1 | P a g e

HERIOT-WATT UNIVERISTY

Piezoelectric Micro Power Generator

Mechanical Engineering BEng(Hons)

Matthew Gary Nesbitt

4/15/2011

[Type the abstract of the document here. The abstract is typically a short summary of the

contents of the document. Type the abstract of the document here. The abstract is typically a

short summary of the contents of the document.]

2 | P a g e

1 Contents

2 Introduction ................................................................................................................... 4

3 Aim ............................................................................................................................... 4

3.1 Objective ................................................................................................................ 4

4 Background ................................................................................................................... 5

4.1 Materials ................................................................................................................. 5

4.1.1 Crystals ............................................................................................................ 5

4.1.2 Ceramics .......................................................................................................... 5

4.2 Application ............................................................................................................. 6

4.2.1 Example of Piezoelectric Applications in Automotive industry ........................ 6

4.2.2 How piezoelectric materials are applied in Energy Harvesting ......................... 6

4.3 Piezoelectric Theory ............................................................................................... 6

5 Literature Review .......................................................................................................... 9

6 Experimental Testing of Original Design ..................................................................... 11

6.1 Method ................................................................................................................. 11

6.2 Results .................................................................................................................. 12

6.3 Discussion............................................................................................................. 12

6.4 Conclusion and follow up...................................................................................... 13

7 Sine Square wave form comparison ............................................................................. 14

7.1 Method and Expectations ...................................................................................... 14

7.2 Results .................................................................................................................. 14

7.3 Discussion............................................................................................................. 14

7.4 Conclusion ............................................................................................................ 15

8 Direct application of bending force .............................................................................. 15

8.1 Method and Expectations ...................................................................................... 15

8.2 Results .................................................................................................................. 15

8.3 Discussion............................................................................................................. 16

8.4 Conclusion ............................................................................................................ 16

9 Mass loading ............................................................................................................... 17

9.1 Method and expectations ....................................................................................... 17

9.2 Results .................................................................................................................. 17

9.3 Discussion............................................................................................................. 17

9.4 Conclusion ............................................................................................................ 18

10 Parallel Rewiring ......................................................................................................... 18

10.1 Generators Old state .............................................................................................. 18

10.2 Generators New state ............................................................................................ 18

3 | P a g e

11 Parallel Testing............................................................................................................ 19

11.1 Method and expectations ....................................................................................... 19

11.2 Problems encountered and Results ........................................................................ 19

12 Conclusion .................................................................................................................. 19

13 Looking at efficiency of energy conversion ................................................................. 19

14 Conclusion .................................................................................................................. 21

15 Future Work ................................................................................................................ 21

16 Acknowledgements ..................................................................................................... 22

17 References ................................................................................................................... 22

4 | P a g e

2 Introduction With smaller and smaller electronics

coming into day to day usage, it is

necessary to develop a method of reliable

power for these devices. The usual small

device is powered by a

replaceable/rechargeable battery, but with

batteries comes a problem. What to do

when they are depleted? Usually it is just a

simple matter of swapping out/recharging

the battery. Sometimes though it is not

possible to replace a depleted battery due

to its location within the world or maybe

the battery itself is integrated into the

structure of the device, either way it seems

that the only method of restoring power

left is to recharge the existing battery.

The problem though still exists

when recharging a battery. With devices

that are in hard to reach places; be they

devices in geographical situations, devices

in inhospitable environments or even

devices implanted into animals or humans,

it is not possible to physically go in

remove these batteries and then replace the

fully charged battery back into the device.

A method of deriving power from the

surrounding environment must be devised,

so that these devices are continuously

powered on site, and could possibly last

for a lifetime without further physical

contact, or at least none relating to any

power issue.

This method of drawing power

from the surrounding environment is

called energy harvesting.

There are many forms of Energy

Harvesting in existence, electrostatic and

electromagnetic to names just two, but the

most promising form of Energy Harvesting

is by the use of piezoelectric materials to

absorb vibrations. The reason for

piezoelectric systems being the most

promising is because of the simplicity of

the idea; A material that through being put

under strain will directly generate

electricity without the use of an external

power source. The simplicity of these

materials means that they can be made on

the microscopic scale and integrated into

other micro systems.

So the idea is, to have an energy

harvesting system generating enough

power to drive a small electronic device

such as an Mp3 player or remote sensor, or

possibly a system that could be integrated

into the human body to recharge a battery

while on the move.

3 Aim The aim of this project is to continue the

construction of a micro power generator,

started by the years previous, and to

improve on their design by analysing data

from electrical output tests and

determining where flaws exist, if any, and

eliminating them by modifying and

improving the design.

3.1 Objective 1. Test previous design

2. Test parallel circuitry over current

series circuitry

“Energy harvesting is the conversion of

ambient energy into electricity to drive small or mobile electronic and electrical devices.” http://www.energyharvestingjournal.com/ Fig.1 Micro Mechanical

System

5 | P a g e

3. Review possible new piezoelectric

materials

4. Test new materials

5. Design a Micro power generator that

will successfully recharge a battery in

an acceptable time frame

4 Background 1(Inman 2004) Power harvesting devices

work in many ways but one of the most

popular methods is a system that uses

mechanical vibration to apply mechanical

strain to a piezoelectric material. This type

system often uses ambient vibration

around the power harvesting device and

then converts it into a useful electrical

energy.

As described in the introduction materials

that generate a current when undergoing

strain are called piezoelectric materials,

but that is not all they do. They also do the

opposite, the material will strain when a

current is passed through it, these effects

are called direct piezoelectric and converse

piezoelectric respectively. With these two

effects a piezoelectric material can be used

as both a sensor and an actuator.

4.1 Materials Piezoelectric materials are divided into 3

categories; crystals, ceramics and others.

4.1.1 Crystals2 Quartz (SiO2) – one of the most common

crystals on the earth’s surface and shows a

strong piezoelectric effect perpendicular to

the prism axis.

Berlinite – structure is identical to that of

quartz but rarely forms crystals.

Gallium orthophosphate (GaPO4) – not

found in nature, has to be synthesised, but

it has twice the piezoelectricity of Quartz.

1 A Review of power harvesting from vibration using piezoelectric materials – Henry A. Sodano

and Daniel J. Inman 2 www.piezomaterials.com

Tourmaline – commonly black but can

range in colour, shows piezoelectric

qualities.

4.1.2 Ceramics Barium Titanate (BATiO3) – used as a

piezoelectric material for microphones.

Lead zirconate titanate (PZT) – considered

the most economical piezoelectric

material.

(Henry Sodano) The most common

material used is PZT and it comes in many

differing forms. All these forms exist

because they are all designed to suit

slightly different purposes. There are three

main types of PZT sold; Hard, Soft and

custom and there are many different types

of each. In the appendix is an extract from

a catalogue supplied by Morgan Electro

ceramics.

6 | P a g e

4.2 Application

4.2.1 Example of Piezoelectric Applications in Automotive industry

Above is a picture that shows the varying

uses in of piezoelectric materials in today’s

automotive industry. Obviously

piezoelectric materials have a wide range

of applications and are very important in

industry. Most of the applications shown

above are for small electrical sensors.

Most of these sensors work by allowing

the piezoelectric material to generate

power and then recording that power

output as data to analyse. It is the purpose

of this investigation to see whether the

power generation properties of this

material are great enough to implement

into biological bodies or even to power

larger electrical devices.

4.2.2 How piezoelectric materials are applied in Energy Harvesting

Piezoelectric materials can be

manufactured to absorb ambient vibrations

from machines. The vibrations have a

power output which can be calculated from

the following equation.

P = power

M = mass

A = acceleration

= Damping Coefficient

ω = frequency

This calculated power would also be the

ideal power output for the piezoelectric

generator when put in position but

obviously through losses this power could

not be achieved. Knowing what the power

from the vibrations is and from the final

generator means that the efficiency of the

power conversion can be calculated. The

aim is to get the highest possible efficiency

so to capture the greatest possible energy.

4.3 Piezoelectric Theory The piezoelectric effect relates to a

materials ability to convert strain energy

into electrical energy. Taking this one step

further, piezoelectric materials can also do

this process in reverse, i.e. inputting a

current, into a piezoelectric material, will

FIG.3. Piezoelectric applications in

today’s automotive industry1

7 | P a g e

cause it to deform in a specific way. This

is called the converse piezoelectric effect

or sometimes the electromechanical effect.

There are few materials that are truly

piezoelectric but of the few that are they

are mostly crystal or ceramic. A crystal

usually has a random polar axis resulting

from the charge of each individual atom

that makes up the whole, to make the polar

axis useful they must first be aligned and

this is done by heating up the crystal and

then applying a strong electrical field

which forces all of the dipoles to line up

and face the same general direction.

Fig.2.2. Polarization of Ceramic Material

to Generate Piezoelectric Effect3

If the above material is under compression

it will produce a voltage of the same

polarity as the poling voltage while if it is

under tension an opposite polarity would

be produced, conversely if a voltage is

applied on the material with the opposite

polarity as the poling voltage the material

will deform, in this case expanding

outward. Finally if an AC supply was to be

attached the material would vibrate to the

same frequency as the AC.

3 PZT APPLICATION MANUAL

4Once a piezoelectric material is poled as

above its properties are unstable. The

longer the time period after poling the

more stable the materials becomes. The

values given for certain constants (i.e.

dielectric and piezoelectric) by the

manufacturer can only be specified for a

standard time after poling.

An electro ceramic can age more rapidly if

its limitations are exceeded in one of the

following areas.

4.3.1.1 Temperature The Piezoelectric performance of electro

ceramics decrease as the operating

temperature increases. This eventually

leads to complete de-poling of the ceramic

at the Curie point. The Curie point is the

maximum exposure temperature for any

piezoelectric ceramic. Every ceramic has

its own individual Curie point usually

given by the manufacturer. It is

recommended not to exceed half of the

Curie point to reduce ageing due to

temperature. The closer a material operates

to its Curie point the more rapidly it ages

due to the temperature.

4.3.1.2 Voltage A strong voltage applied in the opposite

direction to the poling voltage can lead to

de-poling of the ceramic. How rapidly it

affects the ceramic is dependent on the

material, duration of the applied voltage

and the operating temperature. It should be

considered that alternating voltage will

also have the same aging effect for the half

cycle it is opposite the poling voltage.

4.3.1.3 Mechanical Stress High mechanical stress can depolarise an

electro ceramic but it is dependent of the

type of ceramic and duration of the applied

stress in much the same way as the

voltage.

4 MORGAN ELECTRO CERAMICS

8 | P a g e

Below is a table of relevant piezoelectric

and physical properties and their

definitions, shown in equation format. The

values for these properties are often given

by the manufacturer but some of them can

also be obtained through experimentation.

The above definitions can be applied into

the following equations that govern the

relationships between the electrical and

mechanical behaviour of the material.

E = Field (V/m)

T = Stress (N/m2)

S = Strain (SI)

D = Dielectric displacement (C/m2)

ε r = relative permittivity or dielectric

constant

ε 0 = permittivity of free space (8.85x10-12

F/m)

Property Definition

Electrical

Coupling

Coefficient

k

or

Piezoelectri

c Constants

d

or

Relative

Dielectric

Constant

K

Modulus of

Elasticity

Y

Density

ρ

Frequency

Constant

N

Controlling dimension x

Resonant frequency

9 | P a g e

5 Literature Review 1. “A Review of Power Harvesting from

Vibration using Piezoelectric

Materials” Henry A.Sodano and

Daniel J.Inman 2004

This is a paper reviewing other papers that

are evaluating the use of piezoelectric

materials in energy harvesting systems, so

to understand whether or not they would

be viable to use in everyday life. The paper

talks about the theory and methods behind

the preparation of piezoelectric materials

i.e. poling. It also confirms that the battery

has better storage capabilities than the

capacitor. One of the final parts of the

paper discusses the possibility of

incorporating piezoelectric materials into

clothes and biological systems, then going

on to look deeply into the power generated

through walking. The damping effect

caused by the energy extraction is looked

at and found to resemble the damping of a

shunt system but with the energy being

stored instead of lost.(A J Fleming)5

Finally the paper discusses the future of

piezoelectric materials saying that the

harvesting devices are producing energy

too small to power current technology and

the future may lie in advances in low

power electronics

Definition

Shunt Damping: Piezoelectric shunt

damping systems reduce structural

vibration by shunting an attached

piezoelectric transducer with electrical

impedance

Other material suggested by paper:

Papers

Crawly and de Luis 1987, Crawly and

Anderson 1990, Hagood et al 1990, Smits

and Choi 1991, Smits et al 1991, Near and

Craig 1996, Inman and Cudney 2000,

Niezrecki et al 2001.

5 Adaptive piezoelectric shunt damping, A

J Fleming1 and S O R Moheimani

Books

Ghandi and Thompson 1992, Ikeda 1996,

Banks et al 1996, Culshaw 1996, Clark et

al 1998, Srinivasan and Mcfarland 2001,

Worden et al 2003

2. “Comparison of Piezoelectric Energy

Harvesting Devices for Recharging

Batteries” (J.Inman 2005)

This is a report comparing the

piezoelectric materials PZT, MFC and QP,

and their ability to convert vibration

energy into electrical energy, to power

simple electronics. Using their own

conclusions from other reports, shown in

“review 1”, Sodano and Inman continue

their investigation into power generation

through piezoelectric materials. Setting up

each material as a cantilever beam to

absorb vibrations, they were tested for the

time period taken to fully recharge a

battery. Efficiency of each system was also

calculated.

V= voltage drop across load resistance

R= Resistance

F= force applied to base of plate

D= displacement of plate

T= time

N= data point index

M=total number of total points

It is found from experimentation that the

QP performs better at resonant frequencies

but the PZT performs better at random

frequencies while the MFC doesn’t

perform well in any situation. PZT and QP

were then brought on for the battery

charging experiment which showed that

while the QP was good at charging smaller

batteries at its resonant frequency, as the

battery sized increased the performance

fell off. This results in the PZT being the

better choice of material for power

generation and random and resonant

frequencies.

Definition

PZT: Lead Zirconate Titanate

10 | P a g e

MFC: Macro Fibre Composite

QP: Quick Pack

3. “Human Powered Wearable

Computing” Thad Starner,

Massachusetts Institute of

Technology (Starner)

In this paper Starner discusses in depth the

amount of energy expended in actions

undertaken by the human body. After

discussing many methods of energy

recovery from human movement he finally

discusses the possibility of using

piezoelectric materials in clothing. He

states that it is the most promising and

least obstructive of the ideas previously

discussed in his paper but also points out

that the materials that could be used are, at

the moment, to inefficient to fully utilise

the power available. Also in the paper

power requirements for electronic systems

are discussed and they are analysed to see

which could be powered by the day to day

movements of the human body. Also

discussed where the current trends in

electrical goods and battery sizes and life

spans. In conclusion of his paper he states

that the next step is to develop a

piezoelectric generator for testing of

energy harvesting through something as

natural as walking.

“Increasing Electrical Power

Generation for a Piezoelectric Power

Harvester” (Garnett E. Simmers Jr)

This short paper shows the power

generation abilities of piezoelectric

actuators. It shows that piezoelectric

cantilevers do have the potential to

recharge a battery when connected

electrically in parallel rather than in series,

which was usually the case. They also

show that that to obtain the maximum

energy output then the beams must be

turned to resonate in the same frequency

range as the ambient vibrations expected.

A picture of their experimental set up was

also included in the short report.

Fig.3. the mobile power harvester

attached to a shaker for experimentation

11 | P a g e

6 Experimental Testing of Original Design

Below is an image of the generator from

the previous year. It is a small black block

hollowed out with a screw hole in the

bottom so it can be attached to a

mechanical shaker. There are 3

piezoelectric beams over the hollowed out

area supported by small screws and then

connected electrically in series just beyond

that.

The generator works on the premise that

the beams will vibrate with the whole

generator and bend with their own inertia,

although this is not the most efficient

method of energy production a small

improvement was to add masses to the end

of the beams adding to their inertia and

bending them much more with the

vibrations.

Although the generator worked well

through testing during last year’s

experimentation the addition of a

rectifying circuit before completion of the

project effectively broke the device. The

circuit contained a chip that only activated

once voltage reached a constant 5V and

currently the generator peaked just below

that output meaning that no power output

at all. This circuit was removed and has

been scrapped as it isn’t of much use.

As the rectifying circuit was scrapped the

output from any testing will be an

alternating result. This being the case it

was decided that the program Lab View

would be used to record the results. Below

is a list of the apparatus used in the first

experiment.

Apparatus

Amplifier

Frequency Generator

Mechanical Shaker

Computer with Lab View program

Piezoelectric Generator

6.1 Method

Below is picture showing the general set

up of the experiment. The signal generator

puts out a variable frequency and wave

form of this frequency can be altered to

represent a sine wave, square wave or even

a triangular wave form. This signal is then

run through the amplifier which allows the

amplitude at which the mechanical shaker

to be controlled. To begin with the

amplitude will be set to 1 and depending

on results may be increased upon from

there. Then of course the generator is

attached to the top of the mechanical

shaker.

The generator will be shaking a varying

frequencies starting from 5 Hertz and

increasing in 5 Hertz intervals until 50

Hertz is reached and at the amplitude set to

1. The output of the generator will then be

measured for current and voltage and the

results will be analysed for maximum

power output and efficiency at reaching

maximum power. The results are shown on

graphs on the following page.

12 | P a g e

6.2 Results A full set of results can be found on page 4

of the appendix, only a summarised set of

results are shown here.

Below are the current, voltages and power

graphs from the experiment at increasing

frequencies from 5- 50Hz.

6.3 Discussion

It is impossible to compare the current and

therefore the power results from the

previous year to the results obtained for

this test as there was no discernable

current output from that test. This might be

put down to a loose connection during that

test or the measuring device used for the

recording the results. The student from last

year used a multimeter to record all his

results but this year a multimeter was only

used to record the voltage output while the

current was recorded using Lab view

software which allowed for a much more

accurate reading of the peak current output

and even allowed for the varying current to

be plotted on sine wave form graphs

(shown in appendix).

The results shown on this page

though show the peak current, voltage and

power output for each frequency tested,

the power been calculated was the

maximum power output from the generator

when the voltage and current at their

maximum points using the power equation

shown below.

Even with the results for this test not being

comparable with the results from last year

an analysis can still be carried out.

Firstly, from looking at the graphs

and then looking at the data provided in

the tables, that form the graphs, it can be

seen that there is a flaw with the lab view

software used to obtain the results. A few

tables show this flaw more obvious than

others, graphs 4 and 5. It can be seen that

there is a gap in the data obtained, a small

0.02-0.03 second interval that occurs at

almost the same point for each test. It

becomes more obvious during the tests

with higher frequency vibrations but it is

also present during the lower frequency

testing.

Next thing noticed which may be

obvious, is that power generation increases

as frequency increases until it reaches a

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 20 40 60

C

u

r

r

e

n

t

Frequency

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 20 40 60

Volt

age

Frequency

0

0.001

0.002

0.003

0.004

0.005

0 20 40 60

Pow

er

Frequency

13 | P a g e

maximum at 25Hz and then falls unevenly

again. On the next page is a table that

shows the maximum peak height against

frequency.

Although high current generation is key

for recharging a battery effectively the

efficiency at reaching a high current is also

a factor. It can be seen from the graphs, in

the appendix, that although the highest

current generation occurred at 25Hz the

generator was much more efficient at

higher frequencies as shown by the graph

below which displays the generators

ability to reach 90% of its peak output at

each frequency.

6.4 Conclusion and follow up Although the testing went as planned and

the results obtained are expected they are

not exactly desirable if the final

application of this generator is to be

incorporated in biological systems with

low frequencies. As the error value of lab

view is 0.0003 Amps this meant that

values obtained for 5Hz where possibly

wrong due to the low values shown.

The next experiment will be to test

a theory that different wave forms will

affect the output. It will be a direct

comparison between a sine and square

wave form. The hope is that the square

wave will increase the power output at

lower frequencies but also keep the same

output at higher frequencies as at higher

frequencies all wave forms begin to look

similar.

Frequency Max. Peak Current

5 0.000138

10 0.001241

15 0.008815

20 0.001845

25 0.011775

30 0.004415

35 0.003

40 0.002214

45 0.003084

50 0.002903

14 | P a g e

7 Sine Square wave form comparison

The reason for testing using a square wave

form is because of the motion from most

natural systems. Looking at a natural

system like the human body you realise

that that any motion is not smooth and

flowing but more rapid and instant, for

example the contractions of the human

heart. Below is a picture of a print out

from a heart monitor.

The heart muscle contracts rapidly creating

the large peaks in the picture and a square

wave form will represent this motion better

that the smooth form of the sine wave.

7.1 Method and Expectations A similar testing method to previous test is

being used except that this time the

frequency generator will be set to the

square wave form instead of sine. The

amplitude will remain set to 1 and

frequency will again increase in intervals

of 5Hz from 5 to 50.

In this test I expect to see the

square wave form producing a larger

output at lower frequencies and then

becoming more like the sine wave form

output as it increases.

7.2 Results Again a full set of results can be found in

the appendix section and only the

summary results are shown here. The

graphs show the current, voltage and

resulting power output from the generator

and are each plotted against the rising

frequency.

7.3 Discussion Again there were gaps in the data, shown

on the graphs in the appendix, which

meant that the results don’t quite show the

whole picture but they do show enough to

extrapolate useable information and form a

conclusion to the theory.

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 20 40 60Curr

ent

Frequency

Sine Peak Square Peak

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 20 40 60

Volt

age

Frequency

Square Sine

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0 20 40 60

Pow

er

Frequency

Sine Square

15 | P a g e

7.4 Conclusion For higher frequencies it turns out the

square wave form does not increase the

output but instead decreases the overall

output but it can also be seen that the two

waves closely resemble each other which

does at least prove half of the theory.

On the other hand the output at

lower frequencies is increased. When

looking at the graphs, ignoring all the

minor variations as these could be down to

the errors and interference in the line.

Instead focus on the large peaks in output,

these peaks show increased output over the

regular sine wave. This increase could be

put down to the large increase in the rate

of change, in position, from sine to square

wave. At lower frequencies a sine wave is

very smooth and while this amplitude (if

applied directly to the beams) will generate

an output, on this design it will not

because of little to no deflection of the

beams relative to the generator. With this

in mind it is worth testing to see what

effect applying the bending force directly

to the beams will have.

The application of the bending

force directly to the beams is not a new

idea on this project, it was originally

designed to work that way but during the

previous year the student redesigned the

generator to work without it which reduced

the efficiency of energy transfer at lower

frequencies but increased it at higher

frequencies. The reason for this change

was never made clear so the aim of the

next experiment is to determine exactly

why this change was made and establish

whether this was the best course of action.

8 Direct application of bending force

This experiment is a test to determine

whether applying the bending force

directly to the beams will increase or

decrease the power output from the

generator.

8.1 Method and Expectations For this test the set up of the generator has

to be changed, instead of bolting the

generator to the mechanical shaker and

relying on the inertia of the beams to bend

them, a small aluminium plate with a hole

centred at one end will be secured to the

shaker and the beams will rest on top of

that. The generator of course has to be

lifted to the right height so that the beams

rest on the plate in their datum position

(unbent) and the generator will be secured

down so that no energy is lost through the

movement of the generator during testing.

A picture taken of the experimental set up

is shown below.

Again the generator will be tested at

varying frequencies from 5 to 50 Hertz and

the amplitude will remain at one to keep

the testing method consistent throughout

all experiments.

The results expected from this test

will hopefully show a direct relationship

between frequency input and power output

as the beams will no longer rely on their

own resonance frequency to vibrate

efficiently.

8.2 Results The graph that follows shows the peak

current output for this experiment at the

increasing frequencies.

16 | P a g e

8.3 Discussion Comparing this graph to the graph shown

in the results of the initial test, a few

differences can be seen. The most obvious

of which is that the peak power output at

25Hz, due to the beams vibrating at their

resonant frequency, has been eliminated.

The forced vibration does not allow the

beams to move freely thus eliminating the

possibility of them vibrating at greater or

lesser amplitudes at different frequencies,

that is why in this test a much more regular

increase is observed in the power output

compared that of the initial test. This

increase then peaks at 45Hz before

dropping again this is might be due to the

beams moving at such a high frequency

that they inhibit their own power

generation capabilities.

8.4 Conclusion This test:

shows a more linear increase in

power output as frequency

increases

increases power output at the

lowest frequency

increases the efficiency of reaching

the peak power output for each

frequency

While the direct bending did all of these

things it did eliminate any free motion that

allowed the beams to bend beyond the

amplitude set by the amplifier, because of

this a method should be devised to both

increase the power output and allow for

free motion.

From research a lot of companies

add masses to the piezoelectric beams, this

will also be tried here to solve the

problem.

0

0.005

0.01

0.015

5 15 25 35 45

Curr

ent

Frequency

0123456789

5 15 25 35 45

Volt

age

Frequency

0

0.02

0.04

0.06

0.08

0.1

0.12

5 15 25 35 45

Pow

er

Frequency

17 | P a g e

9 Mass loading In this experiment three 5 gram masses

where loaded on the end of the beams.

These masses will provide added force

during vibration making the beams bend

more than they normally would when

subjected to a vibrating source.

9.1 Method and expectations The experimental setup for this test is the

same as the previous tests, before the

direct bending experiment. The generator

is secured to the top of the mechanical

shaker which is again connected to the

frequency generator, amplifier and

measuring equipment. From this

experimental setup the results should show

an increase in power for each frequency

especially at lower frequencies. There is

also the possibility that at higher

frequencies the beams move so fast that

the masses barely move in relation.

9.2 Results Again a full set of results is shown in the

appendix section of this report.

9.3 Discussion Before discussing the results there was an

observations made during the testing. You

may have seen that the frequency doesn’t

go higher that 35Hz during this test, this is

because during the test the beams were

observed to bend a great distance. There

was a chance that the beams could have

broken with further testing so the test was

finished prematurely.

This being the case looking the

results shows a definite downward trend

towards the end of the graph, so even if the

test had carried on with increasing

0

0.01

0.02

0.03

0.04

10 15 20 25 30 35

Current

Frequency

0

2

4

6

8

10

12

0 10 20 30 40

Volt

age

Frequency

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

10 20 30

Pow

er

Frequency

18 | P a g e

frequencies there may not have been any

further increase in power output.

The graphs show that the power for

each frequency is increased over the

original design tested at the same

amplitudes which satisfies the aim of his

test, but can further power be produced

from using this generator by modifying it

another way.

During the literature review I came

across a 1 page paper that displayed the

advantages of wiring the generator in

parallel over wiring it in series. It stated

that when wired in parallel their generator

produced 4 times the power it did when

wired in series. If the same could be done

with this generator it could be possible to

push the maximum power output of the

unit over 1W.

9.4 Conclusion The addition of masses has increased the

power output at each frequency

dramatically by forcing the beams to

deflect greater distances while being tested

at the same amplitude level. Now to see if

more power can be created another way

the circuit will be rewired from series to

parallel to test a claim from a report

covered in the literature review which

stated that the power output would

increase again.

10 Parallel Rewiring

10.1 Generators Old state

The picture in the next column shows the

generator as it appeared before the changes

with clips around the beams allowing for

all connections to be made across the top

for ease of access. Each beam is connected

positive to negative.

10.2 Generators New state

In these images the positive connections

are blue and the negative is red, also in the

first diagram the connections between

beams are black. The second diagram

shows the new state of the generator with

the all the positive connections joined and

all the negative connections joined.

In series when a beam deflects the energy

produced has to travel through the

remaining beams in the circuit, and as

piezoelectric materials are governed by

both direct and converse piezoelectric laws

any energy input could be used to bend the

next beam in the series. As all the beams

are joined to the same generator they are

all subjected to the same bending force so

any energy input won’t affect bending too

much but there still could be losses in the

beam itself, so connecting the beams in

parallel allows for all the energy from each

beam to be collected with only losses in

the connecting wires to take into account.

19 | P a g e

11 Parallel Testing Like stated in the previous section the aim

of this experiment is to determine whether

the theory that states that wiring the

generator in parallel will increase the

power output dramatically over the same

generator wired in series.

11.1 Method and expectations This test is set up identical to the initial

test, the only difference being the

generator has been rewired. The generator

will be tested without masses to see the

original increase in power output before

further testing.

11.2 Problems encountered and Results

During testing of the design a serious

problem occurred, during initial testing the

substrate within two of the three beams

cracked meaning that any results obtained

could not be comparable with any past

results. For all intensive purposes the

generator at this point is considered

damaged and unusable.

Series Parallel

<0.0004 0.002197

The above result is the current output from

being tested at 5Hz. It is obvious to see

that there is a massive increase on current

output almost a 550% increase. Sadly the

no voltage readings were recorded during

this test as it was simply a test to confirm

the wiring worked so no power output can

be calculated but assuming voltage wasn’t

affected too much by the wiring change

this is a dramatic increase in power output

at just this one frequency.

12 Conclusion As said this is a huge increase in output at

this one frequency but no solid

conclusions can be drawn without further

testing and analysis.

13 Looking at efficiency of

energy conversion As stated in the theory section of this

report the power output from a vibration is

calculated using the below equation and

have calculated the power output from

each experiment it is possible to calculate

the efficiency of energy conversion from

kinetic to electrical for each set up.

Assuming that there is no damping force

due to the vibrations been powered to

remain constant the final equation can be

rewritten.

On the following page is a table containing

the maximum power recorded for each

frequency for each test, it is these power

recordings that will be used in the

efficiency calculations.

20 | P a g e

The next table shows the final result of using the equation and calculating the efficiency of

the tests.

Efficiency %

Initial Square Direct Masses Parallel

0.005819 0.006817 5.070862 0.365268

0.00291 0.009144 2.576996 3.657671

0.048769 0.002161 1.884255 16.84745

0.015794 0.011222 1.8704 8.936355

0.139657 0.008645 1.529572 8.246386

0.030481 0.014409 1.607159 0.526483

0.019001 0.010094 1.733831 0.380018

0.010599 0.010391 2.140569

0.014224 0.010714 2.032039

0.012968 0.007814 1.296811

From this table it can be clearly seen that the mass loading gives the highest overall

efficiency reaching a maximum of 16.8% but if you look closely there is a dramatic increase

in efficiency from the initial design in series to the new design in parallel. This could mean

that if the new design was to be tested with masses an even greater efficiency could possibly

be the resultant.

Power Out

Frequency Power In Initial Square Direct Masses Parallel

5 0.601476 3.50E-05 4.10E-05 0.0305

0.002197

10 1.202951 3.50E-05 1.10E-04 0.031 0.044

15 1.804427 8.80E-04 3.90E-05 0.034 0.304

20 2.405903 3.80E-04 2.70E-04 0.045 0.215

25 3.007378 4.20E-03 2.60E-04 0.046 0.248

30 3.608854 1.10E-03 5.20E-04 0.058 0.019

35 4.210329 8.00E-04 4.25E-04 0.073 0.016

40 4.811805 5.10E-04 5.00E-04 0.103

45 5.413281 7.70E-04 5.80E-04 0.11

50 6.014756 7.80E-04 4.70E-04 0.078

21 | P a g e

14 Conclusion The aim of this project was to further develop a micro power generator by modifying a

current macro scale generator to better its electrical output and increase it to the point where

it could be at a useful level for electronics and also analyse the power conversion efficiency.

Through general improvements and minor additions to the design the power output has

improved somewhat from its original state. Initially the generator failed to output any power

at frequencies below 10Hz. Now, with testing, it is apparent that if the generator was

implemented in a situation which allowed the vibration force to be applied directly to the

beams a power output can be seen. If the force cannot be applied directly to the beams then

the addition of masses will increase the efficiency of the generator.

Also it is apparent from the results that if the generator where to be wired in parallel over the

original state series the power would increase even more at lower frequencies and make it

even more efficient.

Although all these improvements have been made the main problem with piezoelectric

materials is that power generation is never constant. Even under vibration at the same

frequency the power output is always fluctuating, that is why I believe that the best

application currently for these materials is to charge batteries rather than being a direct power

source for any electronic device that has to be on longer than a few seconds.

Also as the highest power output recorded in all the tests was only 0.25W I believe a more

efficient form of piezoelectric material needs to be developed so that it may be applied to

technology today or it could be applied to future low power electronics.

15 Future Work If a chance was provided to continue working on this project the generator would need to be

fixed. There are more recent piezoelectric materials been made all the time and the beams

used for these tests where at least 2 years old before this report was started, if a newer

material was selected and tested I would expect to see an increase in power output.

The testing of the parallel circuitry should be repeated with the new materials and also with

mass loadings.

Also smaller beams should be tested. It is apparent from reading relevant material that

piezoelectric materials become more efficient the smaller they are, this should be tested and

applied to the generator is true.

22 | P a g e

16 Acknowledgements

I would like to thank Dr. R. Fu, Professor B. Richards and Mohammad Ghaleeh for all their

support and help in this project, without which I could not have understood this project fully

or set up successful experiments.

17 References

A J Fleming, S. O. R. M. "Adaptive Piezoelectric Shunt Damping."

Garnett E. Simmers Jr, H. A. S. "Increasing Electrical Power Generation for a Piezoelectric

Power Harvester." Center for Intelligent Materials Systems and Structures, Virginia Tech.

Henry Sodano, E. A. M., Gyuhae Park, Daniel J. Inman "Electric Power Generation using

Piezoelecric Devices." Virginia Polytechnic Institute and State Univeristy.

Inman, H. A. S. a. D. J. (2004). "A Review of Power Harvesting from Vibration using

Piezoelectric Materials." The Shock and Vibration Digest 36(3): 197-205.

J.Inman, H. A. S. a. D. (2005). "Comparison of Piezoelectic Energy Harvesting Devices for

Recharging Batteries." Journal of Intelligent Material Systems and Structures 16(10): 799-

807.

Starner, T. "Human Powered Wearable Computing." Massachussetts Institute of Technology.

23 | P a g e

Appendix

18 Contents

19 Morgan Electro Ceramics Catalogue Information ........................................................ 24

20 Results ........................................................................................................................ 26

20.1 Testing of Original Design .................................................................................... 26

20.2 Sine/Square wave comparison ............................................................................... 28

20.3 Direct Bending ...................................................................................................... 34

20.4 Mass Loading ....................................................................................................... 39

20.5 Parallel Wiring ...................................................................................................... 42

24 | P a g e

19 Morgan Electro Ceramics Catalogue Information

HIGH POWER “HARD” MATERIALS

High power or “hard” ceramics can withstand high levels of electrical excitation and

mechanical stress. These materials are suited for high voltage or high power generators and

transducers.

PZT400 SERIES (NAVY TYPE I)

This material is ideally suited for ultrasonic cleaning, sonar, and other high power acoustic

radiation applications. PZT400 Series is a Lead Zirconate Titanate material capable of

producing large mechanical drive amplitudes while maintaining low mechanical and

dielectric losses. In addition, it can be used under both constant and repetitive conditions. See

page 30 for more specific material properties.

PZT800 SERIES (NAVY TYPE III)

This material is used in high power applications; even though its piezoelectric activity level is

slightly lower than PZT400 Series. With an extremely low loss factor, PZT800 Series has the

ultimate power handling capability. See page 32 for more specific material properties.

HIGH SENSITIVITY “SOFT” MATERIALS

High sensitivity or “soft” ceramics feature high sensitivity and permittivity, but under high

drive conditions are susceptible to self-heating beyond their operating temperature range.

These materials are used in various sensors, low-power motor type transducers, receivers, and

low-power generators.

PZT5A SERIES (NAVY TYPE II)

This material is used as the receiver or generator element in hydrophones, accelerometers,

and vibration sensors. PZT5A Series is a Lead Zirconate Titanate with a high sensitivity,

permittivity, and time stability. See page 31 for more specific material properties.

PZT5J1 (NAVY TYPE V)

This material is used in fuses, hydrophones, and other applications that require a combination

of high energy and high voltage output. PZT5J1 is a Lead Zirconate Titanate with a high

permittivity and a high piezoelectric voltage constant. See page 33 for more specific material

properties.

PZT5H SERIES (NAVY TYPE VI)

This material is used in sensitive receivers and applications requiring fine movement control.

It has been used in a wide range of applications from hydrophones to ink jet printers. PZT5H

Series provides extremely high permittivity, coupling, and piezoelectric constant. It has the

lowest Curie temperature of the “soft” materials (or PZT500 Series family), which restricts its

operating temperature range. It has lower time stability. See page 33 for more specific

material properties.

CUSTOM MATERIALS

Morgan Electro Ceramics manufacture a number of materials that do not fall within the

Department of Defence (DOD) standards that are often used to define PZT materials.

PZT501 – PZT506 (SOFT)

These materials are all “soft” and fall between DOD Categories II and V. They range in Curie

temperatures from 270°C to 350°C. All the materials have similar dielectric constants, but

have been optimised for charge constants or coupling coefficients for specific applications.

25 | P a g e

PZT502 is used as an alternative to PZT5A Series when higher sensitivity is required.

PZT502 has high acoustic sensitivity, and high coupling, while maintaining a high

permittivity. See page 34 for more specific material properties.

PZT507 (SOFT)

This material is an improved PZT5H Series, developed specifically for bimorph applications.

See page 34 for more specific material properties.

PZT601 (HARD)

This material was designed for transducer applications requiring reduced dielectric constant,

high Qm, low dielectric losses and improved electromechanical coupling coefficients. See

page 35 for more specific material properties.

PZT508 (SOFT)

This material has been developed to surpass the electrical performance of PZT5H Series

materials while improving the temperatures characteristics by raising the Curie temperature

to 220°C. See page 34 for more specific material properties.

PZT5K SERIES (SOFT)

This material outperforms PZT5H Series and PZT508 while at the expense of Curie

temperature. This material has very high “d” coefficients and permittivity.

See page 36 for more specific material properties.

PZT700 SERIES (SOFT)

These materials have been developed for a number of property optimisations. The materials

have a combination of property stability, good sensitivity and have found use in a variety of

sensor applications. See page 35 for more specific material properties.

PZT407 (HARD)

This material was developed for its specific combination of permittivity, loss and “d”

coefficient. The material in many aspects is similar to materials PZT400 Series, but falls

outside the Navy I classification. See page 35 for more specific material properties.

PT1

This material is a Lead Titanate. Unlike PZT it has low radial mode coupling coefficients,

which therefore provides excellent hydrostatic properties and has the highest (figure of merit)

for any Morgan Electro Ceramic materials. See page 35 for more specific material properties.

PMN-PT28/30

This new single crystal piezoelectric material has been designed for use in transducer and

actuator devices. It has been formulated to exhibit very large electromechanical coupling

coefficients and also offers high dielectric constants and low dielectric losses.

26 | P a g e

20 Results

20.1 Testing of Original Design

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0 0.5 1 1.5 2 2.5 3

Cu

rren

t (a

mp

s)

Time (secs)

5-10Hz5

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Cu

rren

t (a

mp

s)

Time (secs)

15-20Hz1

27 | P a g e

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Cu

rren

t (a

mp

s)

Time (secs)

25-30Hz2…3…

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

35-40Hz34

28 | P a g e

20.2 Sine/Square wave comparison

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

45-50Hz4…

0

0.0005

0.001

0.0015

0.002

0.0025

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

5HzSquare 5Hz

Sine 5Hz

29 | P a g e

0

0.0005

0.001

0.0015

0.002

0.0025

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

10HzSine 10Hz Square 10Hz

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

15HzSine 15Hz

Square 15Hz

30 | P a g e

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

0.002

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

uren

t (a

mp

s)

Time (secs)

20HzSine 20Hz

Square 20Hz

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

25HzSine 25Hz

Square 25Hz

31 | P a g e

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

30HzSine 30Hz

Sqaure 30Hz

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

35HzSine 35Hz

Square 35Hz

32 | P a g e

0

0.0005

0.001

0.0015

0.002

0.0025

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

40HzSine 40Hz

Square 40Hz

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

45HzSine 45Hz

Square 45Hz

33 | P a g e

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Cu

rren

t (a

mp

s)

Time (secs)

50HzSine 50Hz

Square 50Hz

34 | P a g e

20.3 Direct Bending

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

2 2.5 3 3.5 4 4.5 5 5.5 6

5

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

2 2.5 3 3.5 4 4.5 5

10

35 | P a g e

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

15

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

20

36 | P a g e

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3

25

-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

0.01

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

30

37 | P a g e

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

35

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4

40

38 | P a g e

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

3 3.2 3.4 3.6 3.8 4

45

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4

50

39 | P a g e

20.4 Mass Loading

0.02004

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0 0.1 0.2 0.3 0.4 0.5 0.6

10

0.029866

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

15

40 | P a g e

0.024571

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

20

0.027199

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

25

41 | P a g e

0.004785

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

30

0.004342

-0.004

-0.003

-0.002

-0.001

0

0.001

0.002

0.003

0.004

0.005

0.006

0 1 2 3 4 5 6

35

42 | P a g e

20.5 Parallel Wiring

0.002197

-0.0025

-0.002

-0.0015

-0.001

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0 0.5 1 1.5 2 2.5 3 3.5 4

Parallel

43 | P a g e