EAP

There are many EAP materials. In order to make a clear distinction between their activation
mechanisms, the author divided them into two major groups including: ionic (involving mobility
or diffusion of ions) and electronic (driven by electric field or Maxwell forces). The
currently available leading EAP materials are listed in Table 1 and a summary of the advantaged and disadvantages of these two groups of materials are listed in Table 2. The electronic polymers (electrostrictive, electrostatic, piezoelectric, and ferroelectric) can be made to hold the induced displacement under activation of a DC voltage, allowing them to be considered for robotic applications. Also, these materials have a greater mechanical energy density and they can be operated in air with no major constraints. However, they require a high activation field (>100-V/m) close to the breakdown level. In contrast, ionic EAP materials (gels, polymermetal composites, conductive polymers, and carbon nanotubes.) are driven by diffusion of ions and they require an electrolyte for the actuation mechanism. Their major advantage is the requirement for drive voltages as low as 1-2 Volts. However, there is a need to maintain their wetness, and except for conductive polymers and carbon nanotubes, it is difficult to sustain DC induced displacements. The produced displacement of both the electronic and ionic EAP can be geometrically designed to bend, stretch or contract. Any of the existing EAP materials can be made to bend with a significant curving response, offering actuators with an easy to see reaction and an appealing response. However, bending actuators have relatively limited applications due to the low force or torque that can be induced.

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