Piezoelectric ignition systems are much simpler, much more compact, and less expensive than alternative systems incorporating permanent magnets or high voltage transformers and capacitors.
The volume of the ceramic element and the amount of stress exerted on the element are key factors in converting mechanical input to electrical energy. The stress on the element is the ratio of the applied force to the surface area of the element. Consequently, when the composition of the ceramic, the volume of the ceramic element, and the applied force are constant, the element that has the smallest surface area will generate the most electrical energy.
In squeeze-type piezoelectric fuel ignitors a static mechanical energy input -- very low frequency, relative to the resonance frequency of the ceramic -- generates the electrical energy for ignition. In the impact ignition design a spring-loaded hammer delivers a dynamic input to the ceramic element. The pressure wave generated when the hammer strikes the element once is reflected multiple times in both the element and the hammer, in accord with the elastic and acoustical properties of the ceramic and the hammer. Until the flashover at the spark gap, stress varies along the height of the ceramic element, and exact values for voltage must be calculated by integration over the height of the element. Approximate values usually are sufficient for simple ignition devices.
