阅读说明：本技术 一种基于overhauser效应的新型射频激励系统 (Novel radio frequency excitation system based on overhauser effect ) 是由 张柏和 于 2020-04-28 设计创作，主要内容包括：本发明提供了一种基于overhauser效应的新型射频激励系统,属于磁场测量传感器技术领域,包括射频信号源模块、射频功率放大模块及射频激励模块。射频激励模块采用Alderman-Grant线圈代替传统结构,线圈品质因数更高,输出信号灵敏度高,对overhauser磁力仪中的工作物质极化程度高。在线圈尺寸一定的情况下,仿真过程中,仅通过调节调谐电容值就可以获取线圈所需的谐振频率,使得线圈能够适应不同的工作物质。线圈等效电路结构简单,更容易将线圈调谐在所需的频率范围内。(The invention provides a novel radio frequency excitation system based on an overhauser effect, belongs to the technical field of magnetic field measurement sensors, and comprises a radio frequency signal source module, a radio frequency power amplification module and a radio frequency excitation module. The radio frequency excitation module adopts an Alderman-Grant coil to replace a traditional structure, the coil quality factor is higher, the output signal sensitivity is high, and the polarization degree of working substances in the overhauser magnetometer is high. Under the condition that the size of the coil is fixed, in the simulation process, the resonant frequency required by the coil can be obtained only by adjusting the tuning capacitance value, so that the coil can adapt to different working substances. The coil equivalent circuit has a simple structure, and the coil is easier to tune in a required frequency range.)

1. A novel radio frequency excitation system based on the overhauser effect is characterized by comprising a radio frequency signal source module, a radio frequency power amplification module and a radio frequency excitation module which are sequentially in signal connection, wherein the radio frequency excitation module is an Alderman-Grant coil; the radio frequency signal source module generates a radio frequency excitation signal, the radio frequency power amplification module performs power amplification on the radio frequency excitation signal, and the radio frequency excitation module generates electromagnetic waves and polarizes working substances.

2. The radio frequency excitation system according to claim 1, wherein the working substance is 4-Oxo-TEMPO.

3. The radio frequency excitation system according to claim 1, wherein the radio frequency signal source module comprises an MCU and a crystal oscillator connected to an AD9959, and the AD9959 is further connected to a low pass filter.

4. The radio frequency excitation system according to claim 1, wherein the radio frequency power amplification module includes an attenuator, a class a power amplifier, a matching network, a class AB power amplifier, and a matching network, which are connected in sequence, and the DC/DC power supply supplies power to the radio frequency power amplification module.

5. A radio frequency excitation system according to claim 2, wherein the Alderman-Grant coil comprises a coil body (1), a guard ring (2), a coil wing (3) and a tuning capacitor (4).

6. The radio frequency excitation system according to claim 5, wherein in the equivalent circuit of the Alderman-Grant coil, the coil guard ring (2) is equivalent to an inductance L₁The equivalent between the coil wings (3) is capacitance C₁The coil slot (5) part is equivalent to an inductorThe equivalent between the coil protection ring (2) and the coil wing (3) is a capacitor C₂。

7. A radio frequency excitation system according to claim 6, wherein the tuning capacitance (4) is calculated as follows:

wherein, w₀Represents the angular frequency of the coil, and w₀＝2πf₀，f₀Representing the coil resonant frequency.

8. The radio frequency excitation system according to claim 7, wherein the dimensional parameter calculation formula of the coil is as follows:

wherein H represents the height of the coil body (1); mu.s₀Represents the permeability in vacuum; k (K), K (K') each represent a first type of complete elliptic integral, as shown below:wherein k, k' both represent the modulus of the integral;represents an integration angle; theta represents the angle of the coil slot (5);

wherein D represents the outer diameter of the coil; w represents the height of the coil wing (3);

wherein, ξ₀Representing the dielectric constant in vacuum ξ_rA relative dielectric constant of 2.55 for the spacer layer (6); indicating isolating layer (6)The thickness of (2) is 0.1 cm.

9. A radio frequency excitation system according to claim 8, wherein the height of the coil body (1) is 11cm, the height of the coil limbs (3) is 0.5cm, the outer diameter of the coil is 2.3cm, the thickness of the isolation layer (6) is 0.1cm, and the angle of the slot (5) is 100 °.

10. A radio frequency excitation system according to claim 9, wherein the return loss is minimized at a coil resonance frequency of 59.8MHz, and the coil resonance frequencies corresponding to return losses of-10 dB are 59.70MHz and 60.10MHz, respectively, and the quality factor of the coil is:

wherein, W₀Representing the total energy stored by the coil, P_LRepresenting the energy consumed by the coil; BW (Bandwidth)_fIndicating the bandwidth.

Technical Field

The invention belongs to the technical field of magnetic field measurement sensors, and particularly relates to a novel radio frequency excitation system based on an overhauser effect.

Background

The proton magnetometer is an important scientific instrument for measuring the geomagnetic field, the common proton magnetometer mainly adopts a static polarization mode, the coil is electrified with direct current, the exciting current is cut off after a period of time, a Larmor precession signal is induced on the coil at the moment, the precession frequency of the signal has a certain proportional relation with the intensity of the earth magnetic field, and the total intensity of the geomagnetic field can be calculated by measuring the precession frequency of protons. However, in the static polarization mode, the proton excitation degree is low, so that the amplitude of an output signal is very weak, the signal-to-noise ratio after passing through an amplifier is low, and the precision and the sensitivity of the proton magnetometer are not particularly high; and the static polarization mode also causes the magnetometer to have larger power consumption, and the use is limited and inconvenient.

In order to improve the precision of output signals and solve the problem that the traditional proton magnetometer is low in polarization mode, an overhauser magnetometer based on the overhauser effect is provided. In recent years, the university of geology in china and the university of jilin are at the leading level in the aspect of overhauser magnetometer research, and the great progress is mainly made in the aspects of sensor signal processing and magnetic field gradient, and certain gaps are still formed between the quality of output signals, sensor structures and the like and abroad. Since the research on the overhauser magnetometer and the sensor in China is started late, no mature commercial overhauser magnetometer is developed independently so far, and only a corresponding prototype exists.

For the overhauser magnetometer, a radio frequency excitation system is a main part of the overhauser magnetometer and comprises a radio frequency signal source module, a radio frequency power amplification module and a radio frequency excitation module, wherein the radio frequency excitation module of the conventional overhauser magnetometer mainly has two structures, namely a capacitance loading type coaxial resonant cavity and a cage coil. For the capacitance loading type coaxial resonant cavity, because the resonant frequency of the capacitance loading type coaxial resonant cavity is related to various parameters such as the size of the resonant cavity, the tuning capacitance value and the like, various simulation experiments need to be carried out by simultaneously changing the parameters such as the size of the resonant cavity, the tuning capacitance value and the like, and the workload is huge and more difficult. For the birdcage coil, the quality factor is too low, the power loss is large, and the power transmitted by the radio frequency excitation is mostly consumed by the birdcage coil rather than being stored inside the birdcage coil, which is very bad for the radio frequency polarization of the radical solution, and can affect the acquisition quality of the larmor precession signal, and affect the sensitivity of the magnetometer.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a novel radio frequency excitation system based on the overhauser effect, wherein an Anderman-Grant (Alderman-Grant) coil is adopted to replace the traditional radio frequency excitation structure, the quality factor is higher, the power loss is small, the polarization degree of a working substance is higher, the equivalent circuit structure of the Alderman-Grant coil is simple, and the adjustment of the resonance frequency of the coil is simpler and more convenient.

The present invention achieves the above-described object by the following technical means.

A novel radio frequency excitation system based on the overhauser effect comprises a radio frequency signal source module, a radio frequency power amplification module and a radio frequency excitation module which are in signal connection in sequence, wherein the radio frequency excitation module is an Alderman-Grant coil; the radio frequency signal source module generates a radio frequency excitation signal, the radio frequency power amplification module performs power amplification on the radio frequency excitation signal, and the radio frequency excitation module generates electromagnetic waves and polarizes working substances.

Further, the working substance is 4-Oxo-TEMPO.

Further, the radio frequency signal source module comprises an MCU and a crystal oscillator connected with the AD9959, and the AD9959 is also connected with a low pass filter.

Furthermore, the radio frequency power amplification module comprises an attenuator, an A-type power amplifier, a matching network, an AB-type power amplifier and a matching network which are connected in sequence, and the DC/DC power supply supplies power to the radio frequency power amplification module.

Further, the Alderman-Grant coil includes a coil body, a guard ring, a coil wing, and a tuning capacitor.

Furthermore, in the equivalent circuit of the Alderman-Grant coil, a coil protection ring is equivalent to an inductor L₁Equivalent between the coil wings is capacitance C₁The slotted part of the coil is equivalent to an inductorThe equivalent between the coil protection ring and the coil wing is a capacitor C₂。

Further, the tuning capacitance (4) is calculated as follows:

wherein, w₀Represents the angular frequency of the coil, and w₀＝2πf₀，f₀Representing the coil resonant frequency.

Further, the size parameter calculation formula of the coil is as follows:

wherein H represents the height of the coil body; mu.s₀Indicating vacuumMedium magnetic permeability; k (K), K (K') each represent a first type of complete elliptic integral, as shown below:wherein k, k' both represent the modulus of the integral;represents an integration angle; theta represents the angle of the coil slot;

wherein D represents the outer diameter of the coil; w represents the height of the coil limb;

wherein, ξ₀Representing the dielectric constant in vacuum ξ_rThe relative dielectric constant of the isolation layer is 2.55; the thickness of the spacer layer was 0.1 cm.

Further, the height of the coil body is 11cm, the height of the coil wing is 1cm, the outer diameter of the coil is 2.3cm, the thickness of the isolation layer is 0.1cm, and the slotting angle is 100 degrees.

Further, when the coil resonance frequency is 59.8MHz, the return loss reaches the minimum, and the coil resonance frequencies corresponding to the return loss of-10 dB are 59.70MHz and 60.10MHz, respectively, then the quality factor of the coil is:

wherein, W₀Representing the total energy stored by the coil, P_LRepresenting the energy consumed by the coil; BW (Bandwidth)_fIndicating the bandwidth.

The invention has the following beneficial effects:

compared with the prior art, the radio frequency excitation module in the radio frequency excitation system adopts the Alderman-Grant coil, the problem that the simulation parameters of the capacitance loading type coaxial resonant cavity are difficult to adjust is solved, and under the condition that the size of the coil is certain, the resonance frequency required by the coil can be obtained only by adjusting the tuning capacitance value in the simulation process, so that the coil can adapt to different working substances. The radio frequency excitation module has the advantages of simple polarization mode, higher coil quality factor, high output signal sensitivity and high polarization degree on working substances in a magnetometer; the coil equivalent circuit has a simple structure, and the coil is easier to tune in a required frequency range.

Drawings

FIG. 1 is a block diagram of a RF signal source according to the present invention;

FIG. 2 is a block diagram of an RF power amplifier module according to the present invention;

FIG. 3 is a block diagram of the RF excitation module of the present invention;

FIG. 4 is an equivalent circuit diagram of the coil of the present invention;

FIG. 5 is a coil model simulation diagram according to the present invention;

fig. 6 is a graph of the resonance frequency and return loss of the coil of the present invention.

In the figure: 1-a coil body; 2-a guard ring; 3-a coil limb; 4-a tuning capacitor; 5-slotting; 6-isolating layer.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.

The novel radio frequency system based on the overhauser effect comprises a radio frequency signal source module, a radio frequency power amplification module and a radio frequency excitation module which are in signal connection in sequence. As shown in fig. 1, the rf signal source module includes a single chip Microcomputer (MCU) connected to a digital frequency synthesizer (AD9959), a 25MHZ crystal oscillator, and the digital frequency synthesizer (AD9959) is further connected to a 200MHZ low pass filter; the MCU controls the AD9959 to generate a radio frequency excitation signal, and the radio frequency excitation signal is filtered and output by a 200MHZ low-pass filter. As shown in fig. 2, the rf power amplifying module includes a 3db attenuator, a class a power amplifier, a matching network, a class AB power amplifier, and a matching network, which are connected in sequence, and the DC/DC power supply supplies power to the rf power amplifying module; the radio frequency excitation signal filtered and output by the filter is input to the attenuator and finally output through the matching network, and the power of the radio frequency excitation signal processed by the radio frequency power amplification module is between 4W and 5W. The radio frequency excitation module is an Alderman-Grant coil, as shown in fig. 3, the coil is composed of a coil body 1, a protection ring 2, coil wings 3 and tuning capacitors 4, the coil is in a cylindrical symmetrical structure, the coil wings 3 are symmetrically arranged at two ends of the coil body 1, the tuning capacitors 4 are arranged between the coil wings 3, two slots 6 are symmetrically arranged between the coil body 1, and the protection rings 2 are arranged at two ends of the coil body 1; the radio frequency excitation signal output by the matching network is loaded on the coil, and the coil resonates at a specific frequency, so that electromagnetic waves are generated and the working substance is polarized.

The equivalent circuit diagram of the coil is shown in fig. 4, in which the coil guard ring 2 is equivalent to the inductor L₁The equivalent between the coil wings 3 is a capacitor C₁The slot 5 part of the coil is equivalent to an inductorThe equivalent between the coil protection ring 2 and the coil wing 3 is a capacitor C₂。

The coil tuning capacitance 4 is obtained by the following equation:

wherein, w₀Representing angular frequency, w, of the coil₀＝2πf₀And, f₀Representing the coil resonance frequency; l is_aRepresents the sum of the equivalent inductances of the coil slot 5 sections; l is₁Representing the equivalent inductance of the coil guard ring 2; c₁Represents the capacitance between the coil limbs 3, i.e. the tuning capacitance 4; c₂Representing the equivalent capacitance between the guard ring 2 and the coil limb 3.

The coil size parameter calculation process is as follows:

wherein H represents the height of the coil body 1; mu.s₀Represents the permeability in vacuum; k (K), K (K') each represent a first type of complete elliptic integral, as shown below:

wherein k, k' both represent the modulus of the integral;represents an integration angle; θ represents the angle of the coil slot 5.

Wherein D represents the outer diameter of the coil; w represents the height of the coil limb 3; mu.s₀Indicating the permeability in vacuum.

Wherein, ξ₀Representing the dielectric constant in vacuum ξ_rIndicating the relative dielectric constant of spacer 6 between guard ring 2 and coil limb 3, spacer 6 is typically filled with polytetrafluoroethylene, ξ_rThe value is generally 2.55; the thickness of the spacer layer 6 is shown, in this example, to be 0.1 cm.

The frequency required for polarization of the working substance in the Overhauser magnetometer is known, and the working substance selected in this embodiment is 4-Oxo-TEMPO (4-carbonyl-tetramethylpiperidinyloxy radical), and the polarization frequency is about 60MHZ, and the resonance frequency of the coil of the present invention is 60 MHZ. Overall height of coil (H + 2W)₁) Is definite, and the value of H is required to ensure that the magnetic field in the coil is uniform as much as possibleIs a little bigger as possible; the outer diameter D of the coil is selected according to the signal receiving coil, and is typically 2cm to 3 cm. The coil size parameters in this example were selected as shown in table 1 below:

TABLE 1 coil parameter table

A coil simulation model shown in fig. 5 is established according to coil related parameter data shown in table 1, when a working substance is changed, only the value of a coil tuning capacitor is needed to be adjusted, so that the coil resonance frequency is adapted to the polarization frequency of the working substance, and compared with a traditional capacitance loading type coaxial resonant cavity, the parameter adjustment in simulation is simpler and more convenient.

Fig. 6 is a diagram of the resonance frequency and the return loss of the coil, and it can be known from the simulation result in the diagram that when the resonance frequency of the coil is 59.8MHz, the return loss S11 of the coil is the lowest and is-23 d B, and normally, when the value of the return loss S11 is smaller than-10 d B, the loss change of the coil to the power is not large, and the resonance frequencies corresponding to S11 being-10 dB are 59.70MHz and 60.10MHz, respectively, so the quality factor of the coil of the present invention is:

wherein, W₀Representing the total energy stored by the coil, P_LRepresenting the energy consumed by the coil; BW (Bandwidth)_fIndicating the bandwidth.

The quality factor of the traditional cage coil can only reach about 70, but the coil of the invention has higher quality factor, low power loss and better polarization effect on working substances.

The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.