CHAPTER I 



Quartz Crystal Applications 



By W. P. MASON 



1.1. Introduction — Purpose of Serif . 



THIS paper is the first one of a series of papers deaii '^ with quartz 

 crystals, their apphcations in oscillators, filters, and transducers, and 

 the methods of producing them from the natural crystal. This series was 

 prepared first to make available to the Western Electric Co. and other 

 manufacturers of quartz crystals some of the specialized knowledge on 

 these subjects that has been acquired at the Bell Telephone Laboratories. 

 Sufficient interest has been expressed in this series to make it desirable to 

 publish them in serial form. 



This first paper in the series is a general introductory paper covering 

 the application of crystals to oscillators, filters and transducers. An appen- 

 dix is given which discusses the elastic and electric relations in crystals and 

 gives recent measurements of the elastic constants, their temperature coeffi- 

 cients, and the piezoelectric constants of quartz. This paper is followed 

 by more detailed papers by Messrs. Bond, Willard, Sykes, McSkimin, and 

 Fair which give consideration to quartz crystallography; determination of 

 orientation by optical methods. X-ray methods, and etching methods; the im- 

 perfections occurring in quartz crystals; modes of motion and their calcu- 

 lation; the dimensioning of crystals to avoid undesirable resonances; and 

 the use of crystals in oscillators. 



1.2 Early History of Piezoelectricity and its Applications 



The direct piezoelectric effect was discovered by the brothers Curie in 1880. 

 They measured the effect first for a quartz crystal by putting a weight on the 

 surface and measuring the charge appearing on the surface, the magnitude 

 of which was proportional to the applied weight. A simple model for demon- 

 strating this effect can be made by using a large piece of Rochelle salt cut 

 with its length 45° from the Y and Z crystallographic axes and placing tinfoil 

 electrodes normal to the A" axis. If these electrodes are connected to a 

 neon lamp, and the crystal is compressed by hitting it with a hammer, a 

 charge is generated on the surface and a voltage applied to the lamp sufficient 

 to break it down. In fact as much as 2000 volts can be generated by striking 

 the crystal hard. 



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