Electrostatic Actuation Research Articles

Port-Hamiltonian modeling and control of a curling HASEL actuator

This paper is concerned with the modeling and control of a curling Hydraulically Amplified Self-healing Electrostatic (HASEL) actuator using the port-Hamiltonian (PH) approach. For that purpose, we use a modular approach and consider the HASEL actuator as an interconnection of elementary subsystems. Each subsystem is modeled by an electrical component consisting of a capacitor in parallel with an inductor connected through the conservation of volume of the moving liquid to a mechanical structure based on inertia, linear, and torsional springs. The parameters are then identified, and the model is validated on the experimental setup. Position control is achieved by using Interconnection and Damping Assignment-Passivity Based Control (IDA-PBC) with integral action (IA) for disturbance rejection. Simulation results show the Efficiency of the proposed controller.

Microelectromechanical system for in situ quantitative testing of tension-compression asymmetry in nanostructures.

Tension-compression asymmetry is a topic of current interest in nanostructures, especially in strain engineering. Herein, we report a novel on-chip microelectromechanical system (MEMS) that can realize in situ quantitative mechanical testing of nanostructures under tension-compression functions. The mechanical properties of three kinds of nanostructures fabricated by focused ion beam (FIB) techniques were systematically investigated with the presented on-chip testing system. The results declare that both Pt nanopillars and C nanowires exhibit plastic deformation behavior under tension testing, with average Young's moduli of 70.06 GPa and 58.32 GPa, respectively. However, the mechanical deformation mechanisms of the two nanostructures changed in compression tests. The Pt nanopillar exhibited in-plane buckling behavior, while the C nanowire displayed 3D twisting behavior with a maximum strain of 25.47%, which is far greater than the tensile strain. Moreover, asymmetric behavior was also observed in the C nanospring during five loading-unloading tension-compression deformation tests. This work provides a novel insight into the asymmetric mechanical properties of nanostructures, with potential applications in nanotechnology research.

Rigid electrodes enhance the strain and force output of Peano-HASEL actuators

Peano-HASEL (hydraulic amplified self-healing electrostatic) actuators represent a recent advancement in the field of muscle-like soft actuators. They typically consist of flexible electrodes, a flexible and inextensible shell, and liquid dielectric. However, Peano-HASEL actuators employing flexible electrodes can only utilize the electrostatic force generated by a limited area of electrodes to maintain compression of the liquid, resulting in a restricted strain and force outputs. In this Letter, we show that a Peano-HASEL actuator employing rigid electrodes exhibits a significantly enhanced strain and force output. Compared to the conventional flexible-electrode Peano-HASEL actuator, the actuator with rigid electrodes demonstrates a remarkable improvement, with a more than 200% increase in strain output and a more than 140% increase in force output. Notably, we successfully showcase the capability of a Peano-HASEL actuator with rigid electrodes to reliably lift a 50 g load at an 8 kV voltage, a task that the counterpart with flexible electrodes of the same electrode length, width, and oil volume fails to accomplish. This highlights the great potential of rigid-electrode Peano-HASEL actuators for applications such as robotic manipulation.

Deep Learning for Nonlinear Characterization of Electrostatic Vibrating Beam MEMS

In this paper, we integrate deep learning techniques with the motion-induced current method to analyze the nonlinear response of electrostatic MEMS resonators consisting of vibrating beams under electrostatic actuation. The motion-induced current method relies on a transduction mechanism that converts the motion of the resonator to a current signal. The third harmonic of the induced current captures the motion characteristics of the MEMS resonator. We conduct electrical measurements on a MEMS device comprising a microcantilever beam subject to electrostatic actuation using a side electrode. The electrical measurements are verified against their optical counterparts to confirm the suitability of the motion-induced current method to analyze the motion of the MEMS resonator. Next, we develop a model by combining deep learning methods with experimental data aiming to detect the nonlinear dynamics associated with the motion of the resonator when subjected to large actuation voltages. The results demonstrate high prediction accuracy of the data-driven model in terms of capturing the peak resonance, the onset of bifurcation, the occurrence hysteresis and its bandwidth.

Linear electrostatic actuators with Moiré-effect optical proprioceptive sensing and electroadhesive braking

Muscles in animals and actuation systems in advanced robots consist not of the actuation component alone; the motive, dissipative, and proprioceptive components exist in a complete set to achieve versatile and precise manipulation tasks. We present such a system as a linear electrostatic actuator package incorporated with sensing and braking components. Our modular actuator design is composed of these actuator films and a dielectric fluid, and we examine the performance of the proposed system both theoretically and experimentally. In addition, we introduce a mechanism of optical proprioceptive sensing utilizing the Moiré pattern innately generated on the actuator surface, which allows high-resolution reading of the position of the actuator without noise. The optical sensor is also capable of measuring the force exerted by the actuator. Lastly, we add an electroadhesive brake in the package in parallel with the actuator, introducing a method of mode switching that utilizes all three components and presenting control demonstrations with a robot arm. Our actuation system is compact and flexible and can be easily integrated with various robotic applications.

Electrostatic actuators with constant force at low power loss using matched dielectrics

Electrostatic actuators with constant force at low power loss using matched dielectrics

Optimized self-excited electrostatic actuators with insulated-electrodes configuration for micro air vehicles

Optimized self-excited electrostatic actuators with insulated-electrodes configuration for micro air vehicles

Nonlinear vibrational analysis and linearization error investigation in size-dependent resonant pressure microsensors

Dynamic and vibrational behavior of nonlinear resonant pressure micro sensors is studied in this paper using a proposed dynamic model. The basic part of the device is a microplate deflects due to external pressure in presence of electrostatic actuation. The frequency changes because of the microplate deformation is used to estimate the external pressure. For modeling of the micro sensor, the nonlinear governing equation of size dependent microplate in polar coordinate system and based on the modified couple stress theory is presented. Assuming specified number of Taylor expansion terms for electrostatic force, the linear and nonlinear ODE is obtained and nonlinear equation is solved both with multiple time scales method (MTS) and finite difference numerical method. Results indicate that considering finite terms of Taylor expansion (1 term for linear and three terms for MTS method) is the source of error in estimation of pressure or system stability. Using sufficient terms of Taylor Expansion, the error in linear and MTS solutions is vanished. Therefore, the limited values of microplate vibrational amplitude is extracted to increase the accuracy of the sensor in linear action. The effect of size dependency, applied voltage on nonlinear behavior and linearization error is also studied.

Adaptive RBFNN‐based predictive control for the nanopositioning of an electrostatic MEMS actuator

AbstractElectrostatic micro electro mechanical system (MEMS) as an actuator is one of the most widely used actuators in micro dimension systems. Due to the high nonlinear characteristics in the micro actuator's model, nanopositioning has been a challenging problem for researchers. In addition, the system is subject to uncertainties associated with the system's unknown parameters and un‐modelled dynamics. Thus, to overcome these problems and achieve precise positioning a robust non‐linear control method is required. In this research, an optimal voltage control algorithm is initially designed utilizing the nonlinear predictive control approach. The Taylor expansion sequence is used to estimate the final position of the parallel plate actuator. To approximate unknown disturbances, a radial basis function neural network (RBFNN) has been designed. The estimations made were used in updating the control input in the previous step, and the obtained results showed an increase in the robustness of the designed controller. The stability of the closed‐loop system is also analyzed. Finally, a comparison is accomplished between the potential of the proposed controller and that of the feedback linearization and sliding mode controllers. The obtained results indicate better performance and robustness of the suggested controller.

Nonlinear dynamics of a piezoelectrically laminated initially curved microbeam resonator exposed to fringing-field electrostatic actuation

In this paper, the nonlinear dynamics of a piezoelectrically sandwiched initially curved microbeam subjected to fringing-field electrostatic actuation is investigated. The governing motion equation is derived by minimizing the Hamiltonian over the time and discretized to a reduced-order model using the Galerkin technique. The modelling accounts for nonlinearities due to the fringing-field electrostatic force, initial curvature and mid-plane stretching. The electrostatic force is numerically computed using finite element simulation. The nonlinear dynamics of the microbeam in the vicinity of primary resonance is investigated, and the bifurcation types are determined by investigating the location of the Floquet exponents and their configuration with respect to the unit circle on the complex plane. The branches on the frequency–response curves, which originate from the period-doubling bifurcation points, are introduced, and the transition from period-1 to period-2 response is demonstrated by slight sweep of the excitation frequency over the time. The effect of DC and AC electrostatic excitation and the piezoelectric excitation on the response of the system are examined, and their effect on the bifurcation types is determined. The force response curves assuming the AC voltage as the bifurcation parameter are also introduced; it is illustrated that in contrast to in-plane electrostatic excitation, in fringing field-based resonators the resonator is not limited by pull-in instability, which is substantially confining the amplitude of the motion in in-plane resonators.

Mechanics, modeling, and shape optimization of electrostatic zipper actuators

Generating actuation for haptic feedback is a major challenge for wearable devices and soft robotics. Current methods such as piezoelectric, pneumatic, or responsive material actuators are limited by the response time, power consumption, and their reliance on external mechanisms such as pumps or large voltage amplifiers. The emerging technology of electrostatic zipper actuators, where a dielectric-filled pouch is sandwiched between flexible conducting electrodes, is a promising alternative. However, the voltage required to actuate such systems remains in the relatively large kilovolt range. Additionally, there do not currently exist efficient modeling methods to explore more effective designs. Our work looks to address both of these issues. We start by discussing the mechanics of the zipping phenomenon which leads to actuation. Then, we formulate a novel mechanics model for these systems. By considering an elastic plate coupled with the electrostatic interactions, we develop an efficient and robust numerical method to simulate the actuation process. We then verify the model by demonstrating excellent agreement to analytical predictions for simplified cases. As the complex physics of such systems create challenges for intuitive design, we turn to optimal design methods. We formulate the shape optimization problem through the method of mappings to design actuators for maximum actuation pressure and work of actuation. Our method navigates the trade-offs between zipping susceptibility and volume displacement, and we explore optimal designs for various geometric and loading scenarios. Finally, we discuss further directions and open problems relevant to the industrial deployment of zipper actuators moving forward.

Dual-Backplate CMUTs with Wide Bandwidth and Low Driving Voltage for Airborne Applications.

In this work, novel airborne capacitive micromachined ultrasonic transducers (CMUTs) based on a dual-backplate (DBP) technology are presented. In contrast to conventional CMUTs, these transducers use a three-electrode-based capacitive system, where the membrane is placed between two highly-perforated counter electrodes, enabling enlarged displacement amplitudes in electrostatic actuation and wide and tunable bandwidth due to a ventilated air cavity. Fabricated DBP-CMUT prototypes therefore show exceptionally high receive and transmit sensitivities of -34.5 dB(V/Pa) and 259 nm/V, respectively, in their 84 kHz resonance. The viscous dissipation introduced by ventilating the cavity results in a wide factional bandwidth (FBW) of 29%. An applicability of the developed CMUT for airborne ranging is demonstrated in pulse-echo based ranging measurements, where the distance of a sound reflecting metal plate can be clearly detected by a single CMUT operated in a transceiver mode.

Modeling of fully hermetic electrostatic microfluidic valve actuator with increased displacement

Modeling of fully hermetic electrostatic microfluidic valve actuator with increased displacement

Ultrathin internal dielectric electrostatic actuator for reduced pull-in voltage and bidirectional actuation

Direction and analog deflection control, as well as low voltage digital switching are the most desirable attributes in electrostatic actuators for current MEMS applications. In this work we show how internal dielectric transduction can be used to reduce pull-in voltages without reducing the air gap, and to effect bi-directional actuation. The actuator is a metal–dielectric–metal sandwich. For hybrid actuation to achieve reduced pull-in, the device has a thick bottom metal and a thin top metal, while for the upward actuator the device has a thick top metal and a thin bottom metal. An out-of-plane deflection of 108 nm is achieved using 5 V applied voltage for the upward actuator, while the hybrid actuator shows over 50% reduction in pull-in voltage from 1.26 V to 0.62 V.

Rapid and spatially programmed electrostatic actuation of anisotropic polymers

Liquid crystal elastomers (LCEs) are a fascinating class of anisotropic soft actuating materials that can respond to various stimuli. However, achieving both fast actuation and a high degree of freedom (DOF) in the LCE is one of the main challenges to overcome. In this study, we demonstrate rapid actuation (∼25 Hz) of LCEs driven by electrostatic force via direct charging. Notably, the end of the LCE film in our system is physically separated from the electrode, unlike conventional dielectric elastomer actuators, which allow a high DOF actuation when applying the DC or AC voltage in a spatially controlled manner. As a proof-of-concept, various functional actuators, including popup letters, a Kirigami-inspired spring, a dynamic segments device, a freeform oscillator, and a flapping motion of beetle, are successfully demonstrated. We envision our electrostatically actuating LCEs with sophisticatedly engineered electric fields in 1D, 2D, and 3D environments as a valuable platform for investigating the fundamental mechanics of electric field-driven soft actuators.

Design and Considerations: Microelectromechanical System (MEMS) Vibrating Ring Resonator Gyroscopes

Microelectromechanical system (MEMS) vibrating gyroscope design considerations are always intriguing due to their microscale mechanical, electrical, and material behavior. MEMS vibrating ring gyroscopes have become important inertial sensors in inertial measurement units (IMU) for navigation and sensing applications. The design of a MEMS vibrating ring gyroscope incorporates an oscillating ring structure as a proof mass, reflecting unique design challenges and possibilities. This paper presents a comprehensive design analysis of the MEMS vibrating ring gyroscope from the mechanical, electrical, and damping perspectives. The mechanical design of the MEMS vibrating ring gyroscope investigates the various frame designs of the vibrating ring structure, as well as the various beam structures, including rectangular and semicircular beam structures, which are analyzed using mathematical models and finite element analysis (FEA) simulations that provide an in-depth analysis of the stiffness and deflection of the vibrating structures. The electrical designs of the MEMS vibrating ring gyroscope are analyzed using various electrode configurations, electrostatic actuation, and capacitive detection mechanisms. The design analysis of various forms of damping, including viscous, structural, thermoelastic, and anchor damping, is discussed. The variety of design structures is investigated for MEMS vibrating ring gyroscopes’ mechanical, electrical, and damping performance.

A non-destructive electro-acoustic method to characterize the pull-in voltage of electrostatic actuators

For electrostatic actuators, the pull-in marks an upper limit for the operation range. Once reached, the electrodes come into contact and are shorted without further protection. A non-destructive measurement technique to predict this failure mode is of high interest to allow, e.g. fabrication monitoring or reliability studies. To this end, we develop a surprisingly simple nonlinear lumped parameter model (LPM) for a rather complex electrostatic actuator, designed for an in-ear loudspeaker application. It turns out that a single degree-of-freedom model with only one parameter is sufficient. Our key approach is to experimentally determine this free model parameter by analysing harmonic distortions at low frequencies. Harmonic distortions are a very sensitive tool for nonlinearities. Our method is suggested by simulations with a 2D stationary finite element method (FEM), demonstrating how the analysis of harmonic distortions for voltages far below the pull-in can predict not only the DC pull-in but also the quasi-static AC pull-in voltages at different working points. The distortion analysis of electrostatic actuator ensembles therefore seems a viable route for their non-destructive characterization in the nonlinear domain.

3D‐Printed Electrostatic Microactuators for Flexible Microsystems

AbstractDeveloping small‐scale, lightweight, and flexible devices with integrated microactuators is one of the critical challenges in wearable haptic devices, soft robotics, and microrobotics. In this study, a novel fabrication process that leverages the benefits of 3D printing with two‐photon polymerization and flexible printed circuit boards (FPCBs) is presented. This method enables flexible microsystems with 3D‐printed electrostatic microactuators, which are demonstrated in a flexible integrated micromirror array and a legged microrobot with a mass of 4 mg. 3D electrostatic actuators on FPCBs are robust enough to actuate the micromirrors while the device is deformed, and they are easily integrated with off‐the‐shelf electronics. The crawling robot is one of the lightest legged microrobots actuated without external fields, and the legs actuated with 3D electrostatic actuators enable a locomotion speed of 0.27 body length per second. The proposed fabrication framework opens up a pathway toward a variety of highly integrated flexible microsystems.

Optimization of hydraulically amplified electrostatic actuators based on an evolutionary strategy and finite element model to match the performance of the human triceps surae muscle fibres

Artificial muscles are required to improve prosthetics, exoskeletons and other industrial robotics applications. Compared to other technologies like pneumatic actuators and shape memory alloys, Peano hydraulically amplified self-healing electrostatic (HASEL) actuators have the most similar stress output, work density and specific energy as biological muscle. This work designs an artificial muscle fibre that simulates human triceps surae muscle fibre using Peano-HASEL actuators. Analytical models are derived to calculate the capacitance and efficiency of the actuator. A three-stage methodology of an evolutionary strategy, finite element (FE) model and a severity analysis is proposed to optimize the geometrical parameters of the artificial muscle fibre, evaluate its performance, and identify potential risks. The finite element model created in this work produces a full multi-physics simulation coupling the electro-mechanical and fluid–solid interactions, which fits any liquid dielectric volume and for the first time simulates an entire activation cycle. The finite element model further simulates the force-length and force-velocity relationships not seen in previous work and facilitates understanding of the dynamics of the Peano-HASEL actuator, including damping characteristics. Plastic deformation and fluid pocket phenomenon due to materials are found during the simulation, which could give new insights for the analysis of electrical breakdown and mechanical stress failure. The three-stage design methodology described in this paper suggested that an artificial muscle with 80 mm width, 0.4 radian initial central angle, 20 um film thickness and 7.6 kV activation voltage would best match the human triceps surae muscle behaviour. The designed artificial muscle fibre can produce 80% of peak maximum strain (∼18.8%), have an efficiency of 22%, generate high loads within 5% strain and restore muscle-like performance beyond 5% strain.

Investigating the effect of interatomic distance on friction force through MEMS-AFM based experiment

Investigations on the influence of the interatomic distance (IAD) on friction are crucial for gaining a better understanding of friction and comprehending the essential nature of graphene friction. We obtained friction force microscopy (FFM) images of strained surfaces to examine how the IAD affects the friction force. First, using microelectromechanical system (MEMS) fabrication techniques, we fabricated a strain-generating microdevice that can generate surface strain on its Si surface by an electrostatic comb actuator. The microdevice was installed in a high vacuum atomic force microscope. Next, FFM measurements were performed on the stress concentration section of the microdevice using a Si cantilever. The driving voltage on the comb actuator was switched on/off for each scan line during a single raster scan. This procedure allowed us to obtain FFM images representing the surface strain (i.e., the IAD variation) by excluding friction/wear-induced disturbances. The FFM images agreed well with the strain distribution calculated by the elastic finite element method analysis. The relative reduction of the friction was approximately 9% against the calculated strain of 1.2%.