Ultrasonic sensors are widely used as external sensors for mobile robots, because they are simple to build and use, and are of low cost. Generally, in the pulse-echo method the distance to the target can be accurately measured, but accurate measurement of the reflecting target direction
is difficult. To realize navigation of a mobile robot in a complicated environment like a doorway or surface tracking of the wall, the resolution of the lateral direction and surface angle of the reflecting target are very important. In this paper, we propose a method which can find the direction
of the target by analyzing the frequency spectrum of the echo in the pulse-echo method. The new method is based on the consideration of the physical properties of the ultrasonic transducer and its environment. Using this method, we will be able to determine the direction angle to the reflecting
object surface from the sensor, using only a single receiver in the pulse-echo method. We present experimental results to show the potential for practical application.