Standard Energy Harvesting Research Articles

Self-made electromagnetic vibration energy harvester of different stroke length and number of coil turns

This paper presents the experimental work on a new tube-shape electromagnetic vibration energy harvester to obtain its optimum peak-to-peak voltage output based on different stroke length, number of coil turns and optimum frequency. The harvester is fabricated using Acrylonitrile Butadiene Styrene (ABS) material. It consists of housings with three different stroke lengths, top and bottom covers, Neodymium Iron Boron (NdFeB) magnets, spring and copper coil. The tested stroke lengths are 40 mm, 45 mm and 50 mm while the number of coil turns are 10, 20 and 30. A standard energy harvesting circuit which consists of full-wave bridge rectifier and a capacitor is designed and fabricated to conduct this experiment. The importance of this circuit is to convert alternating current (AC) to direct current (DC) as well as to enable harvesting and storing processes of electrical energy. The harvester is tested on external vertical vibrations generated by shaker with frequency ranged from 5 Hz to 50 Hz with interval of 5 Hz. The raw voltage readings have been extracted from Oscilloscope and are analysed using Microsoft Excel and Octave software. From the results obtained, the optimum peak-to-peak voltage harvested is 39.41 mV at resonant frequency of 5 Hz by 50 mm stroke length and 30 coil turns device. The higher the stroke length and number of coil turns, the higher the peak-to-peak voltage can be harvested.

New insight into piezoelectric energy harvesting with mechanical and electrical nonlinearities

This letter investigates the piezoelectric energy harvesting system with mechanical and electrical nonlinearities. Through impedance model, nonlinear interface circuits for energy harvesting purpose can be simplified as an electrical impedance with real and imaginary parts. Their effects on the mechanical structure can be regarded as circuit-induced damping and stiffness. The resulted equivalent mechanical vibratory system allows us to analytically obtain the system responses under different excitation and loading conditions by harmonic balance method. Furthermore, it becomes possible to achieve a comprehensive comparison among different nonlinear interface circuits, including the standard energy harvesting circuit, synchronized electric charge extraction circuit, series synchronized switching on inductor circuit, parallel synchronized switching on inductor circuit and parallel synchronized triple bias-flip circuit. The results from the theoretical model and experiments together reveal that the nonlinearities play a significant role in the energy harvester’s hysteresis region size, displacement amplitude, and piezoelectric voltage level. This investigation provides an insight into the design, optimization and implementation for the nonlinear energy harvester.

Modelling of a cantilevered energy harvester with partial piezoelectric coverage and shunted to practical interface circuits

This article presents a modelling methodology for a cantilevered energy harvester with partial piezoelectric coverage and shunted to practical power conditioning interface circuits. First, the distributed parameter model of the partially covered piezoelectric energy harvester is developed and the associated analytical solution is derived. Subsequently, the single-degree-of-freedom representation model is developed and the explicit expressions of equivalent lumped parameters are derived by taking the static deflection as the approximated fundamental vibration mode. Based on the comparison with the single-mode expression of the distributed parameter model, a correction factor is proposed to improve the accuracy of the single-degree-of-freedom model. The results of both the distributed parameter and the corrected single-degree-of-freedom models are compared. The accuracy of the corrected single-degree-of-freedom representation model is verified against the analytical and the finite element models. Finally, practical interface circuits including the standard energy harvesting circuit and the parallel synchronized switch harvesting on inductor circuit are considered. A modified equivalent impedance modelling method is proposed for the analysis of the standard energy harvesting and parallel synchronized switch harvesting on inductor circuits. The results of the modified equivalent impedance modelling method are verified against the existing method in the literature.

A Nonlinear Electromagnetic Energy Harvesting System for Self-Powered Wireless Sensor Nodes

The Internet of things requires long-life wireless sensor nodes powered by the harvested energy from environments. This paper proposes a nonlinear electromagnetic energy harvesting system which may be used to construct fully self-powered wireless sensor nodes. Based on a nonlinear electromagnetic energy harvester (EMEH) with high output voltage, the model of a nonlinear interface circuit is derived and a power management circuit (PMC) is designed. The proposed PMC uses a buck–boost direct current-direct current (DC–DC) converter to match the load resistance of the nonlinear interface circuit. It includes two open-loop branches, which is beneficial to the optimization of the impedance matching. The circuit is able to work even if the stored energy is completely drained. The energy harvesting system successfully powered a wireless sensor node. Experimental results show that, under base excitations of 0.3 g and 0.4 g (where 1 g = 9.8 m·s−2) at 8 Hz, the charging efficiencies of the proposed circuit are 172% and 28.5% higher than that of the classic standard energy-harvesting (SEH) circuit. The experimental efficiency of the PMC is 41.7% under an excitation of 0.3 g at 8 Hz.

Boosting the efficiency of a footstep piezoelectric-stack energy harvester using the synchronized switch technology

In this article, the self-supported power conditioning circuits are studied for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on the synchronized switch harvesting on inductance (SSHI) technology, the power conditioning circuits are designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, for example, standard energy harvesting circuit, series-SSHI, and parallel-SSHI, are compared in terms of their output power to find the best candidate for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 74% more power than the standard energy harvesting counterpart, while the use of series-SSHI circuit demonstrates a similar performance in comparison to the standard energy harvesting interface. The reasons for such a huge efficiency improvement using the parallel-SSHI interface are detailed in this article.

Synchronized Triple Bias-Flip Interface Circuit for Piezoelectric Energy Harvesting Enhancement

The power conditioning interface circuit plays a crucial role in the energy harvesting (EH) capability enhancement in piezoelectric EH (PEH) systems. The principle of most existing synchronized switch circuits for PEH enhancement was summarized under the recently introduced synchronized multiple bias-flip (SMBF) model. The optimal bias-flip strategy derived from SMBF provides valuable insights for future circuit development. Based on such theoretical foundation, this paper implements a new interface circuit called the parallel synchronized triple bias-flip (P-S3BF) for further boosting the harvesting capability beyond the state-of-the-art solutions. By sophisticatedly allocating more bias-flip actions, it makes the best compromise between higher extracted power and lower dissipated power for power conditioning, toward maximum net harvested power. Moreover, the bias voltage reference in P-S3BF is self-contained and self-adaptive. Compared to the other existing solutions involving active voltage manipulations, these two conveniences brought in by P-S3BF are the most significant and necessary features, which facilitate the practical stand-alone implementation of P-S3BF under different periodic vibrations. Experimental result shows that, with the piezoelectric cantilever in use, which vibrates at a constant deflection magnitude, the P-S3BF circuit harvests 24.5% more power than its single bias-flip counterpart, the extensively studied parallel synchronized switch harvesting on inductor; and 287.6% more power than its null bias-flip counterpart, the standard EH bridge rectifier.

A Shock-Optimized SECE Integrated Circuit

This paper presents a fully integrated, self-starting shock-optimized Synchronous Electric Charge Extraction (SECE) interface for piezoelectric harvesters (PEHs). After introducing a model of the electromechanical system under shocks, we prove that the SECE is the most appropriate electrical interface to maximize the harvested energy from our PEH. The proposed interface is then presented, both at system-and transistor-levels. Thanks to a dedicated sequencing, its quiescent current is as low as 30nA. This makes the proposed interface efficient even under time-spaced shocks occurring at sporadic and unpredictable rates. The circuit is for instance able to maintain its self-powered operation while harvesting very small shocks of 8uJ happening every 100 seconds. Our chip was fabricated in CMOS 40nm technology, and occupies a 0.55mm^2 core area. The measured maximum electrical efficiency under shocks reaches 91%. Under shocks, the harvested energy by the proposed shock-optimized SECE interface is 4.2 times higher than using a standard energy harvesting circuit, leading to the best shock FoM among prior art.

Circuit nonlinearity effect on the performance of an electromagnetic energy harvester-structure system

Scavenging energy from structural vibration requires an efficient energy harvesting circuit which could introduce nonlinearity into the harvester-structure system. This study examines the performance of a linear structure equipped with an Electromagnetic (EM) energy harvester connected to a nonlinear standard energy harvesting circuit (SEHC) consisting of a full-wave bridge rectifier and a capacitor in parallel with a resistor. To facilitate the understanding of the nonlinear circuit effect on the behavior of the coupled harvester-structure system under sinusoidal excitation, a first-order harmonic balance approximation method is employed. Numerical simulation and experimental study are conducted to validate the accuracy of the proposed approximation method. Results suggest that the blockage effect of diodes in the bridge rectifier in the SEHC should be reduced by using diodes with small voltage drop value or by designing an EM energy harvester with large electromechanical coupling coefficient to improve the vibration mitigation performance and to enhance the optimal energy harvesting capability of the EM energy harvester. Results also show that circuit nonlinearity should be considered in order to estimate the response of the system accurately.

An Efficient Self-Powered Piezoelectric Energy Harvesting CMOS Interface Circuit Based on Synchronous Charge Extraction Technique

An efficient self-powered synchronous electric charge extraction CMOS interface circuit dedicated to piezoelectric harvesters is proposed in this paper. Self-powered peak detection (PKD) and switch circuits are used to reduce quiescent current so that the backup or pre-charged power can be saved. A new low phase lag (LPL) PKD circuit is designed to improve the synchronous extraction efficiency, which only requires one detection capacitor to perform positive and negative PKD. The circuit can be set at general mode (G-mode) or LPL mode (LPL-mode). Under LPL-mode, the phase lag can be reduced typically by 50%, the synchronous extraction efficiency can obtained up to 94%, while the output power can reach 659 μW when the piezoelectric transducer original opencircuit voltage Voc,org = 5 V, which is 3.56 times of that of full-bridge rectifier standard energy harvesting circuit at the maximum power point. The minimum harvesting startup voltage is 1.7 V and is independent of the energy storage capacitor voltage VDC. The harvesting efficiency can still reach 71.3% at Voc,org = 5 V. The size of the active area is 0.5 mm2 in a 0.18-μm CMOS technology. Circuit may be invoked as a functional block for energy autonomous wireless sensor network node of the Internet of Things.

Piezoelectric beam generator based on MFC as a self-powered vibration sensor

A piezoelectric generator is a device used to convert mechanical energy into electrical energy. The basic element of the generator is made from piezoelectric material in which electrical energy is created as a result of deformations caused by reactions of mechanical structure of the generator. The generators, in which the main element is a cantilever beam constructed from basic material and from piezoelectric material, are one of structures, which are used to the energy harvesting from the mechanical vibrations. The piezoelectric generator are used as a part of self-powered wireless sensor in many scientific research. Such self-powered sensor consists of a sensor measuring selected parameter, a radio transmitter, and aforementioned piezoelectric beam generator. However, the piezoelectric beam generator has a limited application in supply a sensor, because the amount of electric energy generated by such generator does not exceed a few mili Watts and is achieved only if the vibration frequency of mechanical energy source equals the resonant frequency of a cantilever beam of piezoelectric generator. This problem is mainly tried to solve by modifications of the generator beam structure or by introducing additional elements with geometry adapted to the source of mechanical vibration. In contrast to these approaches, the article presents the experimental investigation on the action of self-powered wireless sensor in which a decrease of consumed energy amount was achieved through an using of piezoelectric beam generator, which power the radio transmitter, as a vibration sensor. The piezoelectric beam generator should product an amount of electric energy which is enough to supply only the radio transmitter. Such self-powered wireless sensor is dedicated to a vibration monitoring, in which the basic purpose is a detection of an appearance of the dangerous for building structure vibration. The presented self-powered vibration sensor based on a piezoelectric beam generator equipped with a standard energy harvesting circuit, a radio transmitter and a system of energy transfer control enabling power of a radio transmitter for established level of stored energy in capacitor allows a detection of dangerous vibrations for building structure, monitored by this sensor. In laboratory stand vibration amplitudes of the free end of piezoelectric generator were obtained by changes of vibration frequency and vibration amplitudes of its fixed end. In laboratory experiments the time among radio signal was measured for selected values of capacitor capacity and for changed vibration amplitude of free end of piezoelectric generator beam. On the basis of this experiments it was found that full robustness of tested self-powered sensor was achieved for the capacitor capacity equal to 440μF. The sending of a full package of data by such sensor can be realized only above a minimum value of the capacity of applied capacitor equals 220μF. The capacity of capacitor in piezoelectric self-powered vibration sensor should be selected between minimum value for which full packages of data are sending, in tested sensor it equals 220μF, and maximum values for which full robustness to disturbances is achieved. It was found that an increase of the capacitor capacity caused an improvement of data sending robustness to disturbances in radio transmission. The full robustness manifested the sending of every package of data. On the other hand, an increase of capacitor capacity led to the decrease of detection sensitivity of appearance of short-lived vibrations with the big amplitudes due to longer time of capacitor charging. It was noted that the increase of capacitor capacity did not improve the acting of such sensor in case of appearance of long-lived vibrations.

Using an elastic magnifier to increase power output and performance of heart-beat harvesters

Embedded piezoelectric energy harvesting (PEH) systems in medical pacemakers have been a growing and innovative research area. The goal of these systems, at present, is to remove the pacemaker battery, which makes up 60%–80% of the unit, and replace it with a sustainable power source. This requires that energy harvesting systems provide sufficient power, 1–3 μW, for operating a pacemaker. The goal of this work is to develop, test, and simulate cantilevered energy harvesters with a linear elastic magnifier (LEM). This research hopes to provide insight into the interaction between pacemaker energy harvesters and the heart. By introducing the elastic magnifier into linear and nonlinear systems oscillations of the tip are encouraged into high energy orbits and large tip deflections. A continuous nonlinear model is presented for the bistable piezoelectric energy harvesting (BPEH) system and a one-degree-of-freedom linear mass-spring-damper model is presented for the elastic magnifier. The elastic magnifier will not consider the damping negligible, unlike most models. A physical model was created for the bistable structure and formed to an elastic magnifier. A hydrogel was designed for the experimental model for the LEM. Experimental results show that the BPEH coupled with a LEM (BPEH + LEM) produces more power at certain input frequencies and operates a larger bandwidth than a PEH, BPEH, and a standard piezoelectric energy harvester with the elastic magnifier (PEH + LEM). Numerical simulations are consistent with these results. It was observed that the system enters high-energy and high orbit oscillations and that, ultimately, BPEH systems implemented in medical pacemakers can, if designed properly, have enhanced performance if positioned over the heart.

Electromagnetic energy harvesting from structural vibrations during earthquakes

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

Synchronized bias-flip interface circuits for piezoelectric energy harvesting enhancement: A general model and prospects

Piezoelectric energy harvesting (PEH) systems, as a kind of electromechanically coupled system, are composed of two essential parts: the piezoelectric structure and the power conditioning interface circuit. Previous studies have shown that the energy harvesting capability of a piezoelectric generator can be greatly enhanced by up to several hundred percent by using synchronized switch harvesting on inductor (SSHI) interface circuits, the most extensively investigated family of synchronized bias-flip interface circuits. After SSHI, some other bias-flip circuit topologies, which utilize active approaches for PEH enhancement, have been proposed sporadically. Yet, how active is active enough for harvesting as much energy as possible was not clear. This paper answers this question through the generalization and derivation of existing bias-flip solutions. The study starts by analyzing the energy flow in existing featured interface circuits, including the standard energy harvesting (bridge rectifier) circuit, parallel-SSHI, series-SSHI, pre-biasing/energy injection/energy investment scheme, etc. A synchronized multiple bias-flip (SMBF) model, which generalizes the bias-flip control and summarizes the energy details in these circuits, is then proposed. Based on the topological and mathematical abstraction, the optimal bias-flip (OBF) strategy towards maximum harvesting capability is derived. A case study on the series synchronized double bias-flip (S-S2BF) circuit shows that the potential of the PEH interface circuits can be fully released by using the OBF strategy. The proposed SMBF model and OBF strategy set the theoretical foundation and provide a new insight for future circuit innovations towards more powerful PEH systems.

An efficient self-powered synchronous electric charge extraction interface circuit for piezoelectric energy harvesting systems

Harvesting ambient vibration energy using piezoelectric elements is a popular energy harvesting technique. Energy harvesting efficiency is the research focus. Using synchronous electric charge extraction technology in piezoelectric energy harvesting systems can greatly improve the energy harvesting efficiency. This article presents a self-powered efficient synchronous electric charge extraction circuit for piezoelectric energy harvesting systems, in which four self-powered switch circuits are used to optimize the time sequence of charge extraction so that the rectifier bridge circuit used in traditional synchronous electric charge extraction can be saved. The effect of phase lag on extraction efficiency, system energy, and loss of overall circuit is analyzed. A piezoelectric vibration experimental platform is built for testing the power generation performance of the self-powered efficient synchronous electric charge extraction and those published energy harvesting circuits. The experimental results accord with the theoretical analysis. Moreover, the harvesting energy of the proposed self-powered efficient synchronous electric charge extraction is about three times more than those of the standard energy harvesting circuit under its maximum power point and the self-powered synchronized switch harvesting on inductor in most cases. The energy harvesting efficiency of self-powered efficient synchronous electric charge extraction remains at a high level (>80%) in most cases, and the maximum energy harvesting efficiency is up to 85.1%.

Energy harvesting from electrospun piezoelectric nanofibers for structural health monitoring of a cable-stayed bridge

Wireless monitoring could greatly impact the fields of structural health assessment and infrastructure asset management. A common problem to be tackled in wireless networks is the electric power supply, which is typically provided by batteries replaced periodically. A promising remedy for this issue would be to harvest ambient energy. Within this framework, the present paper proposes to harvest ambient-induced vibrations of bridge structures using a new class of piezoelectric textiles. The considered case study is an existing cable-stayed bridge located in Italy along a high-speed road that connects Rome and Naples, for which a recent monitoring campaign has allowed to record the dynamic responses of deck and cables. Vibration measurements have been first elaborated to provide a comprehensive dynamic assessment of this infrastructure. In order to enhance the electric energy that can be converted from ambient vibrations, the considered energy harvester exploits a power generator built using arrays of electrospun piezoelectric nanofibers. A finite element analysis is performed to demonstrate that such power generator is able to provide higher energy levels from recorded dynamic loading time histories than a standard piezoelectric energy harvester. Its feasibility for bridge health monitoring applications is finally discussed.

Dielectric loss against piezoelectric power harvesting

Piezoelectricity is one of the most popular electromechanical transduction mechanisms for constructing kinetic energy harvesting systems. When a standard energy harvesting (SEH) interface circuit, i.e., bridge rectifier plus filter capacitor, is utilized for collecting piezoelectric power, the previous literature showed that the power conversion can be well predicted without much consideration for the effect of dielectric loss. Yet, as the conversion power gets higher by adopting power-boosting interface circuits, such as synchronized switch harvesting on inductor (SSHI), the neglect of dielectric loss might give rise to deviation in harvested power estimation. Given the continuous progress on power-boosting interface circuits, the role of dielectric loss in practical piezoelectric energy harvesting (PEH) systems should receive attention with better evaluation. Based on the integrated equivalent impedance network model, this fast track communication provides a comprehensive study on the susceptibility of harvested power in PEH systems under different conditions. It shows that, dielectric loss always counteracts piezoelectric power harvesting by causing charge leakage across piezoelectric capacitance. In particular, taking corresponding ideal lossless cases as references, the counteractive effect might be aggravated under one of the five conditions: larger dielectric loss tangent, lower vibration frequency, further away from resonance, weaker electromechanical coupling, or using power-boosting interface circuit. These relationships are valuable for the study of PEH systems, as they not only help explain the role of dielectric loss in piezoelectric power harvesting, but also add complementary insights for material, structure, excitation, and circuit considerations towards holistic evaluation and design for practical PEH systems.

A performance-enhanced energy harvester for low frequency vibration utilizing a corrugated cantilevered beam

This note proposes a performance-enhanced piezoelectric energy harvester by replacing a conventional flat cantilevered beam with a corrugated beam. It consists of a proof mass and a sinusoidally or trapezoidally corrugated cantilevered beam covered by a polyvinylidene fluoride (PVDF) film. Compared to the conventional energy harvester of the same size, it has a more flexible bending stiffness and a larger bonding area of the PVDF layer, so higher output voltage from the device can be expected. In order to investigate the characteristics of the proposed energy harvester, analytical developments and numerical simulations on its natural frequency and tip displacement are carried out. Shaking table tests are also conducted to verify the performance of the proposed device. It is clearly shown from the tests that the proposed energy harvester not only has a lower natural frequency than an equivalent sized standard energy harvester, but also generates much higher output voltage than the standard one.

Impedance Modeling and Analysis for Piezoelectric Energy Harvesting Systems

In a piezoelectric energy harvesting (PEH) system, the dynamics and harvested power vary with different interface circuits connected. The impedance matching theory was regarded as the theoretical base for the harvested power optimization in the harmonically excited PEH systems. The previous literature started the impedance analyses based on the proposition that the harvested power is maximized when the output impedance of the piezoelectric transducer is matched by the input impedance of the harvesting circuit. Yet, retrospecting to the origin of the impedance matching theory, a philosophical problem is found with this proposition. Moreover, the definition, constraint, and composition of the equivalent impedance in the real (nonlinear) harvesting circuits were not clear as well. This paper clarifies these concepts and provides the impedance modeling and analysis for the PEH systems with different interface circuits, including standard energy harvesting, parallel synchronized switch harvesting on inductor, and series synchronized switch harvesting on inductor. The equivalent impedance network and corresponding mechanical schematics of a general PEH system are proposed. The difference between the PEH equivalent impedance network and the conventional impedance network is discussed. The harvested power is investigated based on this impedance analysis. The analytical results show good agreement with the experiments carried out on a base excited PEH device.

Improved Design and Analysis of Self-Powered Synchronized Switch Interface Circuit for Piezoelectric Energy Harvesting Systems

In piezoelectric energy harvesting (PEH), with the use of the technique named synchronized switch harvesting on inductor (SSHI), the harvesting efficiency can be greatly enhanced. Furthermore, the introduction of its self-powered feature makes this technique more applicable for stand-alone systems. In this paper, a modified circuit and an improved analysis for the self-powered SSHI (SP-SSHI) are proposed. With the modified circuit, direct peak detection and better isolation among different units within the circuit are achieved, both of which result in the further removal on the dissipative components. In the improved analysis, details in the open circuit voltage, switching phase lag, and intermediate voltages among different phases are discussed, all of which lead to a better understanding on the working principle of SP-SSHI. The total power dissipation from the piezoelectric source is also investigated. It is of concern but has not been considered in the previous literatures. Both analyses and experiments show that, in terms of the harvested power, the higher the excitation level, the closer between SP-SSHI and ideal (externally powered) SSHI; at the same time, the more beneficial the adoption of SP-SSHI treatment in PEH, compared to the standard energy harvesting (SEH) technique. Under the four excitation levels investigated, the SP-SSHI can harvest up to 200% more power than the SEH interface circuit.

Energy flow in piezoelectric energy harvesting systems

In the research of piezoelectric energy harvesting (PEH), the previous foci were mostly onthe amount of energy that can be harvested from the ambient vibration sources. Otherportions of energy, e.g., the energy dissipated during the harvesting process, were seldomconsidered in PEH systems. Yet, the ignorance on these energies might cause somemisunderstanding in the studies of energy harvesting. This paper sets up an energy flowbased framework for the analysis of PEH systems. An energy flow chart is introduced tocomprehensively illustrate the energy paths within the PEH system. Taking the interfacecircuits of standard energy harvesting (SEH) and synchronized switch harvesting oninductor (SSHI) as examples, different branches of energy flow in the PEH systems arequantitatively investigated. In the previous literature, only the harvested energywas emphasized as a function of the rectified voltage or its corresponding DCload resistance. To be more general, we show that both the harvesting energyand dissipated energy change with the rectified voltage; in addition, these twoportions of energy also depend on the ratio between the rectifier voltage dropand the open circuit voltage. Three experiments are carried out with an SSHIdevice to measure its performances on energy harvesting, energy dissipation, andstructural damping. The experimental results show good agreement with theoreticalanalysis. The functional relations among these branches of energy flow are found.