ELECTRICAL WAVE FILTERS 



435 



ing there is I think evident from a consideration of Fig. 28. Here in 

 solid Hnes are drawn two frequency curves one of which, B, is the shear 

 frequency curve of Fig. 27. The other curve, D, has a rising frequency 

 with an increase in the optical axis dimension. Assuming these vibra- 



>- 320 



o 



f?[ 300 



220 



0.2 0.3 0.4 05 0.6 0.7 0.8 



RATIO OF OPTICAL TO MECHANICAL AXIS 



Fig. 27 — Theoretical resonances of a perpendicularly cut crystal showing effect of 



coupling. 



tions coupled a resonance frequency curve shown by the dotted line 

 will be obtained. If this curve is substituted for the shear curve of 

 Fig. 27 and the actual resonant frequency raised to take account of the 

 effect of coupling with the longitudinal motion along the mechanical 

 axis, a curve very similar to the measured curve of Fig. 25 is obtained. 

 The type of motion coupled to the shear motion is easily found. Its 



