1. An introduction to the physics of echolocation;McKerrow,1990
2. Autonomous mobile robot Yamabico and its ultrasonic range finding module;Song,1989
3. Polaroid Corp., Cambridge, MAS, 02139, Ultrasonic Ranging System.
4. Implementation of a small size experimental self-contained autonomous robot — sensors, vehicle control and description of sensor based behavior;Yuta,1993
5. Ultrasonic sensing for a mobile robot to recognize an environment — measuring the normal direction of walls;Nagashima,1992