of the transmission line 302, or when the spiral is tightly wound, the minimum radius of curvature of the spiral-wound portion 304 is the diameter of the spiral-wound portion as a whole. By placing a spacer between the two legs of the spiral, the spiral can be wound less tightly, effectively increasing the radius of the spiral. By reducing the thickness of the outer insulating layer of the transmission line, the helix can be wound more tightly. The minimum radius of curvature for the resonant trap is limited by the diameter of the helix as a whole. The maximum diameter of the spiral is generally application dependent and is a function of the self-shielding properties of the trap required for the application. The self-shielding properties depend on how tightly the resonant trap is wound (twist per length) and how close the two legs of the twist are to each other (helix radius). The particular application determines the level of self-shielding required.

The first transmission line segment 308a and the second transmission line segment 308b, which are components of the continuous transmission line portion, are joined at a junction defined by a folded portion 320. A portion of the outer insulating layer of the transmission line 302 is stripped to allow fine tuning of the inductance. In the example resonant trap 300, an example capacitor 306, which may be an integrated circuit capacitor or a ceramic chip capacitor, for example, electrically couples the first base 307a of the first helical winding segment 308a and the second base 307b of the second helical winding segment 308 b. A portion of the outer insulating layer of the transmission line 302 is also stripped to expose the opposing portions 313a, 313b of the outer surface 318 so that the capacitor 306 can be electrically coupled (e.g., soldered) therebetween. In an alternative example resonant trap, a plurality of individual capacitors (not shown) may be coupled to be distributed longitudinally between the first helical winding segment 308a and the second helical winding segment 308 b. In another alternative embodiment, a single distributed capacitive element may be coupled along the length of the helical twist 304. As explained above, the first helical winding segment 308a and the second helical winding segment 308b each comprise a portion of the continuous transmission line 302.

An external current, sometimes referred to as a common mode current, flows in opposite directions within the first spiral winding segment 308a and the second spiral winding segment 308b of the spiral twist 304. For example, a common mode current may be induced in the resonant trap when a high energy excitation pulse is transmitted by the transmit coil during the excitation mode. Current flows in a first direction within the first spiral winding segment 308a between the first base portion 307a and the folded portion 320. Current flows in a second direction opposite the first direction within the second spiral winding segment between the second base portion 307b and the folded portion 320. In this manner, current flows in either direction along a continuous path on the outer surface 318 of the portion of the transmission line 312 that is twisted to form the helically twisted portion 304, for example, along a path from the base 307a through the first helically wound segment 308a to the folded portion 320, and then along the second helically wound segment 308b to the base 307 b.

The resonant frequency of the resonant tank circuit is determined by the following factors: including the total length of the transmission line included in the helically twisted portion 304, the approximate cross-sectional area of the helically twisted portion 304, the number of turns in the helically twisted portion 304, and the value and location of the capacitor 306. Further, a resonant tank circuit having more than one resonant frequency may be created by providing different capacitors across different regions of the spiral winding portion 304. Additionally, the inductance may depend on the dielectric properties associated with the transmission line 302. During the transmit mode, the inductance of the spiral winding portion 304 in combination with the capacitance of the capacitor 306 form a resonant circuit on the outer conductor surface 318 of the first and second spiral winding segments 308a, 308b to create a high impedance circuit. This high impedance prevents current from flowing freely within the spiral winding portion 304 along the outer surfaces of the first and second spiral winding segments 308a, 308 b. During the receive mode, differential currents flowing in opposite directions along the first (inner) conductor 310 of the transmission line and along the inner surface 316 of the second conductor 312 flow undisturbed through the center of the resonant trap due to the skin effect of the current in the second conductor 312 of the cable. In the example resonant trap 300, the inner surfaces 316 of the first and second conductors 310, 312 act as differential lines to conduct differential signals. The outer surface 318 of the second conductor 312 does not carry (host) differential current, but will serve as a conducting surface to carry common mode current.

While the example transmission line 302 is implemented using a coaxial cable, alternative example resonance trap circuits may include, for example, a triaxial or biaxial cable. Example resonant notch circuits may include planar transmission lines including, but not limited to, for example, striplines, microstrip lines, coplanar waveguides, coplanar strips, slotlines, substrate-integrated waveguides, finlines, image lines, or any multi-layer variation of such lines. Example resonance trap circuits may include balanced lines including, but not limited to, twisted pair, shielded pair, star-twisted four-wire cable, double lead, Leschel line (conductor line), or parallel line or parallel wire transmission lines. For example, an example resonance trap may include a metal or dielectric waveguide. For example, each of the above example transmission lines may be implemented in one or more layers on a flexible printed circuit board, a standard printed circuit board, or created using solution processing (e.g., printed electronics).

Figure 5A is an illustrative side view of the spiral winding portion 304 of the example resonant trap 300 of figure 3. Figure 5B is an illustrative diagram showing a simulated magnetic field map resulting from outer surface current flow within the spiral winding portion 304 of the example resonant trap 300 of figure 3. Figure 5C is an illustration showing an example simulation of an outer surface current path within the spiral winding portion 304 of the example resonant trap 300 of figure 3.

Fig. 5A shows an axis of symmetry 510 extending longitudinally within the spiral winding portion 304, the axis of symmetry 510 being equidistant from the first winding segment 308a and the second spiral winding segment 308 b. Fig. 5B shows a first region of strongest magnetic field 502, indicated in red, and a second region of weakest magnetic field 504, indicated in blue, the first region of strongest magnetic field 502 being located where the surfaces of the opposing spiral winding segments 308a, 308B face each other, and the second region of weakest magnetic field 504 being located where the surfaces of the opposing spiral winding segments 308a, 308B face away from each other. The respective arrows in fig. 5C indicate the current flow direction. The size and color of the arrows indicate the magnitude of the current flow. The larger size arrows indicate a larger magnitude of current flow, and the smaller size arrows indicate a smaller magnitude of current flow. The direction of the arrows indicates the direction of current flow. The red arrows represent the current of maximum magnitude and the blue arrows represent the current of minimum magnitude. The current flows in opposite directions along the opposing spiral winding segments 308a, 308 b. FIG. 5C shows that a larger current flows along the mutually facing surface portions of the opposing spiral winding segments 308a, 308b where the magnetic field is largest; a smaller current flows along the surface portions of the opposing spiral winding segments 308a, 308b that face away from each other where the magnetic field is smallest.

More specifically, electromagnetic simulations of the operation of an example resonant trap circuit show that the external surface current, e.g., induced by the transmission of an excitation pulse, follows the shortest induction path. As shown in fig. 5C, in the case of the example spiral winding 304, the shortest path between the respective first and second base portions 307a, 307b and the folded portion 320 of the spiral winding 304 is a path along the inner facing surface portions of the spirally wound first and second transmission line segments. As shown in fig. 5C, a current such as a common mode current flows in opposite directions along the facing inner surfaces of the first and second spiral winding segments 308a and 308b that are spirally wound. As shown in fig. 5B, the magnetic field generated by the common mode current flow is thus confined to the central portion of the spiral winding 304 between facing portions of the opposing spiral winding segments 308a, 308B. Thus, the resultant magnetic field (residual magnetic field) from each leg 308a, 308b of the spiral winding is self-shielding, rather than radiating. This inherent self-shielding of the spiral winding 304 makes the example resonant circuit 300 less sensitive to external magnetic fields and load variations, and may prevent the resonant circuit 300 from radiating and creating field sensitivity issues. For example, an optional conductive cover formed of a braid, foil or tube may be placed over the entire resonant trap assembly to provide, for example, additional electromagnetic shielding.

The example resonant trap 300 can be tuned by selecting an appropriately sized capacitor 306 for electrically coupling the bases of the first and second helical winding segments 308a, 308 b. The technique of incorporating the capacitor 306 to the spiral winding 304 generally does not affect the performance of the resonant trap circuit 300 as long as a mechanically strong and resilient electrical connection (e.g., soldering, crimping, bonding, etc.) is produced. Resonance frequency compliance of a resonant trapWherein L is the inductance of the resonant trap, dominated by the inductance of the spiral twist, and C, the distributed capacitance of the circuit, comprises the lumped capacitor 306. For fine tuning of the frequency, the position where the capacitor 306 is coupled to the first and second spiral winding segments may be selected prior to splicing to adjust the inductor length, since changing the position of the capacitor changes the length of the spiral and thus the inductance. Further, for fine tuning, a selectable amount of conductive material 324, such as solder, may be added to the folded region 320 at the apex of the spiral winding to adjust the inductance by changing the current flow path to, in effect, adjust, for example, the inductor length. By way of illustration, consider for example that the fold region 320 is a small ring, and the addition of solder will fill some areas of the ring, effectively making the ring smaller, and therefore less inductive. Further, for frequency tuning, the diameter of the spiral winding may be adjusted to modify the overall inductance, for example, by placing a spacer between the first spiral winding segment and the second spiral winding segment, by increasing or decreasing the radius of the winding or the number of turns per length by changing the twist on the spiral winding portion 304, or by changing the thickness of the outer coating on the transmission line. Increasing the pitch increases the radius of the helix and, therefore, the helixCross-sectional area of the spiral. Increasing the radius should increase the inductance, although it does reduce some of the distributed capacitance along the spiral, so its linearity is slightly worse. The capacitance of the lumped capacitive element 306 or the distributed capacitive element may also be adjusted in order to tune the frequency.

For use in MRI, the example resonant trap 300 may be tuned to resonate at the larmor frequency of the scanner. As an example, a resonant tank circuit with a spiral inductor has been tuned to operate at 127MHz, operating on a 3T MRI system. The measured reduction in common mode current is between-10 dB and-30 dB, depending on the cable length, with-15 dB being typical for a resonant circuit with a helical winding length of about 3.5 cm. Thus, an example resonant trap may have a resonant frequency suitable for operation at 3 tesla, which is approximately 127 MHz. An example resonant trap can have a resonant frequency suitable for operation at 1.5 tesla, which is approximately 64 MHz. An example resonant trap may have a resonant frequency suitable for operation at 7 tesla, which is about 300 Mhz. Currently available scanners (non-clinical) include 0.35T to 10.5T (14MHz to 450 MHz). The blocking (block) at these frequencies for these scanners is different and in order to produce a reasonable blocking, the total length, radius and number of turns in the spiral will need to be varied accordingly.

In the example resonant trap 300 tuned to operate at 127MHz, the frequency blocking was measured to be between 10dB and 30 dB. Industry standards for cable traps are also frequency specific, typically: blocking at 3T>Blocking at 15dB/1.5T>20 dB. The amount of blocking also affects B₁Turbulence and coil heating. Sufficient blocking should result in B₁And pass temperature tests per IEC 60601-1 and IEC 60601-2-33 guidelines (fig. 6A-6C).

FIGS. 6A-6C are illustrative diagrams showing flip angles within an exemplary structure consisting of two homogeneous water-filled regions to show a receive coil, transmission line wiring, and a pair of resonant traps B₁The effect of the stimulus. FIG. 6A shows the baseline flip angle in a slice of a region where no receiver coil is present, and can be considered performance-specific "Gold standard ". Fig. 6B to 6C show the flip angles of the same slice directly below the receive coil without and with the resonant trap coupled to the receive coil array (fig. 6B) respectively. The plot produced when the coil has no resonant trap on it (figure 6B) has a larger flip angle deviation from the baseline (figure 6A), while the plot from the receive coil with the resonant trap (figure 6C) is more like the baseline plot (figure 6A). Thus, the absence of resonant traps that absorb excitation energy at the receive coil and/or along the receive transmission line adds non-uniformity B₁The possibility of flip angles, which can reduce MRI results. B is₁Is also considered a safety issue for MRI because B₁Often occurs simultaneously with local changes in SAR. The figure shows that the resonant trap can provide a high impedance block to absorb excitation energy and prevent the receive coil and transmission line from interfering with B₁And (4) exciting.

Fig. 7A-7B are illustrative diagrams showing an alternative example flexible capacitor 700 including a first flexible conductive plate 702a and a second flexible conductive plate 702B separated by a flexible dielectric 704. Fig. 7A is an illustrative diagram showing a cross-sectional end view of respective first and second bases 307A, 307b including an unassembled arrangement of a flexible capacitive layer 700 and first and second segments of a spiral winding. Fig. 7B is an illustrative diagram showing flexible capacitive layer 700 of fig. 7A, wherein first conductor 702a is rolled into contact with first base 307B and wherein second conductor 702B is rolled into contact with second base 307A. More specifically, fig. 7B is an explanatory diagram showing a flexible capacitor arranged such that a first conductor 702a electrically contacts an outer surface 318 of a second conductor 312 at a first base 307a and a second conductor 702B electrically contacts an outer portion 318 of the second conductor 312 at a second base 307B. The flexible capacitor 700 is bonded to the bases 307a, 307b such that an electrically stable connection (e.g., solder) is established. In an example flexible capacitor, a copper clad laminate coating each side of a flexible dielectric material is used as a capacitive element. The flexible capacitor is then soldered to the helically wound transmission line, for example at the junctions 307a, 307b, ensuring that the two plates of the flexible capacitor 702a, 702b are bonded to opposite sides of the helix. The flexible capacitor may then be wound around the spiral, ensuring that no electrical contact is made between 702a and 702 b.

For example, an example flexible capacitor may include first and second conductive plates formed in a flexible Printed Circuit Board (PCB) material. Alternatively, for example, an example flexible capacitor may include first and second conductive plates formed from copper cladding on either side of a flexible dielectric sheet. The value of the example flexible capacitance may be tuned based on one or more factors, such as the material properties of the dielectric, the thickness of the dielectric, and the area of the conductive patch. The capacitance can also vary based on the number of internal conductive layers within the dielectric 704 between the outer conductive surface 702a and the outer conductive surface 702 b. Thus, the flexible capacitor may add another way to tune the resonant frequency of the example resonant trap. For example, since the area of the conductor plate determines the capacitance, tuning of the resonant trap can be achieved by varying the total area of the flexible capacitor (e.g., cutting a piece of capacitance to reduce the area size reduces the capacitance). Additionally, varying the thickness of the dielectric of the flexible capacitor may vary the capacitance. Further, as shown in fig. 7B, the flexible capacitive element 700 may be wound around a portion of the transmission line to reduce the profile of the resonant trap without reducing its flexibility. Further, longer roll winding of the capacitors may allow longer capacitors to be used without shorting the sides together (702a, 702b) or significantly increasing the size/profile of the resonant trap. Arrow 713 indicates how scrolling may optionally continue to wrap.

For example, the flexible capacitive element may exhibit improved mechanical stability, such as improved resistance to damage due to impact. The mechanical limitation of flexible capacitors (under impact) is the bond between the cable and the capacitor, whereas ceramic chip capacitors or integrated circuit capacitors can be more easily broken under impact. The resonant trap with the flexible capacitor may be tuned by cutting a capacitive sheet rolled into contact with the bases of the first and second sections. Thus, the resonant trap with the flexible capacitor can be tuned relatively easily.

Figure 8A is an illustrative diagram showing an example resonant trap 800 having a spiral winding (not visible) enclosed within a cover 802 and including a wound capacitor 804, wherein the spiral winding (under the cover) extends in a substantially linear arrangement. Figure 8B is an illustrative graph showing the measured frequency attenuation response of the corresponding example resonant trap of figure 8A at 127 Mhz. The cover, which may be plastic, for example, prevents the spiral from unwinding.

Figure 9A is an illustrative diagram showing the example resonant trap 800 of figure 8A, wherein the spiral winding (not visible) within the cover 802 is bent at an angle of about one hundred and eighty degrees at about the middle along the length of the spiral winding portion thereof. Figure 9B is an illustrative graph showing the frequency attenuation response measured for a corresponding example of a folded trap at about 127 Mhz. Therefore, the bending of the spiral winding portion of the resonant trap has a small influence on the frequency blocking characteristic. More specifically, the self-shielding provided by the spiral winding portion 304 results in the resonant trap 300, 800 being substantially unaffected by bending along the central axis 510. Furthermore, the self-shielding also results in the resonant trap 300, 800 being substantially unaffected by twisting about the central axis 510. Furthermore, the absence of rigid solid core material within the trap 800 and the absence of rigid faraday cages surrounding the trap 800 allows for flexibility of the windings of the trap so that it can fold without changing its frequency attenuation.

Figure 10A is an illustrative diagram showing two example resonant traps 800A, 800B, each identical to the resonant trap 800 of figure 8A arranged side-by-side. Figure 10B is an illustrative diagram showing the measured frequency attenuation response for a corresponding example of two side-by-side traps 800A, 800B at 127 Mhz. It will be appreciated that the inherent self-shielding of the elastic traps 800A, 800B allows them to be placed in close proximity to each other without altering the frequency attenuation of either of them. The self-shielding of the helical structure 304 makes the resonant trap insensitive to external fields and load variations.

Figure 11A is an illustrative side view showing an example resonant trap 1100, the example resonant trap 1100 including a transmission line folded and woven to create three spiral winding segments 1108a, 1108b, 1108 c. Figure 11B is a simplified layout schematic of the resonant trap 1100 showing a folded and woven representation of three spiral winding segments 1108a, 1108B, 1108 c. The resonant trap 1100 comprises a first folded portion 1120a between the second segment 1108b and the third segment 1108c and comprises a second folded portion 1120b between the third segment 1108c and the first segment 1108 a. To simplify the drawing, the second segment 1108b is shown as a straight line. Figure 11C is an exemplary electrical schematic representation of the resonant trap 1100. The first capacitor 1106a is coupled at the junction between the second segment 1108b and 1120b, and between the first segment 1108a and the third segment 1108 c. The second capacitor 1106b is coupled at the junction between the first segment 1108a and 1120a, the second segment 1108b and the third segment 1108 c. Figure 11D is an illustrative diagram showing corresponding example frequency attenuation responses at 75MHz and 160MHz for the example resonant trap 1100. It will be appreciated that more than three spiral winding segments may be wound within the trap circuit and corresponding capacitor circuits may be provided to add further attenuation response. However, adding more segments increases the stiffness of the trap and decreases the flexibility of the trap. The capacitance and inductance may also be selected in the respective sub-sections to tune each sub-section of the trap to a single frequency, thereby providing an additional point of resistance for common mode current.

Figure 12A is a perspective view of an example Printed Circuit Board (PCB) (hereinafter referred to as 'PCB trap') resonant trap circuit 1200. Figure 12B is an illustrative side cross-sectional view of an example PCB trap 1200 showing a plurality of stacked flat conductive layers embedded in a substrate, such as a dielectric, e.g., a polymer or ceramic material, the example PCB trap 1200 arranged to form respective first and second spiral segments 1208a, 1208B of a spiral winding 1204. The flexibility of the PCB trap is directly related to the flexibility of the substrate layer. If the example PCB trap is printed on a flexible film, such as a polyimide film, the PCB trap will be inherently flexible, whereas if the example PCB trap is printed on a non-flexible film, such as XPC, the PCB trap will not be flexible. Fig. 12C is an explanatory diagram showing six separate cross-sectional views of fig. 12B schematically showing a single stacked conductive layer arranged side by side. The example PCB trap 1200 includes conductive layers 1-6. The conductive layer 1 is at the top of the PCB trap and the conductive layer 6 is at the bottom of the PCB. Each of the substrate layers 1 to 6 is printed on a separate layer of the PCB trap and vias are used to electrically connect the different layers of the PCB together. For example, references to top, bottom, and vertical are used for convenience only and are not intended to be limiting. For example, other example PCB traps (not shown) may include different numbers of layers. It will be appreciated that the PCB trap may comprise a stripline, or microstrip or other microstrip line constructed from a flexible circuit board, for example.

Referring to fig. 12A, the top conductive layer 1 of the PCB trap 1200 includes first and second signal pads 1222 and 1224, including first and second ground pads 1226 and 1228. Capacitor 1230 is not shown. Referring to figure 12B, a first base 1207a of the first spiral segment 1208a of the first spiral segment 307a, similar to the resonant trap 300 of figure 3, extends between the locations of the first signal pad 1222 and the first ground pad 1226 and a vertex portion 1220 of the folded portion 320 of the resonant trap 300, similar to figure 3. A second base 1207b of the second spiral segment 1208b, similar to 307b of the resonant trap 300 of figure 3, extends between the locations of the second signal pad 1224 and the second ground pad 1228 and the apex portion 1220. The first and second spiral segments 1208a, 1208b form a continuous circuit extending through the apex portion 1220 such that, for example, current can flow up one of the first and second spiral segments 1208a, 1208b and down the other. In operation, the first spiral segment 1208a and the second spiral segment 1208b shield external magnetic fields from each other by the same self-shielding mechanism as the resonant trap 300 of figure 3.

Referring to fig. 12B-12C, the spiral winding segments 1208a, 1208B include three conductive traces that pass between layers on the PCB to create the spiral twist. Referring to the first spiral winding segment 1208a as an example, the differential signal passes to the trap at the signal pad input 1222 and the ground pad input 1226, respectively. The signal transmitted to 1222 is then directed to layer 2 through the via and travels along path 1208a, passing between layer 2 and layer 5, to vertex portion 1220. The ground reference passed to the PCB through pad 1226 connects to path 1208a directly on layer 1 and through the via to path 1208a on layer 3. The ground trace then travels 1208a, passing back and forth between layers 1 and 3 and between layers 4 and 6, to vertex 1220. Example conductor layer 1 and example conductor layer 3 are wider than example conductor layer 2 and in the vertical stack configuration of fig. 12B, signal conductor layer 2 serves as a signal conductor trace between ground conductor layer 1 and ground conductor layer 3, and ground conductor layer 1 together with ground conductor layer 3 serve as a ground plane surrounding the signal. Similarly, the example conductor layers 4 and 6 serve as grounds, and the example conductor layer 5 serves as a signal conductor trace. The example conductor layer 4 and the example conductor layer 6 are also wider than the example conductor layer 5, and in the stacked configuration of fig. 12B, the signal conductor layer 5 is located between the ground conductor layer 4 and the ground conductor layer 6.

Each conductor via formed in the substrate material is electrically coupled to a corresponding location of the conductor layers 2 and 5. Each conductor via formed in the dielectric material is also electrically coupled to a respective location of the outer ground conductor layers 1 and 6. The respective conductor vias formed in the dielectric material may also be placed to electrically couple with corresponding locations between the equivalent ground planes 1 and 3 and 4 and 6 (not shown).

The currents in the PCB trap take the shortest path along the conductor layers in the PCB trap 1200 as they are shown in the resonant trap 300 of figure 5C. The ground conductor layers 3 and 4 are the closest to each other facing the inscribed ground layer within the PCB trap and therefore the largest current flow is possible within the ground conductor layers 3 and 4. This is similar to the larger current flow at the inward facing portions of the first and second helical winding segments 308a, 308b of the coaxial cable resonant trap 300 of figure 3, for example. The ground conductor layers 1 and 6 are the outwardly facing layers that are furthest from each other and, therefore, the least current flow is possible within the ground conductor layers 1 and 6. This is similar to, for example, the smaller current flow at the outwardly facing portions of the first and second helical winding segments 308a, 308b of the coaxial cable resonant trap 300 of figure 3.

The ground layer 1 is electrically coupled to the first ground pad 1226. A corresponding via couples the second ground pad 1228 to the ground layer 6. A corresponding via electrically couples the first signal pad 1222 to the signal conductor layer 2. Corresponding vias electrically couple the second signal pads 1224 to the signal conductor layer 5. A first terminal of capacitor 1230 is electrically coupled to ground conductor layer 1 and a via at pad 1230 electrically couples a second terminal of the capacitor to ground conductor layer 6.

Fig. 13 is an illustrative schematic diagram showing example signal currents flowing up, down, and through within the PCB trap 1200 between the signal conductor layer 2 and the signal conductor layer 4. An example current 1340 flows into the PCB through pad 1222 on layer 1 and passes through the via onto layer 2. Current then flows along signal conductor segment 1251 through layer 2 and through via 1351 to signal conductor segment 1252 in layer 5. Current 1340 then flows along signal conductor segment 1252 through layer 5 and through via 1352 to signal conductor segment 1253 in layer 2. Current 1340 then flows along signal conductor segment 1253 through layer 2 and through via 1353 to signal conductor segment 1254 in layer 5. Current 1340 then flows along signal conductor segment 1254 through layer 5 and through via 1354 to signal conductor segment 1255 in layer 2. Note that vias 1354 generally correspond to the fold region 320 at the apex of the spiral winding 300 of fig. 3. Current 1340 then flows along signal conductor segment 1255 through layer 2 and through via 1355 to signal conductor segment 1256 in layer 5. Current 1340 then flows along signal conductor segment 1256, through layer 5 and through via 1356 to signal conductor segment 1257 in layer 2. Current 1340 then flows along signal conductor segment 1257 through layer 2 and through via 1357 to signal conductor segment 1258 in layer 5. The signal is then passed back through the vias to the pads 1224 on layer 1. Example conductor segments 1251, 1252, 1253, and 1254 are part of the first spiral segment 1208 a. Example conductor segments 1255, 1256, 1257, and 1258 are part of the second spiral segment 1208 b. In the color version of fig. 13, the portion of the current path 1340 within the first spiral segment 1208a is color-labeled white, and the portion of the current path 1340 within the second spiral segment 1208b is color-labeled blue. Thus, the example arrangement of signal conductor segments 1251, 1253, 1255, and 1257 in substrate layer 2 and the arrangement of signal conductors 1252, 1254, 1256, and 1258 in substrate layer 5 and the coupling of the segments by vias 1351-1357 such that the current follows a spiral path flow within the substrate material of PCB trap 1200 is similar to the spiral current flow within resonant trap 300 of fig. 3. Those skilled in the art will appreciate that the ground conductor layers 1, 3, 4 and 6 are similarly arranged to follow segments of a spiral ground conductor path within the substrate material of the PCB trap 1200 with conductor segments therebetween.

The example resonance trap circuits 300, 1100, and 1200 have a wide range of applications. Power lines carrying digital or analog power control signals may extend through the magnetic field. For example, an example resonance trap circuit may be used to prevent a power line from acting as an antenna by attenuating signals at magnetic field frequencies in the presence of a magnetic field. The resonant trap essentially cuts the power line into shorter segments that will not resonate in the presence of a magnetic field. For example, the example resonant trap circuit may be used in other Radio Frequency (RF) applications, such as cell phones, RF broadband, laptop computers.

Various examples

Examples of the resonant trap may include:

example 1 includes a resonance trap comprising: a conductor wire arranged to include a spiral winding portion including a first spiral winding segment and a second spiral winding segment that are spirally twisted together; and a capacitor arranged to provide a capacitance between the first and second spiral winding segments.

Example 2 may include the subject matter of example 1, wherein a flexibility of the spiral winding portion is commensurate with a flexibility of the conductor wire.

Example 3 may include the subject matter of example 1, wherein the resonant trap has a frequency dependent resistance; wherein the helical winding portion comprises an axis of symmetry extending longitudinally within the helical winding portion equidistant from the first and second helical winding segments; and wherein the spiral winding portion is capable of bending along the axis of symmetry without substantially altering the frequency attenuation response.

Example 3 may include the subject matter of example 3, wherein the spiral winding portion is capable of bending up to one hundred eighty degrees along the axis of symmetry without substantially changing the frequency attenuation response.

Example 5 may include the subject matter of example 1, wherein the resonant trap has a frequency attenuation response; wherein the helical winding portion comprises an axis of symmetry extending longitudinally within the helical winding portion equidistant from the first and second helical winding segments; and wherein the spiral winding portion is deformable about the axis of symmetry without substantially altering the frequency attenuation response.

Example 6 may include the subject matter of example 3, wherein the spiral winding portion is capable of deforming up to three hundred sixty degrees about the axis of symmetry without substantially changing the frequency attenuation response.

Example 7 may include the subject matter of example 1, wherein a thickness of the spiral winding is commensurate with a thickness of the conductor wire.

Example 8 may include the subject matter of example 1, wherein a thickness of the spiral winding is commensurate with a number of winding segments in the spiral winding portion.

Example 9 may include the subject matter of example 1, wherein the helical winding portion is arranged to include a folded portion, the folded portion defining a junction of the first helical winding segment and the second helical winding segment.

Example 10 may include the subject matter of example 1, further comprising:

a conductor material deposited on a portion of the folded portion to adjust an inductance of the spiral winding portion.

Example 11 may include the subject matter of example 1, wherein the conductor wire segment is arranged to include a folded portion having a one-hundred-eighty degree fold at a junction of the first and second helical winding segments.

Example 12 may include the subject matter of example 1, wherein the helical winding portion comprises a folded portion at a junction of the first helical winding segment and the second helical winding segment; wherein the first spiral winding segment includes a first base and extends between the first base and the folded portion; and wherein the second spiral winding segment includes a second base and extends between the second base and the folded portion.

Example 13 may include the subject matter of example 1, wherein the capacitor comprises a self-capacitance between the first spiral winding segment and the second spiral winding segment.

Example 14 may include the subject matter of example 1, wherein the capacitor comprises at least one external capacitor electrically coupled between the first base and the second base.

Example 15 may include the subject matter of example 1, wherein the first spiral winding segment includes one or more respective first inwardly facing surface portions; wherein the second spiral winding segment comprises one or more respective second inner-facing surface portions; and wherein the one or more first inwardly facing surface portions face the one or more second inwardly facing surface portions.

Example 16 may include the subject matter of example 1, wherein oppositely facing surfaces of the first and second helical winding segments are arranged within the helical portion to self-shield magnetic and electric fields caused by current flow within the helical winding portion.

Example 17 may include the subject matter of example 1, wherein the conductor line comprises a transmission line and the spiral winding portion comprises a continuous portion of the transmission line.

Example 18 may include the subject matter of example 1, wherein the conductor line comprises a transmission line comprising a first conductor, a second conductor, and a dielectric material between the first conductor and the second conductor; and wherein the capacitor comprises at least one external capacitor coupled between a portion of the second conductor at the first helical winding section and a portion of the second conductor at the second helical winding section.

Example 19 may include the subject matter of example 1, wherein the conductor line comprises a coaxial cable comprising an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor;

wherein the capacitor comprises at least one external capacitor coupled between a portion of the outer conductor at the first spiral winding segment and a portion of the outer conductor at the second spiral winding segment.

Example 20 may include the subject matter of example 1, wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric.

Example 21 may include the subject matter of example 1, wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric; and wherein at least a portion of the at least two conductors are coupled to the at least one capacitor and at least another portion of the at least two conductors are not coupled to the at least one capacitor.

Example 22 may include the subject matter of example 1, wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric; wherein at least a portion of the at least two conductors function as a differential signal line; and wherein at least another portion of the at least two conductors serves as a potential reference for the differential signal line.

Example 23 may include the subject matter of example 1, wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the conductor line comprises a transmission line comprising at least two conductors separated by a dielectric; the transmission line comprises a differential line and a grounding shield; and wherein the at least one capacitor is coupled between a portion of the ground shield at the first helical winding section and a portion of the ground shield at the second helical winding section.

Example 24 may include the subject matter of example 1, wherein the at least one capacitor comprises a plurality of capacitive elements.

Example 25 may include the subject matter of example 1, wherein the at least one capacitor comprises a distributed capacitance between the first spiral winding segment and the second spiral winding segment.

Example 26 may include the subject matter of example 1, wherein the conductor line comprises a coaxial cable comprising an outer conductor, an inner conductor, and a dielectric material between the outer conductor and the inner conductor; and wherein the at least one capacitor comprises a distributed capacitance supplied by one of the two or more shields of the coaxial cable.

Example 27 may include the subject matter of example 1, wherein the capacitor comprises at least one external capacitor coupled between the first spiral winding segment and the second spiral winding segment; wherein the at least one capacitor comprises a dielectric layer comprising first and second conductor layers on respective opposite sides thereof, the first and second conductor layers being arranged such that the first conductor layer is in mechanical and/or electrical contact with the first spiral winding section and the second spiral winding section is in mechanical and/or electrical contact with the second spiral winding section.

Example 28 may include the subject matter of example 27, wherein the dielectric material comprises a flexible dielectric material.

Example 29 may include the subject matter of example 1, further comprising: a flexible cover surrounding at least a portion of the spiral winding portion and preventing unwinding of the spiral winding portion.

Example 30 may include the subject matter of example 1, wherein the conductor line comprises a multilayer printed circuit.

Example 31 may include the subject matter of example 30, wherein the multilayer printed circuit includes a layered dielectric substrate and a conductor trace coupled to a signal conductor and a ground conductor, the signal conductor and the ground conductor located at different layers within the layered dielectric substrate; wherein both the signal conductor line and the ground conductor line follow parallel spiral paths within the substrate.

Example 32 may include the subject matter of example 30, further comprising: a rigid layered dielectric substrate or a flexible layered dielectric substrate; wherein the conductor line comprises a first ground conductor and a second ground conductor located at different layers within the substrate and following a spiral path within the substrate; and wherein the conductor line further comprises a signal conductor located between the first and second ground conductors within the substrate and following a helical path within the substrate.

Example 33 may include the subject matter of example 1, wherein the spiral winding portion further comprises a third spiral winding segment; wherein the first, second and third helical winding segments are twisted together, and further comprising: a capacitance between the second spiral winding segment and the first spiral winding segment or the third spiral winding segment.

Examples of the receiving circuit may include:

example 34 includes a receive circuit for a magnetic resonance imaging system, comprising: a receiving coil; a transmission line coupled to the receive coil; and a first resonance trap circuit, the first resonance trap circuit comprising: a first portion of a transmission line arranged to comprise a first spiral winding portion; and a first capacitor arranged to provide a capacitance across a portion of the first spiral winding portion.

Example 35 may include the subject matter of example 34, wherein the first capacitor comprises a self-capacitance across the first spiral winding portion.

Example 36 may include the subject matter of example 34, wherein the first capacitor comprises at least one external capacitor coupled across the first spiral winding portion.

Example 37 may include the subject matter of example 34, further comprising: two or more resonance trap circuits, each comprising: a respective second portion of the transmission line arranged to comprise a second spiral winding portion; and a respective second capacitor arranged to provide a capacitance across a portion of the second spiral winding portion.

Example 38 may include the subject matter of example 37, wherein the first resonant trap and the corresponding second resonant trap have matched frequency attenuation; wherein the first resonance trap and the corresponding second resonance trap are spaced from each other by no more than a quarter wavelength of the resonance frequency.

Example 39 may include the subject matter of example 37, wherein the first resonant trap and the corresponding second resonant trap attenuate different frequencies.

Example 40 may include the subject matter of example 35, wherein the first resonance trap and the respective second resonance trap are located side-by-side.

Example 41 may include the subject matter of example 35, wherein at least one of the first resonance trap and the respective second resonance trap is folded at least one hundred and eighty degrees.

Example 42 may include the subject matter of example 34, wherein the receive coil is formed of a flexible material.

Examples of the receiving circuit array pad may include:

example 43 includes a receive circuit array pad for a magnetic resonance imaging system, comprising: a plurality of receive coils arranged such that each receive coil overlies at least a portion of another receive coil; a plurality of transmission lines, each transmission line coupled to a different receiving coil; and wherein each respective transmission line is arranged to provide a respective first resonance trap, the first resonance trap comprising: a respective first portion of a respective transmission line arranged to comprise a respective first spiral winding portion; and a respective first capacitor arranged to provide a capacitance across a portion of the respective first spiral winding portion.

Example 44 may include the subject matter of example 43, wherein the respective first capacitor comprises a self-capacitance across the respective first spiral winding portion.

Example 45 may include the subject matter of example 43, wherein the respective first capacitors comprise respective at least one external capacitor coupled across the respective first spiral winding portions.

Example 46 may include the subject matter of example 43, wherein each respective transmission line is arranged to provide a respective second resonance trap circuit, the respective second resonance trap circuit comprising: a respective second portion of the transmission line arranged to comprise a respective second spiral winding portion; and a respective second capacitor arranged to provide a capacitance across a portion of the respective second spiral winding portion.

Example 47 may include the subject matter of example 46, wherein respective first and second resonant traps formed from respective transmission lines each attenuate a different frequency; wherein the respective first and second resonance traps formed by the respective transmission lines are spaced from each other by no more than a quarter wavelength of the resonant frequency.

Example 48 may include the subject matter of example 43, wherein the receive coil is formed of a flexible material.

Example 49 may include the subject matter of example 44, further comprising:

a housing surrounding the plurality of receive coils, the housing being formed of a flexible material.

Examples of the manufacturing method may include:

example 50 includes a method for generating a resonance trap circuit, comprising: twisting a portion of the transmission line to form a helical winding portion, the helical winding portion comprising first and second helical winding segments helically twisted together and comprising a folded portion at a junction of the first and second helical winding segments; and coupling at least one capacitor between the first spiral winding segment and the second spiral winding segment.

Example 51 may include the subject matter of example 50, wherein coupling comprises: capacitors are coupled between respective ground shield portions of the transmission lines at the respective first and second spiral winding segments.

Example 52 may include the subject matter of example 50, wherein the coupled capacitive element is made of a flexible dielectric sheet covered on both sides with a flexible conductive coating; wherein the flexible capacitive element is wound around the helical twist of the transmission line in a roll-like manner such that the profile of the circuit is reduced without shorting the capacitor.

Example 53 may include the subject matter of example 52, wherein the second order inductance and capacitance of the roll wound tuning element of the capacitive element is tightened or loosened.

Example 54 may include the subject matter of example 50, further comprising: the inductance of the spiral winding is adjusted.

Example 55 may include the subject matter of example 54, wherein adjusting the inductance of the spiral winding includes adjusting an amount of conductor at the folded portion.

Example 56 may include the subject matter of example 54, wherein adjusting the inductance of the spiral winding comprises adjusting a radius of a portion of the spiral winding.

Example 57 may include the subject matter of example 54, wherein adjusting the inductance of the spiral winding comprises adjusting an amount of conductive shielding around the spiral winding.

Example 58 may include the subject matter of example 54, wherein adjusting the inductance of the spiral winding comprises adjusting a position at which a capacitor is coupled to the spiral winding.

Example 59 may include the subject matter of example 50, further comprising: a flexible cover is placed around the spiral winding.

Example 60 may include the subject matter of example 50, wherein a length of transmission line passes through the spiral winding, forming an additional leg of the spiral.

Example 61 may include the subject matter of example 60, wherein the transmission line forming the additional leg of the spiral is electrically continuous with the transmission line forming one of the first two legs of the spiral winding.

Example 62 may include the subject matter of example 60, wherein the transmission line is added to a spiral winding comprising more than two portions.

Example 61 may include the subject matter of example 60, wherein the capacitor is coupled between the ground shield of the additional leg of the spiral and one or more of the original spiral windings.

The above description is presented to enable any person skilled in the art to create and use a resonant trap. Various modifications to the examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the invention. In the foregoing description, numerous details are set forth for the purpose of explanation. However, it will be appreciated by one of ordinary skill in the art that the examples in the present disclosure may be practiced without these specific details. In other instances, well-known processes are shown in block diagram form in order not to obscure the description of the present invention with unnecessary detail. The use of the same reference symbols in different drawings indicates different views of the same or similar items in different drawings. Accordingly, the foregoing description and drawings of embodiments and examples are merely illustrative of the principles of the invention. It will therefore be appreciated that various modifications may be made to the embodiments by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.