Research Of Micro Eddy Current Sensor

Eddy current sensor is the kind of sensor based on the principle of eddy current effect.It is a special kind of non-contact sensor with excellent performance.Eddy current sensor is mainly used to measure the static and dynamic distance between the sensor probe and the object.The object is generally a kind of conductor,and then some electrical parameters of the sensor probe change.The sensor's electronic circuit will sense and deal with those changes.In addition to sensing the distance,eddy current sensor can also realize the the non-contact measurement many physical properties such as thickness,strain and hardness.Besides,eddy current sonser can also detect the vibration,speed,temperature and acceleration.In the industry field,eddy current sensor is applied to non-destructive testing.In this paper,we propose an innovated micro eddy current sensor which derives from planar coil.Its main structure consists of two coils.One is used to introduce the electronic signal and generate the magnet field and called driving coil.Then another coil will generate electromotive force and called sensing coil.If a testing object of conductive materials gets near to the sensor,then there will be eddy current on the object leading to energy losss and the eleceromotive on the sensing coil will vary.Accoding to the rule the sensor can detect the distance,flaw and materials.Next,finite element analysis is used analyse some parameters which may influence the function of the sensor.Taking all elements including the MEMS technology into account,the detailed structure parameter is determined such as the width and height of the coil.Then an optimization of MEMS fabrication process is made to secure the property of the sensor.Trdationally,MEMS technology use photoresist and silicon oxide.However,they both has drawbacks which depress the function of the sensor.So an exploration about two materials is conducted and finally we find that the polyimide is the most suitable material.After the fabrication of the micro eddy current sensor,the test is made to find out the practical property of the sensor.The results show that it can effectively measure the distance within 1.5mm and its sensitivity is about 20 um.The testing result is similar to the simulation result.Also,the sensor can be applied to detect the flaw on the object and tell different matrials apart.Finally,an analysis about the sensor temperature under the working condition is made to secure that even after a long time of working,the sensor can still work normally.