Piezo generators convert force and motion to voltage and charge. A sheet bonded to a structural member which is stretched or flexed will induce electrical generation. Applying a mechanical stress to a laminated two layer element results in electrical generation depending on the direction of the force, the direction of polarization, and the wiring of the individual layers. Essentially, the element acts like a single sheet of piezo. The metal shim sandwiched between the two piezo layers provides mechanical strength and stiffness while shunting a small portion of the force.
Charge develops across each layer in an effort to counteract the imposed strains.
This charge may be collected as observed here. It is suitable for handling high force and collecting a large volume of charge. Closed-circuit current, I CC , refers to the total current developed, at the maximum recommended strain level and operating frequency, when the charge is completely free to travel from one electrode to the other, and not asked to build up voltage. Open-circuit voltage, Voc, refers to the voltage developed at the maximum recommended strain level, when charge is prohibited from traveling from one electrode to the other. Current is at a maximum when the voltage is zero, and voltage is at a maximum when the charge transfer is zero.