Question

The piezoelectric spark generator, as used in various applications such as lighters and car ignitions, operates by stressing a piezoelectric crystal to generate a high voltage which is discharged through a spark gap in air. Consider a piezo sample in the form of a cylinder. Suppose that the piezoelectric coefficient d = 200x10-12 m V-1 and the relative permittivity is εr = 1000 (the permittivity is εr x ε0). The piezoelectric cylinder has a length of 10 mm and a diameter of 3 mm. The spark gap is 1 mm and the breakdown of air with this gap is about ~5 kV mm-1. What is the force required to spark the gap? Is this a realistic force?

Answer 1

Piezo electric voltage constant can be calculated as follows: 200x10-12 m/ (1000) (8.85x10-12 C° / N.mº) = 0.02259 Dielectric field strength developed in the sample is, E = 5x10v 10x10 m = 5x10%V/m Stress developed in the piezo-electric crystal is, 6 00 PE DO = 27.0250" [1(1.510m)] = 156.45N * 156.5N*