Analysis of thermal energy harvesting using ferromagnetic materials

This Letter aims at giving a preliminary investigation of the thermal energy harvesting capabilities of a technique using the temperature-dependent permeability of ferromagnetic materials. The principles lie in the modification of the magnetic field caused by the variation of the permeability due to the temperature change, hence generating a voltage across a coil surrounding the circuit. The technique can be made truly passive by the use of magnets for applying bias magnetic field. Theoretical results, validated by experimental measurements, show a voltage output of 1.2 mV at optimal load of 2 Ω under 60 K temperature variation in 5 s (with a maximum slope of 25 K s⁻¹). Further improvements, such as the use of low resistivity coil and magnet with high remnant magnetic field, indicate that it is possible to convert up to 7.35 μJ cm⁻³ K⁻² cycle⁻¹.     

Electrostrictive conversion enhancement of polymer composites using a nonlinear approach

Recent trends in electromechanical conversion demonstrated the advantages of using electrostrictive polymers for actuation or energy harvesting. However, their conversion abilities are lower than usual electroactive materials, such as piezoelectrics. The purpose of this Letter is to propose a solution for artificially increasing the coupling factor of electrostrictive materials. Based on an intermittent switching on an electrical circuit that leads to a voltage increase as well as a reduced phase between voltage and velocity, it is shown that such a process allows increasing the converted energy by 1200% and a gain up to 4 in terms of transferred electrical energy.     

Power management in heterogeneous networks with energy harvesting base stations

In this paper, heterogeneous cellular networks (HCNs) with base stations (BSs) powered from both renewable energy sources and the grid power are considered. Based on a techno-economic analysis, we demonstrate that by controlling both transmit power and stored energy usage of BSs, energy costs can be effectively reduced. Specifically, we propose a two-stage BS operation scheme where an optimization and control subproblem is solved at each stage, respectively. For the first subproblem, transmit power of BSs is adjusted while quality of service (QoS) experienced by users is preserved. In the second subproblem, we consider the strategic scheduling of renewable energy used to power the BSs. That is, harvested energy may be reserved in the battery for future use to minimize the cost of on-grid power that varies in real-time. We propose: (1) an optimization approach built on a lattice model with a method to process outage rate constraint, and (2) a control algorithm based on nonlinear model predictive control (NMPC) theory to solve the two subproblems, respectively. Simulation results include a collection of case studies that demonstrate as to how operators may manage energy harvesting BSs to reduce their electricity costs.     

Nonlinear dynamics for broadband energy harvesting: Investigation of a bistable piezoelectric inertial generator

Vibration energy harvesting research has largely focused on linear electromechanical devices excited at resonance. Considering that most realistic vibration environments are more accurately described as either stochastic, multi-frequency, time varying, or some combination thereof, narrowband linear systems are fated to be highly inefficient under these conditions. Nonlinear systems, on the other hand, are capable of responding over a broad frequency range; suggesting an intrinsic suitability for efficient performance in realistic vibration environments. Since a number of nonlinear dynamical responses emerge from dissipative systems undergoing a homoclinic saddle-point bifurcation, we validate this concept with a bistable inertial oscillator comprised of permanent magnets and a piezoelectric cantilever beam. The system is analytically modeled, numerically simulated, and experimentally realized to demonstrate enhanced capabilities and new challenges. In addition, a bifurcation parameter within the design is examined as either a fixed or an adaptable tuning mechanism for enhanced sensitivity to ambient excitation.     

Broad-band polarization-independent metamaterial absorber for solar energy harvesting applications

A novel broad-band polarization-independent with wide-angle metamaterial absorber(MA) is investigated and demonstrated for solar energy harvesting applications. The proposed MA is composed of two metal layers which have different thickness and a dielectric layer which is sandwiched between these metal layers. By this combination, the proposed MA indicates plasmonic resonance characteristic. Numeric results show that proposed MA has perfect absorption characteristic which is above 88.28% with wide-angle for all visible region. It shows almost perfect absorption of 98.4% at the resonance frequency of 621.76 THz and has also 90% absorption between frequencies of 445 THz and 770 THz which is nearly all visible light region. Besides, numerical results validate that the proposed MA could achieve very high absorption at wide-angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.. The proposed MA and its variations enable for solar cell applications due to have upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. In order to show additional features of the proposed structure, parametric studies are realized and discussed. Furthermore, the absorption characteristic of proposed MA is investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

Broadband energy harvesting via magnetic coupling between two movable magnets

Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.     

A prototype DC triboelectric generator for harvesting energy from natural environment

A prototype direct current Triboelectric Generator (DC-TEG) has been demonstrated to generate dc voltages by converting rotational mechanical energy into electrical energy. The generator primarily consists of four rotating wheels (two copper electrodes and two triboelectric wheels) utilizing polytetrafluoroethylene (PTFE) tape and nylon fabric as the triboelectric materials in its design. Once subjected to mechanical rotation, the interaction between the two triboelectric materials generates equal, but opposite charges and deposits them on the copper electrodes resulting in a dc voltage across an external load resistor. The power performance of the generator, with changes in angular frequency, has been measured. The DC-TEG can generate a dc voltage of about 1.5 mV across an external load of 15.14 kΩ at a rotational speed of 10 rev/sec. The dependences of current and power on the angular frequency have also been measured. Preliminary results suggest that the relationship between the dc voltage and angular frequency of rotation is quadratic, however further measurements at relatively higher angular frequencies are needed before a proper mathematical model may be established. The work here presents a new, cost-effective DC-TEG design for power scavenging from any naturally or artificially occurring rotational mechanical motion facilitated by either wind or flowing water for self-powered systems.     

Adaptive multimode transmission in wireless sensor networks with energy harvesting

Limited energy has always been an important factor restricting the development of wireless sensor networks. The unbalanced energy consumption of nodes will accelerate the death of some nodes. To solve the above problems, an adaptive routing algorithm for energy collection sensor networks based on distributed energy saving clustering (DEEC) is proposed. In each hop of data transmission, the optimal mode is adaptively selected from four transmission modes: single-hop cooperative, multi-hop cooperative, single-hop non-cooperative and multi-hop non-cooperative, so as to reduce and balance the energy consumption of nodes. The performance of the proposed adaptive multi-mode transmission method and several benchmark schemes are evaluated and compared by computer simulation, where a few performance metrics such as the network lifetime and throughput are adopted. The results show that, the proposed method can effectively reduce the energy consumption of the network and prolong the network lifetime; it is superior to various benchmark schemes.     

Power and rate control in wireless communication systems with energy harvesting and rateless codes

In this paper, for a wireless communication system with energy harvesting and rateless error correction codes, the joint optimization of transmit power, modulation scheme and code rate to maximize the long-term average achievable transmission rate under the constraint of available energy is studied. The method is given first to determine the codeword length (or code rate) for a signal-to-noise ratio (SNR) under the constraint of a pre-defined decoding error probability. Then the formula of the actual transmission rate is deduced with a specific modulation and code rate, and the optimization problem to maximize the long-term average actual transmission rate is constructed under the constraints of available harvested energy and the decoding complexity of the rateless code. Since energy harvesting and channel fading are both stochastic processes, the optimization problem is difficult to solve. By using the Lyapunov optimization framework, the original long-term optimization problem is transformed into a per time slot one. Then an efficient numerical method is proposed to obtain the solution to the problem. The proposed algorithm is verified by simulation, and the results show that the proposed algorithm can achieve a higher average actual transmission rate than the comparison algorithms aiming at optimizing the channel capacity.     

非线性磁式压电振动能量采集系统建模与分析

为便于评价、优化磁式压电振动能量采集系统的性能,系统研究了该类系统的建模与分析方法,建立了非线性的分布参数模型用于描述系统的非线性动力学行为,并采用谐波平衡法给出了谐波响应的解析解.随后利用仿真模型分析了磁铁间距、加速度幅值、负载阻抗对输出功率的影响,比较了不同激励频率和加速度幅值下的最优阻抗.结果表明:双稳态特性适用于低强度的振动环境,且愈接近临界区域,输出功率愈高,而单稳态渐硬特性适用于高强度振动环境,其最优间距并不靠近临界区域;阱间大幅运动和阱内小幅运动均存在高低能量态共存的现象,愈接近临界区域,现象愈明显;激振频率是影响最优负载阻抗的决定性因素.     

Stacked and folded piezoelectrets for vibration-based energy harvesting

ABSTRACT

Vibration-based energy harvesting with piezoelectrets can be significantly improved by using multiple layers of these materials. In particular, folding or stacking of piezoelectrets or a combination of these methods results in increased power output of the energy harvesters. The possibilities of these procedures are explored, together with the effect of seismic mass, resonance frequency, and terminating resistance. It is found that with seismic masses of about 20 g and using radiation-crosslinked polypropylene (IXPP) as a piezoelectret, power outputs of up to 80 µW can be achieved for an acceleration of 1 g. Expected dependencies of generated power on frequency, folding and stacking parameters, in particular number of layers, and on seismic mass, are confirmed.     

On energy harvesting for augmented tags

In this paper, the harmonic signals generated by UHF RFID chips, usually considered as spurious effects and unused, are exploited. Indeed, the harmonic signals are harvested to feed a supplementary circuitry associated with a passive RFID tag. Two approaches are presented and compared. In the first one, the third-harmonic signal is combined with an external 2.45-GHz Wi-Fi signal. The integration is done in such a way that the composite signal boosts the conversion efficiency of the energy harvester. In the second approach, the third-harmonic signal is used as the only source of a harvester that energizes a commercial temperature sensor associated with the tag. The design procedures of the two “augmented-tag” approaches are presented. The performance of each system is simulated with ADS software, and using Harmonic Balance tool (HB), the results obtained in simulation and measurements are compared also.     

旋转椭球形电容器的静电能

利用复数坐标系z上的儒可夫斯基变换,计算带电旋转椭球形电容器的静电能,并对结果进行了讨论.     

Electromagnetic ferrofluid-based energy harvester

This Letter investigates the use of ferrofluids for vibratory energy harvesting. In particular, an electromagnetic micro-power generator which utilizes the sloshing of a ferrofluid column in a seismically-excited tank is proposed to transform mechanical motions directly into electricity. Unlike traditional electromagnetic generators that implement a solid magnet, ferrofluids can easily conform to different shapes and respond to very small acceleration levels offering an untapped opportunity to design scalable energy harvesters. The feasibility of the proposed concept is demonstrated and its efficacy is discussed through several experimental studies.     

Relay selection and nonlinear energy harvesting in full-duplex multi-relay cooperative network

Energy harvesting (EH) is a promising technique to extend the lifetime energy-constrained devices in wireless networks. This paper analyses the significance of relay selection and non-linear EH in evaluating the performance of Full-duplex (FD) decode-and-forward (DF) multi-relay cooperative network. The relay selection is considered under three scenarios based on channel state information (CSI) availability. We compare the EH performance of a hybrid power-time-splitting (PTS)-based non-linear energy harvester with time-spitting (TS) and power-splitting (PS) EH at the relay node. We derive the expression of outage probability (OP) of FD DF multi-relay cooperative network over independent and identically distributed Rayleigh fading channels. Numerical results show that the outage performance of the system is significantly enhanced by deploying an ideal relay selection scheme. This paper also gives insights about the combined effect of saturation threshold of non-linear EH and residual self-interference (RSI) on the system performance. Unlike linear EH systems, the non-linear EH causes the outage floor even when the RSI is significantly small. The response of the system is also analysed for the impact of TS and PS ratios. Furthermore, we also investigate the system’s performance in terms of other system parameters like the number of relays and data transfer rate. Monte Carlo simulations are used to verify the analytical expressions.     

Analysis of the energy extracted by a harvester based on a piezoelectric tile

In this paper, we analyze the maximum energy that can be extracted from a piezoelectric harvester subject to pulsed excitation, with an interface circuit composed by a standard bridge rectifier. We show that the optimal voltage of the DC load of the bridge rectifier is a fraction, comprised between 1/3 and ½, of the open-circuit voltage, depending on the piezoelectric losses and excitation time. A simple analytical model is provided, whose accuracy has been assessed against SPICE simulations. Furthermore, preliminary experimental tests carried out over a commercial piezoelectric tile confirm the validity of the proposed model.