Showing papers on "Bimorph published in 2018"

Translucent soft robots driven by frameless fluid electrode dielectric elastomer actuators.

Abstract: Dielectric elastomer actuators (DEAs) are a promising enabling technology for a wide range of emerging applications, including robotics, artificial muscles, and microfluidics. This is due to their large actuation strains, rapid response rate, low cost and low noise, high energy density, and high efficiency when compared with alternative actuators. These properties make DEAs ideal for the actuation of soft submersible devices, although their use has been limited because of three main challenges: (i) developing suitable, compliant electrode materials; (ii) the need to effectively insulate the actuator electrodes from the surrounding fluid; and (iii) the rigid frames typically required to prestrain the dielectric layers. We explored the use of a frameless, submersible DEA design that uses an internal chamber filled with liquid as one of the electrodes and the surrounding environmental liquid as the second electrode, thus simplifying the implementation of soft, actuated submersible devices. We demonstrated the feasibility of this approach with a prototype swimming robot composed of transparent bimorph actuator segments and inspired by transparent eel larvae, leptocephali. This design achieved undulatory swimming with a maximum forward swimming speed of 1.9 millimeters per second and a Froude efficiency of 52%. We also demonstrated the capability for camouflage and display through the body of the robot, which has an average transmittance of 94% across the visible spectrum, similar to a leptocephalus. These results suggest a potential for DEAs with fluid electrodes to serve as artificial muscles for quiet, translucent, swimming soft robots for applications including surveillance and the unobtrusive study of marine life.

Concomitant sensing and actuation for piezoelectric microrobots

Abstract: Sensor fabrication for microrobots is challenging due to their small size and low mass. As a potential solution, we present a technique for estimating the velocity of piezoelectric bending bimorph actuators, a popular choice for driving such microscale devices, that requires simple electronics and no additional mechanical components. Our approach relies on the insight that motion of the actuators causes varying strains on the surface on the piezoelectric material, which via the direct piezoelectric effect, results in a current proportional to the actuator velocity. We propose that the actuator be electrically approximated as a parallel combination of a frequency and voltage dependent resistor and capacitor, and a velocity proportional current source. We develop an experimental procedure to measure these quantities, and are able to experimentally determine the actuator tip velocity to within 10% accuracy over a range of voltages (25–200 V) and frequencies (1–2000 Hz, well beyond actuator resonance). We successfully apply this sensing methodology to two microrobots, the RoboBee and the Harvard Ambulatory MicroRobot (HAMR), to estimate the wing and limb motion respectively. We further use sensor feedback to close the loop on HAMR's leg phase and obtain desired leg trajectories near transmission resonance. The proposed sensor methodology is generic and can be applied to piezoelectric actuators of different geometries and configurations for uses in microrobotic applications.

Nano-electromechanical Drumhead Resonators from Two-Dimensional Material Bimorphs

Abstract: Atomic membranes of monolayer 2D materials represent the ultimate limit in the size of nano-electromechanical systems. However, new properties and new functionalities emerge by looking at the interface between layers in heterostructures of 2D materials. Here, we demonstrate the integration of 2D heterostructures as tunable nano-electromechanical systems, exploring the competition between the mechanics of the ultrathin membrane and the incommensurate van der Waals interface. We fabricate electrically contacted 5 or 6 μm circular drumheads of suspended heterostructure membranes of monolayer graphene on monolayer molybdenum disulfide (MoS2), which we call a 2D bimorph. We characterize the mechanical resonance through electrostatic actuation and laser interferometry detection. The 2D bimorphs have resonance frequencies of 5–20 MHz and quality factors of 50–700, comparable to resonators from monolayer or few-layer 2D materials. The frequencies and eigenmode shapes of the higher harmonics display split degenera...

Vibration analysis of size-dependent bimorph functionally graded piezoelectric cylindrical shell based on nonlocal strain gradient theory

Abstract: Functionally graded piezoelectric materials (FGPMs) have emerged as promising candidates for electronic nanodevices. In this paper, a study on dynamic response of a bimorph FGP cylindrical nanoshell based on nonlocal strain gradient theory is presented. The material properties are assumed to be variable across thickness direction according to power law distribution. The electric potential is considered to be quadratic through thickness direction. The governing equations and boundary conditions are obtained on the basis of first-order shear deformation theory using Hamilton’s principle. As case study, free vibration of simply supported bimorph FGP cylindrical nanoshell is studied and the influences of different parameters on natural frequency are illustrated. The results obtained provide detailed insights into dynamic response of bimorph FGP cylindrical nanoshell and provide evidence for its size dependency especially by increase in thickness and decrease in length, which is an important conclusion for obtaining appropriate functionality in sensors and actuators.

Wearable inertial energy harvester with sputtered bimorph lead zirconate titanate (PZT) thin-film beams

Abstract: Energy harvesting from human motion addresses the growing need for self-powered wearable health monitoring systems which require 24/7 operation. Human motion is characterized by low and irregular frequencies, large amplitudes, and multi-axial motion, all of which limit the performance of conventional translational energy harvesters. An eccentric rotor-based rotational approach originally used in self-winding watches has been adopted to address the challenge. This paper presents a three-dimensional generalized rotational harvester model that considers both linear and rotational excitations. A hypothetical power upper bound for such architectures derived using this generalized model demonstrated the possibility for harvesting significantly more energy compared to existing devices. A wrist-worn piezoelectric rotational energy harvester was designed and fabricated attempting to narrow this gap between existing devices and the theoretical upper bound. The harvester utilizes sputtered bimorph PZT/nickel/PZT thin-film beams to accommodate the need for both flexibility and high piezoelectric figure of merit in order to realize a multi-beam wearable harvester. The prototype was characterized using a bench-top swing arm set-up to validate the system-level model, which provides many degrees of freedom for optimization.

Bimorph material/structure designs for high sensitivity flexible surface acoustic wave temperature sensors

Abstract: A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.

Small size piezoelectric impact drive actuator with rectangular bimorphs

Abstract: A new small size linear type piezoelectric inertia-friction actuator has been developed The actuator is self-inertia type and operation principle is based on the impact drive Piezoelectric actuator has simple design and consists of four rectangular bimorph piezoelectric plates fixed in two metal holders that are connected by the two springs Actuator can operate as self-moving slider on the clamped carbon fiber reinforced plastic rod or it can be clamped to drive the rod Size of the actuator is 8 × 85 × 56 mm Excitation of the actuator can be carried out by single saw tooth or rectangular pulse type signal Bidirectional motion of the slider is achieved by changing phase of the saw tooth electrical signal by π or duty ratio of the rectangular pulse signal Numerical investigation of the piezoelectric actuator was performed to analyze natural frequencies, modal shapes and response of the actuator to the different excitation signals A prototype piezoelectric actuator was made and operating principle of the actuator was validated Measurements of electrical and mechanical output characteristics were performed The maximum no load velocity of the slider reaches 40376 mm/s with driving voltage of 40 V Actuator achieves maximum thrust force of 021 N with the same input voltage

A method of broadening the bandwidth by tuning the proof mass in a piezoelectric energy harvesting cantilever

Abstract: We propose and demonstrate a new method for broadening the bandwidth of a piezoelectric energy harvesting cantilever by tuning a proof mass. Our approach is to make the bandwidth broad by decreasing the difference between two consecutive flexural resonance frequencies of the cantilever. The prototype broadband energy harvesting device consists of a cantilever with double piezoelectric patch and a tuned proof mass, which is composed of two different materials: aluminium and brass. We tuned resonance frequencies of the device based on the optimal design framework. In order to prove the effectiveness of the proposed device, prototypes of two cantilevers, one with a tuned proof mass and the other with a conventional proof mass, were manufactured and the same bimorph cantilever were used in prototypes. Performances of the manufactured prototypes were evaluated and compared. It is observed that the proposed device shows a 426.6 % increase in bandwidth at the same output level and 508.5 % increase in power compared to the conventional device.

A Low Mass Power Electronics Unit to Drive Piezoelectric Actuators for Flying Microrobots

Abstract: This paper presents a power electronics design for the piezoelectric actuators of an insect-scale flapping-wing robot, the RoboBee The proposed design outputs four high-voltage drive signals tailored for the two bimorph actuators of the RoboBee in an alternating drive configuration It utilizes fully integrated drive stage circuits with a novel highside gate driver to save chip area and meet the strict mass constraint of the RoboBee Compared with previous integrated designs, it also boosts efficiency in delivering energy to the actuators and recovering unused energy by applying three power saving techniques, dynamic common mode adjustment, envelope tracking, and charge sharing Using this design to energize four 15 nF capacitor loads with a 200 V and 100 Hz drive signal and tracking the control commands recorded from an actual flight experiment for the robot, we measure an average power consumption of 290 mW

Resonant nonlinearities of piezoelectric macro-fiber composite cantilevers with interdigitated electrodes in energy harvesting

Abstract: We explore the modeling and analysis of nonlinear nonconservative dynamics of macro-fiber composite (MFC) piezoelectric structures, guided by rigorous experiments, for resonant vibration-based energy harvesting, as well as other applications leveraging the direct piezoelectric effect, such as resonant sensing. The MFCs employ piezoelectric fibers of rectangular cross section embedded in Kapton with interdigitated electrodes to exploit the 33-mode of piezoelectricity. Existing modeling and analysis efforts for resonant nonlinearities have so far considered conventional piezoceramics that use the 31-mode of piezoelectricity. In the present work, we develop a framework to represent and predict nonlinear electroelastic dynamics of MFC bimorph cantilevers under resonant base excitation for primary resonance behavior. The interdigitated electrodes are shunted to a set of resistive electrical loads to quantify the electrical power output. Experiments are conducted on a set of MFC bimorphs over a broad range of mechanical excitation levels to identify the types of nonlinearities present and to compare the harmonic balance model predictions and experiments. The experimentally observed interaction of quadratic piezoelectric material softening and cubic geometric hardening effects is captured and demonstrated by the model. It is shown that the linearized version of the model yields highly inaccurate results for typical base acceleration levels and frequencies involved in vibration energy harvesting, while the nonlinear framework presented here can accurately predict the amplitude-dependent resonant frequency response.

Harvesting the Ultimate Electrical Power From MEMS Piezoelectric Vibration Energy Harvesters: An Optimization Approach

Abstract: Optimized MEMS piezoelectric vibration energy harvesters with maximum possible power generation have been proposed. The energy harvesters work based on the transduction of the applied vibration induced stress on the cantilever beams into the electrical power. Particle swarm optimization approach has been used to design the optimum unimorph and bimorph structures. The optimization has been done for different combinations of the top and bottom piezoelectric layers in bimorph energy harvesters. The geometries of the proposed structures and their harvested powers before and after the optimization have been calculated and compared. The optimization parameters have been chosen so that asymmetric structures with partial coverage of piezoelectric layers would be investigated. The results show that the proposed structures serve as the maximum power generators and provide the largest possible electrical power. In order to limit the beam free end displacement, a guided two beam design has been proposed and optimized. The proposed bimorph guided two beam energy harvester could achieve the minimum displacement which has a key effect on the lifetime of the energy harvesters.

Electrode Coverage Optimization for Piezoelectric Energy Harvesting from Tip Excitation.

Abstract: Piezoelectric energy harvesting using cantilever-type structures has been extensively investigated due to its potential application in providing power supplies for wireless sensor networks, but the low output power has been a bottleneck for its further commercialization. To improve the power conversion capability, a piezoelectric beam with different electrode coverage ratios is studied theoretically and experimentally in this paper. A distributed-parameter theoretical model is established for a bimorph piezoelectric beam with the consideration of the electrode coverage area. The impact of the electrode coverage on the capacitance, the output power and the optimal load resistance are analyzed, showing that the piezoelectric beam has the best performance with an electrode coverage of 66.1%. An experimental study was then carried out to validate the theoretical results using a piezoelectric beam fabricated with segmented electrodes. The experimental results fit well with the theoretical model. A 12% improvement on the Root-Mean-Square (RMS) output power was achieved with the optimized electrode converge ratio (66.1%). This work provides a simple approach to utilizing piezoelectric beams in a more efficient way.

Finite Element Modellingand Simulations of Piezoelectric Actuators Responses with Uncertainty Quantification

Abstract: Piezoelectric structures are widely used in engineering designs including sensors, actuators, and energy-harvesting devices. In this paper, we present the development of a three-dimensional finite element model for simulations of piezoelectric actuators and quantification of their responses under uncertain parameter inputs. The implementation of the finite element model is based on standard nodal approach extended for piezoelectric materials using three-dimensional tetrahedral and hexahedral elements. To account for electrical-mechanical coupling in piezoelectric materials, an additional degree of freedom for electrical potential is added to each node in those elements together with their usual mechanical displacement unknowns. The development was validated with analytical and experimental data for a range of problems from a single-layer piezoelectric beam to multiple layer beams in unimorph and bimorph arrangement. A more detailed analysis is conducted for a unimorph composite plate actuator with different design parameters. Uncertainty quantification was also performed to evaluate the sensitivity of the responses of the piezoelectric composite plate with an uncertain input of material properties. This sheds light on understanding the variations in reported responses of the device; at the same time, providing extra confidence to the numerical model.

Analysis and Experimental Validation of a Piezoelectric Harvester with Enhanced Frequency Bandwidth

Abstract: The use of a single bimorph as a harmonic oscillator aimed at harvesting vibrational energy is not effective due to its inherent narrow frequency bandwidth stemming from the need to adjust the natural frequency of the harvester to the platform excitation frequencies. Therefore, the present research focuses on the development, manufacturing, and testing of an advanced system based on three bimorphs, capable of adjusting their natural frequencies using tip end masses, and interconnected by springs, thus enlarging the system’s bandwidth. An analytical model was developed for three bimorphs interconnected by two springs with three end masses. The model can predict the output generated voltage from each bimorph, and then the total output power is measured on a given outside resistor as a function of the material properties, the geometric dimensions of the vibrating beams, the end-masses, and the spring constants. The analytical model was then compared with data in the literature, yielding a good correlation. To further increase the reliability of the model, a test set-up was designed and manufactured that included three bimorphs with three end-masses connected by two springs. The system was excited using a shaker, and the output voltage was measured for each bimorph for various configurations. Then, the analytical model was tuned based on the test results by introducing two factors, the quality and the stiffness factors, and the predictions of the calibrated analytical model were compared with the experimental results, yielding a good correlation. The calibrated analytical model was then used to perform a comprehensive parametric investigation for two and three bimorphs systems, in which the influences of various parameters—like spring constant, mass value, thickness, and width and length of the bimorph and the substrate beam—on the output generated power were investigated. The main conclusion from this parametric investigation was that by correctly choosing the geometric sizes of the cantilevers, the adequate tip end masses, and the ratio between constants of the springs, the frequency bandwidth is expanded yielding a higher harvested power. Typical harvested power of the present designed system can reach up to 20 mW at the first natural frequency and up to 5 mW for the second natural frequency.

Flexible piezoelectric liquid volume sensor

Abstract: We report a non-contact type polyvinylidene fluoride (PVDF)-based liquid volume sensor. When a liquid container vibrates due to an applied impact, our sensor that is attached to the wall of the container detects the resonance frequency of vibration, which shifts as a result of change in liquid volume. The sensitivity of our sensor was enhanced by stacking multiple sensors in series. A PVDF bimorph actuator was also fabricated to demonstrate an integrated actuator-sensor system. We believe that the results presented in this work will pave the way for novel applications in volume sensing.

Moisture-triggered actuator and detector with high-performance: interface engineering of graphene oxide/ethyl cellulose

Abstract: Actuators that can directly convert other forms of environmental energy into mechanical work offer great application prospects in intriguing energy applications and smart devices. But to-date, low cohesion strength of the interface and humidity responsive actuators primarily limit their applications. Herein, by experimentally optimizing interface of bimorph structure, we build graphene oxide/ethyl cellulose bidirectional bending actuators --- a case of bimorphs with fast and reversible shape changes in response to environmental humidity gradients. Meanwhile, we employ the actuator as the engine to drive piezoelectric detector. In this case, graphene oxide and ethyl cellulose are combined with chemical bonds, successfully building a bimorph with binary synergy strengthening and toughening. The excellent hygroscopicity of graphene oxide accompanied with huge volume expansion triggers giant moisture responsiveness greater than 90 degrees. Moreover, the open circuit voltage of piezoelectric detector holds a peak value around 0.1 V and exhibits excellent reversibility. We anticipate that humidity-responsive actuator and detector hold promise for the application and expansion of smart devices in varieties of multifunctional nanosystems.

Programmable and functional electrothermal bimorph actuators based on large-area anisotropic carbon nanotube paper.

Abstract: Electro-active polymer (EAP) actuators, such as electronic, ionic and electrothermal (ET) actuators, have become an important branch of next-generation soft actuators in bionic robotics. However, most reported EAP actuators could realize only simple movements, being restricted by the small area of flexible electrodes and simple designs. We prepared large-area flexible electrodes of high anisotropy, made of oriented carbon nanotube (CNT) paper, and carried out artful graphic designs and processing on the electrodes to make functional ET bimorph actuators which can realize large bending deformations (over 220°, curvature > 1.5 cm−1) and bionic movements driven by electricity. The anisotropy of CNT paper benefits electrode designs and multiform actuations for complex actuators. Based on the large-area CNT paper, more interesting and functional actuators can be designed and prepared which will have practical applications in the fields of artificial muscles, complicated actuations, and soft and bionic robotics.

A single-chip flow sensor based on bimorph PMUTs with differential readout capabilities

Abstract: This work reports the measurements of air flows for both magnitude and direction based on piezoelectric micromachined ultrasonic transducers (PMUTs) for the first time. The sensor operates in the pulse-echo mode to detect changes in flow with a measured sensitivity that is 286% of that for previously reported MUT-based flow meters, all without commanding any voltage over 5V. The enhancement is a result of four unique features reported herein: (1) the high-sensitivity bimorph structure of the fabricated PMUTs; (2) the spatial separation between the transmitter (Tx) and receiver (Rx) transducer elements; (3) the high directivity of the transmitted acoustic pulse; and (4) the differential readout. Owing to the single-chip design, our flow sensor is the first of its kind capable of measuring flow direction in addition to speed with high sensitivity.