Is piezo electricity generated by constant pressure or does it require variation like ac power?
Piezo electricity always occurs in crystalline non-conductors. Stress on the crystal lattice causes a charge separation which, in conjunction with the capacitance produce by connecting electrodes to the crystal, results in a voltage across the electrodes: V = Q/C, where Q is the amount of charge separated by the stress (or pressure) and C is the capacitance between the electrodes. If C is small, on the order of a few picofarads, very large voltages can be generated from the stress-induced charge separation. However, as soon as an external circuit is completed, either through a spark or a resistive load, the charge separation is neutralized by electrons flowing in the external circuit. Electrical energy is briefly released into the external circuit. Energy is also stored mechanically in the stressed state of the crystal. If the stress (or pressure) is removed, this stored mechanical energy is again converted to electrical energy by charge separation in the other direction. And again, th
