BOX- SHAPE CAVITIES 



Cavity Properties and Construction 



-The rectangular prism resonators with free surface 

 have several advantages relative to other forms mentioned: 



1. The boundary surfaces are made of flat sheets, and 

 therefore are relatively easy to wipe clean. 



2. The boundary will allow pressure release by bending 

 in contrast to the spherical and cylindrical cavities, where 

 pressure release must be accomplished by stretching of 

 the boundary. 



3. The sound field in the corners of the box is very weak 

 and theoretically zero in the corner itself. The corners 

 are therefore well suited for support of the cavity. 



4. The seams where the sheets are united will naturally 

 fall in the corners, where the effect from them will be at 

 a minimum. 



5. The corners allow loose coupling of the transducers, 

 and the coupling can easily be changed. 



6. Finally, this type of cavity is relatively easy to manu- 

 facture. 



The square -cornered cavities therefore seemed to 

 offer the greatest promise and the largest amount of work 

 was devoted to their development. 



Cavities were made of a great variety of materials, 

 and in many different sizes. The materials ranged from 

 plastic films and thin shim stock of copper, brass, bronze, 

 and stainless steel, to heavier sheets as well as readily 

 available plastic containers. It was found that stainless 

 steel was superior to any of the other materials. The 

 power loss within the steel sheets is small and the steel 

 alloy is chemically inactive when exposed to sea water. 

 However, stainless steel is not easy to weld or solder. 



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