Orlowski, Rafal John (1976) Ultrasonic echo reinforcement for the blind. PhD thesis, University of Nottingham.
The ability that many blind people develop of detecting near objects by means of echo-location is well known. This investigation is concerned with the development of an aid that will enhance this ability by transmitting ultrasonic pulses into the environment and receiving the echoes returning from surrounding objects. The echoes are detected and heard as clicks by the user, who is able to determine the direction from which the sound is coming by using his natural localisation ability. Further, the clicks are "coded" by switching the receivers on and off, so that the rate of clicking indicates the distance of an object.
A key component of the system is the ultrasonic transducer. Piezoelectric bimorph transducers have been selected for use as both transmitters and receivers, although the characteristics of the standard type have been readjusted to meet the requirements of the aid. In particular, the transducer bandwidth has been considerably extended to ensure a sharp sounding click.
In order to provide accurate directional information it has been necessary to closely simulate naturally occurring interaural differences. Interaural time differences are readily provided by spacing the receiving transducers at the 'inter-ear distance apart, whereas the provision of accurate interaural intensity differences has necessitated the shaping of the directional response of the receiver to match that of the ear.
A series of psychophysical tests has been performed to measure the ability of subjects using the device to localise objects in the horizontal plane. Considerable accuracy was shown with the best results being obtained using interaural time information alone or interaural intensity information alone, rather than a combination of both.
Elementary outdoor trials with the device have shown the range and directional information to be effective with the indication of the shoreline being particularly clear. A progressive refinement of the aid should lead it to a stage where its usefulness to blind people can be evaluated.
|Item Type:||Thesis (PhD)|
|Uncontrolled Keywords:||Echolocation, Ultrasonic transducers, Mobility aids for the blind|
|Faculties/Schools:||UK Campuses > Faculty of Engineering > Department of Electrical and Electronic Engineering|
|Deposited By:||Mrs K.J. Blore|
|Deposited On:||15 Nov 2010 09:33|
|Last Modified:||15 Nov 2010 09:33|
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