Efficient acoustic energy harvesting by deploying magnetic restoring force

Abstract

Acoustic piezoelectric energy harvesters in quarter-wavelength resonator tubes undergo linear resonant vibration due to the external force. However, the variation of environmental conditions, such as temperature, directly alters the speed of sound in air, which in turn changes the tube resonance frequencies. This discrepancy between the tube acoustic and harvester resonance frequencies leads to reduced power generation. This paper proposes the addition of a nonlinear restoring force onto an acoustic cantilever beam piezoelectric energy harvester to tune and broaden the resonance bandwidth. The restoring force is applied by the attachment of permanent magnets at the beam tip and two external magnets. First, the nonlinear distributed parameter model of the bimorph is provided. Then, the associated dimensionless lumped-parameter model, including the magnetically coupled equations, is developed. To study the system response, an approximate-analytical solution based on the harmonic balance method is constructed. Initially, the variations of the speed of sound, and subsequently the tube resonance frequency, versus temperature, based on real statistical data, are studied. Furthermore, the effects of two scenarios of hardening and softening magnetic restoring forces are investigated. The results show that, at relatively low sound pressure levels (SPLs), the restoring forces can improve the efficiency by tuning the resonance frequency of the energy harvester. As the SPL increases, the force of the additional magnets tunes the natural frequency and broadens the resonance region. Finally, it is observed that the added magnets can change the optimum time constant ratio.

Energy Harvesting Technologies for Structural Health Monitoring of Airplane Components—A Review

“…When a nonlinear restoring force is introduced into such a system via permanent magnets ( Figure 37 -cf. also the above Section 2.2.1 ), it is possible to tune the resonance of the bimorph PEH device to that of the cavity, despite its changes induced by temperature variations, thus optimising the performances of the device [ 207 ].…”

“…When a nonlinear restoring force is introduced into such a system via permanent magnets (Figure 37-cf. also the above Section 2.2.1), it is possible to tune the resonance of the bimorph PEH device to that of the cavity, despite its changes induced by temperature variations, thus optimising the performances of the device [207]. In any case, although conceptually interesting, AEHS are still generally at the proof-of-concept technology level and allow attaining very small power output densities, so that their actual applications for the herein considered autonomous SHM systems in airplanes are yet to be developed.…”

Recent acoustic energy harvesting methods and mechanisms: A review

“…23 And the common example of a noisy site is manufacturing industries; hence, the assessment of manufacturing industrial noise has been done. 24 Here, the investigation of noise level has been already estimated, and only the harvesting system needs to be incorporated and analysed with respect to noise levels. Hence, as shown in Figure 1, there are different applications of the AEH system to utilise the noise such as that from industries, traffic, runways, launching sites, train stations and the engine testing sites.…”

Energy harvesting from the secondary resonances of a nonlinear piezoelectric beam under hard harmonic excitation

“…Accordingly, electrical energy can be harvested through vibrations [2][3][4], flow-induced instabilities [5][6][7][8][9], combined loadings [10], and so on. The wasted energy can be converted to electrical form with the aid of electrostatic [11,12], electromagnetic [13][14][15][16], and piezoelectric [17][18][19] transducers. Although each of these mechanisms has their own benefits and inevitable drawbacks, piezoelectricity is pursued increasingly owing to the possibility of downsizing devices and operation over a wide range of frequencies.…”