Piezo Ceramics Tutorial 8 of 15

Typical Arrangements

Unimorph®
The magnitude of piezoelectric forces, actions and voltages is relatively small. The maximum extension of a single element is in the order of fractions of a micron. Amplification is often required and can be achieved by various arrangements of the piezo ceramic such as Unimorph, Bimorph and Stacks.

A Unimorph is made by bonding a thin piece of piezo ceramic to an inactive substrate. Driving the piezo-ceramic will lead to deformation of the entire structure. Transducer Products Division has expertise in making various high specification Unimorphs for Hydrophones, Sensors and Actuators.

Bimorphs ®
A Bimorph is made by bonding two pieces of piezo-ceramic together so that differential changes in length of the two pieces can produce relatively large movements. This element consists of two transverse expander plates secured together face to face in such a manner that a voltage applied to the electrodes causes the plates to deform in opposite directions, resulting in a bending action. The displacement of the Bimorph in response to an applied voltage is many times greater than the corresponding displacement of a single plate, typically in excess of 10µm per volt. Thus Bimorphs have, in effect, 'built-in' levers to provide or require much greater motion but less force than single plates.

Actuator Stacks
Stacks are several piezoelectric elements connected mechanically in series and electrically in parallel. The displacement of each transducer element adds to the total displacement. The displacement of the whole stack assembly is equal to the sum of the individual displacements. Stacks are generally required for applications requiring large displacements (typically between 5 and 180µm).

Sandwich Transducers
It is difficult to make single blocks of ceramic resonating below about 100 KHz. Instead a composite half wave resonator is used consisting of two or more piezo-ceramic rings sandwiched between metal layers.

This arrangement can achieve low frequencies at high drive levels.

Indepth technical information can also be found in the Technical Publication Archives as Acrobat® pdf files.