Actuation Voltage Research Articles

Electrocapillary Actuation of Liquid Metal in Microchannels.

Controllable deformation of liquid metal by electrocapillary actuation (ECA) is empirically characterized in fluidic channels at the sub-millimeter-length scale. In 100-µm-deep channels of varying widths, the Galinstan liquid metal could move at velocities of more than 40 mm/s. The liquid metal could extend more than 2.5 mm into the channels at an electrocapillary actuation voltage of 3 V DC. The dynamic behavior of the liquid metal as it moves in the microchannels is described. These results are useful for designing microsystems that use liquid metal as a functional material.

Hydrodynamics of electro-capillarity propelled non-Newtonian droplets through micro-confinements.

In this article, we theoretically explore the dynamics of droplet motion and its evolution during electro-capillarity propelled actuation within microfluidic systems. The study covers a wide gamut of fluids, wherein we investigate the dynamics of both pseudoplastic and dilatant fluid droplets. It is observed that change in the fluid rheology of the non-Newtonian fluids leads to significant morphing of the droplet dynamics during the actuation and propulsion event when compared to the Newtonian counterparts. We validate the theory using experimental reports on similar systems employing Newtonian droplets. The influence of governing parameters such as the actuation voltage and its transients, dielectric layer thickness on the electrodes and electrode spacing is probed. We also explore the influence of the interfacial properties of the system, such as channel wall friction, droplet wettability, and capillary friction, and establish that the fluid rheology, in conjunction with the interfacial features regulate the electro-actuation and propulsion of the droplets. We further provide theoretical estimates on the optimal design of the electro-actuation system in terms of a proposed electro-interfacial tension parameter. The findings may hold significance towards design and development of microfluidics with electro-actuation systems.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1140/epje/s10189-022-00196-0.

Design, simulation and optimization of an RF MEMS capacitive switch to reduce actuation voltage

Design, simulation and optimization of an RF MEMS capacitive switch to reduce actuation voltage

Millimeter-scale focal length tuning with MEMS-integrated meta-optics employing high-throughput fabrication

Miniature varifocal lenses are crucial for many applications requiring compact optical systems. Here, utilizing electro-mechanically actuated 0.5-mm aperture infrared Alvarez meta-optics, we demonstrate 3.1 mm (200 diopters) focal length tuning with an actuation voltage below 40 V. This constitutes the largest focal length tuning in any low-power electro-mechanically actuated meta-optic, enabled by the high energy density in comb-drive actuators producing large displacements at relatively low voltage. The demonstrated device is produced by a novel nanofabrication process that accommodates meta-optics with a larger aperture and has improved alignment between meta-optics via flip-chip bonding. The whole fabrication process is CMOS compatible and amenable to high-throughput manufacturing.

Closed form solutions for thermo-mechanical buckling analysis of shallow piezo-laminated spherical shells

Thermo-mechanical buckling analysis of laminated spherical shells bounded with the piezoelectric actuator layers has been presented in this article. Applied loads are a combination of thermal, mechanical and electrical loads. Derivations of equilibrium and stability equations are based on the classical laminated shell theory and Sanders’s nonlinear kinematic relations. The analysis employs the Galerkin method to achieve closed-form formulas for the buckling loads of the piezo-laminated spherical shell. Effects of applied actuator voltage, voltage sign, geometrical parameters of the shell (length, diameter, and thickness), material properties, and layout of composite layers on the buckling strength are investigated. Analytical solutions are obtained for three types of thermal loading, and one thermo-mechanical loading condition. The results are validated by the known data in the literature.

Study on the improved electromechanical properties of composited dielectric elastomer by tailoring three-dimensional segregated multi-walled carbon nanotube (MWCNT) network

High permittivity and large actuation strain under low actuation voltage have been the “hotspot” on the development and application of dielectric elastomer actuators (DEAs) for decades. In this work, by coating multi-walled carbon nanotube (MWCNT)/silicon rubber (SR) composite on the surface of nickel foam, after which the nickel foam was etched, the segregated MWCNT network structure was filled and encapsulated by SR. As a result, an isolated three-dimensional (3D) MWCNT network was successfully introduced into the SR elastomer matrix. Studies showed that owing to the large amount of accumulated charge on the large polarization interface between MWCNT and SR, high dielectric constant value as high as 10.39 at 1 kHz under 0.8 wt % MWCNT can be endowed to the composited elastomer. In addition, because discontinuity of adjacent MWCNTs in the 3D MWCNT network, the dielectric loss and elastic modulus of the composited elastomer has been significantly lowered, providing a high actuated strain of about 11.61% at a low electric field of 10.1 V·μm−1 under a filler content of 0.6 wt % to the composites. This finding raises a long-range prospect to readily and reliably prepare high-performance polymer based dielectric materials, and the 3D-MWCNT/SR composite elastomer seizes a great potential to be applicated as high-performance DEAs.

Efficient voltage actuators based on rapid heat and electric dual-response poly(aryl ether ketone) shape memory composites reinforced with radially aligned CNTs

In this paper, we synthesized the shape memory poly(aryl ether ketone) (PAEK) and fabricated the radially oriented CNTs enhanced PAEK composite actuators. The introduction of highly aligned CNTs endowed PAEK matrix great thermal stability, good mechanical properties, and excellent shape memory effect. The formation of CNTs conductive path in PAEK matrix was instrumental in improving thermal and electrical conductivity, promoting efficient heat/electric dual triggered shape memory effect with high recovery ratio, rapid shape recovery and low triggering voltage. In addition, we used aligned CNTs/PAEK composites with 15 wt% CNTs as voltage actuators, and designed the two kinds of voltage actuators (angle-mode and time-mode) to achieve the different actuating actions via the applied voltage (range from 8 V to 50 V). These efficient composite voltage actuators exhibited the excellent stability and durability in continuous voltage actuating, which were expected to open door for smart actuators and electronic devices.

Nonlinear Lumped Parameter Model and Snap-Through Stability Analysis of Hydraulically Amplified Dielectric Elastomer Actuators

Abstract Hydraulically amplified dielectric elastomer actuators (HADEAs) are soft actuators comprising a pair of elastic electrodes connected to an inflatable membrane where the membrane and space between the electrodes are filled with an incompressible dielectric fluid. A lumped parameter model (LPM) was developed based on a nonlinear hyper-elastic Mooney–Rivlin material model. We compared the nonlinear LPM with a previous linear model and with a multiphysics finite element model with Mooney–Rivlin materials. The proposed nonlinear LPM showed good agreement in the estimation of strain and internal hydrostatic pressure as a function of actuation voltage compared to the finite element analysis results. Moreover, it better predicts the quasi-static equilibrium state and snap-through instability than the linear LPM.

Micromechanical resonant cantilever sensors actuated by fringing electrostatic fields

We report on the architecture and operational principle of a resonant cantilever-type displacement sensor. The device is actuated electrostatically by a side electrode that is coplanar with the cantilever and by a gap-closing electrode positioned underneath the beam. The unique electrode geometry combined with the appropriate actuating voltages allows positioning of the cantilever in close proximity to the bistability threshold, where the frequency sensitivity to the electrode displacement is enhanced. Using a reduced order model backed by numerical simulations, the dependencies of the device frequency on the beam’s deflections and the actuation voltages were mapped. We show wide-range tunability that spans a range between softening and hardening behavior. We demonstrate displacement sensing using fabricated single crystal silicon ≈2000 µm long, ≈5 µm thick cantilevers. When compared to a resonant cantilever sensor actuated solely by a gap-closing electrode, measurements from our fringing field actuated devices show a four times higher sensitivity of ≈98 Hz µm−1. The suggested approach may find applications in a broad range of micro and potentially nano-scale applications including resonant inertial, force, mass and bio-sensors.

Modeling and Control Design of a Contact-Based, Electrostatically Actuated Rotating Sphere

The performance of micromirrors in terms of their maximum deflection is often limited due to mechanical constraints in the design. To increase the range of achievable deflection angles, we present a novel concept in which a free-lying sphere with a flat side as reflector can be rotated. Due to the large forces needed to move the sphere, multiple electrostatic actuators are used to cooperatively rotate the sphere in iterative steps by impacts and friction. A parameterized system-level model of the configuration is derived, which considers arbitrary multi-contact scenarios and can be used for simulation, analysis, and control design purposes. Due to the complex, indirect relation between the actuator voltages and the sphere motion, model-based numerical optimization is applied to obtain suitable system inputs. This results in rotation sequences, which can be understood as a sequence of motion primitives, thus transforming the continuous time model into an abstract discrete time model. Based on this, we propose a feedback control strategy for trajectory following, considering model uncertainties by a learning scheme. High precision is achieved by an extension controlling the angular change of each rotation step. The suitability of the overall approach is demonstrated in simulation for maximum angles of 40°, achieving angular velocities of approximately 10°/s.

Fabrication and actuation characterisation of a new UV curing acrylic dielectric elastomer

Most commonly used dielectric elastomers (DEs) such as acrylic dielectric elastomers VHBTM 4910 need a high actuation voltage and pre-stretching to obtain a large actuation strain, and present high mechanical loss caused by viscoelasticity. In this work, we fabricated a new acrylic elastomer by UV curing based on CN9021 and lauryl acrylate. By manipulating crosslinker content, crosslink density changed and physical entanglements of the new material can be affected. Therefore, mechanical properties such as Young's Modulus and mechanical loss of the new material can be controlled, and little change of its glass transition temperature was induced. Results of the actuation test show that the new DE is capable of 9.0% actuation area strain under 11 kV/mm and a good performance under oscillating voltage with different waveforms and frequencies.

A lumped parameter model to describe the electromechanics of mesoscale droplets

An understanding of droplet electromechanics will advance the development of droplet-based technologies, such as lab-on-chip platforms, precision additive manufacturing tools, and fluid property sensors. To describe the electromechanics of mesoscale droplets, a simplified mathematical model is derived by treating the droplet as a spring–mass–damper system and validated with finite-element simulation and experiments. Through the model and experiments, the role of fluid properties on droplet electromechanics is investigated using different fluids—with over three orders of magnitude in dynamic viscosity—for a range of actuation voltage amplitudes V¯ and frequencies f. Despite the simplified modeling approach, the lumped model predicts two important droplet characteristic parameters: coalescence time tc and critical electric field Ecr with less than 30% error. Three observations are reported here: (1) applying the scaling laws to the electric field–time E–t relation for E≫Ecr shows that the coalescence time tc is proportional to the droplet length scale characterized in terms of radius r; (2) at lower voltage actuation frequencies f≤ 10 Hz and sub-critical electric fields E≪Ecr, the droplet dynamics is strongly dependent on the surface tension, while at higher voltage actuation frequencies f > 10 Hz, the droplet dynamics is dictated by all the three fluid properties, namely, surface tension, viscosity, and density; and (3) droplets of different fluids exhibit characteristics of a second-order system—validating our approach of modeling the droplet as the spring–mass–damper system.

Assembled Comb-Drive XYZ-Microstage With Large Displacements and Low Crosstalk for Scanning Force Microscopy

This paper proposes and demonstrates a chip-level-microassembly comb-drive XYZ-microstage for providing large displacements and low crosstalk in scanning force microscopy applications at low temperatures. The three-dimensional structure of the comb-drive XYZ-microstage, consisting of an in-plane XY-microstage, two out-of-plane Z-actuators, and a base substrate, was accurately and orderly constructed using microassembly technology. This configuration can overcome the out-of-plane stroke-space limitation of conventional monolithic-wafer-based XYZ-microstages, and the crosstalk movements resulting from the coupling connection between in-plane and out-of-plane actuation units can be avoided. The in-plane actuation unit of the XY-microstage can provide low-crosstalk movements in the X- and Y-directions, due to the design of the decoupling-motion structure and constraint of the capacitance-coupling crosstalk of the actuation voltages. Folded-flexure springs with high stiffness were adopted in the XYZ-microstage to enhance the lateral stability of movable combs and improve the range of achievable strokes. The assembled comb-drive XYZ-microstage could provide quite large displacements of 49.2 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$27.9~\mu \text{m}$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$50.5~\mu \text{m}$ </tex-math></inline-formula> in the X-, Y-, and Z-directions, respectively. Furthermore, to demonstrate the feasibility of the fabricated XYZ-microstage, a magnetic resonance force microscopy measurement system was constructed using the scanning XYZ-microstage with a specimen of 1, 1-Diphenyl-2-picrylhydrazyl radical. The magnetic resonance force from the electron spin resonance excited in the specimen could be detected by scanning the specimen in a specific resonance region. The results demonstrate that the proposed microassembly with the optimized actuation-unit structure is a promising means of establishing a comb-drive XYZ-microstage with large displacements, low crosstalk, and high adaptability. [2021-0112]

Poly(acrylic acid)-Based Hydrogel Actuators Fabricated via Digital Light Projection Additive Manufacturing

Electroactive polymers that exhibit controlled deformation under an applied electric field, either in liquid or air, have great potential as soft robotic actuators. However, materials for soft robotics currently face challenges, including slow response, high actuation potential, and a lack of underlying mechanistic understanding. Additionally, fabrication of soft robotic actuators with complex design features has historically been restricted by two-dimensional fabrication methods. In this work, we investigate cross-linked poly(acrylic acid)-based actuators prepared utilizing digital light projection (DLP), an additive manufacturing technique that enables fabrication of actuators with complex geometries. A series of photopolymerizable inks are prepared incorporating acrylic acid (monomer), trimethylolpropane trimethacrylate (cross-linker), and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator). Soft actuators are 3D-printed utilizing a commercial DLP 3D printer operating under 405 nm UV light. These 3D-printed actuators exhibit large deformation (up to 43°), high actuation speed (up to 1.08°/s), and stable actuation performance for bending cycles under relatively low actuation voltage (4–6 V). Factors such as acrylic acid content, cross-linker concentration, actuator thicknesses, and electric field strength are varied, and their impact on the 3D-printed actuators are evaluated and discussed. Lastly, a membrane valve actuator is fabricated, and its ability to open and close under applied potential is demonstrated.

Investigation of the Dynamics of Cavitation Bubbles in a Microfluidic Channel with Actuations.

This work presents experimental and numerical studies on the dynamics of cavitation bubbles in a nozzle-shaped microfluidic channel with PZT (lead-zirconate-titanate) actuations. It is found that a cloud of bubbles can be generated near the center of the microfluidic channel when the actuation voltage is larger than a threshold at 1 kHz. After being generated, the bubbles under actuations oscillate radially with violent expansion and compression, and simultaneously translate upstream towards the opening of the nozzle. Along with radial oscillation and translation, the bubbles undergo frequent and drastic coalescence and breakup, leading to vigorous churning of surrounding liquids. The pressure variation and distribution in the microchannel are calculated by numerical simulation in Ansys Fluent, and results show that there is a low-pressure zone inside the microfluidic channel within each cycle of the actuation period, which is responsible for bubble generation observed in the experiments. The method of bubble generation in this study is novel and can be applied for the enhancement of heat and mass transfer in microfluidic operations.

Piezoelectric benders with strain sensing electrodes: Sensor design for position control and force estimation

Piezoelectric benders are widely used in industrial applications due to their low-cost and compact size. However, due to the large relative size and cost of displacement sensors, bender actuators are often operated in open-loop or with feed-forward control, which can limit positioning accuracy to 20% of full-scale. To improve the positioning accuracy of piezoelectric benders, this article proposes integrating resistive strain gauges into the electrode surface by chemical etching or laser ablation. These strain sensors are then used to measure and control the tip displacement. The proposed sensors are shown to suffer from significant cross-coupling between the actuator voltage and measured signal; however, this can be mitigated by judicious choice of the sensor location and actuator driving scheme. In addition to position sensing, a method is also presented for simultaneous estimation of the contact force between the actuator tip and load. The proposed methods are validated experimentally by controlling the tip position of a piezoelectric bender while simultaneously estimating the force applied to a reference load cell.

A high contact force and high‐isolation radio‐frequency microelectromechanical systems switch for radio‐frequency front‐end applications

AbstractA new structure for low‐loss and high‐isolation radio‐frequency microelectromechanical systems (RF MEMS) switches is presented. The high contact force of the switch leads to very small ranges for contact resistance which is the main constrain of DC‐contact RF MEMS switches. The contact resistance of the switch is 27 mΩ leading to negligible thermal noise which is one of the most important parameters for devices operating at RF front‐ends immediately after the antenna where there is not any active stage. The switch is composed of two actuators: an electrothermal actuator for actuation of the switch from OFF to ON state and an electrostatic actuator to hold the switch at ON state. The insertion loss, return loss, and isolation of the switch for frequencies below 70 GHz are −0.35, −20, and −10 dB, respectively. The contact force and contact resistance of the switch are 0.93 mN and 0.027 Ω, respectively. Electrothermal and electrostatic actuators require 0.91 and 50 actuation voltages, respectively. During the ON‐state, the power consumption of the switch is near zero. The low contact resistance and high‐isolation characteristics of the switch make it very suitable for mobile front‐ends.

Air Damping Analysis of a Micro-Coriolis Mass Flow Sensor.

A micro-Coriolis mass flow sensor is a resonating device that measures small mass flows of fluid. A large vibration amplitude is desired as the Coriolis forces due to mass flow and, accordingly, the signal-to-noise ratio, are directly proportional to the vibration amplitude. Therefore, it is important to maximize the quality factor Q so that a large vibration amplitude can be achieved without requiring high actuation voltages and high power consumption. This paper presents an investigation of the Q factor of different devices in different resonant modes. Q factors were measured both at atmospheric pressure and in vacuum. The measurement results are compared with theoretical predictions. In the atmospheric environment, the Q factor increases when the resonance frequency increases. When reducing the pressure from 1 bar to bar, the Q factor almost doubles. At even lower pressures, the Q factor is inversely proportional to the pressure until intrinsic effects start to dominate, resulting in a maximum Q factor of approximately 7200.

Design of a large-range rotary microgripper with freeform geometries using a genetic algorithm

This paper describes a novel electrostatically actuated microgripper with freeform geometries designed by a genetic algorithm. This new semiautomated design methodology is capable of designing near-optimal MEMS devices that are robust to fabrication tolerances. The use of freeform geometries designed by a genetic algorithm significantly improves the performance of the microgripper. An experiment shows that the designed microgripper has a large displacement (91.5 μm) with a low actuation voltage (47.5 V), which agrees well with the theory. The microgripper has a large actuation displacement and can handle micro-objects with a size from 10 to 100 μm. A grasping experiment on human hair with a diameter of 77 μm was performed to prove the functionality of the gripper. The result confirmed the superior performance of the new design methodology enabling freeform geometries. This design method can also be extended to the design of many other MEMS devices.

Novel ionic bioartificial muscles based on ionically crosslinked multi-walled carbon nanotubes-mediated bacterial cellulose membranes and PEDOT:PSS electrodes

High-performance bioartificial muscles with low-cost, large bending deformation, low actuation voltage, and fast response time have drawn extensive attention as the development of human-friendly electronics in recent years. Here, we report a high-performance ionic bioartificial muscle based on the bacterial cellulose (BC)/ionic liquid (IL)/multi-walled carbon nanotubes (MWCNT) nanocomposite membrane and PEDOT:PSS electrode. The developed ionic actuator exhibits excellent electro-chemo-mechanical properties, which are ascribed to its high ionic conductivity, large specific capacitance, and ionically crosslinked structure resulting from the strong ionic interaction and physical crosslinking among BC, IL, and MWCNT. In particular, the proposed BC-IL-MWCNT (0.10 wt%) nanocomposite exhibited significant increments of Young’s modulus up to 75% and specific capacitance up to 77%, leading to 2.5 times larger bending deformation than that of the BC-IL actuator. More interestingly, bioinspired applications containing artificial soft robotic finger and grapple robot were successfully demonstrated based on high-performance BC-IL-MWCNT actuator with excellent sensitivity and controllability. Thus, the newly proposed BC-IL-MWCNT bioartificial muscle will offer a viable pathway for developing next-generation artificial muscles, soft robotics, wearable electronic products, flexible tactile devices, and biomedical instruments.