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.
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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