Page 59 - HydrophoneHandbook_eReader_Ed2_20151208

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12. Glossary of Terms
Term Definition Symbol Units Reference
Beamwidth cm
Greatest distance between two points on a www.electropedi
Decibel specified axis perpendicular to the beam dB a.com, 802-01-20
axis, where the pulse-pressure-squared ---
Directional integral falls below its maximum on the mm https://en.wikipe
Response specified axis by a specified amount. Ω dia.org/wiki/Deci
Effective w6, w10,
Hydrophone Note – Commonly used beamwidths are bel
specified at –6 dB, –10 dB and –20 dB levels w20 62127-3 3.1
Radius 62127-3 3.2
Electric Load below the maximum. The decibel 62127-3 3.3
Impedance calculation implies taking 10 times the
logarithm (to the base 10) of the ratios of
the integrals.
The decibel (dB) is a logarithmic unit that dB
expresses the ratio of two values of a
physical quantity. For power or intensity, it
is calculated using the formula LP =
10log10(P/P0) or LI = 10log10(I/I0) where
LP is the ratio expressed in dB, P is
measured power, P0 is reference power,
and where LI , I, and I0 are the
corresponding parameters for intensity.
For pressure, it is calculated using the
formula LF = 20log10(p/p0) where Lp is the
ratio expressed in dB, p is the measured
pressure, and p0 is the reference pressure.
Description, generally presented ---
graphically, of the response of a
hydrophone, as a function of direction of
propagation of the incident plane sound
wave, in a specified plane through the
reference centre and at a specified
frequency
Radius of a stiff disc receiver hydrophone ah,
that has a predicted directional response ah3,
function with an angular width equal to the ah6,
observed angular width NOTE 1 The ae,
angular width is determined at a specified ae3,
level below the peak of the directional ae6
response function. For the specified levels
of 3 dB and 6 dB, the radii are denoted by
ah3 and ah6 respectively
Complex electric input impedance ZL
(consisting of a real and an imaginary part)
to which the hydrophone or hydrophone
assembly output is connected or is to be
connected
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