(Dr. Christopher Lynch, advisor)
"Electromechanical Efficiency of Actuator Materials"
Military and commercial trends demand that actuator materials operate at large stress ad electric field, conditions under which they exhibit nonlinear and hysteretic behavior. This investigation serves to characterize the electromechanical efficiency of piezoelectric stack actuators operating in this nonlinear region. Efficiency of piezoelectric materials is defined as the ratio of the mechanical work output divided by the electrical work input. The theoretical efficiency of the electrical to mechanical conversion of a linear reversible actuator is 100% for a full thermodynamic cycle. Real actuators have an irreversible component in the thermodynamic cycle, which leads to efficiencies less than 100%
The thermodynamic cycle used to define the electromechanical coupling
factor, k^2, is analyzed, and experiments are designed to demonstrate this
cycle. Several compositions of stack actuators are subjected to combined
stress and electric field loading, in efforts to determine material ability
to convert stored energy to mechanical or electrical work. Preliminary
measurements on stack actuators fabricated from soft PZT indicate efficiencies
that range from 20% to 50% depending on the applied preload and electric
field level. The efficiency decreases with increasing electric field.
At at given, electric field, there is a maximum efficiency with preload.
A discussion of these results and the effects of non-linearity and hysteresis
on actuator efficiencies will be included.