Dynamic capacitor having a peripherally driven element and system incorporating the same

A capacitor in which one plate or electrode element is vibratable to achieve a variation in capacitance is described. The capacitor includes two spaced stationary elements. The third element is supported at its center and in the form of a thin diaphragm which is vibrated at its inherent mechanical resonant frequency to achieve a corresponding variation in capacitance between one of the stationary elements and the vibrating diaphragm.