Research Of Piezoelectric Geophone Based On PVDF Piezoelectric Film

Seismic exploration is the most common method to explore mineral resources in modern society,which is of great significance for solving the energy problem in China.Besides,seismic exploration plays an important role in the detection of engineering safety and geological hazard assessment.As the most front-end equipment of seismic exploration,the performance of geophone determines the performance parameter of seismic exploration system to a large extent.The development of geophone has gone through three stages of moving coil geophone simulation geophone,digital seismometer and MEMS digital geophone.There are various geophones such as magnetoelectric geophone,piezoresistive geophone,piezoelectric geophone,electrochemical geophone,optical fiber geophone and MEMS digital geophone.The magnetoelectric geophone and piezoresistive geophone have low sensitivity,narrow frequency bandwidth and small dynamic range,which make it can't meet the needs of future seismic exploration engineering.Electrochemical geophone,optical fiber geophone and MEMS digital geophone are more advanced and expensive,and their suitability in different areas is still need to be verified.The piezoelectric geophone has high sensitivity,wide bandwidth,large dynamic range,strong applicability and moderate price,so it has a good application prospect.The current piezoelectric geophone is mostly based on the piezoelectric ceramics,which is limited to the heavy and fragile defects of the piezoelectric ceramics.The piezoelectric ceramic geophone structure is not flexible enough and the low frequency cut-off frequency is about 10Hz,so the broad bandwidth characteristics of piezoceramic as electromechanical transducer can't be utilized,and it still can't meet the requirements of the future low frequency seismic exploration.PVDF is a new type of piezoelectric copolymer material.Compared with traditional piezoelectric ceramics,PVDF piezoelectric film has the advantages of high voltage constant,wide effective frequency range,large dynamic range,light,flexible,easy to process into various shapes,easy to match the acoustic impedance and resist chemical corrosion.It has been widely used in various MEMS sensors.It is very promising to develop a new kind of piezoelectric geophone which has new structure,higher sensitivity in band frequency range and better low frequency cut-off frequency based on PVDF piezoelectric film.A new type of piezoelectric geophone with lower frequency cut-off frequency and wider frequency response.According to the excellent characteristics of PVDF,this paper will study the geophone based on PVDF piezoelectric film utilizing theoretical model analysis,finite element simulation analysis,contrast experiment analysis,signal conditioning and digitalization,data storage,calibration test and other technical methods.The main contents of this paper are as follows:1.We discussed the basic principles of seismic exploration,the importance of low frequency seismic exploration,the essence and characteristics of seismic reflection waves.Based on the above contents,the overall research plan of digital geophone based on PVDF piezoelectric thin film is proposed.2.The working principle and advantages of PVDF film are discussed.The vibration characteristics of the cantilever beam are analyzed.The sensitive element structure that the PVDF piezoelectric film combined with a spiral cantilever beam with mass is designed.3.Through theoretical deduction,finite element simulation and comparative experiments,the influence of structural parameters on the performance of sensitive element is studied.4.According to the electrical properties of the piezoelectric film and the application environment of the seismic geophone,a signal conditioning circuit composed of amplification and filtering is designed,and a digital module circuit is designed to enhance the anti-interference ability of the signal transmission.5.The encapsulation design of the geophone is carried out.The property test and calibration experiment of the designed geophone verify the effectiveness of the digital piezoelectric geophone based on the PVDF piezoelectric film.After relative calibration and absolute calibration,the sensitivity of 230mV/m/s~2 is stable in the range of 4~90Hz frequency.This research provides a new idea and reference for the development of piezoelectric geophone based on PVDF piezoelectric thin film.