Research On Piezoelectric Geophone Based On Force Balance Feedback

China's economy has maintained rapid development for a long time,and the demand for mineral resources has gradually increased,causing the supply to exceed demand.Therefore,it is necessary to increase the exploration of mineral resources.Seismic exploration methods are widely used in marine and terrestrial oil and gas resource exploration.Seismic data acquisition is an important foundation of the entire seismic exploration.As a key instrument for seismic data acquisition,geophones have a direct impact on the effect of seismic exploration.As the demand for mineral resources increases,my country needs to increase the depth of seismic exploration.In the process of deep seismic exploration,the reflected waves received by geophones are mainly low-frequency signals.Natural frequency is an important performance index of geophones.As the natural frequency decreases,the ability of geophones to detect weak low-frequency signals is stronger.In order to realize deep seismic exploration,it is necessary to rely on geophones with lower natural frequencies.The use of force balance feedback technology can make the performance of the geophone not completely dependent on its internal mechanical structure.By changing the feedback network parameters,the natural frequency and frequency band range of the geophone can be changed under the condition of the same mechanical structure.It is of great significance to introduce force balance feedback technology in the research of the device.Currently,there are three main types of force balance feedback geophones used in deep seismic exploration:moving coil type,differential capacitive type and electrochemical type.They use electromagnetic actuators to generate a balance force to extend the natural vibration period of the sensitive unit structure.The feedback network is mostly an analog PID circuit,which has disadvantages such as complex structure and inaccurate control.This paper designs a piezoelectric geophone based on force balance feedback.The cantilever beam structure is used as the base,and PVDF piezoelectric films are pasted on its upper and lower surfaces,which are used as piezoelectric sensors and piezoelectric actuators.The cantilever beam and piezoelectric film form the sensitive unit structure of the geophone.Piezoelectric sensors are used to detect vibration signals.Because the output charge signal is relatively weak,the designed signal conditioning circuit has the function of amplifying and filtering,which can be converted into a voltage signal that the single-chip microcomputer can recognize and process.The built-in ADC of the STM32F407 microcontroller converts the analog voltage signal into a digital signal.On the one hand,it stores data,and on the other hand,it calculates and outputs the digital control quantity according to the pre-designed PID control algorithm.The built-in DAC of the single-chip microcomputer converts the digital control quantity into an analog control signal.The analog control signal acts on the piezoelectric actuator through the piezoelectric driving power supply and outputs a high-voltage driving signal.The piezoelectric actuator deforms due to the inverse piezoelectric effect and balances the cantilever beam.The vibration of the structure extends its natural vibration period,thereby reducing its natural frequency.The main contents are as follows:First,the basic properties of piezoelectric materials are analyzed,and PVDF piezoelectric films are selected as sensors and actuators.The vibration characteristics of the cantilever beam structure are analyzed,and the finite element simulation analysis is carried out using COMSOL Multiphysics 5.4 software to study the natural frequency of the cantilever beam with or without sticking actuators and different structural parameters and materials.The simulation results show that the pasted actuator can effectively reduce the natural frequency of the cantilever beam structure,and a force balance feedback closed-loop control system is designed.Secondly,in view of the high internal resistance of the PVDF piezoelectric film,the charge amplifier circuit based on CA3140 operational amplifier and the voltage amplifier circuit and filter circuit based on OP07 operational amplifier are designed,and the minimum system of STM32F407 single-chip microcomputer and its peripheral circuits are designed for data storage.And PID control.The PID control strategy is simulated and analyzed through MATLAB Simulink module,and the software design is completed.Finally,the absolute calibration method is used to test and calibrate the performance of the piezoelectric geophone.The experimental results show that the output sensitivity of the piezoelectric geophone studied in this paper is about245m V/m/s~2,the distortion is about 0.46%,and the dynamic range is about 102d B.Compared with the piezoelectric geophone without force balance feedback,the natural frequency is reduced from 5 Hz to 3 Hz,which verifies the effectiveness of the piezoelectric geophone.