Performance Of Energy Harvesting Systems Research Articles

A triboelectric-piezoelectric hybrid nanogenerator for rotational energy harvesting based on bistable cantilever beam

This study presents a triboelectric-piezoelectric hybrid nanogenerator for harvesting rotational energy based on a bistable cantilever beam. The nonlinear bistable behavior effectively enhances the collision force with the triboelectric nanogeneration (TENG) boundary, enlarges the effective contact area of the triboelectric functional materials, and significantly increases the deformation of the piezoelectric cantilever beam, thereby improving the overall electrical output performance of the system. Excessive deformation of the piezoelectric cantilevers is effectively constrained by the TENG boundary, which prevents the degradation and failure of the piezoelectric material. A prototype is prepared and verified experimentally. The effects of key parameters on the output performance are systematically analyzed. According to the results on the overall electrical output of hybrid nanogenerator with and without bistable behavior, the hybrid nanogenerator with bistable behavior achieved an energy density of 29.04 W/m3 at a rotational speed of 450 r/min, which is 2.65 times higher than that of the hybrid nanogenerator without bistable behavior. In addition, the rotational speed range is broadened by more than 1.5 times, and the prototype can realize self-powered temperature monitoring and wireless transmission. Overall, the proposed rotational energy harvester with a magnetic coupling cantilever bistable behavior and TENG boundary mechanism offers a novel means to improve the electrical performance of energy harvesting systems for self-powered internet of things.

Miniaturized Energy Harvesting Systems Using Switched-Capacitor DC-DC Converters

This tutorial brief reviews highly-integrated switched-capacitor (SC) DC-DC converter topologies for miniaturized energy harvesting (EH) IoT systems. Aiming to provide a concise overview of SC converter-based EH interfaces, we first discuss the system level design considerations for energy balancing between source, storage, and load under different environmental conditions. The key factors dominating the energy extraction and power conversion efficiencies, including the source adaptation strategies and SC power stage intrinsic losses, are outlined to establish a fundamental understanding on the EH system performance. After studying different state-of-the-art SC topologies in terms of their rational boost voltage conversion ratio (VCR) generation flexibility, loss characteristics, and implementation tradeoffs, we further introduce two advanced SC converter-based EH system examples, highlighting the SC converter operation in enhancing the EH system functionality and performance. The pros and cons of different SC converter topologies for EH systems will also be discussed.

System Implementation Trade-Offs for Low-Speed Rotational Variable Reluctance Energy Harvesters.

Low-power energy harvesting has been demonstrated as a feasible alternative for the power supply of next-generation smart sensors and IoT end devices. In many cases, the output of kinetic energy harvesters is an alternating current (AC) requiring rectification in order to supply the electronic load. The rectifier design and selection can have a considerable influence on the energy harvesting system performance in terms of extracted output power and conversion losses. This paper presents a quantitative comparison of three passive rectifiers in a low-power, low-voltage electromagnetic energy harvesting sub-system, namely the full-wave bridge rectifier (FWR), the voltage doubler (VD), and the negative voltage converter rectifier (NVC). Based on a variable reluctance energy harvesting system, we investigate each of the rectifiers with respect to their performance and their effect on the overall energy extraction. We conduct experiments under the conditions of a low-speed rotational energy harvesting application with rotational speeds of 5 rpm to 20 rpm, and verify the experiments in an end-to-end energy harvesting evaluation. Two performance metrics—power conversion efficiency (PCE) and power extraction efficiency (PEE)—are obtained from the measurements to evaluate the performance of the system implementation adopting each of the rectifiers. The results show that the FWR with PEEs of 20% at 5 rpm to 40% at 20 rpm has a low performance in comparison to the VD (40–60%) and NVC (20–70%) rectifiers. The VD-based interface circuit demonstrates the best performance under low rotational speeds, whereas the NVC outperforms the VD at higher speeds (>18 rpm). Finally, the end-to-end system evaluation is conducted with a self-powered rpm sensing system, which demonstrates an improved performance with the VD rectifier implementation reaching the system’s maximum sampling rate (40 Hz) at a rotational speed of approximately 15.5 rpm.

Promote efficiency of harvesting vibration energy by tailoring potential energy with addition of magnets

Large-amplitude snap-through motion might happen between two equilibria of a buckling inverted piezoelectric beam under vibration excitation, therefore enhancing the energy harvesting performance of system significantly. However, in practical application, owing to the deep potential well of a buckling beam, relatively large excitation amplitude is needed to trigger such snap-through motion. To overcome this limitation, we herein propose an improved inverted beam harvester that comprises an inverted beam with an affixed tip magnet and two additional magnets mounted in the vicinity of the equilibrium positions. By introducing this repulsive magnetic force, the potential energy could be tailored to promote the occurrence of snap-through motion. Numerical simulation is conducted and it is shown that with the proposed design the harvester would be able to realize snap-through motion more easily compared to the original buckling system. This has also been validated by the experiment in which large deflection and voltage output are both observed when snap-through motion is activated under low excitation frequency.

Exploiting cooperative relays to enhance the performance of energy-harvesting systems over Nakagami-m fading channels

This paper investigates a time-switching energy-harvesting system in which a source communicates with a destination via energy-constrained amplify-and-forward relays. To exploit the benefit of using multiple relays, we propose a relay scheduling called consecutive relay selection (CRS), which allows all relays to assist the source-to-destination communication, to improve the transmission efficiency of the time-switching policy. The partial relay selection (PRS) is examined for performance comparison. The selected relay in the PRS protocol is considered in two cases: in one, it is selected based on the first-hop channel gains (PRS-1 protocol), and in the other, it is selected based on the second-hop channel gains (PRS-2 protocol). For performance evaluation, the analytical expressions of the outage probability and throughput for Nakagami-m fading channel are derived. Our results show that the CRS protocol outperforms the PRS protocol in terms of throughput, the PRS-1 protocol achieves better performance than the PRS-2 protocol. Moreover, we discuss the effects of various key system parameters on system performance, such as the energy-harvesting ratio, source transmission rate, and locations of relays, to provide insights into the various design choices.

Performance analysis of energy harvesting relay systems under unreliable backhaul connections

In this study, the performance of energy harvesting systems in the presence of unreliable backhaul links is investigated over independent but not necessarily identically distributed Nakagami-m fading channels. In particular, the energy-constrained relay uses the amount of harvested energy from the best small-cell transmitter based on time switching-based relaying protocol to process for the next hop transmission. The authors derived the closed-form expressions of the outage probability and the effective throughput with two distinct transmission schemes: (i) delay-limited transmission, and (ii) delay-tolerance transmission are attained. In order to assess the impacts of unreliable backhaul links, they thus obtain the asymptotic expression of the outage probability in high signal-to-noise ratio (SNR) regime. The numerical results are conducted to analyse the effects of energy harvesting fraction time, energy efficiency, backhaul reliability, and the fading parameters on the system performance. The authors' results show that under the unreliable backhaul links the outage probability yields the error-floor in the high SNR regime which demonstrates the significant impact of the backhaul unreliability.

An energy harvesting converter to power sensorized total human knee prosthesis

Monitoring the internal loads acting in a total knee prosthesis (TKP) is fundamental aspect to improve their design. One of the main benefits of this improvement is the longer duration of the tibial inserts. In this work, an electromagnetic energy harvesting system, which is implantable in a TKP, is presented. This is conceived for powering a future implantable system that is able to monitor the loads (and, possibly, other parameters) that could influence the working conditions of a TKP in real-time. The energy harvesting system (EHS) is composed of two series of NdFeB magnets, positioned into each condyle, and a coil that is placed in a pin of the tibial insert and connected to an implantable power management circuit. The magnetic flux variation and the induced voltage are generated by the knee's motion. A TKP prototype has been realized in order to reproduce the knee mechanics and to test the EHS performance. In the present work, the experimental results are obtained by adopting a resistive load of 2.2 kΩ, in order to simulate a real implanted autonomous system with a current consumption of 850 µA and voltage of 2 V. The tests showed that, after 7 to 30 s of walking with a gait cycle frequency of about 1.0 Hz, the EHS can generate an energy of about 70 μJ, guaranteeing a voltage between 2 and 1.4 V every 7.6 s. With this prototype we can verify that it is possible to power for 16 ms a circuit having a power consumption of 1.7 mW every 7.6 s. The proposed generator is a viable solution to power an implanted electronic system that is conceived for measuring and transmitting the TKP load parameters.

Nonlinear modeling and simulation of waste energy harvesting system for hybrid engine: Fuzzy logic approach

Fuel consumption could be cut significantly if waste heat energy of internal combustion engine (ICE) is harvested. Currently, ICEs lose their 42% of energy to exhaust and 28% of energy to the coolant. Several methods for waste thermal energy recovery from ICE have been studied by using supercharger or turbocharger or combined. This study presents the modeling and simulation of coolant based waste energy harvesting system (weHS). The supercharger compressed air gains heat during passing through the inner duct of the weHS while the coolant releases heat. The heated supercharged air is forced to the engine cylinders. The energy harvesting system performance is simulated by varying the supercharged air mass flow rate by keeping constant the coolant mass flow rate and vice versa. The waste energy recovery from the coolant by using weHS is simulated for the coolant flow rate of 2.0 kg/s, 2.5 kg/s, and 3.0 kg/s. The simulations result shows that the waste energies that could be recovered by using weHS are 30.9% for 2.0 kg/s, 32.57% for 2.5 kg/s, and 35% for 3.0 kg/s of the energy that engine lost to the coolant. The efficiency of the engine is expected to increase significantly if weHS is equipped with the engine. The optimum mass flow rate of coolant and mass flow rate of supercharged air are identified by using the fuzzy logic model for the maximum supercharged air temperature of 120 °C.