The principle of magnetostriction is comparatively old, 

 but its technological utilization dates from the middle 1920 's. 

 In the period which elapsed following the pioneer work of G„ W. 

 Pierce, the development of magnetostriction transducers as un- 

 derwater sound projectors was carried forward, as previously 

 described, by the staff of the Naval Research Laboratory, 

 Magnetostriction transducers are well adapted for use in the 

 frequency range extending from 10 to 100 kilocycles, or per- 

 haps even higher, and can easily produce sustained sound 

 waves of intensities sufficient to produce cavitation in all 

 ordinary liquids. 



The echo-ranging sound projectors available and in use 

 at the beginning of World War II left much to be desiredo 

 They were the product of experimental trial and error, and of 

 intuition, rather than the result of accurate quantitative 

 analysis „ 



The Harvard Underwater Sound Laboratory carried on through- 

 out the war a research program devoted to elucidating the fund- 

 amental factors affecting the performance of magnetostriction 

 transducers. As a result of the studies of this group and the 

 collateral investigations of the other laboratories engaged 

 in similar work, it not only became possible to construct im- 

 proved transducers for sonar and ordnance purposes, but also 

 to put the problem of designing such transducers on a sound 

 engineering basis which actually permitted calculation of 

 performance in advance of construction. 



The research program carried out by HUSL and by BTL and 

 New London can be described under three broad headings § 



First of all, it was necessary to make a careful, theo- 

 retical analysis of the electromagnetic conversion process. 

 Emphasis was placed upon a mathematical analysis of the 

 magnetostrictive coupling between the electrical driving 

 circuit and the active material of the transducer, so that 

 this fundamental characteristic of the transducer could be 

 described quantitatively in terms of the magnetic properties 

 of the active material and the configuration of the electric 

 and magnetic circuits. This study made It possible to draw 

 equivalent electrical circuits which could represent the 

 performance of the electro-acoustical system, not only in a 

 qualitative way, but also with quantitative precision. 



It was also necessary to make extensive measurements of 

 the magnetic properties of the magnetostrictive materials 



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