Nr. Brown et al., MEASUREMENT OF VISCOUS SOUND-ABSORPTION AT 50-150 KHZ IN A MODEL TURBID ENVIRONMENT, The Journal of the Acoustical Society of America, 104(4), 1998, pp. 2114-2120
The visco-thermal absorption of sound by suspended particulate matter
can be reliably measured using a reverberation technique. This absorpt
ion may have an adverse effect on the performance of sonars operating
at 50-300 kHz in coastal waters where suspensions are often present in
significant concentrations. A series of experiments has been performe
d to study the viscous absorption by suspensions in the frequency rang
e of 50-150 kHz. In the test volumes employed, the effect is small. It
is therefore measured by taking the difference in reverberation times
of a volume of water with and without particles. This greatly reduces
the effect on the measurement of the other sources of absorption. Eve
n so, it is necessary to design the experiment to characterize and min
imize acoustic losses which occur at the surfaces of the container, th
e hydrophones, and their cables, and losses associated with bubbles an
d turbulence. These effects are discussed and results for particulate
absorption for suspensions of spherical glass beads are presented and
compared to theoretical predictions. Measured absorption agrees well w
ith that predicted by theory for concentrations above 0.5 kg/m(3) and
up to 2.0 kg/m(3). [S0001-4966(98)01610-5]