U] 



o O 





(} i 

 I 



k 



I 



DRIVE VOLTAGE OUTPUT VOLTAGE 



o 



50 



I 



! 



■+■ 



so 



MATERIAL CONSIDERATIONS 



too 



2S0 



Fig. k. 



/SO ZOO 



FREQUENCY - KC 



Spectrum of similar resonator. 



300 



3S0 



Some factors that are important in order to 

 produce a good resonator should be discussed. 

 The material must have high heat conductivity. 

 Aluminum has more than twice the conductivity 

 of brass and four times that of steel. Copper 

 and silver have about twice the conductivity of 

 aluminum but are not hard enough to permit a 

 high Q. Aluminum has another advantage in that 

 its heat capacity is low due to its low density. 

 Two aluminum alloys have been used, designated 

 606I-T6 and 7075-T6. The latter is the harder 

 and results in a higher mechanical Q. Also, two 

 other materials have been used, Invar and Ni 

 Span C. Invar does not expand with temperature 

 changes; its applications make use of this fact. 

 An Invar resonator has a positive temperature 

 coefficient of 200 ppm instead of the usual 

 negative one. Ni Span C is used in resonant 

 magnetostrictive applications and its frequency 

 is relatively stable with change in temperature. 

 A high Q resonator can be made with this material 

 for temperature independent applications. 



39 



