Notiser - Material

Processing of Fibers for Actuator Composites, Professor Michael J. Cima
A novel piezoelectric fiber composite is being developed in MIT's Aero-Astro Department for actuation of air-foil surfaces. The fibers that make up this composite are ceramic piezoelectric materials and the matrix is composed of structural epoxy resin. The required electric field is applied via a series of interdigitated comb electrodes on the surface of the composite. Efficient methods for fiber production are being explored that do not require the usual compounding procedure which is difficult and requires large batch sizes. Our approach is to doctor blade on to silicone substrates with grooved surfaces. The grooves define the shape of the cast fiber. Firing procedures that maintain the shape and stoichiometry of the fiber are also being developed.

Force transduction materials for human-technology interfaces, by R. Fletcher, Reprint Order No. G321-5629.
Given the trade-off between stiffness and strain, perhaps the more interesting physical limit to consider is the maximum actuation strain that is achievable by a material. Emulating the function of muscle groups in biological organisms, low-stiffness materials with large actuation strains can provide an effective source of tensile actuation ("pulling force"). Although the various mechanisms that produce strain take place on a microscopic scale, certain mechanisms such as the phase transitions of shape-memory alloys can produce relatively large strains approaching 10 percent, limited mainly by the yield strength of the metal. However, in the case of polymer gels, the ability of long molecular chains to reorient themselves in response to electrochemical stimuli can produce very dramatic macroscopic contractile strains of 1000 percent or more, which is basically a function of the molecular geometry and local electronic structure. [29] If such active polymers prove to be practical, it may suggest future approaches to force actuation based on molecular motors.