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Research Papers

Frequency Tuning of a Nonlinear Electromagnetic Energy Harvester

[+] Author and Article Information
Longhan Xie

School of Mechanical and
Automotive Engineering,
South China University of Technology,
Guangzhou 510640, China

Ruxu Du

Institute of Precision Engineering,
Chinese University of Hong Kong,
Hong Kong, China

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received May 4, 2013; final manuscript received August 4, 2013; published online October 23, 2013. Assoc. Editor: Brian P. Mann.

J. Vib. Acoust 136(1), 011010 (Oct 23, 2013) (7 pages) Paper No: VIB-13-1147; doi: 10.1115/1.4025445 History: Received May 04, 2013; Revised August 04, 2013

This paper investigates a frequency-tunable nonlinear electromagnetic energy harvester. The electromagnetic harvester mainly consists of permanent magnets supported on the base to provide a magnetic field, and electrical coils suspended by four even-distributed elastic strings to be an oscillating object. When the base provides external excitation, the electrical coils oscillate in the magnetic field to produce electricity. The stretch length of the elastic strings can be tuned to change their stretch ratio by tuning adjustable screws, which can result in a shift of natural frequency of the harvester system. The transverse force of the elastic strings has nonlinear behavior, which broadens the system's frequency response to improve the performance of the energy harvester. Both simulation and experiment show that the above-discussed electromagnetic energy harvester has nonlinear behavior and frequency-tunable ability, which can be used to improve the effectiveness of energy harvesting.

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Figures

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Fig. 1

Schematic of a tunable electromagnetic energy harvester

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Fig. 2

Equivalent mechanical model of an electromagnetic harvester

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Fig. 5

The change in frequency of vibration as a function of the stretch ratio of the elastic string, where the initial conditions of the system are set to u(0) = u0 = 0.3 l0 and u·(0) = u·0 = 0. The curve marked with triangle is drawn according to Eq. (15), and that marked with circle is drawn by Ω1 = γ1.

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Fig. 3

The schematic model of elastic strings and mass

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Fig. 6

Frequency-response curves with constant ξ = 0.1 and various levels of excitation, where solid line is stable region and dashed line unstable region, and the dashed-dotted line shows the boundary of the unstable region

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Fig. 7

Frequency-response curves with constant f = 1 and various levels of damping, where solid line is stable region and dashed line unstable region

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Fig. 8

Relative velocity response of the oscillator with respect to excitation frequency with different levels of damping under excitation amplitude F = 3 m/s2

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Fig. 9

Relative velocity response of the oscillator in terms of different stretch length of elastic strings with the same initial length l0 = 100 mm, where solid line is stable region and dashed line unstable region

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Fig. 10

The relative velocity response for different initial stretch length of elastic strings with the same stretch ratio in linear and nonlinear system

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Fig. 11

Relative velocity response of linear and nonlinear systems in terms of different excitation amplitudes

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Fig. 12

The experimental prototype

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Fig. 13

Experimental setup

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Fig. 14

The measured average power output (circles) compared with theoretical prediction (solid line) under external excitation F = 5 m/s2. Graph (a) shows the results for stretch ratio l˜ = 0.85, and Graph (b) for l˜ = 0.96.

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Fig. 4

The nondimensional force-deflection characteristic given by Eq. (6) (solid line), and its approximation by Eq. (8) (dashed line), for the stretch ratio l˜ = l0/l = 0.9, where the error of points marked by triangle is greater than 5%

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