Miah A. Halim

A non-resonant, frequency up-converted electromagnetic energy harvester from human-body-induced vibration for hand-held smart system applications

We present a non-resonant, frequency up-converted electromagnetic energy harvester that generates significant power from human-body-induced vibration, e.g., hand-shaking. Upon excitation, a freely movable non-magnetic ball within a cylinder periodically hits two magnets suspended on two helical compression springs located at either ends of the cylinder, allowing those to vibrate with higher frequencies. The device parameters have been designed based on the characteristics of human hand-shaking vibration. A prototype has been developed and tested both by vibration exciter (for non-resonance test) and by manual hand-shaking. The fabricated device generated 110 μW average power with 15.4 μW cm−3 average power density, while the energy harvester was mounted on a smart phone and was hand-shaken, indicating its ability in powering portable hand-held smart devices from low frequency (<5 Hz) vibrations.

Frequency up-converted wide bandwidth piezoelectric energy harvester using mechanical impact

This paper presents an impact based frequency up-converted wide bandwidth piezoelectric energy harvester in which two high frequency piezoelectric generating beams are struck at the same time by a low frequency driving beam having horizontally extended tip mass. Change of driving beams effective stiffness during coupled vibration after impact allows the device to broaden the −3dB bandwidth to approximately 170% and to acquire more than 61% of the maximum power generation in the vicinity (from 7 to 10.5 Hz) of the −3 dB bandwidth region as well. The efficiency of electrical power transfer is increased to approximately 85%. Each generating beam produces 377 μW peak power at 14.5 Hz under 0.6 g acceleration with corresponding power density 58.8 μW cm−3.

A magnetic-spring-based, low-frequency-vibration energy harvester comprising a dual Halbach array

Energy harvesting that uses low-frequency vibrations is attractive due to the availability of such vibrations throughout the ambient environment. Significant power generation at low-frequency vibrations, however, is challenging because the power flow decreases as the frequency decreases; moreover, designing a spring-mass system that is suitable for low-frequency-vibration energy harvesting is difficult. In this work, our proposed device overcomes both of these challenges by using a dual Halbach array and magnetic springs. Each Halbach array concentrates the magnetic-flux lines on one side of the array while suppressing the flux lines on the other side; therefore, a dual Halbach array allows for an interaction between the concentrated magnetic-flux lines and the same coil so that the maximum flux linkage occurs. During the experiment, vibration was applied in a horizontal direction to reduce the gravity effect on the Halbach-array structure. To achieve an increased power generation at low-amplitude and low-frequency vibrations, the magnetic structure of the dual Halbach array and the magnetic springs were optimized in terms of the operating frequency and the power density; subsequently, a prototype was fabricated and tested. The prototype device offers a normalized power density of 133.45 μW cm−3 g−2 that is much higher than those of recently reported electromagnetic energy harvesters; furthermore, it is capable of delivering a maximum average power of 1093 μW to a 44 Ω optimum load, at an 11 Hz resonant frequency and under a 0.5 g acceleration.

Low Frequency Vibration Energy Harvester Using Stopper-Engaged Dynamic Magnifier for Increased Power and Wide Bandwidth

We present a piezoelectric energy harvester with stopper-engaged dynamic magnifier which is capable of significantly increasing the operating bandwidth and the energy (power) harvested from a broad range of low frequency vibrations (<30 Hz). It uses a mass-loaded polymer beam (primary spring-mass system) that works as a dynamic magnifier for another mass-loaded piezoelectric beam (secondary spring-mass system) clamped on primary mass, constituting a two-degree-of-freedom (2-DOF) system. Use of polymer (polycarbonate) as the primary beam allows the harvester not only to respond to low frequency vibrations but also generates high impulsive force while the primary mass engages the base stopper. Upon excitation, the dynamic magnifier causes mechanical impact on the base stopper and transfers a secondary shock (in the form of impulsive force) to the energy harvesting element resulting in an increased strain in it and triggers nonlinear frequency up-conversion mechanism. Therefore, it generates almost four times larger average power and exhibits over 250% wider half-power bandwidth than those of its conventional 2-DOF counterpart (without stopper). Experimental results indicate that the proposed device is highly applicable to vibration energy harvesting in automobiles.

A frequency up-converted electromagnetic energy harvester using human hand-shaking

We present a frequency up-converted electromagnetic (EM) energy harvester that is capable of powering various portable devices and systems by hand-shaking. It consists of a freely movable ball to impact periodically (at low frequency) on the parabolic top surface of a mass of a cantilever beam allowing it to vibrate at higher (resonant) frequency. Relative motion between a magnet attached to the cantilever and a coil induces voltage. A prototype of the energy harvester has been fabricated and characterized by applying vibration from handshaking. The frequency and acceleration of the applied hand-shaking vibration has been experimentally found to be 4.6 Hz and 2g, respectively. With an optimum distance between magnet and coil, a maximum 672 mV peak-peak open circuit voltage of 370 Hz frequency and a maximum 413μW peak power delivered to an 85Ω matched load resistance have been obtained, respectively.

Performance enhancement of a low frequency vibration driven 2-DOF piezoelectric energy harvester by mechanical impact

We present a low frequency vibration driven 2-DOF piezoelectric energy harvester with increased performance, in terms of both bandwidth and output power, by mechanical impact. It consists of two series spring-mass systems (positioned in a parallel manner) one of which responds to low frequency vibration, engages with the harvester base stopper periodically by piecewise linear impact, and transfers a secondary shock to the second spring- mass system comprising of power generating element. It introduces a non-linear frequency up- conversion mechanism which, in turn, generates increased output power within a wide range of applied frequency. A 2-DOF prototype harvester without stopper shows two narrow resonant peaks and delivers maximum 2.11μW peak power to its matched load resistance at 17Hz frequency and 0.5g acceleration. On the other hand, it offers a -3dB bandwidth of 15Hz (9Hz- 24Hz) and delivers maximum 202.4μW peak power to its matched load resistance at the same operating condition when a stopper is placed below the primary mass at 0.5mm distance. Generated power increases up to 449μW as the acceleration increases to 1g.

Impact based frequency increased piezoelectric vibration energy harvester for human motion related environments

This paper presents a frequency increased piezoelectric vibration energy harvesting device where the low frequency periodic impact of a driving beam with a horizontally extended rectangular tip makes two piezoelectric generating beams to vibrate at the same time, with their higher resonant frequencies, producing higher power output. The dimension of the flexible driving beam was 58×4.8×1 mm3 and that of each piezoelectric generating beam with styrene support was 15×3.5×0.8 mm3. Each generating beam of the proposed energy harvester produced a maximum peak output power of 46.51 μW across an optimum resistive load of 200 KΩ under 4 ms-2 acceleration and was increased up to 129.15 μW while the acceleration was increased up to 6 ms-2 at an operating frequency of 12.5 Hz. The output of both generating beams with series connection doubled the overall output of the device.

Optimization of a human-limb driven, frequency up-converting electromagnetic energy harvester for power enhancement

We present an optimized electro-magnetic energy harvester (EMEH) that generates significant power from the motion of human limbs, to be used in hand-held and wearable smart device applications. The proposed EMEH is designed to up-convert the vibration of human limb-motion to high-frequency by mechanical impact of a freely movable ball on two optimized frequency up-converted generators. Each generator comprises a compact and reliable helical compression spring. The generators have been optimized through the design parameters such as frequency, spring stiffness, mechanical and electrical damping, to minimize the power loss. The device offers 333μWcm-3 average power density (a maximum 2.15mW of average power while two generators are connected in series) which is considerably higher than the current state-of-the-art devices.

A wrist-band coupled, human skin based triboelectric generator for harvesting biomechanical energy

Effectively harvesting ambient mechanical energy is very important for realizing self-powered and autonomous electronics, which has numerous applications in sensor networks, wireless devices, and wearable or implantable electronics, etc. This paper presented a human skin based triboelectric generator (TEG), coupled to a light and flexible wrist-band to be used for wearable smart device applications. We developed a simple, cost effective, and feasible fabrication method of a micro-structured Polydimethylsiloxane (PDMS) thin film as one of the triboelectric layers, the other layer being the human skin. Here, electricity was generated by repetitive contact-separation actions between these two triboelectric surfaces. Results showed the fabricated prototype is capable of generating a maximum open circuit voltage of 28.2V and 12μW peak power by mild finger pressing over the device at 2.9Hz frequency. The proposed harvester responds to low-frequency kinetic energy of human-body-induced motion; so it has the potential to convert the mechanical energy of finger pressing into electrical energy.

A PDMS based triboelectric energy harvester as self-powered, active tactile sensor system for human skin

In this paper, we present a Polydimethylsiloxane (PDMS) based triboelectric generator (TEG) that can either harvest biomechanical energy or be utilized as a self-powered tactile sensor system. We developed a novel and cost effective fabrication method of a micro-structured PDMS film by using sand paper template to be used in our proposed TEG. Here, triboelectricity is generated by a conjunction of triboelectric and electrostatic induction due to repetitive contact-separation actions between an area of human skin and PDMS layer. The working mechanism of the TEG is based on the charge transfer between the PDMS electrode and ground. The as-fabricated prototype generates a maximum open circuit voltage of 17.34 V and short-circuit current of 187 nA by mild finger pressing on the device and thus demonstrates its self-powered tactile sensing capabilities by recording the output voltage signals.