Unimorph Piezoelectric Energy Harvester Research Articles

Effect of scandium concentration on the performances of cantilever based AlN unimorph piezoelectric energy harvester with silicon nitride substrate

Microelectromechanical systems (MEMS) offer its ability to sense, control and actuate on sub-micron scale and exhibit its effect on macro scale. To implement any specific MEMS system, small, efficient and long-lifespan micro power sources are required. Piezoelectric energy harvester (PEH) along with radioactive source is one of the most promising approaches to harness electrical energy at micro to millimeter range. In this report, a scandium (Sc) doped Aluminium Nitride (AlN) unimorph piezoelectric energy harvester has been demonstrated. Unimorph piezoelectric layer is built on Silicon Nitride (Si3N4) substrate platform that act as cantilever beam and that can be vibrated by inbuilt radioactive system. In particular, Si3N4 as cantilever material and the impact of Sc doping concentration on electrical and mechanical properties of AlN piezoelectric thin film materials have been studied in MATLAB simulation platform. Results obtained from numerical study suggests that the proposed energy harvester model composed of AlScN unimorph piezoelectric (with 10% Sc doping concentration, Sc-10%) layer and Si3N4 cantilever can yield a maximum power output of ~ 19.33 μW and overall mechanical energy conversion efficiency of ~ 91.07%. These are the maximum output power and mechanical energy conversion efficiency numerically obtained from Sc doped AlN piezoelectric energy harvester systems to the best of our knowledge.

Electromechanical simulation and analysis of perovskite piezoelectric ‎unimorph cantilever nanogenerator with interdigitated electrodes in ‎vibration energy harvesting application

This paper addresses a unimorph cantilevered piezoelectric nanogenerator having high ‎output power through vibrational energy harvesting that is simulated using finite element ‎method (FEM). The simulations are done for three types of perovskite piezoelectric ‎materials including PZT, PMN-PT and MAPbI3. The interdigitated electrodes were ‎exploited‏ ‏to obtain longitudinal vibration mode using d33 mode of piezoelectric layer during ‎the bending of nanogenerator structure. The presented structure consists of a piezoelectric ‎nanolayer with gold interdigitated electrodes on it, which is placed on a flexible PET ‎polymeric substrate. To encapsulate the piezoelectric layer, an SU-8 epoxy is placed over ‎the surface. The poling process is also simulated by applying high voltage through IDs to ‎piezoelectric layer. Generally, the electric potential distribution of the piezoelectric layer ‎must be performed by applying mechanical loadings. Then the output voltage, ‎power for free vibrations and base excitation (0.25-2g) of the nanogenerator at resonance ‎frequency are investigated. The resonance frequency of the PZT, PMN-PT, and MAPbI3 were ‎calculated to be 549 Hz, 560.5 Hz and 631 Hz, respectively. We found that PZT ‎piezoelectric materials yields maximum output voltage and electrical power values of 91.69 ‎V and 350 mW which shows better performance in vibrational energy harvesting ‎application. In comparison, the results of the simulation implied a good agreement with ‎other experimental studies. The unimorph piezoelectric energy harvester system generates ‎high voltage and output power in response to sub-kilohertz ambient vibration‎.‎‎

Nonlinear analysis of unimorph and bimorph piezoelectric energy harvesters with flexoelectricity

This work investigates the nonlinear behaviors of nanoscale unimorph and bimorph piezoelectric energy harvesters under harmonic base excitations. In the modeling, the energy harvesters are based on cantilevered beams with tip mass, and the effects of geometric nonlinearity, inertial nonlinearity and flexoelectricity are considered. Based on the Hamilton’s principle and the theory of flexoelectricity, the nonlinear coupled governing equations of the system are derived. Galerkin’s method is employed to discrete the nonlinear equations, which are then numerically solved. Results indicate that geometric nonlinearity leads to a typical hardening nonlinear behavior of the frequency response curve while inertial nonlinearity leads to a softening behavior in contrast. In addition, influences of the tip mass and amplitude of the base acceleration on the harvesters’ electrical outputs are examined. By comparing lead zirconate titanate (e.g. PZT-5H) and polyvinylidene difluoride (i.e. PVDF) as the material for piezoelectric layers, it is found that the performance enhancement of PVDF energy harvester due to flexoelectricity is more prominent. It is also interesting to observe the flexoelectricity-induced size-dependent voltages. This work compares the performance of energy harvesters with various structures and materials, which will provide guidance for the design and optimization of piezoelectric energy harvesters utilizing flexoelectricity.

Design of a Unique Unimorph and Bimorph Cantilever Energy Harvesting System

Piezoelectric energy conversion has received considerable attention for vibration-to-electric energy conversion over the past decade. A typical piezoelectric energy harvester is a unimorph or a bimorph cantilever located on a vibrating host structure. This paper presents a comparison between unimorph and bimorph cantilever beam having a number of segmented PMN-PT piezo-elements on the input and output power. The numerical simulation was carried out by applying the finite element analysis (FEA) using COMSOL multi-physics software in order to predict output voltage and power over a frequency range of 60–200 Hz for the first resonant frequencies. The simulation results show maximum output voltage and power harvested of 7.38 V and 135.73 μW, respectively, by the unimorph piezoelectric energy harvester at resonant frequency value of 84 Hz with electromechanical coupling factor (ke) of 77.29%. These results highlight that the highest value of the output electrical power can be obtained when the piezoelectric element is attached on the top of a clamped end of a cantilever piezoelectric beam. Moreover, in an unimorph or bimorph cantilever beam system, increasing the number of piezoelectric elements results in a higher resonant frequency shift and significantly decreasing in the harvested power.

Effect of damage and support damping mechanisms on unimorph piezoelectric energy harvester

Damping plays a critical role in power generation by piezoelectric energy harvesting, and yet there is a lack of sensitivity studies on different sources of damping. In this paper, two damping sources in unimorph piezoelectric energy harvesters, namely support loss and damage damping mechanisms, are experimentally investigated. Variations of the power generation are evaluated with respect to the sources of damping. Accordingly, the power generation model is developed according to the experimental results in this work and using a single degree of freedom analytical model. This study focuses on the debonding effect, as an internal damping source, and support loss, as a critical source of external energy dissipation. The results show that the debonding reduces the output power dramatically at resonance and, particularly, at anti-resonance frequencies. Moreover, investigation of the support loss shows that the material of clamp as well as installation torque have an impact on the support loss and, consequently, affect the output power.

Enhancement of vibration based piezoelectric energy harvester using hybrid optimization techniques

MEMS unimorph piezoelectric vibration energy harvester is designed and optimized based on Hybrid Optimization techniques [genetic algorithm (GA), bat algorithm (BA), grey wolf optimization (GWO), hybrid bat algorithm tuned genetic algorithm (HBAGA) and hybrid grey wolf optimizer tuned genetic algorithm (HGWOGA)] for performance improvement. In this research work, unimorph piezoelectric vibration energy harvester is modeled using analytical equations, which is derived to determine the amount of voltage and power, harvested from the piezoelectric energy harvester. These derived analytical equations are used as the fitness function of Hybrid optimization techniques, which is a design optimization technique to improve the amount of power and voltage harvested from the unimorph piezoelectric energy harvester, by optimizing the parameters and a comparison is made within these techniques. The effects of geometry optimization on natural frequency and stress are also studied. The un-optimized results are compared with the optimized results (GA, BA, GWO, HBAGA and HGWOGA) and the results obtained, proves that, the optimized results are more efficient in all aspects, which has significantly improved the efficiency of the piezoelectric harvester to a larger extent. Finally, a comparison is made within the optimization techniques and HGWOGA has proved to be more efficient than HBAGA, GWO, BA, GA and this work of MEMS piezoelectric vibration energy harvester is simulated using the MATLAB software.

Effect of elastic modulus of cantilever beam on the performance of unimorph type piezoelectric energy harvester

Piezoelectric energy harvesting is a technique that can utilize ambient vibration energy to generate useful electrical energy, which is promising for powering small-scale autonomous devices such as sensors for wearable, biomedical, and industrial applications. Typically, cantilever-type piezoelectric energy harvesters (PEHs) are operated under resonance condition to achieve the maximum output power at low frequency stimuli. Along with resonance matching, it is also necessary to optimize the PEH configuration with high electromechanical properties for the efficient energy conversion. The purpose of this study is to investigate the effect of the elastic modulus of the passive layer in the cantilever structured PEH on the electromechanical properties and thus harvesting performance. In this regard, two unimorph type PEHs having the identical geometry, piezoelectric properties, and proof mass but with different elastic modulus (55 GPa and 97 GPa) of Ti alloy-based passive layers were fabricated and their output performance was compared under the same acceleration amplitude excitation stimuli. The PEH with the smaller elastic modulus passive layer exhibited almost 53% improvement in the maximum power than that with the higher elastic modulus passive layer, which is attributed to a smaller mechanical damping ratio, higher quality factor, and larger vibration amplitude.

Analysis of delamination of unimorph cantilever piezoelectric energy harvesters

Unimorph piezoelectric energy harvesters are typically a unimorph cantilever beam located on a vibrating host structure. Delamination is one of the major failure modes of such unimorph cantilevers and therefore is studied in this article. The delaminated cantilever unimorph is modeled with one through-width crack using four Euler beams connected at delamination edges. The governing equations, the corresponding boundary conditions, and the kinematic continuity conditions are derived based on the Hamiltonian principle. The solutions of the voltage and power output for the present model are derived. The influence of the position and the length of the delamination, frequency of input base excitation, and load resistance on the voltage and power output are discussed in detail. The results show that delamination in the unimorph of the energy harvester will impressively decrease the voltage and power outputs. Influences of the delamination located at the free end of the cantilever are more obvious. For a given active length of the delaminated cantilever energy harvester, it is useful to increase the overall length of the cantilever to obtain a higher voltage and power outputs.

Design and Optimization of Piezoelectric MEMS Vibration Energy Harvesters Based on Genetic Algorithm

Low-power electronic applications are normally powered by batteries, which have to deal with stringent lifetime and size constraints. To enhance operational autonomy, energy harvesting from ambient vibration by microelectromechanical systems (MEMS) has been identified as a vivid solution to this universal problem. This paper proposes an automated design and optimization methodology with minimum human efforts for MEMS-based piezoelectric energy harvesters. The analytic equations for estimating the harvested voltage by the unimorph piezoelectric energy harvesters are presented with their accuracy validated by using the finite element method (FEM) simulation and prototype measurement. Thanks to their high accuracy, we use these analytic equations as fitness functions of genetic algorithm (GA), an evolutionary computation method for optimization problems by mimicking biological evolution. Our experimental results show that the GA is capable of optimizing multiple physical parameters of piezoelectric energy harvesters to considerably enhance the output voltage. This harvesting efficiency improvement is also desirably coupled with physical size reduction as preferred for the MEMS design process. To demonstrate capability of the proposed optimization method, we have also included a commercial optimization product (i.e., COMSOL optimization module) in our comparison study. The experiments show that our proposed GA-based optimization methodology offers higher effectiveness in the magnitude improvement of harvested voltage along with less runtime compared with the other optimization approaches. Furthermore, the effects of geometry optimization on mechanical and electrical properties (e.g., resonant frequency, stiffness, and internal impedance) are also studied and an effective solution to producing maximum power from unimorph piezoelectric harvesters is proposed.

Closed-form solutions for forced vibrations of piezoelectric energy harvesters by means of Green’s functions

In this article, the closed-form solutions are obtained for the forced vibrations of cantilevered unimorph piezoelectric energy harvesters. A tip mass is attached at the free end, and the moment of its inertia to the fixed end is considered. Timoshenko beam assumptions are used to establish a coupled electromechanical model for the harvester. Two damping effects, transverse and rotational damping effects, are taken into account. Green’s function method and Laplace transform technique are used to solve the coupled electromechanical vibration system. The conventional case of a harmonic base excitation is considered, and numerical calculations are performed. The present model is validated by comparing its predictions with the existing data, the experimental results, and the finite element method solutions. The influences of shear deformation and rotational inertia on the predictions are discussed. The effect of load resistance on the electrical power is studied, and the optimal load resistances are obtained. Ultimately, the optimal schemes are proposed to improve electricity generation performance for the soft piezoelectric materials: PZT-5A/5H.

Shape Design Optimization of Unimorph Piezoelectric Cantilever Energy Harvester

The most promising method for micro scale energy scavenging is via vibration energy harvesting which converts mechanical energy to electrical energy. Using piezoelectric cantilevers is the most common method for vibration energy harvesting. Changing the shape of the cantilevers can lead to changing the generated output voltage and power. In this work vibration energy harvesting via piezoelectric resonant unimorph cantilevers is studied and new design for obtaining more efficient piezoelectric energy harvester is suggested. This study provides comprehensive analysis of the output voltage relationships and deducing a considerable precise rule of thumb for calculating resonance frequency in cantilever-type unimorph piezoelectric energy harvesters using Rayleigh method. The analytical formula, is then analyzed and verified by FEM simulation in ABAQUS. The analytical data was found to be very close to simulation data. A key finding is that among all the unimorph trapezoidal V-shaped cantilever beams with uniform thickness, the triangular tapered cantilever, can lead to highest resonance frequency and by increasing the ratio of the trapezoidal bases, the resonance frequency decreases. These new findings provide guidelines on system parameters that can be manipulated for more efficient performance in different ambient source conditions.

Piezoelectric materials for bistable energy harvester: A comparative study

ABSTRACTThis paper deals with the potential of various lead-free piezoelectric materials for energy harvesting. The performance of these materials is simulated for unimorph bistable piezoelectric energy harvester. The finite element method considering first-order shear deformation theory is used to model the system. The energy harvesting potential of bistable system (Non-linear) is compared with its linear counterpart. The results depict that the mean power density is almost 100% higher in case of bistable system. K0.5Na0.5NbO3-LiSbO3 (KNN-LS) family exhibited better performance than the conventional lead-based piezoelectric material lead zirconate titanate (PZT). The mean power density of K0.5Na0.5NbO3-LiSbO3-CaTiO3 (2 wt.%) is reported to be 65% higher than PZT.

An analytical model for nanoscale unimorph piezoelectric energy harvesters with flexoelectric effect

Harvesting mechanical vibration energy in the surrounding medium is an attractive way to provide sources for self-powered micro and nano devices. At nanoscale, the properties of materials exhibit strong scaling with size. In this paper, an analytical model incorporating flexoelectric effect is developed for nanoscale unimorph piezoelectric energy harvesters with arbitrary length and position of piezoelectric layer and proof mass. The governing equation is derived based on the Hamiltonian principle. Approximated closed-form solutions for voltage out, power output and optimal load resistance are obtained. Results show that the influence of flexoelectric effect on voltage output and power output is significant, for small thickness of piezoelectric layer. In some cases, the maximum power output of the model with flexoelectric effect is almost twelve times that of classical model which only includes piezoelectric effect. Attaching the piezoelectric layer on the clamped end of the beam can get the largest power output. To obtain higher power output and conversion efficiency, especially to fit the vibration environment, attached proof mass on the end of cantilever energy harvesters is a useful way.

Experimental study and analysis of unimorph piezoelectric energy harvester with different substrate thickness and different proof mass shapes

An experimental study of unimorph piezoelectric energy harvester with proof mass has been presented in this paper. The placement of the proof mass shift the operating frequency of an energy harvester to a lower range. The main advantage of placing a proof mass over an energy harvester other than frequency shift is to maximize the output power generation. Also analysis of an energy harvester with different substrate thickness is performed to find its effect on performance of energy harvester. The experimental results reveals that presence of proof mass and thickness of substrate affects the power generation of piezoelectric energy harvester.

Analytical simulation of the cantilever-type energy harvester

This article describes an analytical model of the cantilever-type energy harvester based on Euler–Bernoulli’s beam theory. Starting from the Hamiltonian form of total energy equation, the bending mode shapes and electromechanical dynamic equations are derived. By solving the constitutive electromechanical dynamic equation, the frequency transfer function of output voltage and power can be obtained. Through a case study of a unimorph piezoelectric energy harvester, this analytical modeling method has been validated by the finite element method.

Parametric analysis of multilayered unimorph piezoelectric vibration energy harvesters

The use of a multilayer piezoelectric cantilever beam for vibration-based energy harvesting applications has been investigated as an effective technique to increase the harvested electrical power. It has been shown that the multilayered energy harvester performance is very sensitive to the number of layers and their electrical connection due to impedance variations. The objective of this work is to suggest a comprehensive mathematical model of multilayered unimorph piezoelectric energy harvester allowing analytical solution for the harvested voltage and electrical power. The model is used to deeply investigate the influence of different parameters on the harvested power. A distributed-parameter model of the harvester using the Euler–Bernoulli beam theory and Hamilton's principle is derived. Gauss's law is used to derive the electrical equations for parallel and series connections. A closed-form solution is proposed based on the Galerkin procedure and the obtained results are validated with a finite element 3D model. A parametric study is performed to ascertain the influence of the load resistance, the thickness ratio, the number of piezoelectric layers on the tip displacement and the electrical harvested power. It is shown that this model can be easily used to adjust the geometrical and electrical parameters of the energy harvester in order to improve the system's performances. In addition, it is proven that if one of the system's parameter is not correctly tuned, the harvested power can decrease by several orders of magnitude.

Preloaded freeplay wide-bandwidth low-frequency piezoelectric harvesters

We propose a technique for increasing the bandwidth of resonant low-frequency (<100 Hz) piezoelectric energy harvesters based on the modification of the clamped boundary condition of cantilevers, termed here as preloaded freeplay boundary condition. The effects of the preloaded freeplay boundary condition are quantified in terms of the fundamental frequency, frequency response, and power output for two beam configurations, namely, classical cantilevered bimorph piezoelectric energy harvester and zigzag unimorph piezoelectric energy harvester. A comparative analysis was performed between both the harvesters to empirically establish the advantages of the preloaded freeplay boundary condition. Using this approach, we demonstrate that the coupled degree-of-freedom dynamics results in an approximate 4–7 times increase in half-power bandwidth over the fixed boundary condition case.

Optimal piezoelectric beam shape for single and broadband vibration energy harvesting: Modeling, simulation and experimental results

Harvesting energy from the surroundings has become a new trend in saving our environment. Among the established ones are solar panels, wind turbines and hydroelectric generators which have successfully grown in meeting the world’s energy demand. However, for low powered electronic devices; especially when being placed in a remote area, micro scale energy harvesting is preferable. One of the popular methods is via vibration energy scavenging which converts mechanical energy (from vibration) to electrical energy by the effect of coupling between mechanical variables and electric or magnetic fields. As the voltage generated greatly depends on the geometry and size of the piezoelectric material, there is a need to define an optimum shape and configuration of the piezoelectric energy scavenger. In this research, mathematical derivations for unimorph piezoelectric energy harvester are presented. Simulation is done using MATLAB and COMSOL Multiphysics software to study the effect of varying the length and shape of the beam to the generated voltage. Experimental results comparing triangular and rectangular shaped piezoelectric beam are also presented.

Finite element analysis of vibration energy harvesting using lead-free piezoelectric materials: A comparative study

In this article, the performance of various piezoelectric materials is simulated for the unimorph cantilever-type piezoelectric energy harvester. The finite element method (FEM) is used to model the piezolaminated unimorph cantilever structure. The first-order shear deformation theory (FSDT) and linear piezoelectric theory are implemented in finite element simulations. The genetic algorithm (GA) optimization approach is carried out to optimize the structural parameters of mechanical energy-based energy harvester for maximum power density and power output. The numerical simulation demonstrates the performance of lead-free piezoelectric materials in unimorph cantilever-based energy harvester. The lead-free piezoelectric material K0.5Na0.5NbO3-LiSbO3-CaTiO3 (2 wt.%) has demonstrated maximum mean power and maximum mean power density for piezoelectric energy harvester in the ambient frequency range of 90–110 Hz. Overall, the lead-free piezoelectric materials of K0.5Na0.5NbO3-LiSbO3 (KNN-LS) family have shown better performance than the conventional lead-based piezoelectric material lead zirconate titanate (PZT) in the context of piezoelectric energy harvesting devices.

Unimorph and bimorph piezoelectric energy harvester stimulated by β-emitting radioisotopes: a modeling study

We use energy methods and lumped-element modelling in the analysis and optimization of a miniaturized aluminum nitride based piezoelectric energy harvester which utilizes tritiated silicon as an uninterrupted energy source. Tritiated silicon serves as a radioisotope source which emits energetic β particles that results in an electrostatic force between the radioactive source and collector that traps the emitted particles. The generated electrostatic force will drive the charging and actuating cycles of the piezoelectric cantilever leading to a continuous charge---discharge cycles, thus inducing vibrations in the piezoelectric cantilever. The energy generated from the piezoelectric thin-film is appropriately rectified and stored to provide continuous and uninterrupted electrical power to a low-power devices. The modelled results have been benchmarked against available experimental data for a unimorph piezoelectric harvester with very good agreement. Furthermore, the model was applied to a bimorph piezoelectric harvester, showing that the output power can be doubled in relation to a unimorph design. Moreover, the model accounts for the entire range of design and operating factors such as the ambient medium and associated damping losses, current leakage, and device scaling.