A study of the effect of different coplanar dual-coil geometries on the performance of mutual inductance

Abstract

This paper studies the sensing performance of different coplanar dual-coil geometries, which affects the phase variation of mutual inductance. Five micro-coil designs, including square, circular and three rounded rectangular types, are proposed in this study. These are fabricated using a simple silicon-based micro-electroplating process. By measuring the phase variation between the excitation and sensing coils, the sensing performance of different coil designs, with the effect of eddy current, are characterized quantitatively. Commercial COMSOL software and Multisim are used to evaluate the equivalent electrical properties for each type of coil under the same specification. Analysis results show that the phase difference is dominated by mutual inductance and coupling capacitance, and the square-like coils produce a smaller phase difference. The experimental results also show that the more it approached a square-type coil, the smaller the phase difference became. Using saline concentrations from 0% to 20%, the positive phase shift for the square-type coil increased as the concentration increased to a maximum value of plus 4°. The opposite is true of circular coils, with a maximum negative phase shift of minus 5.5°. It is revealed that a specific sensing performance is easily realized by changing the coil geometry and its feature size.