Microactuators

Reversible electrochemical actuators comprise of an anode, a cathode and a separating electrolyte. Either electrode or both can be conducting polymers. However, other redox materials such as graphite have also been used as electromechanical electrodes. The nature of redox processes for conducting polymer electrodes has been found to be rate dependent. For instance, an electrode that is anion doped can be reduced either during the addition of cations or the removal of anions. 

It has been shown that electrically conducting polymers are versatile electronic materials that display a unique range of properties for application to molecular electronics. However, there are several problems associated with these materials, namely reproducibility, stability 

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Dubois, P., Rosset, S., Koster, S., Bufom, J.M., Stauffer, J., Mikhailov, S., Dadras, M., Rooij, Nico- F. de., and Shea, H., Microactuators based on ion-implanted dielectric electroactive polymer membranes (EAP), Presented at 13th International Conference on Solid-State Sensors, Actuators and Microsystems, Seoul, Korea, June 5-9, 2005, 2048. 

The sensitivity of hydrogels to a large number of physical factors like temperature [149], electrical voltage [150], pH [151-153], concentration of organic compounds in water [154], and salt concentration [155] make them promising materials for a broad range of applications as microsensors [156] and microactuators [154] in MEMS devices. 

The IR filter is realized by a PS layer with a modulation of porosity, which constitutes an interference filter as described in detail in the next section. The 30 pm thick porous layer is then released from the substrate by electropolishing, which is easily done in situ by increasing the etching current density above JPS. This process is commonly applied to form free-standing PS membranes and PS tubes [Tj 1], The internal strain between the Si3N4 layer used for masking and the porous layer lifts the filter up to its rest position, as shown in Fig. 10.10. The filter is suspended at two microactuator arms, which work as thermal bimorph actua-... 

Fig. 10.10 SEM micrograph of a tunable IR Bragg filter (1.1 xl. 85 mm) of density-modulated PS, suspended at two microactuator arms. Its rest position is more than 180°...

Combustion in small volumes has recently become of interest to applications of micropower generation [77-81], micropropulsion [82-94], microengines [95-102], microactuation [103-105], and microfuel reforming for fuel cells... 

Fig. 87. Drift free microactuator (a) thermal deformation and (b) magnetostriction deformation. After Betz...

Optical microactuators like a micromirror for scanning applications have been proposed by Orsier et al. (1996). A two-dimensional bimorph (Si 4- magnetostrictive film) is driven remotely by two differently oriented magnetic fields working at different frequencies in order to obtain the bending and torsional vibrations due to the magnetostrictive strain. 

Silicon micropumps offer major advantages in terms of system miniaturization and control over low flow rates with a stroke volume 160 nL.14 The micropump has the characteristics of very small in size, implantability in the human body, low flow rates (in the range of 10 pL/min), moderate pressure generation from the microactuator to move the drug, biocompatibility, and most important, a reliable design for safe operation. The implantable device is particularly suitable (over the injectable drug delivery systems) for patients with Parkinson s disease, Alzhiemer s disease, diabetes, and cancer, as well as chronically ill patients, because the catheter that is attached to the device can transport drug to the required site. 

Even with their impressive physical changes, electrorheological materials have not solved the microactuator problem. This is due to the complex fabrication schemes required to incorporate these materials into microfluidic manifolds. Therefore,... 

Porous silicon is compatible with standard silicon K-MOS technology and different microsystems based on this nanostructured material have been successfully fabricated [1], Porous silicon impregnating with solid state oxidants demonstrats combustion and explosion processes [2-5]. These processes can be used for various microactuators [6], In present work we have studied the influence of the porous silicon structure on the combustion and explosion processes. 

Lee, J. Kim, C.-J. Surface-tension-driven microactuation based on continuous electrowetting. J. Microelectromech. Syst. 2000, 9 (2), 171-180. 

An implantable drug delivery system based on microactuation devices has been developed (36) (Fig. 4) by which doses can be controlled to an accuracy of 5 pL. One form of the invention can dispense solid drug, which of course is a more complex task, because of the... 

Figure 4 The design of the implantable drug delivery system based on shape memory alloy microactuation, showing the main reservoir, pressure chamber, and the printed circuit board (PCB) with electronics and valve system. The basic concept is to have a reservoir under constant pressure pushing liquid through a calibrated flow channel and valve system. Dimensions are 50 mm with a height of 15 mm. Source From Ref. 36.

Numerous examples of developing conducting polymer actuators to operate as artificial muscles have been described in the literature. For example, a steerable cochlear implant with the CRC Cochlear Implant. (Melbourne, Australia), is under development.126 The microactuator will assist surgeons during implantation of the Bionic... 

M.G. Pollack, Electrowetting-based Microactuation of Droplets for Digital Microfluidics. Ph.D. Thesis, Duke Uiuversity (2001). 

Yanagisawa K, Tago A, Ohkubo T and Kuwano H 1990 Magnetic microactuator Proc. IEEE Micro-Electro-Mechanical Systems Workshop (Napa Valley, CA) (New York IEEE) pp 120-4... 

Hoffmann J, Plotner M, Kuckling D, Fischer W-J (1999) Photopatteming of thermally sensitive hydrogels useful for microactuators. Sens Actuat 77 139-144 Houbenov N, Minko S, Stamm M (2003) Mixed polyelectrolyte brush from oppositely charged polymers for switching of surface charge and composition in aqueous environment. Macromolecules 36 5897-5901... 

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