A Coupled Model of Eddy Current Sensor and Sensitivity Optimization

The thickness is a key parameter of the metal film, which can apparently influence the properties of metal films, such as the conductivity and magnetic. The eddy current technique is a useful method of in-situ metal film thickness measurement due to the crucial properties of non-contact and fast response. Generally, an eddy current sensor consists of a coil and a detection circuit, both of which have direct effects on the measurement performance. And the coupling of the two parts should be paid more attention to application research. For the metal film thickness measurement of nano accuracy, we establish a complete model of eddy current sensor by coupling an electromagnetic field and a circuit field. Using the coupled model, the effects of the coil parameters and excitation signal frequency on the thickness sensitivity are revealed firstly, and it is found there is a big difference between the effects of some parameters on the coil inductance and the output voltage. Based on the effects of the excitation signal frequency, a frequency modulation method is proposed, which provides a theoretical basis for expanding the measurement range with high accuracy and linearity.