Sec. 1-2] MECHANICAL IX ITT TRAXSDCCi; 1!S 



75 



where a is the area of the crystal, t its thickness, and Y is Young's 

 modulus. 



stress Ft 



strain a At 



The charge at the electrodes gives rise to a voltage E = Q/C, 

 where C is the capacitance between the electrodes. Since C = eaft 

 (e, dielectric constant), the output voltage is 



dt „ t, 



E = — F = g-F =gtP 



ear a 



(3) 



where g is a constant of the crystal (values for g are given in Table 5), 

 and P is the pressure applied to the piezoelectric crystal. 



The piezoelectric element is usually a slab, or "cut," taken from a 



Table 5. Piezoelectric Constants 



