A. B. Wood 165 
Fig. 10.4, is cemented to the center of one face of the piezoelectric disc, the 
vibrations of the disc being transmitted though the wire to the water (or con- 
versely in the case of the receiver). The active tip of the wire is bent at a right 
angle to send or receive preferably in a horizontal direction in the water layer. 
The cylindrical side of the wire is coated with a pressure-release material to 
ensure that only the tip takes part in the transmission or reception of sound. 
The coatings are various thin, watertight layers containing free gas films or 
bubbles, e.g., (a) rubber latex to which small quantities of MnO, and H,O, have 
been added, (b) "microballoons" in " pliobond" adhesive, or (c) plastic tube con- 
taining an air film. Such wire-tip transducers are good "point" sources or re- 
ceivers in all practical cases encountered in the model experiments. The direc- 
tional properties ofthe types oftransducers used, directional and omnidirectional, 
are shown in the records of Fig. 10.5, the frequency in these cases being 1 Mcps, 
approximately. 
PULSE 
MODULATOR 
AVO 
SIGNAL 
GENERATOR 
75 OHMS 
POWER 
AMPLIFIER 
BARIUM 
TITANATE 
(a) TRANSMITTER SUPPLY CIRCUIT C.W. AND PULSE 
SYNC FROM 
AMPLITUDE TRANSMITTER 
«+ — CRO 
(b) RECEIVER AMPLITUDE AND PHASE RECORDER 
Fig. 10.6 Receiver amplitude and phase recorder. 
