Page 307 - Concise Encyclopedia of Robotics

Sonar
bances do not occur as often, or with as much intensity, as they do within
the hearing range.
A simple sonar
The simplest sonar scheme is shown in the block diagram. An ultrasonic
pulse generator sends bursts of alternating current (AC) to a transducer.
This converts the currents into ultrasound, which is sent out in a beam.
This beam is reflected from objects in the environment, and returns to a
second transducer, which converts the ultrasound back into pulses of AC.
These pulses are delayed with respect to those that were sent out. The
length of the delay is measured, and the data fed to a microcomputer that
determines the distance to the object in question.
Ultrasonic
emitter
Pulse
generator
Delay
Target
timer
Ultrasonic
pickup
Computer

Sonar

This system cannot provide a detailed picture of the environment unless
it is refined, and a computer is incorporated to analyze the pulses coming
in. Sonar beams tend to be rather broad; acoustic waves are difficult to
focus. This limits the image resolution obtainable with sonar. Another
problem with this simple system is that it can be fooled if the echo delay
is equal to, or longer than, the time between individual pulses.
Refinements
Researchers know that high-end sonar systems can rival vision systems as
a means of mapping the environment, because bats—whose “vision” is
actually sonar—can navigate as well as if they had keen eyesight.

