Arrays Of Microactuators Research Articles

Self-Assembled Microactuators Using Chiral Liquid Crystal Elastomers.

Materials that undergo reversible changes in form typically require top-down processing to program the microstructure of the material. As a result, it is difficult to program microscale, 3D shape-morphing materials that undergo non-uniaxial deformations. Here, a simple bottom-up fabrication approach to prepare bending microactuators is described. Spontaneous self-assembly of liquid crystal (LC) monomers with controlled chirality within 3D micromold results in a change in molecular orientation across thickness of the microstructure. As a result, heating induces bending in these microactuators. The concentration of chiral dopant is varied to adjust the chirality of the monomer mixture. Liquid crystal elastomer (LCE) microactuators doped with 0.05 wt% of chiral dopant produce needle-shaped actuators that bend from flat to an angle of 27.2 ± 11.3° at 180 °C. Higher concentrations of chiral dopant lead to actuators with reduced bending, and lower concentrations of chiral dopant lead to actuators with poorly controlled bending. Asymmetric molecular alignment inside 3D structure is confirmed by sectioning actuators. Arrays of microactuators that all bend in the same direction can be fabricated if symmetry of geometry of the microstructure is broken. It is envisioned that the new platform to synthesize microstructures can further be applied in soft robotics and biomedical devices.

Evolution of clusters in large-scale dynamical networks

Recent tremendous progress in electronics, complexity theory and network science provides new opportunities for intellectual control of complex large-scale systems operating in turbulent environment via networks of interconnected miniature devices, serving as actuators, sensors and data processors. Actual dynamics of the resulting control systems are too sophisticated to be examined controlled by traditional methods, which primarily deal with ordinary differential equations. However, their complexity can be dramatically reduced by fast processes, organizing the elementary units of the system (called agents) into relatively small number of clusters. The clusters emerge and deteriorate in response to changes in the environment, and the processes of their formation and destruction are very short in time. During the periods of the clusters’ existence, the system’s dynamics is essentially low-dimensional due to synchronization between the agents in each cluster. An enormously complicated system is thus reduced to a finite-dimensional model with time-varying structure of the state vector. The low-dimensionality of the reduced model allows to control it by using classical methods, e.g. model-predictive or adaptive control. This philosophy of complex systems control is illustrated on an experimental setup, called the “airplane with feathers”. The wings of this airplane are equipped with arrays of microsensors, microcomputers, and microactuators (“feathers”). The feathers self-organize into clusters by using a multi-agent consensus protocol; the aim of this coordination is to reduce the perturbing forces, affecting the airplane in a turbulent flow.

A Low-Stress Microactuator Array With Integrated Thin-Film Resistors

In this letter, we present a novel approach for integrating an electrostatic microactuator with a spiral thin-film resistor on a coplanar silicon substrate. We demonstrate a technique for fabricating large arrays of silicon nitride microactuators using low-stress plasma-enhanced chemical vapor deposition films. The process for integrating thin-film resistors spiraled around these actuators using sputtered films of tantalum nitride (sheet resistivity up to 1.4 k $\Omega $ per square) is then presented. We discuss a key application of this technology in optically addressable adaptive optics micromirror arrays.

Mechanically Amplified Piezoelectric Microactuators for Laminar-Turbulent Transition Control on Airfoils

Drag reduction on airfoils using arrays of micro-actuators is one application of so-called Aero-MEMS. These microactuators interact with TS instabilities (Tollmien-Schlichting waves) inside a transitional boundary layer by superimposing artificially generated counterwaves in order to delay the transition process. These actuators need to exhibit a relatively large stroke at relatively high operational frequencies when operated at high Mach numbers. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is proposed. The mechanical lever is provided by a sliced nickel titanium membrane. In this work, the actuator is explained in detail and wind tunnel experiments are carried out to investigate the effect of this mechanically amplified piezoelectric microactuator on thin transitional boundary layers. The experiments have been carried out in the transonic wind tunnel facility of the Berlin University of Technology on an unswept test wing with an NACA 0004 leading edge. The effectiveness of the actuator for flow control applications is determined in an open-loop setup consisting of one actuator having a relevant spanwise extension and a microstructured hot film sensor array located downstream. The aerodynamic results at Mach 0.33 are presented and discussed. It is shown that the actuator influences TS wave specific frequencies between 2.5 kHz and 7.4 kHz. The actuator amplitude is large enough to influence a transitional boundary layer significantly without bypassing the natural transition process which makes this type of micromachined actuator a candidate for high speed TS-control.

Generation and registration of disturbances in a gas flow. 1. Formation of arrays of tubular microheaters and microsensors

A new method is proposed for creating “smart” surfaces for suppressing turbulence and retaining a laminar supersonic flow. Methods of formation of super-fast-response sensors and actuators for such surfaces are developed. Such sensors and actuators are structurally designed as microtubes made of SiO2/Si3N4/Au and InGaAs/GaAs/Au heterofilms and suspended above a substrate; the wall thickness of these tubes is in the nanometer range; the tubes are connected to electrical contacts. Models of distributed arrays of tubular microsensors and microactuators are fabricated in a single technological process, which involves the well-established planar technology and the technology of rolling of stressed heterofilms.

Precision bi-directional motion of a linear mechanical shuttle with an electrothermal microengine

This research is focused on the design and experimental characterization of an electrothermal microengine that is capable of precise bi-directional motion. The microengine is operated with arrays of microelectromechanical systems (MEMS) asymmetrical electrothermal microactuators that are synchronously activated. The fundamental MEMS polysilicon electrothermal microactuator uses resistive (Joule) heating to generate thermal expansion and movement. In a conventional planar asymmetrical electrothermal microactuator, the “hot” arm is positioned parallel to the “cold” arm, but since the “hot” arm is narrower than the “cold” arm, the electrical resistance of the “hot” arm is greater. When an electrical current passes through the electrothermal microactuator (through the series connected electrical resistance of the “hot” and “cold” arms), the “hot” arm is heated to a higher temperature than the “cold” arm. This temperature increase causes the “hot” arm to expand along its length, thus forcing the tip of the device to rotate about its mechanical flexure element. The practical integration of arrays of MEMS electrothermal microactuators to realize a monolithic microengine is presented. The microengine has been operated to control the position of a linear mechanical shuttle.

Electrokinetic Microactuator Arrays and System Architecture for Active Sublayer Control of Turbulent Boundary Layers

Results are presented from development of microactuator arrays that function on the electrokinetic principle to provide active control of streamwise sublayer vortical structures in turbulent boundary layers. The electrokinetic microactuatorarraysinducevolumedisplacementsinthesublayerbyelectrokineticpumpingunderan impulsively applied electric e eld. These microactuator arrays consist of individual microchannels formed in a substrate and e lled with a 1- πm-scale doped porous polymer matrix that provides the required ‡ ‡-potential when wetted by the corresponding electrolyte. A system architecture is presented for large dense arrays of such microactuators that provides for greatly reduced control processing requirements within individual unit-cells containing a relatively small number of sensors and actuators. The resulting microactuator arrays have characteristics that make them potentially suited for practical sublayer control on full-scale aeronautical and hydronautical vehicles. Essentially loss-less frequency response of the electrokinetic microactuators has been demonstrated to 10 kHz. Several such microelectrokinetic actuator (MEKA) arrays have been fabricated from a basic three-layer design. A MEKA-5 full-scale hydronautical array, composed of 25,600 individual electrokinetic microactuators with 350- πm centerto-center spacings, arranged in a 40 £40 pattern of unit-cells, each composed of a 4 £ £4 matrix of actuators, was successfully fabricated in a 7 £7 cm 2 tile in 250-πm-thick Mylar substrate material. Microelectromechanical system design and fabrication processes were used to produce a top layer for the MEKA-5 hydronautical-scale array. DC performance tests indicate that the MEKA-5 array achieves the required e ow rates for active sublayer control on hydronautical vehicles with applied voltages of no more than 15‐ 20 V.

Limited communication control

This work in limited communication control is directed towards bringing together classical control theory and communication theoretical issues that are of practical importance in the design of control systems. It is common to “decouple” the communication aspects from the underlying dynamics of a system, as this simplifies the analysis and generally works well for classical models. However, in situations where a single decision maker controls many subsystems over a communication channel of a finite capacity, the computation of control signals and their transmission to each system may take significant amounts of time. To address such cases, we consider a class of discrete-time models that jointly optimize over control and communication goals. Real-world examples where these models play a role include remotely controlled unmanned autonomous vehicles (UAVs), planetary rovers, arrays of microactuators and power control in mobile communication.

MEMS applications in turbulence and flow control

Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 μm, that combine electrical and mechanical components and that are fabricated using integrated circuit batch-processing techniques. Electrostatic, magnetic, pneumatic and thermal actuators, motors, valves, gears and tweezers of less than 100 μm size have been fabricated. These have been used as sensors for pressure, temperature, mass flow, velocity and sound, as actuators for linear and angular motions, and as simple components for complex systems such as micro-heat-engines and micro-heat-pumps. In this paper, we focus on the use of microelectromechanical systems for the diagnosis and control of turbulent shear flows. We survey the status and outlook of microsensors and microactuators as used for those particular applications, and compare the minute devices to their larger cousins. Microsensors can resolve all relevant scales even in high-Reynolds-number turbulent flows. Arrays of microsensors and microactuators make it feasible, for the first time, to achieve effective reactive control targeted toward specific small-scale coherent structures in turbulent wall-bounded flows.

Computational methods for design and control of MEMS micromanipulator arrays

As improvements in fabrication technology for microelectromechanical systems, or MEMS, increase the availability and diversity of these micromachines, engineers are defining a growing number of tasks to which they can be put. The idea of carrying out tasks using large coordinated groups of MEMS units motivates the development of automated, algorithmic methods for designing and controlling these groups of devices. We report on progress towards computational MEMS, taking on the challenge of design and control of massively parallel arrays of microactuators. Arrays of MEMS devices can move and position tiny parts, such as integrated circuit chips, in flexible and predictable ways by oscillatory or ciliary action. The theory of programmable force fields can model this action, leading to algorithms for various types of micromanipulation that require no sensing of where the part is. Experiments support the theory.