Frequency response of polypyrrole trilayer actuator displacement

Conducting polymer trilayers are attractive for use in functional devices, given low actuation voltages, operation in air and potentially useful stresses and strains; however, their dynamic behavior must be understood from an engineering perspective before they can be effectively incorporated into a design. As a step towards the identification of the actuator dynamics, frequency response analysis has been performed to identify the magnitude and phase shift of displacement in response to a sinusoidal voltage input. The low damping of the trilayer operating in air and the use of a laser displacement sensor has allowed the frequency response to be continuously identified up to 100Hz, demonstrating a resonant peak at 80Hz for a 10mm long actuator. Two linear transfer function models have been fitted to the frequency response of the trilayer displacement (i) a 3(rd) order model to represent the dynamics below 20Hz and (ii) a higher complexity 6(th) order model to also include the resonant peak. In response to a random input signal, the 3(rd) order model coarsely follows the experimental identified displacement, while the 6(th) order model is able to fully simulate the real trilayer movement. Step responses have also been obtained for the 3(rd) and 6(th) order transfer functions, with both models capable of following the first 4 seconds of experimental displacement. The application of empirical transfer function models will facilitate accurate simulation and analysis of trilayer displacement, and will lead to the design of accurate positional control systems.