FUNDAMENTAL STUDIES AND OPERATIONAL PERFORMANCE 



'2 ROLE OF PRECISION ACOUSTIC: 

 MEASUREMENTS IN THE 

 IMPROVEMENT OF UNDERWATER 

 SOUND EQUIPMENT 



1 -' ' Improvements in Transducer Design 



An example of the importance of precision acous- 

 tic measurements and fundamental research in im- 

 proving sonar gear is afforded by developments in 

 transducer design and construction in the period 

 1940-1945. Two types of electroacoustic coupling, 

 magnetostrictivc and piezoelectric, had been found 

 most useful. Fundamental investigations of magneto- 

 strictive phenomena conducted by Division C, Navy, 

 and industrial laboratories have greatly increased 

 knowledge of the source of power losses in magneto- 

 striction transducers. Application of this knowledge 

 led to a 400 per cent increase in transducer efficiency. 

 This increase in efficiency not only markedly im- 

 proved operation but also greatly reduced the bulk, 

 cost and critical materials requirements of the equip- 

 ment. 



Improvement in equipment using piezoelectric 

 crystal coupling closely parallels that obtained for 

 magnetostrictivc equipment. Thus, initial efficiencies 

 of the order of 10 to 20 per cent have been increased 

 to values as high as 75 to 80 per cent. 



Improvements in transducers have not been lim- 

 ited to increased efficiency. The development of am- 

 monium dihydrogen phosphate [ADP] crystals made 

 possible crystal transducers with negligible tempera- 

 ture dependence and, more important, with ability 

 to withstand greater temperature extremes without 

 damage. Furthermore, new construction methods 

 for both crystal and magnetostriction transducers 

 made possible the fabrication of transducers with 

 special characteristics. Many other examples of spe- 

 cific improvement are available to demonstrate the 

 importance of fundamental research. 



.2.2 



Improvements in Dome Design 



In 1942, one of the most pressing sonar problems 

 was that of designing domes which, when mounted 

 on vessels, would not hopelessly distort the direc- 

 tional patterns of the transducers they en closed. In- 

 ternal reflections from the walls of domes, then 

 available, were nullifying the effort to attain satis- 

 factory directional patterns. This effect, together 



with the high transmission loss through the dome 

 wall sharply reduced the effectiveness of the equip- 

 ment. British experience in meeting this problem, 

 coupled with an experimental research program on 

 domes at the Naval Research Laboratory, at Division 

 6 NDRC laboratories, and at the Bell Telephone 

 Laboratories, supplemented by theoretical research, 

 in which the Division was given invaluable assistance 

 by the Applied Mathematics Panel, effectively dem- 

 onstrated the principles necessary to reduce internal 

 reflections to a negligible amount. On the basis of 

 these principles, various manufacturers were able to 

 produce acoustically satisfactory domes with high 

 mechanical strength without a corresponding in- 

 crease in thickness of the dome wall. Flic solution of 

 the dome problem during 1943 was so effective that 

 dome construction was never again a major problem. 



'3 FUNDAMENTAL STUDIES AND 



OPERATIONAL PERFORMANCE OF 

 UNDERWATER SOUND EQUIPMENT 



131 Relation to Calibration and Test 

 Measurements 



It has previously been stated that the goal of anti- 

 submarine research is improvement in the opera- 

 tional performance of gear. The relation of funda- 

 mental studies to operational performance is largely 

 indirect and finds expression in their influence on 

 development. One of the purposes of these studies 

 has been to determine the relation between the 

 parameters (power output, response, directivity, sig- 

 nal-to-noise ratio, etc.) of underwater sound gear to 

 its effectiveness in operation. This relationship is 

 important, as it helps determine by laboratory meas- 

 urements on the gear itself its probable operational 

 effectiveness. Such a technique provides many ad- 

 vantages, including: (1) efficiency of time and effort, 

 (2) closer liaison with development work, (3) the 

 possibility of making tests under controlled condi- 

 tions, at any time, and (4) clearly defined conclusions 

 from tests. 



t.3.2 Relation to Development of 



Equipment 



These studies reveal, also, important information 

 bearing on the equipment design. In evaluating the 

 relationship between gear parameters and opera- 



