There are two different types of piezo actuators / piezo multilayers. The first is a stack actuator. A stack actuator is constructed in one of two ways: discrete stacking or co-firing depending on the user's requirements.

The other type of piezo actuator is a stripe actuator or bending actuator, in which thin layers of piezoelectric ceramics are bonded together; the thin layers allow the actuator to bend with a greater deflection but a lower blocking force than a stack actuator.

Alternatively, if physical displacement is prevented, a piezo actuator will develop a usable force.

       A piezoelectric ceramic element exposed to an alternating electric field changes dimensions cyclically, at the frequency of the field. The frequency at which the element vibrates most readily in response to the electrical input, and most efficiently converts the electrical energy input into mechanical energy -- the resonance frequency -- is determined by the composition of the ceramic material and by the shape and volume of the element.

      As the frequency of cycling is increased, the element's oscillations first approach a frequency at which impedance is minimum (maximum admittance). This frequency also is the resonance frequency. As the frequency is further increased, impedance increases to a maximum (minimum admittance), which also is the anti-resonance frequency. These frequencies are determined by experiment - to see how, refer to Determining Resonance Frequency.

      The values for minimum impedance frequency and maximum impedance frequency can be used to calculate the electromechanical coupling factor, k, an indicator of the effectiveness with which a piezoelectric material converts electrical energy into mechanical energy or mechanical energy into electrical energy. k depends on the mode of vibration and the shape of the ceramic element. Dielectric losses and mechanical losses also affect the efficiency of energy conversion. Dielectric losses usually are more significant than mechanical losses.