Versatile micro sensor for micro machine applications

Most conventional eddy current sensors are used for position measurements where the target approaches the sensor coil along its axial direction. In this paper we investigate a versatile eddy current micro sensor that can not only be used for measuring displacements parallel to the axis of the sensor coil but also for transverse displacement measurement in micro magnetic bearings for micro machines. In the transverse mode, the sensor coil impedance variation has been typically found to be less than when used in the axial mode. A number of approaches and techniques have been investigated and will be discussed to overcome the problem of low sensitivity. As a result a versatile eddy current sensor has been developed which is suitable for transverse position measurement in micro magnetic bearings. Experimental results shown that micro sensor sensitivities up to 20mV/mu m can be achieved when the target moves between two sensor coils. The performance of the micro sensor suggests that it will have considerable scope for application in the micro machine area.