EVALUATION OF THE VESSEL 



In the evaluation of the vessel it was necessary to 

 determine acoustically (1) the circular uniformity of the 

 capsule walls, (2) the reflective and absorptive behavior 

 due to pressure alone, (3) the effect of the vessel on fre- 

 quency response, and (4) the effect of the vessel on direc- 

 tivity patterns. 



Capsule Walls Uniform 



Uniform wall thickness of the capsule permits trans- 

 ducers to be mounted in random orientation with respect to 

 the walls. Thickness is more important acoustically at 

 high frequency, where the behavior of materials is more 

 critical. Specifically, a high-frequency test checks the 

 uniformity of the consolidation of the fiber windings and the 

 thickness of the epoxy. The high-frequency measurement 

 was performed by comparing cylindrical free -field polar 

 patterns made by a probe mounted on the cap with and with- 

 out the capsule attached. No measurable difference in pat- 

 terns was observed. Several checks of this type indicated 

 that the walls are uniform enough for this application. 



Directivity Unaffected by Pressure 



The vessel was tested for change in acoustical be- 

 havior due to pressure alone with a selection of nonpressure- 

 sensitive transducers with directivity indexes varying from 

 very low to very high. Patterns plotted at psig and at in- 

 crements of 100 psig to 800 psig show no change, and it is 

 presumed that vessel behavior is independent of pressure. 



Attenuation Uniform to 100 kc/s 



Change in acoustical behavior as a function of fre- 

 quency was expected, since the frequency spectrum of interest 

 encompasses the range from a fraction of a cycle to several 



