Development Of Miniaturized Electromagnetic Wave Sensor Suitable For Seismic Electromagnetic Monitoring

Earthquake is a frequent and highly destructive natural disaster,it is very necessary to realize the effective prediction of earthquake before it comes.Studies have shown that the low-frequency electromagnetic disturbances before earthquakes contain abundant information of earthquake precursors.Therefore,monitoring the anomalous signals of low-frequency electromagnetic waves before earthquakes is particularly important for earthquake prediction.At present,the electromagnetic wave sensor used to monitor the seismic electromagnetic disturbance has the defects of large volume and heavy weight.Aiming at the above problems,the miniaturized electromagnetic wave sensor developed in this paper has greater advantages in earthquake precursor monitoring.The research work of this paper is as follows:(1)This paper focuses on the monitoring of pre-earthquake low-frequency electromagnetic disturbance,and takes the development of miniaturized electromagnetic wave sensors as the research goal.Firstly,the working principle of the sensor is analyzed,the control model of the sensor is established,and then the sensitivity formula of the sensor is deduced.According to the simulation results of different sizes of magnetic flux concentrators and the analysis of the characteristics of the hollow magnetic core,the hollow magnetic core structure with magnetic flux concentrators is designed.In order to make the developed sensor more suitable for the harsh environment at the seismic fault zone,the digitalization of the electromagnetic wave sensor is further realized by combining the digital acquisition system.Then by analyzing the noise source and mass distribution of the sensor,a low-noise preamplifier circuit is designed,and the noise and mass model of the sensor is established.Finally,in order to realize the miniaturization of the sensor,the quality of the sensor is optimized by particle swarm optimization with the constraints of the sensor's equivalent input magnetic field noise and the diameter of the magnetic flux concentrator.(2)According to the performance requirements of the electromagnetic wave sensor's analog voltage output range,frequency band and noise,a low-noise acquisition system is designed.Firstly,the working principle of the sensor acquisition system is analyzed in detail,and the design of the signal conditioning circuit,analog-to-digital conversion circuit and low-noise power supply circuit of the acquisition system is completed.After testing,the short-circuit noise of the acquisition system in the frequency band of0.5Hz?60Hz is about-120d B,and its corrected fitted straight line is approximately the same.(3)According to the sensor design requirements,a test platform for the equivalent input magnetic field noise and sensitivity of the sensor is built,and the self-made acquisition system and the high-precision 4431 acquisition card produced by NI are used to test the equivalent input magnetic field noise and sensitivity of the self-made sensor.The test results show that in the 0.5Hz?60Hz frequency band,the measured sensor sensitivities are:22.89m V/n T@1Hz and 22.67m V/n T@1Hz,respectively,and the equivalent input magnetic field noise is 2.91p T/Hz^1/2@1Hz and 2.94p T/Hz^1/2@1Hz,the test results are approximately consistent with the theoretical optimization results.The mass of the electromagnetic wave sensor is 130g,which realizes the design of the miniaturized electromagnetic wave sensor.