Dual-mode thickness-shear quartz pressure sensors for high pressure and

Abstract

A dual-mode thickness-shear quartz pressure transducer includes a unitary piezoelectric crystal resonator and cylindrical housing structure wherein the resonator is located on a median radial plane of the housing and the exterior of the housing is provided with a pair of parallel flat surfaces which are located at an angle relative to the X' axis of the resonator. According to the presently preferred embodiment, the transducer is made from an SC-cut or a WAD-cut solid quartz crystal cylinder which is ultrasonically milled to form a plano-convex or bi-convex resonator disk in the medial radial plane of a hollow cylinder and the pair of exterior flats. The wall thickness of the cylinder is altered at the location of the flats such that stresses at the center of the resonator disk are anisotropic. According to the invention, the ratio of the stresses at the center of the resonator disk along the X' and Z' axes are optimized such that the pressure sensitivity of the third thickness harmonic of C mode vibration is maximized. Optimization of the ratio of the stresses along the X' and Z' axes is accomplished in particular by altering the (azimuthal) angle of the flats. According to a presently preferred embodiment of the invention, the flats are located at an azimuthal angle of approximately 134.degree. relative to the X' axis of a WAD-cut resonator.