•This paper presents a multi-modal energy harvester to extract vibration energy from five frequency bands.•The spiral-shaped configuration is shown to be beneficial to narrowing the band spacings.•The frequency spacings can be further reduced under the magnetic coupling.Most vibration energy harvesters use conventional cantilever configuration and typically perform well for a specific frequency at the first resonant mode, this makes the devices less effective in ambient vibrations with varying frequencies. This paper presents a multi-modal vibration energy harvester achieving multiple peaks in the frequency response and causing the possibility of widening the operation frequency range. A spiral-shaped cantilever with tip mass in the form of magnets coupling with a magnetoelectric (ME) transducer is adopted in this harvester. The spiral-shaped beam is shown to be conductive to presenting multi-modal responses and lowering the natural frequencies of the harvester. Furthermore, due to the magnetic coupling between the magnets and the transducer, the peak frequencies are tunable and the frequency spacing between the adjacent modes can be obviously reduced. The operating principle of energy conversion is based on the relative movement of the magnets and the transducer, and the effects of magnetic coupling working on the peak frequencies are experimentally determined. The experimental results indicate that the proposed harvester can obtain five obvious peak values in the range of 15–70 Hz, which are concentrated around 20.7, 26.1, 32.3, 42.2 and 63.7 Hz, respectively.

This paper presents a passive self-tuning energy harvester based on magnetoelectric (ME) transducer for potential powering the wireless sensors in rotational applications. The harvester has two cylindrical magnets arranged on the free end of a cantilever beam, and two hollow magnets with ME transducers inside their cavities are located symmetrically beside the beam and enfaced with the cylindrical magnets. With the beam radial-oriented, the harvester rotates around a horizontal axis, and the alternation of the gravity component causes the magnets on beam to move relative to the transducers, which induces the electrical power generation. Due to the axial tensile stress caused by the centrifugal force, the resonant frequency is tuned to track the rotation frequency over a wide frequency range, which enables the harvester a broad working bandwidth. Furthermore, the attractive magnetic forces between the magnets lower the initial resonant frequency of the beam and enlarge the vibration amplitude. Consequently, the electrical output performances over the target frequency range (below 20 Hz) are improved. A prototype is fabricated and tested. The experimental results are in agreement with the theoretical predictions. The prototype generates a maximum power of 517 μW at a rotation frequency of 9.8 Hz, corresponding to a half-power bandwidth of 13.5 Hz.Highlights► The resonant frequency of the energy harvester is self-tuned to track and match the rotation frequency over a wide frequency range. ► A magnetic force technique is employed to lower the initial resonant frequency of the cantilever beam and enlarge the vibration amplitude. ► The ME transducers are optimally biased by employing an inverse pre-bias magnetic field. ► The maximum output power on load achieves 517 μW at a rotation frequency of 9.8 Hz, and the corresponding half-power bandwidth achieves 13.5 Hz.

This paper presents an energy harvester employing a cantilever beam and a magnetostrictive/piezoelectric (ME) laminate transducer to transform rotation energy into electrical energy. The harvester has a magnetic circuit attached to the free end of the beam, and the ME transducer is placed in the air gap of the magnetic circuit. When the harvester is attached to a host structure rotating around a horizon axis, the alternation of the gravity component causes the beam to vibrate along its transverse direction. The vibration induces an alternating magnetic field applied on the transducer, which causes the ME transducer to generate electrical power. Based on Hamilton principle and the assumed mode method, the dynamic equation is derived to study the influences of the nonlinear dynamic behavior of the harvester on the energy harvesting. A prototype is fabricated and tested. The experimental results are in agreement with the analytical results. The maximum voltage is achieved at the second-order super-harmonic resonance rather than the main resonance, when the rotation rate is 588 rpm, and a power of 157.4 μW is obtained across a 3.3 MΩ resistor.

This paper describes an energy harvester employing multiple Terfenol-D/Pb(Mg1/3Nb2/3)O3–PbTiO3/Terfenol-D laminate magnetoelectric transducers to convert ambient mechanical vibration into electrical energy. The harvester uses four magnets arranged on the free end of a cantilever beam. The multiple transducers are placed in the air gap between the magnets. The optimal initial positions of the transducers at the static equilibrium are analyzed. And the output characteristics of the harvester employing various numbers of transducers are experimentally studied. Experimental results indicate that the harvester employing multiple transducers can provide higher power and power density. The harvester employing four transducers produces a maximum output power of 7.13 mW, which is 3.95 times higher than that of the harvester employing a single transducer, and the harvester employing two transducers produces a maximum output power of 4.07 mW, which is 1.83 times higher than that of the harvester employing a single transducer.

Vibration energy harvesting has been receiving a considerable amount of interest as a means of powering wireless sensors and low-power devices. In this paper, an energy harvester is presented to convert ambient mechanical vibration into electrical energy employing the Terfenol-D/PZT/Terfenol-D laminate magnetoelectric (ME) transducer. The harvester uses four magnets arranged on the free end of a cantilever beam. The magnets produce a concentrated flux gradient in the air gap, and the ME transducer is placed in the air gap between the magnets. When the harvester is excited, the magnetic circuit moves relative to the ME transducer. The ME transducer undergoes magnetic field variations and produces a power output. An analytical model is developed to analyze the nonlinear vibration and electrical-output performances of the harvester. A prototype is fabricated and tested. The experimental results are in agreement with the analytical results. The prototype produces a power of 2.11 mW for an acceleration of 1 g at resonant frequency of 51 Hz.