MANUFACTURING DEVIATIONS IN CRYSTAL UNITS 



269 



defects are described in Chapter TV"'. The conclusions drawn there for 

 oscillator plates are also applicable to filter plates. These are: (1) Evidence 

 that a particular defect is perm'ssible in a given t.)npe of plate docs not prove 

 that a similar defect is permissible in seme other type of plate, and (2) 

 proof that a particular defect is permissible in a given type of plate can be 

 obtained only by a statistical study. 



Seme qualitative statements can be made regarding the effect of mechan- 

 ical flaws. Cracks result in instabilit)- of resonant frequency and effective 

 resistance and must be avoided. The effect of inclusions or chips depends 



.1 15 .2 .3 .4 .5 



RATIO OF WIDTH TO LENGTH 

 Temperature coefficient for +5° flexural crystal units as a function of the 



Fig. 14.7 

 ratio of width to length of the plates. 



on the size of these defects relative to the size of the finished plates and also 

 on their location in the plate. 



Twinning in quartz may be either of the optical t>^e (Brazil twin) or of 

 the electrical type (Dauphine twin)^. The effect of these two types of 

 twinning on the performance of oscillator crystal units has been described 

 thoroughly in Chapter V^. 



When optical twinning is present, the plate will exhibit the same elastic 

 properties throughout, but the two portions of the plate will tend to expand 



7 "Raw Quartz, its Defects and Inspection", G. VV. Willard, B. S. T. J., October 1943, 

 pp. 338-361. 



* "The Properties of Silica", R. B. Sosman, Chapter XII. 



^ "Use of the Etch Technique for Determining Orientation and Twinning in Quartz 

 Crystals", G. \V. WiUard, B. S. T. J., January 1944, pp. 11-51. 



