The heart of the torque sensor is a strain sensitive SAW device. SAW stands for Surface Acoustic Wave and refers to the principle by which high frequency mechanical vibrations can exist on a solid surface – basically analogous to waves on top of the sea. ”The Transense sensor consists of a preformed piezo-electric quartz die on which up to 3 resonators are deposited using well-established photo-lithographic technology,” explains David Vile. In response to a nominal 433 MHz interrogation signal, this passive sensor returns signals at the natural frequencies of the resonators, which are directly related to the mechanical and thermal strains on the quartz die from which torque and temperature can be derived. Transense is also taking a new route with respect to data transmission, because, in order for the sensor to be able to measure torque accurately, it has to be welded or bonded directly to gear shafts or disk components and therefore be exposed to oil at high temperature. Sliding electrical contacts are unreliable in this environment; therefore Transense is successfully relying on non-contacting signal transmission that uses radio frequency couplers.
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