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Research Papers

Increasing the Efficiency of Energy Scavengers by Magnets

[+] Author and Article Information
S. M. Shahruz1

 Berkeley Engineering Research Institute, P.O. Box 9984, Berkeley, CA 94709shahruz@cal.berkeley.edu

1

Corresponding author.

J. Comput. Nonlinear Dynam 3(4), 041001 (Aug 19, 2008) (12 pages) doi:10.1115/1.2960486 History: Received August 31, 2007; Revised February 08, 2008; Published August 19, 2008

In this paper, a methodology for designing efficient energy scavengers is proposed. The scavenger consists of a cantilever beam on which piezoelectric films and a mass are mounted. The mass at the tip of the beam is known as the proof mass and the device is called either an energy scavenger or a beam-mass system. The proof mass is a permanent magnet, where in its vicinity attracting permanent magnets are placed. When a scavenger is mounted on a vibration source, the cantilever beam would vibrate. Due to the vibration of the beam, the piezoelectric films generate electric charge. The generated charge is proportional to the amplitude of vibration of the tip of the beam. It is shown that when the magnets have appropriate strengths and are placed appropriately, the vibration of the tip of the beam can be amplified, thereby the scavenger efficiency is increased. Examples are given throughout the paper.

FIGURES IN THIS ARTICLE
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Copyright © 2008 by American Society of Mechanical Engineers
Topics: Magnets , Force , Vibration , Springs
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Figures

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Figure 1

A typical energy scavenger consists of a cantilever beam on which piezoelectric films and a mass, known as the proof mass, are mounted

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Figure 2

A schematic of a beam with a proof mass at its tip. The vibration source exerts the acceleration ü(⋅). The transversal displacement of the beam at an x∊[0,l] and a t⩾0 is denoted by y(x,t).

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Figure 3

A free magnet separated from a fixed attracting magnet by a glass plate of thickness γ. The free magnet moves toward the fixed one.

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Figure 4

(a) A cantilever beam with a magnetic proof mass. A collection of attracting magnets is placed in the vicinity of the beam-mass system. The magnets above and below the x-axis are the mirror image of each other geometrically and with respect to the strengths of the magnets; (b) The distances between the magnetic proof mass and the fixed magnets (lengths of the dashed lines) are determined using this figure.

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Figure 5

The graph of the nonlinear spring restoring force y↦Fd(y) in Eq. 16 in Example 3.1 and the graph of the linear spring force y↦ky with k=1

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Figure 6

Response of the linear beam-mass system (7), yl, and that of the nonlinear beam-mass system (13), y, in Example 3.1, respectively, in (a) and (b). The amplitude of y is four times larger than that of yl.

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Figure 7

Power spectral densities of yl and y in Example 3.1

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Figure 8

The graph of y↦Fs(y) in Eq. 14 constructed in Example 3.2 compared to that of y↦Fd(y) in Eq. 16

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Figure 9

The strengths and positions of the 24 magnets determined in Example 3.2

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Figure 10

(a) Response of system (13), y, in which the function y↦Fs(y) is that determined in Example 3.2 and (b) power spectral densities of yl and y

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Figure 11

The graphs of y↦Fd(y) and y↦Fs(y) in Example 3.4 and that of y↦ky with k=1

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Figure 12

(a) Response of system (13), y, in Example 3.5, where there are four magnets in the vicinity of the magnetic proof mass and (b) power spectral densities of yl and y

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Figure 13

The graph of y↦Fs(y) in Example 3.6 and that of y↦ky with k=1

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Figure 14

(a) Response of system (13), y, in Example 3.7, where there are two magnets in the vicinity of the magnetic proof mass and (b) power spectral densities of yl and y

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