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Piezoelectric wind energy harvesters based on flow-induced vibration are attracting widespread attention because they can provide long-term sustainable power to wireless sensor network nodes. In order to improve the harvesting performance, this paper proposes a multi-interference local pressure modulation mechanism, and a three-plate multi-interference structure is applied for verification. Computational fluid simulations indicate that this three-plate multi-interference structure can effectively combine the double wake flow effect of the upstream double plates and the high-pressure feature in front of the downstream single plate. So that the local pressure of the fluid field can be effectively modulated to generate a significant lift force on the bluff body. Experiments show that this structure can promote the VIV(vortex-induced vibration)-based energy harvester to exhibit galloping vibration. Moreover, compared to the cases with only a single downstream plate or a double-plate upstream structure, lower cut-in wind speed and higher harvesting efficiency can be achieved by using the multi-interference structure. When the horizontal distance of the downstream plate, the horizontal and vertical offset distances of the upstream plates are set as 0.5D, 0.5D and 1.5D (D: windward width of the bluff body), respectively, the harvester can generate the highest output power of about 1.4 mW at a wind speed of 5 m/s. By introducing a spring–damper coupling mechanism, the synchronous movement of two side-by-side energy harvesters can be realized, thereby realizing the synchronous output of voltage and increasing the output power per unit volume.

The Artificial Intelligence of Things (AIoT) connects everything with intelligence, while the increase in energy consumption generated by numerous electronic devices puts forward an impending demand on the power supply. Energy harvesting technology has emerged as a compelling innovation technology for the net zero emissions of the power supply for the AIoT. Although significant advances have been witnessed in energy harvesting, some issues such as poor electrical output, weak environmental adaptability, and low reliability are difficult to satisfactorily resolve. Mechanical intelligent energy harvesting can be defined as the system identifying the external excitation or its own state and reacting to it, rather than relying on electrical sensing elements or a central controller for certain adaptive or programmed functions. The adaptive and programmed functions exhibit great potential in solving the above‐mentioned issues that seriously restrict the development of the energy harvesting technology. Here, a generalized definition of mechanical intelligent energy harvesting is given critically and the design methodology is elaborated. The typical reported energy harvesting systems with the characteristics of mechanical intelligence are reviewed. The key research directions in mechanical intelligent energy harvesting are discussed. The mechanical intelligence is expected to revolutionize the development of the energy‐harvesting technology and pave the way for applications. [ABSTRACT FROM AUTHOR]

Human energy harvesting for powering wearable or portable electronics has been extensively studied. We propose an electromagnetic energy harvester with a magnetic orbit (EMH-MO) for low-frequency and irregular human motion energy harvesting. A circular uniform low potential orbit is designed using the reasonable arrangement of multiple magnetic fields. Driven by irregular excitations, the moving magnet is magnetically modulated to move more regularly along the noncontact magnetic orbit, which is conducive to electromechanical energy conversion. A theoretical model is established to characterize the proposed energy harvester. Both simulations and experiments indicate that EMH-MO can work effectively under ultralow frequency (<5 Hz) weak excitation. The peak-peak open-circuit voltage is 4.3 V, and the average power is 0.33 mW under a reciprocating motion of 10 Hz and 20 mm. Besides, the EMH-MO can effectively harvest energy from walking, jogging, and running of people with different physical characteristics (chunky males, tall males, and petite females). [ABSTRACT FROM AUTHOR]

Highlights • A novel water-proof hybrid wind energy harvester is proposed. • The optimized magnetic arrangement is utilized to reduce the resistance torque. • A coupled dynamic model is developed and experimentally validated. • The hybrid harvester is flexible for practical applications as well as higher power. • The mechanical durability under the rainfall condition is experimentally validated. Abstract Small-scale wind energy harvesting can be a potential way to yield endless electrical energy for small and micro mechanical systems, which has gained extensive interest from both the academia and industry. The environmental adaptability and reliability of the harvester are key issues that cannot be ignored in practical applications. To overcome these challenges, we propose a novel water-proof hybrid wind energy harvester (WP-HWH) using magnetic coupling and force amplification mechanisms. Using a symmetrical opposite magnetic arrangement, the resistance torque is reduced as much as possible and the effective magnetic force is enhanced, which is beneficial to harvest energy at low wind speeds. The magnetic force can be further amplified and applied to the piezoelectric layer more evenly, thereby achieving higher power density and better reliability. The key components of the energy harvester can be packaged easily owing to the non-contact magnetic coupling mechanism. Thus, it can operate effectively in a harsh environment, such as rainfall. A theoretical model is developed to characterize the WP-HWH. Both simulations and experiments are performed to validate the design and analysis of the WP-HWH. The experimental results indicate that combining the advantages of piezoelectric energy harvester and electromagnetic energy harvester, the WP-HWH has enhanced flexibility for practical applications as well as an outpower. Additionally, under rainfall, the WP-HWH can operate continuously for more than 100,000 cycles and saturates at 3157.7 μW at a wind speed of 7.0 m/s, implying good mechanical durability. [ABSTRACT FROM AUTHOR]

Harvesting wave energy to power wireless sensors can realize marine environment monitoring. However, the low frequency and irregularity of waves, as well as the harsh marine environment, have become bottlenecks limiting the development of wave energy harvesting. Herein, we propose a novel concept of mechanical intelligent energy harvesting, i.e., adaptive external excitation and regulation of energy harvesting system by mechanical structure or mechanism rather than electrical components, and illustrate this concept by designing an irregular wave energy harvesting system. The proposed gravity-driven roller and seesaw-inspired structure are sensitive to low-frequency and irregular excitation, thereby wave energy can be more easily harvested into the system. Further, the bidirectional swinging of the seesaw is converted into a high-speed unidirectional rotation of the permanent magnet disc in one direction, resulting in a significant increase in the efficiency of electromechanical conversion. Moreover, symmetrical discs on both sides can rotate synchronously via magnetic coupling mechanism, which increases the magnetic flux in the coils for higher output power and the consistent phase of the voltage is conducive to the use of electricity. Besides, the rolling behavior is used by the triboelectric nanogenerator (TENG) to convert more mechanical energy into electricity without affecting the electromagnetic energy harvester. The experimental results show that the harvester can work effectively at the ultra-low frequency (0.1 Hz) and it can charge a 0.47 F capacitor to 5 V within 6 min to achieve a self-powered wireless marine environment monitoring system under simulated wave excitation. This work demonstrates that mechanical intelligent energy harvesting is a potential solution for irregular energy harvesting and self-powered Internet of Things (IoT). [Display omitted] • A novel concept of mechanical intelligent energy harvesting is proposed. • The seesaw-inspired structure is designed to adapt to irregular wave excitation. • Mechanically-driven and soft-driven mechanisms are combined for synchronous motion. • A self-powered wireless marine environment monitoring system is realized. [ABSTRACT FROM AUTHOR]

[Display omitted] • A design methodology of maximum utilization strategy for hybrid harvesting is proposed. • The centrifugal stiffening, nonlinearity and boundary modulation are systematically considered. • The electromechanical coupling dynamic model of the proposed system is established. • The self-powered rotor condition (temperature and tire pressure) monitoring is realized. The energy harvesting technology is capable of harnessing the intrinsic rotating energy of the rotor system to realize self-powered rotor condition monitoring for the Internet of Things (IoT). It is promising to solve the issue of sustainable energy supply of the rotor monitoring system and achieve a self-powered IoT. In this work, we propose a novel maximal utilization strategy for piezoelectric-electromagnetic-triboelectric energy harvesting in a broad speed range and achieve the self-powered rotor condition monitoring system. The piezoelectric energy harvester (PEH), triboelectric nanogenerator (TENG), and electromagnetic energy harvester (EMH) are respectively arranged in the place where the system exhibits the maximum strain, the maximum contact area, and the maximum displacement, respectively, which can make full use of their characteristics in the structural space. The modulation boundaries (parts of TENG) render a more controllable dynamic behavior of the harvester, and realize the vibration and impact coordinated power generation mode, which can harvest more mechanical energy in the time domain. The theoretical mathematical model and working criteria of the proposed system are established and verified experimentally. In addition, the prototype can operate effectively in a wide speed range (0–1000 r/min) and it can charge a 100 μF capacitor to 5 V within 11 s. The self-powered rotor wireless temperature monitoring and self-powered wireless tire pressure monitoring are realized during the practical road tests. The maximum utilization strategy provides a new design methodology for hybrid energy harvesting, which has potential applications in intelligent driving and rotating machinery condition monitoring. [ABSTRACT FROM AUTHOR]

Small wind harvesting can be integrated with sensors for self-powered environmental ecological monitoring, climate monitoring, natural disaster monitoring and on-site infrastructure monitoring, which is of great importance for protecting and improving the living environment of human beings. However, the randomness and irregularity of wind seriously limit the application of wind energy harvesting and self-powered sensing technology. In this paper, a self-regulation strategy for triboelectric nanogenerator (TENG-SS) is proposed and a self-powered wind-speed sensor is achieved. By rationally designing the centrifugal and nonlinear magnetic forces, the separation and contact degrees of the functional materials of TENG can be adjusted automatically for different wind speeds. When the wind speed is low, the aerodynamic force is small, and the frictional resistance is also small due to self-regulation, the device is easy to start, and the wear is small; at high wind speed, the aerodynamic force overcomes greater frictional resistance to generate more electricity. Based on the working principle of TENG-SS, a dynamic model is established and verified experimentally, and the influence of the key parameters on the performance of the TENG-SS is analyzed. Furthermore, the prototypes of TENG with and without the self-regulation strategy are compared in a natural wind environment for 21,600 s, which proves that the proposed TENG-SS exhibits better performance and robustness. The proposed TENG-SS is used for self-powered wind speed measurements and wireless information transmission. This study provides a new perspective for improving the performance of TENG in the natural environment through self-regulation strategy. [Display omitted] • A self-regulation strategy with centrifugal force and magnetic force is proposed. • Higher power and robustness of TENG-SS are verified by natural wind experiments. • The electromechanical coupling dynamic model of the proposed system is established. • The self-powered wind speed measurement and wireless transmission are realized. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dynamically synergistic regulation mechanism for rotation energy harvesting is proposed. • The adaptive-anastomotic barricades can both regulate the dynamic behavior and generate electricity. • The electromechanical coupling dynamic model of the proposed system is established. • The results show that the proposed harvester can harvest energy effectively in a wide speed range. To realize the sustainable energy supply of wireless sensor networks, a novel dynamically synergistic regulation mechanism is proposed for rotation energy harvesting under the guidance of the dynamic regulation evolution. The connotation of synergy includes: (1) Nonlinear magnetic force and variable stiffness (centrifugal stiffening effect and penalty stiffness of adaptive-anastomotic barricades) synergistically regulate the dynamic behavior of the system; (2) The adaptive-anastomotic barricades also convert mechanical energy into electrical energy when regulating the dynamic behavior of the system, i.e., the triboelectric nanogenerator synergistically generates electricity with piezoelectric energy harvester in different states (collision and vibration) of the system, respectively. Based on the energy method of Hamiltonian principle, the electromechanical coupling dynamic model of the system is developed. The parameters analysis is performed for the discussion of dynamic characteristics and electrical performance of the system in a wide rotation speed range. The prototype is fabricated and the experiments under different conditions are carried out. The experimental data are in good agreement with the simulation results, which verifies the effectiveness of the theoretical model. The experimental results show that the proposed harvester can harvest energy effectively in a wide speed range of 0–1000 r/min. The peak-peak voltage and the average power for PEH and TENG can reach 122.1 V, 1600 μW; 774.3 V, 205.1 μW, respectively. The proposed dynamically synergistic regulation mechanism provides a new perspective to improve the comprehensive performance of the rotation energy harvester, which exhibits a promising application prospect in the self-powered IoT applications. [ABSTRACT FROM AUTHOR]

• A magnetic coupling piezoelectric wind energy harvesting method is proposed. • The effective magnetic coupling modes for wind energy harvesting are clarified. • The dynamics models with different magnetic coupling modes are established. • The robustness of the proposed method is verified by outdoor natural wind tests. Harvesting wind energy is becoming increasingly significant for its availability and abundance in the ambient environment, which is a promising strategy to develop self-powered small-scale electromechanical systems. However, the drawbacks of the current small-scale wind energy harvesters, namely, low robustness, narrow wind speed range, and low output power hinder the application in natural environment. Here, we propose an innovative approach for rotational piezoelectric wind energy harvesting using magnetic coupling and force amplification mechanisms, which has a higher equivalent piezoelectric coefficient, better robustness and broader wind speed range for application. Thanks to the reasonable symmetrical opposite magnetic arrangement, the resistance torque has been reduced significantly while the effective force can be maximized. The effective magnetic coupling modes are clarified, and the corresponding dynamic models are established. The effects of key parameters on the output performance are analyzed and the effects of assembly errors on reluctance torque are discussed as well. The performances of the proposed harvester are investigated through laboratory experiments and outdoor natural wind tests. The results show that the established model can characterize the energy harvester precisely. In an outdoor natural wind environment, the prototype is able to work continuously for more than 12,000 s with the wind speed from ~3 m/s to ~10 m/s. After a long period of experiments, no damage to the prototype is observed. Besides, the proposed harvester can generate high and relatively stable open-circuit voltages from low wind speeds to high wind speeds. These results reveal that the proposed harvester has high robustness and broad wind speed range for the application. [ABSTRACT FROM AUTHOR]

• The concept of mechanical modulation energy harvesting is classified. • The methods and principles of mechanical modulation energy harvesting are summarized. • The applications of mechanical modulations to energy harvesting systems are reviewed. • The prospects of the research on mechanical modulation energy harvesting are presented. Mechanical kinetic energy harvesting, which converts the mechanical motions and vibrations that are commonly available in the surrounding environment to electrical energy, can realize self-power sensing, control and actuation, with the advantages of convenience, energy saving, ecofriendliness and sustainability. It has broad application prospects in the fields of aerospace, biomedical engineering, environmental monitoring and military engineering. The forms of mechanical energy in the ambient are various and may be time-varying, and its direct conversion to electrical energy may result in low output power, low conversion efficiency, and even damage to the device. In order to improve the performance of energy harvester, the mechanical energy can be mechanically modulated and then be converted to electrical energy. In this paper, the key roles of mechanical modulations for energy harvesting are emphasized. The methods and principles of mechanical modulations and their applications to energy harvesting systems are reviewed and classified into three categories: excitation type conversions, frequency up-conversions, force/motion amplifications. The prospects of the research on mechanical modulation based energy harvesting are also presented. [ABSTRACT FROM AUTHOR]

Energy harvesting from streets, squares, and other areas to supply power to equipment and systems in these environments is environmentally friendly and more convenient for functions requiring low power consumption. To harvest more pulsed mechanical energy and improve the quality of electrical output for immediate utilization, we propose a bidirectional energy harvesting floor with a sustained-release regulation mechanism (BEHF-SRM). The pulse and irregular excitation on the road can be converted into continuous unidirectional rotation of the working wheel and the reset motion of the system can also drive the work wheel unidirectional rotation, and the rotational kinetic energy is slowly converted into electrical energy. A dynamic model is established and validated experimentally. One person can easily light up 20 LED bulbs (rated power 1 W) by stepping on the prototype of BEHF-SRM. The prototype can continue to provide electricity for about 7 s after stepping on it. Self-powered automated pedestrian crosswalk warnings that can improve pedestrian safety was demonstrated based on BEHF-SRM. The results show that the proposed harvester has the potential to provide a sustainable, convenient, green, and zero carbon energy supply to smart transport and smart cities. • Energy harvesting floor with sustained-release regulation mechanism is proposed. • The dynamic model of the system is established and validated experimentally. • A person can light up 20 LED bulbs (rated power 1 W) by stepping on the prototype. • Self-powered automatic light warning for pedestrian crosswalks is realized. [ABSTRACT FROM AUTHOR]

This study presents a new magnetically coupled bistable piezoelectric energy harvesting approach for underwater applications. The flextensional piezoelectric transducer is used to harvest the energy of fluid induced vibration by magnetic coupling. Because of non-contact mechanical energy transfer, vulnerable key components can be packaged without affecting the normal operation. In addition, the magnetically coupled system has nonlinear bistable characteristics, which are beneficial to enhance the performance of the flow energy harvester. The magnetic excitation force can be amplified and uniformly applied to the piezoelectric layer through the flextensional structure, thereby exhibiting a higher equivalent piezoelectric coefficient and improved reliability. The prototypes were fabricated to verify the advantages of the design and a series of tests were carried out in a water tunnel. At a flow rate of 4 m/s, the peak-to-peak voltage and maximum power of the 390 kΩ load resistor were 26 V and 450.5 μW, respectively. The magnetically coupled bistable piezoelectric energy harvester exhibited stable power output performance after 144 h in the water (approximately 50% of the time in the working state). The results indicate that the magnetic coupling and flextensional mechanisms have great potential for energy harvesting in harsh environments such as underwater. • A magnetically coupled underwater flow energy harvesting approach is developed. • A pair of wings are set to facilitate flow-induced vibration. • A coupled dynamic model is presented and experimentally validated. • The prototypes with different wing angles are fabricated and tested. • The mechanical durability is verified by the experiments in water for 144 h. [ABSTRACT FROM AUTHOR]

• A double-plate structure is proposed to enhance performance of wind energy harvester. • Wake flow induced by upstream plates increases lift force on bluff body. • The optimized VIV energy harvester outputs energy beyond critical wind speed. • Voltage of galloping energy harvester is increased and cut-in wind speed is reduced. Small-scale wind energy harvesting system is being considered to provide green long-term electric power to unattended sensor network nodes which are widely used in urban and natural environments. This paper proposes that placing a double-plate structure upstream of the bluff body in the wind energy harvesting system can significantly improve the output performance. At a certain wind speed, two wake flow zones with low-pressure are formed behind two upstream side-by-side plates, which induced the bluff body at the downstream intermediate position to deviate to both sides. Even at a low wind speed, the vibration of bluff body can still occur because the pressure fluctuation of the wake zone disturb the static equilibrium. Placing the double plates upstream of a wind energy harvester with a cylinder can change the vibration response from VIV (vortex-induced vibration) to galloping. Moreover, when the ratios of the horizontal and vertical distances to the windward width of the cylinder are 1 and 0.5, respectively, the cut-in wind speed is as low as 1.5 m/s. For the galloping-based wind energy harvester with a square prism, after the double plates are placed upstream, the cut-in wind speed decreases from 3.5 m/s to 1 m/s and the output voltage increases from 1 V to 12 V at 1.5 m/s. The increase of voltage caused by the addition of double plates to the upstream of six different bluff bodies indicates the good adaptability of this structure. The higher voltage output capability by this method at low wind speed significantly expands the application scope of wind energy harvesters. [ABSTRACT FROM AUTHOR]