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BELL SYSTEM TECHNICAL JOURNAL 



shear. For the case oiAT plates experiment has shown these to be given by 



kilocycles 6.19 



1338.4 

 fxf = -^i7- ^'f 



X 



where X = length of X axis in millimeters, 

 Uxf = order of flexure along X axis 

 = 1, 2, 3, 4, etc. 



In this equation as well as those of a similar nature to follow it is assumed 

 that the thickness is such as to result in the same frequency for the high 



Fig. 6.15 — High frequency flexure and shear resonances in an ^T-cut quartz plate. 



frequency Xy shear mode. As shown in Fig. 6.14 only the even orders are 

 strongly coupled to the fundamental thickness shear. 



The coupling between high even orders of the flexure along the X axis and 

 the high frequency shear in the case of BT-c\xi plates is similar to that for 

 .4r-cut plates. Fig. 6.17 shows the various resonant frequencies observed 

 in a BT-axt crystal as a result of changing the ratio of the length or X 

 axis to the thickness or Y' axis. The curve niifii represents the high fre- 

 quency Xy, shear. Curves m\nz, min^, Wi«7 and min^ represent other Xy, 

 shear modes as discussed in section 6.23 resulting from higher orders along 

 the length or X axis. The dashed hues represent even order flexure modes 

 along the X axis. The same regularity is observed here as in the case of the 



