at

210

Sound pressureElectric output powerEnergy conversion efciency

menair

opedt. Wate

ity but also between open circuit voltage and airow velocity. A power of above 85 mW is released on a

t trendasinglcompalicatio

transducers.Many scholars have studied uid energy harvesting devices

from the motion of uid theoretically and experimentally. Allenand Smits placed a piezoelectric membrane or eel in the wakeof a bluff body and used the von Karman vortex street formingbehind the bluff body to induce oscillations in the membrane to

ung and Matveevtex inducergy was pment. Wan

and H-H Ko have developed a new piezoelectric and electnetic energy harvester for harnessing energy from ow-invibration [68]. It converts uid energy into electric energy by pie-zoelectric conversion with oscillation of a piezoelectric lm. Dam-ing and Ya have developed a mean ow acoustic engine (MFAE)based on the mean ow induced acoustic oscillation effect [9,10].It converts wind energy and uid energy in pipeline into acousticenergy which can be used to drive generators without anymechanical moving parts. Corresponding author. Tel.: +86 13515104865.

E-mail address: zhj88000@163.com (H. Zou).

Mechatronics 26 (2015) 2935

Contents lists availab

tr

evienergy generated aerodynamically can be harnessed and convertedinto electricity for powering sensors or other devices, thuseliminating the need for their battery replacement. The conversionof acoustic energy to electric power takes place in piezoelectric

by wind-induced uttering motion. Hernandez, Jhave studied acoustic energy harvesting from vorsound in a bafed pipe [5]. Generated sound eneconverted into electrical energy by a piezo elehttp://dx.doi.org/10.1016/j.mechatronics.2015.01.0020957-4158/ 2015 Elsevier Ltd. All rights reserved.d tonalartiallyg D-A

romag-ducedsystem (or microelectronics system) also need the power ofself-sustaining supply or supplying other energy sources. Inaddition, the incoming airow during the ight is a kind of meanow with remarkable kinetic energy. Based on aero-acousticprinciple, the incoming airow can be used to induce an acousticeld with steady frequency and high power density. The acoustic

man Street around a micro-prism in the laminar ow regime forenergy harvesting [3]. They presented design guidelines for theirenergy harvesting devices. Shuguang, Jianping and Lipson havestudied ambient wind energy harvesting by using cross-ow ut-tering [4]. They proposed and tested a bio-inspired piezo-leafarchitecture which converts wind energy into electrical energy1. Introduction

As the miniaturized developmenand intelligence degree become increpowers with good electromagneticneeded. All kinds of complicated apppassive electric load of 3 kX by using a single piezoelectric element of 10 mm diameter at relative airowvelocity of 159 m/s. And the maximum total energy conversion efciency of the piezoelectric energy har-vester is about 1.2. It has laid a solid foundation for powering sensors or other devices, thus eliminatinga need for batteries.

2015 Elsevier Ltd. All rights reserved.

of aircrafts, electricaly higher, small physicaltibility are desperatelyn systems of electronic

generate electricity [1]. Taylor et al. developed an eel structure ofpiezoelectric polymer to convert mechanical ow energy to electricpower [2]. They have focused on characterization and optimizationof the individual subsystems of the eel system with a generationand storage units in a wave tank. Sanchez-Sanz et al. accessedthe feasibility of using the unsteady forces generated by the Kar-Keywords:Piezoelectric energy harvesting

corresponding to the rst resonator acoustic mode, is a regular sinusoidal pattern. Within the study rangeof airow velocity, a linear relationship can be found not only between sound pressure and airow veloc-Piezoelectric energy harvesting from vibrsystem

Huajie Zou , Hejuan Chen, Xiaoguang ZhuSchool of Mechanical Engineering, Nanjing University of Science & Technology, Nanjing

a r t i c l e i n f o

Article history:Received 23 September 2014Accepted 11 January 2015Available online 2 February 2015

a b s t r a c t

Inspired by musical instrumodes when subjected tosystem of aircrafts is develtransducer during the ighenergy harvester are fabric

Mecha

journal homepage: www.elsions induced by jet-resonator

094, Jiangsu, China

ts that create high amplitude tones corresponding to resonator acousticow, a new piezoelectric energy harvester for powering the electronic. It converts the incoming airow energy into electricity via a piezoelectricith the airow simulated by an air cylinder, prototypes of the developed

d and tested. Experimental results show that the curve of sound pressure,

le at ScienceDirect

onics

er .com/ locate/mechatronics

In this paper, a new piezoelectric energy harvester based onaero-acoustic principle and piezoelectric transducer mechanismis developed, which can convert the incoming airow energy intoelectricity during the ight [11,12]. It is motivated by the phenom-enon occurring in many practical musical instruments such asutes, organs, and whistles [13]. When a jet is coupled with a res-onator, it can lead to excitation of high amplitude tones corre-sponding to resonator acoustic modes. The cross section view ofthe piezoelectric energy harvester is shown in Fig. 1. As shown,the piezoelectric energy harvester mainly consists of an annular

This paper focuses on the investigation of energy extraction

The bending moments per unit length can be written byintegrating stress over the dimension z of the layers. From (6)and (7), we get:

Mr R hmhp0 Tr zdz

T1@2uz@r2 rmr @uz@r T2@2uz@r2

rpr

@uz@r T3Dz

8

Mh Z hmhp0

Th zdz ! !

30 H. Zou et al. /Mechatronifrom the developed piezoelectric energy harvester. The experimen-tal setup used to measure the sound pressure at the closed end ofthe resonator, open circuit output voltage, output power andenergy conversion efciency of the piezoelectric energy harvesteris reported. The results can provide reference for future studies.

2. A model of mechanical and electrical conversion

The model of piezoelectric transducer, shown schematically inFig. 2, is fabricated from a brass disk bonded with one PZT-5H disk.The piezoelectric ceramic disk, poled along the z-direction, has aradius of rp, a thickness of hp. The brass disk has a radius of rm, athickness of hm. The diameter of piezoelectric ceramic disk andbrass disk are much larger than their thickness. The piezoelectrictransducer is simply supported at r = rm by a xture, which vibratesalong the z-direction harmonically driven by sound pressure p at agiven frequency x. If the device is vibrated harmonically, there isharmonic output voltage across the two electrodes, which is placedupon the upper and lower surfaces of the transducer.

Considering the axially symmetric exural motions of the trans-ducer in the z-direction, and the deection is much smaller thanthe thickness of the transducer. Consequently, the strain compo-nents can be expressed in terms of deection uz as follows:nozzle, which is comprised of the inlet and clog, an open-closedresonator and a piezoelectric transducer. During ight, when therelatively incoming airow is guided into the inlet, annular jetstream is formed by the annular nozzle. The annular jet streamissuing from the orice impinges on the leading edge of the reso-nator, and then produces a dipole sound source known as edgetone. The sound travels inside the resonator and reects at theclosed end, which nally leads to the formation of a stable standingwave resonance inside the resonator. And the maximum soundpressure is produced at the closed end of the resonator. As a resultof the resonator feedback system, the vocal efciency can begreatly improved. And it can produce stable sound mainly deter-mined by the resonator. When the aforementioned sound pressureis applied to the surface of piezoelectric transducer installed at theclosed end of resonator, the piezoelectric transducer can be driveninto vibration. Strain can be produced in piezoelectric material. Bynormal strain, charges are accumulated on both sides of piezoelec-tric lm. Finally, voltage is formed in thickness direction.Fig. 1. Cross section view of the piezoelectric energy harvester.Sr z @2uz@r2

; Sh zr@uz@r

; Sz Srz Shz Srh 0 1

The convention that a comma followed by an index denotespartial differentiation with respect to the coordinate associatedwith the index is used. The electric eld in the piezoelectric layercorresponding to the electrode congurations, shown in Fig. 2, isof the following components:

Er 0; Eh 0; Ez V=h 2where V denotes the voltage across the piezoelectric layer.

The relevant constitutive relations for the piezoelectric layercan be written as

Sr sD11Tr sD12Th g31DzSh sD12Tr sD11Th g31DzEz g31Tr g31Th b33Dz

8>: 3where s11 and s12 denote the elastic compliances under the constantelectric displacement, g31 denotes the piezoelectric voltage con-stant, b33 denotes the dielectric impermeability under the constantstress. From (3) we solve for the radial stress Tr, the circumferentialstress Th, and the transverse electric eld Ez:

Tr 1sD111r2p

Sr rpsD111r2p

Sh g31sD111rpDz

Th rpsD111r2p Sr 1

sD111r2pSh g31sD111rpDz

Ez g31sD111rp Sr

g31sD111rp Sh b33Dz

8>>>>>:

4

where kp is the electromechanical coupling coefcient, rp is Pois-sons ratio of piezoelectric element.

rp s12s11 ; b33 b331 k2p; k2p

2g231b33s11 s12

5

By substitution of (1) into (3), we have:

Tr zsD111r2p @2uz@r2

rpr

@uz@r g31sD111rpDz

Th zsD111r2p rp@2uz@r2 1r @uz@r g31sD

111rpDz

Ez zg31sD111rp @2uz@r2 1r @uz@r b33Dz

8>>>>>>>:

6

For the brass layer element, its constitutive relation is given by:

Tr zE1r2m @2uz@r2 rmr @uz@r

Th zE1r2m rm@2uz@r2 1r @uz@r

8