Xiudong Tang

Large-scale vibration energy harvesting

Nowadays, harvesting energy from vibration is one of the most promising technologies. However, the majority of current researches obtain 10 µW to 100 mW power, which has only limited applications in self-powered wireless sensors and low-power electronics. In fact, the vibrations in some situations can be very large, for example, the vibrations of tall buildings, long bridges, vehicle systems, railroads, ocean waves, and even human motions. With the global concern on energy and environmental issues, energy harvesting from large-scale vibrations is more attractive and becomes a research frontier. This article is to provide a timely and comprehensive review of the state-of-the-art on the large-scale vibration energy harvesting, ranging from 1 W to 100 kW or more. Subtopics include energy assessment from large vibrations, piezoelectric materials and electromagnetic transducers, motion transmission and magnification mechanisms, power electronics, and vibration control. The relevant applications discussed in this article include vibration energy harvesting from human motion, vehicles, transportations, and civil structures. The unique challenges and future research directions of large-scale vibration energy harvesting are also discussed.

Energy harvesting using a PZT ceramic multilayer stack

In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a ‘33’ mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated electrical energy/power in the PZT-Stack, the mechanical to electrical energy conversion efficiency, the power delivered from the PZT-Stack to a resistive load, the electrical charge/energy transferred from the PZT-Stack to a super-capacitor were systematically addressed. Theoretical models for power generation and delivery to a resistive load were proposed and experimentally affirmed. In a quasi-static regime, 70% generated electrical powers were delivered to matched resistive loads. A 35% mechanical to electrical energy conversion efficiency, which is more than 4 times higher than other reports, for the PZT-Stack had been obtained. The generated electrical power and power density were significantly higher than those from a similar weight and size cantilever-type piezoelectric harvester in both resonance and off-resonance modes. In addition, our study indicated that the capacitance and piezoelectric coefficient of the PZT-Stack were strongly dependent on the dynamic stress. (Some figures may appear in colour only in the online journal)

Simultaneous energy harvesting and vibration control of structures with tuned mass dampers

The vibrations of the tall buildings are serious concerns to both engineers and architects for the protection of the safety of the structure and occupant comfort. In order to mitigate the vibration, different approaches have been proposed, among which tuned mass dampers are one of the most preferable and have been widely used in practice. Instead of dissipating the vibration energy into heat waste via the viscous damping element, this article presents an approach to harvest the vibration energy from tall buildings with tuned mass dampers, by replacing the energy-dissipating element with an electromagnetic harvester. This article demonstrates that vibration mitigation and energy harvesting can be achieved simultaneously by the utilization of an electricity-generating tuned mass damper and relevant algorithms. Based on the proposed switching energy harvesting circuit, three control strategies are investigated in this article, namely, semi-active, self-powered active, and passive-matching regenerative. The functions of the energy harvesting circuit on damping force control and power regulation, as well the effectiveness of the control strategies, are illustrated by simulation. The simultaneous energy harvesting and vibration control are demonstrated, for the first time, by experiment based on a three-story building prototype with the electricity-generating tuned mass damper, which is composed of a rotational brushed direct current motor and rack–pinion mechanism.

Vibration energy harvesting from random force and motion excitations

A vibration energy harvester is typically composed of a spring–mass system with an electromagnetic or piezoelectric transducer connected in parallel with a spring. This configuration has been well studied and optimized for harmonic vibration sources. Recently, a dual-mass harvester, where two masses are connected in series by the energy transducer and a spring, has been proposed. The dual-mass vibration energy harvester is proved to be able to harvest more power and has a broader bandwidth than the single-mass configuration, when the parameters are optimized and the excitation is harmonic. In fact, some dual-mass vibration energy harvesters, such as regenerative vehicle suspensions and buildings with regenerative tuned mass dampers (TMDs), are subjected to random excitations. This paper is to investigate the dual-mass and single-mass vibration harvesters under random excitations using spectrum integration and the residue theorem. The output powers for these two types of vibration energy harvesters, when subjected to different random excitations, namely force, displacement, velocity and acceleration, are obtained analytically with closed-form expressions. It is also very interesting to find that the output power of the vibration energy harvesters under random excitations depends on only a few parameters in very simple and elegant forms. This paper also draws some important conclusions on regenerative vehicle suspensions and buildings with regenerative TMDs, which can be modeled as dual-mass vibration energy harvesters. It is found that, under white-noise random velocity excitation from road irregularity, the harvesting power from vehicle suspensions is proportional to the tire stiffness and road vertical excitation spectrum only. It is independent of the chassis mass, tire–wheel mass, suspension stiffness and damping coefficient. Under random wind force excitation, the power harvested from buildings with regenerative TMD will depends on the building mass only, not on the parameters of the TMD subsystem if the ratio of electrical and mechanical damping is constant.

Towards Meso and Macro Scale Energy Harvesting of Vibration

The ambient environment is full of energy of different forms such as sun light, wind, heat, hydraulic energy, and mechanical motion including vibration. People have been seeking ways to convert the ambient energy into useful forms since ancient time. With the global concern of energy and environmental issue, energy harvesting provides one attractive solution and becomes a new research frontier. However, the majority of current research on energy harvesting from mechanical vibration obtains 10μW to 100mW energy, which has only limited applications like self-powered wireless sensors. More than ten review articles appeared in the past five years on vibration energy harvesting, whereas, the majority of which focuses on the applications in microelectronics and wireless sensors. The objective of this review is to survey the research and applications of meso and marco scale energy harvesting from vibration, and discuss the particular challenges and future research directions. Topics include piezoelectric materials and electromagnetic transducers, relevant motion and magnification mechanisms, and power electronics and control, with applications on energy harvesting from human motions, vehicle suspensions and civil structures.Copyright

Regenerative semi-active control of tall building vibration with series TMDs

This paper studies the semi-active control of a novel configuration of tuned mass damper (TMD) using a modified clipped optimal control strategy, with the intention to harvest the vibration energy and control the vibration at the same time. One of the authors recently proposed and optimized the so called series TMD, in which multiple auxiliary masses and absorbers are connected to the primary system in series. It has been proven that it is more effective and robust than other types of TMDs with the same mass ratio such as parallel multiple TMDs, multi-degree-of-freedom (DOF) TMDs and three- or four-element TMDs. In this paper, by replacing the viscous damping element between the two auxiliary masses of series TMD system with an electromagnetic transducer, we implement the semi-active series TMD by controlling the current flow through the transducer in a semi-active way, which also means that the electromagnetic motor works in the driven mode and acts as a electricity generator. The proposed control strategy is a combination of LQG and clipped control. LQG control with acceleration feedback is first designed and then a modified clipped control is used to realize it in a semi-active manner with a practical maximum force or damping limitations. Numerical simulations are carried out based on a tall building with semi-active series TMD under random and harmonic excitations, in comparison with the active and passive strategies. The results show that the proposed semi-active series TMD is very effective to control the vibration while harvesting large amount energy from the vibration of buildings.

Self-powered Active Control of Structures with TMDs

This paper studies the feasibility of self-powered active vibration control of structures with Tuned Mass Dampers (TMDs). Without consuming external energy, the proposed self-powered vibration control strategy can provide better performance than the passive TMD in mitigating the vibration of buildings induced by wind load. the vibration-dissipative element of TMD is replaced with an electromagnetic machine, which serves as actuator and harvester at the same time. First, the desired force is obtained by adopting Linear Quadratic Regulator (LQG) optimal control. Then, the self-powered active control strategy is designed based on the essence of the desired force, which can be passive or active types. The energy of the vibration can be harvested as electricity in energy harvesting mode, and pumped back into the mechanical system when instant active force is required. Switch based circuits with capability of bi-directional power flow are presented for the implementation of self-powered active TMDs. With taking the efficiency of the harvesting and driving circuits into account, numerical simulations are carried out based on a tall building with a TMD under random and harmonic excitations. The results indicate the feasibility and effectiveness of self-powered active TMDs.

Improved design of linear electromagnetic transducers for large-scale vibration energy harvesting

This paper presents the design and optimization of tubular Linear Electromagnetic Transducers (LETs) with applications to large-scale vibration energy harvesting, such as from vehicle suspensions, tall buildings or long bridges. Four types of LETs are considered and compared, namely, single-layer configuration using axial magnets, double-layer configuration using axial magnets, single-layer configuration using both axial and radial magnets, double-layer configuration using both axial and radial magnets. In order to optimize the LETs, the parameters investigated in this paper include the thickness of the magnets in axial direction and the thickness of the coils in the radial direction. Finite element method is used to analyze the axisymmetric two-dimensional magnetic fields. Both magnetic flux densities Br [T] in the radial direction and power density [W/m3] are calculated. It is found that the parameter optimization can increase the power density of LETs to 2.7 times compared with the initial design [Zuo et al, Smart Materials and Structures, v19 n4, 2010], and the double-layer configuration with both radial and axial magnets can improve the power density to 4.7 times, approaching to the energy dissipation rate of traditional oil dampers. As a case study, we investigate its application to energy-harvesting shock absorbers. For a reasonable retrofit size, the LETs with double-layer configuration and both axial and radial NdFeB magnets can provide a damping coefficient of 1138 N·s/m while harvesting 35.5 W power on the external electric load at 0.25 m/s suspension velocity. If the LET is shorten circuit, it can dissipate energy at the rate of 142.0 W, providing of a damping coefficient of 2276 N·s/m. Practical consideration of number of coil phases is also discussed.

Analytical Solutions to H2 and H∞ Optimizations of Resonant Shunted Electromagnetic Tuned Mass Damper and Vibration Energy Harvester

When optimized, tuned mass dampers (TMDs) can effectively mitigate the vibration of the primary structure, because additional resonance and damping are introduced by the auxiliary mass-spring-damper system. Similar effect can be realized without auxiliary mass when an electromagnetic transducer shunt with the R-L-C resonant circuit is placed between the primary structure and the base. This paper is to analytically optimize the parameters of the R-L-C circuits for vibration mitigation. Both H2 and H∞ optimization criteria are investigated, which are to minimize the root-mean-square (RMS) vibration under random excitation and the peak magnitude in the frequency domain, respectively. The concise closed-form solutions of the optimal parameters are then summarized together with the ones obtained the using fixed-point method, for practical implementation convenience. The H2 and H∞ optimizations of energy harvesting are also discussed in this paper. Furthermore, we also investigate the sensitivity of system performances to the tuning parameter changes of the electromagnetic shunt circuit.

Circuit Optimization and Vibration Analysis of Electromagnetic Energy Harvesting Systems

In this paper we investigate an electrical circuit and its optimization for vibration energy harvesting using electromagnetic transducer. A step-up DC-DC converter regulated by Pulse-Width Modulation (PWM) is used to boost the voltage and control the power flow. An analytical expression for the optimal power flow from the rectified electromagnetic harvester is derived as a function of PWM duty cycle, vibration amplitude and frequency. Optimal duty cycles for both continuous and discontinuous modes are obtained analytically. The impedance of electromagnetic transducer and forward voltage drop of the diodes have been taken into account. It is also interesting to note that if a large inductor is adopted between the rectifier and step-up DC-DC converter, the energy harvesting system will exactly have the effect of Coulomb friction damper.Copyright