Study On The Underwater Electric Field Sensor Used In Target Detection

With the status of the sea being more outstanding,underwater target detection becomes increasingly important.Ship electric field is an important signal of underwater target detection target.Aiming at the problem of complexity to computing ship electric and large noise of underwater electric field sensor,this paper systematically researches the electric field distribution characteristics from the ship,the equivalent circuit model of measuring,and underwater electric field sensor low-noise designing.A ship source model was built based on finite element method,according to the generating mechanism of ship electric field and corrosion protection system.The precision of ship electric is improved from the signal source level.An air-sea-seafloor three-layer model was built,and the finite element method was used to compute the ship electric field of three-layer model,which avoids the complicated calculating process.An equivalent circuit model of underwater electric field measurement was established,by analyzing the electrical characteristics under the action of underwater electric field of seawater and measuring electrodes.It is discovered that noise of pre-amplifier is the key factor to limit sensor noise performance improvement,by analyzing the noise of the equivalent circuit.The noise of the carbon electrode was analyzed by analyzing fluctuation of capacitance value.It was found that: the carbon electrode avoids the electrochemical noise which Ag/AgCl electrode has,and the noise of carbon electrode is weaker than noise of Ag/AgCl electrode.Structure of underwater electric field sensor based on the principle of magnetic measuring current and the carbon electrode was proposed.Using the advantages of high sensitivity and low noise of GMR,this paper presents the module of measuring current by magnetic,which realizes the function of pre-amplifier,and conducts a verification experiment.The test demonstrates,in the situation of the magnetic sensitive materials being modulated,equivalent input noise voltage in low frequency band of module of measuring current by magnetic is 0.5 nV/Hz.the module's noise level decreases nearly an order of magnitude.The results prove that,it is believed that the ship electric field plays an important role in the field of underwater target detection,as well as feasibility of improving noise levels of the underwater electric field sensors by carbon electrode and module of measuring current by magnetic.