Array Of Actuators Research Articles

Designing a tuned-shunt electrodynamic metamaterial in the presence of uncertainties

Resonant structural vibrations are a common source of disruptive noise, and suppressing these vibrations is often the most direct way to reduce the noise levels. Elastic metamaterials (EMMs) consist of distributed resonant substructures, at a scale which is small compared to the wavelength of vibration. This allows these materials to be used in applications where space is limited, and more traditional vibration suppression techniques would be impractical. Tuned resonators can be designed through selection of geometry or material properties, but an alternative approach, which requires significantly less prototyping, is through the use of shunted electrodynamic inertial actuators. In this paper, a novel electrodynamic metamaterial (EDMM) is proposed consisting of an array of mass-produced inertial actuators, each connected to a tuned shunt impedance. It is considered impractical to measure the dynamic and electrical parameters of a large number of actuators, and so the effect of uncertainties in the actuators is investigated on both the performance and the stability of the EDMM.

Flow Characteristics of Dielectric Barrier Discharge Plasma Actuator Array in Burst Mode

To understand the fundamental physics of dielectric barrier discharge (DBD) actuator array for flow control, the flowfield induced by two successive DBD actuators is investigated under burst-mode actuation. The vortical structures generated by the actuators are revealed using particle image velocimetry (PIV) and high-speed schlieren visualization, allowing their interactions to be explored. Proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) are used to analyze the plasma-induced flow. Both POD and DMD modes indicate staggered vortical structures, whose dynamic features are associated with the burst frequency of the DBD actuation and its harmonics. The POD–DMD coherence indicates that the most relevant dynamic structure is also the most energetic. Spatial DMD analysis reveals an increase in the convection speeds of the flow structures from the upstream DBD actuator to the downstream DBD actuator. The effects of duty cycle and burst frequency on the coherent structures are explored. For different duty cycle cases, the most energetic mode structures evolve in a similar fashion. As the burst frequency increases, the size of the coherent structures decreases, but their number increases. Both POD and DMD analyses reveal that the burst frequency has a greater effect on the coherent structures than the duty cycle.

Digital Electrochemistry: Digital Electrochemistry for On‐Chip Heterogeneous Material Integration (Adv. Mater. 26/2021)

In article number 2101272, Bin Bao, Daniil Karnaushenko, Oliver G. Schmidt, and co-workers develop a digital electrochemistry approach for on-chip heterogeneous material integration. An amorphous indium-gallium-zinc oxide thin-film-transistor (a-IGZO TFT) active-matrix is used to address pixels within the matrix and locally control electrochemical reactions for material growth and actuation. Multicolored electrochromic patterns and actuator arrays can be fabricated. The approach can be extended to a broad range of materials and structures, opening up a new path for advanced heterogeneous microsystem integration.

Fabrication and applications of stimuli‐responsive micro/nanopillar arrays

AbstractThe functional surface features of living creatures are driven by the complex morphology of periodically arranged micro/nanoscale structures. Various fabrication processes have been devised mimic the performance of natural features; these methods morph hierarchical and multi‐leveled pillar arrays, such as top‐down, bottom‐up, and a hybrid of top‐down and bottom‐up processes. Different methodologies are employed depending on the materials, such as polymeric composites, metal oxides, metals, and carbon nanotubes. In this review, we discuss the shape‐reconfiguration of stimuli‐responsive micro/nanopillar arrays achieved by capillary force, light, magnetic field, and heat. In particular, photo‐ and magnetic actuation of pillar arrays revealed programmability according to the arrangement of the liquid crystal molecules or magnetic particles by remote control. Furthermore, applications of micro/nanopillar arrays, such as adhesives, omniphobicity, optics, and biomedical technologies, are also discussed.

Experimental investigation on compression ramp shock wave/boundary layer interaction control using plasma actuator array

Particle image velocimetry measurement on shock wave/boundary layer interaction in a Mach 2.0 supersonic wind tunnel is performed to quantitatively reveal the plasma flow control effect in this paper. The typical flow structure is produced by a 24-degree compression ramp model and the streamwise plasma actuator array with five pulsed spark discharge plasma actuators is adopted as the control device. In the midspan plane, the results show that although the separation region exhibits an obvious extension, the foot of the separation wave moves upstream and the shock wave angle decreases from 41.6° to 22.3°, proving the decline in shock intensity. The shock wave drag is estimated to be reduced by 45%. According to the phase-averaged velocity field, the reason that the high-frequency actuation plays a key role in achieving the continuous control effect is revealed through the temporal evolution of the separation region area. Also, another interesting phenomenon that the flow deflects when passing through the actuation region is found, which may induce the upwash and downwash motions of the boundary layer and further reduce the flow separation on both sides of the actuation region. At last, a preliminary conceptual model is proposed to reveal the probable flow control mechanism.

Digital Electrochemistry for On-Chip Heterogeneous Material Integration.

Many modern electronic applications rely on functional units arranged in an active-matrix integrated on a single chip. The active-matrix allows numerous identical device pixels to be addressed within a single system. However, next-generation electronics requires heterogeneous integration of dissimilar devices, where sensors, actuators, and display pixels sense and interact with the local environment. Heterogeneous material integration allows the reduction of size, increase of functionality, and enhancement of performance; however, it is challenging since front-end fabrication technologies in microelectronics put extremely high demands on materials, fabrication protocols, and processing environments. To overcome the obstacle in heterogeneous material integration, digital electrochemistry is explored here, which site-selectively carries out electrochemical processes to deposit and address electroactive materials within the pixel array. More specifically, an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film-transistor (TFT) active-matrix is used to address pixels within the matrix and locally control electrochemical reactions for material growth and actuation. The digital electrochemistry procedure is studied in-depth by using polypyrrole (PPy) as a model material. Active-matrix-driven multicolored electrochromic patterns and actuator arrays are fabricated to demonstrate the capabilities of this approach for material integration. The approach can be extended to a broad range of materials and structures, opening up a new path for advanced heterogeneous microsystem integration.

Mechanisms of SWBLI control by using a surface arc plasma actuator array

Mechanisms for controlling the shock wave boundary layer interaction (SWBLI) by a plasma actuator array are investigated by two experiments. Low-frequency and high-frequency actuation modes are compared. The experimental results yield valuable insights into the control mechanism of SWBLI using a surface arc plasma actuator array. The schlieren snapshots and the mean and root mean square error of the image sequence and pressure measurements are analyzed to determine the control mechanisms. The high-frame schlieren images for flow visualization indicate a significant modification of the separation shock in both experiments due to thermal injection. More importantly, because the high-frequency actuation mode operates at relatively low energy, it can provide quasi-continuous perturbations, providing stable control for separation shock weakening. The Iband/Itotal ratio for low-frequency unsteadiness obtained from the pressure spectrum is reduced below 5% at 10 kHz forcing. The integrated schlieren intensity IRMS and power spectrum indicate a dominant vortex forcing effect as an additional actuation mechanism in addition to the gas heating effect that may affect the separation shock and its interaction with the boundary layer. As the plasma actuation is activated, numerous periodic streamwise vortices and small-scale trailing vortices are produced in the high-frequency actuation mode, resulting in an enhancement of the mixture upstream of the interaction region and promoting the momentum transfer to the boundary layer. In addition, the large-scale turbulence structures characterized by low-frequency unsteadiness are subject to artificial vortex shedding by the plasma perturbation, further increasing the momentum transfer in the boundary layer. We propose a conceptual model describing the vortical activity due to actuation and the interaction between plasma actuation and the SWBLI flow. Thus, a hybrid mechanism of SWBLI control associated with vortical activity exists.

Input-output framework for actuated boundary layers

This work extends the input-output approach to the study of wall-bounded shear flows manipulated using actuators common in experimental flow control studies. In particular, we adapt this powerful analytical framework to investigate the flow response to specified geometric actuation patterns (e.g., different plasma actuators) that can be applied over a range of different temporal input signals. For example, the commonly studied steady-state (time-averaged) flow response corresponds to a superposition of step responses in our modeling framework. The approach takes advantage of the linearity of the transfer function representation to construct the actuated flow field as a weighted superposition of the flow responses to point sources of varying intensity comprising the actuation model. We first validate the proposed method through comparisons with numerical and experimental studies of the time-averaged behavior of a transitional boundary layer actuated using a dielectric-barrier discharge plasma actuator operating in constricted discharge mode. The method is shown to reproduce the streamwise velocity field and the vortical structures observed downstream from the tested plasma actuator configurations. We then demonstrate that the method provides even better agreement with the steady-state response of the boundary layer subject to actuation from arrays of symmetric plasma actuators arranged in both spanwise and serpentine geometries. These results indicate the utility of this extension to the widely used input-output framework in analyzing the effects of certain actuation modalities that have shown promise in flow manipulation strategies for drag reduction. An important benefit of this analytical method is the low computational cost associated with its use in extensive parametric studies that would be cost-prohibitive using experiments or high-fidelity simulations.

Design, modeling, and constraint-compliant control of an autonomous morphing surface for omnidirectional object conveyance

AbstractIn this paper, we conceptualize, analyze, and assemble a prototype adaptive surface system capable of morphing its geometric configuration using an array of linear actuators to impose omnidirectional movement of objects that lie on the surface. The principal focus and contribution of this paper is the derivation of feedback control protocols–for regulating the actuators’ length in order to accomplish the object conveyance task–that scale with the number of actuators and the nonlinear kinematic constraints of the morphing surface. Simulations and experimental results demonstrate the advantages of distributed manipulation over static-shaped feeders.

A strip speaker using the traveling bending wave on a beam controlled by three actuators

The inherent weakness of conventional panel speakers is the inevitable multi-modal vibration behavior, resulting in severe fluctuation in the radiated sound spectrum, which is detrimental to the sound quality. A panel speaker that is actively controlled by array actuators at the panel edges has been proposed as a solution to the problem, but the increased cost and complexity due to a large number of actuators remain a challenge. In this study, a panel speaker using a thin beam, called a strip speaker, that adopts only three actuators is proposed to alleviate the modal fluctuation problem. When the middle position of the beam is excited by the primary actuator, the propagated bending wave field there from is controlled by two actuators at either end of the beam that prevents reflection of the wave. To achieve this, the inverse problem is derived by using the transfer function between the actuators and the coefficients of the reflected waves, from which an appropriate gain of the two control actuators is obtained as the inverse solution. For validation, a thin beam with a size of 315 × 40 × 2 mm3 is tested by simulation and experiment. Peaky resonant responses are made to disappear by controlling the vibration field, and the input mobility of the primary actuator becomes like that of an infinite beam. The boundary of the beam, which is newly defined at the location of the control actuators, is converted into an anechoic termination. The effect of the beam material is also tested by comparing aluminum and acrylic beams. It is shown that the damping of the acrylic beam is favorable in resulting a flat response, but its effective frequency range is lowered from that of the aluminum beam. In the experiment, the control actuators near the ends of unknown boundary conditions are located at the position to minimize the total input power for control. The experimental results of the controlled vibration field and radiated sound spectrum agree well with the predicted characteristics. It is shown that the proposed strip speaker with the traveling wave control method can be used to produce excellent acoustic performance.

Exploiting Pull-In/Pull-Out Hysteresis in Electrostatic MEMS Sensor Networks to Realize a Novel Sensing Continuous-Time Recurrent Neural Network

The goal of this paper is to provide a novel computing approach that can be used to reduce the power consumption, size, and cost of wearable electronics. To achieve this goal, the use of microelectromechanical systems (MEMS) sensors for simultaneous sensing and computing is introduced. Specifically, by enabling sensing and computing locally at the MEMS sensor node and utilizing the usually unwanted pull in/out hysteresis, we may eliminate the need for cloud computing and reduce the use of analog-to-digital converters, sampling circuits, and digital processors. As a proof of concept, we show that a simulation model of a network of three commercially available MEMS accelerometers can classify a train of square and triangular acceleration signals inherently using pull-in and release hysteresis. Furthermore, we develop and fabricate a network with finger arrays of parallel plate actuators to facilitate coupling between MEMS devices in the network using actuating assemblies and biasing assemblies, thus bypassing the previously reported coupling challenge in MEMS neural networks.

A Printable Thin Film‐Based Digital Peristaltic Sticker‐Pump for a Simple and Robust Integration into Microfluidics

AbstractA micropump is pivotal for routing and multiplexing fluids in microfluidic channels, especially for point‐of‐care diagnostic devices. In this regard, a simple and easily mountable micropump‐platform needs to be developed to expand the applications of microfluidic devices. Here, the sticker type‐peristaltic pump, called “sticker‐pump,” is developed by incorporating an array of biocompatible polymeric bimorph actuators. The sticker‐pump can be activated via digital input sequence to control the flow rate in response to the operating voltage and switching speed. Furthermore, the programmed digital sequence demonstrates the generation of pulsatile and continuous flows without any back pressure. The sticker‐pump is further studied through a systematic characterization to validate the working mechanism of one sticker‐pump (1‐bit) and the flow rates (3.77–36.90 µL min−1) attained by the combination of three sticker‐pumps (3‐bit) on microfluidics. Since the sticker‐pump is all solution‐processed, an inexpensive sticker‐pump can be manufactured by scalable printing technologies.

Compensation of Temperature Effects on Lamb Waves Using Mode Decomposition and a Nonlinear Model.

Active Lamb-wave-based structural health monitoring techniques have been widely studied to inspect large structures using permanently installed arrays of sensors and actuators. Most of these methods depend on comparing baseline signals recorded from the structure before going into service and test signals acquired during inspection. Temperature changes affect the propagation of the wave in a nonlinear and mode-dependent manner. As a result, baseline comparison methods fail when the test and baseline signals are acquired at vastly different temperatures. Approximate methods that compensate for the effects of temperature on the waves using signal stretch models have been introduced in the literature. These methods are effective when the temperature changes are small and the propagation distances are short. However, they perform poorly when these conditions are not satisfied. Consequently, there is a need for better temperature compensation algorithms than presently available. This article presents a data-driven approach that separately compensates for the effects of temperature on different mode components of the sensor signals. The performance of the temperature compensation algorithm of this article is compared with that of a commonly used baseline signal stretch (BSS) algorithm using experimental signals measured from an aluminum panel and a unidirectional composite panel. Analysis results indicate that the method of this article outperforms the BSS algorithm for large temperature differences. The usefulness of the temperature compensation algorithm is further validated by demonstrating the ability of compensated signals to accurately reconstruct anomaly maps associated with damaged composite structures.

Influence Function Measurement Technique Using the Direct and Indirect Piezoelectric Effect for Surface Shape Control in Adaptive Systems

Since the introduction of adaptive systems for corrective measures, static and dynamic disturbances have been reduced through the manipulation of surface shape in a well-controlled manner. One important application where adaptive systems are highly needed is in the future photo-lithography machines, particularly the wafer table where disturbances affect overlay and focus performance. To reduce overlay and focus errors, a dense array of actuators must be integrated into the wafer table to apply both in- and out-of-plane corrective deformations to the wafer surface. To realize a certain wafer shape, influence functions are linearly superimposed. Accurate models of the influence functions result in an accurate prediction of the final wafer shape. To reduce calibration errors, the influence function of every actuator needs to be determined. Here, we propose a technique to rapidly measure the influence function: the influence function measurement (IFM) technique. Using the actuate-sense property of piezoelectric materials, the influence function is determined by activating one piezo-actuator and measuring the charge induced on the neighboring piezo-actuators. The measured charges are compared to the results of finite element simulations and the absolute difference of 0.3 &#x0025; is reported for the inter-actuator charge coupling parameters. This clearly indicates the potential of the proposed technique. <i>Note to Practitioners</i>&#x2014;A critical step during the integrated-circuit lithographic fabrication process is the exposure. A particular practical challenge in this step is to correct for the mismatch between the optical image plane and the wafer surface, caused by wafer deformations. The mismatch negatively impacts the overlay and focus performance. To reduce the mismatch, actuators can be embedded into the wafer table to counteract wafer deformations, where the overall wafer surface shape is a superposition of each actuator&#x2019;s influence function. As part of the calibration for the embedded actuators, their influence functions are measured and stored. However, errors arise when influence functions are not measured for every actuator. Additionally, for different wafers, the influence functions vary hence the calibration should be done per wafer. This calibration process takes time and should not influence throughput. Our paper presents a viable approach that reduces the calibration time of active wafer tables, which is also relevant for other adaptive systems such as deformable mirrors. Since the technique requires the actuators to be mechanically coupled, it is limited to continuous surfaces. The proposed technique is numerically tested and experimentally verified to demonstrate performance.

Linear control of coherent structures in wall-bounded turbulence at [formula omitted

We consider linear feedback flow control of the largest scales in an incompressible turbulent channel flow at a friction Reynolds number of Reτ=2000. A linear model is formed by linearizing the Navier–Stokes equations about the turbulent mean and augmenting it with an eddy viscosity. Velocity perturbations are then generated by stochastically forcing the linear operator. The objective is to reduce the kinetic energy of these velocity perturbations at the largest scales using body forces. It is shown that a control set-up with a well-placed array of sensors and actuators performs comparably to either measuring the flow everywhere (while limiting actuators to a single wall height) or actuating the flow everywhere (while limiting sensors to a single wall height). In this way, we gain insight (at low computational cost) into how the very large scales of turbulence are most effectively estimated and controlled.

Compression ramp shock wave/boundary layer interaction control with high-frequency streamwise pulsed spark discharge array

A streamwise array of pulsed spark discharge operating at a high frequency of 10 kHz is used to control the shock wave/boundary layer interaction (SWBLI) induced by a 24° compression ramp (CR) in a Mach 2.0 flow. High-speed schlieren imaging at 50 000 frames/s is deployed for flow visualization. The schlieren snapshots, as well as statistics of the schlieren sequence, show that the intensity weakening effect on the shock wave can be achieved for a long time up to 20 ms, which is the first experimental demonstration of stable control on the CR-SWBLI with plasma actuators. Then, based on fast Fourier transform analyses, the low-frequency unsteadiness of the shock wave is also significantly modified and the dominant oscillation frequency is switched to the high frequency St = 0.32. The mechanism of the encouraging control outcome is finally discussed that the strong separation wave induced by a CR is replaced by a multistage weak compression wave produced through a high-frequency actuator array.

Experimental and Numerical Investigation of Active Flow Control of a Serpentine Diffuser

Total-pressure losses and distortion in an aggressive offset diffuser, induced by secondary-flow vortices and boundary-layer separation, are mitigated using fluidic actuation for the aerodynamic interface plane Mach number up to 0.57. Although total-pressure recovery is primarily impacted by separation in each of the diffuser’s turns, distortion is governed by counter-rotating streamwise vortices that advect low-momentum fluid from the wall region into the core flow. The present investigations have shown that secondary-flow vortices couple to the outboard segments of the separated-flow domains. Therefore, fluidic control of the scale and topology of the trapped vorticity within the internally separated flow can be leveraged to control the structure and strength of the ensuing secondary vortices, and thereby significantly reduce flow distortion and losses. In the present investigations, fluidic control is effected by a spanwise array of oscillating jets that are placed just upstream of the second-turn separation domain. Actuation directly affects the local flow separation, but it also alters the spacing and diminishes the strength of the base-flow streamwise vortices by forming and adjoining streamwise-vorticity concentrations of opposite sense. Additionally, the spanwise distribution of the actuator array was optimized to reduce circumferential distortion by 60% at actuation to a diffuser mass-flow-rate ratio lower than 0.5%.

Haptic Display Responsive to Touch Driven by Soft Actuator and Soft Sensor

Haptic display transfers the sense of touch by applying forces, vibrations, or motions to the user. This article presents a novel bidirectional haptic display responsive to touch. The device is composed of a flexible tactile sensor and tactile actuator, and the actuator is actuated according to the touch signals from the tactile sensor. The tactile sensor is a thin array of resistive type sensors that covers the top of the soft dielectric elastomer actuator array. The tactile sensor measures the normal forces (0 $-$ 6 $N$ ) and positions of touches and then sends these signals to control the corresponding tactile actuator cells. The tactile actuator works within the frequency range of 0 $-$ 300 Hz, provides up to 520 $\mu \text{m}$ of displacement and, 600 mN of normal force, much greater than the human hand threshold (50 mN). And thus, the device can transfer different feelings to users. In this research, we develop and evaluate a stand-alone bidirectional haptic display. Then, we took the psychophysical test and introduced the master—slave system whereby the master device controls the slave device depending on the master input.

An experimental study on different plasma actuator layouts for aircraft icing mitigation

An experimental study was conducted to examine the effects of dielectric-barrier-discharge plasma (DBD) actuator layout on the plasma-induced thermal characteristics and evaluate their effectiveness for aircraft icing mitigation. The experimental investigation was performed in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT) with an airfoil/wing model embedded with an array of DBD plasma actuators around the airfoil leading edge. The plasma actuators were arranged in different layouts (e.g., orientation, number, and width of exposed electrodes) to evaluate their effects on the anti-icing performance under a typical glaze icing condition pertinent to aircraft inflight icing phenomena. While the dynamics ice accretion or anti-icing process over the airfoil surface before and after turning on the plasma actuators was recorded by using a high-resolution imaging system, a high-speed infrared thermal imaging system was used to quantitatively map the temperature distributions over the airfoil surface. The experimental results clearly reveal that, with the same power consumption level, the plasma actuators in streamwise layout would result in higher plasma-induced surface heating and faster runback of the unfrozen water over the airfoil surface, thereby, having a noticeably better anti-icing performance, in comparison to those in spanwise layout. The plasma actuators in streamwise layout were found to not only be able to prevent ice accretion near the airfoil leading edge, but also allow the plasma-induced surface heating to convect further downstream to delay/prevent the runback ice formation near the airfoil trailing edge. A proper combination of the plasma actuation strength and the plasma discharge coverage over the airfoil surface was found to result in the optimum performance for aircraft anti-icing applications.

Linearizing Control of a Distributed Actuation Magnetic Bearing for Thin-Walled Rotor Systems

This paper describes an exact linearizing control approach for a distributed actuation magnetic bearing (DAMB) supporting a thin-walled rotor. The radial DAMB design incorporates a circular array of compact electromagnetic actuators with multi-coil winding scheme optimized for supporting thin-walled rotors. A distinguishing feature is that both the x and y components of the radial bearing force are coupled with all four of the supplied coil currents and so a closed form solution for the linearizing equations cannot be obtained. To overcome this issue, a gradient-based root-finding algorithm is proposed to solve the linearizing equations numerically in real-time. The proposed method can be applied with any chosen constraints on current values to achieve low RMS values while avoiding zero-current operating points. The approach is implemented and tested experimentally on a rotor system comprising two radial DAMBs and a uniform cylindrical shell rotor. The results show that the method achieves more accurate reproduction of demanded bearing forces, thereby simplifying the rotor suspension control design and providing improved stability and vibration control performance compared with implementations based on operating point linearization.