Energy harvesting generators are attractive as inexhaustible replacements for batteries in low-power wireless electronic devices and have received increasing research interest in recent years. Ambient motion is one of the main sources of energy for harvesting, and a wide range of motion-powered energy harvesters have been proposed or demonstrated, particularly at the microscale. This paper reviews the principles and state-of-art in motion-driven miniature energy harvesters and discusses trends, suitable applications, and possible future developments.

/pdf/energy-harvesting-from-human-and-machine-motion-for-wireless-3lsf4oudvo.pdf

Energy Harvesting From Human and Machine Motion for Wireless Electronic Devices

Ambient energy harvesting has been in recent years the recurring object of a number of research efforts aimed at providing an autonomous solution to the powering of small-scale electronic mobile devices. Among the different solutions, vibration energy harvesting has played a major role due to the almost universal presence of mechanical vibrations. Here we propose a new method based on the exploitation of the dynamical features of stochastic nonlinear oscillators. Such a method is shown to outperform standard linear oscillators and to overcome some of the most severe limitations of present approaches. We demonstrate the superior performances of this method by applying it to piezoelectric energy harvesting from ambient vibration.

/pdf/nonlinear-energy-harvesting-1c9nlmso3f.pdf

Nonlinear energy harvesting.

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

The last two decades have witnessed several advances in microfabrication technologies and electronics, leading to the development of small, low-power devices for wireless sensing, data transmission, actuation, and medical implants. Unfortunately, the actual implementation of such devices in their respective environment has been hindered by the lack of scalable energy sources that are necessary to power and maintain them. Batteries, which remain the most commonly used power sources, have not kept pace with the demands of these devices, especially in terms of energy density. In light of this challenge, the concept of vibratory energy harvesting has flourished in recent years as a possible alternative to provide a continuous power supply. While linear vibratory energy harvesters have received the majority of the literature’s attention, a significant body of the current research activity is focused on the concept of purposeful inclusion of nonlinearities for broadband transduction. When compared to their linear resonant counterparts, nonlinear energy harvesters have a wider steady-state frequency bandwidth, leading to a common belief that they can be utilized to improve performance in ambient environments. Through a review of the open literature, this paper highlights the role of nonlinearities in the transduction of energy harvesters under different types of excitations and investigates the conditions, in terms of excitation nature and potential shape, under which such nonlinearities can be beneficial for energy harvesting. [DOI: 10.1115/1.4026278]

On the Role of Nonlinearities in Vibratory Energy Harvesting: A Critical Review and Discussion

The dramatic reduction in power consumption of current integrated circuits has evoked great research interests in harvesting ambient energy, such as vibrations, as a potential power supply for electronic devices to avoid battery replacement. Currently, most vibration-based energy harvesters are designed as linear resonators to achieve optimal performance by matching their resonance frequencies with the ambient excitation frequencies a priori. However, a slight shift of the excitation frequency will cause a dramatic reduction in performance. Unfortunately, in the vast majority of practical cases, the ambient vibrations are frequency-varying or totally random with energy distributed over a wide frequency spectrum. Hence, developing techniques to increase the bandwidth of vibration-based energy harvesters has become the next important problem in energy harvesting. This article reviews the advances made in the past few years on this issue. The broadband vibration-based energy harvesting solutions, covering re...

/pdf/toward-broadband-vibration-based-energy-harvesting-555rshl9tt.pdf

Toward Broadband Vibration-based Energy Harvesting

Vibration energy harvesting is an attractive technique for potential powering of wireless sensors and low power devices. While the technique can be employed to harvest energy from vibrations and vibrating structures, a general requirement independent of the energy transfer mechanism is that the vibration energy harvesting device operate in resonance at the excitation frequency. Most energy harvesting devices developed to date are single resonance frequency based, and while recent efforts have been made to broaden the frequency range of energy harvesting devices, what is lacking is a robust tunable energy harvesting technique. In this paper, the design and testing of a resonance frequency tunable energy harvesting device using a magnetic force technique is presented. This technique enabled resonance tuning to ±20% of the untuned resonant frequency. In particular, this magnetic-based approach enables either an increase or decrease in the tuned resonant frequency. A piezoelectric cantilever beam with a natural frequency of 26 Hz is used as the energy harvesting cantilever, which is successfully tuned over a frequency range of 22‐32 Hz to enable a continuous power output 240‐280 μW over the entire frequency range tested. A theoretical model using variable damping is presented, whose results agree closely with the experimental results. The magnetic force applied for resonance frequency tuning and its effect on damping and load resistance have been experimentally determined. (Some figures in this article are in colour only in the electronic version)

/pdf/a-vibration-energy-harvesting-device-with-bidirectional-6ns3qqmtim.pdf

A vibration energy harvesting device with bidirectional resonance frequency tunability

Vibration energy harvesting is being pursued as a means to power wireless sensors and ultra-low power autonomous devices. From a design standpoint, matching the electrical damping induced by the energy harvesting mechanism to the mechanical damping in the system is necessary for maximum efficiency. In this work two independent energy harvesting techniques are coupled to provide higher electrical damping within the system. Here the coupled energy harvesting device consists of a primary piezoelectric energy harvesting device to which an electromagnetic component is added to better match the total electrical damping to the mechanical damping in the system. The first coupled device has a resonance frequency of 21.6 Hz and generates a peak power output of ~332 µW, compared to 257 and 244 µW obtained from the optimized, stand-alone piezoelectric and electromagnetic energy harvesting devices, respectively, resulting in a 30% increase in power output. A theoretical model has been developed which closely agrees with the experimental results. A second coupled device, which utilizes the d33 piezoelectric mode, shows a 65% increase in power output in comparison to the corresponding stand-alone, single harvesting mode devices. This work illustrates the design considerations and limitations that one must consider to enhance device performance through the coupling of multiple harvesting mechanisms within a single energy harvesting device.

/pdf/a-coupled-piezoelectric-electromagnetic-energy-harvesting-4g1984d6oc.pdf

A coupled piezoelectric-electromagnetic energy harvesting technique for achieving increased power output through damping matching

Future deployment of wireless sensor networks will ultimately require a self-sustainable local power source for each sensor, and vibration energy harvesting is a promising approach for such applications. A requirement for efficient vibration energy harvesting is to match the device and source frequencies. While techniques to tune the resonance frequency of an energy harvesting device have recently been described, in many applications optimization of such systems will require the energy harvesting device to be able to autonomously tune its resonance frequency. In this work a vibration energy harvesting device with autonomous resonance frequency tunability utilizing a magnetic stiffness technique is presented. Here a piezoelectric cantilever beam array is employed with magnets attached to the free ends of cantilever beams to enable magnetic force resonance frequency tuning. The device is successfully tuned from �27% to +22% of its untuned resonance frequency while outputting a peak power of approximately 1 mW. Since the magnetic force tuning technique is semi-active, energy is only consumed during the tuning process. The developed prototype consumed maximum energies of 3.3 and 3.9 J to tune to the farthest source frequencies with respect to the untuned resonance frequency of the device. The time necessary for this prototype device to harvest the energy expended during its most energy-intensive (largest resonant frequency adjustment) tuning operation is 88 min in a low amplitude 0.1g vibration environment, which could be further optimized using higher efficiency piezoelectric materials and system components. (Some figures in this article are in colour only in the electronic version)

/pdf/towards-an-autonomous-self-tuning-vibration-energy-2600lu6175.pdf

Towards an autonomous self-tuning vibration energy harvesting device for wireless sensor network applications

A near-field, electrodynamically coupled wireless power transmission system is presented that delivers electrical power from a transmitter coil to a compact electromechanical receiver. The system integrates electromechanical energy conversion and mechanical resonance to deliver power over a range of distances using low-amplitude, low-frequency magnetic fields. Two different receiver orientations are investigated that rely on either the force or the torque induced on the receiver magnet at separation distances ranging from 2.2 to 10.2?cm. Theoretical models for each mode compare the predicted performance with the experimental results. For a 7.1?mApk sinusoidal current supplied to a transmitter coil with a 100?cm diameter, the torque mode receiver orientation has a maximum power transfer of 150??W (efficiency of 12%) at 2.2 cm at its resonance frequency of 38.4?Hz. For the same input current to the transmitter, the force mode receiver orientation has a maximum power transfer of 37??W (efficiency of 4.1%) at 3.1?cm at its resonance frequency of 38.9?Hz.

https://iopscience.iop.org/article/10.1088/0964-1726/21/11/115017/pdf

Wireless power transmission to an electromechanical receiver using low-frequency magnetic fields

We present a micro-fluidics actuated galvanic cell for on demand power generation. The galvanic cell is an aluminum anode/alkaline electrolyte/air cathode cell. The concept is based upon an actuation mechanism that pushes an electrolyte into a micro-channel containing electrodes. When the electrolyte reaches the electrodes of a galvanic cell, it produces energy through an electrochemical reaction. The proof of concept is presented herein by fabricating and characterizing a single cell using micro-fabrication techniques. The actuation mechanism is based on the thermal expansion of a working fluid. A brief discussion on the optimization of this actuation is also presented. The open voltage of this micro-cell was experimentally measured to be around 1.9 V. The Al/air galvanic cell chemistry has been compared with commercial Zn/air battery and has been found to perform better. The present micro-cell design (with an area of 0.75 cm 2 ), is capable of providing an energy of 5 J after 6.0 min when subjected to a load of 20 � . The actuation mechanism takes less than a minute and consumes about 3.5 J. © 2003 Elsevier B.V. All rights reserved.

Vinod R. Challa

Papers

A vibration energy harvesting device with bidirectional resonance frequency tunability

A coupled piezoelectric-electromagnetic energy harvesting technique for achieving increased power output through damping matching

Towards an autonomous self-tuning vibration energy harvesting device for wireless sensor network applications

Wireless power transmission to an electromechanical receiver using low-frequency magnetic fields

A micro-fluidic galvanic cell as an on-chip power source