X. ULTRASONIC VIBRATIONS 



325 



tainable is definitely limited by the circuit and also that the crystal is 

 at a high d.c. potential. The latter factor comphcates the handUng 

 of the crystal and mount. In h the tank inductance forms the pri- 

 mary of a high voltage transformer, the secondary of which is con- 

 nected to the crystal. Very high voltages are attainable if the crys- 

 tal capacitance, stray capacitance of the secondary, and the secondary 

 inductance form a circuit resonant at the natural period of the quartz. 

 As with the magnetostriction oscillator C is varied until the electronic 

 circuit oscillates at the crystal resonant frequency. In 6, L2 may be 

 separated from L by a fairly large distance and connected to it by a 



Crystal 



- - - -\- -I 



Crystal 



{0) 



Fig. 10. Typical electronic oscillator with two methods of coupling to a piezo- 

 electric crystal: (a) direct-coupled; (h) transformer-coupled. B — , B-1-, Fil, and 

 C are the electrical supply voltages. 



low impedance feeder link. In this manner, the high voltage source 

 and crystal may be mounted in an oil-filled tank away from the elec- 

 tonic oscillator and greatly enhance the flexibility of the system. 

 Other coupling systems have been described in the literature (29). 



As with most electronic circuits, there are a large number of varia- 

 tions, each with different characteristics. The choice remains with 

 the experimenter as to the type used since this is usually decided by 

 the material and funds available. Salisbury and Porter (6) and 

 Smith and Stumpf (29) describe some typical circuits and over-all 

 generator designs used especially in chemical and biological studies. 

 Present day sources of commercial ultrasonic equipment are listed at 

 the end of the bibliography. Current books contain design data 

 (Sh,c). 



While the power outputs of most generators of this type vary from 

 about 200 to 2000 watts, the maximum acoustic power delivered by 

 the crystal depends on mounting, frequency, and acoustic loading, 



