164 



ASSOCIATED EQUIPMENT: DOMES AND BAFFLES 



ure 8 shows the attenuation versus frequency charac- 

 teristics for different sizes of bubbles. 



The use of bubble screens offers interesting possi- 

 bilities, especially since, at least theoretically, it is 

 possible by this means to intercept sound waves of 

 certain frequencies while others are transmitted 

 freely. The design and control of all these factors has 

 not been fully worked out, but air bubbles fixed in 

 space by means of an enclosing material are being 

 used generally in sonar work. For instance, the effec- 



tiveness of air cell rubber as an acoustic shield de- 

 pends on this principle. 



Bubbles also have absorptive properties which are 

 used in a bubble layer recently developed by the Mas- 

 sachusetts Institute of Technology. 11 " This material 

 has been applied by USRL as a lining for the high- 

 pressure tank in order to obtain sound absorption at 

 the walls. (See Chapter 6.) It is applicable for testing 

 tanks generally and should find extensive use in pro- 

 duction testing. (See Chapter 8.) 



