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The inertial navigation system uses both gyroscopes and accelerometers to measure the state of motion of a target or a vehicle by sensing the changes in that state caused by accelerations. The required features in many of these applications are high precision, wide dynamic range and wide frequency range. In this paper, recent advances made on Wireless MEMS-IDT based accelerometers and gyroscopes are presented. The concept and design principles underlying a MEMS-IDT (Interdigital Transducer) based accelerometer and gyroscope are based on using surface acoustic waves (SAW) and polysilicon seismic mass for acceleration and proff mass for gyro. This unique concept is a departure from the conventional comb driven MEMS accelerometer design. By designing the seismic mass of the accelerometer to float just above a high frequency Rayleigh Surface Acoustic Wave Sensor (SAWS), we are able to realize the accuracy and versatility required for the measurement of accelerations from 10-6g to 100g. The gyro design is based on the combination of Surface Acoustic Wave Resonator (SAWR) and Surface Acoustic Wave Sensor, which operates at the Rayleigh mode. They possess typical advantages of MEMS sensors including the additional benefits of robustness, excellent sensitivity (about 1 deg./hr.), surface conformability and durability. The transmitter IDT creates SAW (Surface Acoustic Wave) that propagates back and forth between the reflectors and forms a standing wave pattern within the cavity space between the IDTs. The particles at the anti- nodes of standing wave pattern experience large amplitude of vibration perpendicular to the plane of the substrate, which serves as the reference vibrating motion for this gyroscope. A number of metallic (proof) masses are strategically positioned at the anti-node locations so that the effect of the Coriolis force can be used to sense the gyroscopic motion. Another unique feature of the device is that because the SAW device operates at RF frequencies, one could easily connect the IDT device to a microstrip antenna and read the acceleration and gyro rate remotely by wireless transmission and reception using the Bluetooth technology. This concept is proposed in this paper.
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