Sonar Sight for the Blind?  
Nearly 40 years in the making, Leslie Kay's headband device uses sound waves
to create dynamic "pictures" of the wearer's surroundings 

Bats and dolphins find their way around with natural sonar systems that
enable them to perceive the dimensions of their world with reflected sound.
So why not humans? It's an idea that Leslie Kay, an expert in submarine sonar
from New Zealand, has devoted nearly 40 years to researching. He's developing
sonar systems to help the visually impaired navigate their darkened world. 

http://www.businessweek.com/bwdaily/dnflash/dec2000/nf20001211_136.htm