The MEMS Handbook MEMS Applications (2nd Ed) - M. Gad el Hak Episode 1 Part 9 ppsx

makes it possible to control the final bending angle rather well. A reversible bending angle can be obtained as a result of the thermal expansion of the cured polyimide. A metal conductor is used as a resis- tive heater which produces local power dissipation in the joint. A temperature increase results in an expansion of the polyimide and a dynamic change in the bending angle. Sensors and Actuators for Turbulent Flows 6-61 (a) (b) Probe Probe FIGURE 6.47 An external manipulator is used to fold and supply the structure with a reshaping voltage. The Joule's heating raises the temperature of the arm to cause annealing effect which results in stress release and plastic defor- mation.After removal of the voltage, the arm cools down and the structure retains its three-dimensional shape. (Reprinted with permission from Fukuta, Y., Akiyama, T., and Fujita, H. [1995] “A Reshaping Technology with Joule Heat for Three-Dimensional Silicon Structures,” Technical Digest, Inter. Confer. on Solid-State Sensor and Actuator [Tranducers ’95], pp. 174–177, 25–29 June, Stockholm, Sweden.) FIGURE 6.48 Illustration of a three-dimensional self-assembled polysilicon structure based on scratch-drive actuators. (Reprinted with permission from Akiyama, T., Collard, D., and Fujita, H. [1997] “Scratch Drive Actuator with Mechanical Links for Self-Assembly of Three-Dimensional MEMS,” J. MEMS 6, pp. 10–17.) © 2006 by Taylor & Francis Group, LLC 6.6 Microturbomachines 6.6.1 Micropumps There have been several studies of microfabricated pumps. Some of them use non-mechanical effects. The so-called Knudsen pump uses the thermal-creep effect to move rarefied gases from one chamber to another. Ion-drag is used in electrohydrodynamic pumps [Bart et al., 1990; Richter et al., 1991; Fuhr et al., 1992]. These rely on the electrical properties of the fluid and are thus not suited for many applications. Valveless pumping by ultrasound has also been proposed by Moroney et al. (1991), but produces very little pressure difference. Mechanical pumps based on conventional centrifugal or axial turbomachinery will not work at micromachine scales where the Reynolds numbers are typically small, on the order of 1 or less. Centrifugal forces are negligible and, furthermore, the Kutta condition through which lift is normally generated is invalid when inertial forces are vanishingly small. In general there are three ways in which mechanical micro- pumps can work: positive-displacement pumps; continuous, parallel-axis rotary pumps; and continuous, transverse-axis rotary pumps. Positive-displacement pumps are mechanical pumps with a membrane or diaphragm actuated in a reciprocating mode and with unidirectional inlet and outlet valves. They work on the same physical prin- ciple as their larger cousins. Micropumps with piezoelectric actuators have been fabricated [Van Lintel et al., 1988; Esashi et al., 1989); Smits, 1990]. Other actuators, such as thermopneumatic, electrostatic, 6-62 MEMS: Applications Moveable part 2w Meltable pad Substrate b (a) Molten pad (b) Further rotation (d) Further rotation Hinge gap opening (c) Solidified pad Rotation limiter (e) FIGURE 6.49 Production of a three-dimensional structure with Si mechanical parts based on surface tension forces (top figure), and SEM photo of the resulting three-dimensional structure (bottom figure). (Reprinted with permission from Syms, R.R.A. [1998] “Demonstration of Three-Dimensional Microstructure Self-Assembly,” Sensors and Actuators A 65, pp. 238–243.) © 2006 by Taylor & Francis Group, LLC electromagnetic, or bimetallic can be used [Pister et al., 1990; Döring et al., 1992; Gabriel et al., 1992]. These exceedingly minute positive-displacement pumps require even smaller valves, seals, and mecha- nisms, a not-too-trivial micromanufacturing challenge. In addition there are long-term problems associ- ated with wearor clogging and consequent leaking around valves. The pumping capacity of these pumps is also limited by the small displacement and frequency involved. Gear pumps are a different kind of positive-displacement device. A continuous, parallel-axis rotary pump is a screw-type, three-dimensional device for low Reynolds num- bers and was proposed by Taylor (1972) for propulsion purposes and shown in his seminal film. It has an axis of rotation parallel to the flow direction implying that the powering motor must be submerged in the flow, the flow turned through an angle, or that complicated gearing would be needed. Continuous, transverse-axis rotary pumps are a machines that have been developed by Sen et al. (1996). They have shown that a rotating body, asymmetrically placed within a duct, will produce a net flow due to viscous action. The axis of rotation can be perpendicular to the flow direction and the cylinder can thus be easily powered from outside a duct. A related viscous-flow pump was designed by Odell and Kovasznay (1971) for a water channel with density stratification. However, their design operates at a much higher Reynolds number and is too complicated for microfabrication. As evidenced from the third item above, it is possible to generate axial fluid motion in open channels through the rotation of a cylinder in a viscous fluid medium. Odell and Kovasznay (1971) studied a pump based on this principle at high Reynolds numbers. Sen et al. (1996) carried out an experimental study of Sensors and Actuators for Turbulent Flows 6-63 t  t 54.74° Soft baked polyimide a polyimide Cured (1-)a (1-)b 54.74° b FIGURE 6.50 Principle of the polyimide V-groove joint. The polyimide in the V-groove shrinks when the polyimide is cured. The absolute lateral-contraction length of the polyimide is larger at the top of the V-groove than at the bottom, resulting in a rotation which bends the free-standing structure out-of-the-wafer plane. (Reprinted with permission from Ebefors, T., Kälvesten, E., and Stemme, G. [1997a] “Dynamic Actuation of Polyimide V-Grooves Joints by Electrical Heating,” in Eurosensors XI, September 21–24, Warsaw, Poland.) © 2006 by Taylor & Francis Group, LLC a different version of such a pump. The novel viscous pump, shown schematically in Figure 6.52, consists simply of a transverse-axis cylindrical rotor eccentrically placed in a channel, so that the differential vis- cous resistance between the small and large gaps causes a net flow along the duct. The Reynolds numbers involved in Sen et al.’s work were low (0.01 Ͻ Re ϵ 2 ω a 2 /v Ͻ 10, where ω is the radian velocity of the rotor, and a is its radius), typical of microscale devices, but achieved using a macroscale rotor and a very viscous fluid. The bulk velocities obtained were as high as 10% of the surface speed of the rotating cylin- der. Sen et al. (1996) have also tried cylinders with square and rectangular cross-sections, but the circular cylinder delivered the best pumping performance. A finite-element solution for low-Reynolds-number, uniform flow past a rotating cylinder near an impermeable plane boundary has already been obtained by Liang and Liou (1995). However,a detailed two- dimensional Navier–Stokes simulations of the pump described above have been carried out by Sharatchandra et al. (1997), who extended the operating range of Re beyond 100. The effects of varying the channel height 6-64 MEMS: Applications 30 µm Cured polyimide Heater  Silicon plate Bonding pads Metal (1-e)b (1-e)a Silicon a b 500 µm 600 µm 500 µm 30 µm FIGURE 6.51 Isometric view of a three-dimensional structure based on a polyimide joint with three V-grooves. The metal lead-wires through the V-grooves are used to realize electrical connections to the out-of-plane rotated struc- ture. Exploiting the thermal expansion of the polyimide, the metal can also be used as a heater in the V-grooves to obtain reversible movements. (Reprinted with permission from Ebefors, T., Kälvesten, E., Vieider, C., and Stemme, G. [1997b] “New Robust Small Radius Joints Based on Thermal Shrinkage of Polyimide in V-grooves,” in Transducers ’97, June 16–19, Chicago.) X Y A B h u 2a ␻ x h L h FIGURE 6.52 Schematic of micropump developed by Sen et al. (Reprinted with permission from Sen, M., Wajerski, D., and Gad-el-Hak, M. [1996] “A Novel Pump for MEMS Applications,” J. of Fluids Eng. 118, pp. 624–627.) © 2006 by Taylor & Francis Group, LLC H and the rotor eccentricity ε have been studied. It was demonstrated that an optimum plate spacing exists and that the induced flow increases monotonically with eccentricity; the maximum flowrate being achieved with the rotor in contact with a channel wall. Both the experimental results of Sen et al. (1996) and the two-dimensional numerical simulations of Sharatchandra et al. (1997) have verified that, at Re Ͻ 10, the pump characteristics are linear and therefore kinematically reversible. Sharatchandra et al. (1997; 1998a; 1998b) also investigated the effects of slip flow on the pump performance as well as the thermal aspects of the viscous device. Wall slip does reduce the traction at the rotor surface and thus lowers the perform- ance of the pump somewhat. However, the slip effects appear to be significant only for Knudsen numbers greater than 0.1, which is encouraging from the point of view of microscale applications. In an actual implementation of the micropump, several practical obstacles need to be considered.Among those are the larger stiction and seal design associated with rotational motion of microscale devices. Both the rotor and the channel have a finite, in fact rather small, width. DeCourtye et al. (1998) numerically investigated the viscous micropump performance as the width of the channel, W, becomes exceedingly small. The bulk flow generated by the pump decreased as a result of the additional resistance to the flow caused by the side walls. However, effective pumping was still observed with extremely narrow channels. Finally, Shartchandra et al. (1998b) used a genetic algorithm to determine the optimum wall shape to maximize the micropump performance. Their genetic algorithm uncovered shapes that were nonintuitive but yielded vastly superior pump performance. Though most of the previous micropump discussion is of flow in the steady state, it should be possible to give the eccentric cylinder a finite number of turns or even a portion of a turn to displace a prescribed minute volume of fluid. Numerical computations will easily show the order of magnitude of the volume discharged and the errors induced by acceleration at the beginning of the rotation and deceleration at the end. Such a system can be used for microdosage delivery in medical applications. 6.6.2 Microturbines DeCourtye et al. (1998) have described the possible utilization of the inverse micropump device as a turbine. The most interesting application of such a microturbine would be as a microsensor for measuring exceed- ingly small flowrates on the order of nanoliters (i.e., microflow metering for medical and other applications). The viscous pump described operates best at low Reynolds numbers and should therefore be kinematically reversible in the creeping-flow regime. A microturbine based on the same principle should therefore, lead to a net torque in the presence of a prescribed bulk velocity. The results of three-dimensional numerical sim- ulations of the envisioned microturbine are summarized in this subsection. The Reynolds number for the turbine problem is defined in terms of the bulk velocity, since the rotor surface speed is unknown in this case: Re ϭ (6.69) where U – is the prescribed bulk velocity in the channel, a is the rotor radius, and v is the kinematic viscosity of the fluid. Figure 6.53 shows the dimensionless rotor speed as a function of the bulk velocity for two dimensionless channel widths W ϭ ∞ and W ϭ 0.6. In these simulations, the dimensionless channel depth is H ϭ 2.5 and the rotor eccentricity is ε / ε max ϭ 0.9. The relation is linear as was the case for the pump problem. The slope of the lines is 0.37 for the two-dimensional turbine and 0.33 for the narrow channel with W ϭ 0.6. This means that the induced rotor speed is, respectively, 0.37 and 0.33 of the bulk velocity in the channel. (The rotor speed can never exceed the fluid velocity even if there is no load on the turbine. Without load, the integral of the viscous shear stress over the entire surface area of the rotor is exactly zero, and the tur- bine achieves its highest albeit finite rpm.) For the pump, the corresponding numbers were 11.11 for the two-dimensional case and 100 for the three-dimensional case. Although it appears that the side walls have bigger influence on the pump performance, in the turbine case, a vastly higher pressure drop is required in the three-dimensional duct to yield the same bulk velocity as that in the two-dimensional duct (dimen- sionless pressure drop of ∆p* ϵ ∆p(2a) 2 / ρ v 2 ϭ Ϫ29 vs. ∆p* ϭ Ϫ1.5). U – (2a) ᎏ v Sensors and Actuators for Turbulent Flows 6-65 © 2006 by Taylor & Francis Group, LLC The turbine characteristics are defined by the relation between the shaft speed and the applied load. A turbine load results in a moment on the shaft, which at steady state balances the torque due to viscous stresses. At a fixed bulk velocity, the rotor speed is determined for different loads on the turbine. Again, the turbine characteristics are linear in the Stokes (creeping) flow regime, but the side walls have weaker, though still adverse, effect on the device performance as compared to the pump case. For a given bulk velocity, the rotor speed drops linearly as the external load on the turbine increases. At large enough loads, the rotor will not spin, and maximum rotation is achieved when the turbine is subjected to zero load. At present it is difficult to measure flowrates on the order of 10 Ϫ12 m 3 /s (1 nanoliter/s). One possible way is to directly collect the effluent over time. This is useful for calibration but is not practical for on-line flow measurement. Another is to use heat transfer from a wire or film to determine the local flowrate as in a thermal anemometer. Heat transfer from slowly moving fluids is mainly by conduction so that tempera- ture gradients can be large. This is undesirable for biological and other fluids easily damaged by heat. The viscous mechanism that has been proposed and verified for pumping may be turned around and used for measuring. As demonstrated in this subsection, a freely rotating cylinder eccentrically placed in a duct will rotate at a rate proportional to the flowrate due to a turbine effect. In fact other geometries such as a freely rotating sphere in a cylindrical tube should also behave similarly. The calibration constant, which depends on system parameters such as geometry and bearing friction, should be determined computa- tionally to ascertain the practical viability of such a microflow meter. Geometries that are simplest to fab- ricate should be explored and studied in detail. 6.6.3 Microbearings Many of the micromachines use rotating shafts and other moving parts that carry a load and need fluid bear- ings for support, most of them operating with air or water as the lubricating fluid. The fluid mechanics of these bearings are very different compared to that of their larger cousins. Their study falls in the area of microfluid mechanics, an emerging discipline which has been greatly stimulated by its applications to micro- machines and which is the subject of this chapter. Macroscale journal bearings develop their load-bearing capacity from large pressure differences which are a consequence of the presence of a viscous fluid, an eccentricity between the shaft and its housing, a large sur- face speed of the shaft, and a small clearance to diameter ratio. Several closed-form solutions of the no-slip flow in a macrobearing have been developed. Wannier (1950) used modified Cartesian coordinates to find an exact solution to the biharmonic equation governing two-dimensional journal bearings in the no-slip, creeping flow regime. Kamal (1966) and Ashino and Yoshida (1975) worked in bipolar coordinates; they assumed a general form for the streamfunction with several constants which were determined using the boundary conditions. Although all these methods work if there is no slip, they cannot be readily adapted to 6-66 MEMS: Applications 0.07 0.06 0.6 W = ∞ 0.05 0.04 0.03 0.02 0.01 0 0.02 0.06 0.1 0.14 0.18 U(2a) (a)(2a)   FIGURE 6.53 Turbine rotation as a function of the bulk velocity in the channel. (Reprinted with permission from DeCourtye,D., Sen, M., and Gad-el-Hak, M. [1998] “Analysis of Viscous Micropumps and Microturbines,”Inter. J. Comp. Fluid Dyn. 10, pp. 13–25.) © 2006 by Taylor & Francis Group, LLC slip flow. The basic reason is that the flow pattern changes if there is slip at the walls and the assumed form of the solution is no longer valid. Microbearings are different in the following aspects: (1) being so small, it is difficult to manufacture them with a clearance that is much smaller than the diameter of the shaft; (2) because of the small shaft size, their surface speed, at normal rotational speeds, is also small (the microturbomachines being devel- oped presently at MIT operate at shaft rotational speeds on the order of 1 million rpm,and are therefore oper- ating at different flow regime from that considered here); and (3) air bearings in particular may be small enough for non-continuum effects to become important. For these reasons the hydrodynamics of lubri- cation are very different at microscales. The lubrication approximation that is normally used is no longer directly applicable and other effects come into play. From an analytical point of view there are three con- sequences of the above: fluid inertia is negligible, slip flow may be important for air and other gases, and relative shaft clearance need not be small. In a recent study, Maureau et al. (1997) analyzed microbearings represented as an eccentric cylinder rotating in a stationary housing. The flow Reynolds number is assumed small, the clearance between shaft and housing is not small relative to the overall bearing dimensions, and there is slip at the walls due to non- equilibrium effects. The two-dimensional governing equations are written in terms of the streamfunction in bipolar coordinates. Following the method of Jeffery (1920), Maureau et al. (1997) succeeded in obtaining an exact infinite-series solution of the Navier–Stokes equations for the specified geometry and flow con- ditions. In contrast to macrobearings and due to the large clearance, flow in a microbearing is character- ized by the possibility of a recirculation zone which strongly affects the velocity and pressure fields. For high values of the eccentricity and low slip factors, the flow develops a recirculation region, as shown in the streamlines plot in Figure 6.54. Sensors and Actuators for Turbulent Flows 6-67 (g) (h) (i) (d) (e) (f) (a) (b) (c) FIGURE 6.54 Effect of slip factor and eccentricity on the microbearing streamlines. From top to bottom, eccentric- ity changes as ε ϭ 0.2, 0.5, 0.8. From left to right, slip factor changes as S ϵ [(2 Ϫ σ v )/ σ ], Kn ϭ 0, 0.1, 0.5. (Reprinted with permission from Maureau, J., Sharatchandra, M.C., Sen, M., and Gad-el-Hak, M. [1997] “Flow and Load Char- acteristics of Microbearings with Slip,” J. Micromech., and Microeng. 7, pp. 55–64.) © 2006 by Taylor & Francis Group, LLC From the infinite-series solution, the frictional torque and the load-bearing capacity can be determined. The results show that both are similarly affected by the eccentricity and the slip factor: they increase with the former and decrease with the latter. For a given load, there is a corresponding eccentricity which gen- erates a force sufficient to separate shaft from housing, i.e., sufficient to prevent solid-to-solid contact. As the load changes, the rotational center of the shaft shifts a distance necessary for the forces to balance. For a weight that is vertically downwards, the equilibrium displacement of the center of the shaft is in the horizontal direction. This can lead to complicated rotor dynamics governed by mechanical inertia, vis- cous damping, and pressure forces. A study of these dynamics may be of interest. Real microbearings have finite shaft lengths, and end walls and other three-dimensional effects influence the bearing characteristics. Numerical simulations of the three-dimensional problem can readily be carried out and may also be of interest to the designers of microbearings. Other potential research includes determination of a criterion for onset of cavitation in liquid bearings. From the results of these studies, information related to load, rotational speed, and geometry can be generated that would be useful for the designer. Finally, Piekos et al. (1997) have used full Navier–Stokes computations to study the stability of ultra-high- speed gas microbearings. They conclude that it is possible, despite significant design constraints, to attain stability for specific bearings to be used with the MIT microturbomachines [Epstein and Senturia, 1997; Epstein et al., 1997], which incidentally operate at much higher Reynolds numbers (and rpm) than the micropumps, microturbines, and microbearings considered thus far in this chapter. According to Piekos et al. (1997), high-speed bearings are more robust than low-speed ones due to their reduced running eccentricities and the large loads required to maintain them. 6.7 Conclusions In a presentation to the 1959 annual meeting of the American Physical Society, Richard Feynman anticipated the extension of electronic miniaturization to mechanical devices. That vision is now a reality. Micro- electromechanical systems, a fledgling field that took off just this decade, are already finding numerous applications in a variety of industrial and medical fields. This chapter focused on MEMS-based sensors and actuators especially as used for the diagnosis and control of turbulent flows. The miniaturization of sensors leads to improved spatial and temporal resolutions for measuring useful turbulence quantities at high Reynolds numbers. The availability of inexpensive, low-energy-usage microsensors and microactuators that can be packed densely on a single chip promises a quantum leap in the performance of reactive flow control systems. Such control is now in the realm of the possible for future vehicles and other industrial devices. In a turbulent flow, an increase in Reynolds number will automatically generate smaller length- scales and shorter time-scales, which both in turn require small and fast sensors for a correct resolution of the flow field. MEMS offer a solution to this problem since sensors with length- and time-scales of the order of the relevant Kolmogorov microscales can now be fabricated.Additionally, these sensors are produced with high accuracy at a relatively low cost per unit. For instance, a MEMS pressure sensor can be used to determine fluctuating pressures beneath a turbulent boundary layer with a spatial resolution that is about one order-of-magnitude finer than what can be achieved with conventional microphones. In this chapter, we have reviewed the state-of-the-art of microsensors used to measure the instantaneous velocity, wall-shear stress, and pressure, which are quantities of primary importance in turbulence diag- nosis. For each group, we provided general background, design criteria, calibration procedure, and examples of measurements conducted with MEMS-based sensors and when possible compared the results to conven- tional measurements. Microsensors can be fabricated at low unit-cost and can be spaced close together in dense arrays. These traits are particularly useful for studies of coherent structures in wall-bounded tur- bulent flows. Reactive flow control is another application where microdevices may play a crucial future role. MEMS sensors and actuators provide opportunities for targeting the small-scale coherent structures in macroscopic turbulent shear flows. Detecting and modulating these structures may be essential for a successful con- trol of wall-bounded turbulent flows to achieve drag reduction, separation delay, and lift enhancement. To cover areas of significant spatial extension, many devices are needed requiring small-scale, low-cost, 6-68 MEMS: Applications © 2006 by Taylor & Francis Group, LLC and low-energy-use components. In this context, the miniaturization, low-cost fabrication, and low-energy consumption of microsensors and microactuators are of utmost interest and promise a quantum leap in control system performance. Combined with modern computer technologies, MEMS yield the essential matching of the length- and time-scales of the phenomena to be controlled. Numerous actuators have been developed during the past few years. This chapter reviewed the state- of-the-art of microactuators based on the bi-layer effect, electrostatic or electromagnetic forces, mechanical folding, and one-layer structures. We have also briefly described recently advanced ideas for viscous micro- pumps and microturbines. Future challenges include achieving significant actuation perpendicular to the plane of what is basically a two-dimensional chip, further reducing unit cost and energy expenditure of microactuators, and designing microdevices that are capable of withstanding the harsh field environment of, for example, an aircraft. These are not easy tasks, but the payoff if air, water, or land-vehicle drag for example, could be reduced by a mere few percentage points, would translate into fuel savings in the bil- lions of dollars as well as tremendous benefits to the environment. Microelectromechanical systems have witnessed phenomenal advances in a mere ten-year period. The 1960s and 1970s were arguably the decades of the transistor and it is likely that the first few years of the third millennium will be the MEMS decades. Medical and industrial breakthroughs are inevitable with every advance in MEMS technology, and the future worldwide market for micromachines is bound to be in the tens of billions of dollars. Acknowledgments The authors would like to acknowledge the valuable help of Dr. Andrey Bakchinov and Mr. Peter Johansson for preparing the figures. Our thanks are extended to Professors Haim Bau, Ali Beskok, Kenneth Breuer, Chih-Ming Ho, Stuart Jacobson, and George Karniadakis, who all shared with us several of their reports and papers. Our sincere appreciation to Professor Mihir Sen for sharing his ideas regarding shear-sensor calibration and microturbomachines. References Akiyama, T., Collard, D., and Fujita, H. (1997) “Scratch Drive Actuator with Mechanical Links for Self- Assembly of Three-Dimensional MEMS,” J. MEMS, 6, pp. 10–17. Aronson, D., and Löfdahl, L. (1994) “The Plane Wake of a Cylinder: An Estimate of the Pressure Strain Rate Tensor,” Phys. Fluids, 6, pp. 2716–2721. 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IEEE MEMS ’92, pp. 12–18, 4–7 February, Travemunde, Germany. Ebefors, T., Kälvesten, E., and Stemme, G. (1997a) “Dynamic Actuation of Polyimide V-Grooves Joints by Electrical Heating,” in Eurosensors XI, September 21–24, Warsaw, Poland. Ebefors, T., Kälvesten, E., and Stemme, G. (1998) “New Small Radius Joints Based on Thermal Shrinkage of Polyimide in V-Grooves for Robust Self-Assembly 3-D Microstructures,” J. Micromech. Microeng., 8, pp. 188–194. Ebefors, T., Kälvesten, E., Vieider, C., and Stemme, G. (1997b) “New Robust Small Radius Joints Based on Thermal Shrinkage of Polyimide in V-grooves,” in Transducers ’97, June 16–19, Chicago. 6-70 MEMS: Applications © 2006 by Taylor & Francis Group, LLC 46–47 [...]... microconveyance systems (Figure 7.2b) [Kim et al., 19 90 ; Pister et al., 19 90 ; Ataka et al., 19 93 a; 19 93 b; Konishi and Fujita, 19 93 ; 19 94 ; Goosen and Wolffenbuttel, 19 95 ; Liu et al., 19 95 ; Böhringer et al., 19 96 ; 19 97 ; Nakazawa et al., 19 97 ; Suh et al., 19 97 ; 19 99 ; Hirata et al., 19 98 ; Kladitis et al., 19 99 ; Nakazawa et al., 19 99 ; Ruffieux and Rooij, 19 99 ; Smela et al., 19 99 ]: see Table 7.3 for more details Robots... Electron Devices, 35, pp 750–757 Sen, M., Wajerski, D., and Gad- el- Hak, M ( 19 96 ) “A Novel Pump for MEMS Applications, ” J Fluids Eng., 11 8, pp 624–627 Sessler, G ( 19 91 ) “Acoustic Sensors,” Sensors Actuators A, 25–27, pp 323–330 Sharatchandra, M.C., Sen, M., and Gad- el- Hak, M ( 19 97 ) “Navier–Stokes Simulations of a Novel Viscous Pump,” J Fluids Eng., 11 9, pp 372–382 Sharatchandra, M.C., Sen, M., and Gad- el- Hak, ... and Gad- el- Hak, M ( 19 98 a) “Thermal Aspects of a Novel Micropumping Device,” J Heat Transfer, 12 0, pp 99 10 7 Sharatchandra, M.C., Sen, M., and Gad- el- Hak, M ( 19 98 b) “A New Approach to Constrained Shape Optimization Using Genetic Algorithms,” AIAA J., 36, pp 51 61 Sherman, F.S ( 19 90 ) Viscous Flow, McGraw-Hill, New York Smela, E., Inganäs, O., and Lundström, I ( 19 95 ) “Controlled Folding of Micrometer-Size... developed so far could be categorized as moveable links: microcatheters [Haga et al., 19 98 ; Park and Esashi, 19 99 ], according to Figure 7.2a; microgrippers [Kim et al., 19 92 ; Keller and Howe, 19 95 ; 19 97 ; Greitmann, 19 96 ; Keller, 19 98 a; 19 98 b; Ok et al., 19 99 ] as those in Figure 7.2d; or the microgrippers [Jager, 2000a, 2000b] shown in Figure 7.2e Among the research publications covering locomotive microrobots,... and Fujita, H ( 19 92 ) “Surface-Normal Electrostatic/ Pneumatic Actuator,” in Proc IEEE MEMS 92 , pp 12 8 13 1, 4–7 February, Travemunde, Germany Gad- el- Hak, M ( 19 94 ) “Interactive Control of Turbulent Boundary Layers: A Futuristic Overview,” AIAA J., 32, pp 17 53 17 65 Gad- el- Hak, M ( 19 98 ) “Frontiers of Flow Control,” in Flow Control: Fundamentals and Practices, M Gad- el- Hak, A Pollard, and J.-P Bonnet, eds.,... assembly (“pick-andplace”) can be the only assembly approach that allows integration of electrical and mechanical components Such micro pick-and-place systems can be achieved by microrobotic devices in the form of microtweezers and microgrippers [Kim et al., 19 92 ; Keller and Howe, 19 95 ; 19 97 ; Greitmann, 19 96 ; Keller, 19 98 a; 19 98 b; Ok et al., 19 99 ] and will be further described in Section 7.5 .1 To extend... Research and Development Center, DTNSRDC Tech Rep No 12 60, Bethesda, Maryland Hinze, J.O ( 19 75) Turbulence, 2nd ed., McGraw-Hill, New York Ho, C. -M., and Tai, Y.-C ( 19 96 ) “Review: MEMS and its Applications for Flow Control,” J Fluids Eng., 11 8, pp 437–447 Ho, C. -M., and Tai, Y.-C ( 19 98 ) “Micro-Electro-Mechanical Systems (MEMS) and Fluid Flows,” Annu Rev Fluid Mech., 30, pp 5 79 612 Ho, C. -M., Tung, S.,... 90 ϫ 10 3 2.5% efficiency [Bexell and Johansson, 19 99 ; Johansson, 2000] Linear magnetic 0.4 ϫ 0.4 ϫ 0.5 10 00 2 .9 ϫ 10 Ϫ6 10 Ϫ4 3000 NA [Liu et al., 19 94 ] Scratch drive actuator (SDA) 0.07 ϫ 0.05 ϫ 0.5 50 6 ϫ 10 Ϫ5 16 0 ϫ 10 9 300 NA [Akiyama and Fujita, 19 95 ] Rotational magnetic 2 ϫ 3.7 ϫ 0.5 15 0* 10 Ϫ6** 3 ϫ 10 3 0.002% efficiency [Teshigahara et al., 19 95 ] Rotational magnetic 10 ϫ 2.5 ϫ ?? 20* 350 ϫ 10 Ϫ**... Physics, vol 53, pp 10 9 15 3, Springer-Verlag, Berlin © 2006 by Taylor & Francis Group, LLC 6-7 2 MEMS: Applications Gad- el- Hak, M (2000) “Flow Control: Passive, Active, and Reactive Flow Management,” Cambridge University Press, London, United Kingdom Gad- el- Hak, M., and Bandyopadhyay, P.R ( 19 94 ) “Reynolds Number Effect in Wall Bounded Flows,” Appl Mech Rev., 47, pp 307–365 Gad- el- Hak, M., and Tsai, H .M.. . microrobotic applications TABLE 7.2 Comparison of a Selection of Microactuators for Microrobotic Applications Actuator Type Volume (10 9 m3) Speed (s 1 or rad/s*) Force (N) 10 Ϫ7 Stroke (m) Torque (Nm)** 6 ϫ 10 Ϫ6 Power Density (W/m3) Power Consumption (W) Ref 200 NA [Kim et al., 19 92 ] 2 ϫ 10 Ϫ7** 90 0 NA [Nakamura et al., 19 95 ] 30* 2 ϫ 10 11 ** 0.7 NA [Udayakumar et al., 19 91 ] π/4 ϫ 4.52 ϫ 4.5 1. 1* 3.75 ϫ 10 Ϫ3** 90 . M. C., Sen, M. , and Gad- el- Hak, M. ( 19 97) “Navier–Stokes Simulations of a Novel Viscous Pump,” J. Fluids Eng., 11 9, pp. 372–382. Sharatchandra, M. C., Sen, M. , and Gad- el- Hak, M. ( 19 98a) “Thermal. 12 8 13 1, 4–7 February, Travemunde, Germany. Gad- el- Hak, M. ( 19 94) “Interactive Control of Turbulent Boundary Layers: A Futuristic Overview,” AIAA J., 32, pp. 17 53 17 65. Gad- el- Hak, M. ( 19 98). pp. 15 9 16 8. Ried, R., Kim, E., Hong, D., and Muller, R. ( 19 93) “Pizoelectric Microphone with On-Chip CMOS Circuits,” J. MEMS, 2, pp. 11 1 12 0. Riethmuller, W., and Benecke, W. ( 19 88) “Thermally