High-efficiency Energy Harvesting Research Articles

A novel nonlinear mechanical oscillator and its application in vibration isolation and energy harvesting

The nonlinear design of a new vibration structure is an essential part of the development of vibration isolation and energy harvesting technologies, and is one of the most effective technical means to improve the efficiency of low-frequency excitation. Due to structural constraints, high-efficiency vibration isolation and energy harvesting from ultra-low frequency or low intensity excitation has been a theoretical bottleneck and technical challenge in this field. In this study, this paper firstly proposes the theory and method of vibration isolation and energy harvesting based on the high-order quasi-zero stiffness (HQZS) mechanism, which is expected to break through the above bottleneck. Secondly, a detailed study of the HQZS oscillator with electromagnetic transduction under both stochastic and harmonic excitations is emphasized. The HQZS oscillator can not only achieve arbitrarily small stiffness near the equilibrium position through geometrically nonlinear parameter design, but also achieve vibration isolation or high-energy interwell oscillation under ultra-low frequency or low intensity excitations. Finally, compared with quad-stable and quasi-zero stiffness (QZS) systems, the results show that the HQZS oscillator has better vibration isolation and energy harvesting performance for ultra-lower stochastic excitation intensity or harmonic excitation frequency. Also, the initial isolation frequencies and maximum harvested power frequencies of the HQZS oscillator are lower than that of the QZS oscillator. The results will not only help to deepen the understanding of HQZS systems, but also provide new theoretical support and technical approaches for vibration isolation and energy harvesting under ultra-low frequency or low intensity excitation.

Large Bulk Piezophotovoltaic Effect of Monolayer 2H-MoS2.

The bulk photovoltaic effect in noncentrosymmetric materials is an intriguing physical phenomenon that holds potential for high-efficiency energy harvesting. Here, we study the shift current bulk photovoltaic effect in the transition-metal dichalcogenide MoS2. We present a simple automated method to guide materials design and use it to uncover a distortion to monolayer 2H-MoS2 that dramatically enhances the integrated shift current. Using this distortion, we show that overlap in the Brillouin zone of the distributions of the shift vector (a quantity measuring the net displacement in real space of coherent wave packets during excitation) and the transition intensity is crucial for increasing the shift current. The distortion pattern is related to the material polarization and can be realized through an applied electric field via the converse piezoelectric effect. This finding suggests an additional method for engineering the shift current response of materials to augment previously reported methods using mechanical strain.

Nanofluidic osmotic power generators - advanced nanoporous membranes and nanochannels for blue energy harvesting.

The increase of energy demand added to the concern for environmental pollution linked to energy generation based on the combustion of fossil fuels has motivated the study and development of new sustainable ways for energy harvesting. Among the different alternatives, the opportunity to generate energy by exploiting the osmotic pressure difference between water sources of different salinities has attracted considerable attention. It is well-known that this objective can be accomplished by employing ion-selective dense membranes. However, so far, the current state of this technology has shown limited performance which hinders its real application. In this context, advanced nanostructured membranes (nanoporous membranes) with high ion flux and selectivity enabling the enhancement of the output power are perceived as a promising strategy to overcome the existing barriers in this technology. While the utilization of nanoporous membranes for osmotic power generation is a relatively new field and therefore, its application for large-scale production is still uncertain, there have been major developments at the laboratory scale in recent years that demonstrate its huge potential. In this review, we introduce a comprehensive analysis of the main fundamental concepts behind osmotic energy generation and how the utilization of nanoporous membranes with tailored ion transport can be a key to the development of high-efficiency blue energy harvesting systems. Also, the document discusses experimental issues related to the different ways to fabricate this new generation of membranes and the different experimental set-ups for the energy-conversion measurements. We highlight the importance of optimizing the experimental variables through the detailed analysis of the influence on the energy capability of geometrical features related to the nanoporous membranes, surface charge density, concentration gradient, temperature, building block integration, and others. Finally, we summarize some representative studies in up-scaled membranes and discuss the main challenges and perspectives of this emerging field.

Distributed-parameter modeling and dynamic analysis of rotational compressive-mode energy harvesters

This paper presents a modeling and dynamic analysis of a rotational high-efficiency compressive-mode piezoelectric energy harvester (HC-PEH) with partially thickened bow-shaped beams. Based on the Euler–Bernoulli beam theory and the extended Hamilton’s principle, the governing equations of the rotational HC-PEH system are formulated. The nonlinear electromechanical coupling partial differential equations of the system are transformed into ordinary differential equations in the truncated modal coordinates. The developed distributed-parameter model is validated against experimental data, and a good agreement is achieved. The stability and the nonlinear dynamic behavior of the rotational HC-PEH system in conditions of different offset distances and preloaded axial forces are investigated by numerical simulation results. A parametric study of the parameters directly related to the system design is also performed to provide fundamental guidance for understanding the electrical output performance and modulating the voltage–rotation speed responses of the harvester. The result shows that the design parameters of the bow-shaped beam and the PZT plate have apparent effects on the electrical output of the harvester system.

A Self-Adaptive Integration of Photothermal and Radiative Sky Cooling for Continuously Efficient Harvesting of Energy From the Sun and Outer Space

The sun (~6000 K) and outer space (~3 K) are two significant renewable thermodynamic resources for human beings on Earth. The solar thermal conversion by photothermal (PT) and harvesting the coldness of outer space by radiative sky cooling (RSC) have already attracted tremendous interest. However, most of the approaches for PT and RSC are static and mono-functional, which can only provide heating or cooling under sunlight or darkness. Here, we develop a spectrally self-adaptive absorber/emitter (SSA/E) with strong solar absorption and switchable emissivity within the atmospheric window (i.e., 8-13μm) for the dynamic combination of PT and RSC, corresponding to continuously efficient energy harvesting from the sun and universe. The as-fabricated SSA/E not only can be heated to ~170°C above ambient temperature under sunshine and but also be cooled to 20°C below ambient temperature, and thermal modeling captures the high energy harvesting efficiency of the SSA/E, enabling new technological capabilities.

On the offset distance of rotational piezoelectric energy harvesters

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.

A novel kinetic energy harvester using vibration rectification mechanism for self-powered applications in railway

Rail transit system has been considered to have a large energy harvesting potential, and to be usable to achieve self-powering for rail-attached electrical installations. Dowty retarder is a key device installed on the side of rails to assist train braking, which can be used as a carrier for kinetic energy harvesting. In this paper, a high-efficiency kinetic energy harvester (KEH) based on a railway Dowty Retarders (DRs) is investigated. This new KEH can accumulate the kinetic energy of a decelerating train using a novel vibration rectification mechanism. The current study comprises four main components: energy input module, motion transmission module, generation module, and energy storage module. The energy input module has a screw-nut mechanism that can convert linear vibration into rotational motion. As a core component of the entire device, the motion transmission module contains a special closed-loop shaped gear train that converts the two-way rotary motion into a unidirectional rotation. The final unidirectional rotation is transferred to the generation module for power generation and the generated energy is stored in the energy storage module. Finally, both experimental and simulation approaches were performed to verify the dynamics response of the KEH mechanism. The maximum efficiencies of 55.4% and 51.9% are obtained during the simulation and experimental analyses. It is validating that the KEH mechanism is promising and practical in self-powered applications for the heavy haul railway.

Theoretical modeling and experimental validation of the centrifugal softening effect for high-efficiency energy harvesting in ultralow-frequency rotational motion

Recently, the energy harvesting technique has been a promising way to power low-powered wireless sensor nodes. Considering the advantages of rotational motion, various energy harvesters were designed and investigated for rotational energy harvesting. Among these previous studies, it has been demonstrated that the centrifugal force plays an important role in the dynamic response and the generated power of a piezoelectric energy harvester (PEH). As a result, this paper aims to reveal the mechanism of the centrifugal softening effect caused by the centrifugal force, and by which to enhance the energy harvesting performance in ultralow-frequency rotational motion (less than 2 Hz). Therefore, an inverse PEH configuration in rotational motion is proposed in this paper. A compressive theoretical model describing its dynamic response and output voltage is derived according to Lagrange equation and other assumptions. An experimental setup is established to verify the proposed theoretical model and to investigate the influence of the centrifugal softening effect on the output voltage. According to the experimental results, the root-mean-square (RMS) output voltage of the proposed PEH with the centrifugal softening effect reaches 4 V, which is improved over 100% under the rotational speed range of 75–120 rpm (1.2–2 Hz) compared with the forward PEH configuration. Furthermore, such a significant enhancement due to the centrifugal softening effect is theoretically explained via the derived theoretical model. Overall, the centrifugal softening effect is markedly beneficial for energy harvesting in ultralow-frequency rotational motion, and the derived theoretical model has been validated by the experiments to be effective. This study provides the theoretical and experimental guidance for the further research and applications of the centrifugal softening effect.

Simultaneous Energy Harvesting and Gait Recognition Using Piezoelectric Energy Harvester

Piezoelectric energy harvester (PEH), which generates electricity from stress or vibrations, is attracting tremendous attention as a viable solution to extend battery life of wearable devices. More interestingly, besides the energy harvesting capability, recent research has demonstrated the feasibility of leveraging PEH as an power-free sensor for gait recognition as its stress or vibration patters are significantly influenced by the gait. However, as PEHs are not designed for precise motion sensing, the gait recognition accuracy remains low with conventional classification algorithms. The accuracy deteriorates further when the generated electricity is stored simultaneously. In this work, to achieve high performance gait recognition and efficient energy harvesting at the same time, we make two distinct contributions. First, we propose a preprocessing algorithm to filter out the effect of energy storage on PEH electricity signals. Second, we propose long short-term memory (LSTM) network-based classifiers to accurately capture temporal information in gait-induced electricity generation. We prototype the proposed gait recognition architecture in the form factor of an insole and evaluate its gait recognition as well as energy harvesting performance with 20 subjects. Our results show that the proposed architecture detects human gait with 12 percent higher recall and harvests up to 127 percent more energy while consuming 38 percent less power compared to the state-of-the-art.

Efficiency evaluation of energy harvesting from discrete gust response for plate wing

Gust response of aircraft can become a potential energy source thanks to energy harvesting (EH) methods, one of which can transform mechanical energy to electrical energy, applying piezoelectric ceramic transducers (PZTs). Harvested electrical energy needs to be evaluated for reuse, but current beam-model-based evaluation methods of EH performance for a plate model are insufficient because the plate is two-dimensional. This paper proposes two types of EH evaluation methods to analyze the gust exciting low-aspect-ratio plate wing model. One method focuses on the ratio of electrical energy to kinetic energy, and the other reflects energy output density per unit weight. These two methods can reveal the higher energy harvesting efficiency positions when utilizing PZTs on the flight EH system. Plate model, three-dimensional doublet lattice unsteady aeroelastic method and piezoelectric equation are used to build piezoaeroelastic wing model, and 1-cosine discrete gust load is the base excitation. A time-domain aero-electro-elastic state-space equation of the low-aspect-ratio piezoaeroelastic plate wing model is established, and the time-history analysis is used to solve the EH output. Results show that EH outputs are influenced by various parameters including load resistance, PZT thickness, gust intensity and wavelength, and PZT location variation. The optimal values of the proposed EH efficiency evaluation methods are found and explained.

Design of high efficiency energy harvesting circuit using dual switching technique

Energy harvesting technique has been popularly used as a powering methodology for various low power applications like wireless sensor nodes, wearable and implantable devices. This paper mainly focuses novel rectifier design to enhance the performance of energy harvesting circuit. The sound signals produced from smartphone or loud speaker are the main input source for the energy harvesting circuit consisting of transducer, rectifier, regulator. The existing active diodes of rectifier are replaced with dual switching technique. This technique maintains constant gate bias, reduces reverse leakage current and area and increases the power conversion efficiency of rectifier. The proposed rectifier yields maximum power conversion efficiency (PCE) of 85% with an input voltage of 800mv. The energy harvesting circuit has been designed and simulated within CMOS standards.

An experimental study on a high-efficient multifunctional U-shaped piezoelectric coupled beam

In order to improve the energy harvesting efficiency of the piezoelectric energy harvester (PEH), we propose a multifunctional U-shaped piezoelectric coupled beam (MUPCB) that has a high energy harvesting efficiency for an uniform strain in its piezoelectric coupled segments (PCSs) in the process of vibration. The forced-vibration experiments of the MUPCB are designed and conducted with the consideration of different dimensions, excitation frequencies, load resistance, proof mass and constraints. The experimental results show that the output power can reach up to 19.50 mW and 56.20 mW for a piezoelectric patch with a dimension of 40 mm × 10 mm × 0.5 mm when the MUPCB is excited in the two-end-clamped and one-end-clamped configurations. This research provides a novel MUPCB which is efficient in transferring vibration energy into useful electric power and attenuating harmful vibration of machines as an absorber by converting the vibration energy into electric energy. More importantly, it brings a possibility of generating a considerable electric power through a piezoelectric harvester or attenuating vibration with huge energy through a piezoelectric absorber assembled by array of MUPCBs.

Rashba Splitting in Two Dimensional Hybrid Perovskite Materials for High Efficient Solar and Heat Energy Harvesting.

The physical properties of two-dimensional (2D) lead halide based hybrid perovskites are quite exciting and challenging. Further, the role of organic cations in 2D perovskites is still in a debate. We investigated layered (CH3(CH2)3NH3)2(CH3NH3)Pb2I7 2D Ruddlesden-Popper (2DRP) phase (M1) and 2D derivative of CH3NH3PbI3 (M2) using density functional theory. The spin orbit coupling mediates the significantly large Rashba splitting energy of 328.5 meV for M2, which is higher than earlier 2D hybrid perovskites. At the picosecond time scale, the dynamical Rashba effect was observed due to organic and inorganic cation dynamics. Two step absorption suggests an indirect optical gap of 2.38 and 2.15 eV for M1 and M2, respectively and solar performance depicts excellent power conversion efficiency of 14.92% and 19.75% for M1 and M2, respectively. For the first time, we explored the thermoelectric properties of 2D hybrid perovskites and perceived high power factor for p-type doping in M2. Our findings suggest that these novel 2D perovskites have the potential to be used in solar and heat energy harvesting.

Small‐scale experimental study on the optimisation of a rooftop rainwater energy harvester using electromagnetic generators in light rains

This research proposes a new rooftop rainwater energy harvester using electromagnetic generators, which demonstrates better rain-energy harvesting performance than the traditional rainwater energy harvesters that use electromagnetic generators under light rain conditions. Conventionally, the rainwater collected from the roof of a building or a residential attic using the installed roof gutter system is drained directly along a pipe to drive water turbines combined with electromagnetic generators for generating electricity. Such an energy harvesting method has high energy harvesting efficiency under heavy rain conditions but is inefficient under light rain conditions. To improve the energy harvesting efficiency in light rains, a pipe-connected tank including a passive rainwater buffer is introduced and fixed below the rooftop gutters in the proposed structure. The passive rainwater buffer is attached above the pipe-connected tank. After collecting a certain amount of rainwater from the gutters, the passive rainwater buffer automatically releases the rainwater periodically into the pipe-connected tanks. The released rainwater results in a large flow along the pipe, which can drive water turbines with electromagnetic generators to work at a high efficiency for a short period of time. A small-scale experimental prototype was built for validating the energy harvesting performance of the proposed structure. The results show that the intermittent high-efficiency power generation of the proposed structure is better than the continuous low-efficiency power generation of the traditional structure during light rains. The proposed structure can charge a 680 μF capacitor with at least nine times the electrical energy that is stored in a conventional capacitor for a rainwater flow rate of less than 300 mL/min in the same amount of time. However, with the increase in the rainwater flow, the energy harvesting performance gap between the proposed structure and the traditional one gradually narrows. Highlights A new rooftop rainwater electromagnetic energy harvester is proposed; A pipe-connected tank including a passive rainwater buffer is fixed below the rooftop gutters; The proposed structure can charge a capacitor with at least nine times as much electrical energy as the conventional one in light rain conditions.

Measurement of the heat flux normalized spin Seebeck coefficient of thin films as a function of temperature.

The spin Seebeck effect (SSE) has generated interest in the thermoelectric and magnetic communities for potential high efficiency energy harvesting applications and spintronic communities as a source of pure spin current. Understanding the underlying mechanisms requires characterization of potential materials across a range of temperatures; however, for thin films, the default measurement of an applied temperature gradient (across the sample) has been shown to be compromised by the presence of thermal resistances. Here, we demonstrate a method to perform low temperature SSE measurements where, instead of monitoring the temperature gradient, the heat flux passing through the sample is measured using two calibrated heat flux sensors. This has the advantage of measuring the heat loss through the sample as well as providing a reliable method to normalize the SSE response of thin film samples. We demonstrate this method with an SiO2/Fe3O4/Pt sample where a semiconducting-insulating transition occurs at the Verwey transition, TV, of Fe3O4 and quantify the thermomagnetic response above and below TV.

Performance evaluation of a dual-piezoelectric-beam vibration energy harvester with a lever and repulsive magnets

This study proposes a novel dual-piezoelectric-beam vibration energy harvester with a lever and repulsive magnets (DPBLM-VEH) for performance improvement. The DPBLM-VEH integrates the benefits of the dual-beam configuration, the leverage effect and the magnetic nonlinear behavior. First, a theoretical model of the DPBLM-VEH is developed. It is found that the energy harvester exhibits two resonances in the low-frequency band, where the high-efficiency energy harvesting can be realized. A parametric study is then performed to understand the effects of various system parameters on the energy harvesting performance. Detailed design strategies in terms of tuning the lever length ratio, lever mass ratio, tip mass ratio and internal resistor towards system optimization have been proposed. Subsequently, an experimental study is conducted for validating the theoretical predictions. Experimental results show that compared to the conventional dual-piezoelectric-beam vibration energy harvester (DPB-VEH), introducing a lever (i.e. DPBL-VEH) can amplify the peak powers of the 1st and 2nd beams, respectively, by 225.8% and 134.1% around the second resonance. Similarly, the DPBLM-VEH with a further introduction of the magnetic nonlinearity can realize an amplification by 204.8% and 119.8% for the two beams. In addition, compared to the DPBL-VEH, the DPBLM-VEH can further broaden the effective bandwidths of the two beams by 98.0% and 50.6%, respectively. Therefore, we can conclude that due to the leverage effect and magnet-induced nonlinearity, the DPBLM-VEH can significantly enhance the energy conversion efficiency and broaden the operation bandwidth.

Size-dependent dynamics of a FG Nanobeam near nonlinear resonances induced by heat

This study explores heat-induced nonlinear vibration of a functionally graded (FG) capacitive nanobeam within the framework of nonlocal strain gradient theory (NLSGT). The elastic FG beam, which is firstly deflected by a DC voltage, is driven to vibrate about its deflected position by a periodic heat load. The nano-structure, which consists of a clamped-clamped nanobeam, is modeled assuming Euler–Bernoulli beam assumption which accounts for the nonlinear von-Karman strain and the electrostatic and intermolecular forcing. To simulate the static and dynamic responses, a model reduction procedure is carried out by employing the Galerkin method. The method of Averaging as a regular semi-analytic perturbation method is applied to obtain governing equations of the steady-state responses. With the purpose of establishing the validity of the solution, a Shooting technique in conjunction with the Floquet theory is used to capture the periodic motions and then examine their stability. The nonlinear resonance frequency of the FG nanobeam near its fundamental natural frequency (primary resonance) and near principal parametric resonance is investigated while the emphasis is placed on studying the effect of various parameters including DC voltage, amplitude of the periodic heat source, material index, damping ratio, and small scale parameters. The main objective of this study is to model a miniature structure which can be used as either a sensitive remote temperature sensor or a high-efficiency thermal energy harvester.

High-efficiency Electrostatic Vibrational MEMS Energy Harvester for IoT Sensors

1．背景

A Visible-NIR Responsive Dye-Sensitized Solar Cell Based on Diatom Frustules and Cosensitization of Photopigments from Diatom and Purple Bacteria

Diatoms exhibit high solar energy harvesting efficiency due to their remarkably organized, hierarchical micro/nanoporous, light-trapping, and scattering frustules. At present, few studies focus on cosensitization of natural near-infrared dye to expand the spectral response of dye-sensitized solar cells. In this study, the diatom frustule-TiO2 (12 : 5) composite film was prepared and assembled it on the TiO2 electrode. Compared to the single TiO2 layer film, diatom frustule-TiO2 (12 : 5) composite film sensitized by diatom’s dye showed the conversion efficiency of 0.719%. To expand the light-harvesting response to near-infrared region spectra, the cosensitized dyes were used to fabricate the visible-near-infrared responsive dye-sensitized solar cells. The cosensitization diatom frustule-TiO2 (12 : 5) composite film exhibited two distinct absorption bands in the near-infrared region and reached a higher conversion efficiency of 1.321%, which was approximately 1.4 or 1.7 folds higher than that of cosensitization double-TiO2 film or single TiO2 layer film, respectively, and approximately 3.7 or 1.7 folds higher than that of the single TiO2 layer film sensitized by diatom dye or purple bacterial dye, respectively. The results showed that the combination between diatom frustule-TiO2 with cosensitization natural dyes could significantly improve the photoelectric performance of visible-near-infrared responsive dye-sensitized solar cells.

A High-Efficiency and Wide-Input Range RF Energy Harvester Using Multiple Rectenna and Adaptive Matching

In this paper, a Radio Frequency (RF) energy harvester (EH) system for Internet of Things (IoT)-related applications is presented. The proposed EH architecture operates at 5.2 GHz band and utilizes multiple rectenna. This approach enhances the efficiency of the whole system over a wide dynamic RF input range. In the presented circuit, configuration of the rectenna is controlled by Field-Programmable Gate Array (FPGA) with respect to the input power level of the received RF input signal. In addition, an automatic adaptive matching based on the configuration of the rectenna, level of the received signal, and load current adjusts the matching network. The rectenna is realized through the Radio Frequency-Direct Current (RF-DC) converter composed of two Schottky diodes and generates the output DC voltage. Finally, a buck-boost converter provides the flattened and fixed voltage for the IoT and wearable devices. The 5.2 GHz band reconfigurable system demonstrates 67% high efficiency and 6.1 V output DC voltage where the power level of RF input is +20 dBm. The main application of the proposed structure is for charging wearable smart devices such as a smart watch and bracelet.