You are designing a piezoelectric bimorph actuator with the

You are designing a piezoelectric bimorph actuator with the following constraints. The width of the laminate cantilever is 200 ?m with 50 ?m of PZT (E = 61 GPa, d13 = 320*10-12 C/N) on top and 10 ?m of silicon (E = 160 GPa) on the bottom. The PZT is poled so that the 1 direction points along the length of the cantilever and the 3 direction points up through the thickness – applying E3 = 100 V bends the cantilever downward. Assume a top electrode is thin enough to be ignored and the silicon provides the bottom electrode for the PZT.

d. What is the blocked force for the bimorph actuator?

Solution

d)PZT actuators convert electrical signals like voltages or charges into mechanical displacements or forces. The operating frequency range of actuators is from static up to about half the resonant frequency of the mechanical system. As for sensors, a reasonably linear relationship between input signal and movement is required. On the other hand, there is the special class of actuators, which is purposely driven at their resonant frequency, known as ultrasonic transducers. These transducers convert electrical energy into mechanical energy and are treated in PZT actuators can be divided in three main groups - axial actuators (d33-mode) - transversal actuators (d31-mode) - flexural actuators (d31-mode). Axial and transversal actuators have high stiffness and are optimized for small movements and high forces. Flexural actuators (bimorphs), on the other hand cover the applications where larger movements are required. If a voltage is applied to an actuator there will be a displacement. When this displacement is blocked, a force will develop, the so-called blocking force, which is, in fact, a measure of the stiffness of the actuator. gives a survey the possible stroke-blocking force combinations.

Bimorphs are designed as double layer elements. In operation, one of the layers extends while the other compresses. As a result, it courses the element to bend. Piezo bimorphs is a class of electromechanical transducers converting an electrical voltage into a mechanical displacement and vice versa. These types of actuators provide the value of a bending displacement much more than planar ones. As compared with stack actuators, bimorphs have higher stroke value but develop lower force and have lower resonance frequency

APPLICATIONS

Scanning systems in laser technique;

Micro positioning devices for looms and Braille reading systems;

Medical sensors ;

Fans for local cooling of electronic units ;

Sensory commutating devices for ON/OFF switching electrical contacts.