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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]

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]

Thin cylindrical shells are commonly employed to connect adjacent disks in large rotating machinery. The vibration characteristics of coupled cylindrical shell and annular plate components have a significant influence on the rotor dynamics. This paper provides a general approach for the vibration analysis of a rotating cylindrical shell coupled with an annular plate. The Sanders shell theory and Mindlin plate theory are employed to calculate the strain energy of the shell and plate, respectively. The Coriolis and centrifugal effects due to the rotation are taken into account. The artificial spring technique is adopted to simulate the coupling and boundary conditions. By taking Chebyshev polynomials as the admissible functions, the Rayleigh–Ritz method is employed to derive the motion equations for the rotating shell-plate combination. The approach proposed is validated by comparing with the available results in literature and finite element analysis results. The traveling wave motion of the coupled shell and plate structure is investigated. The effects of the geometric parameters and the boundary and coupling conditions on the vibration behavior of the coupled structure are evaluated. The present approach can not only evaluate free vibrations of coupled shell and plate structures, but also be extended to vibration analysis of disk–drum rotors involving cylindrical shells. [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]

This paper presents the modeling and experimental parametric study of a nonlinear multi-frequency broad bandwidth piezoelectric vibration-based energy harvester. The proposed harvester consists of a tri-leg compliant orthoplanar spring (COPS) and multiple masses with piezoelectric plates attached at three different locations. The vibration modes, resonant frequencies, and strain distributions are studied using the finite element analysis. The prototype is manufactured and experimentally investigated to study the effect of single as well as multiple light-weight masses on the bandwidth. The dynamic behavior of the harvester with a mass at the center is modeled numerically and characterized experimentally. The simulation and experimental results are in good agreement. A wide bandwidth with three close nonlinear vibration modes is observed during the experiments when four masses are added to the proposed harvester. The current generator with four masses shows a significant performance improvement with multiple nonlinear peaks under both forward and reverse frequency sweeps. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting technology is regarded as a remedy to the short-life battery issue in low-power electronic devices, and has been extensively studied in the past two decades. Although a variety of new structures and mechanisms have been proposed for piezoelectric energy harvesters (PEHs), there is not much progress made on the piezoelectric materials that play a determinant role in PEHs performance. Most energy harvesters are still constructed with lead zirconate titanate (PZT). Recently, the new-generation piezoelectric materials PMN-PT and PZN-PT single crystals are proposed and start to be used in transducers. Their electromechanical coupling factor ( k 33 ) is over 90%, and the piezoelectric coefficient ( d 33 ) can reach three times of that of PZT. This study characterizes the PMN-PT and PZN-PT single crystals used in energy harvesters, compared with the polycrystalline PZT, in terms of charging capacitors. Systematic discussions are presented on the voltage, power and energy responses, as well as the reverse coupling effect on the mechanical response and the self-discharge effect of capacitors. Furthermore, a self-powered synchronized switch harvesting on inductor (SSHI) circuit is constructed and tested with the new single-crystal based energy harvesters. Experiments indicate that PMN-PT and PZN-PT can significantly boost the charging capability of energy harvesters, and that performance can be further enhanced by the SSHI circuit. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting is envisioned as an ideal complement to batteries for long-life operation of wireless or remote electronic devices. Most piezoelectric energy harvesters (PEHs) utilize piezoelectric plates or discs as the energy transducing elements, and they cannot generate enough power for most potential applications. In this study, we explore a new way of using arc-shaped piezoelectric patches as the core transducing elements in energy harvesters to improve their performance. An analytical model is developed via the Castigliano’s theorem to elucidate the low stiffness characteristic of the arc-shaped structure. A finite element analysis is conducted, and the results indicate that high and evenly-distributed stress can be easily induced in the arc-shaped PEHs. Prototypes are fabricated with arc-shaped piezoelectric elements and flat piezoelectric plates, respectively, and tested under the same conditions. The experimental data demonstrate that the arc-shaped PEHs are capable of generating 2.55–4.25 times as much power as the equivalent flat-plate PEHs. This study lays the foundation to enhance energy harvester performance by utilizing arc-shaped piezoelectric structures. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting has been a research subject of growing interest over the past few years, and is envisaged as a remedy to the unsatisfactory battery issue in low-power electronic devices. In this study, we propose a new magnetostrictive transducer to harvest energy from finger tapping. Galfenol is selected as the transducing material due to its high piezomagnetic coefficient and excellent machinability. To effectively harness energy in low-frequency conditions, we develop a frequency up-conversion mechanism that succeeds in converting vibration below 10 Hz from finger tapping up to the system's resonance of a few hundred Hz. Furthermore, multiple impacts are induced in each working cycle deliberately to boost the efficiency. A comprehensive model is built and solved to analyze the mechanical-magnetic-electrical coupling system. Based on the model, we elucidate the design criteria for high-performance magnetostrictive transducers. A prototype is fabricated with a Galfenol beam of 0.5 × 5 × 25 mm 3 and, under finger tapping, it generates 5.3 mW power and instantaneously lights up 10 commercial LEDs and a numeric LCD. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting has a great potential to achieve self-powered operations for wireless sensors, wearable devices and medical electronics, and thus has attracted much attention in academia and industry. The majority of research into this subject has focused on the piezoelectric effect of synthetic materials, especially the perovskite PZT ceramics. Recently the new-generation piezoelectric materials PMN-PT and PZN-PT single crystals have gained significant interest because of their outstanding piezoelectric properties. They can be used to replace the widely-adopted PZT ceramics for improving energy harvesters’ performance substantially. However, there is little research on comparing PMN-PT and PZN-PT energy harvesters against PZT harvesters. In this paper, we present a systematic comparison between vibration energy harvesters using the PMN-PT, PZN-PT single crystals and those using the PZT ceramics. Key properties of the three materials are summarized and compared. The performance of the PMN-PT and PZN-PT energy harvesters is characterized under different conditions (beam length, resistance, frequency, excitation strength, and backward coupling effect), and is quantitatively compared with the PZT counterpart. Furthermore, the effect of the synchronized switch harvesting on inductor (SSHI) circuit on the three harvesters is discussed. The experimental results indicate that energy harvesters using the PMN-PT and PZN-PT single crystals can significantly outperform those using the PZT ceramics. This study provides a strong base for future research on high-performance energy harvesters using the new PMN-PT and PZN-PT single crystals. [ABSTRACT FROM AUTHOR]

Harnessing ambient vibration energy using piezoelectric materials is a promising alternative solution to batteries to inexhaustibly power small-scale mobile devices. This paper presents an innovative energy harvester, named high-efficiency compressive-mode piezoelectric energy harvester (HC-PEH). It consists of a pair of elastic beams and a flex-compressive center where the piezoelectric element bears a dynamic compressive load. The compressive mode is preferred than the commonly-used bending mode and tensile mode due to the superior compressive strength of piezoceramics. To cater to the characteristic of piezoceramics: large ultimate stress, but extremely small ultimate strain, a multi-stage force amplification mechanism is developed in the design. The HC-PEH shows superior capability of high power output and favorable nonlinear phenomena at low frequency range. Under an acceleration of 0.5 g (g = 9.8 m/s 2 ), a maximum power of 19 mW is produced at 21 Hz, which is about one order of magnitude higher than the power output of energy harvesters previously reported. The capability of high power output of the HC-PEH demonstrates the practicability of using energy harvesters to power most of wireless sensors. [ABSTRACT FROM AUTHOR]

The utilization of hydrogels in soft electronics has led to significant progress in the field of wearable and implantable devices. However, challenges persist in hydrogel electronics, including the delicate equilibrium between stretchability and electrical conductivity, intricacies in miniaturization, and susceptibility to dehydration. Here, a lignin‐polyacrylamide (Ag‐LPA) hydrogel composite endowed with anti‐freeze, self‐adhesive, exceptional water retention properties, and high stretchability (1072%) is presented. Notably, this composite demonstrated impressive electrical conductivity at room temperature (47.924 S cm−1) and extremely cold temperatures (42.507 S cm−1). It is further proposed for microfluidic‐assisted hydrogel patches (MAHPs) to facilitate customizable designs of the Ag‐LPA hydrogel composite. This approach enhances water retention and offers versatility in packaging materials, making it a promising choice for enduring soft electronics applications. As a proof‐of‐concept, soft electronics across diverse applications and dimensions, encompassing healthcare monitoring, environmental temperature sensing, and 3D‐spring pressure monitoring electronics are successfully developed. The scenery of an extremely cold environment is further extended. The conductivity of the embedded Ag‐LPA hydrogel composite unveils the potential of MAHPs in polar rescue missions. It is envisioned that MAHPs will impact the development of sophisticated and tailored soft electronics, thereby forging new frontiers in engineering applications. [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]

Flow-induced energy harvesting has attracted more and more attention among researchers in both fields of the wind and the fluid. Piezoelectric energy harvesters and triboelectric nanogenerators are exploited to obtain superior performance and sustainability, and the electromagnetic conversion has been continuously improved in the meantime. Aiming at different circumstances, researchers have designed, manufactured, and tested a variety of energy harvesters. In this paper, we analyze the state-of-the-art energy harvesting techniques and categorize them based on the working environment, application targets, and energy conversion mechanisms. The trend of research endeavors is analyzed, and the advantages, existing problems of energy harvesters, and corresponding solutions of energy harvesters are assessed. [ABSTRACT FROM AUTHOR]

The triboelectric nanogenerator (TENG) represents a burgeoning approach for harvesting ambient mechanical energy. However, practical applications suffer from the issues of insufficient charge density and material abrasion. Here, a rotational TENG that attains exceptional output performance and durability in mechanical energy harvesting and couples an ingenious coplanar charge pump by soft contact with a suspended electrostatic induction mode is presented. Thanks to the continuous and synchronous charge injection from the central charge pumping unit, the charge density can be up to 74.62 µC m−2, resulting in an outstanding peak power density of 20.72 W m−2. Moreover, the utilization of yielding polyester fur in the charge pumping unit as a tribo‐layer for soft contact decreases the material abrasion and then enhances durability and robustness. And the experimental results show that the TENG can maintain 99.2% electrical output after 100 000 operating cycles. With the optimized design, the prototype can continuously drive four commercial lamps rated 12 W in series. Furthermore, a wireless powering system is demonstrated to power the electronics, demonstrating an extensive application of the TENG. Given the compelling characteristics, this work is expected to provide a sound strategy for improving TENGs' output and durability in the field of self‐powered sensor systems. [ABSTRACT FROM AUTHOR]

• Multiple nonlinear energy harvesters are developed based on compliant orthoplanar springs and piezoelectric materials. • Experiments with both harmonic and random excitations are performed. The proposed COPS harvesters could show an extended operational bandwidth in both conditions. • The study quantitatively demonstrates the effectiveness of interaction of multiple nonlinear vibration modes on harvester performance enhancement, and which effect can be tuned by the addition of multiple masses and spring legs. • The quad-leg design shows a broad bandwidth of 35 Hz while maintaining a voltage response of 4 V. This paper compares the performance of three nonlinear compliant orthoplanar springs, namely, bi-leg, quad-leg and pent-leg designs to study the vibration mode interaction effect for widening the operational bandwidth of piezoelectric vibration energy harvester. All the designs have three or more vibration modes below 150 Hz with the addition of multiple masses. Finite element analysis results of spring designs and vibration mode shapes are presented and compared with experiments. The prototypes were manufactured and experimentally tested to analyze their dynamic voltage-frequency responses and operational bandwidths under sinusoidal and band-limited excitations. The experimental results demonstrate that the operational bandwidth is significantly broadened by the geometric nonlinearity of the structure. The addition of multiple masses brings the vibration modes of the system closer, and thus further helps to extend the operational bandwidth. In addition, we introduce multiple piezoelectric plates into harvesters to enable energy harvesting in all vibration modes. The quad-leg design shows the largest frequency bandwidth of 35 Hz, maintaining a peak-to-peak voltage of 4 V under the forward frequency-sweep excitations. Under the reverse frequency-sweep excitations, the voltage response and the operational bandwidth are comparable to those of the forward-sweep ones as a result of continuous overlapping of linear and nonlinear voltage peaks. Random excitation experiments demonstrate the effectiveness of the proposed mutli-leg structure in harvesting energy from wideband environmental vibrations. [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]

[Display omitted] Bulk piezoceramics are widely used and functional materials, but they are hard to be shaped to adapt to complex 3D surfaces. Most existing ceramic shaping techniques, like 3D printing, come at the cost of physical properties such as piezoelectricity and thermal stability. Here to fabricate 3D piezoceramic sheets, we report a mold-assisted sintering (MAS) method that can replicate 3D surfaces with nonzero Gaussian curvatures while maintaining the intrinsic properties. Assisted with supporting molds, the MAS exploits elastic-to-viscous transition of piezoceramic powder compacts during sintering, bypassing the boundaries of deformation and surface development in an elastic continuum. We successfully replicate shapes to sintered lead zirconate titanate (PZT) ceramics from designed molds with saddle, sine and spherical surfaces, respectively. The PZT ceramic replicas show high piezoelectricity and excellent conformability towards nonplanar surfaces (maximum deviation 90 μm). We further demonstrate the advantage of the conformal curved piezoceramics by using them for wirelessly transferring power over a pipeline. The MAS method is low-cost, simple, scalable and applicable to various 3D energy transducers. [ABSTRACT FROM AUTHOR]

Low-resistance contact has long been pursued in the two-dimensional (2D) electronic/optoelectronic device community. Still, an economy-efficient method highly compatible with the conventional 2D device fabrication process in laboratory remains to be explored. Herein, we report a plasma-optimized contact strategy for high-performance PdSe2 nanoflake-based field-effect transistors (FETs). Selenium vacancies created by air plasma can introduce p-type doping in the contact area, thus optimizing the device performance. The effect of plasma treatment on PdSe2 nanoflake is corroborated by high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy spectrum, atomic force microscopy, and Kelvin probe force microscopy. The PdSe2 FET with plasma-optimized contact exhibits significantly improved field-effect carrier mobilities, current on/off ratios, and reduced contact resistance than that without plasma treatment fabricated from the same PdSe2 nanoflake. Moreover, this strategy has also been proven effective to prepare high-performance FETs based on 2D WSe2 and MoSe2 nanoflakes, further demonstrating its application prospect. [ABSTRACT FROM AUTHOR]

The rainbow trapping effect demonstrates great potential in multiple-band energy harvesting. However, the existing finite-size devices with the rainbow trapping phenomenon hardly harvest energy efficiently due to the mismatch between rainbow trapping frequencies and resonance frequencies of the devices. In this study, for the first time, we report a periodically perforated metamaterial beam, which achieves both the flexural wave rainbow trapping and resonance simultaneously for the multiple-band and multiple-position energy harvesting. The band structure of the unit cell in the metamaterial beam is analyzed to illustrate its ability to realize strong dispersion and energy concentration. The study first indicates that the rainbow trapping effect activated by resonance frequencies causes much more intense spatial separation and localization of flexural waves compared with that by cutoff frequencies for the periodically perforated bare beam. We, then, demonstrate that the resonance rainbow trapping phenomenon allows the proposed design to show superiority in piezoelectric energy harvesting compared with the counterpart with off-resonance rainbow trapping. Simulations indicate that the optimal resistance and the highest output power vary much for different pairs of piezoelectric patches at the corresponding resonance rainbow frequencies; by contrast, the positions of piezoelectric patches have little influence on the performance of the device. The design concept of on-resonance rainbow trapping in metamaterials in this study will help engineers to open a new venue for high-performance piezoelectric energy harvesters. [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]

Highlights: Freestanding lead-free piezoceramic thin films can be derived via water peeling. The d33 value of the freestanding BCZT thin film reaches 209 pm V−1. The freestanding piezoceramic films obtain versatile application scenarios such as energy harvest and virus detection. Most electronics such as sensors, actuators and energy harvesters need piezoceramic films to interconvert mechanical and electrical energy. Transferring the ceramic films from their growth substrates for assembling electronic devices commonly requires chemical or physical etching, which comes at the sacrifice of the substrate materials, film cracks, and environmental contamination. Here, we introduce a van der Waals stripping method to fabricate large-area and freestanding piezoceramic thin films in a simple, green, and cost-effective manner. The introduction of the quasi van der Waals epitaxial platinum layer enables the capillary force of water to drive the separation process of the film and substrate interface. The fabricated lead-free film, Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 (BCZT), shows a high piezoelectric coefficient d33 = 209 ± 10 pm V−1 and outstanding flexibility of maximum strain 2%. The freestanding feature enables a wide application scenario, including micro energy harvesting, and covid-19 spike protein detection. We further conduct a life cycle analysis and quantify the low energy consumption and low pollution of the water-based stripping film method. [ABSTRACT FROM AUTHOR]

In this paper, we originally present a gravity induced self-excited vibration generator based on a cantilever piezoelectric resonator. The configuration is composed of a sliding rod, a sleeve, a transduction unit. To estimate output voltage and investigate dynamic responses of the generator, an equivalent model based on mechanical structure was established and numerically solved. The effects of the cantilever length, tip mass and linear coupling factor on the open circuit voltage were discussed. In addition, we also conducted series of experiments to validate the theoretical responses. In a 10s cycle (namely 0.1Hz excitation frequency) scenario, the transduction unit responds with structural resonant frequency of 8.621Hz. The results of the experiments show that the open circuit voltage of the generator increases with increment of the cantilever beam length and the tip mass, which agrees well with simulation estimations. We also conducted impedance matching experiments to examine power response in the load spectrum, of which the results indicate that the prototype peak power reaches maximum 1.897 mW. We also discussed the change of gravity potential energy of the prototype and compared it with electric energy. This work provides a novel approach for piezoelectric energy harvesting from extremely low frequency excitations. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: The growth of high-quality single-crystalline Te nanobelts is reported by introducing atomically flat hexagonal boron nitride (h-BN) nanoflakes into the chemical vapor deposition system as the growth substrate. The field-effect transistor based on Te grown on h-BN exhibits an ultrahigh hole mobility up to 1370 cm2 V−1 s−1 at room temperature. The lack of stable p-type van der Waals (vdW) semiconductors with high hole mobility severely impedes the step of low-dimensional materials entering the industrial circle. Although p-type black phosphorus (bP) and tellurium (Te) have shown promising hole mobilities, the instability under ambient conditions of bP and relatively low hole mobility of Te remain as daunting issues. Here we report the growth of high-quality Te nanobelts on atomically flat hexagonal boron nitride (h-BN) for high-performance p-type field-effect transistors (FETs). Importantly, the Te-based FET exhibits an ultrahigh hole mobility up to 1370 cm2 V−1 s−1 at room temperature, that may lay the foundation for the future high-performance p-type 2D FET and metal–oxide–semiconductor (p-MOS) inverter. The vdW h-BN dielectric substrate not only provides an ultra-flat surface without dangling bonds for growth of high-quality Te nanobelts, but also reduces the scattering centers at the interface between the channel material and the dielectric layer, thus resulting in the ultrahigh hole mobility. [ABSTRACT FROM AUTHOR]

Wearing masks has been a recommended protective measure due to the risks of coronavirus disease 2019 (COVID‐19) even in its coming endemic phase. Therefore, deploying a "smart mask" to monitor human physiological signals is highly beneficial for personal and public health. This work presents a smart mask integrating an ultrathin nanocomposite sponge structure‐based soundwave sensor (≈400 µm), which allows the high sensitivity in a wide‐bandwidth dynamic pressure range, i.e., capable of detecting various respiratory sounds of breathing, speaking, and coughing. Thirty‐one subjects test the smart mask in recording their respiratory activities. Machine/deep learning methods, i.e., support vector machine and convolutional neural networks, are used to recognize these activities, which show average macro‐recalls of ≈95% in both individual and generalized models. With rich high‐frequency (≈4000 Hz) information recorded, the two‐/tri‐phase coughs can be mapped while speaking words can be identified, demonstrating that the smart mask can be applicable as a daily wearable Internet of Things (IoT) device for respiratory disease identification, voice interaction tool, etc. in the future. This work bridges the technological gap between ultra‐lightweight but high‐frequency response sensor material fabrication, signal transduction and processing, and machining/deep learning to demonstrate a wearable device for potential applications in continual health monitoring in daily life. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvester (PEH) arrays are practical solutions to the low and unreliable power output of a single PEH. However, most PEH circuits are developed for addressing the one-channel ac input from a single PEH. In this article, an extensible rectifier-less synchronized switch harvesting on inductor (ReL-SSHI) array interface with the maximal power point tracking (MPPT) function to manage the multiple ac inputs from the PEH arrays is designed. The ac–dc conversion is performed by the ReL-SSHI topology with passive peak switches featured with self-powered characteristic and fast cold-start. Only one shared inductor is employed, greatly reducing the circuit volume and cost. The MPPT module for each channel is implemented by a simple envelope detector and an ultra-low power hysteresis controller and achieves continuous energy extraction by adapting the fractional normal-operation voltage method. A developed discrete array interface able to handle three PEHs effectively executes the MPPT for each channel with the uphill and downhill response speeds of 2.0 and 7.1 V/s, and a maximal MPPT efficiency of 97.1%. This circuit boosts the power output by 485% compared with that by the traditional full-bridge rectifier, around 33% higher than that from existing synchronous electric charge extraction array interfaces. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvester (PEH) arrays are promising in many application scenarios. However, few interface circuits have been developed to manage the multiple ac inputs from PEHs. This article proposes an extensible parallel synchronized switch harvesting on inductor array interface scheme to realize a multiinput conversion from PEH arrays. We develop a split-inductor-capacitor topology that can extract electrical energy from multiple PEHs. The proposed circuit topology effectively handles the inductor access conflict in the cases of PEHs with close, identical, and opposite vibration phases, insensitive to ac input phase changes. For demonstrating the capability of dealing with multiple ac inputs from PEHs and the enhancement effect on power output, we construct and test a self-powered three-channel array circuit with the passive peak detection function. Excited by sinusoidal vibrations, our circuit effectively avoids the energy return and efficiently achieves the power combination of the three PEHs. Compared with the classic full-bridge circuit, the proposed circuit helps increase the power output by 4.8 times. Also, to show the universality of the circuit, the circuit's operation under various excitations istested and analyzed. [ABSTRACT FROM AUTHOR]

Self‐assembled monolayers (SAMs) have been widely employed as an effective way to modify interfaces of electronic/optoelectronic devices. To achieve a good control of the growth and molecular functionality of SAMs, we develop a co‐assembled monolayer (co‐SAM) for obtaining efficient hole selection and suppressed recombination at the hole‐selective interface in inverted perovskite solar cells (PSCs). By engineering the position of methoxy substituents, an aligned energy level and favorable dipole moment can be obtained in our newly synthesized SAM, ((2,7‐dimethoxy‐9H‐carbazol‐9‐yl) methyl) phosphonic acid (DC‐PA). An alkyl ammonium containing SAM is co‐assembled to further optimize the surface functionalization and interaction with perovskite layer on top. A champion device with an excellent power conversion efficiency (PCE) of 23.59 % and improved device stability are achieved. This work demonstrates the advantage of using co‐SAM in improving performance and stability of PSCs. [ABSTRACT FROM AUTHOR]

Self‐assembled monolayers (SAMs) have been widely employed as an effective way to modify interfaces of electronic/optoelectronic devices. To achieve a good control of the growth and molecular functionality of SAMs, we develop a co‐assembled monolayer (co‐SAM) for obtaining efficient hole selection and suppressed recombination at the hole‐selective interface in inverted perovskite solar cells (PSCs). By engineering the position of methoxy substituents, an aligned energy level and favorable dipole moment can be obtained in our newly synthesized SAM, ((2,7‐dimethoxy‐9H‐carbazol‐9‐yl) methyl) phosphonic acid (DC‐PA). An alkyl ammonium containing SAM is co‐assembled to further optimize the surface functionalization and interaction with perovskite layer on top. A champion device with an excellent power conversion efficiency (PCE) of 23.59 % and improved device stability are achieved. This work demonstrates the advantage of using co‐SAM in improving performance and stability of PSCs. [ABSTRACT FROM AUTHOR]

Piezoceramic films are an essential class of energy‐conversion materials that have been widely used in the electronics industry. Although current methods create a great freedom for fabricating high‐quality piezoceramic films, it requires well‐controlled synthesis conditions, including special high‐cost equipment and planar substrates particularly. The limited substrate selections hinder the applications of piezoceramic films in 3D conformal structures where most objects possess complex curvilinear surfaces. To overcome such limitations, a fast, energy‐efficient, and cost‐effective approach, named flame treated spray (FTS) coating, is developed for preparing piezoceramic films on free‐form surfaces. The flame treatment significantly enhances the hydrophilicity of a substrate, assisting in forming a uniform and continuous thin film. The followed spray coating deposits hundreds of nanometers to several micrometers thick films on 3D free‐form surfaces. Given the size controllability and arbitrary surface compatibility of the FTS method, a highly conformal piezoelectric tactile sensor array (4 × 4) is assembled on a spherical surface for mimicking robot fingers and an on‐site thin‐film sensor on the wing of an aircraft model to monitor the vibration in real‐time during flight. The FTS film deposition offers a highly promising methodology for the application of functional thin‐film from micro‐ to marcoscale devices, regardless of conformal problems. [ABSTRACT FROM AUTHOR]

• SE-tattoo is conformable, sweat permeable, and imperceptible on hairy skin. • Design a biocompatible water-based conductive ink for spray fabrication method. • SE-tattoo shows high adhesiveness, high conductivity, and fast curing ability (<20 s) • Reliable and versatile solution for bidirectional human–machine interaction. Biopotential signals recorded by skin surface electrodes reflect the state of the body and corresponding organ functions. These signals are commonly utilized in clinical diagnosis, health monitoring, sports training, and human–computer interaction. However, the utilization of conventional electrodes on hairy skin causes a number of issues, including suboptimal skin compliance, obstructed sweat secretion and impaired tactile perception, making it difficult to obtain long-term and high-fidelity biopotential recordings. Here, we propose an imperceptible spray-on electrode tattoo (SE-tattoo) with sweat-permeability, high adhesiveness, high conductivity, and fast curing ability (<20 s). The water-based conductive ink is sprayed directly on the hairy skin to form a conformable conductive tattoo that neither affects nor is affected by the skin hair. We demonstrate it for heart health monitoring, sports training, electro-tactile display and close-loop teleoperation control. The SE-tattoo offers a reliable and versatile solution to biopotential recordings and serves as a promising platform for bidirectional human–machine interaction. One-Sentence Summary: Imperceptible sweat-permeable SE-tattoo enables high-fidelity biopotential recordings for bidirectional human–machine interaction. [ABSTRACT FROM AUTHOR]

Softening of piezoelectric materials facilitates the development of flexible wearables and energy harvesting devices. However, as one of the most competitive candidates, piezoelectric ceramic-polymer composites inevitably exhibit reduced power-generation capability and weak mechanical strength due to the mismatch of strength and permittivity between the two phases inside. Herein a flexible, air-permeable, and high-performance piezoceramic textile composite with a mechanically reinforced hierarchical porous structure is introduced. Based on a template-assisted sol-gel method, a three-order hierarchical ceramic textile is constructed by intertwining submillimeter-scale multi-ply ceramic fibers that are further formed by twisting micrometer-scale one-ply ceramic fibrils. Theoretical analysis indicates that large mechanical stress can be easily induced in the multi-order hierarchical structure, which greatly benefits the electrical output. Fabricated samples generate an opencircuit voltage of 128 V, a short-circuit current of 120 μA, and an instantaneous power density of 0.75 mW cm-2, much higher than the previously reported works. The developed multi-order and 3D-interconnected piezoceramic textile shows satisfactory piezoelectricity (d33 of 190 pm V-1), air permeability (45.1 mm s-1), flexibility (Young's modulus of 0.35 GPa), and toughness (0.125 MJ m-3), collectively. The design strategy of obtaining balanced properties promotes the practicality of smart/functional materials in wearables and flexible electronics. [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]

This paper originally investigates the influence of frequency-up conversion effect on piezoelectric stack generators for high-performance energy harvesting. A compressive-mode piezoelectric generator is proposed comprised of a piezostack and a spring-mass system for electromechanical transduction and mechanical excitation, respectively. The frequency-up conversion effect is induced by amplitude truncations of the mass under external excitation. A control group, i.e. without truncation, is set for performance comparisons. Experimental results indicate that, with the frequency-up conversion, instantaneous power and average power are enhanced by over 1000 and 177 times, respectively. Each voltage response cycle consists of two stages: high-frequency high-amplitude oscillation and the rest of low-frequency low-amplitude harmonic vibration. The frequency of the former stage determines impedance matching. Due to the frequency converted up by 69 times, and intrinsic high capacitance of the stack, the matched resistance is significantly reduced from over 5 kΩ to 73.10 Ω, resulting much higher power response than that without conversion. Additionally, increase of spring stiffness causes the decrease of voltage responses and less effectiveness of frequency conversion effect. In this work we conclusively report that an instantaneous peak power output of 0.32 W can be generated from a millimeter-size piezoelectric generator, which can foster development of high-viability self-powered applications. [Display omitted] • Original study on frequency-up conversion effect on the piezostack-based generators. • Achieving over two orders of magnitude enhancement of instantaneous power. • Matched impedance is lowered from 5.1 kΩ to 73Ω. • Average power enhanced by over 200 times after frequency conversion. • Study on the restoration spring stiffness affecting frequency converting behaviors. [ABSTRACT FROM AUTHOR]

Real‐time detection and differentiation of diverse external stimuli with one tactile senor remains a huge challenge and largely restricts the development of electronic skins. Although different sensors have been described based on piezoresistivity, capacitance, and triboelectricity, and these devices are promising for tactile systems, there are few, if any, piezoelectric sensors to be able to distinguish diverse stimuli in real time. Here, a human skin‐inspired piezoelectric tactile sensor array constructed with a multilayer structure and row+column electrodes is reported. Integrated with a signal processor and a logical algorithm, the tactile sensor array achieves to sense and distinguish the magnitude, positions, and modes of diverse external stimuli, including gentle slipping, touching, and bending, in real time. Besides, the unique design overcomes the crosstalk issues existing in other sensors. Pressure sensing and bending sensing tests show that the proposed tactile sensor array possesses the characteristics of high sensitivity (7.7 mV kPa−1), long‐term durability (80 000 cycles), and rapid response time (10 ms) (less than human skin). The tactile sensor array also shows a superior scalability and ease of massive fabrication. Its ability of real‐time detection and differentiation of diverse stimuli for health monitoring, detection of animal movements, and robots is demonstrated. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) has been widely studied in the fields of vibration control, building construction, and underwater vehicles. Recently, researchers began utilizing the VIV phenomenon for flow energy harvesting. Here, we describe that vortex shedding causes periodic rotational motions and explore these vortex-induced swing (VIS) motions for harvesting flow energy and measuring flow speed. An arc-bluff structure was constructed to enlarge the VIS motions, and a phenomenological model was developed using the Van der Pol equation. Swing characteristics when flow velocities were in the range of (0.15, 0.45) m/s were assessed. Experiments showed that the maximum swing amplitude of the device is 120°, and it converges to 80° as the water velocity increases. The frequency, amplitude, and initial angle curve of the VIS device can be used to represent the water speed vector. The proposed flowmeter showed a flow rate sensitivity of 7∼10 Hz/(m·s−1) in the experimental range. Energy harvester prototypes demonstrated a peak-peak output of 3.28 V in water with a velocity of 0.45 m/s. The present work provides an approach for the flow measurement and energy harvesting under low-speed and low-frequency conditions. [ABSTRACT FROM AUTHOR]

• A novel hybrid scheme of piezoelectric and electromagnetic energy harvesting. • The harvester can yield a peak power of 0.33 W with a compact size. • The piezoelectric transduction operates in compressive mode. • The magnet array in electromagnetic transduction unit is arranged alternatively. • Applications of building self-powered sensors and electronics with the harvester. In this paper, we present a 0.33 W piezoelectric and electromagnetic hybrid energy harvester to tackle the problem of efficiently harnessing energy from low-frequency vibrations. Two types of transduction cores-one piezoelectric element and two sets of magnets and coils, are embedded into a compact design. Several techniques are employed to enhance the performance of the harvester. A pair of truss mechanisms are added into the system to amplify the strain of the piezoelectric element. A stopper is used to induce impact to take advantage of the frequency up conversion effect as well as nonlinearity. We used an array made of multiple small cubic magnets and alternative magnet arrangement rather than one magnet block, for abrupt magnetic flux density changes. Experimental results based on a fabricated prototype validate the proposed techniques that work collectively and enable the harvester to yield a maximum peak power more than 0.33 W at resonance under an excitation of 0.70 g. We also examined the capability of the harvester for self-powered applications. The harvester displays excellent charging performance to millifarad or farad-scale capacitors. An LED array consisting of 99 diodes was lit up in real time. More importantly, experimental results indicate that not just can the harvester simultaneously power a temperature and humidity sensor, and a calculator, but also when the excitation stops, the remaining charges stored can power them for ~20.38 min and ~8.33 min, respectively. This study can be of great significance for high-performance energy harvesting and further development of self-powered sensing and battery-free electronic systems. [ABSTRACT FROM AUTHOR]

The soft millirobot is a promising candidate for emerging applications in various in‐vivo/vitro biomedical settings. Despite recent success in its design and actuation, the absence of sensing ability makes it still far from being a reality. Here, a radio frequency identification (RFID) based battery‐less soft millirobot that can move, sense, and communicate remotely by coupling the magnetic and piezoelectric effects is reported. This design integrates the robot actuation and power generation units within a thin multilayer film (<0.5 mm), i.e., a lower magnetic composite limb decorated with multiple feet imparts locomotion and a flexible piezoceramic composite film recovers energy simultaneously. Under a trigger of external magnetic guidance, the millirobot can achieve remote locomotion, environment monitoring, and wireless communication with no requirement of any on‐board battery or external wired power supply. Furthermore, this robot demonstrates the sensing capability in measuring environment temperature and contact interface by two different sensing models, i.e., carried‐on and build‐in sensing mode, respectively. This research represents a remarkable advance in the emerging area of untethered soft robotics, benefiting a broad spectrum of promising applications, such as in‐body monitoring, diagnosis, and drug delivery. [ABSTRACT FROM AUTHOR]

The pyroelectric effect provides an efficient route to convert low-grade waste heat into electricity. (Bi 0.5 Na 0.5)TiO 3 -based ceramic is one of the most attractive lead-free pyroelectric candidates due to its high polarization. However, the low breakdown strength (BDS) restricts its ability to achieve a high polarization, hindering the application for thermal energy harvesting based on the Olsen cycle. In this work, by incorporation of AlN into BNT-BZT ceramics to form the BNT-BZT: AlN composites, the BDS is enhanced from 160 kV cm−1 to 260 kV cm−1, leading to a high energy density of 1.54 J cm−3 which is ∼5 times that of the pristine BNT-BZT. The reason for the high energy harvesting performance is due to the addition of AlN that can depress the conductivity of the matrix, resulting in the high BDS that permits high electric fields to be applied on the samples to induce high polarization that changes pronouncedly with temperature. [ABSTRACT FROM AUTHOR]

Over the centuries, scientists and engineers have been fascinated by the directional transport of water on the peristome of pitcher plant. Through experimental investigation and theoretical analysis, here we reveal the more complex picture of droplet transport on this peculiar natural surface. First, we demonstrate that in addition to the presence of the asymmetric arch-shaped microcavity with gradient wedge corners and sharp edges, the structural gradient in the first-tier microgroove of the pitcher's peristome also plays an important role in the regulation of the directional droplet transport. Moreover, the directional liquid transport only occurs in a limited condition. Without the intricate control of the interplay between its multiscale structures and multiscale sources of water, as well as the dynamic conditions of water, the preferential directional droplet transport will collapse. The new transport phenomenon and the mechanisms we reveal will provide important insights for the design of asymmetric morphologies for droplet manipulation. The way many natural surfaces transport water has been a fascinating subject for many centuries. The paper presents an experimental and theoretical investigation of droplets transport on the peristome of pitcher plants and shows that this depends on the multiscale structures of both the surface and the water. [ABSTRACT FROM AUTHOR]

Energy harvesting devices that prosper in harsh environments are highly demanded in a wide range of applications ranging from wearable and biomedical devices to self-powered and intelligent systems. Particularly, over the past several years, the innovation of triboelectric nanogenerators (TENGs) that efficiently convert ambient kinetic energy of water droplets or wave power to electricity has received growing attention. One of the main bottlenecks for the practical implications of such devices originates from the fast degradation of the physiochemical properties of interfacial materials under harsh environments. To overcome these challenges, here we report the design of a novel slippery lubricant-impregnated porous surface (SLIPS) based TENG, referred to as SLIPS-TENG, which exhibits many distinctive advantages over conventional design including optical transparency, configurability, self-cleaning, flexibility, and power generation stability, in a wide range of working environments. Unexpectedly, the slippery and configurable lubricant layer not only serves as a unique substrate for liquid/droplet transport and optical transmission, but also for efficient charge transfer. Moreover, we show that there exists a critical thickness in the liquid layer, below which the triboelectric effect is almost identical to that without the presence of such a liquid film. Such an intriguing charge transparency behavior is reminiscent of the wetting transparency and van der Waals potential transparency of graphene previously reported, though the fundamental mechanism remains to be elucidated. We envision that the marriage of these two seemingly totally different arenas (SLIPS and TENG) provides a paradigm shift in the design of robust and versatile energy devices that can be used as a clean and longer-lifetime alternative in various working environments. [ABSTRACT FROM AUTHOR]

Abstract Colloidal quantum dots (CQDs) have shown their advantages in gas-sensing applications due to their extremely small particle size and facile solution based processes. In this study, a high sensitivity of surface acoustic wave (SAW) NO 2 sensor was demonstrated using SnS CQDs as the sensing layer. The delay line based SAW device with a resonant frequency of 200 MHz were fabricated on ST-cut quartz substrate. The SnS CQDs with average sizes of 5.0 nm were synthesized and deposited onto SAW sensors using a spin-coating method. The fabricated SAW sensor was capable of detecting a low concentration of NO 2 gas at room temperature with a good efficiency and selectivity e.g., with a 1.8 kHz decrease of center frequency of the SAW delay line when exposed to 10 ppm NO 2 at room temperature. Highlights • Small-size and high-crystallinity SnS CQDs were synthesized via hot injection. • The SnS CQDs were successfully integrated onto the SAW delay lines by spin-coating. • The SnS CQD-coated SAW sensor exhibited high response to NO 2 at room temperature. [ABSTRACT FROM AUTHOR]

Highlights: • Improved harvester power output via abrupt magnetic-flux-density changes. • Fabricated magnet arrays of alternating north and south poles to abrupt flux changes. • Constructed alternative and Halbach arrays with triangular and cubic magnets. • Achieved a max RMS power output of 35.5 mW under an excitation of 9.8 m/s2. Abstract Electromagnetic energy harvesters have been studied intensively in the past decade as non-stop power solutions for low-power wireless electronic devices. We here exploit a new way, i.e., forming an abrupt change of magnetic flux density, to improve harvester performance. A new transducer is proposed, which is primarily composed of a set of magnet array, a pair of springs and a coil array. Four cases are investigated: cubic magnets in Halbach and alternative configurations; triangle magnets in Halbach and alternative configurations. We examined the magnetic flux density distribution via the finite element method (FEM) and ensured the nonexistence of phase difference in two contiguous coils. We fabricated a prototype and conducted comprehensive tests, of frequency sweep with and without external resistances, of matching impedance and of obtaining maximum RMS power output. The FEM analysis indicates that the harvester in the cubic alternative case has the largest changing rate of the magnetic flux density (MFD) in terms of the magnitude and the distance range of the change. Experiments verify the FEM simulation and the prototype with the cubic alternative magnet array shows the highest voltage response of 20 V and a maximum RMS power output of 35.5 mW under a harmonic excitation of 9.8 m/s2, which is much higher than those in the other cases. In term of the volume and mass power density, the alternative arrangement of cubic magnets displays the most desirable outputs at 0.4955 mW/cm3 and 0.28 mW/g, respectively, which are three and two times as high as those of the second best case - the triangle Halbach case. This detailed study reveals the considerable benefits brought by the magnet arrays of alternating polarity and configuration, and paves a new way to improve the performance of electromagnetic energy harvesters. [ABSTRACT FROM AUTHOR]

• The RMS voltage response of the energy harvester is increased by up to 1225%;. • We present a new quasi-zero stiffness mechanism for energy harvesters;. • We derive a stable solution to the adverse effect of the offset distance;. • The nonlinear dynamics of the proposed systems are analyzed comprehensively. The self-powered sensing technology based on gravity-rotation-excited vibration energy harvesting (GRE-VEH) enables information acquisition directly from rotatory machines online. However, the centrifugal effect due to the distance between the mass centroid of the energy harvester and the rotating axis (i.e., offset distance) seriously limits its broad engineering applications. To address this issue, we propose methods of using a tensile force provided by pre-deformed springs to counter the constant centrifugal force around the target rotation speed for improving the performance of the energy harvester affected by offset configurations. The GRE-VEH system with a linear spring is first studied by experiments and simulations, where a distributed-parameter model is developed and experimentally validated. The results well validate the proposed mechanism, where the performance of the harvester prototype significantly increases (by up to 1225%). A parametric study is also performed theoretically. The results indicate that the best performance improvement can be obtained by tuning the parameters related to the tensile length, the stiffness, and the damping of the spring. To enable the proposed mechanism in large centrifugal force cases, a pair of negative springs is introduced to the system for constructing a quasi-zero stiffness (QZS) structure together with the linear spring. The new GRE-VEH system is theoretically studied by an updated model, where the system's main characteristics are revealed. The simulation results well indicate the feasibility of the method using the QZS mechanism. This work paves a new way of solving the offset distance problem for the application of the GRE-VEH and also provides new insight into the application of the QZS mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

B Smart Masks b In article number 2203565 by Ho-yin Chan, Xinge Yu, Jianping Wang, Wen Jung Li, and co-workers, a "smart mask" is developed by using an ultrathin nanocomposite-based soundwave sensor with high sensitivity and wide-bandwidth dynamic range, i.e., integrated with machine/deep learning algorithms, the smart mask can identify breath, two-/tri-phase coughs, and spoken words directly. The smart mask could be a new wearable Internet of Things device for personal health monitoring and respiratory disease identification tool in the future. Wide-Bandwidth Nanocomposite-Sensor Integrated Smart Mask for Tracking Multiphase Respiratory Activities (Adv. Sci. 31/2022). [Extracted from the article]

• T-phage-inspired multilegged design for microrobot. • A rotationally asymmetric structure. • Multiple working modes: forward motion, backward motion, steering, climbing, and swimming. • The maximum velocity of 120 mm/s under a driving voltage of 50 V p-p and the maximum carrying weight of 10.6 gs, 6 times more than the weight of the microrobot. • Miniaturization capability and ability to work in various environments, i.e., a narrow tube and water. T-phages use contractile tails to recognize host bacterial and move on the surface of bacterial. This virus demonstrates remarkable locomotive capabilities in recognition and infection progress. The field of microrobotics focuses on achieving these functions in mobile robotic systems of centimeter size. However, owing to the structure size and weight, it has been a challenge to satisfy high robustness, fast motion, adequate carrying capacity, low driving voltage, and versatile environmental adaptability in one robot. In addition, functional microrobots require multimodal locomotive strategies that reconcile the constraints imposed by different applications. Inspired by the unique structure of T-phage in the micro-world, we develop a T-phage Mimic MicroRobot (TMMR), which is composed of a triangular prism core with piezoelectric elements and legs attached on bases, mimicking the core and the tail fibers of the T-phage, respectively. The triangular prism structure avoids rollover while moving, indicating the robustness of the design. TMMR of 2.5 × 2.5 × 2.6 mm3 weighs 1.74 gs and can be easily further miniaturized. It is capable of moving forward, backward, and steering at a low voltage of 25 V. Working mechanisms for each type of motion are analyzed using the finite element method. Results show that TMMR reaches 120 mm/s, 4.8 body lengths per second (BL/s), and carry an object weighing 10.6 gs, 6 times more than its weight. By sealing the body and adding passive flaps, TMMR achieves a "swimming" motion with a velocity of 16 mm/s. TMMR shows potential for versatile applications in a narrow and constrained environment. [Display omitted] [ABSTRACT FROM AUTHOR]

• Distributed-parameter model for a doubly-clamped energy harvester affected by the misalignment-induced torsions in vibration environments. • Experimental validation for the developed model and the effects of the bending-torsional coupling vibration on the harvester. • Characterizations of the bending-torsional coupling vibration for the doubly-clamped beam structures. • Investigations on the effects of the key parameters on the torsion-induced jump-down phenomenon. This article presents a theoretical and experimental study on the unique bending-torsional coupling vibration of a doubly-clamped nonlinear piezoelectric energy harvester due to the misalignment of the centroid and the torsional axis in vibration environments. Based on the Euler-Bernoulli beam theory, the extended Hamilton's principle, and the Galerkin discretization, a distributed-parameter model considering the misalignment is developed, and the corresponding governing equations are formulated. The developed model is validated against experimental data and Finite Element Analysis, where good agreements are achieved. Effects of the key parameters on the system's responses, and the characteristics and the causes of the bending-torsional coupling vibration are studied numerically based on the developed model. The results show that the torsion-induced chaotic motion can activate the jump-down phenomenon, largely reducing the electrical output of the harvester. Additionally, the occurrence of the torsion-induced jump-down phenomenon is sensitive to the system's initial state in some cases and can be reduced or even avoided by effectively tuning parameters that have slight effects on the bending resonance, such as the preloaded axial force and the distance between the torsional axis and the centroid. [ABSTRACT FROM AUTHOR]

• A comprehensive electrode coverage design principle is developed. • Equivalent stiffness and damping are introduced to evaluate coupling coefficients. • Strongly coupled harvesters are compatible with a wide range of electrode coverage. Cantilevers are widely used for piezoelectric vibration energy harvesters (PEHs), thanks to the low resonance frequency and large mechanical strain under weak excitations. Electrode coverage optimization is essential for maximizing output power. In this study, bimorph cantilevers with segmented electrodes are developed to investigate the correlation between effective electrode coverage (EEC) and the harvesting behavior of piezoelectric cantilevers. A nonlinear electromechanical model is established using Hamilton's principle, numerically solved with the method of harmonic balance, and further validated by experimental measurements. Equivalent linear stiffness and equivalent mechanical damping ratio are firstly introduced for evaluating the equivalent effective electromechanical coupling coefficients and identifying strong and weak coupling harvesters. Both harvesters fabricated with and without proof mass behave mainly as strongly coupled systems and can obtain the maximum possible power at a very low EEC. Variation of EEC in higher range acquires almost constant maximum power on dramatically changing resistance. A comprehensive EEC design principle for acquiring the maximum output power is obtained for cantilevered PEHs. An optimal EEC obtaining the maximum effective electromechanical coupling coefficient is needed for acquiring the unique maximum power pick for weakly coupled harvesters, whereas a wide range of EEC can be used to maximize output power for harvesters those mainly behave as strongly coupled systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Propose an auxetic nonlinear piezoelectric energy harvester. • Utilize a pure mechanical structure to enhance both efficiency and bandwidth. • Perform finite element analysis to analyse the performance of the harvester. • Experimentally validate the proposed design and model and conduct parametric studies. In this paper, we design and experimentally validate an auxetic nonlinear piezoelectric energy harvester. This harvester adopts a clamp-clamp beam with auxetic structures, which can improve the efficiency and bandwidth of the energy harvesting based on a pure mechanical structure without outer magnets or stoppers. Finite element analysis is performed to analyse the effects of the auxetic structures on the efficiency and nonlinearity of the energy harvester. The lumped parameter model is utilized to predict the performance of the energy harvester, which well matches the experimental results. In the experimental validation, at 0.1 g base acceleration, the power output of the two types of auxetic energy harvesters is 173% and 94% higher than the conventional nonlinear energy harvester. Besides, the bandwidths of the two types of auxetic energy harvesters are broadened by 1556% and 2142% compared with the linear systems. [ABSTRACT FROM AUTHOR]

• Segmented arc-shaped piezoelectric energy harvester is proposed. • A new distributed-parameter electromechanical coupling model is developed. • The analytical solutions are validated with FEM and experiments. • Energy harvester characteristics with optimal parameters to generate maximum output voltage of 50 V are fully investigated. Advances in energy harvesting techniques, along with low-power electronic devices open up the possibility of developing self-powered engineering systems. Most existing energy harvesters are constructed with beams such as cantilevers, fully-clamped beams and buckled beams. Here we present an attempt to add a new design dimension to the piezoelectric energy harvesters (PEHs) by exploiting a curved-beam structure. This design will be shown to dramatically improve the contemporary harvester performance. To establish an analytical base for curved PEHs, we take a variable-curvature unimorph as the general modelling object and derive its governing equations based on the Timoshenko beam theory. Using the mode expansion method with the consideration of boundary conditions and continuous conditions, we present analytical solutions of the electrical and mechanical response of the PEH. The model developed is verified via the finite element method and it can accurately estimate the modal response of the curved PEH. Prototypes are fabricated and tested to validate the analytical model and solutions. Furthermore, we comprehensively analyzed the key parameter effects including the length of the straight beam, thickness ratio and Young's modulus on the performance of the PEH. The proposed analytical model provides an analytical guidance for composite arc-shaped PEHs with variable curvature and it also helps in the design and optimization of new PEHs. [ABSTRACT FROM AUTHOR]