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The biosafety and sustainability of inorganic perovskites or organic piezopolymers is a major concern in the field of wearable piezoelectric sensors. Naturally occurring, silk fibroin (SF), is a promising alternative for the realization of organic piezoelectric devices due to its excellent biocompatibility and tunable material properties. Nevertheless, its scope for practical sensing applications is limited by the weak innate piezoelectricity of 1 pC N−1. This research aims to improve the piezoelectricity of pristine SF by intrinsically growing non‐toxic metal‐free perovskite (MFP) to achieve organic and bendable silk fibroin‐metal free perovskite (SF‐MFP) composite films. The increase in MFP loading has an influence on the resulting morphology and crystallinity of SF‐MFP films. In comparison to pristine SF, the films with the highest perovskite loading exhibit an enhanced normal piezoelectric response of 4.6 pm V−1. The poled SF‐MFP sensors display an appreciable sensitivity of 0.61 ± 0.05 V N−1 with a fast response time and outstanding stability arising from a synergistic combination of mechanically robust SF and piezoelectric MFP. Furthermore, these sensors can detect various joint bending and muscle movements in human subjects, proving their suitability for wearable bioelectronics. This research demonstrates the potential of biomaterials and organic perovskites for the development of biocompatible and sustainable wearable piezoelectric solutions. [ABSTRACT FROM AUTHOR]

Anthropogenetic environmental deterioration and climate change caused by energy production and consumption pose a significant threat to the future of humanity. Renewable, environmentally friendly, and cost-effective energy sources are becoming increasingly important for addressing future energy demands. Mechanical power is the most common type of external energy that can be converted into useful electric power. Because of its strong electromechanical coupling ability, the piezoelectric mechanism is a far more successful technique for converting mechanics energy to electrical energy when compared to electrostatic, electromagnetic, and triboelectric transduction systems. Currently, the scientific community has maintained a strong interest in piezoelectric micro-power generators because of their great potential for powering a sensor unit in the distributed network nodes. A national network usually has a large mass of sensor units distributed in each city, and a self-powered sensor network is eagerly required. This paper presents a comprehensive review of the development of piezoelectric micro-power generators. The fundamentals of piezoelectric energy conversion, including operational modes and working mechanisms, are introduced. Current research progress in piezoelectric materials including zinc oxide, ceramics, single crystals, organics, composite, bio-inspired and foam materials are reviewed. Piezoelectric energy harvesting at the nano- and microscales, and its applications in a variety of fields such as wind, liquid flow, body movement, implantable and sensing devices are discussed. Finally, the future development of multi-field coupled, hybrid piezoelectric micropower generators and their potential applications are discussed. [ABSTRACT FROM AUTHOR]

To merge the gap between the low-power output of piezoelectric energy harvesters (PEHs) and the high-power demand of sensors of Internet of Things, researchers recently start to explore PEHs arrays. However, few circuits have been developed to manage the multiple ac inputs from PEHs arrays. This article presents a self-powered PEH array interface circuit based on the synchronized switching and discharging to a storage capacitor through an inductor (SSDCI) technique. The array interface can output a maximum total power greater than the sum of each individual peak power, and achieve a high efficiency when multiple PEHs connect to the SSDCI array circuit. Simulation and experiment are performed to demonstrate the advantages of the SSDCI array interface. The tested results show that the designed SSDCI array circuit achieves an efficiency of 82.3% with three input sources, and allows a gain up to 300% in terms of maximal output power compared to the full-bridge rectifier. In addition, only the peak detection is utilized for the switching control; therefore, the SSDCI array circuit is realized more easily and with fewer components compared to the existing synchronous electric charge extraction array interfaces. [ABSTRACT FROM AUTHOR]

In this paper, a hinge mechanism is introduced into one compressive-mode piezoelectric energy harvester to improve its performance. First, the concept of implementing hinge mechanisms is introduced on a high-efficiency compressive-mode piezoelectric energy harvester (HC-PEH). Second, a numerical model based on the piezoelectric constitutive equation and the Duffing oscillator equations is formulated to obtain voltage responses, velocity responses, and the fundamental frequency and bandwidth. Then, a prototype is fabricated to validate the results of the model. Depending on the number of hinges applied to the HC-PEH, three cases are investigated: fully hinged, partially hinged, and clamped. In both numerical modeling and experimental studies, the HC-PEH prototypes in the three cases are exposed to frequency-sweep excitations to illustrate the dynamic and transduction behaviors. The results demonstrate that the overall performance in the hinged cases is improved significantly compared to that in the clamped case. The output voltage and output power are increased by 2–3 times and up to 5 times, respectively, and fundamental resonant frequency is lowered to below 20 Hz. Furthermore, it is shown that the operational bandwidth is widened by up to 37%. [ABSTRACT FROM AUTHOR]

We proposed a nonlinear multi-mode tri-leg compliant orthoplanar spring piezoelectric vibration-based energy harvester (COPS-PVEH), which provided the improved performance using a pure geometric nonlinearity, in terms of a wide bandwidth, and a high-voltage output in forward and reverse sweeps. This paper presents an application of magnetic force interaction to further enhance the performance of the COPS-PVEH. A repulsive magnetic force is added to the spring to change the harvester system’s stiffness. A lumped parameter model is derived and analytically solved for the designed harvester with a magnetic coupling. The experiments are carried out by adding a moving magnet at the center of the spring and a pair of fixed magnets at the top and bottom sides of the harvester. Both experimental data and simulation results show the benefits brought through the dynamics of a magnetic oscillator. In an experiment by adding magnetic force, a slight increase is observed in the operating bandwidth and a 10% increase in the magnitude of voltage output is achieved at the same excitation level. The magnetic interaction on the COPS-PVEH with an addition of multiple masses has also achieved an increase in voltage output and bandwidth. In addition, the gap between the three vibration modes has been reduced. [ABSTRACT FROM AUTHOR]

The performance of vibration-based energy harvesters deteriorates when used in rotational environments with an offset distance. To address this issue, we propose a method of using magnets to improve the performance of the high-efficiency compressive-mode piezoelectric energy harvester (HC-PEH) with the offset configuration in rotational environments. The performance of the magnetically coupled rotational HC-PEH system with offset distances is experimentally studied. The results show the proposed method is feasible and significantly improves the performance (peak-peak voltage) by 254.2%. To attain comprehensive insight into the electromechanical behaviors of the system, we develop a theoretical model with consideration of nonlinear stiffness, nonlinear damping, and nonlinear piezoelectricity. The governing equations of the system are obtained by using Hamilton's principle and their approximate analytical solution is derived via the harmonic balance method. The simulation results closely render the experimental data and are used to characterize the system. Based on the developed theoretical model, a parametric study is performed and the results indicate that the best performance improvement can be obtained via tuning the parameters related to the magnetic force, the centrifugal force, and the initial deformation of the elastic beams. This work helps overcome a major obstacle for the application of rotational energy harvesting. • Verification on adverse effects of the offset distance in rotational environments. • A brand-new solution by using magnetic repulsion and its experimental verification. • The peak-peak voltage of the energy harvester shows a maximum increase by 254.2%. • Model of the magnetically coupled rotational HC-PEH system with offset distances. • Discussions on the dynamical characteristics of the system. [ABSTRACT FROM AUTHOR]

In this paper, we originally report an approach for cantilever piezoelectric energy harvesters (PEHs) for frequency tuning and performance improvement. The proposed scheme implements embedment of revolute joint(s) into PEH structure. We investigated two ways of embedment: the prior one is to replace the clamped edge partially with a joint and the other is to incorporate joint(s) into the substrate plane. Introducing joint mechanism reduces stiffness of the harvester, leading to more intense vibration and higher voltage of the piezoelectric element. We conducted FEA to validate hypothetical stiffness reduction by deriving resonant frequency considering parameters of joint width, length and number. Furthermore, experimental studies were conducted to compare open-circuit voltages in the frequency domain, power generation and capacitor-charging capabilities. The resonant frequencies from experiments display a good agreement with those from our simulation estimations. The embedded joint(s) effectively lowers resonant frequency by ∼43.1%. The output voltage of jointed cases increases ∼71.2 V, 2.83 times as high as that of the counterpart case. The mean power of the jointed cases reaches 0.49 mW, 7.3 times as high as that of the counterpart case. Furthermore, experimental charging results indicate remarkable improvement in charging capabilities regarding much higher charging rates and higher saturated voltage. • Original study of favorable effects of joints on piezoelectric energy harvesters. • Embedded joints can effectively tune the resonant frequency of the harvester. • A 630% output power improvement due to the joint embedment. • Much higher charging rates and voltages in charging performance of capacitors. [ABSTRACT FROM AUTHOR]

Highlights • Hybridization of piezoelectric and triboelectric energy generators. • Bifurcation induced superharmonic resonances for low-frequency energy harvesting. • High power outputs with force amplification effect by a truss mechanism and impact. • Capability of harnessing energy from a broad frequency range. • Frequency up conversion approach for higher output power. Abstract In this paper, we report a hybrid generator to harness energy from low-frequency ambient vibrations. The generator is designed with a piezoelectric energy harvester (PEH) patch, a triboelectric nanogenerator (TENG) patch, a spring-mass system and an amplitude limiter. The spring-mass system receives energy from excitations and applies forces to the piezoelectric element and the triboelectric layers. The unique amplitude limiter is deliberately introduced into the system, not only achieving the desired frequency up-conversion effect, but also boosting the voltage responses significantly. The limiter also causes hardening nonlinearity and dynamic bifurcation triggering superharmonic resonance so that the generator resonates at a frequency of about 3 Hz. Furthermore, the proposed PEH adopts the strong compressive operation mode, and employs a truss mechanism to effectively amplify the impact forces. In experiments, open-circuit voltages are 58.4 V from PEH and 60 V from TENG under an excitation of 1.0 g at resonance. The hybridized generator is capable of achieving a maximum power of 19.6 mW from the two sources with matched impedances. The working bandwidths of the PEH and the TENG reach up to 5.39 Hz and 7.25 Hz, respectively, out of our targeted frequency domain [2.5 Hz, 10 Hz] due to the multiple resonances and nonlinearity. In the applications to charge capacitors, the high saturation voltage and relatively short charging time validate the effectiveness of our power management technique. Furthermore, the generator proves to be able to effectively scavenge energy from human body motions and charge a capacitor of 4.7 μF to 7.6 V in around 50 s, which indicates a great potential of practical applications in wearable devices. [ABSTRACT FROM AUTHOR]