MODES OF MOTION IN QUARTZ CRYSTALS 



79 



flexure frequencies and the curve labeled wz3«i and the curve labeled W3W3 

 correspond to two different values of the high frequency shear near its com- 

 monly called third harmonic. 



An examination of Figs. 6.14 and 6.15 indicates that a regular pattern 

 is formed of the ratios of axes at which the high frequency shear and succes- 



5 I 660 



5 



9 1 620 



1 520 



1 500 

 t 46 



I 460 



30 31 



X 

 Y' 



Fig. 6.14 — High frequency flexure and shear resonances in an ^T-cut 

 quartz plate. 



sive even orders of the length-thickness flexure coincide. Rather than 

 define these points on the basis of specific ratios of axes it is more convenient 

 to place them on a frequency basis. Therefore we may say that for a given 

 size plate there will be specific frequencies at which some mode of the fle.xure 

 motion along the length will be the same as the high frequency thickness 



