A broadband vibration energy harvester using double transducers and pendulum-type structures

Abstract

As cantilever-based vibration energy harvesters are easily fractured under large amplitude vibration excitation, in this paper we present a vibration energy harvester based on a pendulum-type structure with broadband and frequency-doubling characteristics. The harvester consists of two Terfenol-D/PMN-PT/Terfenol-D magnetoelectric transducers and a rotary pendulum embedded with six magnets. These six magnets are arranged into an optimum configuration and can produce a concentrated flux gradient which makes the magnetoelectric transducers generate a high power. While the two transducers are used to further improve the output power and power density of the harvester without increasing the volume of the harvester. The rotary pendulum of the harvester changes linear vibration into a back-and-forth swing of the rotary pendulum. When the rotary pendulum swings, the stress is hardly generated in the interior of the rotary pendulum. Therefore the rotary pendulum is not easily fractured under the large amplitude vibration. Therefore the proposed pendulum-based vibration energy harvester is suitable for scavenging the large amplitude ambient vibration energy. The swing equation of the rotary pendulum is established. The nonlinear dynamic equation of the rotary pendulum is solved by the Lindstedt-Poincar method. The frequency response characteristic and the mechano-magneto-electric transduction characteristic of the harvester at resonance are analyzed by combining the swing equation of the harvester with the magnetoelectric characteristics of the magnetoelectric transducers. The spectrum of the output voltage waveform of the harvester is discussed. The analytical and experimental results indicate that the harvester has broadband and frequency-doubling characteristics. The broadband characteristic of the harvester is derived from the nonlinear magnetic force between the magnets and magnetoelectric transducers. The voltage frequency-doubling characteristic is derived from the nonlinearity of the magnetic field produced by the magnets. It does not need frequency conversion mechanism for the proposed harvester, so the proposed harvester has some advantages, such as simple structure and easy manufacture. Under 1 g (1 g = 9.8 m/s2) RMS vibration acceleration excitation, the measured maximum RSM voltage and the resonant frequency of the prototype are 90.9 V and 16.9 Hz, respectively. The 3 dB bandwidth for the sweep-down condition is 4.8 Hz from 16.9 Hz to 21.7 Hz and that for the sweep-up condition is 2.1 Hz from 22.8 Hz to 24.9 Hz. Compared with other harvesters, the proposed harvester has a wide relative bandwidth. The load output power of the prototype reaches 3.569 mW across a 1.9 M optimal resistor at resonant frequency of 16.9 Hz with 1 g RMS vibration acceleration. The output RMS powers of the prototype across 1.9 M resistor are 0.156 mW, 0.6863 mW, 1.777 mW at 0.3 g, 0.5 g and 0.7 g with resonance, respectively. The proposed harvester can effectively improve the output powers at lower frequency vibrations for its two transducers, broadband and frequency-doubling characteristics.