LOW TEMPERATURE COEFFICIENT QUARTZ CRYSTALS 87 



Practically all the work done has been on square or nearly square 

 plates. Some time ago Bechmann ^* and Koga ^^ published work done 

 on crystals which departed from the square shape for which zero coeffi- 

 cients were obtained at somewhat different angles and different frequen- 

 cies than those given for the CT and DT crystals. This is due to the 

 fact that when the crystal shape departs from the square, the frequency 

 approaches more nearly the resonant frequency of the crystal vibrating 

 in its second flexure mode and the increased coupling changes the angle 

 for which the coefficient becomes zero. The square crystal is the one 

 which has fewer secondary frequencies and is therefore more desirable. 



2 6 000 





< 4800 



I- 

 <0 



ir -90° -60° -30° 0° 30° 60° 90° 



^ ROTATION ABOUT X AXIS IN DEGREES 



Fig. 9 — Frequency constant for E and F type vibrations. 



III. Zero Temperature Coefficient Crystals for More 

 General Orientations 



Shortly after the discovery of the ^ T and BT crystals it was realized 

 that zero temperature coefficient crystals could be obtained at a variety 

 of angles provided two rotations of the crystal with respect to the 

 crystallographic axes were used. This would allow the direction of 

 the shearing axis to point in any direction with respect to the crystallo- 

 graphic axes. Using the c^g constant as the elastic constant determin- 

 ing the frequency, it was found that there was a whole series of zero 



" R. Bechmann, Hochfrequenstechnik u ElektroakusHc, Vol. 44, No. 5, p. 145. 

 " I. Koga, Report of Radio Research in Japan, Vol. IV, No. 2, 1934. See also 

 Patents 2,111,383 and 2,111,384 issued to S. A. Bokovoy. 



