322 



EARLE C. GREGG, JR. 



Figure 8 shows a hand unit designed by Pohlmann (30) for therapeu- 

 tic purposes. The membrane is pressed against the flesh of the sub- 

 ject. 



As mentioned previously, the type of clamping and acoustic load 

 determine to a great extent the amplitude of vibration of either a 



Matching Transformer 



Membrane 



Crystal 



|i;\s Metallic 

 &;\ backing plate 



\ 



Fig. 8. Hand ultrasonic unit designed for therapeutic purposes. 

 60 



< 

 ?40 



ijj 



Q 



Q- 20 

 < 



UJ 



> 



UJ 



oc 



-4% 



Fig. 9. 



■2% 







2% 



47„ 



RELATIVE CHANGE OF FREQUENCY 

 Effect of light, medium, and heavy damping on the reso- 

 nance curve of a vibrating quartz crystal. 



fjuartz crystal or magnetostrictive rod. Figure 9 shows the effect of 

 various loads or "damping" on the resonance curve of a quartz crys- 

 tal. The "medium" damping condition corresponds approximately 

 to the effect of a liquid load on a vibrating quartz crystal. Crystal 

 clamping devices damp the crystal vibration in a similar manner. 

 Some investigators have taken pains to support a crystal in the me- 



