Deformation sensitive cuts of quartz for torque sensor

Single crystal quartz is a common substrate used in sensors for measurement of pressure, stress and torque. We report on the calculation of the torque sensitivity of SAW resonators arranged on all possible orientations of quartz substrate. The calculation is based on third order material constants and it has predicted useful orientations combining good sensitivity (3-3.5 times better than that of the ST-quartz) with practical wave propagation properties. The wafers with selected cuts of quartz have been fabricated; four resonator layouts were designed in order to work with arbitrary phase of reflection coefficient from electrodes. Resonators were tested and measurements prove the validity of the calculations. An important feature of torque sensors is the temperature dependence of the torque sensitivity that cannot be predicted in calculations with third order constants and that may be prohibitively large. This feature has been measured and relatively weak temperature dependence has been found for some cuts, notably for Y+27° cut with the propagation direction of 50° to the X axis.