LECTURE 7 
SOME AREAS IN WHICH UNDERWATER ACOUSTICS 
RESEARCH IS NEEDED 
H.R. Baker 
The North Atlantic Treaty Organization 
Scientific Affairs Division, Paris, France 
It is with some hesitation that I speak to this group of experts in underwater 
acoustics on the subject of areas of underwater acoustics where research is 
particularly needed. Most of you have contributed greatly to the present state of 
knowledge in this field and will continue to contribute, as the papers presented 
at this Institute demonstrate. I need not elaborate on the importance of the 
problem of submarine detection to the NATO Alliance. We are all aware that 
underwater sound techniques are the only promising means for detecting sub- 
marines at acceptable ranges. I warn you that my remarks are likely to be 
biased in the direction of submarine detection, classification, and identification; 
at the same time, I am aware that the solution to these problems depends upon a 
basic understanding of acoustic phenomena in the oceans. 
Almost every area in which I intend to suggest the need for research has 
been or will be touched upon in talks given at this Insitute, but let us proceed in 
the hope that I may stimulate your thinking about a few areas where basic and 
applied research are needed. 
7.1. SOUND TRANSDUCERS 
Basic research on transducing materials should continue, but perhaps we need 
most to concentrate on the effective use of the knowledge we already possess in 
this area. First, I must point out that research could profitably be done into the 
conversion of mechanical energy directly to sound. Hydraulic devices are capable 
of exerting a great force through a small distance; and this is exactly what is 
needed, if we can find ways to exert this force in a controlled periodic manner. 
This approach seems very attractive for low-frequency sound sources because 
it offers high power capability, ruggedness, and reliability. 
Large open arrays of transducer elements seem to be the answer to many 
sonar problems, yet the criteria for designing such arrays to a given specifica - 
tion are not well understood. Perhaps what is not understood is the interaction 
between elements of an array when it is driven at high power or when delay lines 
are used to form and steer acoustic beams. This problem requires both theo- 
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