Vibration-driven Energy Harvester Research Articles

Frequency tuning design for vibration‐driven electromagnetic energy harvester

The common resonant-based vibration energy harvester effectively converts mechanical vibration to electrical power when an ambient excitation frequency matches the specific resonant frequency of the device. The resonant frequencies of energy harvesters are generally fixed during the design process and cannot be changed after fabrication. Therefore frequency tuning technology that allows for operation in a wide frequency range is desirable for a vibration energy harvester. In this study, the authors proposed a novel frequency tuning design of vibration-driven energy harvester, which used electromagnetic conversion. The proposed frequency tuning method uses a rotatable spring in order to adjust the spring constant. Through this tuning method, the resonant frequency of the harvester can be manipulated simply by rotating the spring. The proposed tuning-based energy harvester has been successfully tuned to have a resonant frequency from 23 to 32 Hz. These test results agree with the ANSYS analysis presented. The experimental results demonstrated that the proposed energy harvester can generate a maximum power output of 60 μW with an acceleration of 0.5 g (1 g = 9.81 m/s2). When the proposed harvester was attached to an automobile engine, a maximum open-circuit voltage of 1.78 Vpp was produced at 700 RPM.

Electromagnetic Energy Harvester With Flexible Coils and Magnetic Spring for 1–10 Hz Resonance

This paper presents an energy harvester with microfabricated flexible coils (rolled and aligned to a magnet array for maximum magnetic flux change) and magnetic spring to generate electrical power from human body motion. The magnet array is suspended by a magnetic spring for a resonant frequency of several hertz. An analytical model of vibration-driven energy harvester with magnetic spring through magnet and coil arrays is developed to explore the power generation with various magnet ranges and vibration amplitudes. Experimental results show that the electromagnetic energy harvester with six 7-turn microfabricated coils (occupying 3.8 cc and weighing 8.5 gram) generates an induced electromotive force (EMF) of $\mathrm{V}_{\mathrm {rms}} =6.7$ mV with 0.53- $\mu $ W power output (into 21- $\Omega $ load) from 0.27-g acceleration at 8 Hz (corresponding to 1.05-mm vibration amplitude). Its larger-scale version with sixteen 200-turn wire-wound coils (occupying 26 cc and weighing 98 gram) generates an EMF of $\mathrm{V}_{\mathrm {rms}} =1.3$ V with 4.3-mW power output (into 100- $\Omega $ load) from 0.5-g acceleration at 5.5 Hz (corresponding to 4.1-mm vibration amplitude). When the larger-scale version of the energy harvester is placed in a backpack of a human walking at various speeds, the power output is increased as the walking speed is increased from 0.45 m/s (slow walking) to 2.68 m/s (slow running), and reaches 14.8 mW at 2.68 m/s. [2014-0323]

Power generation from human body motion through magnet and coil arrays with magnetic spring

This article presents a hand-held electromagnetic energy harvester which can be used to harvest tens of mW power level from human body motion. A magnet array, aligned to a coil array for maximum magnetic flux change, is suspended by a magnetic spring for a resonant frequency of several Hz and is stabilized horizontally by graphite sheets for reducing the friction. An analytical model of vibration-driven energy harvester with magnetic spring through magnet and coil arrays is developed to explore the power generation from vibrations at low frequency and large amplitude. When the energy harvester (occupying 120 cc and weighing 180 g) is placed in a backpack of a human walking at various speeds, the power output increases as the walking speed increases from 0.45 m/s (slow walking) to 3.58 m/s (slow running), and reaches 32 mW at 3.58 m/s.

6PM3-PMN-008 窒化アルミ圧電薄膜を用いた振動発電デバイスにおいて振動方向が発電量に与える影響の調査研究(OS4 電池レス・デバイスのためのエネルギーハーベストの展開,ポスターセッション)

6PM3-PMN-008 窒化アルミ圧電薄膜を用いた振動発電デバイスにおいて振動方向が発電量に与える影響の調査研究(OS4 電池レス・デバイスのためのエネルギーハーベストの展開,ポスターセッション)

Power Processing Circuits for Piezoelectric Vibration-Based Energy Harvesters

The behavior of a piezoelectric vibration-driven energy harvester with different power processing circuits is evaluated. Two load types are considered: a resistive load and an ac-dc rectifier load. An optimal resistive and optimal dc-voltage load for the harvester is analytically calculated. The difference between the optimal output power flow from the harvester to both load circuits depends on the coupling coefficient of the harvester. Two power processing circuits are designed and built, the first emulating a resistive input impedance and the second with a constant input voltage. It is shown that, in order to design an optimal harvesting system, the combination of both the ability of the circuit to harvest the optimal harvester power and the processing circuit efficiency needs to be considered and optimized. Simulations and experimental validation using a custom-made piezoelectric harvester show that the efficiency of the overall system is 64% with a buck converter as a power processing circuit, whereas an efficiency of only 40% is reached using a resistor-emulating approach.