MODES OF MOTIOX IN QUARTZ CRYSTALS 



57 



the thickness. The simplest type of motion for high frequency shear is 

 shown in Fig. 6.5 where the top of the plate is displaced in the direction 

 along i with respect to the bottom of the plate. This would then be termed 

 the length-thickness shear. When viewed from the edge of the plate, the 

 motion is very similar to that shown in Fig. 6.4 for the case of ni — l,n = 1. 

 In a manner similar to the previous case of shear the front edge of the plate 

 may be divided into segments along C and along /. For example, we may get 



■nn = 1 



n = l 



■m = 2 T1=1 fT^=6 71 = 3 



Fig. 6.4 — Motion of a plate in low frequency shear. 



a double shear along ^ with a single shear along /. This case is illustrated 

 in Fig. 6.5 for m = 1, n = 2 and p = l. In general, m and n may assume 

 any integral value. As in the case of flexure we must also consider the third 

 dimension. The motion associated with the third dimension may be repre- 

 sented by simple reversals of phase as before. For example, in Fig. 6.5 the 

 case for m = 1, n = 1, p = 2 is shown which simply means that the high 

 frequency shear on the front half of the plate is out of phase with that of the 



