Flexible Piezoelectric Energy Harvester Research Articles

A poly(L-lactic Acid)-based flexible piezoelectric energy harvester with micro-zigzag structures

Abstract Piezoelectric energy harvester (PEH) holds great potential for flexible electronics and wearable devices. However, the power conversion efficiency of flexible PEH (fPEH) has often been a limiting factor, especially under variable excitation. Herein, we propose a practical solution: a poly(L-lactic acid)-based fPEH with 3D-printed micro-zigzag structures. This design not only broadens the operational bandwidth and enhances low-frequency response but also offers a tangible improvement in the power conversion efficiency of fPEH. The micro-zigzag structure was designed and fabricated using a digital light processing 3D printing technique with acrylates, a method that is readily accessible to researchers and engineers in the field. Mechanical properties of the 3D-printed acrylic elastomers with different compositions were investigated to obtain the material parameters, and then fPEH with the sandwich structure was fabricated via sputtering and packaging. Subsequently, numerical simulation was conducted on the micro-zigzag structures to determine the structure sizes and oscillation frequencies of fPEH. Finally, four micro-zigzag structures with 3-, 4-, 5- and 6-mm lengths were tested to obtain oscillation frequencies of 51, 37, 22, and 21 Hz consistent with the simulation. The output voltages of fPEH are 11 ~ 30 mV with the load ranges of 60 ~ 100 MΩ. Stability evaluation showed that the fPEH can work under low frequency (<100 Hz) and broadband conditions. The micro-zigzag structure provided new insights for the design of fPEH, paving the way for more efficient and practical energy harvesting solutions in the future.

High-performance piezoelectric energy harvesting in amorphous perovskite thin films deposited directly on a plastic substrate

Most reported thin-film piezoelectric energy harvesters have been based on cantilever-type crystalline ferroelectric oxide thin films deposited on rigid substrates, which utilize vibrational input sources. Herein, we introduce flexible amorphous thin-film energy harvesters based on perovskite CaCu3Ti4O12 (CCTO) thin films on a plastic substrate for highly competitive electromechanical energy harvesting. The room-temperature sputtering of CCTO thin films enable the use of plastic substrates to secure reliable flexibility, which has not been available thus far. Surprisingly, the resultant amorphous nature of the films results in an output voltage and power density of ~38.7 V and ~2.8 × 106 μW cm−3, respectively, which break the previously reported record for typical polycrystalline ferroelectric oxide thin-film cantilevers. The origin of this excellent electromechanical energy conversion is systematically explored as being related to the localized permanent dipoles of TiO6 octahedra and lowered dielectric constant in the amorphous state, depending on the stoichiometry and defect states. This is the leading example of a high-performance flexible piezoelectric energy harvester based on perovskite oxides not requiring a complex process for transferring films onto a plastic substrate.

Efficient energy harvesting enabled by large-area piezoelectric PVDF-based composite film enhanced by carbon nanotubes

Considerable attention has been drawn to the use of flexible piezoelectric energy harvesting devices for powering smart wearable technology. Herein, we employed a melt extrusion casting process to prepare large-area PVDF-based piezoelectric composite films and achieved continuous production. The films were prepared by adding 15 wt% lead zirconate titanate powder modified with a titanium coupling agent (PZT@UP15) and different content of carbon nanotubes (CNTs) exhibiting high conductivity into the PVDF matrix. The addition of CNTs in moderate amounts significantly enhanced the mechanical, dielectric, and piezoelectric properties of the composite films. Remarkably, the composite film containing 0.06 wt% CNTs achieved a d33 value of 28 pC/N, generated an open circuit voltage of 16.85 V, and a maximum power density of 0.46 μW/cm2 in the bending-releasing mode. Furthermore, the film exhibited relatively stable output performance even after 1500 cycles. The enhanced performances of the piezoelectric composite films can be attributed to the factors that the CNTs can effectively promote PVDF polarization by inducing dipole alignment and building an internal electric field, and further improve the piezoelectric performance and the electrostrictive performance. This work shows that the prepared piezoelectric composite film holds great potential as an energy harvesting device to provide power for wearable electronic devices.

Polar Organic Charge-Transfer Complex of the Asymmetrical Component for Flexible Piezoelectric Energy Harvesting and Self-Powered Wearable Sensors.

Organic piezomaterials have attracted much attention because of their easy processing, lightweight, and mechanic flexibility properties. Developing new smart organic piezomaterials is highly required for new-generation electronic applications. Here, we found a novel organic piezomaterial of organic charge-transfer complex (CTC) consisting of dibenzcarbazole analogue (DBCz) and tetracyanoquinodimethane (TCNQ) in the molecular-level heterojunction stacking mode. The DBCz-TCNQ complex exhibited ferroelectric properties (the saturated polarization of ∼1.23 μC/cm2) at room temperature with a low coercive field. The noncentrosymmetric alignment (Pc space group) led to a spontaneous polarization of this architecture and thus was the origin of the piezoelectric behavior. Lateral piezoelectric nanogenerators (PENGs) based on the thermal evaporated CTC thin-film exhibited significant energy conversion behavior under mechanical agitation with a calculated piezoelectric coefficient (d31) of ∼33 pC/N. Furthermore, such a binary CTC thin-film constructed single-electrode PENG could show steady-state sensing performance to external stimuli as this flexible wearable device precisely detected physiological signals (e.g., finger bending, blink movement, carotid artery, etc.) with a self-powered supply. This work provides that the polar CTCs can act as efficient piezomaterials for flexible energy harvesting, conversion, and wearable sensing devices with a self-powered supply, enabling great potential in healthcare, motion detection, human-machine interfaces, etc.

Accurate finite element modeling of multilayered flexible piezoelectric energy harvesting devices with strong coupling of structure, piezoelectricity, and circuit

Multilayered flexible piezoelectric energy harvesting devices (FPEDs) are a new future harvesting technology which are highly flexible and lightweight than familiar cantilever piezoelectric energy harvesters. This mechanical vibration driven FPED is a strongly coupled multiphysics phenomena that involve complex natural three-way interaction among the composite piezoelectric structure, the electric charge accumulated in the piezoelectric material, and a controlling electrical circuit attached to it. Efficient and accurate computational solution approaches are essential for analyzing these mechanical vibration-driven FPEDs to capture the main physical aspect of the coupled phenomena and to accurately predict the output voltage. While there are some numerical models for simple familiar cantilever type piezoelectric energy harvester reported in the literature, a fully three-dimensional strongly coupled model for complex material distributed, complex geometry, and multilayered FPED involving strong coupling of structure, piezoelectricity, and circuit phenomena has not yet been developed. A partitioned iterative algorithm is developed using a hierarchical decomposition approach wherein the coupled three fields are solved separately and coupled through loop union integration techniques that provide an efficient and accurate simulation of FPEDs. The simulation results matched the experiment results very well. This study provides a basis for the natural extension of partitioned iterative finite element coupled algorithm to simulate the future piezoelectric energy harvesting technologies involving a strong coupling of structure, piezoelectricity, and circuit phenomenon.

High-performance flexible piezocomposites based on an enhanced interfacial polarization effect via BCZT@Ag heterostructure design

Flexible piezoelectric energy harvesters (FPEHs) can convert mechanical energy into electric energy in a manner that powers electronic equipment and systems. Structural design of piezoelectric fillers in organic–inorganic piezocomposites is means of enhancing the power generation performance of FPEHs. Herein, a design strategy of piezoelectric fillers is proposed: decorating Ag nanoparticles onto Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) particles, forming a BCZT@Ag heterostructure, thus obtaining BCZT@Ag/poly(vinylidene fluoride) (PVDF) piezocomposites. An extremely high piezoelectric constant d33 of 34 pC/N is achieved in the BCZT@Ag/PVDF sample, which is 2.6 times higher than that of the BCZT/PVDF sample. The greatly improved piezoelectric properties are attributable to enhanced interfacial polarization via BCZT@Ag heterostructure design. More poling electric voltage is applied to the piezoelectric filler particles, resulting in substantially improved poling efficiency. This composite approach of introducing metal particles is a generic design method and can be extended to other organic–inorganic piezocomposite systems.

Electrospinning of Highly Bi-Oriented Flexible Piezoelectric Nanofibers for Anisotropic-Responsive Intelligent Sensing.

Flexible piezoelectric energy harvesters (PEHs) have gained substantial attention owing to their wearability, breathability, and sustainable self-powered supply. However, existing film PEHs cannot identify forces in different bending directions, limiting their applications in wearable electronics and artificial intelligence. This study constructs a fabric PEH for the first time by introducing piezoelectric anisotropic BaTi2 O5 nanorods (BT2-nr) into piezoelectric polyvinylidene fluoride (PVDF) nanofibers with a bi-oriented architecture, in which BT2-nr uniformly aligns in the PVDF nanofiber during electrospinning. The dual-orientation feature endows the flexible PEH with anisotropy, which can sensitively identify the forces at different bending directions (e.g., bent vertically, parallelly, or twisted by 45° along the fiber orientations). Simultaneously, the composite PVDF/BT2 PEH containing 15wt.% BT2-nr delivers an optimal piezoelectric output of 31.2V with a high sensitivity of 5.22V N-1 . The developed anisotropic PEH can be used as a self-powered pressure sensor for multimodal intelligent biomonitoring of human movement. This study provides a feasible strategy for fabricating self-powered flexible PEHs with high electromechanical conversion efficiency and multifunctionality for wearable piezoelectric pressure sensors.

Construction of Flexible Piezoceramic Array with Ultrahigh Piezoelectricity via a Hierarchical Design Strategy

AbstractThe µW‐level power density of flexible piezoelectric energy harvesters (FPEHs) restricts their potential in applications related to high‐power multifunctional wearable devices. To overcome this challenge, a hierarchical design strategy is proposed by forming porous piezoceramics with an optimum microstructure into an ordered macroscopic array structure to enable the construction of high performance FPEHs. The porous piezoceramic elements allows optimization of the sensing and harvesting Figure of merit, and the array structure causes a high level of effective strain under a mechanical load. The introduction of a network of polymer channels between the piezoceramic array also provides increased device flexibility, thereby allowing the device to attach and conform to the curved contours of the human body. The unique hierarchical piezoceramic array architecture exhibits superior flexibility, a high open circuit voltage (618 V), high short circuit current (188 µA), and ultrahigh power density (19.1 mW cm−2). This energy density value surpasses previously reported high‐performance FPEHs. The ultrahigh power flexible harvesting can charge a 0.1 F supercapacitor at 2.5 Hz to power high‐power electronic devices. Finally, the FPEH is employed in two novel applications related to fracture healing monitoring and self‐powered wireless position tracking in extreme environments.

Synergistic influence of surface‒modified SmxZn1-xCoO3‒poly(vinylidene fluoride) as a piezoelectric material for smart IoT applications

Due to the ability of mechanical energy converted to electrical energy, flexible piezoelectric energy harvesters have significant attention in recent years. In this current study, we designed and developed trimetallic oxide-based samarium zinc cobalt oxides, which were prepared using the co-precipitation method. The prepared material was fabricated using a solution casting method with 15% poly (vinylidene fluoride) (PVDF) to obtain a thin film of flexible piezoelectric sensor devices (FPSDs) SmxZn1-xCoO3/PVDF which was characterized by various analytical characterizations. Piezoelectrical characterizations were conducted on the fabricated (FPSDs) such as PVDF and SmxZn1-xCoO3/PVDF, by applying different dynamic forces. The obtained results clearly show that the output voltage of SmxZn1-xCoO3/PVDF improved, (33.3%) more than that of PVDF at 1 N force. Using finger tapping force on the surface of SmxZn1-xCoO3/PVDF FPSD to charge the capacitor, and it reached 245 mV within 16 s, then the light-emitting diodes (LEDs) glowed under amplification. Finally, the fabricated thin film was utilized to control the actions like the ‘jump’ of T-REX and ‘fly’ of flapping bird gaming interfaces using finger tapping. These optimistic results confirm that our fabricated FPSD is capable of energy-harvesting applications and self-powered smart IoT devices and so on.

Development of a flexible piezoelectric and triboelectric energy harvester with piezo capacitive sensing ability from barium tungstate nanorod-dispersed PVDF nanofabrics

Lead-free flexible piezoelectric nanogenerator (PNG) and triboelectric nanogenerator (TENG) are sought after due to their ability to produce electricity by harnessing wasteful mechanical energy. A comprehensive understanding of additives and processing techniques is crucial for fine-tuning the performance of such energy systems. We have investigated in detail the effect of the addition of reverse microemulsion synthesized barium tungstate nanorods (BWN) on morphology, crystallinity, polymorphism of electrospun nanofabrics of poly(vinylidene fluoride) (PVDF). The electroactive phase content of the nanofabrics was enhanced upon the addition of BWN and the highest electroactive phase content of 86.5% was observed in the nanofabric containing 3 wt% of BWN. The dielectric constant of the nanofabric containing 5 wt% BWN was ∼1.96 times higher than that of pristine electrospun PVDF nanofabric (EPVDF). The ratio of relative change in the capacitance to initial capacitance of the sensor fabricated from the same system was ∼4 times greater than that of EPVDF. Consequently, its piezoelectric and triboelectric performances were improved. The PNG fabricated using the nanofabric containing 3 wt% BWN produced the highest open-circuit voltage of 8 V under an applied load of 8 N. A TENG made using the same system was able to produce a voltage output of 200 V, which was 1.77 times as high as that of EPVDF under one-finger tapping in contact-separation mode. The same composite nanofabric produced piezoelectric and triboelectric power densities of 4.3 µW cm−2 and 646 µW cm−2, respectively. The TENG was able to light 40 LEDs under one finger tapping. Fluttering-driven TENG fabricated using the aforementioned nanofabric was able to produce a triboelectric voltage of 84 V at a wind speed of 7 m s−1. Overall, these nanofabrics could be a potential material for energy harvesting devices for powering wearable devices, environmental sensors, and internet of things.

Flexible horizontal piezoelectric energy generator for sea wave applications

Energy harvesting from the environment becomes a valuable technology, especially for sea wave applications, in which it usually ends up wasted despite its potential to be harvested. Due to its wide availability and high energy density, piezoelectric energy harvesting (PEH) is becoming popular for flexible energy harvesting. This paper presents a flexible horizontal piezoelectric (FHP) energy harvester to harvest energy from the surface of sea wave. The harvester is made of bimorph piezoelectric devices; they are utilised to amplify and convert the collected mechanical vibrations into electrical power. A finite element model is established from ANSYS simulations to solve the iteration method by generating resonance frequency (fr). Then, Taguchi method, SN ratio and the ANOVA approach were used by considering the input variable of fr to estimate the optimum performance through control factors; number of blade, length and thickness. From the performance test result, it is proven that the higher numbers of blade including length, and minimum numbers of thickness significantly improve the significant level, α = 0.05% of ANOVA. Three prototypes are developed with approximate body dimensions through the resonance frequency perform and generate a 160.3 Hz on blade dimensions of 10 × 300 × 0.2 mm, with a piezoelectric (PZT) on its surface. This particular study shows that the potential of output power is generated from sea wave surface through a significant relationship between length, thickness, and blade design. This research develops a novelty for energy harvesting from flexible piezoelectric generator on sea wave application that could be easily install on offshore platform.

Optimal Design Towards High Performance of Sandwich Flexible Piezoelectric Energy Harvesters

AbstractThe flexible piezoelectric energy harvester (FPEH), as an effective strategy for long-term power supply of implantable and wearable electronics, requires high areal output energy density, low mechanical stiffness, and high energy efficiency, simultaneously. The widely adopted sandwich FPEH, consisting of one relatively hard substrate sandwiched between two piezoelectric films, can provide a high areal output energy density, but also high mechanical stiffness and low energy efficiency due to its energy-wasting deformation of the hard substrate. Here, we propose a novel optimal soft-substrate sandwich FPEH with designs of sufficient length and optimized Young’s modulus of the substrate, which is much smaller than that of the piezoelectric film. A sandwich beam model considering both the bending and shearing of the soft substrate and the one-way coupling of the piezoelectric effect was adopted for the theoretical analysis and optimal design. The optimal soft-substrate sandwich FPEH exhibits greatly improved overall performance with a 33% increase in areal output energy density, a 51% reduction in mechanical stiffness, and a 177% increase in energy efficiency, simultaneously. Systematic theoretical analysis is performed to illustrate the mechanism and guide the optimal design. The novel optimal soft-substrate sandwich FPEH is then applied to harvesting energy from various living subjects. This optimal design can be extended to other types of mechanical energy harvesters with a similar laminated structure.

Design and Modeling of a PVDF-TrFe Flexible Wind Energy Harvester

This study presents the simulation, experimentation, and design considerations of a Poly(vinylidene fluoride co-trifluoroethylene)/ Polyethylene Terephthalate (PVDF-TrFe / PET), laser-cut, flexible piezoelectric energy harvester. It is possible to obtain energy from the environment around autonomous sensor systems, which can then be used to power various equipment. This article investigates the actuation means of ambient vibration, which is a good candidate for using piezoelectric energy harvester (PEH) devices. The output voltage characteristics were analyzed in a wind test apparatus. Finite element modeling (FEM) was done for von Mises stress and modal analysis. Resonance frequency sweeps, quality factors, and damping ratios of the circular plate were given numerically. For a PVDF-TrFe piezoelectric layer thickness of 18 µm and 1.5 mm radius, a damping ratio of 0.117 and a quality factor of 4.284 was calculated. Vmax was calculated as 984 mV from the wind setup experiments and compared with the FEM outputs.

Design and Fabrication of PVDF Based Flexible Piezoelectric Vibration Energy Harvester

In this work, a novel petal-shaped substrate with a trapezoidal active layer Flexible Energy Harvester(FEH) is modeled using an analytical equation. The trapezoidal shape piezoelectric layer’s geometric parameters are optimized using the Nelder-Mead(NM) method. The active layer PVDF films are fabricated using the solution casting method. The NM-optimized geometry generates a voltage of 1.9 V compared with the un-optimized structure. The three different proof mass shapes cube, ellipsoid, and cylindrical are utilized to tune the resonant frequency. The NM-optimized geometry with cylindrical proof mass provides open circuit AC voltage of 3.68 V at very low frequency air-conditioner vibration.

Textured Lead-Free Piezoelectric Ceramics for Flexible Energy Harvesters

A lead-free (K,Na)NbO3-based piezoelectric ceramic is textured along the (001) direction using the NaNbO3 (NN) seeds. The composition 0.96(K0.5Na0.5)(Nb0.965Sb0.035)O3-0.01CaZrO3-0.03(Bi0.5K0.5)HfO3 (KNN) is found to provide an excellent combination of electromechanical coefficients at room temperature. The textured composition with 5 wt % NN template (KNN-5NN) exhibits considerably improved electromechanical coefficients, d33 ∼ 590 pC/N, k31 ∼ 0.46, and d31 ∼ 215 ×10-12 C/N, at room temperature. A flexible piezoelectric energy harvester (F-PEH) is fabricated using the textured KNN-5NN ceramic and tested under cyclic force. F-PEH exhibits enhanced output voltage (Voc ∼ 25 V), current (I ∼ 0.4 μA), and power density (PD ∼ 5.5 mW/m2) (RL of 10 MΩ) in the off-resonance frequency regime. In comparison to the random ceramic KNN-0NN-based F-PEH (Voc ∼ 8 V and I ∼ 0.1 μA), the textured F-PEH significantly outperformed energy harvesting capability due to the large figure-of-merit value (d31 × g31) ∼ 3354 ×10-15 m3/J. This work provides a methodology for texturing lead-free materials and further implementing them in flexible energy harvesting devices and sensors.

Fabrication and evaluation flexible lead-free piezoelectric energy harvesters on stainless steel foils

Fabrication and evaluation flexible lead-free piezoelectric energy harvesters on stainless steel foils

Advances in wearable flexible piezoelectric energy harvesters: materials, structures, and fabrication

Advances in wearable flexible piezoelectric energy harvesters: materials, structures, and fabrication

All‐Ceramic Flexible Piezoelectric Energy Harvester

AbstractWith the rapid development of self‐powered electronics such as wearables, implantable devices, and sensor networks, there is an increasing demand for power sources that have a high power density and a long lifespan to keep the entire system operational. Flexible piezoelectric materials with the capability of mechanical‐to‐electrical energy conversion have attracted significant interest because of their immense potential for harvesting human biomechanical energy. Herein, 3 mol.% yttrium stabilized zirconia ribbon ceramic is selected as a unique substrate to manufacture a large‐scale and all‐ceramic flexible Pb(Zr0.52Ti0.48)O3 piezoelectric energy harvester via the cost‐effective one‐step process. The flexible piezoelectric energy harvester delivers excellent performance with an open‐circuit voltage of ~105 V and short‐circuit current of ~0.58 µA under mechanical strain equivalent to human movement. Moreover, the output voltage of a flexible piezoelectric energy harvester varies linearly with strain, allowing it a promising candidate as a self‐powered strain sensor. Of particular importance is that a large‐scale piezoelectric energy harvester (4 × 4 cm2) can simultaneously light up eight commercial light emitting diodes without any external power source and circuit. This research provides an innovative approach to the fabrication of high‐performance and large‐scale flexible piezoelectric energy harvesters as well as self‐powered micromechanical devices.

Expedient secondary functions of flexible piezoelectrics for biomedical energy harvesting

Flexible piezoelectrics realise the conversion between mechanical movements and electrical power by conformally attaching onto curvilinear surfaces, which are promising for energy harvesting of biomedical devices due to their sustainable body movements and/or deformations. Developing secondary functions of flexible piezoelectric energy harvesters is becoming increasingly significant in recent years via aiming at issues that cannot be addressed or mitigated by merely increasing piezoelectric efficiencies. These issues include loose interfacial contact and pucker generation by stretching, power shortage or instability induced by inadequate mechanical energy, and premature function degeneration or failure caused by fatigue fracture after cyclic deformations. Herein, the expedient secondary functions of flexible piezoelectrics to mitigate above issues are reviewed, including stretchability, hybrid energy harvesting, and self-healing. Efforts have been devoted to understanding the state-of-the-art strategies and their mechanisms of achieving secondary functions based on piezoelectric fundamentals. The link between structural characteristic and function performance is unravelled by providing insights into carefully selected progresses. The remaining challenges of developing secondary functions are proposed in the end with corresponding outlooks. The current work hopes to help and inspire future research in this promising field focusing on developing the secondary functions of flexible piezoelectric energy harvesters.

A review of flexible lead-free piezoelectric energy harvester

Piezoelectric nanogenerator has emerged as a promising power generation device that converts mechanical energy into electrical energy. Flexible and stretchable piezoelectric energy harvesters can detect low frequencies like heartbeat, footsteps, ambient noise, and airflow, which is promising for further application. Thus, the development of a lead-free piezoelectric nanogenerator is required owing to its less toxic nature. One-dimensional ZnO (nanowire and nanorods) and perovskite-based materials (BaTiO 3 and BiFeO 3 ) have been widely investigated for piezoelectric nanogenerators because of their excellent piezoelectric properties and environmental friendliness. Hitherto, various electrodes, substrates, nanostructures, and polymers have been utilized to improve the efficiency of piezoelectric devices. In this review, we discuss the state-of-the-art achievements, stretchable piezoelectric nanowire, nanocomposite nanogenerators, and future possibilities of lead-free flexible energy harvesting devices.