Microscale Sensors and Actuators

At the microscale level, detailed local temperature and composition control through the staged feed and supply of reactants or the removal of products would result in a higher selectivity and productivity than would the conventional approach. Indeed, this conventional approach imposes boundary conditions and lets a system operate under spontaneous reaction and transfer. To produce a local energy supply, microwave and ultrasound can be used instead of heat. To operate the relevant models on these energies, local sensors and actuators as well as close computer control will absolutely be needed. 

F. Mugele and J. C. Baret, Electrowetting From basics to applications, Journal of Physics-Condensed Matter, vol. 17, no. 28, p. R705-R774, July 2005. J. Lee, H. Moon, J. Fowler, T. Schoellhammer, and C. J. Kim, Electrowetting and electrowetting-on-dielectric for microscale liquid handling, Sensors and Actuators A-Physical, vol. 95, no. 2-3, pp. 259-268, Jan. 2002. 

Klimant, L, Kuhl, M., Glud, R.N. and Holst, G., 1997. Optical Measurement of Oxygen and Temperature in Microscale Strategies and Biological Applications. Sensors and Actuators B 38 29-37. 

Hofmann, O., Miller, P, SuUivan, P., Jones, T.S., deMello, J.C., Bradley, D.D.C., and deMello, A.J., Thin-film organic photodiodes as integrated detectors for microscale chemiluminescence assays. Sensors and Actuators B—Chemical, 106, 878-884, 2005. 

While a linear pump can easily be bruit up from two or more basic actuation units, microscale rotary mechanisms face significant fabrication challenges. Accordingly, rotary peristaltic micropumps have seen very limited implementation. While several rotary mechanical micropumps are described in the literature (e.g., see the summaries in Refs. [1, 3], and [2]), to our knowledge there is only one example in the literature of a true rotary peristaltic micropump Kim et al. (Sensors and Actuators A 128 43—51, 2006) use a sflicmie membrane for the deformable charmel surface and a rotating ferrofluid plug... 

Lee J, Moon H, Fowler J, Schorllhammer T, Kim C-J (2002) Electrowetting and electrowetting-on-dielectric for microscale liquid handling. Sensors and Actuators A 95 259-268... 

Tlie technological requiiements for designing and constructing microfluidic devices for micro- and nano-technology ai e expanding. A microfluidic platform for the constraction of microscale components and autonomous systems consists of a combination of liquid-phase photopolynierization, lithography, and laminar flow to generate channels, valves, actuators, sensors, and systems. " ... 

In our postulation, how to automate machines in terms of operations will soon be a routine problem because of the technological maturity of actuators, sensors, and controllers. The application of automation technology will then focus on the issues of intelligence, integration, and autonomy. Another emerging trend involves the incorporation of micro-electromechanical systems (MEMSs) as sensors and controllers of automation and the microscale. However, education and training of workers who interact with intelligent and autonomous machines may be another important research issue in the future. 

Generally, the computational effort increases when going from the macroscale over the mesoscale up to the microscale. If real sensor or actuator apphcations are of interest, in most cases mesoscopic or macroscopic modeling is predestined. In order to understand the physicochemical mechanisms underlying the conversion, i.e., the mechanical deformation, the theoretical and experimental facts behind the swelling process have to be investigated. 

Because the fabrication process is such an essential part of microfluidics, an overview of the principles underlying the microfabrication technology is presented. Pressure, flow, and temperature measurements are essential variables for characterizing fluid motion in any system. An important goal is the design and construction of self-contained microfluidic systems. Because of their small size, incorporation of pressure, flow, and temperature sensors directly on the microfluid system chip is highly desirable. There are relatively few examples where microfluidic systems have been constructed with these on-board sensors. There have been so many microsensor developments in recent years that it is only a matter of time before such systems will appear. Small-scale actuators to provide either open- or closed-loop control of the flow in microchannels are needed and these efforts are addressed. While experimental work on fluid flow itself in microscale structures is rather sparse, some results will be presented that emphasize the similarity and/or differences between macroscopic and microscopic flow of liquids. Although there are not many applications of... 

As mentioned previously, one of the most important and exciting advantages of conjugated polymer microactuators is the possibility of integrating them into more complex microsystems, such as the cell-based sensors described above. The actuators add the powerful capability of mechanical manipulation of biology on the microscale. This is enabled by their low voltage operation and room temperature microfabrication, and the wide variety of actuator configurations that are possible. 

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