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Cable
Transducer
Housing
Ceramic Element
Acoustic Beam
Echo
Beam
Angle
Two
Objects at
Same
Depth Will
Appear as
7 Reference
Display
Bottom
Theory of Operation
Sonar Basics
Most existing depthsounders and fishfinders in the
marine market use a standard "fixed beam"
technology which was originally developed during
W.W. II to detect the presence and distance of
submarines. Products using this technology usually
have a transducer mounted on the rear of the vessel,
making contact with the water. The transducer is
connected to an electronic display module which is
typically mounted near the boat's steering station.
These transducers are typically made up of a single
piezoceramic element which is encapsulated in a
hydrodynamically shaped plastic or bronze case. The
piezoceramic element has the important property in
that it will vibrate when shocked with a high voltage
vibrating electrical signal and will itself give off a
small vibrating electrical signal when physically
vibrated. If the display unit sends a large pulse of
voltage down the cable to the transducer, the
transducer will vibrate and the resulting acoustic
vibrations will travel through the water until they
strike an object, such as the bottom or suspended
fish. When striking an object, a small amount of the
acoustic energy is reflected and this "echo" returns
and causes a small vibration in the transducer. The
small vibrations in the transducer caused by the
returning acoustic echo cause the transducer to send
a small electrical signal back up the cable to the
display unit. The user can then view the presence of,
and distance to, these underwater objects.
The transducer element, depending on the physical
characteristics of the piezoceramic element
(thickness, diameter, etc.) has a fixed direction in
which it is most efficient at sending and receiving
acoustic signals. This direction is called the "main
beam" and is of critical concern to most
knowledgeable fishermen, as the display will
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