Efficiency Of Piezoelectric Energy Harvesters Research Articles

Investigation and Numerical Simulation of Different Piezoelectric Bimorph Cantilever Designs for Energy Harvesting

The study investigates the dynamic performance and energy harvesting efficiency of different cantilever configurations using numerical simulations. It examines factors such as material properties, geometrical parameters, and excitation conditions to optimize the design for enhanced energy harvesting capabilities. The research contributes to understanding how different cantilever designs affect the overall performance and efficiency of piezoelectric energy harvesters. Vibrational energy harvesters, also known as MEMS, have become popular due to their efficiency and ease of inclusion in microsystems. COMSOL Multiphysics was used to simulate six different forms of piezoelectric bimorph cantilevers for energy harvesting. Designs were analyzed, with each design having a distinct arrangement of proof masses. Design 01 had a rectangular cantilever with a proof mass connected to its top surface, Design 02 used a rectangular cantilever, Design 03 used a novel approach, Design 04 used a trapezoidal cantilever, and Design 05 preserved the trapezoidal form but moved the proof mass to the structure's base. Design 06 successfully completed the trapezoidal cantilever. The study found that design 04 had a significant advantage in power production efficiency at higher resistor values, surpassing design 01 in power output. The use of these varied designs allows for an exhaustive examination of piezoelectric bimorph cantilever configurations, potentially leading to insights that may enhance energy harvesting effectiveness in various applications.

Effects of Mechanical and Electrical Topologies on Piezoelectric Stacked Energy Harvesting in Vehicle Suspensions

The choice of mechanical and electrical topologies can affect piezoelectric energy harvesting efficiency, but the problem of achieving high-efficiency energy conversion in energy harvesters stacked as cantilevers has not been perfectly solved. This study focuses on the topology of piezoelectric elements in a stacked vehicle suspension vibration energy harvesting device. Through theoretical analysis, the stress expressions of the excited and driven elements are derived. The stress of the piezoelectric elements is affected by the positions of the connection and excitation points. A stress model was established for a four-piece piezoelectric element connected by a thin light rod in ANASYS. The simulation results show that the average stress in the piezoelectric bending element model is maximum when the excitation and connection points are located at both ends of the free end. Compared with the middle position of the free end of the piezoelectric element, the average stress of the model is increased by 92.904%. Considering the difference in voltage generated by piezoelectric elements, four kinds of electrical topology are designed and analyzed experimentally. When the driven elements are connected in parallel and then connected in series with the excited element, the output power varied the least with the change of load resistance. The system produces a high power and offers a wide selection of load resistors. When the load is 26 kΩ, a single set of four piezoelectric elements produces 86.407 mW of output power.

Improving energy harvesting from low-frequency excitations by a hybrid tri-stable piezoelectric energy harvester

This paper presents the design of a novel hybrid tri-stable piezoelectric energy harvester (HTPEH) that improves the energy harvesting efficiency of piezoelectric energy harvesters operating at low frequencies. The proposed HTPEH is an extension of a conventional tri-stable cantilever piezoelectric energy harvester with an elastic base (TPEH + EB), and it incorporates vertical and rotational elastic amplifiers that are installed between the mass block at the left end of a cantilever beam and the left side of a U-shaped frame to enhance the system's nonlinear characteristics. By utilizing Hamilton's principle, a HTPEH's nonlinear electromechanical equation is formulated, and the harmonic balance method is used to obtain analytical solutions for the displacement amplitude, voltage amplitude, and power amplitude. The study investigates the effects of various parameters, including the elastic amplifier-to-base stiffness ratio and elastic amplifier-to-piezoelectric cantilever beam mass ratio on the energy harvesting performance of the HTPEH. The results indicate that the displacement and voltage amplitude of the HTPEH exhibit two peaks as the external excitation frequency increases, and adjusting the relative mass and stiffness between the elastic amplifier and the piezoelectric cantilever beam can alter the frequency band interval where the two response peaks of the system are located. This allows the HTPEH to enter inter-well motion at low-level external excitation, resulting in high output power. The HTPEH outperforms the TPEH + EB in terms of energy harvesting efficiency under low-frequency environmental excitation.

Dynamic Characteristic Analysis of Tri-Stable Piezoelectric Energy Harvester with Double Elastic Amplifiers

In order to further improve the vibration energy harvesting efficiency of piezoelectric energy harvester under low frequency environmental excitation, this paper, based on the traditional magnetic tri-stable piezoelectric energy collector model, proposes a tri-stable piezoelectric energy harvester (TPEH+DEM) model with two elastic amplifiers which are installed between the U-shaped frame and the base and between the fixed end of the piezoelectric cantilever beam and the U-shaped frame respectively. Based on Hamilton principle, the motion equation of electromechanical coupling of TPEH+DEM system is established, and the analytical solutions of displacement, output voltage and power of the system are obtained by harmonic balance method. The effects of the mass of elastic amplifier, spring stiffness, magnet spacing and load resistance on the dynamic characteristics of energy harvesting of TPEH+DEM system are analyzed. The result shows that there are two peaks in the response output power of TPEH+DEM system in the operating frequency range. By adjusting the mass and stiffness of the elastic amplifier reasonably, the system can move into the inter-well motion under low external excitation intensity, and produce high output power. Compared with the traditional model which only has an elastic amplifier on the base of piezoelectric energy harvester, TPEH+DEM model has better energy harvesting performance under low frequency and low intensity external excitation.

A Clockless Synergistic Hybrid Energy Harvesting Technique With Simultaneous Energy Injection and Sampling for Piezoelectric and Photovoltaic Energy

In this paper, a mutually synergistic hybrid energy harvesting (SHEH) circuit with both AC and DC energy harvesting capability is proposed. Within the proposed hybrid harvester, the vibration period of the piezoelectric transducer (PZT) is served as the switching signal for photovoltaic (PV) energy harvesting so that a dedicated clock generator is saved. Meanwhile, during the sampling phase, a small portion of the PV energy is injected into the PZT as an investment, which enhances the damping force and charge extraction of the PZT. Theoretically, the total synergistically extracted power from the proposed hybrid harvester is more than the sum of the power obtained from each transducer independently. The proposed SHEH circuit is fabricated with a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process. The buck-boost converter with zero-current switching control achieves a peak efficiency of 82.8%, and the maximum efficiency of piezoelectric energy harvesting can reach 4.5 times that of the full-bridge rectifier.

Four-point bending piezoelectric energy harvester with uniform surface strain toward better energy conversion performance and material usage

Improving the energy conversion efficiency of piezoelectric energy harvesters is of great importance, and one approach is to make more uniform use of the working material by ensuring a uniform strain state. To achieve better performance, this paper presents a four-point bending piezoelectric energy harvester with extensive investigation and modeling to identify the influential parameters. An electromechanical analytical model is presented and verified by experimental data. The frequency-domain method extracts the solutions for a general time-variable force and impact. Four-point bending is compared with the standard cantilever harvesters regarding voltage generation, mechanical strain, and figure of merit. Strain contours are analyzed and interpreted for this innovative approach, and the power generation by the optimal resistance load is studied. Dimensionless parameters are introduced and investigated to find the optimal operating conditions for the four-point bending harvester. Finally, the four-point bending performance and the best figure of merit are discussed with a view to the long-term fatigue life of the harvester. The results show that in the best four-point bending energy conversion conditions; the energy conversion coefficient is more than three times higher than that of typical cantilever energy harvesters. The results also illustrate that the axial strain experienced in a standard cantilever harvester is more than three times higher than that of the four-point bending harvester, suggesting the latter device may have favorable fatigue performance. Overall, the presented piezoelectric harvester has improved energy conversion efficiency and experiences a reduced and uniform surface strain, making it appropriate for high-efficiency energy harvesting systems.

Energy Harvesting from Fluid Flow Using Piezoelectric Materials: A Review

Energy harvesting from piezoelectric materials is quite common and has been studied for the past few decades, but, recently, there have been a lot of new advancements in harnessing electrical energy via piezoelectric materials. In this regard, several studies were carried out in electrochemistry and fluid flow. Furthermore, consideration of productive and valuable resources is important to meet the needs of power generation. For this purpose, energy harvesting from fluids such as wind and water is significant and must be implemented on a large scale. So, developing self-powering devices can resolve the problem like that, and piezoelectric materials are gaining interest day by day because these materials help in energy generation. This review paper discusses different techniques for harnessing energy from fluid flows using piezoelectric materials. In addition, various vibration-based energy-harvesting mechanisms for improving the efficiency of piezoelectric energy harvesters have also been investigated and their opportunities and challenges identified.

Performance optimization and broadband design of piezoelectric energy harvesters based on isogeometric topology optimization framework

Energy harvesting is attracting considerable attention in devices that cannot replace exhausted batteries, where improving the energy harvesting efficiency of piezoelectric energy harvesters (PEHs) through different optimization methods is always a research hotspot. This paper proposes an isogeometric topology optimization framework to implement the simultaneous optimization of fiber angles and piezoelectric material and reveal the feasibility of broadband design for PEHs. We deduce the isogeometric formulation of PEHs based on Kirchhoff plate theory and Hamilton's principle. The optimization formulations are established with minimum energy factor or maximum output power considered, and the distributions of fiber angles and piezoelectric material are respectively defined by the Heaviside Penalization of Discrete Material Optimization (HPDMO) model and the Piezoelectric Material with Penalization (PEMAP) model. The numerical results show that there is only a slight difference in the optimized designs of fiber angles between the static load and harmonic load when the objective function is the minimum energy factor. Furthermore, taking maximum output power as the objective function, resistance has a substantial effect on the optimized distributions of fiber angles and piezoelectric material, and there is an optimal resistance making the output power of the optimized design increase 9 times compared with the initial model. More important, by combining the designability of composite material, the proposed method is extended to the broadband design of PEHs. It is concluded that the optimized design can not only generate two resonance peaks in the predetermined frequency range but also the second-order output power amplitude is 14 times higher than that of the benchmark model.

Piezoelectric Energy Harvesting from Roadways under Open-Traffic Conditions: Analysis and Optimization with Scaling Law Method

Piezoelectric energy harvesting from roadways, which converts ambient vibration energy of roads into electric energy, has a wide range of potential applications in intelligent transportation systems. On-site open-traffic tests revealed that energy harvested by piezoelectric energy harvester (PEH) units embedded in roadways is far less than the value in laboratories, which may be because the parameters of traffic flow load (frequency, distribution, wave shape, etc.) and the road structure are significantly different from the pre-established conditions in laboratories or even on-site tests with only one vehicle passing. To address this issue, an analytical model for piezoelectric energy harvesting from roadways under open-traffic conditions was proposed to examine the mechanical response of the road structure and the electrical performance of the stack PEH units embedded in the road. The influence of all parameters in the energy-harvesting system was then obtained with the scaling law method, revealing that the energy harvested by PEH units is determined by the energy coefficient, the system’s intrinsic parameter, normalized parameters of roadways, and the normalized embedded position of PEH units. It is found that that the energy-harvesting system’s intrinsic parameter should be approximately 0.8 to ensure maximum energy-harvesting efficiency. Meanwhile, the pavement with lower bending stiffness and higher linear density while the foundation with small stiffness and smaller damping coefficient would be more suitable for energy harvesting. Furthermore, the lateral embedded position of PEH units should be carefully chosen, since the units embedded in an optimal position can harvest three times more than that embedded in other positions. The concise criteria presented in this study will be used as a reference not only for material selection, dimension optimization, and embedded positions determination of PEH units but also for choosing of the optimal roadways to achieve maximum piezoelectric energy harvesting efficiency under open-traffic conditions.

Tuning the resonance frequency of piezoelectric energy harvesters by applying direct current electric field on piezoelectric elements

Different from previous strategies utilized to improve the energy conservation efficiency of piezoelectric energy harvesters (PEHs) from the environment, by broadening the frequency-bandwidth of energy harvesters using a specifically designed structure or tuning their resonance frequency (RF) through changing the geometrical/dynamical constraints, we report a method—by applying a direct current (DC) electric field on piezoelectric elements—to tune the RF of PEH based on the phenomenon that the elastic parameters of piezoelectric material are related to its electric field boundary condition. The results of a confirmatory experiment revealed that with a pre-loading DC electric field of −0.5 to 0.75 kV/mm, the RF of a piezoelectric cantilever energy harvester can be tuned from 144 to 156 Hz. The effectiveness of this strategy was further verified by comparing the energy conservation output of the PEH at a frequency that deviates from its RF, and at the same frequency, with pre-loading DC electric field adjustment.

Ultrahigh augmentation of flexible composite-based piezoelectric energy harvesting efficiency via polymer-impregnated nanoparticles network within 3D cellulose scaffold

In the past decade, many flexible piezoelectric energy harvesters (PEHs) that can convert ambient mechanical energy into electrical energy have been developed, which provides a sustainable power source for wearable/implantable devices and Internet of Things (IoTs) applications. However, the performance of flexible composite-type PEHs should be further optimized to meet the standard for future practical applications. Herein, we present a powerful strategy for high-performance piezoelectric energy harvesting with poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE))-impregnated BaTiO3 nanoparticles network within 3-dimensional (3D) cellulose scaffold. We propose three methodologies to precisely adjust the microscopic morphology of the organic-inorganic hybrid piezoelectric composites. The construction of methyl cellulose scaffold results in effective stress transfer with high mechanical flexibility as well as dramatically enhanced energy harvesting output. When the cellulose content is 3 wt%, the optimal energy harvesting performance is obtained, which shows the power density of 42 μW/cm3, which is nearly 800% higher than that of the conventional flexible piezoelectric composites previously reported. Throughout the finite-element simulation and mechanical property quantification, the highly augmented energy harvesting capability of our optimal composite structure is determined to stem from the stress-enforced characteristics. Given the ease of fabrication and scalability, this work opens up the way for the development of flexible and high-performance energy harvesting applications.

Application of the meta-substrates for power amplification in rotary piezoelectric energy harvesting systems: Design, fabrication and testing

In this paper we numerically and experimentally investigate a new proposal of utilizing the auxetic meta-structure concepts to enhance the efficiency of piezoelectric energy harvesters in rotating systems. The proposed energy harvester is designed to be installed on the freight train axel to provide necessary power for the self-powered sensors. The harvester is a resonator consists of a cantilever beam with a tip mass and a piezoelectric patch mounted on its latticed substrate. Three various auxetic patterns are suggested and implemented on the base of the cantilever in order to enhance the harvested powers. The efficiency enhancement of the suggested concepts is compared with a conventional plain resonator. In order to optimize the geometrical parameters of the auxetic patterns and investigate the efficiency of various resonator’s output power, the finite element modeling (FEM) is employed. Maximum output powers according to the optimum electrical resistance and resonance frequency are achieved. Also, the effects of different PZT types on the extracted energy are taken into investigation. Two different substrate materials (aluminum and steel) are used in the fabrication of resonators. The​ numerical models are validated by experimental results in the rotating speed at the range of 6–7 Hz, which is tuned to the operational rotational frequency of the freight train axles. It is shown that for Auxetic-I, Auxetic-II, and Auxetic-III, the magnification factors are 3.28, 2.5, and 2.14 are achieved for the aluminum substrate. These factors are 3.0, 2.6, and 2.3 for the steel resonator, respectively. The experimental results show that the auxetic resonators are able to considerably enhance the efficiency of rotary energy harvesting systems.

Micro windmill piezoelectric energy harvester based on vortex-induced vibration in tunnel

A micro windmill piezoelectric energy harvester is proposed to explore the wind energy translation based on vortex-induced vibration(VIV). The novel power takeoff is composed of a wind turbine with three blades, an air blast blower, an ancillary wind tunnel, and a circular PVDF piezoelectric converter. The air blower improves the airflow speed in the wind tunnel. A bluff body is fixed in the flow field to induce vortex and excite the circular PVDF piezoelectric film vibration. Theory and experiments are conducted to investigate the energy translation. Based on the blade element momentum method(BEM), the theoretical model of the air blast blower is derived. The calculation results show that the axial fan blasts the air into the wind tunnel, and the airflow speeds range from 1.37 m/s to 18.78 m/s. Furthermore, the theoretical model of the VIV is developed to decorated the airflow aerodynamic characteristics around the bluff body. The vortex-induced high-frequency resonance consequently improves the piezoelectric energy harvesting efficiency and promotes the excitation force amplitudes. Correspondingly, the output electric power on the piezoelectric plate is numerically investigated based on the theoretical model and experiment. The optimal output power matches the load resistance and the wind velocity on the bluff body. The maximal output power arrived at 8.97 μW on the external load resistance of 650 KΩ with a wind velocity of 19 m/s. Furthermore, experimental results validate the theoretical dynamic model and show that a windmill piezoelectric energy harvester based on vortex-induced vibration (VIV-WPEH) can increase the output power over either range of the low natural airflow speed and the optimizing bluff body individually.

Isogeometric optimization of piezoelectric functionally graded material for energy harvester

Improving the energy harvesting efficiency of piezoelectric energy harvesters (PEHs) in the scientific domain is essential for the application of self-powered microelectromechanical devices. This paper proposes an isogeometric optimization method to optimize the material distribution of piezoelectric functionally graded material (PFGM) energy harvester. Firstly, we establish the isogeometric formulation of the PFGM energy harvester based on the plane strain hypothesis and Hamilton’s principle. Meanwhile, the same non-uniform rational B-splines basis functions are utilized to represent the distribution of the PFGM. Secondly, three optimization models with the specified eigenfrequency and maximum energy conversion efficiency as objective functions are established. Then we derive the analytical sensitivities by the adjoint method and use the method of moving asymptotes to update the design variables. Furthermore, several numerical examples are performed to study the convergence and accuracy of the numerical solutions and analyze the effects of the metallic volume ratio constraint and the initial design domain on the optimized material distribution. More importantly, the dynamic analysis is executed to further test the energy harvesting efficiency based on the optimized designs. The results show that the presented approach can not only realize the specified eigenfrequency but also effectively improve the energy harvesting efficiency.

Finite Element Modeling and Performance Evaluation of Piezoelectric Energy Harvesters with Various Piezoelectric Unit Distributions.

The piezoelectric energy harvester (PEH) is a device for recycling wasted mechanical energy from pavements. To evaluate energy collecting efficiency of PEHs with various piezoelectric unit distributions, finite element (FE) models of the PEHs were developed in this study. The PEH was a square of 30 cm × 30 cm with 7 cm in thickness, which was designed according to the contact area between tire and pavement. Within the PEHs, piezoelectric ceramics (PZT-5H) were used as the core piezoelectric units in the PEHs. A total of three distributions of the piezoelectric units were considered, which were 3 × 3, 3 × 4, and 4 × 4, respectively. For each distribution, two diameters of the piezoelectric units were considered to investigate the influence of the cross section area. The electrical potential, total electrical energy and maximum von Mises stress were compared based on the computational results. Due to the non-uniformity of the stress distribution in PEHs, more electrical energy can be generated by more distributions and smaller diameters of the piezoelectric units; meanwhile, more piezoelectric unit distributions cause a higher electrical potential difference between the edge and center positions. For the same distribution, the piezoelectric units with smaller diameter produce higher electrical potential and energy, but also induce higher stress concentration in the piezoelectric units near the edge.

A Self-Powered Rectifier-Less Synchronized Switch Harvesting on Inductor Interface Circuit for Piezoelectric Energy Harvesting

In this article, a rectifier-less synchronized switch harvesting on inductor (ReL-SSHI) interface circuit for piezoelectric energy harvesting is presented. The proposed circuit works in two different modes: at the positive peak of the open-circuit voltage of the piezoelectric transducer (PZT), the switch in series with the load is turned on, and is operated in the series synchronized switch harvesting on inductor mode; at the negative peak of the open-circuit voltage of the PZT, the switch in parallel with the load is turned on, and is operated in voltage synchronous inversion mode. The ReL-SSHI circuit does not need a rectifier bridge so that the power loss of the circuit is reduced, and hence the piezoelectric energy harvesting efficiency of the circuit is improved. Theoretical analysis and simulation verify the effectiveness of the ReL-SSHI circuit.

Insights on the crack modeling and effectiveness of piezoelectric energy harvesters

A damage model for investigating the performance of cracked piezoelectric vibrational energy harvesters (VEHs) is developed. The crack model adopted does not alter the piezoelectric properties of the lead zirconate titanate patch but modifies the structural stiffness at the crack location following the Griffith’s strain release formulation. Multiple VEH configurations are considered to determine how the performance of various sized piezoelectric patches are impacted by multiple edge cracks. It is demonstrated that thicker piezoelectric patches are more severely impacted by cracks than thinner patches. The number of cracks, proximity of the cracks to the base of the VEH, and crack depth are shown to affect VEH performance. It is shown that severe cracks have a pronounced influence on the stiffness of the energy harvesting system, thus causing a deviation in the resonance region and amplitudes of the damaged system. The increased flexibility of the cracked piezoelectric patches increases the tip deflection and decreases the resonant frequency which can shift the initial optimal resistance to some higher value thus, greatly affecting the efficiency of piezoelectric energy harvesters.

Optimal design and experimental verification of piezoelectric energy harvester with fractal structure

The important issues in the conventional rotating vibration energy harvester are that the energy transfer efficiency and the fatigue life were limited because considering only the simply transferred force direction. Thus, this work focuses on the improving energy efficiency of piezoelectric energy harvester with a novel fractal structure. The harvester is based not only on an optimization model analysis, but also on an experimental investigation of coupling coefficients (structural and piezoelectric coupling) that can significantly affect efficiency performance. A model with a single-degree of freedom is developed and then optimized a structure model, yielding fractal-form design and verifications of performance analysis. In order to verify the optimized model, experimental tests are undertaken on a partial fractal structure energy harvester with each of the transmitted force angles. The harvester efficiently converts all responses transmitted at various frequencies. However, by incomplete harvester assembly conditions, shows unusual hysteresis curve tendencies. Especially, the nonlinearity by a fractal structure in single-mode tends to average about 40% in vertical vibration, while the nonlinearity by tangent direction tends to decrease to about 20%. When the harvester is applied to the bearing system, it is observed that the stiffness and damping ratios of the bearing-rotor system by the elastic capacity increase according to the electromechanical characteristic of the energy harvester. As a result, it generates up to 7 mW with the force transmitted by the bearing vibration. It is suggested that the optimal harvester design for increasing energy efficiency of bearing applications, and the importance of nonlinearity study (hysteresis behavior by a friction effect) for harvester performance.

Optimization of beam profiles for improved piezoelectric energy harvesting efficiency

Piezoelectric cantilever beams are among the most popular vibration energy harvesting devices. Homogenization of the spatial distribution of axial strain along those beams increases harvesting efficiency. The general approach to minimize axial strain variation is to use triangular or trapezoidal width profiles. In this study, a width profile function that includes curved shapes is proposed and a finite element–based optimization scheme is constructed to maximize harvesting efficiency. A distribution parameter is defined for quantifying the strain uniformity. Optimization is performed for various tip mass values, using this parameter as the objective function. It is shown that curved beam profiles exhibit less variation in axial strain, compared to triangular and rectangular beams. Optimized shapes for minimal strain variation at resonance are determined. Experimental results also validate the findings of the optimization. At least 22% increase in strain uniformity is obtained with the optimized-shaped beam, compared to a triangular beam when no tip mass is used. The increase in strain uniformity becomes 29% when the tip mass is increased to 5 g. The results indicate the potential of employing beam-type piezoelectric energy harvesters with optimized width profiles.

Robust flower-like ZnO assembled β-PVDF/BT hybrid nanocomposite: Excellent energy harvester

Need of renewable green energy sources due to low cost synthesis, mechanically strong, high energy storage capacity with improved dielectric performance have been receiving much attention. Present work render the ZnO particle and flower-like morphology assemble semicrystalline β phase PVDF/BT nanocomposite, successfully synthesized by spin coating method and characterized by XRD, SEM, EDS and FTIR techniques. Also the energy storage density of composite with modified structure is largely increased with value 0.056 Jcm−3 at 6 MV/m which is 66% higher than virgin β-PVDF and 82% piezoelectric energy harvesting efficiency. Maximum dielectric constant is 1774 at 1 Hz for PVDF-BaTiO3-ZnOf [P-BT-ZnOf] nanocomposite film and maximum breakdown strength of 43 kVcm−1. Electrochemical study reveals that P-BT-ZnOf nanocomposite film manifest better potential material. In terms of mechanical performance, P-BT-ZnOf nanocomposite shows maximum Young's modulus of 204 MPa, tensile strength of 28.7 MPa and 23.1% elongation to break. These results provide promising capability to enhance the performance of composites for energy storage application, transducers, sensors, capacitors etc.