Capacitive monitoring of electrostatic MEMS tunable evanescent-mode cavity resonators

This paper presents for the first time a novel concept for monitoring the resonant frequency of electrostatic MEMS tunable high-Q evanescent-mode cavity resonators through capacitance measurement. The proposed scheme relies on the fact that there is a one-to-one correspondence between the actuation capacitance C_s and the resonant frequency f₀. This relationship is derived theoretically using a spring-mass model. The proposed monitoring concept is then validated by static measurement using a capacitance meter. Discussions are given on implementing a dynamic monitoring scheme by using custom-designed integrated high-speed CMOS capacitance sensors.