Linear capacitive microdisplacement transduction using phase read-out

Abstract This paper describes a principles for capcitive transduction of (micro)- displacements. Transducers based on this principle achieve a fixed, built-in sensitivity which is determined only by the transducer's electrode geometry. This geometry can be manufactured accurately by photolithographic processes. The principle renders the transducer immune to small movements in directions other than the main sensitivity axis and to a small rotation and tilt of the electrode planes. The transducers require only one active electrode plane to which wires must be connected. A realization of the principle in thin-film technology is described. This transducer achieves a resolution better than 25 nm, a measurement span of about 1 cm and a non-linearity smaller than 2 μm peak deviation from linear. A large-scale printed-circuit-board realization with an improved electrode geometry results in even better specifications when the scale factor is taken into account.