The design, development and performance evaluation of a novel radio frequency microelectromechanical systems (MEMS) gyroscope, based on a surface acoustic wave resonator (SAWR) and a surface acoustic wave sensor is presented in this paper. Most of the MEMS gyroscopes based on silicon vibratory structures that utilize the energy transfer between the two vibratory modes demand small fabrication tolerances to minimize signal output when there is no rotation (i.e. zero rate output). This 1 cm × 1 cm gyroscope operates based on the principle of a surface acoustic wave (SAW) on a piezoelectric substrate. The SAWR creates SAW standing waves within the cavity space between the interdigital transducers (IDTs). The particles at the anti-nodes of a standing wave experience large amplitudes of vibration perpendicular to the plane of the substrate, which serves as the reference vibrating motion for this gyroscope. A number of metallic dots (proof masses) are strategically positioned at the anti-node locations so that the effect of the Coriolis force due to rotation will amplify the magnitude of the SAW that is generated in the orthogonal direction. The performance of this 74.2 MHz MEMS-IDT gyroscope has been evaluated using rate table and geophone setups , indicating very high sensitivity and dynamic range, which is ideal for many of the commercial applications. Unlike other MEMS gyroscopes, this gyroscope has a planar configuration with no suspended resonating mechanical structures, thereby being inherently robust and shock resistant. In view of its one-layer planar configuration, this gyroscope can be implemented for applications requiring conformal mounting onto a surface of interest.
This paper presents the prediction and measurement of the phase response from a wireless surface acoustic wave (SAW) device for temperature sensing applications. This wireless sensor consists of two or more arrays of an interdigital transducer (IDT) and reflector pair with different IDT-reflector distances. Pulse modulated signals are transmitted from a remote reader system and their echoes are returned with different time delays due to the different IDT-reflector distances. Corresponding intermediate frequency signals are generated in a mixer and their phase differences are calibrated to temperature values. Using the coupled-mode theory of SAWs, the phase characteristic relative to temperature was examined. The effect of the relative distances between the two reflector arrays is demonstrated. The influence of the phase reversal location, which produces multiple temperature values for a given phase difference, is also discussed and a simple solution is illustrated. This sensor is coupled with a small planar antenna, which will be well suited for applications that require passive and conformal sensors.
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