Capacitive displacement transducer for a weak-motion inertial sensor

Abstract

A broadband weak-motion inertial sensor includes a frame, a movable inertial mass, a forcing transducer for keeping the inertial mass stationary relative to the frame during operation, and a flexure for suspending the movable mass in the frame. Two or more closely spaced, substantially parallel capacitor plates, at least one attached to the frame, and one attached to the movable inertial mass, form a capacitive displacement transducer. The capacitor plates have a plurality of apertures with dimensions and arrangement chosen to simultaneously minimize damping induced thermal noise and give a high spatial efficiency. In an implementation, three capacitor plates are provided. The capacitor plates each have a same hexagonal pattern of circular holes; the holes are aligned on all included capacitor plates. Radius and spacing of the holes are dictated by a relationship that determines the minimum damping per unit capacitively effective area for a desired spatial efficiency, gap height and capacitor plate thickness. In an implementation, the capacitor plates are made of a printed circuit board material which, through etching of the thin conductive layer, can be mounted directly to a conductive frame and conductive inertial mass without the use of non-conductive spacers.