Reference Information; Phased Array Technology - Interphase Proble Operation Manual

Reference Information

Phased Array Technology

Most existing depthsounders and fishfinders in the marine
market use a mature "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
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 electrical
signal and will itself give off a small 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 "beam angle" and is of critical
concern to most knowledgeable fishermen, as the display
will typically show only those targets that are within this
beam angle. A large beam angle will show targets from a
larger underwater area, but suffers from lack of
resolution. That means that although several targets may
be in the beam angle, the user can only determine their
distance from the transducer, not their lateral position
within the beam. For example, if one fish target is 10'
below the boat at the far right edge of the beam angle, it
will show the same display as if it were 10' below the
boat at the far left edge of the beam angle. In addition, if
fish are present at exactly the same depth but at different
sides of the underwater beam, the transducer will receive
Cable
Transducer
Housing
Ceramic Element
Two Objects
at Same
Depth Will
Appear as
One Object
47
Display
Acoustic Beam
Echo
Bottom
Beam
Angle