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Introduction Characteristics of Various Vibration Sources Vibration to Electricity Conversion Model Vibrations to Electricity Conversion Methods Proposed

Piezoelectric Vibration Energy Harvester

Paper ID : 295

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Overview

1 Introduction

2 Characteristics of Various Vibration Sources

3 Vibration to Electricity Conversion Model

4 Vibrations to Electricity Conversion Methods

Piezoelectric Power Conversion

5 Proposed Structure

6 Layout of Proposed Structure

7 Meshing of the EH Structure

8 Results

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Introduction

Realising Wireless Sensor Networks (WSN) is of great interest in the research

community for applications like monitoring temperature, light, pressure etc.One of the challenges is powering the WSN nodes.Batteries are not enough.

Harvesting ambient energy from the environment.

Ambient vibrations as an important source.

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Characteristics of Various Vibration Sources

According to the study only the first 500 Hz of the spectra is important.First, there is a sharp peak in magnitude at a fairly low frequency with a few higher

frequency harmonics.

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Vibration to Electricity Conversion Model

Figure:Generic vibration converter model proposed by Williams and Yates[1]

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|P| =men2(

n)3Y2

(2T

n) + (1 (

n)2)2

(1)

|P| = me

3Y2

42T

(2)

where:

e electrical damping ratiom mechanical damping ratioT combined damping ratio(e+ m)n natural frequency of the mass spring system frequency of the driving vibrationsY input displacement

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I d i Ch i i f V i Vib i S Vib i El i i C i M d l Vib i El i i C i M h d P d
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Vibrations to Electricity Conversion Methods

There are mainly three main methods for converting the energy from vibrations to

electrical energy. They areElectromagnetic Power Conversion

Elecrostatic Power Conversion


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I t d ti Ch t i ti f V i Vib ti S Vib ti t El t i it C i M d l Vib ti t El t i it C i M th d P d
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The constitutive equations for a piezoelectric material are given in equations3and4.

=

Y +dE (3)

D=E+d (4)

where:

is mechanical strain

is mechanical stress

Y is the modulus of elasticity (Youngs Modulus)

d is the piezoelectric strain coefficientE is the electric field

D is the electrical displacement (charge density)

is the dielectric constant of the piezoelectric material

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Modes of Operation

(a)

Figure

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Proposed Structure

The device is designed in MEMS design softwares Conventorware and CoventorMems+.

Our structure has dimensions (1000m 200m 714m )

Figure:Proposed EH Structure

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Layout

(a)Cross Section of EH Structure

(b)Top View of EH Structure11/20


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t oduct o C a acte st cs o a ous b at o Sou ces b at o to ect c ty Co e s o ode b at o s to ect c ty Co e s o et ods oposed

Meshing of the EH Structure

Partitioned the model into two - the beam part and the rest.Manhattan Mesher setting is used as structure is orthogonal

Mesh settingFor Beam Part For other parts

X direction: 40m X direction: 40m

Y direction: 4m Y direction: 40m

Z direction: 1m Z direction: 40m

Figure: Meshed Model of the Proposed Structure

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y y p

Analysis of the Structure

The equation for the natural frequency of a cantilever beam with one end fixed and a

proof mass at the other end is given by the equation,

fn= 1

2

Ebd3

4ml3 (5)

E is the effective Youngs Modulus of the beam, b is the width , d is the depth, m is

the effective mass and l is the length of the beam. From this equation, we can see that

the resonant frequency of the device can be reduced by

increasing mass

increasing beam length

reducing the beam width

reducing the beam depth (height)

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Modal Analysis

Analysis is done using Memmech Solver

Done by fixing the anchor end.

Figure:Modal Analysis Results

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Mode Shape

Figure:Shape of the first mode

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Voltage Output at 1g acceleration

Connected an 1 Megaohm resistor across the 2 electrodes

1g acceleration is applied in the vertical directionVoltage output is 4.7 V at 278 Hz.

Power output is 11W

Figure:Voltage at 1g acceleration16/20

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Voltage Output at 2g acceleration

Connected an 1 Megaohm resistor across the 2 electrodes

2g acceleration is applied in the vertical directionVoltage output is 9.5 V at 278 Hz.

Power output is 45W

Figure:Voltage ouput at 2g acceleration17/20

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Comparison with related Works

" High Performance Piezielectric MEMS Energy Harvesteer based on d33 mode of

PZT thin film on buffer layer with PbTiO3 inter layer " by J.C.Park et.al,Transducers IEEE 2009, produces 1.1W from 0.4g at a frequency of 528 Hz.

" A piezoelectric vibration harvester using clamped guided beams " by Z. Wang

et.al at 2012 MEMS Conference IEEE produces 20W at 694 Hz from 1.2g.

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THANK YOU

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Using Coventorware. COVENTOR, 2012, pp. 1116, user Manual for

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