Microactuator Array Research Articles

Vibrotactile using micromachined electromagnetic actuators array

One motivating application of this technology is the development of a tactile display interface, where discrete mechanical actuators apply vibratory excitation at discrete locations on the skin. Specifically, this paper describes the development fabrication and characterization of a 4 x 4 micro-actuator array of vibrating pixels for fingertip tactile communication. The vibrting pixels are generated by using an electromagnetic microresonator. The fabrication sequence and the actuation performance of the array are also presented.

Manipulating objects by discrete excitable media coupled with contact-less actuator array: Open-loop case

Abstract A two-dimensional cellular automaton (CA) model of an excitable medium is coupled with an array of micro-actuators in the form of abstract air-jets. Each cell of the CA is linked to a unique air-jet. A cell state determines the orientation and intensity of the airflow generated by the air-jet corresponding to the cell. We explore the phenomenology of an open-loop configuration in which CA cells do not sense the presence of the object being moved. Excitation waves generated in the initial stimulation of the medium, travel on the lattice and cause waves of actuation in the air-jets, resulting in changing airflow patterns. Thus, the waves of actuation move and rotate the manipulated object. We study the manipulation of three convex shapes by excitable CA, and provide the classification of various types of object motion from straight to sinuous and oscillatory trajectories. The relation between the excitation dynamic and resulting trajectories of the object will be used in future designs of hardware prototypes of massive-parallel manipulators controlled by non-linear media.

Micro-mechanical switch array for meso-scale actuation

Traditional micro-electro mechanical systems (MEMS) actuators have limited stroke and force characteristics. This paper describes the development of a hybrid actuation solution, which utilizes a micro-machined actuator array to provide switching of the mechanical motion of a larger meso-scale piezo-electric actuator. One motivating application of this technology is the development of a tactile display, where discrete mechanical actuators apply vibratory excitation at discrete locations on the skin. Specifically, this paper describes the development, fabrication, and characterization of a 4 × 5 micro-actuator array of individual vibrating pixels for fingertip tactile communication. The individual pixels are turned on and off by pairs of microscopic thermal actuators, while the main vibration is generated by a vibrating piezo-electric plate. The fabrication sequence and actuation performance of the array are also presented.

Hybrid MOEMS tunable filter for interrogation of fiber Bragg grating sensors

Experimental evaluation and performance results of a tunable optical filter based on hybrid microoptoelectromechanical systems technology are described in this letter. The hybrid optical microsystem is built using an off-the-shelf 200-GHz dense wavelength-division-multiplexing interference filter and a rotary microelectromechanical systems platform, suspended and actuated by an array of thermal microactuators fabricated through a commercially available process (SOIMUMPs). Results show a tuning range of over 870 pm, which satisfies the demodulation requirements for fiber Bragg grating sensors.

Micromechanical Digital-to-Analog Converter for Out-of-Plane Motion

This paper describes a novel micromechanical digital-to-analog converter (MDAC) for out-of-plane motion using electrostatic parallel-plate actuators. The proposed mechanism converts an N-bit digital signal to a mechanical out-of-plane displacement that is proportional to the analog value represented by the N-bit binary word. The mechanism is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a movable platform, an array of parallel-plate microactuators each operating in an ON/OFF mode and a set of connection springs that connect the actuators to the platform. The spring constants of the connection springs are weighted so that the stiffness of successive springs is related by a factor of 2. A 4-bit mechanism has been fabricated using the Poly-MUMPS process, achieving a total stroke of 675 nm (full-scale output) and step size (LSB) of 45 nm in a highly repeatable and stable manner. The linearity error (LE) of the device is within /spl plusmn/0.28 LSB, and the differential linearity error (DLE) is within /spl plusmn/0.25 LSB. This mechanism can be configured for many promising applications, particularly in optical devices and systems such as tunable external cavity diode laser, tunable VCSELs, adaptive micromirror array and tunable wavelength filter.

Fiber Bragg Grating Demodulator Based on Hybrid Optical MEMS

This paper describes the design, experimental evaluation and performance results of a tunable optical filter based on hybrid microoptoelectromechanical systems (MOEMS) technology. The tunable filter can meet the demodulation requirements for Fiber Bragg grating (FBG) sensors. The hybrid system is built using an off-the-shelf 200-GHz dense wavelength-division multiplexing filter and a movable MEMS platform actuated by a thermal microactuator array fabricated with silicon-on-insulator multiuser MEMS processes. Results show a repeatable tuning range of over 400 pm, which satisfies the demodulation requirements for FBG sensors.

Micromechanical torsional digital-to-analog converter for open-loop angular positioning applications

This paper reports a novel micromechanical torsional digital-to-analog converter (MTDAC), operated in open-loop with digitally controlled precise multi-level tilt angles. The MTDAC mechanism presented is analogous to that of an electrical binary-weighted-input digital-to-analog converter (DAC). It consists of a rigid tunable platform, an array of torsional microactuators, each operating in a two-state (on/off) mode, and a set of connection beams with binary-weighted torsional stiffnesses that connect the actuators to the platform. The feasibility of the proposed MTDAC mechanism was verified numerically by finite element simulations and experimentally with a commercial optical phase-shifting interferometric system. A prototype 2-bit MTDAC was implemented using the poly-MUMPS process achieving a full-scale output tilt angle of 1.92° with a rotation step of 0.64°. This mechanism can be configured for many promising applications, particularly in beam steering-based OXC switches.

Characterisation of a nanostepper driven optical shutter for application in free-space microoptics

A vertically self-assembled, fibre optic variable optical attenuator (VOA) incorporating a microshutter placed between the end faces of two closely spaced optical fibres is reported. The position of the microshutter with respect to the optical fibre end face was controlled by a nanostepping MEMS motor that was composed of a microactuator array and microsprings. Optical and mechanical tests were performed on the device. It was found that it is possible to obtain a 45 dB dynamic range with an attenuation time of 36 ms. A model of the microshutter was constructed as a plane plate structure with evenly distributed etch holes that are artefacts of the manufacturing process. Geometric and diffraction image analyses were performed and the attenuation characteristic of the system was assessed. It is thus shown that using commercially accessible foundries it is possible to fabricate a high precision VOA for free-space microoptics applications.

Electroactive Polymer Deformable Micromirrors (EAPDM) for Biomedical Optics

AbstractElectroactive polymers (EAPs) are capable of converting energy in the form of electric charge and voltage to mechanical force and movement and vice versa. Several electroactive polymer actuator materials whose responses are controlled by external electric fields, e.g. poly(vinylidene fluoride-trifluoroethylene) based fluoroterpolymers, have generated considerable interest for use in applications such as artificial muscles, sensors, parasitic energy capture, integrated bio-microelectromechanical systems (BioMEMS) and microfluidic devices due to their high electric-field induced strain, high elastic modulus, high electromechanical coupling and high frequency operation, etc. Scaling the EAP down into microsystems is one of the promising trends of EAP actuators and sensors especially for biomedical engineering. The combination of micro-optics and integrated BioMEMS, referred to as bio-micro-opto-electromechanical systems (BioMOEMS), makes a new opportunity for innovation in the EAP field. We present an approach to the fabrication of low-cost, large-stroke deformable micromirrors based on high performance electroactive polymer film microactuator arrays. Integrated Optic-BioMEMS based on electroactive polymer deformable micromirror (EAPDM) technology provide potential applications in biomedical optics such as ophthalmology (retinal imaging and vision care) and cancer detection and treatment.

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.

Generalized MEMS lot monitoring using fully-integrated material and structure mechanical analysis

Industrialization of MEMS devices requires specific tools to verify that their mechanical properties and motions obey the designer’s intent. Accordingly, the following work investigates new on-chip mechanical laboratories that will allow systematic MEMS manufacturing lot monitoring. The first part of the paper investigates mechanical properties of micrometer thick polysilicon films deposited by low pressure chemical vapor deposition (LPCVD). A new standard method allowing direct and immediate measurement of polycrystalline silicon mechanical properties is introduced. Micrometer size polysilicon samples are actuated on the wafer level using electrostatic probing of high driving force electrostatic actuation cells that are monolithically connected to the head of the specimens. Polysilicon fracture strength ranging from 1800 up to 2000 MPa is preliminary observed using parallel actuation of distributed bending test units. Very first micrometer size self-actuated tensile test units are introduced afterwards using arrays of 50μm×50 μm electrostatic actuation cells that recently pointed driving forces as high as 1260 μN (e.g. 400,000 μN/mm2). Experiments show that high-efficiency microactuator arrays, such as proposed in this paper, allow crack propagation to be initiated for a first time within tensile polysilicon specimens having a cross-section 1000 times smaller than that of a hair (e.g. 3 μm2). Self-actuated tensile fracture of the order of 1800 MPa is reported using 0.075 mm2 tensile units, leading to ideal testing configurations down to the micrometer scale, without human handling. The second part of the paper similarly investigates fully-integrated test units dedicated to the mechanical characterization of Φ 500 μm MEMS-based microactuators. Very first acquisition of torque/speed characteristics showing a locking torque on the order of 1.2 μN m with a maximal output mechanical power of 130 nW is also discussed as an illustration of the proposed monitoring methodology.

Active material micro-actuator arrays fabricated with SU-8 resin

Active materials such as piezoelectric ceramics and shape memory metal alloys commonly actuate active control and intelligent material systems. Commercially available piezoelectric materials exhibit small actuation stroke and shape memory metal alloys have limited bandwidth. The proposed micro-actuator array design and fabrication process increases the actuation stroke of piezoceramic material by a factor of 1.5 for a 2 × 2 array; two active material segments connected in parallel and two in series, and doubles the response time of a 1 × 4 shape memory alloy driven array; four active materials segments connected in series. A high aspect ratio fabrication method incorporating SU-8 resin and conventional lithography is the process that forms the array linkages. The SU-8 resin array structures are 300 μm tall.

Preparation of Ferroelectric Thick Film Actuator on Silicon Substrate by Screen-Printing

Piezoelectric actuators were prepared on Si substrates that have membranes fabricated by the wet-etching process. Ferroelectric Pb[Zr0.2 Ti0.3(Mg1/3 Nb2/3)0.3(Zn1/3 Nb2/3)0.1(Mg1/2W1/2)0.1]O3 thick films with a thickness of 25 µm, and Pt bottom electrodes and Ag top electrodes were all prepared by screen printing methods. The actuation properties were investigated for an actuator with the dimensions of 3×10 mm2. The influence of membrane's thickness was examined. The displacement of the center of the actuator with a 100-µm-thick membrane was 0.3 µm at an applied voltage of 25 V. An array of micro actuators with the dimensions of 0.15×5 mm2 were also successfully prepared by screen-printing.

Pattern-forming systems for control of large arrays of actuators

We consider an approach for coordinating the activity of a large array of microactuators via diffusive (i.e., nearest-neighbor) coupling combined with reactive growth and decay, implemented via interconnection templates which have been artificially engineered into the system (for example, in collocated microelectronic circuitry, or through the formulation of active material layers). Such coupled systems can support interesting spatiotemporal patterns, which in turn determine the actuation patterns. Generating such spatiotemporal patterns typically involves stressing the interconnections by raising or lowering a parameter resulting in the crossing of stability thresholds. The possibility of making such parametric adjustments via feedback on a slower timescale offers a solution to the problem of communicating effectively within a large array: The communication is achieved through the interconnection template. The mathematics behind this idea leads us into the rich domain of nonlinear partial differential equations (PDEs) with spatiotemporal pattern solutions. We present a global nonlinear stability analysis that applies to certain model pattern-forming systems. The nonlinear stability analysis could serve as a starting point for control system design for systems containing large microactuator arrays.

Coupled Vibration of Microcantilever Array Induced by Airflow Force

The coupled vibrations of microcantilevers induced by airflow were analyzed to facilitate the development of high-speed information and sensing devices that use microactuator arrays. Simple formulas, from which the vibrational coupling amplitude and damping ratio can be obtained, are derived by replacing the cantilevers with strings of spheres, solving Stokes equation, and combining this with an ordinary beam equation. The coupling amplitude was found to increase as the beam size, beam gap, internal friction, and the difference in the resonant frequencies of the beams decreased and the damping ratio increased as the beam size was reduced. The validity of the theory is verified with actual-size and enlarged model experiments.

Robust Vortex Control of a Delta Wing by Distributed Microelectromechanical-Systems Actuators

Micromachined actuators have been used successfully to control leading-edge vortices of a delta wing by manipulating the thin boundary layer before flow separation. In an earlier work, we demonstrated that small disturbances generated by these microactuators could alter large-scale vortex structures and consequently generate appreciable aerodynamic moments along all three axes for flight control. In the current study, we explored the possibility of independently controlling these moments. Instead of using a linearly distributed array of microactuators covering the entire leading edge as done in the previous study, we applied a shorter array of actuators located on either the forward or the rear half-section of the leading edge. Both one- and two-sided control configurations have also been investigated. Data showed that the pitching moment could be generated independently by appropriate actuation of the microactuators. To understand the interaction between the microactuators and leading-edge vortices, we conducted surface pressure distribution, direct force measurements, and flow visualization experiments. We investigated the effects of microactuators on the vortex structure, especially vortex core location

Design of a Microactuator Array Against the Coupled Nature of Microelectromechanical Systems (MEMS) Processes

Piezoelectric micromirror array is developed based on microelectromechanical systems (MEMS) technology. The inherent coupled nature of the thin-film processes generates many problems unless the design of the microactuator is properly uncoupled or decoupled among the functional domain, the physical domain and the process domain. The design of the first generation microactuator array was highly coupled between the functional domain and the physical domain, and could not be implemented successfully over 24 months of fabrication effort. Once the design has been uncoupled, successful arrays could be fabricated within 6 months and could be upgraded easily. The brightest projection display system has been developed with the microactuator arrays.

Ciliary microactuator array for scanning electron microscope positioning stage

The performance of a ciliary microactuator array as a positioning stage inside a scanning electron microscope is described. Such arrays are attractive because they can provide micron scale positioning resolution with direct electronic control within the sample chamber. The present array uses thermal actuation of a polyimide bimorph to produce long-travel deflection of each cilium and electrostatic actuation to provide a low-power hold-down mode. Each cell in the array consists of four orthogonally oriented cilia which, with proper drive signals, can produce object motion along any direction within the plane of the array. Adapting this array for use inside a scanning electron microscope (SEM) requires only a small mounting block and a modest multiconductor feedthrough. Improved thermal isolation within the vacuum chamber of the SEM drastically reduces the electrical input power requirements over those in air, while still allowing full positioning resolution. The addition of a gold ground plane coating to the array eliminates charging problems by the electron beam and reduces electrical interference from the drive signals.

Organic thermal and electrostatic ciliary microactuator array for object manipulation

An organic thin-film ciliary microactuator array using independent thermal and electrostatic actuation is described. A polyimide thermal bimorph structure provides for large angle deflection with high load capacity. Electrostatic electrodes provide low-power hold-down, capacitive sensing, and feedback control capabilities. Integrating four orthogonally oriented actuators into a unit cell and replicating this cell into an array allows for precise movement of small objects in arbitrary directions. The ciliary microactuator array has immediate applications for positioning, alignment, inspection, and assembly of small parts, such as IC dice, with micron-scale resolution.

System design for cooperative control of a microactuator array

A system design is presented with the aim of controlling many microactuators as autonomous distributed micromachines (ADMs). ADMs consist of many microcells which are smart enough to control their own motions and to cooperate with each other. A conveyance system in a plane is selected as an example of ADMs. We have developed a practical design of ADMs composed of many microcells integrated with actuators, sensors, and circuits which can be fabricated by IC-compatible micromachining. The behavior of the system is examined by simulation on a computer model. A fluidic microactuator array for a conveyor has also been fabricated and operated successfully. >