Dual closed loop optical accelerometer

Abstract

The application provides a double closed-loop optical accelerometer, comprising a sensing head and a signal processing unit; the signal processing unit comprises a laser LD, a first photodetector, a second photodetector, a transimpedance amplifier, an A / D conversion circuit, a phase-locked amplifier, an FPGA, a cantilever phase-locked controller, a light source power-locked controller, a D / A conversion circuit, a linear amplification circuit and a constant current source circuit; the FPGA is used for generating two same-frequency sinusoidal signals; on the basis of stabilizing the cantilever at a closed-loop working point through electromagnetic force driving, and superimposing electromagnetic force modulation to realize phase locking of the cantilever, 1 / f noise of the system is reduced, and the influence of stray light interference is eliminated; in addition, the output power of the light source is locked in a closed loop, low-frequency fluctuation noise and relative intensity noise caused by light power drift are reduced. The light source output power is locked, and the detection precision of the whole optical accelerometer is improved.

Description

Technical Field

[0001] This application belongs to the field of optical accelerometer design, and particularly relates to a dual closed-loop optical accelerometer. Background Technology

[0002] With the advancement of technology, navigation technology is becoming increasingly indispensable to people's production and daily life. Accelerometers are a key component of inertial navigation systems and are widely used in various fields of people's lives and production. Traditional accelerometers rely on capacitive, piezoresistive, or tunneling electron effects. These sensing methods have inherent drawbacks, such as susceptibility to ambient temperature and cross-sensitivity issues caused by electromagnetic interference.

[0003] Compared to traditional accelerometers, MOMES-type optical accelerometers have stronger resistance to electromagnetic interference, smaller size, higher precision, better sensitivity and linearity, and better prospects and application value.

[0004] However, the weak optical signal from an optical accelerometer is susceptible to various noises and uncertainties in optical parameters, which poses a challenge to the theoretical high-precision signal processing of optical accelerometers.

[0005] An optical accelerometer, as an accelerometer using optical detection, applies the sensing principle of two-beam interference. A schematic diagram of the optical sensing working principle is shown below. Figure 1 As shown, when incident coherent light passes through a transparent medium, part of it is reflected by a phase diffraction grating to form diffracted rays; the other part passes through the diffraction grating, is reflected by a mirror glued to the bottom of the detection mass block, and then passes through the diffraction grating again to form diffracted rays. The two diffracted beams undergo an interference similar to a Michelson interferometer in the transparent medium, forming a diffraction interference field where the intensity of each fixed-order fringe varies with the spacing d between the grating reflective surfaces. According to scalar diffraction theory, the diffraction order intensity can be expressed as a function of the gap distance d.

[0006]

[0007]

[0008] Where I0 and I1 represent the intensity of the output light of the zeroth and first diffraction orders, respectively, while I in λ is the intensity of the incident light, and λ is the wavelength of the light source.

[0009]

[0010] Where m, b, and k represent the central mass, damping coefficient, and spring stiffness, respectively, x is the relative displacement of the central detection mass block, and a is the input acceleration. When there is a static acceleration input, the above formula can be simplified to kx = ma. When there is an external acceleration input, the distance between the reflecting surface and the micron grating will change, which will cause the intensity of each order of diffraction fringes in the diffraction interference field to change. The voltage after the detector and transimpedance amplification can be used as the open-loop output of the micron grating accelerometer. Since the open-loop light intensity output and the spacing d satisfy the cosine function form shown in formula (1), the usable open-loop linear measurement area of ​​the actual system is less than λ / 4, and the corresponding acceleration detection range is only tens of mg, which is difficult to meet the needs of actual engineering practice.

[0011] To improve the dynamic detection range of optical accelerometers, the article "Design of Force Feedback System for Micrometer Grating Accelerometer" published in Volume 15, Issue 4 of the journal *Navigation and Control* in 2016 proposed a closed-loop detection scheme based on electrostatic force feedback. The sensing head structure converts changes in external acceleration into changes in light intensity. The detector converts the light intensity signal into an electrical signal, which is then conditioned into the required voltage signal. This voltage is compared with the optimal operating point voltage of the closed loop, and a feedback control signal is output through a digital control circuit. This feedback signal is then used to stabilize the mass block at the optimal operating point of the closed loop via electrostatic force. The electrostatic force feedback signal is positively correlated with the acceleration. Experiments show that this closed-loop detection method increases the range by 11.9 times compared to the open-loop method, improving the dynamic detection range of the optical accelerometer. However, because the electrostatic force drive introduces a second-order nonlinear element, the actual detection accuracy may decrease, and the electrostatic force drive consumes a large amount of power, which is not conducive to engineering application.

[0012] Patent CN109870592 discloses an optical accelerometer based on electromagnetic force drive, which uses electromagnetic drive to achieve closed-loop control of a micrometer grating accelerometer. Through the electromagnetic force drive module, the cantilever beam position is always at the optimal operating point, and the feedback signal is used as the closed-loop output signal of the accelerometer. The electromagnetic force and feedback voltage have a linear relationship, reducing power consumption and improving detection linearity.

[0013] However, there is still room for improvement in the closed-loop detection accuracy of the grating accelerometer in the entire system. Summary of the Invention

[0014] This invention proposes a dual closed-loop optical accelerometer, which improves the closed-loop detection accuracy of the grating accelerometer by taking into account optical power fluctuations, stray light interference, and 1 / f noise of the system.

[0015] This invention proposes a dual closed-loop optical accelerometer, comprising: a sensing head and a signal processing unit;

[0016] The signal processing unit includes: a laser LD, a first photodetector, a second photodetector, a transimpedance amplifier, an A / D conversion circuit, a lock-in amplifier, an FPGA, a cantilever beam phase-locked controller, a light source power-locked controller, a D / A conversion circuit, a linear amplifier circuit, and a constant current source circuit; wherein, the FPGA is used to generate a first high-frequency signal and a second high-frequency signal, the first high-frequency signal and the second high-frequency signal being sinusoidal signals of the same frequency;

[0017] The first photodetector, transimpedance amplifier, A / D conversion circuit, lock-in amplifier, cantilever beam phase-locked controller, FPGA, D / A conversion circuit, linear amplifier circuit and sensing head form the cantilever beam phase-locked loop of the optical accelerometer;

[0018] The laser LD, second photodetector, transimpedance amplifier, A / D conversion circuit, light source power lock controller, D / A conversion circuit, and constant current source circuit form the light source lock loop of the optical accelerometer.

[0019] Optionally, the first photodetector is used to convert the optical signal output by the sensing head into a first current signal and send it to the transimpedance amplifier; the first current signal is used to indicate the working position of the cantilever beam.

[0020] The transimpedance amplifier is used to convert the first current signal into an analog voltage signal containing the detected acceleration information, and then sends it to the lock-in amplifier via an A / D conversion circuit;

[0021] The lock-in amplifier is used to perform digital demodulation and low-pass filtering on the digital voltage signal based on the first high-frequency signal, and send the processed signal to the cantilever beam phase-locked controller.

[0022] The cantilever beam phase-locked controller is used to generate a first closed-loop error signal based on the received signal;

[0023] The D / A conversion circuit is used to receive the mixed signal of the second high-frequency signal and the first closed-loop error signal, convert it to obtain the first analog voltage signal, and send it to the linear amplifier circuit.

[0024] The linear amplifier circuit is used to impedance match the first analog voltage signal and apply it to the magnetic torque of the sensitive head to adjust the working position of the cantilever beam and stabilize the cantilever beam at the closed-loop working point.

[0025] The second photodetector is packaged together with the laser LD and is used to send a second current signal to the transimpedance amplifier; the second current signal is used to indicate the optical power of the laser LD outputting backward.

[0026] The transimpedance amplifier is also used to convert the second current signal into an analog voltage signal containing optical power information, and send it to the light source power lock-in controller via an A / D conversion circuit;

[0027] The light source power lock controller is used to generate a second closed-loop error signal based on the preset optical power and the received signal;

[0028] The D / A conversion circuit is also used to convert the second closed-loop error signal into a second analog voltage signal and send it to the constant current source circuit.

[0029] The constant current source circuit is used to load the received signal onto the laser LD, so that the output power of the light source tends to the preset optical power.

[0030] Optionally, the second closed-loop error signal is used to offset the effects of optical power fluctuations in the phase-locked loop of the optical accelerometer cantilever beam.

[0031] Optional, second high-frequency signal U m Represented as: U m =Acosω0t;

[0032] The first high-frequency signal is represented as: U s =Bcos(ω0Tk);

[0033] Where A and B are amplitudes, ω0 is the modulation angular frequency, t is time, T is the sampling period, and k is the corresponding discrete time.

[0034] Optionally, the intensity of the diffracted light output from the sensing head detected by the first photodetector is represented as U. 0p (t);

[0035]

[0036] Among them, I in The intensity of the incident light provided to the laser LD, R is the transimpedance gain of the first photodetector, α is the optical path loss, d0 is the initial position of the cantilever beam, and I... noise The interference is stray light that does not interfere; Δx is the displacement change of the cantilever beam caused by the external input acceleration. m The displacement change of the cantilever beam caused by the modulation signal; λ is the wavelength of the incident light.

[0037] Optionally, the demodulated signal generated by the lock-in amplifier It is expressed by the following formula:

[0038]

[0039] Among them, U 0p (k) represents the digital voltage before demodulation, k1 represents the gain of the transimpedance amplifier, k2 represents the gain of the A / D conversion circuit, and J nω1 represents the nth-order coefficient of the first-kind Bessel function, n = 1, 2, 3 ... ∞; ω1 corresponds to the angular frequency of the cantilever beam position change Δx.

[0040] Optionally, the output of the lock-in amplifier after low-pass filtering is represented as U(k);

[0041]

[0042] K is the gain coefficient of the forward channel, and Δk is the gain of I. in Gain fluctuations.

[0043] Optionally, the sensing head includes: a mass block, a cantilever beam, a diffraction grating, a transparent medium, a coil, a yoke, a magnet, electrode plates, and a reflector; wherein,

[0044] The diffraction grating is attached to the upper layer of the transparent medium, and the detection mass block and the diffraction grating form a structure similar to an FP resonant cavity; the reflector is set on the mass block and is opposite to the diffraction grating;

[0045] The coil, yoke, magnet, and electrode plates constitute the magnetic torque actuator mechanism, which is used to realize the functions of phase modulation and feedback control of the cantilever beam.

[0046] The beneficial technical effects of this application are as follows:

[0047] This invention proposes a dual-closed-loop optical accelerometer, which improves upon the aforementioned electromagnetically driven optical accelerometer. Based on stabilizing the cantilever beam at the closed-loop operating point through electromagnetic drive, phase locking of the cantilever beam is achieved by superimposing electromagnetic force modulation, thereby reducing the system's 1 / f noise and eliminating the influence of stray light interference. Furthermore, the output power of the light source is locked to reduce low-frequency fluctuation noise and relative intensity noise caused by optical power drift. By locking the cantilever beam operating point through electromagnetic force-driven closed-loop control and monitoring and adjusting the drive current to lock the light source output power, the overall optical acceleration detection accuracy is improved while maintaining dynamic detection range and linearity. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating the sensing principle of an optical accelerometer.

[0049] Figure 2 This is a schematic diagram of the sensing head of an optical accelerometer.

[0050] Figure 3 This is a schematic diagram of the signal processing unit. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setups and methods set forth below, but covers any improvements, substitutions, and modifications to structures, methods, and devices without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the invention.

[0053] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0054] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0055] Please see Figure 1-3 This invention provides a dual closed-loop optical accelerometer.

[0056] This invention proposes a dual closed-loop optical accelerometer, which mainly includes two working loops: an optical accelerometer cantilever beam phase-locking loop and an optical accelerometer light source-locking loop.

[0057] The dual-loop optical accelerometer consists of two parts: a sensing head and a signal processing unit. The signal processing unit is composed of a cantilever beam phase-locked loop and a light source-locked loop.

[0058] Sensitive head structure such as Figure 2 As shown, the device includes a mass block, a cantilever beam, a diffraction grating, a transparent medium, a coil, a yoke, a magnet, electrode plates, and a mirror. The metal diffraction grating is adhered to the upper layer of the transparent medium, and the detection mass block and the diffraction grating form a structure similar to an FP resonant cavity. The coil, yoke, magnet, and electrode plates constitute a magnetic torque actuator mechanism, used to realize the phase modulation and feedback control functions of the cantilever beam. The voltage applied to the coil is controlled by the modulation voltage U.m and feedback voltage U f It consists of two parts. U m This is used to achieve phase modulation of the cantilever beam by introducing a high-frequency carrier signal to modulate the original closed-loop error signal to a high frequency. f The feedback voltage keeps the accelerometer cantilever beam locked at the closed-loop operating point.

[0059] Signal processing unit (see) Figure 3 As shown, it consists of a laser LD (light source), photodetector PD1, photodetector PD2, transimpedance amplifier, A / D conversion circuit, lock-in amplifier, FPGA, D / A conversion circuit, linear amplifier circuit and constant current source circuit.

[0060] The photodetector PD1 is used to convert the optical signal output from the sensing head into a current signal.

[0061] The transimpedance amplifier converts the current signal into an analog voltage signal that contains information about the detected acceleration.

[0062] The A / D conversion circuit converts the analog voltage signal into a digital voltage signal, which then enters the lock-in amplifier to perform digital demodulation and low-pass filtering.

[0063] The FPGA generates a high-frequency sinusoidal signal of the same frequency, which is used for phase modulation of the cantilever beam and phase-sensitive demodulation of the lock-in amplifier.

[0064] The cantilever beam phase-locked controller and the light source power controller are FPGA-based digital closed-loop controllers, including but not limited to digital PID controllers.

[0065] The D / A conversion circuit converts the processed digital voltage signal into an analog signal.

[0066] The linear amplifier circuit performs impedance matching on the converted analog voltage signal and applies it to the coil of the electromagnetic drive module.

[0067] The photodetector PD2 can be packaged together with the laser LD. PD2 is used to monitor the optical power output from the back of the laser LD.

[0068] The current output by photodetector PD2 is used to obtain an analog voltage signal through a transimpedance amplifier. This signal is then digitally acquired through an A / D conversion circuit and processed by the light source power lock controller. The output deviation signal is then applied to the laser LD through a D / A conversion circuit and a constant current source circuit, causing the light source output power to tend to a steady-state value.

[0069] Cantilever beam phase-locked loop workflow: The FPGA generates two high-frequency sinusoidal signals of the same frequency. One of them is used as a modulation signal and is applied to the coil of the sensitive head magnetic torque device through a D / A conversion circuit and a linear amplifier circuit to achieve phase modulation of the cantilever beam. When an acceleration signal is input, the modulated light intensity signal is converted into a digital voltage signal with acceleration information through a photodetector PD1 and then converted into a digital voltage signal with acceleration information through a transimpedance amplifier and an A / D conversion circuit. This digital signal is then phase-sensitively demodulated with the other sinusoidal signal of the same frequency generated by the FPGA to filter out 1 / f noise and background stray light interference. The processed digital signal is then sent to the cantilever beam phase-locked controller for processing to obtain a feedback signal U that is linearly related to the external acceleration signal. f On the one hand, it serves as the digital output of the closed-loop system, and on the other hand, it is loaded onto the magnetic torque device of the sensitive structure to achieve servo balance.

[0070] Modulation signal U m Represented as:

[0071] U m =Acosω0t

[0072] A represents the amplitude of the modulation signal, and ω0 represents the modulation angular frequency. The intensity of the diffracted light detected by photodetector PD1 can be expressed as U. 0p (t);

[0073]

[0074] I in Let R be the intensity of the incident light, R be the transimpedance gain of the photodetector, α be the optical path loss, d0 be the initial position of the cantilever beam, and I be the optical path loss. noise This represents stray light interference that did not interfere. Δx represents the displacement change of the cantilever beam caused by the external input acceleration. m The displacement change of the cantilever beam is caused by external acceleration.

[0075] The phase-sensitive demodulation process is as follows:

[0076]

[0077] U is the demodulated digital voltage. 0p (k) represents the digital voltage before demodulation, B represents the amplitude of the demodulated signal, T represents the sampling period, k represents the corresponding discrete time, k1 represents the gain of the transimpedance amplifier, k2 represents the gain of the A / D conversion circuit, and J n The nth order coefficients of the first kind of Bessel function are represented, where n = 1, 2, 3...ω1 corresponds to the angular frequency of the cantilever beam position change Δx.

[0078] The output of the lock-in amplifier after low-pass filtering is:

[0079]

[0080] k is the gain coefficient of the forward channel, and Δk is the laser power I. in Gain fluctuations. It can be seen that after introducing cantilever beam phase modulation, the demodulated output effectively suppresses I. noise Corresponding stray light interference and 1 / f noise. Compared to the electromagnetic force-driven optical accelerometer mentioned in the background technology, the closed-loop detection accuracy is optimized; however, light source intensity noise still exists within the filtering bandwidth of the lock-in amplifier, and the light source I... in This will generate low-frequency fluctuations Δk, which will still limit the detection accuracy and closed-loop stability of the entire optical accelerometer. To solve this problem, we introduced a light source locking loop to stabilize the light source output power to a constant value.

[0081] Light source locking loop operation: The photodetector PD2 and the laser LD are packaged together. PD2 is used to monitor the optical power output from the back of the laser LD. The output current is converted into a voltage signal by a transimpedance amplifier, and then converted into a digital voltage by an A / D converter. In the light source power locking controller, the difference between this voltage and the voltage reference value corresponding to the ideal optical power generates a deviation signal. After processing, this signal enters the constant current source circuit through a D / A converter, and finally serves as the driving current for the laser LD, achieving a stable output laser power Δk≈0. By introducing a light source locking loop, a stable output laser power is obtained, suppressing the light source intensity noise of the laser and solving the problem of optical power drift with temperature changes. This effectively improves the detection accuracy and the closed-loop stability of the optical accelerometer.

[0082] This invention introduces a cantilever beam phase-locked loop into a traditional electromagnetically driven optical accelerometer. On one hand, it uses electromagnetic force to perform closed-loop control of the cantilever beam; on the other hand, it effectively suppresses Ig by high-frequency modulation of the cantilever beam and demodulating the output. noise The corresponding stray light interference and system 1 / f noise are effectively reduced, while ensuring the dynamic range, thus improving the detection accuracy of the optical accelerometer.

[0083] A light source locking loop is introduced into an electromagnetically driven optical accelerometer. By monitoring the output power of the laser LD in real time, the deviation is sent to the light source power locking controller for processing, accelerating the loop's tracking speed and improving its dynamic characteristics. This enables steady-state output of the laser LD power. It also suppresses laser intensity noise and solves the problem of optical power drift with temperature changes, thereby further improving the closed-loop detection accuracy of the optical accelerometer.

[0084] The above description is merely a further embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope disclosed in the present invention, based on the technical solution and concept of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A dual-closed-loop optical accelerometer, characterized in that, include: Sensitive head and signal processing unit; The signal processing unit includes: a laser LD, a first photodetector, a second photodetector, a transimpedance amplifier, an A / D conversion circuit, a lock-in amplifier, an FPGA, a cantilever beam phase-locked controller, a light source power-locked controller, a D / A conversion circuit, a linear amplifier circuit, and a constant current source circuit; wherein, the FPGA is used to generate a first high-frequency signal and a second high-frequency signal, the first high-frequency signal and the second high-frequency signal being sinusoidal signals of the same frequency; The first photodetector, transimpedance amplifier, A / D conversion circuit, lock-in amplifier, cantilever beam phase-locked controller, FPGA, D / A conversion circuit, linear amplifier circuit and sensing head form the cantilever beam phase-locked loop of the optical accelerometer; The laser LD, second photodetector, transimpedance amplifier, A / D conversion circuit, light source power lock controller, D / A conversion circuit, and constant current source circuit form the light source lock loop of the optical accelerometer. The first photodetector is used to convert the optical signal output by the sensing head into a first current signal and send it to the transimpedance amplifier; the first current signal is used to indicate the working position of the cantilever beam. The transimpedance amplifier is used to convert the first current signal into an analog voltage signal containing the detected acceleration information, and then sends it to the lock-in amplifier via an A / D conversion circuit; The lock-in amplifier is used to perform digital demodulation and low-pass filtering on the digital voltage signal based on the first high-frequency signal, and send the processed signal to the cantilever beam phase-locked controller. The cantilever beam phase-locked controller is used to generate a first closed-loop error signal based on the received signal; The D / A conversion circuit is used to receive the mixed signal of the second high-frequency signal and the first closed-loop error signal, convert it to obtain the first analog voltage signal, and send it to the linear amplifier circuit. The linear amplifier circuit is used to impedance match the first analog voltage signal and apply it to the magnetic torque of the sensitive head to adjust the working position of the cantilever beam and stabilize the cantilever beam at the closed-loop working point. The second photodetector is packaged together with the laser LD and is used to send a second current signal to the transimpedance amplifier; the second current signal is used to indicate the optical power of the laser LD outputting backward. The transimpedance amplifier is also used to convert the second current signal into an analog voltage signal containing optical power information, and send it to the light source power lock-in controller via an A / D conversion circuit; The light source power lock controller is used to generate a second closed-loop error signal based on the preset optical power and the received signal; The D / A conversion circuit is also used to convert the second closed-loop error signal into a second analog voltage signal and send it to the constant current source circuit. The constant current source circuit is used to load the received signal onto the laser LD, so that the output power of the light source tends to the preset optical power.

2. The dual closed-loop optical accelerometer according to claim 1, characterized in that, The second closed-loop error signal is used to offset the effects of optical power fluctuations in the phase-locked loop of the optical accelerometer cantilever beam.

3. The dual closed-loop optical accelerometer according to claim 1, characterized in that, Second high-frequency signal U m Represented as: ; The first high-frequency signal is represented as: ; Where A and B are amplitudes, ω 0 represents the modulation angular frequency, t represents time, T represents the sampling period, and k represents the corresponding discrete time.

4. The dual closed-loop optical accelerometer according to claim 3, characterized in that, The intensity of the diffracted light output from the sensitive head detected by the first photodetector is expressed as: U 0P （t） ; ； in, I in The intensity of the incident light provided to the laser LD R Let α be the transimpedance gain of the first photodetector, and α be the optical path loss. d 0 represents the initial position of the cantilever beam. I noise Stray light interference that did not involve interference; Δ x The displacement change of the cantilever beam caused by external input acceleration, Δ x m The displacement change of the cantilever beam caused by the modulation signal; λ is the wavelength of the incident light.

5. The dual closed-loop optical accelerometer according to claim 4, characterized in that, Demodulated signal generated by lock-in amplifier It is expressed by the following formula: ； in, U 0P （k） The digital voltage before demodulation is given, k1 represents the gain of the transimpedance amplifier, k2 represents the gain of the A / D conversion circuit, and J... n The coefficients of order n for the first type of Bessel function, n = 1, 2, 3 ... ∞; ω 1 corresponds to the change in the position of the cantilever beam Δ x angular frequency.

6. The dual closed-loop optical accelerometer according to claim 5, characterized in that, The output of the lock-in amplifier after low-pass filtering is represented as U(k); K is the gain coefficient of the forward channel, Δ k for I in Gain fluctuations.

7. The dual closed-loop optical accelerometer according to claim 1, characterized in that, The sensing head includes: a mass block, a cantilever beam, a diffraction grating, a transparent medium, coils, a yoke, a magnet, electrode plates, and a reflector; among which, The diffraction grating is attached to the upper layer of the transparent medium, and the detection mass block and the diffraction grating form an FP resonant cavity structure; the reflector is set on the mass block and is opposite to the diffraction grating; The coil, yoke, magnet, and electrode plates form a magnetic torque actuator mechanism, which is used to realize the functions of phase modulation and feedback control of the cantilever beam.

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