阅读说明：本技术 绝热同轴电缆联接器 (Heat-insulating coaxial cable connector ) 是由 E·布拉肯里奇 C·H·韩 F·L·迟 于 2020-10-28 设计创作，主要内容包括：一种绝热同轴电缆(12a)连接器包括机架(60a)和平面传输线(16),所述平面传输线在所述机架(60a)内并且具有第一端和第二端。所述同轴电缆(12a)连接器进一步包括第一同轴至平面过渡部和第二同轴至平面过渡部,所述第一同轴至平面过渡部在所述机架(60a)内并且连接到所述平面传输线(16)的所述第一端,所述第二同轴至平面过渡部在所述机架(60a)内并且连接到所述平面传输线(16)的所述第二端。(A thermally insulated coaxial cable (12a) connector includes a chassis (60a) and a planar transmission line (16) within the chassis (60a) and having a first end and a second end. The coaxial cable (12a) connector further includes a first coaxial-to-planar transition within the chassis (60a) and connected to the first end of the planar transmission line (16), and a second coaxial-to-planar transition within the chassis (60a) and connected to the second end of the planar transmission line (16).)

1. An insulated coaxial cable (12a) connector comprising:

a frame (60 a);

a planar transmission line (16) within the chassis (60a) and having a first end and a second end;

a first coaxial-to-planar transition within the chassis (60a) and connected to the first end of the planar transmission line (16); and

a second coaxial-to-planar transition within the chassis (60a) and connected to the second end of the planar transmission line (16).

2. The insulated coaxial cable (12a) connector of claim 1, wherein the first and second coaxial-to-planar transitions comprise respective connectors exposed at opposite ends of the rack (60a) and each configured to operatively engage a fitting of a coaxial cable (12 a).

3. The insulated coaxial cable (12a) connector of claim 1, wherein the thermal conductivity of the chassis (60a) is less than 0.300 watts per meter kelvin.

4. The insulated coaxial cable (12a) connector of claim 1, wherein the housing (60a) is formed from plastic.

5. The insulated coaxial cable (12a) connector of claim 1, wherein the planar transmission line (16) is a coplanar waveguide (CPW) and a substrate of the CPW has a thermal conductivity of less than 5 watts per meter kelvin.

6. An insulated coaxial cable (12a) connector comprising:

a first coaxial cable (12a) having a first end;

a second coaxial cable (12a) having a second end;

a coaxial cable (12a) connector comprising a planar transmission line (16), the planar transmission line (16) operatively connected between the first and second ends of the respective first and second coaxial cables (12 a).

7. The insulated coaxial cable (12a) connection system of claim 6, wherein the coaxial cable (12a) connection comprises a chassis (60a) containing the planar transmission line (16), the chassis (60a) having a thermal conductivity of less than 0.300 watts per meter kelvin.

8. The insulated coaxial cable (12a) connection system of claim 7, wherein the planar transmission line (16) comprises a substrate having a thermal conductivity of less than 5 watts per meter kelvin.

9. The insulated coaxial cable (12a) connection system of claim 8, wherein the chassis (60a) is formed from polycarbonate or Acrylonitrile Butadiene Styrene (ABS) and the substrate of the planar transmission line (16) is formed from fused silica or quartz.

10. The insulated coaxial cable (12a) connection system of claim 6, wherein the planar transmission line (16) is a coplanar waveguide (CPW).

Background

There are many examples of situations in testing and measurement where a system under test or Device Under Test (DUT) is subjected to a range of environmental conditions. Typically, test equipment used to measure performance is not subjected to the same conditions, and it is often desirable to isolate the test environment of the DUT from associated test equipment. By this, it can be assumed that the test equipment is independent of the test environment. Conversely, devices that are subjected to environmental stresses may be disassociated from stray thermal paths through connections to external test equipment. Such stray thermal paths may affect the device under test in ways other than the conditions that the test chamber is intended to simulate. Ideally, the device to be tested is isolated from external influences, but this is difficult to achieve if it is also necessary to have a connection to an external test device.

In Radio Frequency (RF) power metering applications, it is essential that the sensing element be completely isolated from the external environment. The primary power standard is used to measure the power terminated in the transmission line. Typically, a temperature increase is sensed in termination and may be associated with the RF power. The efficiency of such a standard is calculated by measuring the temperature rise of the entire assembly compared to that reported by the standard. To provide an effective measure of efficiency, it is important to ensure that there is no thermal path from the power standard to the external environment. The galvanic connection to the standard needs to have a minimum thermal conductivity possible to obtain the best performance.

The National Metrology Institute (NMI) and other academic researchers have investigated this problem. Their solutions consist in pure coaxial structures or rectangular waveguides. The fragility of the center conductor in a coaxial waveguide makes it an extremely difficult component to assemble. In addition, there is a fracture in the external conductor that is required in order to reduce thermal conductivity. In many NMIs, RF and mechanical properties suffer and limit the use of coaxial microcalorimeters to < ═ 18GHz (N-type). Some laboratories insist on using coaxiality up to 50GHz, however their measurement uncertainty is not as good as the rectangular waveguide standard. Rectangular waveguides may be less problematic because only the surface is to be treated.

Disclosure of Invention

According to an aspect of the inventive concept, there is provided a thermally insulated coaxial cable connector. The insulated coaxial cable connector includes a chassis and a planar transmission line within the chassis and having a first end and a second end. The coaxial cable connector further includes a first coaxial-to-planar transition within the chassis and connected to the first end of the planar transmission line and a second coaxial-to-planar transition within the chassis and connected to the second end of the planar transmission line.

The first and second coaxial-to-planar transitions may include respective adapters exposed at opposite ends of the chassis and each configured to operatively engage a fitting of a coaxial cable.

The thermal conductivity of the frame may be less than 0.300 watts per meter kelvin. The chassis may be formed of polycarbonate or Acrylonitrile Butadiene Styrene (ABS).

The planar transmission line may be a coplanar waveguide (CPW), and a substrate of the CPW may have a thermal conductivity of less than 5 watts per meter kelvin. The substrate of the CPW may be formed of at least one of fused silica and quartz.

The frame may include a central body surrounding at least a portion of the planar transmission line, and opposing coupling nuts respectively containing at least a portion of the first and second coaxial-to-planar transitions. At least one of the coupling nuts may be detachably connected to the center body. The central body may be a cylinder extending longitudinally around the planar transmission line.

The planar transmission line may be one of a microstrip or a stripline.

According to another aspect of the inventive concept, an insulated coaxial cable connector is provided. The insulated coaxial cable connector includes a first coaxial cable having a first end and a second coaxial cable having a second end. The insulated coaxial cable connector further comprises a coaxial cable connector comprising a planar transmission line operatively connected between the first and second ends of the respective first and second coaxial cables.

The coaxial cable connector may include a chassis including the planar transmission line, and the chassis may have a thermal conductivity of less than 0.300 watts per meter kelvin.

The planar transmission line may include a substrate having a thermal conductivity of less than 5 watts per meter kelvin.

The chassis may be formed of polycarbonate or Acrylonitrile Butadiene Styrene (ABS), and the substrate of the planar transmission line may be formed of fused silica or quartz.

The planar transmission line may be a coplanar waveguide (CPW).

The planar transmission line may be a microstrip or a stripline.

According to yet another aspect of the inventive concept, an insulation system is provided.

The insulation system comprises: a chamber comprising a chamber wall and defining a thermodynamically controlled process volume; a test sensor located within the thermodynamically controlled processing volume; and an RF generator located outside of the thermodynamically controlled processing space. The insulation system further includes a coaxial cable connector, the coaxial cable connector including: a frame; a planar transmission line within the chassis and having a first end and a second end; a first coaxial-to-planar transition within the chassis and connected to the first end of the planar transmission line; and a second coaxial-to-planar transition within the chassis and connected to the second end of the planar transmission line. The insulation system still further comprises: a first coaxial cable coupled between the test sensor and the first coaxial-to-planar transition of the coaxial cable connector; and a second coaxial cable coupled between the RF generator and the second coaxial-to-planar transition of the coaxial cable connector.

The thermal conductivity of the chassis may be less than 0.300 watts per meter kelvin, and the substrate of the planar transmission line may have a thermal conductivity of less than 5 watts per meter kelvin.

The insulation system may be a microcalorimeter.

Drawings

The above and other aspects and features of the inventive concept will become more apparent from the following detailed description, with reference to the accompanying drawings, in which:

FIG. 1 is a conceptual view of a test system for reference in describing embodiments of the inventive concepts;

fig. 2 is a top view of an insulated coaxial cable connector including a coplanar waveguide (CPW) according to an embodiment of the present inventive concept;

fig. 3A and 3B are cross-sectional views of a coplanar waveguide (CPW) taken along line I-I' of fig. 2, according to embodiments of the inventive concept;

fig. 4 is a cross-sectional view of a microstrip that may constitute a planar transmission line according to an embodiment of the inventive concept;

fig. 5 is a cross-sectional view of a strip line that may constitute a planar transmission line according to an embodiment of the inventive concept;

fig. 6 is a perspective view of a chassis of insulated coaxial cable connectors according to embodiments of the present inventive concept;

fig. 7 and 8 are perspective cut-away views of insulated coaxial cable connectors according to embodiments of the inventive concept;

fig. 9 is a schematic view of a calorimeter according to an embodiment of the inventive concept; and is

Fig. 10 and 11 are graphs illustrating simulated transmission characteristics of an insulated coaxial cable connector according to an embodiment of the inventive concept.

Detailed Description

Throughout the drawings, the same or similar components are identified by the same reference numerals. Separately, it should be noted that the figures are not necessarily drawn to scale. For example, the relative thicknesses of layers may be exaggerated for ease of illustration. Also, while one layer may be shown as being deposited directly on another layer, the inventive concept encompasses the provision of one or more intervening layers, unless otherwise specified. Also, while one component may be shown as being directly coupled to another component, the inventive concept contemplates providing one or more intervening components, unless otherwise noted.

As explained in the description of the embodiments below, the inventive concept provides an insulated coaxial wire by switching signal propagation from coaxial to planar and back to coaxial. The section of the signal in the planar transmission mode is more easily thermally controlled and therefore can be constructed in a robust and repeatable manner to provide an effective thermal isolation barrier. As an example, this planar transmission section may be physically realized by a coplanar waveguide, a microstrip, or a stripline, each of which is formed of a material having an adiabatic property.

Attention is directed to the conceptual view of the test system shown in fig. 1. Reference numeral 101 denotes a controlled test environment that includes a Device Under Test (DUT)10 coupled to or within a sensing device 11. Sensing device 11 senses physical properties of DUT 10 and is in RF communication with external environment 102 via coaxial cable 12 a. The external environment 102 contains the test equipment 15. The controlled test environment 101 is thermally isolated from the external environment 102 by a thermal barrier 13. The test equipment 15 of this example is used to transmit and/or receive RF electrical signals to/from the sensing device 11 via the further coaxial cable 12 b.

In the example of this embodiment, the sensing device 11 is sensitive to thermal fluctuations and it is necessary that the controlled test environment 101 is thermally isolated from the external environment 102. As such, the galvanic connections to the controlled test environment 101 need to have the minimum thermal conductivity possible to obtain the best performance, and devices within the controlled test environment 101 should be decoupled from stray thermal paths through the connections to the devices in the external environment 102. Such stray thermal paths may affect the DUT 10 in ways other than the conditions that the controlled test environment 101 is intended to simulate.

In the example of fig. 1, one such stray thermal path H is a coaxial cable connection (including cables 12a and 12b) between sensing device 11 and testing device 15. To enhance the thermal insulation properties of the connection, at least some embodiments herein feature converting coaxial signal propagation to/from the sensor 11 to planar propagation at or near the barrier between the controlled test environment 101 and the external environment 102, and then back to the test equipment 15. This is represented in fig. 1 by a planar transmission line 16. The planar transmission line 16 (i.e., where the signal is in a planar transmission mode) is more readily thermally controlled while at the same time providing excellent RF (or microwave) transmission properties. This allows for the insertion of an insulating barrier (as represented by X in fig. 1) with advantageous RF transmission characteristics between the controlled test environment 101 and the external environment 102.

FIG. 2 is a top schematic view of an embodiment of an insulated coaxial connector according to embodiments of the present inventive concept; in an example of this embodiment, the planar transmission line is implemented by a coplanar waveguide (CPW). Coplanar waveguides are known to have excellent microwave frequency transmission properties and offer the advantage of being easy to manufacture and replicate using well-established printed circuit board technology.

Referring to fig. 2, the CPW includes a center conductor 22 printed onto the surface of the dielectric substrate 21, and a pair of ground (return) conductors 23a and 23b on either side of the center conductor 22. The center conductor 22 is used for signal transmission. All three conductors 22, 23a and 23b are on the same side of the thin film dielectric substrate 21 and are therefore coplanar. The ground conductors 23a and 23b are separated from the center wire 22 by a small gap, which may be constant along all or part of the length of the center wire 22. In the example shown in fig. 2, the gap flares outward at the opposite end of the center conductor 22, but the inventive concept is not limited in this manner.

Fig. 3A is a cross-sectional view taken along line I-I of the CPW of fig. 2, according to an embodiment of the inventive concept. As shown, the CPW includes a thin film dielectric substrate 21. On the upper surface of the thin-film dielectric substrate 21 are a center wire 22 and a pair of ground conductors 23a and 23b located on opposite sides of the center wire 22.

Fig. 3B is a cross-sectional view taken along line I-I of the CPW of fig. 2 according to another embodiment of the inventive concept. As in the example of fig. 3A, the CPW of this embodiment is a thin film dielectric substrate 21 having a center wire 22 and a pair of ground conductors 23A and 23b on its upper surface. The embodiment of figure 3B differs from that of figure 3A by an additional ground plane conductor 23c located on the lower surface of the thin film dielectric substrate 21. Although not shown, the ground plane 23c may be electrically coupled to the ground conductors 23a and 23b by conductive vias extending through the thin film dielectric substrate 21.

Returning to fig. 2, the CPW is connected at opposite ends to a first coaxial cable CC1 and a second coaxial cable CC 2. The first coaxial cable CC1 includes a center conductor 31a, a tubular conductive shield 32a, and a tubular insulating layer 33a between the center conductor 31a and the tubular conductive shield 32 a. Likewise, the second coaxial cable CC2 includes a center conductor 31b, a tubular conductive shield 32b, and a tubular insulating layer 33b between the center conductor 31b and the tubular conductive shield 32 b. The inventive concept is not limited to any particular configuration or material construction of coaxial cables CC1 and CC 2. For example, the center conductors 31a and 31b may be solid or stranded, and may be gold or silver plated. As another example, tubular insulation layers 33a and 33b may be plastic or some other insulation material, and may include air gaps. As yet another example, the tubular conductive shield may be solid or braided, and may be formed of copper or some other metal.

Still referring to fig. 2, a thermally insulated coaxial cable connection is established by electrically connecting the center conductor 31a of the first coaxial cable CC1 to one end of the center conductor 22 of the CPW, and by electrically connecting the center conductor 31b of the second coaxial cable CC2 to the other end of the center conductor 22 of the CPW. Further, the tubular conductive shield 32a of the first coaxial cable CC1 is electrically connected to the ground conductors 23a and 23b at one end of the CPW, and the tubular conductive shield 32b of the second coaxial cable CC1 is electrically connected to the ground conductors 23a and 23b at the other end of the CPW. These connections may be direct connections to the planar conductors of the CPW through components of the coaxial cables CC1 and CC2 (as shown in fig. 2), or through intervening connectors (not shown) that mate components of the coaxial cables CC1 and CC2 to the planar conductors of the CPW. Separately, the configuration of fig. 2 may be designed with non-attenuating S-parameters, i.e., where the S11 and S22 parameters are close to 0 and the S21 and S12 parameters are close to 1.

Meanwhile, thin film dielectric substrates are typically made of ceramic materials optimized for good RF properties (such as low loss) and good fabrication properties. Furthermore, the material of the thin film dielectric substrate 21 according to embodiments may also be selected to have a very low thermal conductivity, for example, less than 5 watts per meter kelvin. That is, the standard choice for CPW substrates can be alumina or sapphire, but these have a thermal conductivity of about 30 watts per meter kelvin. Whereas selecting fused silica/quartz will result in a thermal conductivity closer to 1 watt per meter kelvin, thus increasing the thermal insulation properties of the coupling.

It is noted here that the inventive concept is not limited to the use of CPW as shown in fig. 2. Examples of other level plane transmission line structures that may be used include microstrips and striplines.

Fig. 4 is a cross-sectional view of an example of a microstrip 40 that may be used in embodiments of the inventive concept. As shown, the microstrip 40 includes a conductor 42 on an upper surface of a thin film dielectric substrate 41 and a ground plane 43 on a lower surface of the thin film dielectric substrate 41. When embodiments according to the inventive concept are applied to insulated coaxial cable connectors, the conductor 42 is connected between the center conductors of the opposite coaxial cable ends and the ground plane 43 is connected between the tubular conductive shields of the opposite coaxial cable ends.

Fig. 5 is a cross-sectional view of an example of a ribbon wire 50 that may be used in embodiments of the inventive concept. As shown, the strip line 50 includes a conductive line 42 embedded between the upper and lower surfaces of a dielectric substrate 51, and at least one of ground planes 53a and 53b on the upper and lower surfaces of the dielectric substrate 51. When embodiments according to the inventive concept are applied to insulated coaxial cable connectors, the conductor 52 is connected between the center conductors of the opposite coaxial cable ends, and the ground planes 53a and/or 53b are connected between the tubular conductive shields of the opposite coaxial cable ends.

Referring now to fig. 6-8, perspective views of insulated coaxial cable connectors according to embodiments of the present inventive concept are shown. Fig. 6 is a perspective view of a housing of a thermally insulated coaxial cable connector according to an embodiment of the inventive concept, and fig. 7 and 8 are perspective cut-away views of a thermally insulated coaxial cable connector according to an embodiment of the inventive concept. The connector may be similar in construction to the attenuator except that it does not contain attenuation. That is, as mentioned previously, the structure may be designed to have a non-attenuating S parameter.

The connector of this embodiment includes an outer housing having a central body 61 surrounding at least a portion of the planar transmission line 65 and opposing coupling nuts 60a and 60b containing at least a portion of a first coaxial to planar RF connector 66a and a second coaxial to planar RF connector 66b, respectively. One or both of the coupling nuts 60a and 60b may be removably removable (e.g., via interlocking threads) from the central body 61. The coaxial-to-planar RF connectors 66a and 66b are configured to mate the conductors of the coaxial cable to the planar transmission line 65, as previously described in connection with fig. 2-5.

The structures of fig. 6 to 8 can be applied as the heat insulating member by controlling the thermal characteristics of the materials used in the construction. For example, the thermal conductivity of the frame (61, 60a, 60b) may be less than 0.300 watts per meter kelvin. As examples of materials, the outer frame (61, 60a, 60b) may be constructed entirely of polycarbonate (having a thermal conductivity of 0.19 to 0.22 watts per meter kelvin) or acrylonitrile butadiene styrene ABS (having a thermal conductivity of 0.128 to 0.187 watts per meter kelvin), both of which may provide an effective thermal barrier. Also, as previously discussed, the material of the dielectric substrate of the planar transmission line 65 may also be selected to have a very low thermal conductivity. By way of example, a dielectric substrate of fused silica or quartz will result in a thermal conductivity closer to 1 watt per meter kelvin, thus increasing the thermal insulation properties of the coupling.

Fig. 9 illustrates an example of an insulation system that may incorporate insulated coaxial cable connectors according to one or more embodiments of the present inventive concept. The adiabatic system of this example is an adiabatic microcalorimeter that may be used to measure microwave or RF power.

The adiabatic microcalorimeter of fig. 9 has a triple wall chamber structure with insulating material between walls 91, 92 and 93 for thermal isolation. Furthermore, thermal stability may be enhanced by a peltier element (not shown) acting on one of the walls, while the other two walls act as passive heat shields. Also shown are several conventional components that make up the adiabatic microcalorimeter, namely an RF generator 94, a directional coupler 95 for directing the output of the RF generator 94, first and second coaxial RF transmission paths 96 and 97, an RF sensor 98 and a power meter 99 for determining a reference power, a nano-voltmeter 100 for determining the voltage of a thermopile 104, and a bridge circuit 101 and a voltmeter 102 for determining the bridge voltage of a thermistor power sensor 103 including a thermistor 105.

To suppress stray thermal paths through first coaxial RF transmission path 96 and second coaxial RF transmission path 97, three (3) series insulated coaxial cable connectors 200 are embedded each. As described in connection with the previous embodiments, insulated coaxial cable connector 200 exhibits excellent RF and microwave frequency transmission characteristics while providing thermal insulation properties.

Fig. 10 and 11 show simulation results of an example of the inventive concept using CPW as a planar transmission line. Fig. 10 shows the magnitude in dB of S1,1 over a frequency range in the GHz range, and fig. 11 shows the magnitude in dB of S2,1 over the same frequency range in the GHz range. These representations can be considered as good performance up to 40 GHz.

The present invention includes the following embodiments:

1. a thermally insulated coaxial cable connector comprising:

a frame;

a planar transmission line within the chassis and having a first end and a second end;

a first coaxial-to-planar transition within the chassis and connected to the first end of the planar transmission line; and

a second coaxial-to-planar transition within the chassis and connected to the second end of the planar transmission line.

2. The insulated coaxial cable connector of item 1, wherein the first and second coaxial-to-planar transitions comprise respective connectors exposed at opposite ends of the rack and each configured to operatively engage a fitting of a coaxial cable.

3. The insulated coaxial cable connector of item 1, wherein the thermal conductivity of the chassis is less than 0.300 watts per meter kelvin.

4. The insulated coaxial cable connector of item 1, wherein the housing is formed of plastic.

5. The insulated coaxial cable connector of item 1, wherein the housing is formed of polycarbonate or Acrylonitrile Butadiene Styrene (ABS).

6. The insulated coaxial cable connector of item 1, wherein the planar transmission line is a coplanar waveguide (CPW) and the substrate of the CPW has a thermal conductivity of less than 5 watts per meter kelvin.

7. The insulated coaxial cable connector of item 1, wherein the planar transmission line is a coplanar waveguide (CPW) and the substrate of the CPW is formed of at least one of fused silica and quartz.

8. The insulated coaxial cable connector of item 1, wherein the rack comprises a central body surrounding at least a portion of the planar transmission line, and opposing coupling nuts containing at least a portion of the first and second coaxial-to-planar connectors, respectively.

9. The insulated coaxial cable connector of item 8, wherein at least one of the coupling nuts is removably connected to the center body.

10. The insulated coaxial cable connector of item 8, wherein the central body is a cylinder extending longitudinally around the planar transmission line.

11. The insulated coaxial cable connector of item 1, wherein the planar transmission line is one of a microstrip or a stripline.

12. An insulated coaxial cable connector comprising:

a first coaxial cable having a first end;

a second coaxial cable having a second end;

a coaxial cable connector including a planar transmission line operatively connected between the first and second ends of the respective first and second coaxial cables.

13. The insulated coaxial cable connection system of item 12, wherein the coaxial cable connection comprises a chassis containing the planar transmission line, the chassis having a thermal conductivity of less than 0.300 watts per meter kelvin.

14. The insulated coaxial cable connection system of item 13, wherein the planar transmission line comprises a substrate having a thermal conductivity of less than 5 watts per meter kelvin.

15. The insulated coaxial cable connection system of item 14, wherein the chassis is formed from polycarbonate or Acrylonitrile Butadiene Styrene (ABS) and the substrate of the planar transmission line is formed from fused silica or quartz.

16. The adiabatic coaxial cable connection system of item 12, wherein the planar transmission line is a coplanar waveguide (CPW).

17. The insulated coaxial cable connection system of item 12, wherein the planar transmission line is a microstrip or a stripline.

18. An insulation system comprising:

a chamber comprising a chamber wall and defining a thermodynamically controlled process volume;

a test sensor located within the thermodynamically controlled processing volume;

an RF generator located outside of the thermodynamically controlled processing space;

a coaxial cable connector comprising a chassis, a planar transmission line within the chassis and having a first end and a second end, a first coaxial-to-planar transition within the chassis and connected to the first end of the planar transmission line, and a second coaxial-to-planar transition within the chassis and connected to the second end of the planar transmission line;

a first coaxial cable coupled between the test sensor and the first coaxial-to-planar transition of the coaxial cable connector; and

a second coaxial cable coupled between the RF generator and the second coaxial-to-planar transition of the coaxial cable connector.

19. The thermal insulation system of item 18, wherein the thermal conductivity of the chassis is less than 0.300 watts per meter kelvin and the substrate of the planar transmission line has a thermal conductivity of less than 5 watts per meter kelvin.

20. The insulation system of item 18, wherein the insulation system is a microcalorimeter.

While the present disclosure has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present teachings. Accordingly, it should be understood that the above-described embodiments are not limiting, but illustrative.