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Railway traffic plays a pivotal role within the current transportation system, with ensuring its safety being of paramount importance. Real-time monitoring of train track health through sensor technology has emerged as a significant approach for achieving this objective. However, a persistent challenge lies in providing cost-effective and stable power to sensors in remote areas. This paper proposes the utilization of a novel piezoelectric stack energy harvester in railway systems to address this issue. The substantial and consistent vibration energy produced by railway operations makes it an ideal source for energy harvesting, unaffected by environmental conditions. Through simulation analysis and experimental verification, this study explores the impact of load size, load frequency, and external resistance on the energy harvesting efficiency of the proposed piezoelectric stack energy harvester. The results indicate that the output power of the energy harvester increases with the load size. Furthermore, the frequency significantly influences the energy capture efficiency when below 8 Hz, with minimal impact on frequencies above 8 Hz. Interestingly, the load dramatically affects the energy capture efficiency, even at higher frequencies. With the external resistance set to 250 kΩ, the harvester achieves a maximum output power of 42.76 mW. [ABSTRACT FROM AUTHOR]

This paper proposes a quasi-zero stiffness (QZS) isolator composed of a curved beam (as spider foot) and a linear spring (as spider muscle) inspired by the precise capturing ability of spiders in vibrating environments. The curved beam is simplified as an inclined horizontal spring, and a static analysis is carried out to explore the effects of different structural parameters on the stiffness performance of the QZS isolator. The finite element simulation analysis verifies that the QZS isolator can significantly reduce the first-order natural frequency under the load in the QZS region. The harmonic balance method (HBM) is used to explore the effects of the excitation amplitude, damping ratio, and stiffness coefficient on the system's amplitude-frequency response and transmissibility performance, and the accuracy of the analytical results is verified by the fourth-order Runge-Kutta integral method (RK-4). The experimental data of the QZS isolator prototype are fitted to a nine-degree polynomial, and the RK-4 can theoretically predict the experimental results. The experimental results show that the QZS isolator has a lower initial isolation frequency and a wider isolation frequency bandwidth than the equivalent linear isolator. The frequency sweep test of prototypes with different harmonic excitation amplitudes shows that the initial isolation frequency of the QZS isolator is 3 Hz, and it can isolate 90% of the excitation signal at 7 Hz. The proposed biomimetic spider-like QZS isolator has high application prospects and can provide a reference for optimizing low-frequency or ultra-low-frequency isolators. [ABSTRACT FROM AUTHOR]

• D-AFB has a simple structure and can easily satisfy QZS conditions. • Customizing the design of D-AFB to adapt to load requirements. • The experiment verified the reliability of replacing D-AFB. • Increasing the number of D-AFB can improve the carrying capacity. • The vibration isolator can stably adapt to load fluctuations within 10 %. There is an increasing demand for integrated small vibration isolators in precision sensing instruments and medical equipment. Therefore, a quasi-zero stiffness (QZS) vibration isolator with double-arc flexible beams (D-AFB) is proposed. The QZS isolator consists of D-AFB units, the base, platform, fixture, guide rail, and linear bearing. The static performance of D-AFB is analyzed using the FEA method, and the QZS condition is obtained. The harmonic balance method (HBM) and the pseudo arc length method (PALM) are used to solve the dynamic equations of the nonlinear system, and the analytical solutions of displacement transmissibility and Force transmissibility are derived. In theory, the initial frequency is 77.6 % lower than that of the equivalent linear system. The QZS characteristic of D-AFB is verified by static experiment, and the low-frequency isolation performance of the QZS isolator is verified by dynamic experiment under constant amplitude and constant acceleration excitation. The D-AFB has a simple structure and can easily satisfy QZS conditions. So the D-AFB can be customized according to load requirements. Multiple vibration isolation loads can be obtained by adjusting the assembly of the D-AFB. The QZS isolator can adapt to load changes within 10 % and has an isolation effect on vibrations above 4 Hz. The idea of designing a QZS isolator with D-AFB as an array unit has a good research prospect and great application value in meeting the requirements of miniaturization and integration. [Display omitted] [ABSTRACT FROM AUTHOR]

Industry 4.0 realizes intelligent interconnection through the sensor group of the Internet of Things. A key challenge is to achieve the self-powering of sensors and stable operation of precision instruments. This paper introduces a dual-functional structure (VIPEH) integrating energy harvesting (EH) and vibration isolation (VI) based on the quasi-zero stiffness (QZS) piezoelectric mechanism. The paper analyzes the nonlinear statics of piezoelectric flexible beams under large deformations and conducts parametric analysis. A nonlinear dynamic model with electromechanical coupling was developed to investigate the impact of mechanical and electrical parameters on the system's dynamic bifurcation behavior, EH, and VI performance. Finally, an experimental setup is created to evaluate the VIPEH's characteristics. Sweep frequency excitation experiments demonstrate that the initial isolation frequency of VIPEH is lower than 1.4 Hz. The important thing is that VIPEH can still power the sensor based on the isolation frequency, and the output power of a single piezoelectric material can reach 3.19 mW. This not only enables the isolation of low-frequency vibrations but also presents a highly promising application for achieving self-powering in sensor clusters within the context of Industry 4.0 and the IoTs. • VIPEH based on quasi-zero stiffness piezoelectric mechanism is proposed. • VIPEH achieves energy harvesting while isolating low-frequency vibrations. • The output power can reach 3.19 mW. • The initial vibration isolation frequency of VIPEH is less than 1.4 Hz. [ABSTRACT FROM AUTHOR]

Ship vibration not only causes safety issues, but also easily generates noise pollution. Therefore, this paper introduces the quasi-zero stiffness (QZS) vibration isolator to solve the problem of low-frequency vibration. In terms of static analysis, this paper proposes a discretized beam constraint model (DBCM) to study the static properties of flexible beams with large deformation, and the finite element analysis (FEA) verifies the accuracy of DBCM. Regarding dynamic analysis, this paper combines the harmonic balance method (HBM) and the pseudo-arc length method (PALM) to analyze the dynamic response and explore the influence of excitation and damping ratio on the response stability. In addition, the performance of equivalent linear isolators is compared, revealing significant advantages of QZS isolator in terms of isolation bandwidth and peak transmissibility. The experimental data demonstrates that QZS isolator's initial isolation frequency (2.14 Hz) is 68.5% lower than that of linear isolators (6.79 Hz), and the isolation efficiency at 5.35 Hz can reach 90%, making it suitable for low-frequency isolation. Furthermore, experimental data validate the accuracy of the theoretical model and FEA. The static and dynamic theoretical models can optimize the structural parameters of flexible beams and serve as valuable inspiration and reference for designing and improving isolator. • The QZS isolator is composed of eight flexible beams and a linear spring. • DBCM can accurately calculate the nonlinear statics of flexible beams. • The QZS isolator has a wider isolation frequency band and lower transmissibility. [ABSTRACT FROM AUTHOR]

• Experiments verified the performance of WMPEH with different structural parameters. • Wake excitation and magnetic coupling are used for underwater energy harvesting. • The wake excitation and magnetic coupling can enhance harvesting performance. • Reducing the fixing column diameter can increase the output voltage. • Increasing the vibrating column diameter can enhance performance. • Increasing the vibrating column mass can improve performance. [Display omitted] This paper proposes a wake-excited magnetically coupled piezoelectric energy harvester (WMPEH) to realize the self-powered function of microelectronic devices in a fluid environment. The WMPEH consists of a fixed column, a vibrating column, magnets, and a piezoelectric composite beam. A series of water tunnel experiments are conducted to prove the usefulness of wake excitation and magnetic coupling, and how it positively or negatively affects the harvester's efficacy. Different fixed and vibrating column diameters and the distance between the two columns affect the performance of the WMPEH. The influence of the wake excitation force generated by the fixed columns with diameters of 5 mm, 10 mm and 15 mm on the vibrating column is analyzed respectively in the experiment. The vibrating column diameter is D , and four different distances are considered, namely 2 D , 3 D , 4 D , and 5 D. The results show that the maximum output voltage of WMPEH is increased by 1.96 and 1.34 times, respectively, compared with that of magnetically coupled piezoelectric energy harvester (MPEH) and conventional piezoelectric energy harvester (PEH). Furthermore, increasing the fixed column diameter leads to a decrease in the output voltage of WMPEH in the case of the same vibrating column diameter. Increasing the diameter and mass of the vibrating column for a specific fixed column diameter can enhance the harvester's performance. The maximum output voltage density of the WMPEH is 75.56 V/cm3 when the vibrating column diameter, the fixed column diameter and the distance between the two columns are 20 mm, 5 mm, and 2 D , respectively. This proposed design can provide the groundwork to promote the performance of the conventional PEH, further enabling the realization of underwater self-powered systems. [ABSTRACT FROM AUTHOR]

• The proposed device contains magnetic coupling and vortex-induced vibrations. • The structural parameters of vibrating column affect the efficiency. • The magnetic repulsion system is suitable for low-speed water flow environment. • The magnetic attractive system is suitable for high-speed water flow environment. The rapid development of the fifth-generation mobile networks (5G) and the Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. To solve the problem of self-powered underwater wireless sensor nodes (WSNs), this paper proposes a magnetically coupled piezoelectric energy harvester (MPEH) based on fluid-induced vibration (FIV) to achieve high-efficiency performance in low-velocity water environments. The results show that compared with the non-magnetic PEH, the initial vibration velocity, velocity bandwidth, and maximum output voltage of the magnetic attraction coupling piezoelectric energy harvester (MAPEH) are increased by 18.42%, 41.38%, and 5.79% respectively. Besides, it is also shown that the vertical distance between the magnets, the diameter, and the mass of the vibrating column have a significant effect on the vibration characteristics, water velocity bandwidth, and performance of the magnetic repulsion coupled piezoelectric energy harvester (MRPEH). The initial vibration velocity of the MRPEH is reduced by 42.1%, and when the water speed is 0.2 m/s, its output voltage is 12.21 times that of the classical configuration. This proposed structure can provide a reference for the optimization of underwater FIV-based PEH, and also lay a foundation for further interconnection of underwater self-powered sensors. [ABSTRACT FROM AUTHOR]

• When the flow rate is high, the change of the L and H has a great influence on the of the PEH array. • The single-row parallel-arranged array (PEH-2P and PEH-3P) can improve the system's initial vibration velocity and half-frequency bandwidth. • The single-row series-arranged array (PEH-2S and PEH-3S) can increase the maximum energy harvesting power. • The energy harvesting capacity of nine-vibrators square array is 102.4% higher than the reference value, and the initial vibration velocity is 25.95% lower than the reference value. This paper mainly uses simulation and experimental methods to analyze the output characteristics of different piezoelectric energy harvester (PEH) arrays based on flow-induced vibration, which is mainly used in low-velocity water in a natural environment. Each PEH consists of a piezoelectric beam and an interference cylinder. The PEH arrays presented in this paper include the double-vibrators parallel array (PEH-2P), double-vibrators serial array (PEH-2S), three-vibrators parallel array (PEH-3P), three-vibrators serial array (PEH-3S), and nine-vibrators square array (PEH-9). Prototypes of the different PEH arrays are fabricated and experiments are conducted to explore the energy harvesting capacity, the maximum energy harvesting power, initial vibration velocity and half-power bandwidth of the different PEH arrays. The experimental results demonstrated that the PEH-2P and the PEH-3P can improve the system's initial vibration velocity and half-power bandwidth, but the maximum energy harvesting power of the PEH array is relatively not good. The PEH-2S and the PEH-3S can increase the maximum energy harvesting power of the PEH array, but the initial vibration velocity and half-power bandwidth of the PEH array are relatively not good. The average value of energy harvesting capacity of the PEH-9 is the largest, which is 102.4% higher than the reference value, and the initial vibration velocity of the PEH-9 is the lowest, which is 25.95% lower than the reference value. This work provides a comprehensive experimental guideline for further designing an efficient PEH array used in the low-speed water environment. [ABSTRACT FROM AUTHOR]

This paper designs an underwater magnetic nonlinear piezoelectric energy harvester (PEH) based on the principle of vortex-induced vibration (VIV). The equivalent stiffness of the magnetic nonlinear PEH is significantly changed by varying the relative position of the magnet. It is observed that the proposed PEH displays hardening behavior and softening behavior due to the impact of magnetic forces, which greatly increase the performance of the magnetic nonlinear PEH. The analysis of the results shows that the open-circuit voltage (VRMS) of the hard stiffness system is increased from 9.43 V to 10.31 V, the frequency band is widened by 36.8%, and the efficiency is higher at high flow rates. The initial vibration velocity of the soft stiffness system is reduced. When the water velocity is 0.2 m/s, its VRMS is 10 times that of the classical configuration. Both numerical simulations and experiments prove that the soft stiffness system is more suitable for applications in low-speed water environments. This proposed design can provide the groundwork to promote the performance of the conventional PEH, further enabling to realize self-powered systems. [Display omitted] • An underwater magnetic nonlinear piezoelectric energy harvester is presented. • The position of the magnet has an impact on the performance of the harvester. • The hard stiffness system is suitable for high-velocity water environment. • The soft stiffness system is suitable for low-velocity water environment. [ABSTRACT FROM AUTHOR]

• A bidirectional plucking energy harvester with an orthogonal oscillator is proposed. • Piezoelectric oscillator is excited by bidirectional magnetic component force. • Exploring bending and torsion vibrations of the orthogonal piezoelectric oscillator. • BP-RPEH has multiple resonance regions. • The charge rate could reach 0.39 V/s at 300 rpm. One key challenge of the energy harvesting technology lies in how to fully utilize external environmental excitation to collect ambient energy and convert it into electrical energy efficiently. To address this challenge, this work proposed a bidirectional non-contact plucking rotary piezoelectric energy harvester, based on the spatial distribution characteristics of magnetism. This work was initiated by establishing a mathematical model for the rotating magnetic field and calculating the magnitude of the magnetic forces. Numerical findings indicated that the quantity of rotating magnets had an impact on the magnitude and distribution of these magnetic forces. Leveraging the distinctive attributes of the rotating magnetic forces, this work introduced an orthogonal piezo-oscillator, designed to concurrently respond to magnetic forces along two orthogonal directions. Subsequently, this work conducted experimental research on the piezoelectric oscillators. The experimental results indicated that the number of magnets affects the power output bandwidth and position of the effective frequency. A mathematical relationship exists between the resonant frequency, the number of magnets, and the natural frequency. The results demonstrate that the total peak output power of the harvester could reach 3.29mW calculated by RMS voltage at 301 rpm, and the charging rate could reach 0.39 V/s at 300 rpm. [ABSTRACT FROM AUTHOR]

Batteries with a limited lifespan have gradually failed to meet the development needs of some low-power electronic products. Harvesting wind energy to power the above devices has been a promising way. Facing the time-varying characteristics of wind direction and velocity in the natural environment, an efficient orientation-adaptive energy harvester (OAEH) based on the piezoelectric effect is proposed. An experimental test system is established to probe into the output and adaptive performances of the OAEH. The experimental results indicate that improving the inertia of the tray can abate the initial wind velocity and enhance the output power to a certain extent. The relative deviation (γ) of power integration areas at different inclinations is less than 3%. The harvester has 364.86% enhancement in average power integration area comparing that with the fixed shaft. Besides, the OAEH can drive a monitoring device with a display screen and integrated sensors, which can be utilized to monitor the condition of the bridge, flyover, and so on. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting holds the promise of providing autonomous power for low-power electronic devices. To improve the issue of the limited bandwidth of the piezoelectric energy harvester, this work proposes a novel T-shaped beam bistable piezoelectric energy harvester with a moving magnet. The moving magnet can not only provide nonlinear force to adjust bandwidth, but also increase the number of system resonance peaks, which improves the utilization of the magnet, enhancing the adaptability of the vibration energy harvesting device to the environment. Established a mathematical model and validated it through experiments. Some parameters, such as external resistance, magnet spacing, and spring stiffness, are analyzed by theoretical analysis. The results indicate that, at an acceleration amplitude of 0.3 g and a frequency of 15.7 Hz, the peak output power of the main support beam is 2.36 mW. Similarly, at an acceleration amplitude of 0.3 g and a frequency of 15.6 Hz, the peak output power of the parasitic cantilever beam is 0.56 mW, demonstrating its potential to power low-power electronic components. The moving magnet provides an additional resonance peak for the harvester, offering a new method for the design of broadband magnetic nonlinear piezoelectric energy harvesters in the near future. • A novel T-shaped beam bistable piezoelectric energy harvester with a moving magnet (TBPEH) is proposed. • The moving magnet can not only provide nonlinear force to adjust bandwidth but also increase the number of system resonance peaks. • The coupling of the moving magnet and the T-shaped beam results in the generation of three voltage peaks, thereby expanding the frequency bandwidth. • The stiffness of the spring and the spacing between magnets influence both the size and position of the resonance peaks excited by the moving magnet. • In laboratory testing, the TBPEH demonstrated the capability to illuminate a light strip comprising 23 LEDs. [ABSTRACT FROM AUTHOR]

Energy harvesters capture the ambient vibration to persistently drive lower-power devices employed in wireless applications. For enhancing the harvesting performance, a novel piezoelectric aeroelastic (piezoaeroelastic) energy harvester fitted with different rod-shaped attachments is presented. The attachments include square and D-shape rods, and symmetrically fixed on airfoil surface at chord maximum thickness. The performance comparisons of various harvesters are conducted by using simulation and experimental methods. The results demonstrate that square and D-shape rods change flow field characteristic and enhance aerodynamic loads, which reduce flutter velocity and broaden the working bandwidth. The harvesters with square and D-shape rods demonstrate the better output characteristic in both aeroelastic vibration and harvesting performance than without rod. Output voltage of the harvester with square rod is up to 15.14 V at airflow velocity of 16.84 m/s and plunge stiffness coefficient of 278 N/m, and the corresponding output power is 0.765 mW. A maximum enhancement ratio of output power for square rod can reach to 469.7 % at 11.1 m/s. The power density of the harvester with square rod is 4.78 mW/cm3, which demonstrates the superior harvesting performance over others. This work provides a significant guidance for designing the more efficient piezoaeroelastic harvester with square rod. [Display omitted] • A novel piezoaeroelastic harvester fitted with rod-shaped attachments is presented. • Rods significantly enhance aerodynamic loads and reduce flutter velocity. • Square rod shows the superior harvesting performance than without and D-shape rods. • A maximum enhancement ratio is up to 469.7 % for square rod. [ABSTRACT FROM AUTHOR]

• This paper proposes a piezoaeroelastic harvester with trailing-edge flap. • The mathematical model of plunge-pitch-flap motions is derived. • The numerical results are in well agreement with experimental values. • The capacitor charged for 90 s can power Pedometer for 139 s [Display omitted] This paper presents a piezoaeroelastic energy harvester fitted with trailing-edge flap, for simulating three degrees of freedom plunge-pitch-flap motions and capturing the aeroelastic vibration energy. The flap is fitted with the trailing-edge of the airfoil, and restricted by the torsion spring rod. The governing equations of fluid-structure-electric coupled fields are derived. The influence of the harvester parameters on the output characteristic is investigated numerically. Experimental prototype of the harvester is fabricated, and the numerical results are validated by the experimental method. The results demonstrate that the lesser the pitch stiffness coefficient is and the larger the plunge and flap stiffness coefficients are, the larger aeroelastic vibration and the better harvesting performance can be obtained. The vibration mode changes from flutter-induced vibration to vortex-induced vibration at the smaller flap damping coefficient. The plunge amplitude of 0.057 m and output voltage of 32.18 V are harvested at 18 m/s. The output power can be up to 2.63 mW at 300 kΩ. The plunge amplitude and output voltage obtained numerically are in well agreement with the experimental values. The designed piezoaeroelastic harvester can drive the lower-power microelectromechanical system, which can promote the field application in microelectromechanical systems. [ABSTRACT FROM AUTHOR]