A blind mobility aid modeled after echolocation of bats

A new model of a mobility and for the blind was designed using a microprocessor and ultrasonic devices. This mobility and was evaluated based on psychophysical experiments. In this model, a downswept frequency-modulated (FM) ultrasound signal is emitted from a transmitting array with broad directional characteristics in order to detect obstacles. The ultrasound reflections from the obstacles are picked up by a two-channel receiver. The frequency of the emitted ultrasound is swept from 70 to 40 kHz within 1 ms, so it has almost the same characteristics as the ultrasound a bat produces for echolocation. The frequency of the reflected ultrasound wave is downconverted by about 50:1 by using a microcomputer with analog-to-digital and digital-to-analog converters. These audible waves are then presented binaurally through earphones. In this method obstacles may be perceived as localized sound images corresponding to the direction and the size of the obstacles. From the results of psychophysical experiments, it was found that downswept FM ultrasound was superior to other ultrasonic schemes for the recognition of small obstacles. With it a blind person can recognize a 1-mm-diameter wire. It was also proved that the blind could discriminate between several obstacles at the same time without any virtual images. This mobility aid is very effective at detecting small obstacles placed in front of the head.