Actuation Voltage Research Articles

Homogenization of electrets with ellipsoidal microstructure and pathways for designing piezoelectricity in soft materials

True piezoelectricity in soft materials is rare if not virtually non-existent. This impedes applications where both large deformation and a strong electromechanical coupling are desirable e.g. soft robotics, biomedical sensors and actuators, a class of energy harvesting devices among others. The widely used soft dielectric elastomers rely on the electrostatic Maxwell stress effect for electromechanical coupling — a one-way quadratic effect that requires extremely large voltage for actuation and does not allow for the facile conversion of mechanical deformation into electricity. Prior research has shown that embedding (and stabilizing) immobile charges or dipoles in soft matter i.e. creating so-called electrets, can lead to an emergent piezoelectric effect. In this work, using a recently developed homogenization theory for soft electret materials, we derive closed-form expressions to design soft apparently piezoelectric materials with an ellipsoidal microstructure. Specifically, we determine both effective longitudinal (d33) and transverse (d31) piezoelectric coefficients of the material and study the impact of the material properties on these two coefficients. Conventional electrets exhibit a rather weak d31, which is quite disadvantageous for applications where flexure is important (e.g. energy harvesting). Either an elastic, or a dielectric contrast is essential for the emergence of piezoelectricity in electrets and, depending on the microstructural details, these two effects can either strengthen or diminish the other. Our results indicate that the microstructure and material properties which lead to an optimum d33 effect are different from the conditions underlying the optimal d31 response. The maximum d31 effect is observed in electrets where the inclusions are mechanically harder but dielectrically softer than the matrix material. Finally, we find that a significantly large d33 piezoelectric response is possible for spheroid inclusion microstructures with large aspect ratios.

Piezoelectric bimorph MEMS speakers

One of the key requirements for MEMS speakers is to increase the sound pressure level (SPL) while keeping the size as small as possible. In this paper we present a MEMS speaker based on piezoelectric bimorph cantilevers that produces a higher SPL than conventional unimorph cantilever speakers. The active diaphragm size is 1.4 × 1.4 mm2. The bimorph cantilevers are connected in parallel to make full use of the actuation voltage. At 1 kHz, the measured SPL reached 73 dB and the peak SPL reached 102 dB at the resonance frequency of 10 kHz in a 711 ear simulator under a driving voltage of 10 Vrms. The total harmonic distortion of the MEMS speaker was less than 3% in the range from 100 Hz to 20 kHz. Although the absolute SPL was not the highest, this work provides a better SPL for all piezoelectric MEMS speakers.

Low actuation voltage cantilever-type RF-MEMS shunt switches for 5G applications

Conventional electrostatic RF-MEMS shunt switches suffer from high actuation voltages, owing to their membrane-type structures with large spring constant. Alternatively, in this work, to alleviate the inherent high actuation voltage requirements of electrostatic shunt switches, we propose a fixed-free cantilever-type RF switch in a shunt configuration and systematically optimize it both from electromechanical and RF performance aspects. The proposed switches are carefully modeled via comprehensive finite element simulations, performed using commercially available solvers i.e., COMSOL and HFSS. The electromechanical response of the proposed switches is optimized by studying three different cantilever designs, where low actuation voltage and switching time of 9.1 V and 90 μs are achieved, respectively. To validate the mechanical reliability of the designed switches, the maximum stress values in switch structures during operation were restricted well below the yield strength of the switch beam. Furthermore, RF performance of the designed switches was optimized for mm-wave regime by maximizing the ratio of switch capacitance in OFF-state and ON-state. The cantilever-type RF-MEMS shunt switch design exhibits an insertion loss as low as −0.065 dB and RF isolation as high as −40 dB, at 30 GHz, demonstrating feasibility for 5G mobile applications.

Analysis of discharge characteristics of pulsed plasma power source in the microsecond scale

The characteristics test of plasma discharge is an essential physical basis for studying plasma flow control. The power consumption of pulsed plasma aerodynamic actuation is 30% lower than when the actuation voltage is a continuous sine wave. This paper uses a self-developed pulsed plasma power source to superimpose DC. The power source conducts the discharge measurement on the sliding discharge plasma. The experimental results show that the power source effectively outputs 0-20 kV pulsed high voltage. The superimposed DC power source generates a negative DC high voltage, accelerating the drift speed of positive ions in the plasma and forming a stable and uniform surface discharge. But the essence of pulse discharge is still filamentary discharge. In a cycle, the plasma discharge is mainly concentrated on the rising edge of the pulse. In contrast, the pulse current is bipolar, and the negative pulse current has a more obvious growth trend, which is more effective for improving the flow control ability.

Modeling and design of dielectric elastomer actuated tunable lens with dual chambers

As a novel kind of focus tunable lens, dielectric elastomer actuated liquid lens has a compact structure, fast response, low cost, and outstanding tunability, which makes it attract extensive attention. Here, we present a computational model of a dielectric elastomer actuated lens with dual chambers that consist of three elastic membranes and two disconnected chambers filled with conductive and transparent liquid. The intermediate layer actuated by applied voltage deforms, changing the curvature of passive membranes and obtaining a new focal length. The simulation results calculated by the shooting method with two guessed values agree well with the experimental results. Based on this model, the effects of a set of parameters, including chamber radii, shear modulus, permittivity, prestretch ratios, and injected liquid volumes, on the tuning performance of the lens are analyzed. It is found that, by regulating the liquid volume in each chamber, both the initial focal length and the tuning range can be adjusted easily. Under the condition with specific liquid volumes, the lens possesses both positive and negative focal length during voltage actuation, indicating promoted tuning performance, which is acclaimed for optimal design.

압전 액추에이터를 이용한 저전압 구동 MEMS 가변 캐패시터

In this work, low voltage MEMS variable capacitor was presented. Compare with other RF MEMS technologies, piezoelectric MEMS devices offer certain benefits such as low actuation voltage and fast moving, etc. The proposed structure consists of dual piezoelectric actuation bridges of in-plane polarized lead zirconate titanate (PZT) film to improve actuation voltage and reliability of devices. The PZT thin film, deposited on Au structural layer using RF magnetron sputtering method, was poled and driven with interdigitated electrodes(IDEs) to exploit dSUB33/SUB mode actuation. The in-plane polarized PZT films make it possible to develope dSUB33/SUB mode bending devices which lead to about two times improvement in strain performance. The fabricated variable capacitor shows that the tuning range is varied 100.9 to 111.2 nF with control voltage ranging from 0 to 1 V.

Study on the Method of Charge Accumulation Suppression of Electrostatic Suspended Accelerometer.

Electrostatic suspended accelerometers (ESAs) are widely used in high accuracy acceleration measurement. However, there exist accumulated charges on the isolated mass which damage the accuracy and the stability of ESAs. In this paper, we propose to apply actuation voltage with a combined waveform to suppress the acceleration noise due to deposited charge. A model of the electrostatic force on the mass is established and the deviation voltage is found to be the dominant source of charge noise. Based on the analysis of disturbance electrostatic force under DC and AC signals, actuation combined with DC and AC voltage is designed and the disturbance force due to charge can be suppressed through adjustment towards the duty cycle of different compositions. Simulations and experiments are carried out and the results indicate that the disturbance due to charge can be suppressed up to 40%, which validates the efficiency of the scheme.

Deformation of Carbon Nano Tubes Reinforced Hybrid Laminated Composite Plates induced by Piezoelectric Actuators

Piezoelectric materials, typically used as intelligent materials, can respond according to the design demands of the composite structures autonomously. The excitation of piezoelectric actuators generates the bending effect on the hybrid composite plates. An analytical methodology is developed to calculate the displacements of simply supported laminated composite plates induced by piezoelectric actuators and validate the results by generating MATLAB code. Further, the laminated hybrid composite plates reinforced with carbon nanotubes(CNT) are excited by piezoelectric actuators bonded to the surface on both sides with a variable electrical voltage across the thickness. The effects of location, size and thickness ratio of piezoelectric actuators on the deflection of hybrid composite plates are carried out by extending the code. The transverse displacements vary linearly with the applied voltage and size of the piezoelectric actuators. The effect of CNT volume fraction and the position of CNT lamina plays a vital role in deflections, and also it is observed that maximum displacements decrease rapidly as thickness ratio increases from 0.5 to 5 and from 10 to 50, the maximum displacements gradually decrease. Hence, it illustrated that the present technique provides a simple solution for predicting and controlling the deformed shape of reinforced hybrid composite plates induced by distributed piezoelectric actuators.

Shape Control of Composite Structure with Suitably Placed Piezoelectric Sensors Under Electro-Thermo-Mechanical Condition with Non-linear Analysis

In this paper, the application of piezoelectric actuators to the composite control card is studied statically. The electro-thermo-mechanically coupled mathematical model is used for the analysis. The main section of this paper is static control. Shape control is stated here as determining the shape control parameters, including the actuation voltage and the adjustment of the actuator orientation, so that the structure which is activated using these parameters also adapts as closely as possible to the required shape. In this paper, we have presented FE model for the control analysis of the shape of piezoelectric laminated (PZT) composite plates using Ansys. The piezoelectric layer and composite plate are modeled in the form of additional layers to be attached to the upper or lower surface or to be integrated into the laminated composite plate. Ansys finite element software is used for modeling and has been successfully validated with experimental and numerical results which are readily available in the literature. The present analysis shows that with the application of an appropriate voltage to the piezoelectric actuator, the desired shape of the composite plate can be obtained. Keywords: Composite plate, FEM, Intelligent structure, Non- linear, piezoelectric, sensor, voltage

Digital holographic study of corona wind-assisted evaporation of hydrocarbon from a microliter well

The present study aims to understand the evaporation dynamics of heavy hydrocarbon liquid (cyclohexane) from a circular well cavity under the influence of corona wind. The study explores the effect of corona wind on the modification of vapor phase transport and the evaporation rate from the circular well. Particle image velocimetry is used to characterize the velocity field of the corona wind generated by a needle and plate configuration. Digital holography interferometry is used to decipher the mole fraction distribution of the vapor cloud. Circular well cavities of radius 2.0, 2.5, and 4 mm are studied. The effect of corona wind on the evaporation of different sized well cavities increases with an increase in actuation voltage. The side wall of the cavities influences the distribution of the vapor cloud due to the interaction with the incoming corona wind. More than ten times enhancement of evaporation is observed at 10 kV excitation voltage setting of the corona wind generator. The corona jet-assisted evaporation can be very useful in thin-film evaporative cooling due to its simplicity in design and superior performance.

Ultra‐Thin and Conformable Electrodes Composed of Single‐Walled Carbon Nanotube Networks for Skin‐Contact Dielectric Elastomer Actuators

AbstractSkin‐contact dielectric elastomer actuators (DEAs) consisting of skin‐conformable, stretchable electrodes are fabricated using a roll‐to‐roll‐based gravure coating method. In this method, single‐walled carbon nanotubes (SWCNTs) are continuously applied on a free‐standing ultra‐thin film (nanosheet) of poly(styrene‐b‐butadiene‐b‐styrene) (SBS) to produce an SWCNT‐SBS nanosheet of 101‐nm thickness. After the first SWCNT coating, the SWCNT‐SBS nanosheet shows a Young's modulus (i.e., 80.9 MPa) comparable to that of the SBS film and a sheet resistance of 4.6 kΩ sq−1. Using the free‐standing SWCNT‐SBS nanosheets as electrodes, a ten‐layered DEA is fabricated without glue or dielectric elastomer precursors on three substrates with different stiffness, namely glass, Ecoflex 00–30, and a urethane elastomer model skin. The low flexural rigidity of the ten‐layered DEA (105 nN m) ensures conformability to the shape of an index finger. Application of an actuation voltage of 2100 V produces a two‐fold larger displacement of the DEA on the Ecoflex 00–30 substrate compared with that on the glass substrate. The ability of the DEA to conform to the surface of skin will enable its application in skin‐contact haptic devices.

A piezoelectric MEMS loudspeaker for in-ear and free field applications lumped and finite element models

This paper presents the simulation results of a piezoelectric MEMS loudspeaker. The micro-fabricated device is composed of two wafers, the first one features two bending piezoelectric actuators with large displacements, and the second one features a mobile rigid plate surrounded by a small interstice providing a thermoviscous layer hence avoiding an acoustic short circuit between its front and back sides. Performances of the loudspeaker are evaluated using a lumped element model and a finite element model to estimate the pressure generated by the loudspeaker in free field and in an ear-occluded coupler. Size variants of the design and their models are presented. The current design allows a radiated pressure of 80 dBSPL from 500 Hz at 10 cm and at 30 Vpp for a 64 mm2 footprint in free field, and more than 130 dBSPL in a IEC 60318–4 coupler with the same actuation voltage, which is above the known performances of the state of the art for MEMS loudspeakers with such dimensions.

Electrically Induced Liquid Metal Droplet Bouncing.

Liquid metals, including eutectic gallium–indium (EGaIn), have been explored for various planar droplet operations, including droplet splitting and merging, promoting their use in emerging areas such as flexible electronics and soft robotics. However, three-dimensional (3D) droplet operations, including droplet bouncing, have mostly been limited to nonmetallic liquids or aqueous solutions. This is the first study of liquid metal droplet bouncing using continuous AC electrowetting through an analytical model, computational fluid dynamics simulation, and empirical validation to the best of our knowledge. We achieved liquid metal droplet bouncing with a height greater than 5 mm with an actuation voltage of less than 10 V and a frequency of less than 5 Hz. We compared the bouncing trajectories of the liquid metal droplet for different actuation parameters. We found that the jumping height of the droplet increases as the frequency of the applied AC voltage decreases and its amplitude increases until the onset of instability. Furthermore, we model the attenuation dynamics of consecutive bouncing cycles of the underdamped droplet bouncing system. This study embarks on controlling liquid metal droplet bouncing electrically, thereby opening a plethora of new opportunities utilizing 3D liquid metal droplet operations for numerous applications such as energy harvesting, heat transfer, and radio frequency (RF) switching.

Continuously Adjustable Micro Valve Based on a Piezoelectric Actuator for High-Precision Flow Rate Control

A MEMS-based micro valve fitted with a piezoelectric actuator is presented in order to achieve a continuously adjustable flow rate control. The micro valve is realized using a cost-effective fabrication scheme with simple polyimide (PI) bonding, which has an average shear strength of up to 39.8 MPa, indicating a relatively high reliability. The simulation results based on the finite element method (FEM) show that the valve membrane is able to seal the inlet and cut off the flow successfully with a piezoelectric force of 3N when the differential pressure is 200 kPa. The measurement of the flow rate through the outlets shows that the micro valve can control the flow rate effectively in a large range under different actuation voltages and differential pressures. When the actuation voltage is 140 V, the measured leak flow of the closed micro valve is smaller than 0.5 sccm with a differential pressure of 200 kPa.

Cilia metasurfaces for electronically programmable microfluidic manipulation.

Cilial pumping is a powerful strategy used by biological organisms to control and manipulate fluids at the microscale. However, despite numerous recent advances in optically, magnetically and electrically driven actuation, development of an engineered cilial platform with the potential for applications has remained difficult to realize1-6. Here we report on active metasurfaces of electronically actuated artificial cilia that can create arbitrary flow patterns in liquids near a surface. We first create voltage-actuated cilia that generate non-reciprocal motions to drive surface flows at tens of microns per second at actuation voltages of 1 volt. We then show that a cilia unit cell can locally create a range of elemental flow geometries. By combining these unit cells, we create an active cilia metasurface that can generate and switch between any desired surface flow pattern. Finally, we integrate the cilia with a light-powered complementary metal-oxide-semiconductor (CMOS) clock circuit to demonstrate wireless operation. As a proof of concept, we use this circuit to output voltage pulses with various phase delays to demonstrate improved pumping efficiency using metachronal waves. These powerful results, demonstrated experimentally and confirmed using theoretical computations, illustrate a pathway towards fine-scale microfluidic manipulation, with applications from microfluidic pumping to microrobotic locomotion.

Varifocal liquid lens driven by a conical dielectric elastomer actuator

A varifocal lens is an important part of optical systems with applications in biomedicine, photography, smartphones, and virtual reality. In this paper, we propose and demonstrate a varifocal liquid lens driven by a conical dielectric elastomer actuator. When the conical dielectric elastomer is subjected to an actuation voltage, the conical dielectric elastomer works as an out-plane actuator and makes the surface curvature of the liquid droplet increase; then the focal length of the proposed varifocal liquid lens changes. The overall dimensions of the proposed varifocal liquid lens are 9.4 mm in diameter and 12.5 mm in height. The focal length tuning range is 15.07mm∼9.50mm when the actuation voltage increases from 0 kV to 5.0 kV. The focal power variation of the proposed varifocal liquid lens is 35.5 D. The rise and fall times of the proposed varifocal liquid lens are 215 ms and 293 ms, respectively. The ability of the proposed liquid lens to focus on objects at different distances without any moving parts is demonstrated. The compact varifocal liquid lens driven by the conical dielectric elastomer actuator in the current study has the potential to be used in various compact imaging systems in the future.

Dielectrowetting on curved surfaces

Programmable fluidic systems on curved and flexible substrates are of increasing interest. One approach to achieving programmability is the controlled sequential wetting and dewetting on a surface using voltage actuation. In particular, liquid dielectrophoresis techniques have recently been shown to provide the ability to form a spread liquid film on a normally liquid repellent, but rigid, substrate via applying a spatially periodic electrical potential underneath an initial sessile droplet. In this work, we demonstrate the creation of thin, rectangular shaped, films of electrically insulating liquid on the side of a curved and flexible liquid repellant substrate using dielectrophoresis forces. We find that the experimental threshold voltage VT(κs) for film formation has a monotonic dependence on the value of the substrate curvature κs in the range −0.4 mm−1 < κs < 0.26 mm−1. By considering the balance of stresses acting on the films, including the Laplace pressure and the Maxwell stress, we develop an analytical theoretical expression that is in excellent quantitative agreement with our curvature dependent experimental threshold voltage measurements. The resulting physical insights and the demonstration of programmable wettability on curved and flexible substrates with both positive and negative curvature provide the foundations for applications in imaging, displays, and biochemical analysis.

Effects of swirler blade angle and actuator applied voltage on combustion characteristics and cooling effectiveness

This paper investigated effects of swirlers with blade angles and applied voltage of plasma actuators on combustion and wall temperature of a Can - type gas turbine combustor. Results show that large blade angle of the swirler is beneficial for the mixing of fuel and air, which improves uniformity of the outlet temperature distribution and reduces CO emission but results in temperature rise of the wall. Pattern factor reflects uniformity of the temperature distribution at the outlet of the combustion chamber, and a small value of the pattern factor means a good distribution uniformity. In this paper, the minimum pattern factor is 0.45 when the blade angle of the swirler is 55°, which means the best uniformity of temperature distribution at combustor outlet. Compared with the worst results with a 40° blade angle, the pattern factor for the blade angle of 55° decreases by 66.4%. CO emission decreases with the increase of the blade angle. Compared with the maximum value of CO emission for a 40° blade angle, reductions of CO emission are 67.6%, 95.9% and 99.6% with the blade angles of 45°, 50° and 55°. It is found that CO emission decreases by 1.3% and pattern factor increases by 2.2%, when the blade angle of the swirler changes from 55° to 60°. When the applied voltage changes from 0 kV to 8 kV and 16 kV, cooling effectiveness increases by 3.2% and 0.7%. Cooling effectiveness decreases by 2.9% when the applied voltage increases from 0 kV to 24 kV.

Static High Voltage Actuation of Piezoelectric AlN and AlScN Based Scanning Micromirrors

Piezoelectric micromirrors with aluminum nitride (AlN) and aluminum scandium nitride (Al0.68Sc0.32N) are presented and compared regarding their static deflection. Two chip designs with 2 × 3 mm2 (Design 1) and 4 × 6 mm2 (Design 2) footprint with 600 nm AlN or 2000 nm Al0.68Sc0.32N as piezoelectric transducer material are investigated. The chip with Design 1 and Al0.68Sc0.32N has a resonance frequency of 1.8 kHz and a static scan angle of 38.4° at 400 V DC was measured. Design 2 has its resonance at 2.1 kHz. The maximum static scan angle is 55.6° at 220 V DC, which is the maximum deflection measurable with the experimental setup. The static deflection per electric field is increased by a factor of 10, due to the optimization of the design and the research and development of high-performance piezoelectric transducer materials with large piezoelectric coefficient and high electrical breakthrough voltage.

Phase Change Nanoelectromechanical Relay for Nonvolatile Low Leakage Switching

AbstractThe design, modeling, and experimental validation of a highly scalable phase change electromechanical relay are present. The Phase Change NEMS Relay (PCNR) is a nonvolatile mechanical relay actuated by the volumetric expansion of phase change material. GeTe is used as the active phase change material, and nonvolatile relay states are changed by converting it between amorphous and crystalline phases, which differ in volume by 10%. Phase conversion is induced by Joule heating an adjacent metal layer. Finite element analysis (FEA) models are developed to predict actuator temperature distributions and quench times for varied actuation pulses. Additional models are developed to simulate actuator deflection including reflow of molten phase change material during an actuation pulse. The smallest fabricated device has a heater footprint of 3 µm × 1 µm, with a 20 nm air‐gap. The FEA model, which calculates the actuation voltage, energy, and ON–OFF current ratio for this device to be 1.1 V, 42 nJ, and 108, respectively, are experimentally verified. A PCNR scaled down to a 15 nm × 5 nm heater footprint with a 2 nm air‐gap is predicted to actuate at 400 mV and 1.7 pJ.