MODES OF MOTION IN QUARTZ CRYSTALS 



85 



and the X„' shear such as is shown in Fig. 6.21 at ^ = 31.35 the relative 



coupling of each to the X„' shear is about equal. This arises from the fact 

 that the mutual coupling between them increases the apparent coupling 



5 



? 2540 



>. 24 60 



I lit 



FUND. Xq'SHEAR \ \ 



t- Y'=.450MM. 

 l = X= 17.50MM. 



V^^ 



\ \ » 



^ -' V^n . l 



1_L_A_1 





\ \ 





\ 





\ \ 



-4-+ 



\ \ \ 





12 16 20 24 28 32 36 40 44 48 



y 

 Fig. 6.19 — High frequency shear resonances in a BT-cut plate. 



Xl| shear mode 



Zx SHEAR MODE 



ALONG X (UNCOUPLED) 

 Xq' FLEXURE MODES 



ALONG X(UNCOUPLED) 

 • MEASURED RESONANCES 



t r Y'= .450 MM 

 W= Z'= 18 00 MM 

 l^X 



^ 



Fig. 6.20 — High frequency thickness shear and flexure and shear resonances along the A" 

 axis in a BT-cut quartz plate. 



between the Xy' shear and high orders of Zx shear along X. From this it 

 would appear advisable to avoid such regions in the dimensioning of crystals 

 for oscillator use over wide temperature ranges. Determination of the flex- 

 ure as well as high order Zx shears then must be made in regions where 



