Design of Capacitive Micromachined Ultrasonic Transducers for Application in Electronic Travel Aid for the Blind

A L, Revathy and Dutta, Asudeb (2012) Design of Capacitive Micromachined Ultrasonic Transducers for Application in Electronic Travel Aid for the Blind. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

A low cost, compact Capacitive Micromachined Ultrasonic Transducer (CMUT) based Electronic Travel Aid (ETA) to identify obstacle has been proposed. The aim is to enable free movement of the blind in an environment ridden with stationary obstacles with a target distance of 1-2m. In the present work, SU-8 has been chosen as the membrane material of the CMUT. This has enabled drastic reduction in the DC operating voltage to just 22V- an essential limit for handheld devices to be carried by the user. The CMUT is designed to operate at around 70kHz which minimises frequency dependent loss in air. The simulations are carried out in CoventorWare and COMSOL. The results show that on superimposing an AC of 0.5V on the DC, displacements as large as the gap distance of 5um are obtained resulting in output pressures of 140dB on surface of CMUT. On travelling a to and fro distance of 2m, this pressure drops to about 1uPa. To be able to sense this small pressure, a receiver with thin membrane is designed. A circuit has been implemented off chip to process the received signal and generate a PWM signal to drive the vibrator.

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