阅读说明：本技术 一种钾光泵磁力仪的光磁共振信号数字化检测系统 (digital detection system for optical magnetic resonance signals of potassium optical pump magnetometer ) 是由 杨颖� 李醒飞 辛晨明 任淑艳 耿丽清 于 2019-02-21 设计创作，主要内容包括：本发明公开了一种钾光泵磁力仪的光磁共振信号数字化检测系统,包括光电探测器、信号预处理模块、数据采集模块、数字控制器模块以及射频驱动模块；该系统首先检测透过气室的光学信号,然后经过放大、滤波、锁相处理后,反馈控制气室外围的射频线圈,跟踪锁定磁共振产生时对应的频率,进而推算外界磁场大小,实现磁场测量。其采用软件算法代替硬件电路,避免了硬件电路带来的干扰误差,稳定性好且易于控制,易于实现高精度、高灵敏度的测量效果,并且也为仪器的小型化、低功耗的要求提供了新的技术途径。(The invention discloses a digital detection system for an optical magnetic resonance signal of a potassium optical pump magnetometer, which comprises a photoelectric detector, a signal preprocessing module, a data acquisition module, a digital controller module and a radio frequency driving module, wherein the photoelectric detector is connected with the signal preprocessing module; the system firstly detects optical signals penetrating through the air chamber, then after amplification, filtering and phase locking processing, the system feeds back and controls a radio frequency coil at the periphery of the air chamber, tracks and locks the corresponding frequency generated by magnetic resonance, and further calculates the size of an external magnetic field to realize magnetic field measurement. The software algorithm is adopted to replace a hardware circuit, so that the interference error caused by the hardware circuit is avoided, the stability is good, the control is easy, the measurement effect with high precision and high sensitivity is easy to realize, and a new technical approach is provided for the requirements of miniaturization and low power consumption of the instrument.)

1. The utility model provides a digital detecting system of optical magnetic resonance signal of potassium optical pump magnetometer which characterized in that: the system comprises a photoelectric detector, a signal preprocessing module, a data acquisition module, a digital controller module and a radio frequency driving module;

The signal preprocessing module is composed of an I/V conversion, amplification and filtering circuit, and performs I/V conversion, amplification and filtering processing on a photocurrent signal output by the photoelectric detector;

The data acquisition module comprises a fully differential amplifier OPA1632 and a 24-bit ADS1271, wherein the fully differential amplifier OPA1632 changes an output signal of the signal preprocessing module from single-ended input to double-ended input to the ADS 1271;

The digital controller module is realized in a DSP and comprises a digital phase locker, a digital controller and a digital frequency modulator, wherein an input signal of the digital phase locker is an AD acquisition signal of the data acquisition module, a reference signal of the digital phase locker is a pair of orthogonal signals generated by the digital frequency modulator, the input signal is multiplied with the pair of orthogonal reference signals respectively to obtain a mixing signal, and an in-phase component I and an orthogonal component Q are output through a low-pass filter, wherein the I is used as an input signal of the digital controller;

The digital frequency modulator comprises a phase accumulator and a waveform memory, and in one clock cycle, a K-bit frequency control word and an N-bit phase accumulator are accumulated once; an N-bit adder of the phase accumulator realizes the accumulation of the phase, an N-bit phase register stores the accumulation result, and when overflow occurs, one cycle is completed, namely one frequency cycle of the digital frequency modulator; the waveform memory comprises a pair of orthogonal sequence lookup tables, the stored data is binary digital sine and cosine signal amplitude values corresponding to each phase, high M bits output by the phase accumulator in each clock period address the waveform memory, and finally the waveform memory outputs a pair of orthogonal sequences used for reference signals of the digital phase locker;

The digital controller comprises a frequency sweep control module, a frequency locking module and a mode selection module, the digital controller has two modes A and B, the mode A is open loop control, frequency control words are generated by the frequency sweep control module, the digital frequency modulator is controlled to output signals within a certain frequency range by stepping at regular intervals, and a monitoring system can obtain resonance line types of in-phase component amplitude and quadrature component amplitude in the mode and is used for researching the influence of magnetometer system parameters on the performance of the instrument; the mode B is closed-loop control, the amplitude of an in-phase signal is kept at a zero value by adopting a digital particle swarm algorithm to complete frequency locking, at the moment, a magnetic measurement system is positioned at an optical magnetic resonance point, a locked frequency control word is directly calculated according to a magnetic measurement formula to obtain a magnetic field value, and the calculated magnetic field value is displayed and stored through subsequent processing;

The radio frequency driving module is used for amplifying power to drive the radio frequency coil, so that the radio frequency coil generates an alternating magnetic field to generate a photomagnetic resonance effect.

2. The digital detection system for the optical magnetic resonance signal of the potassium optical pump magnetometer according to claim 1, wherein: the photoelectric detector has the function of converting emergent light signals which are subjected to the photomagnetic resonance effect in the absorption chamber into photocurrent signals, and the PDA36A of Thorlabs company is selected, has the wavelength response range from 350nm to 1100nm, has higher responsivity in the wave band of which the lambda is 894.6nm, has the maximum output current of 100mA, and has the output voltage of 0-5V.

3. the digital detection system for the optical magnetic resonance signal of the potassium optical pump magnetometer according to claim 1, wherein: the signal preprocessing module comprises an operational amplifier A5, an operational amplifier A6, an operational amplifier A7 and an operational amplifier A8, wherein a sampling resistor R9 is connected between the "-" input end and the output end of the operational amplifier A5, a sampling resistor R9 is connected with a filter capacitor C1 in parallel, the output end of the operational amplifier A5 is connected with the "-" input end of the operational amplifier A6 through a direct current blocking capacitor C2 and a resistor R10, and the output end of the operational amplifier A6 is connected to a four-order Butterworth low-pass filter formed by the operational amplifier A7 and the operational amplifier A8; during operation, a photocurrent signal output by the photoelectric detector is converted into a voltage signal through the sampling resistor R9, the sampling resistor R9 and the filter capacitor C1 form a low-pass filter which can primarily filter high-frequency noise, the DC blocking capacitor C2 is used for filtering a DC component of the signal, the operational amplifier A6 forms an inverting amplifier, the voltage signal obtained by conversion of a previous stage is further amplified, and the amplified signal is filtered and subjected to anti-aliasing through the four-stage Butterworth low-pass filter formed by the operational amplifier A7 and the operational amplifier A8.

4. the digital detection system for the optical magnetic resonance signal of the potassium optical pump magnetometer according to claim 1, wherein: the radio frequency driving module adopts a CMOS inverter CD4069, an analog amplifier can be formed when the input end and the output end of the radio frequency driving module are connected with a feedback resistor, and a frequency modulation signal amplified by the inverter drives a radio frequency coil to generate a radio frequency magnetic field in a resistor voltage division mode after the capacitor is isolated.

5. The digital detection system for the optical magnetic resonance signals of the potassium optical pump magnetometer as claimed in claim 1, wherein the particle swarm algorithm randomly distributes the radio frequency as particles between f _min and f _max, so that each particle represents one frequency, then iterates according to a certain rule, and sets the ith generation of particles as X _i (X _i1, X _i2, …, X _in), wherein n is the number of particles, measures the magnetometer probe output at different frequency points, if the particles representing a certain frequency can obtain smaller values, the particles are called more optimal, the optimal velocity of each particle is set as P _i (P _i1, P _i2, … P _in) during each iteration of the particles, all the optimal values are set as P _ig, and the initialized velocity of each particle is set as V _i (V _i1, V _i2, … V _in), the velocity of each particle is updated in each iteration, the current position of the particle is updated with the optimal velocity, the updated historical position of the particle is added to the updated position of the ith generation of the particle, and the updated velocity of the ith generation of the particle is updated particle:

The self-cognition coefficients of c _1j and c _2j and the social cognition coefficients of r _1j and r _2j are two random numbers in the range of 0-1 and are used for balancing the weight of the self-cognition coefficients and the social cognition coefficients.

Technical Field

The invention belongs to the technical field of signal processing and electronic circuits, and particularly relates to a digital detection system for an optical magnetic resonance signal of a potassium optical pump magnetometer.

background

the optical pump magnetometer is a high-precision and high-sensitivity weak magnetic measuring device and is widely applied to the fields of geophysical research, resource exploration, marine geological research, military, national defense and the like. The earliest appeared to be helium optical pumping magnetometers. Thereafter, alkali metal atoms having a hyperfine structure, such as cesium, rubidium, potassium, etc., are put to practical use in the optical pump magnetometer. The cesium optical pump magnetometer is mature in development and has been successfully applied to the aspects of marine geological research, potential exploration and anti-submergence, submarine pipeline and cable detection, magnetocardiogram measurement and the like. The potassium atomic spectral lines have a large pitch and do not overlap with each other, so that the potassium optical pumping magnetometer is superior to the cesium optical pumping magnetometer in terms of absolute accuracy, sensitivity, and the like. The potassium optical pump magnetometer is a main direction for the development of the current magnetometer.

The potassium optical pump magnetometer mainly comprises two parts: the laser optical pump magnetic sensing probe and the optical magnetic resonance signal detection circuit. The former is used for converting weak magnetic signals into electric signals to be processed, controlled and displayed by the latter. The optical magnetic resonance signal detection method comprises a tracking type and a self-excitation type. The potassium optical pump magnetometer adopts a tracking mode for accurately judging the reading because the spectral lines are a plurality of discontinuous discrete values. And the real-time tracking of the larmor frequency is realized by locking the frequency of the radio frequency magnetic field when the transmitted light intensity is the weakest. In the traditional scheme, a resonance point is determined by detecting a fundamental wave signal, a resonance area is judged by adopting a successive frequency sweep method, and then magnetic field measurement is carried out in the resonance area by using a PID (proportion integration differentiation) control method. The method has large calculation amount and long time for searching the resonance point, and can not quickly find the resonance area. If the magnetic field changes rapidly, the phenomenon of 'lock losing' is easy to occur, the magnetometer cannot realize the real-time tracking of the external magnetic field, and the measured data cannot truly reflect the measured magnetic field. In addition, in the implementation of the detection system, the conventional analog signal detection system generally adopts an electronic switch type phase-sensitive detection circuit composed of an operational amplifier or an integrated phase-sensitive detection chip to extract the modulation fundamental wave signal. Due to the difference of the performances of the separating devices, the performances of the whole machine are greatly different, the sensitivity is low, the temperature drift is large, the anti-interference capability is weak, the power consumption is large, the circuit is complex, and the output frequency range of the voltage-controlled oscillator is limited, so that the magnetic measurement range of the instrument is narrow.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides the digital detection system for the photomagnetic resonance signals of the potassium optical pump magnetometer, adopts a software algorithm to replace a hardware circuit, avoids interference errors caused by the hardware circuit, has good stability, is easy to control, is easy to realize the measurement effect with high precision and high sensitivity, and provides a new technical approach for the requirements of miniaturization and low power consumption of instruments.

The invention is realized by the following technical scheme:

An optical magnetic resonance signal digital detection system of a potassium optical pump magnetometer comprises a photoelectric detector, a signal preprocessing module, a data acquisition module, a digital controller module and a radio frequency driving module;

the signal preprocessing module is composed of an I/V conversion, amplification and filtering circuit, and performs I/V conversion, amplification and filtering processing on a photocurrent signal output by the photoelectric detector;

The data acquisition module comprises a fully differential amplifier OPA1632 and a 24-bit ADS1271, wherein the fully differential amplifier OPA1632 changes an output signal of the signal preprocessing module from single-ended input to double-ended input to the ADS 1271;

The digital controller module is realized in a DSP and comprises a digital phase locker, a digital controller and a digital frequency modulator, wherein an input signal of the digital phase locker is an AD acquisition signal of the data acquisition module, a reference signal of the digital phase locker is a pair of orthogonal signals generated by the digital frequency modulator, the input signal is multiplied with the pair of orthogonal reference signals respectively to obtain a mixing signal, and an in-phase component I and an orthogonal component Q are output through a low-pass filter, wherein the I is used as an input signal of the digital controller;

The digital frequency modulator comprises a phase accumulator and a waveform memory, and in one clock cycle, a K-bit frequency control word and an N-bit phase accumulator are accumulated once; an N-bit adder of the phase accumulator realizes the accumulation of the phase, an N-bit phase register stores the accumulation result, and when overflow occurs, one cycle is completed, namely one frequency cycle of the digital frequency modulator; the waveform memory comprises a pair of orthogonal sequence lookup tables, the stored data is binary digital sine and cosine signal amplitude values corresponding to each phase, high M bits output by the phase accumulator in each clock period address the waveform memory, and finally the waveform memory outputs a pair of orthogonal sequences used for reference signals of the digital phase locker;

The digital controller comprises a frequency sweep control module, a frequency locking module and a mode selection module, the digital controller has two modes A and B, the mode A is open loop control, frequency control words are generated by the frequency sweep control module, the digital frequency modulator is controlled to output signals within a certain frequency range by stepping at regular intervals, and a monitoring system can obtain resonance line types of in-phase component amplitude and quadrature component amplitude in the mode and is used for researching the influence of magnetometer system parameters on the performance of the instrument; the mode B is closed-loop control, the amplitude of an in-phase signal is kept at a zero value by adopting a digital particle swarm algorithm to complete frequency locking, at the moment, a magnetic measurement system is positioned at an optical magnetic resonance point, a locked frequency control word is directly calculated according to a magnetic measurement formula to obtain a magnetic field value, and the calculated magnetic field value is displayed and stored through subsequent processing;

the radio frequency driving module is used for amplifying power to drive the radio frequency coil, so that the radio frequency coil generates an alternating magnetic field to generate a photomagnetic resonance effect.

In the technical scheme, the photoelectric detector has the function of converting an emergent light signal which passes through a photomagnetic resonance effect in the absorption chamber into a photocurrent signal, the PDA36A of Thorlabs company is selected, the wavelength response range is from 350nm to 1100nm, the high responsivity is realized in a wave band of which lambda is 894.6nm, the maximum output current is 100mA, and the output voltage is 0-5V.

In the above technical solution, the signal preprocessing module includes an operational amplifier a5, an operational amplifier A6, an operational amplifier a7, and an operational amplifier A8, a sampling resistor R9 is connected between a "-" input terminal and an output terminal of the operational amplifier a5, the sampling resistor R9 is connected in parallel with a filter capacitor C1, the output terminal of the operational amplifier a5 is connected with a "-" input terminal of the operational amplifier A6 through a dc blocking capacitor C2 and a resistor R10, and the output terminal of the operational amplifier A6 is connected to a four-stage butterworth low pass filter formed by an operational amplifier a7 and an operational amplifier A8; during operation, a photocurrent signal output by the photoelectric detector is converted into a voltage signal through the sampling resistor R9, the sampling resistor R9 and the filter capacitor C1 form a low-pass filter which can primarily filter high-frequency noise, the DC blocking capacitor C2 is used for filtering a DC component of the signal, the operational amplifier A6 forms an inverting amplifier, the voltage signal obtained by conversion of a previous stage is further amplified, and the amplified signal is filtered and subjected to anti-aliasing through the four-stage Butterworth low-pass filter formed by the operational amplifier A7 and the operational amplifier A8.

In the technical scheme, the radio frequency driving module adopts a CMOS inverter CD4069, an analog amplifier can be formed when the input end and the output end of the radio frequency driving module are connected with the feedback resistor, and the frequency modulation signal amplified by the inverter drives the radio frequency coil to generate a radio frequency magnetic field in a resistor voltage division mode after the capacitor is isolated.

In the technical scheme, the particle swarm optimization takes radio frequency as particles, the radio frequency is randomly distributed between f _min and f _max, each particle represents one frequency, iteration is performed according to a certain rule, the ith generation of particles is set to be represented as X _i (X _i1, X _i2, … and X _in), wherein n is the number of the particles, the output of magnetometer probes at different frequency points is measured, if the particles representing a certain frequency can obtain smaller values, the particles are called to be more optimal, the optimal speed of each particle in the iteration process is represented as P _i (P _i1, P _i2 and … P _in), all the optimal values are represented as P _ig, the initialized speed of each particle is given as V _i (V _i1, V _i2 and … V _in), the speed of each particle is updated in each iteration, the current position of the particle is made to be close to the optimal of the history, the updated speed is superposed on the position of the particle, the position of the updated position of the particle is updated, the ith generation of the particle is updated as j:

The method comprises the steps that c _1j and c _2j self-cognition coefficients and social cognition coefficients, r _1j and r _2j are two random numbers in the range of 0-1 and are used for balancing the weight of the self-cognition coefficients and the social cognition coefficients, the set particles keep the minimum position in the self iteration process through the iteration mode, the particles which enable a magnetometer probe to output the minimum double-frequency signal in all the particles can be identified, then other particles approach the particles, and finally all the particles are gathered at the minimum point in the whole situation after multiple iterations, so that the purpose of searching the minimum point in the whole situation is achieved, and a resonance point is found.

the invention has the advantages and beneficial effects that:

the invention provides a digital optical magnetic resonance signal detection system, which adopts a software algorithm (particle swarm algorithm) to replace a hardware circuit, avoids interference errors caused by the hardware circuit, has good stability, is easy to control, is easy to realize the measurement effect of high precision and high sensitivity, and provides a new technical approach for the requirements of miniaturization and low power consumption of instruments.

The digital controller module is realized in the DSP and comprises a digital phase lock, a digital controller and a digital frequency modulator. The digital phase lock device is responsible for extracting the amplitude of the fundamental wave signal from the noise; the digital frequency modulator has two functions of providing a reference signal for the digital phase-locked loop, driving the radio frequency coil to generate a radio frequency magnetic field, realizing digital frequency modulation by adopting a mode of adjusting frequency control words, solving the problems of low frequency stability and narrow frequency output range of the voltage-controlled oscillator, and in addition, directly converting the frequency control words into a measured magnetic field value to eliminate a measurement error introduced by a frequency measurement circuit; the digital controller mainly comprises a frequency sweep control module, a frequency locking module and a mode selection module, wherein the frequency sweep module is mainly used for generating frequency sweep signals, and the frequency locking module adopts a digital particle swarm algorithm to rapidly acquire resonance points.

drawings

Fig. 1 is a schematic diagram of an optical magnetic resonance signal digital detection system of the potassium optical pump magnetometer according to the embodiment.

Fig. 2 is a circuit diagram of a signal preprocessing module in an embodiment.

Fig. 3 is a circuit diagram of the OPA1632 in an embodiment.

Fig. 4 is an ADS1271 circuit diagram in an embodiment.

Fig. 5 is a schematic diagram of the structure of the digital phase locker in the embodiment.

Fig. 6 is a schematic diagram of the structure of the digital frequency modulator in the embodiment.

Fig. 7 is a schematic diagram of the structure of the digital controller in the embodiment.

fig. 8 is a flow chart of the particle swarm algorithm in the example.

For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the present invention is further described below with reference to specific examples.

The theoretical curve of the transmission signal of the laser optical pump magnetic sensing probe is a Lorentz line type, the minimum value of the curve is a magnetic resonance point, and the transmission light intensity is the weakest. The detection system is a closed-loop control system and is equivalent to a phase-locked loop. The frequency is taken as a control object, the input signal is a measured magnetic field value which is in direct proportion to the optical magnetic resonance frequency, the feedback signal is a frequency modulation signal of a signal detection system, and the input signal and the feedback signal are respectively realized on the air chamber and the radio frequency coil.

The optical magnetic resonance signal detection system is used for detecting optical signals penetrating through the air chamber, then performing amplification, filtering and phase locking processing, feeding back and controlling a radio frequency coil on the periphery of the air chamber, tracking and locking a corresponding frequency generated by magnetic resonance, and further calculating the size of an external magnetic field to realize magnetic field measurement. As shown in fig. 1, the optical magnetic resonance signal detection system of the present invention mainly includes a photodetector, a signal preprocessing module, a data acquisition module, a digital controller module, and a radio frequency driving module.

the photoelectric detector has the function of converting emergent light signals which pass through the photomagnetic resonance effect in the absorption chamber into photocurrent signals, the PDA36A of Thorlabs company is selected, the wavelength response range is from 350nm to 1100nm, the device has higher responsivity in the wave band of which the lambda is 894.6nm, the maximum output current is 100mA, and the output voltage is 0-5V.

The signal preprocessing module consists of an I/V conversion, amplification and filtering circuit and has the functions of carrying out I/V conversion, amplification and filtering on the photocurrent signal output by the photoelectric detector. The specific circuit of the signal preprocessing module is shown in fig. 2, and includes an operational amplifier a5, an operational amplifier A6, an operational amplifier a7 and an operational amplifier A8, wherein a sampling resistor R9 is connected between a "-" input end and an output end of the operational amplifier a5, the sampling resistor R9 is connected in parallel with a filter capacitor C1, the output end of the operational amplifier a5 is connected with a "-" input end of the operational amplifier A6 through a dc blocking capacitor C2 and a resistor R10, and the output end of the operational amplifier A6 is connected to a four-stage butterworth low pass filter formed by the operational amplifier a7 and the operational amplifier A8. During operation, a photocurrent signal is converted into a voltage signal through the sampling resistor R9, the sampling resistor R9 and the filter capacitor C1 form a low-pass filter which can primarily filter high-frequency noise, the DC blocking capacitor C2 is used for filtering a DC component of the signal, the operational amplifier A6 forms an inverting amplifier, the voltage signal obtained by the preceding stage conversion is further amplified, and the amplified signal is subjected to filtering and anti-aliasing functions through a four-order Butterworth low-pass filter formed by the operational amplifier A7 and the operational amplifier A8.

The data acquisition module selects 24 bits of ADS1271, because ADS1271 is differential input, and the sampling value is single-ended voltage signal, so that a fully differential amplifier (model is OPA1632) is introduced to change the signal from single-ended input to double-ended input, as shown in FIGS. 3-4, FIG. 3 is a circuit diagram of the OPA1632 fully differential amplifier, in which VCOM pin is used to set the common-MODE output voltage of OPA1632, and a decoupling capacitor is added to filter out high-frequency noise, CF1 and CF2 are used for phase compensation, polystyrene capacitors are selected, R1, R2 and C5 constitute input filter, RG 5-2-1 k Ω, CF 1-CF 2-10 nF, R ₁ -R ₂ -49.9, V _OCOM -2.5V, FIG. 4 is a circuit diagram of ADS1271, in which power input capacitors are used to filter out high-frequency noise, AINN 1, AILK and AFLK are connected with DSP input ends of DSP 100. high-precision communication is realized by using a parallel connected with DSP SPI 100. SPRM.

The digital controller module is realized in the DSP and comprises a digital phase lock, a digital controller and a digital frequency modulator.

further, a structural schematic diagram of the digital phase locker is shown in fig. 5, an input signal is an AD acquisition signal, a reference signal is a pair of orthogonal signals generated by the digital frequency modulator, the input signal is multiplied by the pair of orthogonal reference signals to obtain a mixing signal, an in-phase component I and an orthogonal component Q are output by the low-pass filter, the two signals are direct current signals, the two signals are uploaded to an upper computer in an open-loop control mode to analyze a resonance spectrum, and the I in a closed-loop control mode can be used as an input signal of the digital controller.

Further, the digital frequency modulator mainly includes two parts, i.e., a phase accumulator and a waveform memory, as shown in fig. 6, in one clock cycle, the K-bit frequency control word is accumulated with the N-bit phase accumulator once; the phase accumulator is a core part of the digital frequency modulator, wherein the N-bit adder realizes the accumulation of phases, the N-bit phase register stores the accumulation result, and when overflow occurs, one cycle is completed, namely one frequency cycle of the digital frequency modulator; the waveform memory comprises a pair of orthogonal sequence lookup tables, stored data is binary digital sine and cosine signal amplitude values corresponding to each phase, high M bits output by the phase accumulator in each clock cycle address the waveform memory, and finally the waveform memory outputs a pair of orthogonal sequences used for reference signals of the digital phase locker.

Further, the digital controller comprises a frequency sweep control module, a frequency locking module and a mode selection module, as shown in fig. 7, the digital controller has two modes a and B, the mode a is open loop control, the frequency sweep control module generates frequency control words, the digital frequency modulator is controlled to output signals within a certain frequency range by stepping every certain time, and the monitoring system can obtain a resonance line type of an in-phase component amplitude and a quadrature component amplitude in the mode and is used for researching the influence of magnetometer system parameters on the performance of the instrument; and the mode B is closed-loop control, the amplitude of the in-phase signal is kept at a zero value by adopting a digital particle swarm algorithm to complete frequency locking, the magnetic measurement system is positioned at an optical magnetic resonance point at the moment, the locked frequency control word is directly calculated according to a magnetic measurement formula to obtain a magnetic field value, and the calculated magnetic field value is displayed and stored through subsequent processing.

The radio frequency driving module is mainly used for amplifying power to drive the radio frequency coil, so that the radio frequency coil generates an alternating magnetic field to generate a photomagnetic resonance effect. The DSP controller outputs 3.3V level standard frequency modulation square waves, and the amplitude of the frequency modulation signals needs to be amplified in order to reduce the influence of the internal resistance of the radio frequency coil. A CMOS inverter CD4069 is selected, an analog amplifier can be formed when the input end and the output end of the CMOS inverter CD4069 are connected with a feedback resistor, and a frequency modulation signal amplified by the inverter drives a radio frequency coil to generate a radio frequency magnetic field in a resistor voltage division mode after a capacitor is blocked.

the particle swarm optimization is an evolutionary algorithm for simulating bird swarm to search food, can be used for searching a global minimum value of a multi-peak function, randomly initializing a corresponding particle swarm within a pre-estimated range, and is called as particles, wherein radio frequency is used as particles and is randomly distributed between f _min and f _max, so that each particle represents one frequency, then iteration is carried out according to a certain rule, and the ith generation of particles is set as X _i (X _i1, X _i2, … and X _in), wherein n is the number of particles, magnetometer probe outputs at different frequency points are measured, if the particles representing a certain frequency can obtain smaller values, the particles are called as more optimal, the optimal velocity in each particle iteration process is P _i (P _i1, P _i2 and … P _in), all particle optimal values are P _ig, meanwhile, the velocity of each initialization is given, V _i is set as V _i1, V _i2 and … V _in, the velocity of each particle is updated in each iteration process, the current particle position is updated by adding the current velocity to the current position of the particle, and then updating the current position of the particle is carried out:

The method comprises the steps that the self-cognition coefficients of c _1j and c _2j and the social cognition coefficients of r _1j and r _2j are two random numbers in the range of 0-1, and are used for balancing the weight of the self-cognition coefficients and the social cognition coefficients, through the iteration mode, the set particles keep the positions with the minimum self in the self iteration process, the particles which enable a magnetometer probe to output a double-frequency signal to be the minimum can be identified, then other particles approach the particles, and finally all the particles are gathered at the global minimum point through multiple iterations, so that the purpose of searching the global minimum point is achieved, and the resonance point is found.

the invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.