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The development of micro-robots based on bionic motion has garnered increasing attention with the advancement of bionic technology. These micro-robots can be employed in various tasks, such as military applications, disaster search and rescue, in vivo drug delivery, minimally invasive surgery, and tumor treatment. Robot joint motion is commonly achieved through actuators, which encompass motor, hydraulic, or pneumatic components that often carry excessive weight. To achieve the goal of miniaturizing robotic mechanisms, innovative actuators need to be developed. This study focuses on designing a four-limbed micro-robot that utilizes piezoelectric actuators. Automatic Dynamic Analysis of the Mechanical System is employed to investigate the kinematic aspects of the micro-robot’s motion, and finite element analysis is also used to obtain the resonant characteristics of the limbs actuated by piezoelectric bimorphs. The results indicate that the gait pattern of a piezoelectric robot changes according to the walking strategy and the robot dimension. The forward travel speed varies depending on the gait pattern, and adjustments in gait design can reduce the up/down oscillation and right/left offset. The robot’s travel speed increases with both trunk and limb length, although longer thigh and leg lengths might lead to greater offset and vertical oscillation. The resonant frequency and mode shapes change with the limb structure and affect the limb motion style. By adjusting the driving frequency of the bimorph actuators, the gait pattern can be manipulated. The information presented in this study contributes to a deeper understanding of micro-robot design. [ABSTRACT FROM AUTHOR]

Helium is integral in several industries, including nuclear waste management and semiconductors. Thus, developing a sensing method for detecting helium is essential to ensure the proper operation of such facilities. Several approaches can be used for helium detection, including based on the high thermal conductivity of helium, which is several times higher than air. This work utilizes the high thermal conductivity of helium to design and analyze a bimorph MEMS sensor for helium sensing applications. COMSOL Multiphysics software (version 6.2) is used to carry out this investigation. The sensor is constructed from poly-silicon and SiO2 materials with a trenched cantilever beam configuration. The sensor is electrically heated, and its morphed displacement depends on the surrounding gas's composition, which decreases in the presence of helium. Several factors were investigated to probe their effect on the sensor's sensitivity to helium, including the thickness of the poly-silicon layer, the configuration of the trench, and the thickness and location of SiO2 layer. The simulations showed that the best performance, up to 2 ppm helium detection level, can be achieved with thinner beams and medium trench lengths. [ABSTRACT FROM AUTHOR]

A schematic diagram and mathematical model of the functioning of a new piezoelectric membrane (MDS) actuator with double spirals (DS) electrodes on the upper and/or lower surfaces of a thin piezoelectric layer with axisymmetric and periodic (small period) reciprocal electric polarization along the radial coordinate are presented. The polarization of the layer is carried out as a result of connecting the polarizing value of the electrical voltage to the outputs of the double spirals of the electrodes. The electrodes of each (upper and lower) double helix of the MDS actuator are made in the form of electroded tape coatings on the surfaces of the piezoelectric layer in close proximity to each other (due to the small pitch of the helix) to create high electric field strengths along the field lines in local areas of the piezoelectric layer between them when connecting an alternating or direct control electrical voltage to the electrodes, in particular, with positive and negative values of electrical potentials. It is important that the electric field lines and, as a consequence, the polarization of the piezoelectric layer of the MDS actuator are oriented mainly along (i.e., towards or against) the radial coordinate of the membrane, in contrast to many traditional actuator schemes. The results of numerical simulation for a round elastic membrane with piezoelectric actuators installed on its upper and lower surfaces confirmed the effectiveness of the proposed piezoelectric MDS actuator when operating according to the "bimorph" scheme, including using the proposed new structural element (section) - piezoelectric MDS- "compression rings" for various geometric and control parameters. The effect of a significant increase in the deflection of the membrane with installed piezoelectric MDS actuators was revealed compared to the use of traditional homogeneous plate piezoelectric actuators of the bimorph type for various conditions of fastening the membrane, in particular, stationary (rigid) fastening of its center. For a hybrid piezoelectric MDS actuator, including independent concentric circular and annular (i.e., "pressure ring") sections, a non-monotonic character was revealed and a numerical analysis was carried out of the nonlinear dependence of the largest deflection in the center of a membrane hinged and fixed at the edge on the radius ratio its circular and annular MDS sections. Cases have been identified in which the "pressure ring" effect manifests itself, i.e. when the maximum deflection of a membrane with a "pressure ring" exceeds the best possible deflection of this membrane without using it according to the traditional "bimorph" scheme. The new piezoelectric MDS actuator can be used in micromechanics, controlled optics, sensor technology, acoustics, in particular, in the manufacture of piezoelectric acoustic or membrane-type sensor elements, electromechanical transducers for collecting vibration energy. [ABSTRACT FROM AUTHOR]

Helium is integral in several industries, including nuclear waste management and semiconductors. Thus, developing a sensing method for detecting helium is essential to ensure the proper operation of such facilities. Several approaches can be used for helium detection, including based on the high thermal conductivity of helium, which is several times higher than air. This work utilizes the high thermal conductivity of helium to design and analyze a bimorph MEMS sensor for helium sensing applications. COMSOL Multiphysics software (version 6.2) is used to carry out this investigation. The sensor is constructed from poly-silicon and SiO2 materials with a trenched cantilever beam configuration. The sensor is electrically heated, and its morphed displacement depends on the surrounding gas’s composition, which decreases in the presence of helium. Several factors were investigated to probe their effect on the sensor’s sensitivity to helium, including the thickness of the poly-silicon layer, the configuration of the trench, and the thickness and location of SiO2 layer. The simulations showed that the best performance, up to 2 ppm helium detection level, can be achieved with thinner beams and medium trench lengths.

Exact solutions for the electro-elastic static response of simply supported doubly curved (DC) shell piezoelectric bimorph energy harvesters composed of laminated cross-ply or antisymmetric angle-ply composite substrate shell subjected to distributed mechanical loads have been derived. Both series and parallel connections of the piezoelectric layers of the bimorphs are considered for deriving the exact solutions. Derivation of such exact solutions is found to be possible when the piezoelectric layers are orthotropic and generally orthotropic. All linear theories of elasticity and piezoelectricity are used in orthogonal curvilinear coordinate system and a variational principle is employed to determine the boundary conditions associated with the governing equations. The electro-elastic governing equations are solved exactly to obtain the static responses of the harvesters for different shell configurations. The effects of curvature, stacking sequence of the substrate layers and connections of the piezoelectric layers on the harvesting capability of the laminated composite DC shell bimorph harvesters are investigated. It is explored from the exact solutions that the energy harvesting capability of hyperboloid DC Shell piezoelectric bimorph is maximum among the spherical, paraboloid and hyperboloid DC laminated piezoelectric shell harvesters. The expressions of the exact solutions for the DC laminated shell type piezoelectric energy harvesters derived in this paper may be treated as the benchmark solutions for verifying numerical and experimental results. [ABSTRACT FROM AUTHOR]

A novel biomimetic morphing micro aerial vehicle was designed using macro fiber composites (MFCs) as control actuators. The vehicle features variable-sweep, multi-curved wings, and a tail, both of which were embedded with MFC bimorphs. The wing design has a span of 1.1 m unswept (wings fully extended) and 0.65 m swept, resembling falcons (Falco Peregrinus). A design study was conducted on the outboard wing's MFC and carbon fiber substrate orientation to enhance the roll authority of the wings when fully extended. Finite element modeling, wind tunnel testing, and flight testing were conducted to model and optimize the design to obtain linear aerodynamic control with given MFC deflections. In addition, this research explores several configurations to increase roll authority of MFCs using segmented and overlapped sections resembling avian feathers. An overlapped wing configuration was discovered to have the potential to increase roll authority at the expense of adverse yaw. Flight testing proved that MFC-actuated, continuous outboard wings provide sufficient roll authority and handling quality without added compensation for the non-linear behavior of MFCs. This research showed that MFCs can be incorporated into a morphing wing design for manual flight and autonomous flight through feedback from inertial sensors onboard the vehicle. [ABSTRACT FROM AUTHOR]

This paper reports two piezoelectric materials of lead zirconium titanate (PZT) and aluminum nitride (AlN) used to simulate microelectromechanical system (MEMS) speakers, which inevitably suffered deflections as induced via the stress gradient during the fabrication processes. The main issue is the vibrated deflection from the diaphragm that influences the sound pressure level (SPL) of MEMS speakers. To comprehend the correlation between the geometry of the diaphragm and vibration deflection in cantilevers with the same condition of activated voltage and frequency, we compared four types of geometries of cantilevers including square, hexagon, octagon, and decagon in triangular membranes with unimorphic and bimorphic composition by utilizing finite element method (FEM) for physical and structural analyses. The size of different geometric speakers did not exceed 10.39 mm2; the simulation results reveal that under the same condition of activated voltage, the associated acoustic performance, such as SPL for AlN, is in good comparison with the simulation results of the published literature. These FEM simulation results of different types of cantilever geometries provide a methodology design toward practical applications of piezoelectric MEMS speakers in the acoustic performance of stress gradient-induced deflection in triangular bimorphic membranes. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA) thin films have received great importance in the research of smart (or intelligent) materials for their utilization in micro-electromechanical systems (MEMS). It is suggested that the fabrication of SMA thin films on flexible polyimide (PI) substrates paves the way for their utility as micro-actuators and sensors in many microdevices. In this review article, the development of SMA/polyimide thin-film composites using various physical vapor deposition techniques is discussed. The actuation characteristics, the influence of actuation controlling parameters, and the life cycle behavior of these composites are also concisely discussed. Furthermore, the viability of SMA/polyimide composites in various applications is also scrutinized for their shape memory properties and performance. These composites set out to be considered in soft robotic technology, an emerging domain in the field of robotics. The successful implementation of these composite actuators in bio-inspired aquatic and aerial soft robotic systems requires the generation of high actuation force and frequency to carry the payload. In the present article, the prospect of the development of SMA/polyimide sandwich-structured composite is discussed which would possibly facilitate its deployment in soft robotic applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel bimorph Piezoelectric Micromachined Ultrasonic Transducer (PMUT) fabricated with 8-inch standard CMOS-compatible processes. The bimorph structure consists of two layers of 20% scandium-doped aluminum nitride (Sc0.2Al0.8N) thin films, which are sandwiched among three molybdenum (Mo) layers. All three Mo layers are segmented to form the outer ring and inner plate electrodes. Both top and bottom electrodes on the outer ring are electrically linked to the center inner plate electrodes. Likewise, the top and bottom center plate electrodes are electrically connected to the outer ring in the same fashion. This electrical configuration maximizes the effective area of the given PMUT design and improves efficiency during the electromechanical coupling process. In addition, the proposed bimorph structure further simplifies the device's electrical layout with only two-terminal connections as reported in many conventional unimorph PMUTs. The mechanical and acoustic measurements are conducted to verify the device's performance improvement. The dynamic mechanical displacement and acoustic output under a low driving voltage (1 Vpp) are more than twice that reported from conventional unimorph devices with a similar resonant frequency. Moreover, the pulse-echo experiments indicate an improved receiving voltage of 10 mV in comparison with the unimorph counterpart (4.8 mV). The validation of device advancement in the electromechanical coupling effect by using highly doped ScAlN thin film, the realization of the proposed bimorph PMUT on an 8-inch wafer paves the path to production of next generation, high-performance piezoelectric MEMS. [ABSTRACT FROM AUTHOR]

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. HIGHLIGHTS: • This work presents a piezoelectric MEMS speaker with bimorph cantilevers. •The piezoelectric MEMS speaker in this work is made from AlN instead of PZT. •Bimorph speakers have a higher sound pressure level than the commonly used unimorph speakers. [ABSTRACT FROM AUTHOR]

We study the bending of a two-layer piezoelectric semiconductor plate (bimorph). The macroscopic theory of piezoelectric semiconductors is employed. A set of two-dimensional plate equations is derived from the three-dimensional equations. The plate equations exhibit direct couplings among bending, electric polarization along the plate thickness, and mobile charges. In the case of pure bending, a combination of physical and geometric parameters is identified which characterizes the strength of the interaction between the mechanical load and the distribution of mobile charges. In the bending of a rectangular plate under a distributed transverse mechanical load, it is shown that mobile charge distributions and potential barriers/wells develop in the plate. When the mechanical load is local and self-balanced, the induced carrier distributions and potential barriers/wells are also localized near the loading area. The results are fundamentally useful for mechanically manipulating mobile charges in piezoelectric semiconductor devices. [ABSTRACT FROM AUTHOR]

Cardiac auscultation is an orthodox method to prevent and diagnose cardiovascular diseases. Traditional stethoscopes cannot offer a highly reliable diagnosis, and electronic stethoscopes suffer from low signal-to-noise ratio (SNR) and high cost. This paper reports an electronic stethoscope based on piezoelectric bimorph MEMS transducers for cardiac sound monitoring. The stethoscope prototype, measuring 37 $\times 28\times12$ mm3, contains a preamplifier, holders and polydimethylsiloxane (PDMS) packaging. The transducer is designed using a lumped element model, fabricated by MEMS process, packaged, and assembled for final use. A triangular cantilever is chosen as a basic element for the transducer, with analytical analysis showing high sensitivity per unit area as a figure of merit (FoM). Performance parameters such as sensitivity and noise are experimentally characterized and consistent with simulation results. Owing to the outstanding receiving performance of the aluminum nitride (AlN) material and bimorph triangular cantilever structure of the transducer, compared with the commercial electronic stethoscopes, the proposed stethoscope demonstrates real-time phonocardiogram (PCG) with higher SNR. With its small size, high performance and low cost, the stethoscope is developed for portable and wearable cardiac sound monitoring. [2022-0007] [ABSTRACT FROM AUTHOR]

Piezoelectric harvesters use the actuation potential of the piezoelectric material to transform mechanical and vibrational energies into electrical power, scavenging energy from their environment. Few research has been focused on the development and understanding of the piezoelectric harvesters from the material themselves and the real piezoelectric and mechanical properties of the harvester. In the present work, the authors propose a behavior real model based on the experimentally measured electromechanical parameters of a homemade PZT bimorph harvester with the aim to predict its Vrms output. To adjust the harvester behavior, an iterative customized algorithm has been developed in order to adapt the electromechanical coupling coefficient, finding the relationship between the harvester actuator and generator behavior. It has been demonstrated that the harvester adapts its elongation and its piezoelectric coefficients combining the effect of the applied mechanical strain and the electrical behavior as a more realistic behavior due to the electromechanical nature of the material. The complex rms voltage output of the homemade bimorph harvester in the frequency domain has been successfully reproduced by the proposed model. The Behavior Real Model, BRM, developed could become a powerful tool for the design and manufacturing of a piezoelectric harvester based on its customized dimensions, configuration, and the piezoelectric properties of the smart materials. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a new design of bimorph-type electrothermal actuators based on flexible Ni-Co substrates and describes the results of the finite element method (FEM) simulation and performance evaluation of the actuators. In the design of the actuators, a multilayer structure consisting of an adhesion layer, two insulation layers, and a Pt (platinum) heater layer was formed on the Ni-Co flexible substrate that was patterned in an individual shape. The thin-film actuators proposed in this study could be detached from a Si carrier wafer and adhered to other micro or macrostructural elements. To investigate the temperature distribution and mechanical behavior of the actuators, multiphysics FEM simulations combining electrothermal and static structural analyses were carried out. The actuators were fabricated using conventional microfabrication and electroplating technologies on Si carrier wafer; then, the actuators were peeled off from the carrier wafer using the release process proposed in this paper. After fabricating the actuators, the deflection of their tips was evaluated and compared with that obtained from the FEM simulations.

This paper presents a novel bimorph Piezoelectric Micromachined Ultrasonic Transducer (PMUT) fabricated with 8-inch standard CMOS-compatible processes. The bimorph structure consists of two layers of 20% scandium-doped aluminum nitride (Sc0.2Al0.8N) thin films, which are sandwiched among three molybdenum (Mo) layers. All three Mo layers are segmented to form the outer ring and inner plate electrodes. Both top and bottom electrodes on the outer ring are electrically linked to the center inner plate electrodes. Likewise, the top and bottom center plate electrodes are electrically connected to the outer ring in the same fashion. This electrical configuration maximizes the effective area of the given PMUT design and improves efficiency during the electromechanical coupling process. In addition, the proposed bimorph structure further simplifies the device’s electrical layout with only two-terminal connections as reported in many conventional unimorph PMUTs. The mechanical and acoustic measurements are conducted to verify the device’s performance improvement. The dynamic mechanical displacement and acoustic output under a low driving voltage (1 Vpp) are more than twice that reported from conventional unimorph devices with a similar resonant frequency. Moreover, the pulse-echo experiments indicate an improved receiving voltage of 10 mV in comparison with the unimorph counterpart (4.8 mV). The validation of device advancement in the electromechanical coupling effect by using highly doped ScAlN thin film, the realization of the proposed bimorph PMUT on an 8-inch wafer paves the path to production of next generation, high-performance piezoelectric MEMS.

This paper reports a bimorph pinned piezoelectric micromachined ultrasonic transducer (PMUT) for enhanced sound pressure output and electromechanical coupling factor for space imaging applications. An equivalent circuit model has been built to analyze the dynamic behavior of PMUTs and prototype devices have been designed, fabricated. Experimental results show a 58% measured increase in the electromechanical coupling factor and pulse-echo measurements show a 4-meter traveling distance in air under a 133 kHz driving frequency. As a demonstration example, a relatively long-distance (> 1.5 meters) ultrasound imaging test in air is conducted using a 4 × 4 bimorph, pinned dual-electrode PMUTs array based on the transmission beamforming scheme. As such, this work enhances and extends the PMUT performances and capabilities for potential broad applications. [2021-0102] [ABSTRACT FROM AUTHOR]

The taxonomic, ecologo-cenotic and geographical diversity of the flora of forests of the Central Ciscaucasia, counting 735 species of vascular plants belonging to 101 families and 353 genera is considered in the article. The taxonomic structure of the forest flora according to the composition of the first ten families corresponds to the flora of the Ciscaucasia. Forests have a European-sub-Mediterranean-Eurasian with a boreal and Caucasian impurity range of geographic elements. The general course of development of the forest flora of the region as well as the forests of the Eastern European Plain went in the direction of incubation of the European complex into sub-Mediterranean and boreal types with their gradual displacement.

Commonly, linear constitutive equations have been utilized for describing the electromechanical behavior of piezoelectric actuators. These equations are valid for low excitation amplitudes and small strains. In high strain dynamics, nonlinear constitutive equations should be applied which include the material nonlinearity by expressing the stress as a function of higher orders of strain. In this article, nonlinear dynamic modeling of bimorph transverse actuators around the natural frequency has been investigated. The nonlinear equation is solved with perturbation methods and the model parameters are identified with experiments. Experimental results illustrate the improvement of nonlinear dynamic modeling compared with conventional linear models. [ABSTRACT FROM AUTHOR]

In this paper, the stress behaviour and power generation of cymbal bimorph transducer of different piezoelectric ceramics are studied. Comparison of stress, deformation and power is done between different materials cymbal bimorph transducer. The cymbal bimorph design is made on Solidworks, and simulation is carried out on ANSYS 18.0. In this design, the substrate thickness is varied. Its both end surface is bonded to the piezoelectric layers of 0.50 mm thickness and further piezoelectric layers bonded to endcaps. A 100 N of the load is applied at the apex of end caps. The lead-free ceramics and lead-based ceramic are used as a piezoelectric material in the design. The stress and power are calculated for different values of thickness of the substrate, and comparison is made among them. After having a comparison it is found that both types of ceramics can be used, but there are some conditions which prioritise lead-free ceramic over lead-based ceramic. [ABSTRACT FROM AUTHOR]

This paper presents the effect of distance and dimensions of magnetson chaotic behavior and voltage level of a vibratory piezo-magneto-elastic bimorph energy harvesting system. The bimorph model comprises two iezoelectriclayers on a cantilever base structure with one tip magnet as well as two external magnets. The mathematical model is extracted by using distributed model. The validity of the extracted model verified by previously published experimental results.In order to study the nonlinear dynamic of the bimorph, bifurcation diagram, phase plane portrait, time history response, Poincare map, power spectra diagram, and maximum Lyapunov exponents are used. In the bifurcation diagrams, the control parameters are the distances and dimensions of the magnets. It is shown that in the specific region of the control parameters, the sub-harmonic or super-harmonic behavior has minimum harvested voltage and irregular regions has maximum voltage. Also specific dimensions of tip magnet can influence greatly the dynamic behavior as well as output voltage. So these obtained results can give good insights about parameters identification and realization of the nonlinear behavior to reach the broadband higher harvested voltage of the system

This paper proposes a new design of bimorph-type electrothermal actuators based on flexible Ni-Co substrates and describes the results of the finite element method (FEM) simulation and performance evaluation of the actuators. In the design of the actuators, a multilayer structure consisting of an adhesion layer, two insulation layers, and a Pt (platinum) heater layer was formed on the Ni-Co flexible substrate that was patterned in an individual shape. The thin-film actuators proposed in this study could be detached from a Si carrier wafer and adhered to other micro or macrostructural elements. To investigate the temperature distribution and mechanical behavior of the actuators, multiphysics FEM simulations combining electrothermal and static structural analyses were carried out. The actuators were fabricated using conventional microfabrication and electroplating technologies on Si carrier wafer; then, the actuators were peeled off from the carrier wafer using the release process proposed in this paper. After fabricating the actuators, the deflection of their tips was evaluated and compared with that obtained from the FEM simulations. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting (PEH) provides an essential mode for the transformation of mechanical vibration to electrical form for providing continuous power to wireless sensor nodes in today's connected world. This work describes an analytical model based on the Euler-Bernoulli model. The proposed model is in agreement with the FEM simulation model, with results differing by 6%. Variation in geometric parameter, the effect of resonant frequency, output power and stability of the design provides a constraint domain for structure optimization have been described along with the effect of damping. The designed harvester generates a power of 1.31 mW at 90 Hz resonant frequency. [ABSTRACT FROM AUTHOR]

This paper is concerned with the derivation of exact solutions for the responses of piezoelectric bimorph energy harvesters composed of laminated composite beam substrates. An electro-elastic finite element model is also developed based on the layer wise first order shear deformation theory for computing the responses of the bimorphs under general boundary and loading conditions. Both series and parallel connections of the piezoelectric layers of the bimorphs are considered. The responses computed by the finite element model excellently match with that obtained by the exact solutions. The induced electric potential in case of the bimorph in which the piezoelectric layers are connected in series is significantly larger than that in case of the bimorph with piezoelectric layers connected in parallel. If the thickness of the piezoelectric layers and the substrate remain same, the piezoelectric bimorph composed of antisymmetric angle-ply substrate beam is capable of inducing more electric potential than the bimorphs with cross-ply substrate beams. Also, if the bimorph is cantilever, it induces significantly more electric potential than when it is simply supported. Optimum thickness of the piezoelectric layers of the bimorph and unimorph harvesters has been determined. Most importantly, it is found that the bimorph with its piezoelectric layers connected in series performs significantly better than the unimorph if the mass and volume of the piezoelectric layers and the substrates remain same. The results presented here may serve as the benchmark results for verifying experimental and numerical models. [ABSTRACT FROM AUTHOR]

In this paper, the shape influence of piezoelectric beams including triangle, trapezoid, rectangle, inverted trapezoid, convex parabola, concave parabola, and comb-shaped (a combination of two triangular beams with a connector of 4 mm length) are addressed and analyzed by FEM. The analysis is performed for a bimorph piezoelectric beam. The analyzed parameters include the beam length, thickness and width of the piezoelectric layer. The study is performed using COMSOL Multiphysics software for all seven shapes. The results show that due to the mechanical properties of the beams, the natural frequency of the triangular beam is more for all considered parameters. In addition, as the width of the beam end increases, the natural frequency reduces, too. Since natural frequency is inversely related to electric power, the inverted trapezoidal beam has the highest electric power and the triangular beam has the lowest one.

A beam containing a piezoelectric layer or layers is used for piezoelectric harvesting from various processes. The structure of the beam is made by gluing the piezoelectric material on one side (unimorph) or both sides (bimorph) of a carrying substrate. Two piezoelectric layers, glued on both sides of the substrate, may be electrically parallel or series connected. This paper presents an experimental analysis of the impact of parallel and series connections of two Macro Fiber Composite (MFC) MFC patches in a bimorph on the charging of a capacitor. In experiments, the effective charging process of the capacitor was obtained both for parallel and series connection of two MFC patches. The bimorph with a parallel connection generated a larger capacitor charging power than the bimorph with a series connection in the range of voltage across the capacitor from 1 to 18 V. However, the bimorph with a series connection was more effective than a parallel connection for voltage across the charged capacitor from 18 to 20 V. The maximum capacitor charging power generated by the bimorph, in which two MFC patches were parallel connected, was 1.8 times larger than that generated by the bimorph with a series connection and was 3.3 times larger than that generated by a unimorph with one MFC patch. The impact of level of voltage across the capacitor on its discharging process has a significant meaning for the ratio of maximum power between bimorphs and between the bimorph and unimorph.

Piezoelectric actuators are widely used in many fields such as medical instruments, optics, and aerospace due to their small size and high reliability. Piezoelectric cantilever actuators are used in different configurations such as unimorph and bimorph. In this paper, a 3-D lead zirconate titanate (PZT) bimorph was modeled in COMSOL Multiphysics software for investigation of series and parallel configuration. Theoretical analysis has been developed for the measurement of deformation of a piezoelectric cantilever in inverse piezoelectric effect. The experiment was also performed to examine the deformation of piezoelectric bimorph cantilever. It is found that under a constant applied electric field of 100 V bimorph piezoelectric actuator produces maximum deformation at 100 mm length, 30 mm width, and 20 mm thickness. It is also found that piezoelectric series benders have relatively less deformation than piezoelectric parallel benders. Experimental results show good agreement with theoretical and Numerical results. [ABSTRACT FROM AUTHOR]

In the present era, the renewable sources of energy, e.g., piezoelectric materials are in great demand. They play a vital role in the field of micro-electromechanical systems, e.g., sensors and actuators. The cantilever-based piezoelectric energy harvesters are very popular because of their high performance and utilization. In this research-work, an energy harvester model based on a cantilever beam with bimorph PZT-5A, having a substrate layer of structural steel, was presented. The proposed energy scavenging system, designed in COMSOL Multiphysics, was applied to analyze the electrical output as a function of excitation frequencies, load resistances and accelerations. Analytical modeling was employed to measure the output voltage and power under pre-defined conditions of acceleration and load resistance. Experimentation was also performed to determine the relationship between independent and output parameters. Energy harvester is capable of producing the maximum power of 1.16 mW at a resonant frequency of 71 Hz under 1g acceleration, having load resistance of 12 kΩ. It was observed that acceleration and output power are directly proportional to each other. Moreover, the investigation conveys that the experimental results are in good agreement with the numerical results. The maximum error obtained between the experimental and numerical investigation was found to equal 4.3%. [ABSTRACT FROM AUTHOR]

• A complementary strategy can work as a universal design principle for dual-responsive actuators. • Combining moisture-active/alkane-inert GO with alkane-active/moisture-inert PDMS enables dual-responsive actuation. • GO and PDMS bimorph features fast and reversible response to both moisture and alkane. Smart actuators that enable deforming in a predictable manner under external stimuli have revealed great potential for both traditional and emerging industries. Generally, an asymmetric bilayer structure with one layer active and the other inert to a certain stimulus is essential to realize bending behavior. However, towards the development of dual- or multi-responsive actuators, it still lacks universal and effective strategies for rational design and fabrication of such devices through the simplest way. In this paper, we report a complementary strategy to produce dual-responsive bilayer actuators by combining the moisture-active/alkane-inert graphene oxide (GO) layer with the alkane-active/moisture-inert polydimethylsiloxane (PDMS) layer. The GO@PDMS bimorph actuator can switch its active and inert layers in response to moisture and alkane, respectively, realizing dual-responsive deformation under different actuations. Typical dual-responsive actuators, including a selective air valve and a grip and hook smart claw, are successfully fabricated, demonstrating the capability of effective gases and objects transmission. The complementary bimorph actuator may hold great promise for developing intelligent devices and portable delivery systems. [ABSTRACT FROM AUTHOR]

• Deriving the constituent equations of PLZT micro-unimorph/bimorph. • Considering the coupled fields and size effect simultaneously. • Discussing the size effects of PLZT micro-unimorph/bimorph. The constituent equations of both 0–1 and 0–3 polarized PbLaZrTi (PLZT) micro-cantilevers in the form of unimorphs and/or bimorphs are developed. These formulations are based on the modified couple stress theory (MCST), the laminated beam theory, and/or the Euler-Bernoulli beam theory. The thermo-electro-light-mechanical coupled fields and size effect were considered simultaneously in these equations. The present models can capture the size effect in virtue of a material length scale parameter (MLSP). The size-dependent tip deflection, equivalent bending moment and blocking force are discussed. Different materials and thicknesses of the elastic layer are considered in presented models. Furthermore, the present models can be reduced to the classical 0–1/0–3 polarized unimorph/bimorph. [ABSTRACT FROM AUTHOR]

In the current study, we have developed a mathematical model describing the frequency response of a sensor or energy harvester based on a cantilever made of a ferroelectric bidomain single-crystal plate with metal electrodes deposited on opposite faces. The structure is subjected to vibrational excitations. The model allows to predict the dependence of the voltage between the electrodes vs. the vibration frequency and amplitude as well as resonance frequency of the sensor fabricated in form of a rectangular plate, normally with a seismic mass on its free end. The device is placed on a vibration table, whose vibration parameters are set. The relevant differential equation was composed, and an analytic solution describing the required dependencies was obtained. To validate the proposed model, we created a single-crystal bimorph by annealing a lithium niobate (LiNbO3) wafer in air to promote Li out-diffusion and formation of a bidomain ferroelectric structure, i.e. two oppositely polarized domains within the plate (the so called “headto- head” structure). Such a crystal demonstrates a bimorph-like behavior but does not comprise any interface except for an interdomain wall. Thus, our bimorph is not a commonly used structure, typically consisting of two bonded piezoelectric plates (generally made of PZT piezoceramics), but a homogeneous continuous medium. Being made of a lithium niobate (or lithium tantalate) ferroelectric single crystal, the cantilever sensor or energy harvester demonstrates a strong dependence of the voltage between the electrodes on the bending deformations, with almost totally absent hysteresis and ageing in a wide temperature range. The comparison made between the results of the modeling and the experiment shows that the proposed model is in good agreement with the experiment. We have demonstrated that the vibration sensors based on bidomain single-crystal plates possess an exceptionally high sensitivity. The proposed model can be used to estimate and predict the parameters of vibration sensors, accelerometers and waste energy harvesters based on bidomain ferroelectric crystals. [ABSTRACT FROM AUTHOR]

Purpose: Reliable intraoperative delineation of tumor from healthy brain tissue is essentially based on the neurosurgeon's visual aspect and tactile impression of the considered tissue, which is—due to inherent low brain consistency contrast—a challenging task. Development of an intelligent artificial intraoperative tactile perception will be a relevant task to improve the safety during surgery, especially when—as for neuroendoscopy—tactile perception will be damped or—as for surgical robotic applications—will not be a priori existent. Here, we present the enhancements and the evaluation of a tactile sensor based on the use of a piezoelectric tactile sensor. Methods: A robotic-driven piezoelectric bimorph sensor was excited using multisine to obtain the frequency response function of the contact between the sensor and fresh ex vivo porcine tissue probes. Based on load-depth, relaxation and creep response tests, viscoelastic parameters E1 and E2 for the elastic moduli and η for the viscosity coefficient have been obtained allowing tissue classification. Data analysis was performed by a multivariate cluster algorithm.Results: Cluster algorithm assigned five clusters for the assignment of white matter, basal ganglia and thalamus probes. Basal ganglia and white matter have been assigned to a common cluster, revealing a less discriminatory power for these tissue types, whereas thalamus was exclusively delineated; gray matter could even be separated in subclusters.Conclusions: Bimorph-based, multisine-excited tactile sensors reveal a high sensitivity in ex vivo tissue-type differentiation. Although, the sensor principle has to be further evaluated, these data are promising. [ABSTRACT FROM AUTHOR]

Microelectromechanical systems (MEMS) are micrometre-size systems that are capable of transforming electrical signals to mechanical signals. In this paper, the use of MEMS devices as a method for harvesting waste heat is explored. A background for the technology and methods is discussed and a method proposed for a working device based upon a thermally heated bimorph actuated by waste radiation alone is investigated. A chopper interrupts the radiant energy inducing an oscillation in the bimorph temperature and thus creates a mechanical motion which can be taken advantage of using piezoelectric materials. Difficulties in harvesting radiant energy with this method are highlighted and suggestions for non-passive energy generation are made based on the outlined principles. [ABSTRACT FROM AUTHOR]

High-precision delivery of fluids is an important tool in modern science and technology, and the demand for the precise control of insulin amount in the body of patients with diabetes is increasing. In this study, a novel stick–slip piezoelectric actuator based on a V-shaped driving mechanism is proposed to achieve a large lateral displacement. The actuator stator is fabricated using beryllium and lead zirconate titanate thick films, which form a bimorph. It is based on the stick–slip driving principle and uses the coupled motion of the proposed V-shaped stator to produce a clamping action in the stick phase and a release action in the slip phase. A theoretical structure model based on structural mechanics is proposed, and a simulation analysis is conducted to predict output performance. Experimental results indicate that the slider step displacement is 1.04 μ m under 1 Hz, 100 V p p. The slider speed increases linearly as the driving frequency and voltage increase. The step displacement also increases linearly as the driving voltage increases. A displacement difference of 0.04 μ m exists between forward and reverse motions. A sawtooth-holding wave is proposed to reduce backward displacement, achieving an increased step displacement of 32 %. [ABSTRACT FROM AUTHOR]

Kinetic piezoelectric energy harvesters are used to power up ultra-low power devices without batteries as an alternative and eco-friendly source of energy. This paper deals with a novel design of a lead-free multilayer energy harvester based on BaTiO3 ceramics. This material is very brittle and might be cracked in small amplitudes of oscillations. However, the main aim of our development is the design of a crack protective layered architecture that protects an energy harvesting device in very high amplitudes of oscillations. This architecture is described and optimized for chosen geometry and the resulted one degree of freedom coupled electromechanical model is derived. This model could be used in bistable configuration and the model is extended about the nonlinear stiffness produced by auxiliary magnets. The complex bistable vibration energy harvester is simulated to predict operation in a wide range of frequency excitation. It should demonstrate typical operation of designed beam and a stress intensity factor was calculated for layers. The whole system, without presence of cracks, was simulated with an excitation acceleration of amplitude up to 1g. The maximal obtained power was around 2 mW at the frequency around 40 Hz with a maximal tip displacement 7.5 mm. The maximal operating amplitude of this novel design was calculated around 10 mm which is 10-times higher than without protective layers.

Cu-Al-Ni and Cu-Al-Ni-Mn shape memory alloys are deposited on Kapton polyimide sheets by a physical evaporation technique. Detailed investigations on the morphological, structural and thermal behaviour of the ternary and quaternary alloys are conducted. The developed samples exhibit an increase in martensite structures and decrease in transformation temperatures after Mn additions. Furthermore, the suppression of Cu 3 Al precipitates was evident from XRD analysis. The thermomechanical behaviour was analysed by actuating the bimorphs through Joule heating under varying mechanical loads. Fatigue analysis of the bimorphs reveals a superior performance for Cu-Al-Ni-Mn, exhibiting less than 30% loss in displacement after 15,000 cycles. [ABSTRACT FROM AUTHOR]

Highlights • The approach uses coupled actuators to stimulate the finger in two directions. • This stimulation provides a better user experience than conventional approaches. • Each individual actuator requires only a round surface with a diameter of 2.3 mm. • The lateral actuator was described and designed with a comprehensive model. • The concept of the bimodal tactile display is validated by various experiments. Abstract In this paper, a bimodal tactile display used to stimulate the mechanoreceptors is proposed. The use of tactile displays to provide tactile sensations has become the object of increasing interest in recent years. Most of these displays have only one actuator type to generate the tactile perceptions and the spatial resolution of many displays is too rough for good tactile impression. Hence, for the proposed tactile display, two types of actuators for lateral and vertical (normal) excitation are combined. The resolution of the 4 × 4 array is 2.4 mm. Due to its design concept, the presented display is easily expanded. The normal actuator is based on the reluctance principle and the lateral actuator is based on the piezoelectric effect. This contribution focuses on the design and characterization of the piezoelectric actuator. The lateral actuator is mounted on the normal actuator. This has a significant impact on the design of the piezoelectric actuator. To describe the dynamics of this actuator, a Transfer Matrix Method (TMM) Model is created. The mechanical boundary condition at the connection to the normal actuator is included utilizing discrete elements. The model is validated by experiments. Using the model, the geometry of the actuator elements is designed. For performance tests, several experiments have been carried out. The behavior of the lateral actuator has been analyzed in the two end positions of the normal actuators for different load conditions. In terms of performance, the lateral actuators achieve sufficient deflection, even under high load conditions, using imitation human skin as the contact material and with a weight of 50 g. It is shown in a subject test that the lateral actuator works well under real conditions. A measurement of the combined movement has been performed using a Micro System Analyzer (MSA-100-3D) at different frequencies. [ABSTRACT FROM AUTHOR]

Vertical comb drives are critical for electrostatic optical switches and variable optical attenuators (VOAs), but fabricating vertical comb drives requires the formation of two levels of comb fingers and thus suffers from the difficulty of dealing with the comb-finger alignment. This paper presents a vertical comb drive design and its micro-fabrication method that can realize self-aligned two-level comb fingers. The self-aligned vertical comb fingers are enabled by a novel vertically-elevated flat-end (VEFE) bimorph structure. Both the stator and rotor fingers of the vertical comb drive are formed by the same photomask and the same silicon etching step, which automatically ensures accurate alignment of the stator and rotor fingers. The vertical separation between the stator and rotor is created by the VEFE structure. A 1mm-aperture MEMS mirror with the proposed VEFE comb drive has been fabricated using SOI wafers with buried cavities. The mirror rotates 0.94° at 8 Vdc. The resonant frequency is 1.428 kHz. The MEMS mirror has been assembled into a VOA module. Measurements show that the VOA achieved a dynamic range of 55 dB and an insertion loss of less than 0.4 dB and met the telecommunications standards on shock, vibration and long-term stability. [ABSTRACT FROM AUTHOR]

Origami-inspired fabrication presents an attractive platform for miniaturizing machines: thinner layers of folding material lead to smaller devices, provided that key functional aspects, such as conductivity, stiffness, and flexibility, are persevered. Here, we show origami fabrication at its ultimate limit by using 2D atomic membranes as a folding material. As a prototype, we bond graphene sheets to nanometer-thick layers of glass to make ultra- thin bimorph actuators that bend to micrometer radii of curvature in response to small strain differentials. These strains are two orders of magnitude lower than the fracture threshold for the device, thus maintaining conductivity across the structure. By patterning 2-µm-thick rigid panels on top of bimorphs, we localize bending to the unpatterned regions to produce folds. Although the graphene bimorphs are only nanometers thick, they can lift these panels, the weight equivalent of a 500-nm-thick silicon chip. Using panels and bimorphs, we can scale down existing origami patterns to produce a wide range of machines. These machines change shape in fractions of a second when crossing a tunable pH threshold, showing that they sense their environments, respond, and perform useful functions on time and length scales comparable with microscale biological organisms. With the incorporation of electronic, photonic, and chemical payloads, these basic elements will become a powerful platform for robotics at the micrometer scale. [ABSTRACT FROM AUTHOR]

The development of flexible film/substrate composite systems has emerged as a promising strategy to enhance the functionality of sub-micron NiTi (Nickel–Titanium) thin films. Among potential substrates, polyimide foils offer many advantages as they are lightweight, flexible, and durable. However, the properties and behavior of NiTi films deposited on polyimides remain poorly understood compared to films on traditional substrates. In this work, NiTi films were sputter-deposited simultaneously onto polyimide foils (Kapton) and Si wafers under various conditions. The films' composition, crystalline nature, and morphology were analyzed and compared. The films deposited on polyimide exhibited distinct differences in Ni content (1.0 -4.4 at.% lower), thickness, grain morphology, and crystal structure compared to those deposited on Si. The differences in properties between polyimides and Si (e.g., surface energy, thermal conductivity) induced noticeable effects on NiTi film growth and final structure. These discrepancies can lead to different optical, wetting, superelastic, and shape memory behavior, as demonstrated by the pseudo-two-way shape memory effect observed in only one of the NiTi/Kapton actuators. Our findings highlight the need for further investigations of the interactions between NiTi films and polyimide substrates, which will facilitate the development of sub-micron NiTi-based applications such as wearable electronics. [Display omitted] • Sub-micron Nickel–Titanium films were sputtered on polyimide foils and Si wafers. • NiTi films' Ni content on polymide were 1.0 - 4.4 at.% lower than on the Si wafers. • The films on polyimide were 63–123% of the thickness of films on Si. • Films on polyimide were morphologically and structurally different than films on Si. [ABSTRACT FROM AUTHOR]

Grid capacity, reliability, and efficient distribution of power have been major challenges for traditional power grids in the past few years. Reliable and efficient distribution within these power grids will continue to depend on the development of lighter and more efficient sensing units with lower costs in order to measure current and detect failures across the grid. The objective of this paper is to present the development of a miniature piezoelectric-based sensor for AC current measurements in single conductors, which are used in power transmission lines. Additionally presented in this paper are the thermal testing results for the sensor to assess its robustness for various operating temperatures.

Piezoelectric unimorph deformable mirrors offer a cheap solution to adaptive optics, with mass production capability. However, standard solutions have significant drawbacks: (i) the static shape is sensitive to the temperature, and (ii) the low structural damping limits the control bandwidth, because of the interaction between the shape control and the vibration modes of the mirror. This paper discusses how these two problems may be alleviated by using a mirror covered with an array of actuators working in d31 mode on the back side and a ring of transducers (actuators and sensors) on the front side, outside the pupil of the mirror.

Gait stability of the walking robot has great influence on the many functional features related to walking robots, from mechanical construction to control algorithms and generating steps. The goal of the presented research was a development of the concept of hexa-quad bimorph walking robot. Results of the performed static stability analysis allowed the initial verification of the mathematical model and provided information about the design adequacy and the possibilities of controlling the machine. The research involved analysing the characteristic postures of the robot focused on retaining static stability. To achieve this objective the mathematical model was made to determine the centre of gravity for the robot by using Denavit-Hartenberg notation. On this basis the simulation model was created in Matlab Simulink environment, where the described analyses were conducted. Based on the obtained results, the initial model error was determined at approximately 3%. It was also established that the centre of gravity for the design was not significantly different from the effective centre of gravity for the robot. This made it possible to achieve static stability through adequate alignment of the legs in nearly every robot configuration.

Micro-electro-mechanical system (MEMS) mirrors are widely used for optical modulation, attenuation, steering, switching and tracking. In most cases, MEMS mirrors are packaged in air, resulting in overshoot and ringing upon actuation. In this paper, an electrothermal bimorph MEMS mirror that does not generate overshoot in step response, even operating in air, is reported. This is achieved by properly designing the thermal response time and the mechanical resonance without using any open-loop or closed-loop control. Electrothermal and thermomechanical lumped-element models are established. According to the analysis, when setting the product of the thermal response time and the fundamental resonance frequency to be greater than Q/2π, the mechanical overshoot and oscillation caused by a step signal can be eliminated effectively. This method is verified experimentally with fabricated electrothermal bimorph MEMS mirrors. [ABSTRACT FROM AUTHOR]