Page 20 - Electronic Navigation Cyber Book

The sound pulses are created by transducers, which convert electrical
energy on transmission, and reverse the process when the echo is
received. The sound energy is always transmitted as a beam in a
particular direction (directional beam) and it would be very wasteful to
permit spherical radiation.

Transducers are of two types:

Piezo-electric transducer
Magneto-striction transducer.

Piezo-electric transducer

This type makes use of the special properties of crystals (e.g. crystals of
barium-titanate and lead zirconate). If an alternating voltage is applied to
the opposite faces of a flat piece of one of the above materials, the crystal
will expand and contract, and hence vibrate creating sound waves for as
long as the vibrations continue. The process is reversible, i.e. when
varying pressure from a returning echo, is applied to the opposite faces,
an alternating voltage is generated across the faces and the same can
be further amplified and used to activate an indicator.

Magneto-striction transducer
In this type, the use is made of the magnetostriction effect which is a
phenomenon whereby magnetization of ferromagnetic materials produce
a small change in their dimensions, and conversely the application of
mechanical stresses such as weak pressure vibrations, as from an echo
to them, produce magnetic changes in them; e.g. a nickel bar when
placed in the direction of or strength of the magnetic field. If the nickel bar
is placed in a coil with an alternating current flowing through it (a
solenoid), the varying current and magnetic field will cause the ends of
the bar to vibrate and hence create a sound wave. This is what happens
when the transducer is transmitting.
Type with specs 50 kHz - 100 W: Maximum depth measurable - 700
meters Type with specs 20 kHz - 100 W: Maximum depth measurable -
400 meters

The magneto-striction type would be fitted inside a cast elliptical housing
or a circular housing in such a way that the bottoms of the pistons are in
contact with the sea (i.e. pierced hull type - see details of this type later).
Another type, which is fitted internally, consists of a ring of thick nickel
discs enclosed in a winding to which the AC is applied. This resulting
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