Electrothermal actuation

Chen et al. have developed an electrothermally actuated CNT-silicone composite [194]. They have been able to produce a maximal strain of 4.4% with an applied field of only 1.5 kV m by incorporating a CNT network into the silicone... 

Chen EZ, Chen CH, Hu CH, Fan SS (2008) Electrothermal actuation based on carbon nanotube network in silicone elastomer. Appl Phys Eett 92 263104... 

Polymer composite actuators with a bilayer structure of different coefficients of thermal expansion (CTE) can generate bending displacement. When one side of the film is introduced with conductive fillers, the actuator can be electrothermally driven. PDMS/CNT composite was reported to be driven by the thermal expansion of the PDMS with CNTs as... 

FIGURE 8.3 Electrothermally driving actuators. (A) Schematic illustration to the actuation mechanism and configuration... 

In summary, the electrothermally driving actuators exhibit large actuation under a relative low driving voltage. Compared with the electrochemically driving actuators, they show better actuation stability because it is free of electrolyte. Unfortunately, they exhibit a slow responsiveness due to the unsatisfactory heat conduction of the polymer. Therefore, some efforts should be made to improve the heat conduction by decreasing the thickness of the polymeric layer or introducing functional additives. 

Coupling of highly conductive CNT network with a soft polymer matrix with large coefficient of thermal expansion (CTE) leads to a new class of electrothermal CNT-polymer composite actuators,which generates significant strains reversibly at applied electric fields at least two orders of magnitude lower than those reported for electrostrictive polymer nanocomposites. 

Chen et al have reported electrothermal actuation of MWNT-PDMS composites where randomly oriented nanotubes form a conductive network in... 

Figure 2.15 Electrothermal bending of a MWNT-PDMS composite film, (a) Schematic structure of a U-shaped actuator consisting of a thin layer of super-aligned MWNT-PDMS composite and a thick layer of pristine PDMS. The dashed lines represent the direction of CNT alignment, (b) Photographs of the actuator without (left) and with (right) an applied DC voltage of 40 V. Reprinted by permission from the American Chemical Society.

Li L, Uttamchandani D (2004) Modified asymmetric micro-electrothermal actuator analysis and experimentation. J Micromech Microeng 14 1734—1741... 

Microactuators, Fig. 2 Pictures and diagrams of (a) in-plane, surface micromachined electrothermal bimorph MEMS actuator and microactuator bank and (b) in-plane... 

Electrothermal or Thermal Actuation Motion is generated by differential thermal expansion in materials such as sDicon or metals, while heat is typically injected into the actuator by means of Joule heat dissipation. Some actuator components expand more than others due to different cross-sections and therefore electrical resistance. Typical microactuator configurations include in-plane bimorph elements (Fig. 2a), out-of-plane bimorph plates, in-plane Chevron, or bent-beam elements (Fig. 2b) [3]. These types of actuators exhibit larger force capabiUties (in mN range), can achieve displacements of 100 pm or less but generally consume a lot of power (hundreds of mW), and have low bandwidth (Hz to KHz). Common methods of fabrication for electrothermal microactuators include surface micromachining... 

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