Development Of Lightweight Wound Hollow Core Inductive Magnetic Sensor

Inductive magnetic sensor is developed based on Faraday law of electromagnetic induction and because of its high sensitivity,good stability,wide detection range and low cost,it has been widely applied in many fields,such as electronic and electrical application,industrial automation,geological research,space electromagnetic research and biomedical science et.al.With the rapid development in many fields and the increasing demands for the performance and adaptability of weak magnetic field sensors,we are encouraged to involve in continuous innovation in facilitating weak magnetic field detection instrumentsInductive magnetic sensor is widely used in frequency domain of electromagnetic detection.In recent years,there has been great progress in improving the sensitivity of inductive magnetic sensor and reducing the noise of inductive magnetic sensor by optimizing the performance of inductive magnetic sensor.The inductive magnetic sensor is composed of the amplifying circuit at the back end and the sensitive part at the front end which consists of magnetic core and search coil contributing the most mass of the sensor.therefore,the inductive magnetic sensor still have the disadvantages of large volume and insufficient mass in weak field measurement.There is an optimal relationship between the equivalent magnetic field noise and the coil parameters and the coil quality of the inductive magnetic sensor.so,it is of great practical significance to develop a miniature,lightweight,high-performance inductive magnetic sensor.The main research work of this paper is as follows:1.Firstly,analyze the working principle of the inductive magnetic sensor,introduce the factors affecting the sensitivity of the inductive magnetic sensor,analyze the expression of demagnetization factor of the hollow core,the expression of the demagnetization factor of hollow core is obtained by the form of elliptical integral,and then simulate the magnetic flux parameters of the search coil with hollow core and the search coil with rod-shaped core.Finally,obtain the expression of effective magnetic permeability utilizing the equally numerical relation of the magnetic flux between coil with hollow core and the coil with rod-shaped core.2.The noise sources of the inductive magnetic sensor with hollow core are analyzed drawing a conclusion that the equivalent magnetic noise of the inductive magnetic sensor is mainly composed of resistive thermal noise.Since the mass of the coil is also a considerable indicator in the process of design of the inductive magnetic sensor,the dependence of equivalent magnetic field noise and coil mass on diameter of wire enameled in copper and the number of turns of the coil is firstly analyzed respectively,and then the optimum number of coil turns and the optimum diameter of copper enameled wire are obtained by mathematical modeling.3.The composition of the differential amplifier,the voltage noise and current noise of the circuits are analyzed.In order to obtain better sensitivity of the inductive magnetic sensor,the voltage noise of the preamplifier is 3-4 times lower than the thermal noise of the search coil,so the differential amplifier is implemented based on the calculated effective magnetic field noise.4.The accomplished induction magnetic sensor with hollow core is tested and verified,and the results of sensitivity calibration and equivalent magnetic field noise of the inductive magnetic sensor are given respectively.The sensitivity is linear in the range of 1 to 100 Hz with 5.2mV/nT@1Hz and 0.73V/nT in flat part.The noise at100Hz is 0.06pT/Hz^1/2,and the experimental results are consistent with the theoretical analysis.The total mass of the magnetic sensor is 80g,enabling the design of a lightweight,wound,inductive magnetic sensor with hollow core.