Thermal Noise Model Study For Reaction Cavity Of Low Frequency Electrochemical Seismometer

Seismometer is a kind of sensor which directly contacts with the ground and transforms received vibration signal into digital data through data acquisition system. With the advent and application of new technologies, new types of seismometers are gradually being developed. Electrochemical seismometer is a new kind of seismometer developed in recent years. This kind of seismometer is based on the electrochemical sensing technology principle, different with the existing seismometers which are based on the electromagnetic induction principle. Electrochemical seismometer is mainly composed of an electrochemical reaction cavity and external conditioning circuit. A porous sensing element consists of two pairs of electrodes and the insulating layers is embedded in the middle of the electrochemical reaction cavity. The cavity is filled with a certain concentration of mixing electrolyte. We measure the movement through the changes of ion concentration near the electrode which caused by the convection effect of electrolyte in the electrochemical reaction cavity. The conversion factor of electrochemical seismometer is very high, a very small amount of electrolyte solution(several hundred mg to several g) may produce a very high gain. This feature allows the electrochemical seismometer still maintain a high sensitivity at very low operating frequencies. But as a new product, the current technology is not yet fully mature and need to be continue researched and developed. The output signal of the sensor is very small and can easily be lost in the noise signal, so we must focus on the study of noise. Looking for an effective way to suppress noise and reduce the impact of noise on test results. In this paper, we mainly studied the inside noise for the electrochemical reaction cavity of the electrochemical seismometer. We mainly conducted the following research in this paper:(1) Analyzing noise generation mechanism for the reaction chamber of electrochemical seismometer. Self-noise closely affects performance of seismometer. In this paper, we combined other scientists’ previous noise research of electrochemical seismometer, theoretically analyzed various components of electrochemical seismometer and analyzed its generation mechanism.(2) The derivation and verification of the thermal noise model for the reaction cavity of electrochemical seismometer. Thermal noise is one of the most important noise in the reaction cavity. Its research is very significant for reducing the noise of reaction chamber and improving the performance of the seismometer. In this paper, the equivalent circuit of the sensing element is obtained based on the working principle of electrochemical seismometer and the structural characteristics and working principle. On this basis, the mathematical model of thermal noise of reaction chamber is obtained. Then a set of noise test system is built and the mathematical model of thermal noise of reaction chamber is verified through experiments.(3) Building the multi-physics simulation model for the sensing element of electrochemical seismometer and analyzing the influence of the structure parameters of the reaction cavity and the characteristics of the electrolyte on the thermal noise of the reaction cavity based on simulation. In this paper, according to the characteristics of sensitive element of the electrochemical seismometer, we built a multi-physics simulation model which contains fluid field and electric field. This model can fully demonstrates the ion concentration distribution, the potential distribution,current density distribution, the ion flux and other information inside the reaction cavity of electrochemical seismometer. The influence of the structure parameters of the reaction cavity and the characteristics of the electrolyte on the thermal noise of the reaction cavity was analyzed based on simulation. The simulation results provide a reference for the suppression of the reaction cavity noise.