ELECTRICAL WAVE FILTERS 



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the crystal to select currents over a wide band of frequencies and to 

 reject currents whose frequencies lie outside this pass region. Hence 

 it is advantageous for filter uses to obtain a crystal which has sub- 

 stantially a single prominent resonance over a wide range of fre- 

 quencies. Such a vibrating element can usually be obtained only by 

 making the dimension along which the crystal is vibrating, large 

 compared to the other dimensions, and this fact determines the best 

 cut of crystal to use. 



Two principal types of orientations have usually been employed in 

 cutting quartz crystals. The first type is the so-called Curie or per- 

 pendicular cut in which the crystal is so cut that its major surfaces are 

 parallel to the optical axis and perpendicular to an electrical axis. 

 Such a crystal is shown by Fig. 1. The second type of cut is the parallel 



OPTICAL AXIS=Z 



MECHANICAL AX(S = Y 



-ELECTRICAL AXIS=X 



Fig. I — Orientation of a Curie or perpendicular cut with respect to native crystal. 



or 30-degree cut in which the major surfaces of the crystal plate are 

 parallel to both the optical and electrical axes. Since this cut results 

 in a crystal vibrating along its smallest dimension, it is not of much 

 interest for filter uses. 



When using a crystal as part of an electrical system, it is desirable 



