title: On the design of capacitive sensors using flexible electrodes for multipurpose measurements.
abstract: This article evaluates the potential of capacitive measurements using flexible electrodes to access various physical quantities. These electrodes are made of a thin metallic film, typical thickness 0.2 microm, evaporated on a plastic substrate. Their large flexibility enables them to be mounted in complex geometries such as curved surfaces. In the configuration of planar condensers, using a very sensitive commercial capacitive bridge and a three-terminal measurement method, several measurements are presented. A relative resolution of 10(-8) for the thermal expansion of samples is obtained at low temperature in a differential configuration. The same technique adopted for pressure gauge measurements at low temperature led to a typical 0.1 Pa resolution over a dynamic range of 10(4) Pa. In the configuration of interleaved electrodes, condensers have been used to measure wetting by either bulk liquid helium or by thin continuous helium films in a cylindrical pipe. Both experimental and numerical evidence is provided, showing that the close proximity of a reference ground potential significantly increases the relative sensitivity to fluid wetting. Further, interleaved electrodes can be used to access both the area that is covered by a liquid film but also to determine the thickness of this film, provided it is comparable to the periodicity of the electrode pattern.
authors.affiliation: Centre de Recherches sur les Très Basses Températures, Laboratoire Associé à l'Université Joseph Fourier, CNRS, BP 166, Grenoble Cedex 9, France. pierre.thibault@ujf-grenoble.fr
authors.forename: Pierre
authors.initials: P
authors.lastname: Thibault
authors.forename: Pantxo
authors.initials: P
authors.lastname: Diribarne
authors.forename: Thierry
authors.initials: T
authors.lastname: Fournier
authors.forename: Sylvain
authors.initials: S
authors.lastname: Perraud
authors.forename: Laurent
authors.initials: L
authors.lastname: Puech
authors.forename: P-Etienne
authors.initials: PE
authors.lastname: Wolf
authors.forename: Bernard
authors.initials: B
authors.lastname: Rousset
authors.forename: Roser
authors.initials: R
authors.lastname: Vallcorba
mesh_terms: D025802:Electric Capacitance; D004566:Electrodes; D006371:Helium; D011312:Pressure
chemical_list: D006371:Helium