GB1094862A - Improvements in and relating to strain gauges - Google Patents

Abstract

1,094,862. Semi-conductor strain gauges. ETHER ENGINEERING Ltd. March 29, 1965 [March 31, 1964], No. 13333/64. Heading H1K. [Also in Division G1] A transducer has a plurality of elongate piezo-resistive semi-conductor elements formed integrally with an edge-clamped circular diaphragm at one of its faces, and is so designed that substantially no adverse interaction occurs between the response of each element to transverse and longitudinal strain. This is achieved either by so orientating an element relative to the crystal structure that the response to transverse strain is much less than that to longitudinal strain (or vice versa) or by positioning the element on the diaphragm in a region where it will be strained in only one of the transverse and longitudinal directions. The diaphragm is made of a monocrystalline semi-conductor such as silicon and the elements are formed by localized diffusion or epitaxial growth. The embodiments illustrated (not shown) each have four active elements which in operation are used as the four arms of a bridge. The transducer is used to measure the differential pressure between the two sides of its diaphragm. Because of the clamping there will be little tangential strain at the periphery of the diaphragm and the diaphragm will have a double curvature under the impressed load resulting in the presence of a neutral circle at which the radial strain is zero. The position, orientation relative to the crystal axes, and conductivity type of the elements are chosen bearing in mind these facts. It is stated that the transducer may have only two elements (responding in opposite senses) which are connected in a half-bridge arrangement.