Ultrasound mobility aid for the blind using frequency modulated nerve stimulation

摘要

Some of the existing electronic aids for the blind use ultrasound pulsed echoes, and pass on the information through sound signals into the ear. This curtails the normal faculty of hearing which a blind person uses to a great extent in getting information of the surroundings. The present device gets around this shortcoming by passing the information through nerve stimulations, preferably at the wrist. Here time delays of ultrasound echo pulses are used to modulate the frequency of nerve stimulation, higher frequencies for shorter delays, corresponding to shorter object distances. This was designed to match the common psychological response of attributing higher frequencies to danger, creating a natural reaction for moving away. The highest frequency a human nerve can be stimulated to is about 500Hz, and pulses with heights of 100V to 200V are required for stimulating nerves passing just under the skin using surface electrodes. Necessary electronic circuit designs were made and a prototype fabricated in the present work. The prototype was tested for short distances up to 20cm giving very good linear response between object distance and the stimulating frequency, with the inverse characteristics as mentioned above. Reduction of noise through proper housing and shielding will allow the device to be useful to a practical distance of about 10m using 40kHz ultrasound transducers.