Actuation characteristics and applications of piezoelectric materials and ionic polymer-metal composites

Abstract

Smart materials are a special class of materials which have abilities to change their physical properties in response to environmental stimuli. One of the important groups of smart materials is electro-active material (EAM) which responds to external electric potentials. Based on the working mechanism, the EAM can be further divided into two groups, i.e., electronic EAMs which rely on internal electrostatic forces for their actuation and ionic EAMs which depend on ion transportation and interaction for their actuation. Piezoelectric material and ionic polymer-metal composite (IPMC) are typical electronic EAM and ionic EAM, respectively. Piezoelectric materials, when subject to a mechanical force, will become electrically polarized. Tension and compression generate voltages of opposite polarity, and in proportion to the applied force. Conversely, when piezoelectric materials are subject to an electric field parallel to the polarization direction, they will expand or contract according to the polarity of the field, and in proportion to the strength of the field. The two effects are labeled as direct and converse piezoelectric effect and they are the basis for piezoelectric materials as sensors and actuators. Similar to piezoelectric materials, the IPMCs can also respond to electric and mechanical excitations. Instead of extension and contraction as piezoelectric materials, the IPMCs undergo transverse bending motion under an applied electric potential on the electrodes. On the other hand, the IPMCs can generate a measurable electric potential when it is subject to an imposed deformation. Thus, the IPMCs can also serve as sensors and actuators. The two types of smart materials, each has its own characteristics, can be employed for different applications in biomedical engineering. The objective of this research is to study the actuation characteristics of piezoelectric materials and IPMCs and explore the possibility of using the two types of materials for biomedical applications.