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Glossary of Terms

By John L. Butler
From Transducers and Arrays for Underwater Sound

A-C

Acoustic Beam
Acoustic waves concentrated mainly in a limited direction.
Acoustic Center of a Transducer
The apparent center of the spherical waves in the far field of a transducer.
Acoustic Impedance
The complex ratio of acoustic pressure to amplitude of volume velocity.
Acoustic Medium
Any material through which acoustic waves can travel, usually air or water, but also other fluids and solids.
Acoustic Modem
Underwater device which communicates by means of acoustic waves.
Active Sonar
Detection of a target by projecting acoustic waves and listening for an echo, also called echo ranging.
Admittance, Y
1) The reciprocal of the impedance, Z. 2) Y = G + jB where G is the conductance and B is the susceptance.
Antiresonance, f a
1) For an electric field transducer, the frequency at which the mass and open-circuit stiffness cancel or the frequency of maximum impedance or RVS. 2) For a magnetic field transducer, the frequency at which the mass and short-circuit stiffness cancel or the frequency of maximum admittance or TVR.
Armature
1) Part of a magnetic circuit. 2) The moveable part of the magnetic circuit in a variable reluctance transducer.
Array of Transducers
Two or more transducers that are used together usually to achieve a higher intensity and narrower beam.
Astroid
1) Hypocyloid of four cusps. 2) Described by a point on a small circle of radius, R, rolling around the inside of a larger circle of radius 4R.
Beam steering
Changing the principal direction of an acoustic beam by changing...
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