Research and Development of Coaxial-type Self-sensing Piezo-electret Actuator

This thesis focuses on the application of composite electret materials and piezoelectric materials as well as the practicability of a newly-developed coaxial-type self-sensing piezo-electret actuator. The structure of this newly developed self-sensing actuator potentially presented the possibility of creating a self-sensing actuator, is different from the conventional approach of self-sensing actuators as they are generally realized by post-processing the signal using subtraction circuit as that of the Wheatstone bridge circuit. The coaxial structure composed of several dip-coating layers in which the circular electrode is employed as the substrate. Several kinds of copolymers in the form of solutions were prepared, including P(VDF-TrFE), cyclic olefin copolymer and polystyrene. Moreover, based on the knowledge that the thickness of the film depends upon the material of the substrate, the rate of dip coating and the concentration of the solutions, the influences of these parameters are discussed. It is shown to be possible to control the film thickness from the preliminary experimental result, which is essential for voltage control in the poling process adopted. P(VDF-TrFE) copolymer with good ferroelectric properties has been successfully fabricated and its piezoelectric properties are also verified, which can serve as the sensor functions in the newly proposed self-sensing actuator. On the other hand, the actuating function is created by using the composite electrets made of cyclic olefin copolymer and polystyrene. The electret materials are formed in layers in order to store the interfacial charges. The composite electret layer was then coated on the piezoelectric film and the whole structure was poled by the corona charging method. The surface voltage was measured which indicates that the structure possesses charge storage capability. The self-sensing signals were successfully measured on the developed structure, which verified its practicability of serving as the self-sensing actuator. The applications of the self-sensing actuators, which constitute both electrets and piezoelectric materials in the coaxial and multi-layer form, include structure health monitoring, vibration control, etc.