Closed-loop capacitive readout based on mode localization effect in weakly-coupled RLC circuits

Accurate detection of capacitance change is an essential requirement for capacitive sensors development. This paper presents a closed-loop circuit of weakly-coupled RLC resonators for high-resolution capacitive readout. Mode localization effect in the weakly-coupled RLC resonators is studied and the comparison shows superiority in linearity by a closed-loop method. The experimental results validate a capacitive readout resolution of 37.5fF and a 216 times improvement of sensitivity as compared with the frequency shift method. This work indicates that the proposed closed-loop configuration has a better performance than the open loop method, and is less expensive, more compact and much easier for practical application to detect capacitance variance based on mode localization effect in coupled RLC resonators, which makes it a promising method for developing ultra-sensitive capacitive sensors.