D. Schofield 11 
TABLE 1. I 
d-10%,| g-10%, 2 
el legas ie one 
. 11 23 58 
28 24 177 
38 16 175 
: tan 6 at 
Material Ole om 
Quartz, X-cut 
ADP 45°Z 
Lithium sulphate 
Rochelle salt 
45° X-cut 
BaCaTiO, >0.10 
BaCaCoTiO3-NRE 4 0.02 
PZT-4* 0.02 
PZT-5* 0.11 
Pb(NbOs)2 
electrostriction, or magnetostriction phenomena. The most important character - 
istics for transducer applications of piezoelectric, polarized electrostrictive, and 
magnetostrictive materials are summarized in Tables 1.] and 1.1]. The relative 
importance of the various material parameters depends upon the particular re- 
quirement of the transducer incorporating the material, but the parameters 
presented do indicate some of the advantages and disadvantages of the various 
materials. Furthermore, since the materials are not isotropic, the magnitude of 
the parameters depends upon the mode of operation: e.g., the piezoelectric con- 
stants depend onthe cut ofthe sample and the coupling factor changes for different 
modes of vibration. 
Undoubtedly the most important single characteristic of a transducer ma- 
terial is the electromechanical coupling factor. It has already been shown that 
the coupling factor is related to the ratio of stored mechanical energy to total 
electrical input energy for electrical to mechanical conversion and that it con-~ 
trols the maximum bandwidth of a projector. In addition, Kendig [11] recently 
emphasized that for detecting very small acoustic signals, it is the equivalent 
noise pressure of the receiver that is of prime importance, not the sensitivity 
of the hydrophone. He developed expressions for the efficiency and equivalent 
noise pressure of three different shapes of hydrophones, and k*/tan 6, in which 
6 is the dielectric loss angle, is a common factor in each equation. Thus, 
k?/tan 5 appears to be a good criterion for hydrophone materials. This factor is 
TABLE 2.1 
Material 
Nickel Polarized 
Remanent 7-108 
2 V Permendur | Remanent 8.5-1078 
13 Alfer Polarized 9-107 
4% Co-Ni Polarized 10,3:107* 
Ferroxcube A Remanent 
