The effect of electrical parameters of eddy current sensor on metal film thickness measurement performance and the optimization method

Eddy current sensors have been widely used in the field of micro- and nano-measurements. The detection circuit is a key part of eddy current sensors. In particular, the electrical parameters in the signal conversion circuit have an important effect on the measurement performance. It is necessary to study the effect of the electrical parameters on the measurement performance and propose an optimization method. In this study, a simulation model of the eddy current sensor is established by coupling a magnetic field and a circuit field. The circuits include the LC parallel resonance, the AC bridge, and three combination circuits of the LC resonant and AC bridge. The output voltage variation with the thickness of copper film is calculated, and the effect of the electrical parameters on sensitivity K_i is obtained. In the LC parallel resonant circuit, it’ is revealed that K₁ is maximum when the parallel capacitance C_P is equal to the resonant capacitance C₀. An optimization method of adjusting resistance R_S in different thickness intervals is proposed. In the AC bridge circuit, it’ is revealed that there exists an optimal R_S, which makes K₂ maximum. In three combination circuits, K₃, K₄, and K₅ are the maximum when the capacitances (C₁, C₂, and C₃) reach the resonant capacitance C₀. In addition, the sensitivity of each combination circuit is improved compared with that of the AC bridge. The relevant analysis results are further verified by a series of experiments. According to the calculation results and the experimental analysis, the optimization method for electrical parameters is further proposed.