246 Lecture 13 
tivity. This is especially significant if one wishes to detect signals over a broad 
band of frequencies. 
If a low equivalent noise pressure is the principal consideration in the de- 
sign of a low-level, low-frequency listening hydrophone, then the cylindrical 
hydrophone should be as large as possible, and have a wall as thin as possible. 
However, the size will be limited by the requirements of omnidirectionality and 
absence of resonances. The wall must not be so thin as to be crushed by the 
hydrostatic pressure to which it will be subjected. 
A hydrophone, shown in Fig. 13.7, and intended for operation at frequencies 
up to 3 kc was designed in accordance with these principles. It consists of four 
barium titanate cylinders that are coaxially mounted with acoustic isolation 
spacers between the elements. All four cylinders are encased in a rubber boot 
which is closed at both ends with heavy metal plates. Each cylinder is 2 in. long, 
6 in. in diameter, and has a 0.2-in. wall. The barium titanate cylinders are 
KY) 
CABLE SEAL 
GUIDE STUD 
TOP END PLATE 
PHENOLIC 
RING 
Vz 
ie 
ma 
ry“ 
SN 
Co kark 
——) 
SSyI 
2222 
QS 
(x 
io 
a 
Y2 
A. 
REQ 
x 
WN 
= 
oS 
IS 
a 
LLLILLL LLL LAL ALLL LL 
(Z 
TL &re 
LF LF LF LT LE. 
4 
i 
4 
4 
7; 
NT RK 
SNS G 
a 
PHENOLIC 
CYLINDER 
(LZZLLLL IES 
NYA LLL ZINN 
, 
N 
WS 
LILLL/ os 
\ 
LG LD LP LED LD LP 
é LT LD ED LA LT AGED ED AP LTT PF LDA 
N e 
RUBBER BOOT 
THREE SUPPORT AND 
CYLINDER LOCATION POSTS 
BARIUM TITANATE 
CYLINDER 
CLAMP BOTTOM END PLATE 
Fig. 13.7. Sectional view of hydrophone. 
