Leach, R K; Oldfield, S; Awan, S A; Blackburn, J; Williams, J M (2004) Design of a bi-directional electrostatic actuator for realising nanonewton to micronewton forces. NPL Report. DEPC-EM 001

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Abstract

This report describes the design of an electrostatic actuator for incorporation into a low force measuring instrument that operates over the range 1 nN to 10 µN. The force being measured is balanced by applying an equal and opposite electrostatic restoring force. The low force measuring instrument also requires a prior calibration of the capacitance gradient of the actuator. A number of capacitor geometries were considered but the need for a bi-directional actuator and ease of manufacture have led to a system with two sets of parallel plate capacitors (i.e. a four-plate capacitor) with a moving dielectric plate that is displaced by the application of the force being measured. To the authors’ knowledge such a four-plate capacitor arrangement has not been used before and should give a significant improvement over existing low force measuring instruments. The report describes a theoretical model of the four-plate capacitor with moving dielectric. Finite element models that were used to investigate the effects of undesired motion of the dielectric plate are then described. Unlike a two-plate capacitor, a four-plate design requires at least six measurements to determine a capacitance matrix and these measurements are discussed. Finally, the practical realisation of a four-plate capacitor is considered.

Item Type:	Report/Guide (NPL Report)
NPL Report No.:	DEPC-EM 001
Subjects:	Engineering Measurements Engineering Measurements > Dimensional
Last Modified:	02 Feb 2018 13:16
URI:	http://eprintspublications.npl.co.uk/id/eprint/3038

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