Piezoelectric Sensors and Actuators

PZT based actuators can normally generate a maximum strain of about 0.2% (about 2000 μ-strain ). Though, single crystals of PZN and PMN are known to generate strains of the range of 8000 μ-strain , the use of such crystals as actuators are limited due to their high cost and difficulty of integrating in a structure. Even with the maximum available active strain, it is quite difficult to control machine-vibration using the smart materials directly. Various forms of displacement and force amplification techniques have been recently developed towards the use of piezo-electric actuators in industrial scale. These systems are classified into three major groups :

Internally Leveraged System:
In this system, the actuators contain multiple piezoelectric elements to get an amplified effect. The simplest example is a Piezo-stack where many piezoelectric wafers are stacked in such a way that a comparatively larger deformation is obtained in the d₃₃ mode by applying a smaller voltage. More advanced systems include various configurations such as Rainbow, C-block, and Crescent etc.

Externally Leveraged System:
In these actuators mechanical systems are utilized to amplify the output of a piezoelectric actuator – these include actuators like unimorph, bimorph, flexure based actuator, moonie, cymbal etc.

Frequency Leveraged System:
This type of system is based on alternating current supply to a piezo-actuator. Typical examples are piezoelectric inchworm motors, ultrasonic motors, etc.

Even though different designs of actuators achieve different degrees of efficiencies in terms of energy conversion, displacement and force amplification, the basic principle used for strain generation is quite similar.