A new precise ultrasonic range sensor based on the emission of two coded FSK signals combined to a ping-pong strategy

Ultrasonic range sensors are widely used in robotic applications mainly for obstacle avoidance or environment map generation. They are attractive because of the low cost of the transducers, associated electronics and implementation facilities. On the other hand, they suffer from several limitations inherent to the underlying principle. Most of these systems send a short pulse at an ultrasonic frequency, that reflects on some object in
the environment and then that returns back to the emitter. The propagation time in conjunction with the knowledge of the speed of sound in the air are used to compute the distance between the emitter and the object. The main drawbacks are multipaths, echos, diffraction, etc, resulting in unreliable range measurements.
This paper present a new ultrasonic range sensor using ping-pong strategy, FSK modulation and coded signals to overcome those main limitations.