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As wearable microelectronics become more ubiquitous, and the size and power requirements of such devices decrease, there is increasing research interest in harnessing power from ambient environmental sources through embedded systems as alternative to battery replacements. Accordingly, a multimodal hybrid piezo-electromagnetic insole energy harvester (PEM-IEH) has been presented in this paper as a means to reclaim the biomechanical energy wasted in the surroundings during daily walking. The hybrid device consists of two piezo-ceramic wafer plates, two magnets, and two wound coils. The designed harvester has been simulated, fabricated and experimentally validated. From the frequency response, the hybrid harvester exhibits four resonant frequencies concentrated around 8, 25, 50, and 51 Hz. A maximum combined power of 1400 µW is generated across the optimal load resistances of upper and lower electromagnetic generators at first resonant frequency (8 Hz) under 0.5 g base acceleration, and a 269 µW peak power is obtained across the optimum load resistances of the upper and lower piezoelectric generators at 4th resonance (51 Hz) under 0.5 g. The miniature (46.8 cm3) and lightweight (43.3 g) harvester was incorporated into the sole of an adult-sized commercial shoe, and has been shown to be able to charge a 100 µF capacitor, up to 2.4 Volt within approximately 10 min of slow jogging. The capacitor charging performance presents a remarkable potential application of the harvester in development of micro-power monitoring sensors and wearable microelectronic gadgets where batteries pose a practical bottleneck.

Radio frequency (RF) wireless energy transfer (WET) is a key technology that may allow seamlessly powering future massive low-energy Internet of Things (IoT) networks. To enable efficient massive WET, channel state information (CSI)-limited/free multi-antenna transmit schemes have been recently proposed in the literature. The idea is to reduce/null the energy costs to be paid by energy harvesting (EH) IoT nodes from participating in large-scale time/power-consuming CSI training, but still enable some transmit spatial gains. In this paper, we take another step forward by proposing a novel CSI-free rotary antenna beamforming (RAB) WET scheme that outperforms all state-of-the-art CSI-free schemes in a scenario where a power beacon (PB) equipped with a uniform linear array (ULA) powers a large set of surrounding EH IoT devices. RAB uses a properly designed CSI-free beamformer combined with a continuous or periodic rotation of the ULA at the PB to provide average EH gains that scale as $0.85\sqrt{M}$, where $M$ is the number of PB's antenna elements. Moreover, a rotation-specific power control mechanism was proposed to i) fairly optimize the WET process if devices' positioning information is available, and/or ii) to avoid hazards to human health in terms of specific absorption rate (SAR). We show that RAB performance even approaches quickly (or surpasses, for scenarios with sufficiently large number of EH devices, or when using the proposed power control) the performance of a traditional full-CSI based transmit scheme, and it is also less sensitive to SAR constraints. Finally, we discuss important practicalities related to RAB such as its robustness against non line-of-sight conditions compared to other CSI-free WET schemes, and its generalizability to scenarios where the PB uses other than a ULA topology., Comment: 12 pages, 10 figures. Accepted for publication in IEEE IoT Journal

Owing to the shorter wavelength in the millimeter-wave (mmWave) spectrum, miniaturized antennas can receive power with a higher efficiency than UHF bands, promising sustainable mmWave-powered Internet of Things (IoT) devices. Nevertheless, the performance of a mmWave power receiver has not been compared, numerically or experimentally, to its sub-6 GHz counterpart. In this paper, the performance of mmWave-powered receivers is evaluated based on a novel wearable textile-based higher-order mode microstrip antenna, showing the benefits of wireless power transmission (WPT). Firstly, a broadband antenna is proposed maintaining a stable wearable measured bandwidth from 24.9 to 31.1 GHz, over three-fold improvement compared to a conventional patch. The proposed antenna has a measured 8.2 dBi co-polarized gain with the highest thickness-normalized efficiency of a wearable antenna. When evaluated for compact power receivers, the measured path gain shows that WPT at 26 GHz outperforms 2.4 GHz by 11 dB. A rectenna array based on the proposed antenna is then evaluated analytically showing the potential for up to 6.3x higher power reception compared to a UHF patch, based on the proposed antenna's gain and an empirical path-loss model. Both use cases demonstrate that mmWave-powered rectennas are suitable for area-constrained and large-area wearable IoT applications.

Electronic devices, with low power demand, can be energized using vibration energy harvesters which gather and transform energy from mechanical vibrations. This investigation looks at the feasibility of a method of energy harvesting from mechanical vibrations using the naturally occurring charging phenomenon within a system of two bodies which possess different work functions. In this work, a brief review of similar technologies, namely piezoelectric, electromagnetic and electrostatic energy harvesters is first given. This is followed by the development of a theoretical model and an investigation of different Work Function Energy Harvester (WFEH) operation modes, with conclusions on a possible optimum mode of operation. The design of an experiment to test the developed theory is then presented followed by some preliminary results. Generally it is found that a WFEH has potential for use in energy harvesting applications with the possibility of giving equal or better output power when compared to traditional electrostatic harvesters.

The Finite element analysis (FEA) plays a vital role for the design and development of microdevices, which provides the solutions to understand the behaviour virtually for the optimization of specific device. In the present work, we designed two different energy harvesting (EH) models with variable dimensions and analyzed the EH performance for wide range of pressure. The proposed models consist of four piezoelectric microcantilevers coupled with square (Design-I) and circular (Design-II) shaped micro-membranes. The piezoelectric material PZT-5H was used as transduction material and the gold electrodes were used as charge collector. The EH designs (I & II) were modelled with variable membrane thickness viz., 1 µm and 0.5 µm and their output performances like total displacement, von Mises stress, volumetric strain and electric potential were studied for the pressure range of 200–2000 Pa. The EH design-I generated the maximum output potential of 167 µV (1 µm) and 186 µV (0.5 µm) for the applied pressure of 2000 Pa. Similarly, EH design-II generated the maximum output potential of 138 µV (1 µm) and 174 µV (0.5 µm) for the applied pressure of 2000 Pa. Relatively, the EH designs I & II with 0.5 µm thickness exhibited best output performance for the maximum applied pressure of 2000 Pa, which generated maximum output potential of 186 µV and 174 µV, respectively. In comparison with the other designs, the piezoelectric microcantilever coupled with square shaped micro-membrane (Design-I) of 0.5 µm thickness exhibited better EH performance than the circular shaped micro-membrane (Design-II).

In an energy harvesting sensor actor network, a node recharges its battery from harvestable sources, such as solar, wind and vibrations. Sustainability of the network till next recharge time is one of the most important challenges in harvesting sensor networks. In this paper, a fuzzy based adaptive duty cycling algorithm has been proposed to achieve the network sustainability in harvesting sensor actor networks. In this work, current residual energy, predicted harvesting energy (for a futuristic time slot) and predicted residual energy parameters are considered as fuzzy input variables to estimate duty cycle for a sensor node. In this work, a harvesting model has been adopted to predict the harvesting energy. Further, residual energy has been estimated for future time slot using predicted harvesting energy, energy consumption model and current residual energy. Simulation results are presented to show the efficacy of the proposed mechanism by considering network sustainability metrics, such as number of rounds in which network is connected, the round at which first node dies, maximum number of dead nodes and average number of received packets at the actor node.

The study presents the pyroelectric performance improvement by employing exhaust emissions from automobiles. Electric outputs through the material BaSn0.05Ti0.95O3 are recorded after subjecting the surface of the sample for heating under infrared (IR) lamp and flowing water. The thickness of the automobile exhaust ink was nearly 35 µm on the sample surface. Observations show significant improvements with open circuit voltage increase to five times, electric current enhances upto six times across the resistor of 10 Ω and nearly 17 times increment in energy harvested. Peak values of open circuit voltage obtained were 0.3 and 1.2 V for uncoated as well as coated samples respectively. The electric current for the heating & cooling cycle represents peak value of 1.47 µA when compared with uncoated sample with a value of 0.24 µA. Moreover, energy stored across capacitor of10 µF founds an increment from 1.4 µJ for uncoated sample to 23.10 µJ for coated sample. The study proposes effective utilization of harmful automobile exhaust and harvesting of energy for low power electronics. Therefore this study systematically investigates the pyroelectric energy potential of BaSn0.05Ti0.95O3 ceramics by using automobile emission and compares it with similar class of materials.

Large pyroelectric and energy harvesting properties have been attracting increasing attentions due to the practical applications in infrared detectors and energy harvesting technologies. Ferroelectric-antiferroelectric (FE-AFE) phase transitions are usually accompanied by a sharp drop in polarization, which will lead to excellent pyroelectric properties and energy harvesting density. Therefore, FE-AFE phase boundary design is an effective strategy to develop new pyroelectric materials. In this paper, Pb(Lu1/2Nb1/2)O3-PbTiO3 (PLN-PT) single crystals with FE-AFE phase transitions were obtained by molten salt growth method. The temperature-induced FE-AFE phase transition was verified by temperature-dependent macrodomain structure, DSC curves and dielectric properties. Obviously, PLN-PT crystals display excellent peak pyroelectric coefficient (∼6.8 μC/(cm2·K)) with a maximum depolarization temperature of 118 °C. Meanwhile, the pyroelectric energy harvesting density is as high as 2.62 J/cm3, which is much higher than other pyroelectric materials. The results reveal that the PLN-PT crystal is a promising candidate for infrared detectors and energy harvesting devices.

Utilizing the heat energy of exhaust gases is a promising application of thermoelectric generator (TEG), which can convert low grade thermal energy into electricity. The annular thermoelectric generator (ATEG) is thought to be much more feasible for cylindrical heat source compared to the flat-plate thermoelectric generator (FTEG) in reference to the compatibility. Nevertheless, the quantitative comparison is lacking to clarify the prevalent geometry of TEG for cylindrical heat source. In this work, the performances of ATEG and FTEG are compared in detail with varying inlet temperature, velocity and the convective heat transfer coefficient when cylindrical heat source is applied. The turbulent heat source is described by the standard κ - e functions together with the two-equation heat transfer model, while the output power and conversion efficiency of the ATEG and FTEG are calculated by solving the coupled thermo-electric equations. Our results showed that the output powers and the conversion efficiencies of ATEG and FTEG both increase with the increase of the inlet velocity, temperature, and the convective heat transfer coefficient. The conversion efficiency of ATEG is always higher than that of FTEG. The conversion efficiency of ATEG becomes even larger than that of FTEG when inlet temperature and/or convective heat transfer coefficient are relatively larger. In contrast, the output power of ATEG has no obvious difference with that of FTEG. This study addressed the condition when the ATEG has obvious advantage compared to the FTEG with cylindrical heat source applied. Our results suggest the annular TEG is better choice for cylindrical hot source especially when the inlet temperature and/or convective heat transfer coefficient are relatively larger. It could be a helpful guide for choosing suitable geometry of TEGs for energy harvesting in complex condition.

Facing the upcoming energy and environmental crisis, artificial photosynthesis for producing various solar fuels (e.g., hydrogen or carbon products) via a solar-to-chemical energy conversion is receiving increasing attention; however, its low conversion efficiency is a challenge for commercialization. To resolve low-efficiency issues, lead halide perovskite (LHP) with outstanding optoelectronic properties compared to conventional semiconductors can be a promising approach to improve the solar-to-fuel conversion reactions and solar fuel production efficiency. The tunable energy band structure and charge transport properties of LHP have promoted their extensive use in the production of solar fuels. This study summarizes the recent advancements of LHP-mediated solar-to-fuel conversions, classified by their redox reactions, namely solar water splitting, hydrohalic acid splitting, and CO2 reduction. Advanced approaches for achieving high conversion efficiency and long-term durability are discussed, including the configuration of devices, the composition of LHP, and the protection strategy of LHP. Moreover, the reaction mechanisms of LHP-mediated solar-to-chemical energy conversions and obstacles for enhancing the conversion efficiency are discussed. Finally, we present the perspectives on the development of LHP-incorporated solar-to-fuel conversion systems, which might open a new era of energy harvesting and storage.

Sunflower seed is a popular food, but plenty of bio-waste sunflower husks are discharged into the world. If this bio-waste trash can be recycled, it will be reduced not only environmental pollution but also the waste of resources. In this paper, a triboelectric nanogenerator (SFP-TENG) based on a bio-waste sunflower husk powder is proposed and its open-circuit voltage, short circuit current, and instantaneous power are archived as 488 V, 28. 5 μ A , and 1200 μ W , respectively, under the frequency of 10 Hz with the excitation force of 58 N. The proposed SFP-TENG can harvest the biomechanical energy from the human body’s daily motions. The fabricated SFP-TENG device is capable of lighting up 153 commercial LEDs. Furthermore, the SFP-TENG device is also tested under various humid environments such as 38, 49, 60, 79, and 89% relative humidity. Additionally, it can power up microelectronic devices such as calculator and stopwatch. Hence, we are sure that the proposed device can promote cost-effective and eco-friendly green energy harvesting through recycling bio-wastes as sunflower husk.

Energy harnessing from hydrokinetic systems has been explored over several centuries. With advancements in the technology in last decade, and the intermittent nature of other technologies for energy harvesting, interest in harnessing energy from water-based hydrokinetic systems has amplified. This paper reviews and studies the state-of-the-art of these systems in sea- and river-based applications. The history of development, working principles, different turbines classifications, and research prospects and opportunities are reviewed and discussed. We also conduct a survey of currently available commercial technologies. Elements of the design that need to be enhanced are presented in detail, along with further research prospects in areas related to the technology.

In the last decade, two-dimensional organic single crystals (2D OSCs), defined as a class of ultrathin crystals with atomic or molecular level thickness and micrometer-scale-lateral dimension, has emerged as a rising star due to ultrathin feature, high crystallinity, low-structure symmetry, larger material library, diverse processing technique and excellent flexibility, etc. Due to these advantages, 2D OSCs offer exciting application prospects for flexible electronics, optoelectronics, sensing, energy harvesting, biology and medicine, etc. However, it is still challenging to synthesize large-area highly crystalline 2D OSCs as well as investigate their intrinsic properties and structure–property relationships. Herein, we first treat the growth techniques of 2D OSCs carefully and then discuss their novel physics and optoelectronic properties at the 2D limit. A significant effort has been made in evaluating the latest advances in high-performance devices applying 2D OSCs and corresponding heterostructures. In terms of practical applications, their integrations and device arrays are discussed. Furthermore, we point out several important research directions of 2D OSCs and corresponding heterostructures. Finally, the state-of-the-art challenges and future opportunities that include the investigation and application of 2D OSCs have been presented, which will provoke more researchers to come into this field.

The possibility of exploiting electrical energy scavenged from bicycle mechanical vibrations by piezoelectric harvesters is investigated. The bicycle vibrations on a typical city track are characterized through road tests and the power spectral densities (PSDs) of measured vibrations are presented. Both analytical and experimental methods are adopted to estimate the average electric power that can be harvested by a standard piezoelectric harvester with tip mass mounted on the bicycle. The possibility of tuning the harvester by means of liquid tip masses, resulting in a better trade-off between generated power and stress inside the piezoelectric layer, is investigated as well.

Energy harvesting in the railway industry has great potential for many applications. Energy harvesters can provide electrical power for track-side, on-board, and infrastructure instruments, including health monitoring sensors, signaling, switches, and safety equipment. Due to the rapidly growing trend of the railway network, a considerable number of instrumentations need to be located in inaccessible, remote, and harsh locations where providing the energy through cable is almost impossible. In these cases, self-powered sensors and distributed power generators can be used based on energy harvesting techniques. High-intensity sound and vibration levels in the railway environment prove them to be promising sources of energy for self-powered devices. This paper aims to provide a comprehensive review on the railway sound and vibration energy harvesting, from the beginning to the most state-of-the-art. This paper addresses different energy harvesting resources for the railway environment, diverse methods of energy harvesting and their advantages and drawbacks, and at the end, energy harvesting applications in the railway industry. Different models and prototypes of energy harvesters are introduced and compared. Finally, the potential applications of railway energy harvesting are addressed, and future challenges and trends are discussed. The scheme of the present paper is designed in a way to provide readers the most significant principles that need to be considered in the design of railway energy harvesters.

Systems for harvesting and storing solar energy have found practical applications ranging from solar farms to autonomous smart devices. Generally, these energy solutions consist of solar cells for light harvesting and rechargeable batteries to match the solar energy supply to consumption demands. Rather than having a separate energy harvesting and storing device, we report photo-rechargeable zinc-ion batteries (hν-ZIBs) using a photoactive cathode composed of layer-by-layer grown zinc oxide and molybdenum disulfide. These photocathodes are capable of harvesting solar energy and storing it in the same material and alleviate the need for solar cells or power converters. The proposed photocathodes achieve photoconversion efficiencies of ∼1.8% using a 455 nm light source and ∼0.2% of solar-conversion efficiencies. Light not only allows photocharging but also enhances the battery capacity from 245 to 340 mA h g–1 (specific current of 100 mA g–1 and 12 mW cm–2 light intensity at 455 nm). Finally, the proposed hν-ZIBs also demonstrate a capacity retention of ∼82% over 200 cycles.

Consider a battery limited energy harvesting communication system with online power control. Assuming independent and identically distributed (i.i.d.) energy arrivals and the harvest-store-use architecture, it is shown that the greedy policy achieves the maximum throughput if and only if the battery capacity is below a certain positive threshold that admits a precise characterization. Simple lower and upper bounds on this threshold are established. The asymptotic relationship between the threshold and the mean of the energy arrival process is analyzed for several examples.

This article presents a textile antenna for dual-band simultaneous wireless information and power transfer (SWIPT). The antenna operates as a 2.4 GHz off-body communications antenna and a sub-1 GHz (785–875 MHz) broad-beam rectenna. Incorporated within the broadside microstrip antenna is a high-impedance rectenna for sub-1 GHz power harvesting. Utilizing antenna-rectifier co-design, the rectenna eliminates the rectifier matching network. The textile antenna is fabricated on a felt substrate and utilizes conductive fabrics for the antenna. At 2.4 GHz, the antenna achieves a realized gain of 7.2 dBi on a body phantom and a minimum radiation efficiency of 63%, with and without the rectifier. The rectenna achieves a best-in-class RF to dc efficiency of 62% from 0.8 $\mu \text{W}$ /cm2, representing over 25% improvement over state-of-the-art textile rectennas and demonstrating that SWIPT does not detrimentally affect the energy harvesting or communications performance. The antenna/rectenna occupies an electrically small area of $0.213\times 0.19\,\,\lambda ^{2}_{0}$ . This antenna is the first dual-band, dual-mode antenna demonstrated on textiles for SWIPT applications and the first dual-band matching network-free SWIPT rectenna.

Recently, energy harvesting systems that utilize hybrid NVM-SRAM memory in their designs are introduced as a promising alternative for battery-operated systems. Since the ambient input power of an energy harvesting system fluctuates as the environmental conditions change, the system may stop the execution of programs until it receives enough energy to continue the execution. Resuming the execution of a program after the suspension may lead to data inconsistency in an energy harvesting system and threatens the correct functionality of the programs. In this paper, we propose COACH, an energy-efficient consistency-aware memory scheme which guarantees the correct functionality and consistency of the program in an energy harvesting system. The experimental results show that COACH improves forward-progress of the programs in the system by up to 60% compared with the state of the art consistency-aware approaches without imposing considerable energy overhead to the system.

A novel highly efficient radio-frequency (RF) energy harvester (rectenna) array with multifrequency coverages (1.7–1.8 GHz and 2.1–2.7 GHz) as well as an omnidirectional 3-D radiation pattern is presented. The harvester array is very compact and of low-profile, which strategically combines 12 single Vivaldi slot rectenna elements. More importantly, the proposed rectenna array is significantly simplified through a codesigned effective impedance tuning and array combination method to reduce the overall circuit complexity whilst maintaining high energy conversion efficiency (up to 67%) over the desired frequency band under different input powers (−25–5 dBm) and circuit loads (0.2–8 kΩ). Having utilized the proposed wireless energy harvester array, a complete system-level demonstration of ambient RF energy-powered, a self-sustainable IoT sensor node is demonstrated for reliably operating in a typical indoor environment. Such a demonstration has never been reported before. In addition, the proposed rectenna array has novel features in terms of simplified Vivaldi rectenna matching, compact array combination and optimal beam shaping, which has proven to be an effective energy harvester in most domestic environments; therefore, having significant implications in powering small electronics for real-world Internet-of-Things (IoT) and industrial Internet-of-Things (IIoT) applications.

This paper introduces the fractional damping for a piezoelectric energy harvester subjected to Gaussian colored noise and investigates the dynamic response by the stochastic averaging method. To successfully achieve this goal, the original system is decoupled into the equivalent stochastic system through variable transformation at first. Then the stochastic averaging approach is employed to construct the theoretical results. Furthermore, the feasibility and performance of the stochastic averaging method are evaluated with the assistance of the numerical results from Monte Carlo simulation. Finally, we concentrate on discussing the effect of fractional orders and system parameters on the mean square voltage and analyzing the effectiveness of the stochastic averaging method for the piezoelectric energy harvesting system by heat maps of the relative error in a quantitative perspective.

In industrial wireless sensor networks (IWSNs), a lot of energy is wasted in the form of electromagnetic radiations. It can be effectively utilized with energy harvesting (EH), which absorbs part of the energy in the transmission signal but reduces the throughput and reliability of IWSNs. In this article, we study the throughput optimization of IWSNs with EH from the interference radio-frequency (RF) signal considering the reliability constraint of the industrial information transmission. Under the premise of limited energy supply of EH relays, the throughput maximization of IWSNs is formulated as a nonconvex optimization problem. In order to transform the nonconvex problem to a convex optimization problem, the successive convex approximation (SCA) approach is adopted. Furthermore, a power allocation algorithm is designed to maximize the total transmission rate of the network. Simulation results demonstrate that the proposed algorithm can maximize the throughput under the primise of SINR reliability.

Future Internet of Things networks are likely to have radio frequency (RF) energy harvesting sensor devices and also solar-powered hybrid access points (HAPs) that help monitor one or more targets such as assets in a warehouse. In this setting, we outline three contributions that ensure devices’ monitor targets at all times and upload the maximum number of samples to an HAP in order to ensure high monitoring quality. First, we outline a mixed integer linear program (MILP) and use it to optimize the transmission power of HAPs and time used by devices to harvest RF energy, monitor target(s), and data transmissions. Second, we propose two heuristic algorithms to solve large problem instances. The results show that our heuristics achieve almost 97% of the optimal result computed by the MILP.

A novel ultrahigh frequency (UHF)/ultrawideband (UWB) hybrid radio frequency identification (RFID) tag is reported for object-specific remote vital-sign monitoring application. The tag achieves a record energy-harvesting sensitivity at the UHF band by codesigning a meander dipole antenna and a passive rectifier. The especially high quality-factor makes the frontend sensitive to near-field motions such as heartbeats and respiration in a wearable setting. The custom CMOS integrated circuit (IC) of approximately 1- $\mu \text{W}$ power consumption builds around a low-power UWB transmitter and converts the variations in the supply voltage to the impulse repetition rate. The tag consisting of the IC and UHF/UWB antennas requires no other discrete components and features a size of 4.2 cm $\times2.9$ cm and a weight of 0.93 g. A long-distance experiment verifies that the tag can be wirelessly powered up at 51 m from a 4-W effective-isotropic-radiation-power UHF transmitter. Remote vital-sign monitoring is validated on a human subject, in which the UHF power source is placed 2 m away from the subject with a power emission of less than 20 dBm. This work proposes a first-of-its-kind remote vital-sign monitoring solution based on a passively powered noncontact wearable tag. The design of the far-field energy-harvesting frontend with a record sensitivity serves as a reference for future works on battery-free remote sensors.

This article proposes a power source based on alternating electric field energy harvesting, which can be used for the condition monitoring devices for a high-voltage (HV) transmission line. The energy-harvesting ability of online and offline harvesters depending on different sizes and installation positions is studied herein through a finite-element simulation. The power source uses a novel energy conversion circuit with a cascaded ladder-type topology that can multiply the power when increasing the number of cascaded stages. We set up an HV experiment platform to test the performances of the energy harvester and the power source. The energy-harvesting ability of the harvester approaches the simulation results. The tested power source with four cascaded stages demonstrates a harvesting ability of 620 μ W/ μ A, making it superior to the reported solutions in previous studies. The proposed circuit shows the latent capability of realizing a higher power density.

We develop novel statistical models of the harvested energy from renewable energy sources considering harvest-store-consume (HSC) architecture. We consider three renewable energy harvesting scenarios, i.e., (i) harvesting from the solar power, (ii) harvesting from the wind power, and (iii) hybrid solar and wind power. In this context, we first derive the closed-form expressions for the density functions and moments of the harvested power solar and wind power. Then, we calculate the probability of energy outage at UAVs and signal-to-noise ratio (SNR) outage at ground cellular users. The energy outage occurs when the UAV is unable to support the flight consumption and transmission consumption from its battery power and the harvested power. Due to the intricate distribution of the hybrid solar and wind power, we derive novel closed-form expressions for the moment generating function (MGF) of the harvested solar power and wind power. Then, we apply Gil-Pelaez inversion to evaluate the energy outage at the UAV and SNR outage at the ground users. In addition, we formulate the SNR outage minimization problem and obtain closed-form solutions for the transmit power and flight time of the UAV. Furthermore, we demonstrate the application of moments in computing novel metrics such as the probability of charging the UAV battery within the flight time, average UAV battery charging time, probability of energy outage at UAVs, and the probability of eventual energy outage (i.e., the probability of energy outage in a finite duration of time) at UAVs. Numerical results validate the analytical expressions and reveal interesting insights related to the optimal flight time and transmit power of the UAV as a function of the harvested energy.

Energy efficiency plays a vital role in device-to-device communications, which has been recognized as a key challenge. In this article, we study the implications of the peak power constraints and processing cost on the energy scheduling policy, and find that the peak power should be used around the time slots of each energy arrival, and the only time slot in which the intermittent communication may occur is the last time slot. A new optimal energy scheduling algorithm is devised based on these observations. Also, we propose a near-optimal energy scheduling algorithm that simultaneously takes into account the peak power constraints and the processing cost. Our simulation results demonstrate the effectiveness of the proposed energy scheduling algorithm and the validity of the mathematical analyses.

At present, research on interface circuits for environmental energy harvesting is mainly carried out around a single transducer. However, rich ambient energy sources can be harvested with multiple transducers. Hence, in this article, extensible multi-input synchronous electronic charge extraction (EMI-SECE) interface circuit based on triple-stack LC resonance for piezoelectric and thermoelectric energy harvesting is proposed. proposed EMI-SECE interface circuit can simultaneously extract energy from multiple piezoelectric transducers (PZTs) and thermoelectric generators when the peak open-circuit voltage of the PZTs is detected by the passive peak detectors. Theoretical analysis and experiments verify the effectiveness of the circuit. The experimental results show that the proposed EMI-SECE circuit can harvest energy from two PZTs with any phase difference (0−2 π ) based on single inductor. In addition, the circuit can harvest thermoelectric energy at an open-circuit voltage as low as 20 mV, and the maximum harvesting efficiency can be reached 85.7% at $V_{{\rm{oc}}}$ = 200 mV.

In this article, a rectifier-less synchronized switch harvesting on inductor (ReL-SSHI) interface circuit for piezoelectric energy harvesting is presented. The proposed circuit works in two different modes: at the positive peak of the open-circuit voltage of the piezoelectric transducer (PZT), the switch in series with the load is turned on , and is operated in the series synchronized switch harvesting on inductor mode; at the negative peak of the open-circuit voltage of the PZT, the switch in parallel with the load is turned on, and is operated in voltage synchronous inversion mode. The ReL-SSHI circuit does not need a rectifier bridge so that the power loss of the circuit is reduced, and hence the piezoelectric energy harvesting efficiency of the circuit is improved. Theoretical analysis and simulation verify the effectiveness of the ReL-SSHI circuit.

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.

Cognitive industrial Internet of Things (CIIoT) can extend available spectrum resources by accessing the spectrum licensed to primary user (PU) on the premise of not disturbing the PU's communications. However, additional spectrum sensing and long-time working may consume much energy of CIIoT. In this article, a CIIoT with wireless energy harvesting (WEH) is proposed to harvest the radio frequency energy of PU's signal, and energy-efficient resource allocations in different spectrum access modes are presented to maximize the average transmission rate of CIIoT while guaranteeing its energy saving requirements. The underlay and overlay spectrum access modes for CIIoT with WEH are described, respectively, in which the energy-efficient resource allocations are formulated as joint optimization problems that can be solved using the alternating direction optimization and water-filling algorithm. By combining underlay and overlay modes, a hybrid spectrum access mode is proposed to enable the CIIoT to access both idle and busy spectrum without limiting its transmission power at the absence of PU. Simulation results show that the CIIoT with WEH can consume less power to achieve larger transmission rate, and the hybrid mode outperforms the underlay and overlay modes in the aspects of transmission rate and energy saving.

A self-powered multi-input serial synchronized switch harvesting on inductor (MIS-SSHI) interface circuit with arbitrary phase difference for piezoelectric energy harvesting is proposed in this article. The proposed MIS-SSHI can extract energy from multiple PZTs based on S-SSHI technique and handle inductor access conflict to avoid mutual influence between the PZTs, without using extra inductor access controlling circuit. Four cases of different phases between PZTs are discussed to explain how to handle the inductor access conflict. Besides, the diodes in traditional S-SSHI circuit are removed to improve the conversion efficiency. An experimental platform is built for testing the power generation performance of the proposed circuit. The experimental results show that the proposed MIS-SSHI circuit can harvest energy from two PZTs with arbitrary phase difference (0-2π) based on single inductor. The maximum harvested power of the proposed MIS-SSHI circuit for single PZT can reach 3.7 times that of the standard energy harvesting circuit.

This article presents an efficient piezoelectric (PE) energy harvesting (EH) circuit based on the techniques of series synchronized switch harvesting on inductor (Series-SSHI) and maximum power point tracking (MPPT). The MPPT is achieved using the proposed fractional normal-operation voltage (FNOV) method, which is based on the Series-SSHI operating principle. The FNOV method no longer disconnects the PE harvester from the load circuit to measure its open-circuit (OC) voltage. Instead, it measures the peak PE voltage during the normal Series-SSHI operation to enable the continuous EH process. The FNOV-MPPT circuit is implemented based on a variable width hysteresis controller for saving energy. In addition, the prototyped circuit can achieve the figure of merit factor of 2.68 and the maximum MPPT efficiency of 98.1% with the PE OC voltage ranging from 2 to 5 V. The measurements confirm the validity of the proposed FNOV-MPPT solution for the weakly coupled PE harvesters.

In the paper, a new 3D energy harvesting system is provided. This work discussed the Lagrange approach to derive the differential equations of motion in the case of energy harvesting systems. An electromechanical system consists of a mechanical resonator, a piezoelectric transducer and electrical circuit with the load resistor. A flexible slender rod clamped at the bottom and loaded by the tip mass is proposed as the resonator. Moving in the 3D space, it enables the system to avoid the gravitational potential barrier of the straight vertical shape in case of buckling. This paper investigates the response of the rod deflection and the root mean square power output of selected vibration mode shapes with an attached tip mass.

Due to the global energy crisis and environmental degradation, largely as a result of the increased usage of non-renewable energy sources, researchers have become more interested in exploring alternative energy systems, which may harvest energy from natural sources. This research article provides a comparison between various modeling of piezoelectric elements in terms of power generation for energy harvesting solutions. The energy harvesting can be computed and calculated based on piezoelectric materials and modeling for the specific application. The most common type of environmental energy that may be collected and transformed into electricity for several purposes is Piezoelectric transduction, which is more effective, compared to other mechanical energy harvesting techniques, including electrostatic, electromagnetic, and triboelectric transduction, due to their high electromechanical connection factor and piezoelectric coefficients. As a result of this research, scientists are highly interested in piezoelectric energy collection.

The emerging energy-harvesting technology enables charging sensor batteries with renewable energy sources, which has been effectively integrated into Wireless Sensor Networks (EH-WSNs). Due to the limited energy-harvesting capacities of tiny sensors, the captured energy remains scarce and differs greatly among nodes, which makes the data aggregation scheduling problem more challenging than that in energy-abundant WSNs. In this article, we investigate the Minimum Latency Aggregation Scheduling (MLAS) problem in EH-WSNs. First, we identify a new kind of collision in EH-WSNs, named as energy-collision, and design several special structures to avoid it during data aggregation. To reduce the latency, we try to choose the parent adaptively according to nodes’ transmission tasks and energy-harvesting ability, under the consideration of collisions avoidance. By considering transmitting time, residual energy, and energy-collision, three scheduling algorithms are proposed under protocol interference model. Under physical interference model, several approximate algorithms are also designed by taking account of the interference from the nodes several hops away. Finally, the theoretical analysis and simulation results verify that the proposed algorithms have high performance in terms of latency.

This review article summarises the mechanism of the acoustic energy harvester or converter which includes the compact structure of the piezoelectric element, electromagnetic transducer and Helmholtz resonator; different shapes of Helmholtz resonators, piezoelectric cantilever, acoustic metamaterial-based approach, electrostatic transduction method, auxetic structure of material and other techniques. The recently established methods of acoustic energy harvesting and converting mechanisms; devices are carefully reviewed, and their results are compared and listed in the table. The technique of energy conversion by using acoustic metamaterial will tend to be more efficacious due to its complexity and the structure. Even in the few noise attenuation applications, more metamaterial is used, where, with the help of the conversion mechanism, the noise or sound energy can be converted into electrical energy for small electronic applications. It is demonstrated that the acoustic energy-conversion technique will become an essential part of the environmental energy harvesting research field.

The energy harvesting (EH) technique has ignited a rising research interest due to its ability to enhance the battery power of user equipment by harvesting energy by using a simple radio frequency circuit. In this paper, the simultaneous wireless information and power transfer non-orthogonal multiple access (NOMA) technique is investigated over Rayleigh fading channel conditions. EH NOMA improves the power efficiency, and it results in better throughput as compared to conventional NOMA techniques. In this paper, we investigate the achievable data rate and the outage probability performance of the near user, also called the relay user (RU), and the far user (FU). It can clearly be shown that the RU data rate is saturated and at 1 bits/s/Hz will become constant, while the FU data rate increases with an increase in transmitted power. It is seen by analysis that the RU data rate would saturate due to EH. It is further shown that with a transmitted power of 18 dBm, the net output of the FUs is readily shown to be based around a value of 2.80 bits/s/Hz. In comparison, it is shown that the FU’s instantaneous information rate dropped below the target data rate.

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) mixed with single-wall nanotubes (SWNTs) (10:1) and doped with (0.1 M) perchloric acid (HClO4) in a solution-processed film, working as an excellent thin transparent conducting film (TCF) in organic solar cells, was investigated. This new electrode structure can be an outstanding substitute for conventional indium tin oxide (ITO) for applications in flexible solar cells due to the potential of attaining high transparency with enhanced conductivity, good flexibility, and good durability via a low-cost process over a large area. In addition, solution-processed vanadium oxide (VOx) doped with a small amount of PEDOT-PSS(PH1000) can be applied as a hole transport layer (HTL) for achieving high efficiency and stability. From these viewpoints, we investigate the benefit of using printed SWNTs-PEDOT-PSS doped with HClO4 as a transparent conducting electrode in a flexible organic solar cell. Additionally, we applied a VOx-PEDOT-PSS thin film as a hole transporting layer and a blend of PTB7 (polythieno[3,4-b] thiophene/benzodithiophene): PC71BM (phenyl-C71-butyric acid methyl ester) as an active layer in devices. Zinc oxide (ZnO) nanoparticles were applied as an electron transport layer and Ag was used as the top electrode. The proposed solar cell structure showed an enhancement in short-circuit current, power conversion efficiency, and stability relative to a conventional cell based on ITO. This result suggests a great carrier injection throughout the interfacial layer, high conductivity and transparency, as well as firm adherence for the new electrode.

We investigate the impact of the channel statistics on the average harvested energy when directive lightwave power transfer (DLPT) is used for both indoor and outdoor environments. More specifically, for the indoor scenario, the channel randomness is subject to misalignment effects, while for the outdoor one, atmospheric turbulence is further considered. For both scenarios, closed-form expressions are extracted for the average harvested power, validated via Monte Carlo simulations. Interestingly, the final expressions help to assess the energy harvesting capabilities of a DLPT system and provide valuable insights for hardware implementation.

Small Unmanned Aerial Vehicles (SUAVs) are low-cost quick to launch platforms which offer potential for a range of roles in urban environments. However, these environments create complex wind flows that present control issues for small, low-speed platforms. Further to this, battery technology does not yet offer the power-weight capacity to enable the endurance requirements for such missions. In comparison, birds of a similar size and weight are not only able to manage complex wind flow, but also exploit the environment as a locomotive energy source. Birds in migration are known to adjust airspeed to minimize the energetic cost of transport in response to wind conditions however, it is unknown whether birds implement the same velocity optimization strategies in more complex environments and while performing energy harvesting flight strategies. This study used Global Positioning System (GPS) backpacks to track 11 urban nesting gulls and found that during 193 daily commutes the gulls were able to soar 44% of the time by making use of both thermal and orographic updrafts. We outline cost of transport (CoT) theory and propose a model for optimizing airspeed for given wind conditions whilst maintaining a trajectory to a given location. We used the gull flight paths to test for CoT velocity adjustments by considering their flapping and soaring strategies. We found that by having a similar best glide speed and minimum power speed in soaring and flapping flight the gulls were able to make energy savings of as much as 30%. These models calculated optimum ground and airspeeds for known wind conditions assuming trajectory holding throughout flight, and as such could be implemented on a SUAV platform with wind sensing capabilities. This approach could significantly reduce the energy requirements for a SUAV navigating in an urban environment.

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.

Abstract Harvesting abundant mechanical energy has been considered one of the promising technologies for developing autonomous self-powered active sensors, power units, and Internet-of-Things devices. Among various energy harvesting technologies, the triboelectric harvesters based on contact electrification have recently attracted much attention because of their advantages such as high performance, light weight, and simple design. Since the first triboelectric energy-harvesting device was reported, the continuous investigations for improving the output power have been carried out. This review article covers various methods proposed for the performance enhancement of triboelectric nanogenerators (TENGs), such as a triboelectric material selection, surface modification through the introduction of micro-/nano-patterns, and surface chemical functionalization, injecting charges, and their trapping. The main purpose of this work is to highlight and summarize recent advancements towards enhancing the TENG technology performance through implementing different approaches along with their potential applications. Graphic Abstract This paper presents a comprehensive review of the TENG technology and its factors affecting the output power as material selection, surface physical and chemical modification, charge injection, and trapping techniques.

Organic piezoelectric nanogenerators (PENGs) with light weight, good flexibility, and simple processing are promising in mechanical energy conversion. Here, a high-output polymer PENG composed of a poly(vinylidene fluoride-trifluorethylene)/SnSe nanosheet (NS) nanocomposite film has been fabricated and tested. After a treatment with mixed solvents of N,N-dimethylformamide and 1,1,2,2-tetrachloroethane (TCE), the optimal nanocomposite PENG exhibits high piezoelectric properties with a piezoelectric coefficient (d33) of 25.06 pC·N-1, a prominent open-circuit voltage (Voc) of 15.36 V·cm-2, and a short-circuit current (Isc) of 1.02 μA·cm-2. Moreover, the PENG can generate an output power density of up to 10.72 μW·cm-2 under a vertical force of 50 N. The attractive piezoelectric performance results from the doping of SnSe NSs with a high piezoelectric coefficient and also the increased β-phase ascribed to the introduction of nucleating agent NSs and the TCE solvent. The PENGs reveal great application potentials in consumer electronics.

This paper proposes a softening nonlinear aeroelastic galloping energy harvester for enhanced energy harvesting from concurrent wind flow and base vibration. Traditional linear aeroelastic energy harvesters have poor performance with quasi-periodic oscillations when the base vibration frequency deviates from the aeroelastic frequency. The softening nonlinearity in the proposed harvester alters the self-excited galloping frequency and simultaneously extends the large-amplitude base-excited oscillation to a wider frequency range, achieving frequency synchronization over a remarkably broadened bandwidth with periodic oscillations for efficient energy conversion from dual sources. A fully coupled aero-electro-mechanical model is built and validated with measurements on a devised prototype. At a wind speed of 5.5 m/s and base acceleration of 0.1 g, the proposed harvester improves the performance by widening the effective bandwidth by 300% compared to the linear counterpart without sacrificing the voltage level. The influences of nonlinearity configuration, excitation magnitude, and electromechanical coupling strength on the mechanical and electrical behavior are examined. The results of this paper form a baseline for future efficiency enhancement of energy harvesting from concurrent wind and base vibration utilizing monostable stiffness nonlinearities.

Improving the operating efficiency of piezoelectric tiles is currently a significant subject of scientific study. The current work proposes a viable solution for enhancing the efficiency of existin...

The sensors and microprocessor radios of the Internet of Things require power and one possibility is a hybrid source consisting of energy harvesting coupled with a rechargeable battery. This article concerns a system with a low, but near constant, supply of harvested energy that is sufficient to slowly charge a battery, which buffers that energy and can then supply the higher power level necessary at data transmission. The cycle life of the battery is then significant and this article describes the cycling of a commercial lithium coin cell, Panasonic ML2020, for a small depth of discharge. Initial work was on a Bio-Logic battery tester and cells were successfully tested, without failure, for a few million cycles at a very shallow depth of discharge. Thereafter a battery tester was developed, based on the Particle Photon, that was much less expensive than a channel of a commercial battery tester. Four cells have been cycled, using this tester, for more than 50 million times with no deterioration in performance evident. Capacitors and an NiMH cell are being similarly tested.

The era of the Internet of Things (IoT) requires sustainable and convenient methods to power widely distributed sensing devices. Self-powered systems have emerged as a potential solution that utilizes ambient energy from environmental sources such as electromagnetic fields, mechanical motion, solar power, and temperature gradients. Recently, the integration of wireless technologies with self-powered systems has attracted significant attention as a way to address challenges in energy harvesting and transport without the cost and inherent physical constraints of wires. This review summarizes recent progress in the application of wireless technology in self-powered systems for applications in harvesting ambient electromagnetic energy and in transferring power between devices. In addition, challenges and development trends in the future of wireless self-powered sensor networks are discussed.

In this paper, the Radiating element of a patch antenna for energy harvesting application was fabricated using the graphene ink-based screen printed method. Wax-coated paper and polyester were inve...