1

FOOTSTEP ENERGY HARVESTING SYSTEM USING

PIEZOELECTRIC CONCEPT

KAVIRAJ A/L JAYARAMAN (SCSJ - 0010355)

MOHAMAD SYAZWAN BIN SHARI’AT (SCSJ - 0010341)

TELVINDERJIT SINGH (SCSJ - 0010235)

MANRIT SINGH

SEGI COLLEGE SUBANG JAYA

FOOTSTEP ENERGY HARVESTING SYSTEM USING

PIEZOELECTRIC CONCEPT

KAVIRAJ A/L JAYARAMAN (SCSJ - 0010355)

MOHAMAD SYAZWAN BIN SHARI’AT (SCSJ - 0010341)

TELVINDERJIT SINGH (SCSJ - 0010235)

MANRIT SINGH

SEGI COLLEGE SUBANG JAYA

A report submitted in partial fulfillment of the requirements for the award of the

Diploma in Mechanical Engineering

Faculty of Engineering and Information Technology

SEGi College Subang Jaya

APRIL, 2013

i

“We declare that we have read this work and in our opinion this project is qualified in terms

of scope and quality for purpose of awarding the Diploma in Mechanical Engineering”

Student : .......................................................

KAVIRAJ A/L JAYARAMAN (SCSJ - 0010355)

.......................................................

MOHAMAD SYAZWAN BIN SHARI’AT (SCSJ - 0010341)

.......................................................

TELVINDERJIT SINGH (SCSJ - 0010235)

.......................................................

MANRIT SINGH

Date : 22nd April 2013

Supervisor :

..............................................................

NUR HASALLI BINTI HJ IBRAHIM

A special appreciation to our families for their

encouragements and guidances;

A special thanks to

Mr. Sri Jaiandran

for the idea of Piezoelectricity;

It is our pleasure to receive advices and

consultations from:

Ms. Nur Hasalli Binti Hj Ibrahim

Ms. Ida Fahani Binti Md. Jaye

Mr. Gehjanthiran

Mr. Manimaran

A special thanks to

Sivaganesh Vadiveloo

for the advices on circuits and electronic components

And to all of our understanding friends.

ACKNOWLEDGEMENT

The success of this thesis would not have been possible without the constant

encouragement, advice and support from a vast number of people.

Appreciation is extended to our supervisor, Ms. Nur Hasalli Binti Hj Ibrahim, for her

assistance and guidance throughout the whole project. From the beginning of the study, she

has been generous with her time, guidance and supportive. Without her interest and

encouragement, this project would never have been completed.

We would like to convey our millions of thanks to our beloved parents and families

for all of their support and blessing that made us who we are today. Without their involvement

and encouragement, this project would have not have been a realilty.

We would also like to express our sincere appreciation to all others who have played

their part directly or indirectly by contributing for the success of this study. May GOD bless

you.

ABSTRACT

CONTENTS

CHAPTER DESCRIPTION PAGES

DECLARATION i

DEDICATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

CONTENTS v - vi

LIST OF FIGURE vii

NOMENCLATURE viii

LIST OF APPENDIXES ix

1 INTRODUCTION 1 - 4

1.1 Background of study

1.2 Problem Statement

1.3 Objectives of the Study

1.4 Scope of the Study

1.5 Significance of the Study

2 LITERATURE REVIEW 5 - 13

2.1 Introduction to Piezoelectricity

2.2 Ceramic Piezoelectric Disc

2.3 Material used

2.4 Polarization

2.5 Voltage and Current Output

2.5.1 Full Wave Bridge Rectifier

2.6 Connection of Piezo

2.6.1 Voltage

2.6.2 Current

2.7 Battery

2.8 Capacitor

2.9 Circuit Board

3 METHODOLOGY 14 - 26

3.1 Introduction

3.2 Materials and Tools

3.3 Product Preparation

3.3.1 Design

3.3.2 Building the Wood Frame

3.3.3 Building the Circuit and Piezoelectric Arrangement

3.4 Assembly of the Whole Circuit and the Wood Frame

3.5 Measuring the Electrical Output

3.6 Finishing Touch

4 RESULTS AND ANALYSIS 27 - 35

4.1 Introduction

4.2 Design Circuit

4.3 Equations/Simulations/General Circuits

4.3.1 AC/DC Converter

4.3.2 Capacitor Charging/Discharging

5 CONCLUSION AND DISCUSSION 36 - 37

5.1 Conclusion

5.2 limitations and Assumptions

5.3 Recommendation

6 REFERENCES 38 to 39

7 Appendix 40 - 42

LIST OF FIGURES

2.1 Piezoelectric Disc

2.1 Main components on the disc

2.2 Polarization of Piezoelectric Disc

2.3 Relationship between footstep and output voltage

2.4 Ac to DC graph after rectification

2.5 Full wave bridge rectifier

2.6 Footstep Energy Harvesting Concept by Pavegen

3.1 Methodology of study flow chart

3.2 List of material

3.3 Group discussion and planning

3.4 Measuring the wood before cutting process

3.5 Cutting wood process

3.6 Assembling wood part using nails

3.7 Soldering the component to the circuit board

3.8 Connecting the circuit to Piezoelectric

3.9 Assembling the circuit and wood frame

3.10 Arrangement of the Piezoelectric

3.11 Using multimeter to determine the output produced

3.12 Testing the product

3.13 Sand the wood surface using sandpaper

3.14 Painting the product

NOMENCLATURE

Physic Units

N = Newton

V = Volt

A = Ampere

kg = kilogram

W = Watt

Ah = Ampere-hour

mm = milimetre

F = Farad

S = second

Chemical Formulae

PZT = Lead Zirconate Titanate

SiO2 = Silicon Dioxide

LIST OF APPENDIXES

Appendix 1 – Orthographic Projection of the project

Appendix 2 – Dimension Drawing

Appendix 3 – Schematic Diagram of circuit

1 | P a g e

CHAPTER I

INTRODUCTION

1.1 Background of study

Piezoelectricity was discovered in 1880 by Pierre and Paul-Jacques Curie, who found

that when they compressed certain types of crystals including quartz, tourmaline, and

Rochelle salt, along certain axes, a voltage was produced on the surface of the crystal. This

effect is known as piezoelectric effect. [1]

Piezoelectricity is a form of electricity created when certain crystals are bent or

otherwise deformed. These same crystals can also be made to bend slightly when a small

current is run through them, encouraging their use in instruments for which great degrees of

mechanical control are necessary. [2]

The property of piezoelectricity is dictated by both the atoms in the crystal and the

particular way in which that crystal was formed. Some of the first substances that were used

to demonstrate piezoelectricity are topaz, quartz, tourmaline, and cane sugar. Today, there are

many crystals which are piezoelectric, some of which can even be found in human bone.

A piezoelectric crystal consists of multiple interlocking domains which have positive

and negative charges. These domains are symmetrical within the crystal lattice, causing the

lattice as a whole to be electrically neutral. When stress is put on the crystal, the symmetry is

slightly broken, generating voltage. In a large dimension piezoelectric sensor, even a tiny bit

of piezoelectric crystal can generate voltages in the thousands.

Even though a piezoelectric crystal never deforms by more than a few nanometers

when a current is run through it, the force behind this deformation is extremely

2 | P a g e

high, on the order of meganewtons. This deformational power is used in mechanics

experiments and for aligning optical elements many times heavier than the piezoelectric

crystal itself. [2]

A piezoelectric sensor is a device that converts pressure directly into electricity by the

polarization effect. Piezo is derived from the Greek word piezein, “to squeeze.” Piezoelectric

materials produce a voltage when strained. Assemblies of metals, ceramic (SiO) and lead

zirconate titanate. Piezoelectricity is the field of technology that involves the application of

piezoelectric sensors in producing electricity for practical use.

Over time, piezoelectric sensors have proven to be versatile tools for the measurement

of various processes. They are used for quality assurance, process control and also in

automotive industry to manufacture internal combustion engine. [3]

Piezoelectricity serves as a secondary power source. Electricity produced using

piezoelectric sensor is environmental-free – no pollution. But, the only pollution produced is

during the manufacturing of these devices in factories, transportation of the goods, and

installation.

Now, the modern energy processing methods using generators such as to those on

power plants, can be very sounds polluting and also at times the safety becomes a threat.

Instead, energy is produced from piezoelectric sensor very quietly. One of the great pros of

piezoelectricity is the ability to harness electricity in remote locations that are not linked to a

national grid [4].

In today’s world, piezoelectricity is widely being used in many fields. For an instance,

piezoelectric crystals have been used in phonographs as a stylus to create electrical signals

that reflect the sound stored in grooves on a record. Phonograph is a device used for recording

and reproduction of sound recordings. It was introduced in the late 19th

century. [5]

Besides that, piezoelectric is also being used to light up street lamps. There is also a

hot shower mechanism that has piezoelectric nano-tubes installed in the lining of the tube.

Due to water pressure, the sensor is used to generate electricity to heat up the water. [5]

3 | P a g e

Piezoelectric sensors can be installed in the soles of shoes or on the circumference of

car tyre which eliminate the problem of finding the required space for piezoelectric sensor

installation. Another advantage of piezoelectric is the cost. Initially, during installation, the

cost may be high but in the long term a large sum can be saved. Directly, we can reduce the

dependency of the humans on the natural resources as the main form of fuel. This would in a

way conserve the mother nature.

1.2 Problem Statement

Now, electricity production has become one of important causes of global warming.

This is due to the immense heat being dissipated during the process. This heat contribute to

the gradual increase in Earth temperature. Furthermore, burning of fossil fuels also produces

an end product of carbon dioxide and sometimes carbon monoxide which are harmful to

human health. Carbon dioxide tends to radiate heat back into earth.

In addition, the usage of fossil fuel for generation of electricity is very costly. A large

sum could be saved by using a renewable energy. This would enable invest in future projects

rather than just spending it on purchasing fossil fuels alone.

By reviewing and analysing all these critical problem, designing new form of renewable

energy such as piezoelectricity would be a perfect option in which it is useful for domestic

application. Piezoelectricty, on the contrary, is clean and environmentally friendly.

Piezoelectric components require little maintenance, and the initial investment can be

recovered within a relatively short time.

1.3 Objectives of the Study

The aim of this research is to harvest energy from footstep using piezoelectric disk

based on the concept of polarization. The objectives of the study are as follow :-

1) To produce renewable electricity from footstep using piezoelectric disk placed along a

pathway.

2) To reduce the cost for power generation besides increasing the efficiency of power

generation.

4 | P a g e

1.4 Scope of the Study

Piezoelectric sensors would be arranged in two orders, series and parallel. This is to

ensure there would be sufficient generation of electricity. The output be measured using a

multimeter and a row of 5 light emitting diode would be placed to indicate the presence of

electricity.

1.5 Significance of the Study

At the end of this research, we would be able to produce electricity in a minimal scale.

This energy would be used as a secondary power sources to battery. Beside that, we can

reduce the total cost of electricity application. In addition, the maintenance of piezoelectricity

is minimal. The life span of a piezoelectric disk is also relatively long.

5 | P a g e

CHAPTER II

LITERATURE REVIEW

2.1 Introduction to Piezoelectricity

In this section, the fundamental theories that are related to the working principles of

the footstep energy harvesting method would be thoroughly explained. The explanation that

follows would include the principles of ceramic piezoelectric disc, functional output voltage

and current, polarization method in the piezoelectric disc and a few other related concepts.

Furthermore, research was conducted on the previous or current technologies being

used in the real world. These case studies were analyzed and a slight improvement was made

based on the case study to improve the activation of capacitor charging with a battery in a

shorter period of time. The resulting effect was still visible despite being minimal.

Single-Layer Piezoelectric Generators and Multi-Layer

Piezoelectric Generators are the two main types of piezoelectric

generators. Single-layer piezoelectric generator (Figure 1.1) was

used in this project. This type of sensor is known as single layer

due to the single layer of ceramic on the electrode. [6]

Multi-Layer Piezoelectric Generators consist of a stack of

very thin (sub-millimeter-thick) piezoelectric ceramics alternated

with electrodes. The electrical energy produced by a multilayer piezo

generator is of a much lower voltage than is generated by a single-layer piezo generator. On

the other hand, the current produced by a multilayer generator is significantly higher than the

current generated by a single-layer piezoelectric generator. [6]

Figure 2.1 Piezoelectric Disc

6 | P a g e

2.2 Ceramic Piezoelectric Disc

A disc shaped solid sensor that uses the piezoelectric effect by the means of pressure

to produce electrical charge through the concept of polarization. The pressure need to be

applied on the piezoelectric disc in the form of mechanical movement. For instance, walking

or running. This continuous application of pressure on the sensor produces an electric charge

surge that can be used relatively for low power input appliances such as Light Emitting Diode

(LED). [7]

2.3 Material used

PZT, or lead zirconate titanate, is one of the world’s most widely used piezoelectric

ceramic materials. PZT is composed of the two chemical elements lead and zirconium

combined with the chemical compound titanate. The underside of the electrode is made up of

plastic. A very thin layer of ceramic (SiO2) is deposited on the outermost layer of the plastic.

The ceramic element converts the mechanical energy of compression into electrical energy.

The ceramic is a conductor material that acts as the negative terminal while the metal acts as

the positive terminal. [6]

The interaction between the ceramic and the metal works in two ways: if outside

electrical current is supplied, then the piezo will produce sounds. This property allows them to

be used as buzzers and simple speakers. However, if no outside current is supplied and instead

the piezo is subjected to changes in pressure (such as by the vibrations of guitar strings), then

the interaction of the metal and ceramic actually creates a small amount of electrical current.

The ceramic layer acts as the negative terminal meanwhile the metal acts as positive terminal.

Figure 2.7 Main components on the disc

7 | P a g e

2.4 Polarization

The piezoelectric disc used in this project works on the principle of polarization.

Piezoelectric material consists of polarized ions within the crystal. The top and bottom layer

of the piezoelectric disc is positively charged while the side wall is negatively charged.

Mechanical compression or tension on a poled piezoelectric ceramic element changes the

dipole moment, thus creates a voltage surge. [4]

This results in the displacement of the ions within the crystal position. Tension along

the direction of polarization, or compression perpendicular to the direction of polarization,

generates a voltage with polarity opposite that of the poling voltage (Figure 1.4c).

When the mechanical stress is applied, the polarization is negative for tensile and

positive for compressive strain on the lead zirconate titanate layers. Values for compressive

stress and the voltage (or field strength) generated by applying stress to a piezoelectric

ceramic element are linearly proportional up to a material-specific stress. The same is true for

applied voltage and generated strain. [6]

If a voltage of the same polarity as the poling voltage is applied to a ceramic element,

in the direction of the poling voltage, the element will lengthen and its diameter will become

smaller (Figure 1.4d). If a voltage of polarity opposite that of the poling voltage is applied, the

element will become shorter and broader (Figure 1.4e).

Figure 2.8 Polarization of Piezoelectric Disc

8 | P a g e

2.5 Voltage and Current Output

Piezoelectric do not produce a constant steady flow voltage when a mechanical force is

applied on it. An alternating current in produced indeed. The power output by the

piezoelectric harvester is not in a form which is directly usable by normal household

appliances which the harvester powers. The voltage and current output by the harvester needs

to be conditioned and converted to a form usable by the load circuits. The power conditioning

and converting circuits should also be able to extract the maximum power available out of the

piezoelectric energy harvester.

Commonly used analog and digital circuits

require a regulated supply voltage to operate

from. Since the piezoelectric harvester outputs

a sinusoidal current, it first needs to be rectified before it can be used to power circuits. Full

wave bridge rectifier circuits are used commonly to change the the output from AC to DC

discussed below.

2.5.1 Full Wave Bridge Rectifier

Full-bridge rectifiers are commonly used as rectifier circuits to convert the AC output of a

piezoelectric harvester into a DC voltage. The rectifying circuits consist of 4 diodes. The

voltage needs to rectified due to the need for constant supply of voltage light up the series of

LED placed in parallel.

Figure 2.9 Relationship between footstep

and output voltage

9 | P a g e

2.6 Connection of Piezo

Initially, two possible connections were tested - parallel and series connections. The

parallel connection did not show significant increase in the voltage output. Series connection,

resulted in increased of voltage output but not in linear proportion. This may be due to the

non-linear modification of internal impedance of the system.

Despite parallel circuit yielding a poor outcome, the discs had to be connected in

parallel in order to not disrupt the flow of charge. This is because, even when a few disc is

stepped, the electrical charge should flow still through to the output. This same phenomenon

does not takes place if the connection is in series. Practically, its impossible for one to step on

all the discs at one time.

Figure 2.11 Full wave bridge rectifier

Figure 2.10 Ac to DC graph after rectification

10 | P a g e

2.6.1 Voltage

In this particular project, a total of 37 piezoelectric disc have been used on a 1ft wide

and 3ft length platform. Of the 37 piezos, 27 of it were connected in parallel while the

remaining ones were connected in series, in a group of 3 each. The discs connected in series

are placed at 3 spots considered to be ideal in order to boost the output voltage. [8]

As we know,

For parallel circuit :

Thus, by connecting the discs in parallel, the voltage supplied at the output is equivalent to the

voltage produced from one single disc. The recorded voltage within a range of 1.2V < Vave <

2 V. This amount of voltage was not sufficient to power and light up a series of 5 LED’s

brightly.

Therefore, 3 patched of disc in series connection were placed among the parallel piezos.

For series circuit : V = V1 + V2 +… + Vn ………………………..[8]

As expected the result was very much improved as it was possible to obtain voltage ranging

up to 19V. But, the point to note here is, the hike in voltage solely depends on the mass of the

particular person applying mechanical stress (footstep) on the disc.

2.6.2 Current

As of current, the maximum current output of one single disc is 1600 µA. The output

current from the parallel piezos were ‘0.0432 A’ which is relatively low but theoretically and

practically it was sufficient. Since in series the current is the same for all elements,

For parallel circuit : I = I1 + I2 + … = In ………………………….[8]

11 | P a g e

For series circuit :

the current output from the series circuit were constant having a range of not more than 1800

µA. All the voltage and current readings were measured using an digital multimeter.

By default, every circuits have resistance. Resistance is the controlling factor that

limits the amount of current flowing through the circuit when the circuit is closed. For

piezoelectric, the resistance is known as piezoresistive effect. Piezoresistive effect is

described as the changes in the electrical resistivity of a semiconductor when mechanical

stress is applied without affecting the electrical potential. [9]

*Assumption : Mass of 70kg was used as a control for the calculations.

2.7 Battery

Pavegen is a leading company specialized in large scale manufacturing and installation

of piezoelectric systems. Upon applying pressure on the piezoelectric, the charge is used to

light up pedestrian walk lamps and also at the same time charge the battery. When the no

longer mechanical force on the piezo, the charge from the battery is used to continue lighting

up the lamp for a certain period of time. Refer to Figure 1.7. The sensor Pavegen developed is

capable of producing power up to 8 Watt. 80% of the sensor was made up of recycled

materials.

12 | P a g e

Based on this idea, the project was carried out. In this project, the piezoelectric served

as a secondary source of power. The main source of power that lights up the LED’s and also

charges the capacitor is the battery. A 12 V- 2.3 Ah lithium ion rechargeable battery was used

for this purpose. The sole reason behind this was that, piezoelectric disc is not capable of

producing a high amount of voltage that could light up 5 LED’s.

Therefore, it was merely not possible to light up the LED’s with just the charge from

piezo alone because the amount of voltage being produced is very minimal. Series circuits

were also installed to increase the voltage of the whole system, but the output requirement

was relatively high.

2.8 Capacitor

Capacitor is a component that stores charge from external power source. It consist of

two conducting plates separated by an insulating material called the dielectric. The stored

charge is then slowly used up by discharging. A 10000 V - 25µF capacitor was used to light

up the LED. This storage capacity enables the light to discharge over the time span of 12

seconds. The capacitor is charged by the battery on a single contact.

Figure 2.12 Footstep Energy Harvesting Concept by Pavegen

13 | P a g e

To activate the process, a ‘press-on’ switch was used. The switch was placed beneath

the walking path on the wood frame. As mentioned before, the capacitor was not able to be

charged with piezo because the charge produced by the piezo is very small. Therefore,

charging the capacitor with the charge from piezo was not idealistic.

2.9 Circuit Board

A circuit board is used in electronic works for component soldering. Components for

the particular system is solder onto the circuit board according to the schematic diagram. Here

the circuit board was used to hold the resistors, LEDs, capacitor and diode. All the

components were soldered onto the circuit board. Before the components were soldered onto

the circuit board, a schematic diagram was drawn. This is to get a clearer picture of the

positions of the components.

14 | P a g e

CHAPTER 3

METHODOLOGY

3.1 Introduction

The focus of this research is to harvesting green energy from footstep. This research is

carried out by planning and identifying the methodology process since this is very important

as reference and guide to achieve the goal. Figure 3.1 is the flow chart as a guideline of the

study.

15 | P a g e

` Failed

Maximum

load

test

Figure 3.1: Methodology of study flow chart

Failed

Measuring

with

multimeter

Start

Preparing

Testing :

Data Collection

Result and Discussion

Conclusion and Recommendation

End

Circuit

board

Wood

frame

Sturdiness

Output

Analysis

16 | P a g e

3.2 Materials and Tools

Table 3.1: Materials and Tools

No Materials and Tools Figure

1.

Piezoelectric

2.

Wood

3.

Circuit board

4.

Capacitor

5.

Resistor

17 | P a g e

6.

Light-emitting diode (LED)

7.

Diode

8.

Wire

9.

Saw

18 | P a g e

10.

Hammer

11.

Nail

12.

Soldering gun

13.

Flux

14.

Hot glue gun

19 | P a g e

15.

Digital Multimeter

16.

Sandpaper

17.

Paint and brush/roller

Figure 3.2 List of materials

20 | P a g e

3.3 Product Preparation

3.3.1 Design

1) From discussion among group member, decide the size of the product and

the circuit that will be used.

Figure 3.3 Group discussion and planning

2) Draw the design by using design software (e.g. CAD, SolidWork, etc.).

Refer Appendix 1 for the Orthographic Projection View

Refer Appendix 2 for Dimension Drawing

Refer Appendix 3 for schematic diagram of circuit.

21 | P a g e

3.3.2 Building the wood frame

1) Mark the wood with the proper dimensions.

Figure 3.4 Measuring the wood before cutting process

2) Based from the mark that was done, cut the wood using saw or any other

proper tools.

Figure 3.5 Cutting wood process

3) Assemble all the part that was cut based from the design.

22 | P a g e

Figure 3.6 Assembling wood part using nails

3.3.3 Building the circuit and Piezoelectric arrangement

1) Solder the component to the circuit board based from the schematic

diagram.

Figure 3.7 Soldering the component to the circuit board

23 | P a g e

2) Connect the circuit to the Piezoelectric

Figure 3.8 Connecting the circuit to Piezoelectric

24 | P a g e

3.4 Assemble the whole circuit and the wood frame

1) Put the circuit in the compartment inside the wood frame.

Figure 3.9 Assembling the circuit and wood frame

2) Adjust the Piezoelectric location so maximum pressure would be applied on it

when being stepped on.

Figure 3.10 Arrangement of the Piezoelectric

25 | P a g e

3.5 Measuring the Electrical Output

1) Alligator clips will be fasten to the two wires from the circuit to make electrical

contact to the finished device.

Figure 3.11 Using multimeter to determine the output produced

2) The black (–) wire of the multimeter will be attached to the blue wire from the

circuit board (negative).

3) The red (+) wire of the multimeter will be attached to the red wire from the circuit

board (positive).

4) Step on the platform and observe the electrical output.

Figure 3.12 Testing the product

26 | P a g e

3.6 Finishing touch

1) Polish the product with sandpaper to obtain smooth surface.

Figure 3.13 Sand the wood surface using sandpaper

2) Paint the product so it appears attractive.

Figure 3.14 Painting the product

27 | P a g e

CHAPTER 4

RESULTS AND ANALYSIS

4.1 Introduction

When starting doing the project there are many different circuits in mind to

accomplish the goals. The project was started with a circuit that used an amplifier to boost the

electrical signal that could be from the mechanical signal. However, the theory on this circuit

was flawed, as piezoelectric do not behave this way. Thus, in order to accomplish the project,

the operation of piezoelectric must so that the design of new efficient circuit can be determine

to control the generated energy. The project was started by looking at a fly-converter with a

transformer output.

However, with this design the circuit could not control the temporary storage so it did

not meet our performance requirements. However, the next design, which utilizes a low

power, was the MOSFET for voltage sensing. The MOSFET ended up being the deciding

component as we were able to procure a low power MOSFET, as most MOSFETs require

larger power needs than we could not be able to generate, in order to activate their switching.

So, this was not the correct circuit to be installed in the project. Finally, the last design had led

us to begin investigating about the voltage-sensing switches. It is consisted of a system, which

had a converter and load. However in between, the usage of combined temporary storage and

voltage sensing circuit.

This was mainly composed of diodes and a few inductors, along with the capacitors

for storage. Therefore, we found that this circuit was practical for our project to work from

28 | P a g e

input low power to high input power which it can light the led brightly from the charging and

discharging of the capacitor and the piezoelectric.

4.2 Design circuit

Figure 4.1: Equivalent circuit for direct discharge architecture

The piezoelectric source model is connected in parallel to the bucket capacitor and

a variable resistor . When the output regulator stage of such a system is turned OFF,

represents only the leakage current through the dielectric of and the quiescent current of

the regulator and load stage.

When the load is exerted, however, depends upon the impedance of the load and the

loss in the regulator. Finally, the voltage source “2 ” models the diode drops experienced

through a diode bridge rectifier.

Typically, a circuit would require a number of current pulses from the source to charge

at start-up before the load stage is turned ON and begins to draw a significant amount of

current. Once a specified threshold is reached for the voltage , the load stage is activated

and begins to discharge assuming the current required by is greater than that provided

by the source. Moreover, is allowed to discharge to specified voltage and the cycle repeats.

There are a few important aspects of this conditioning scheme which demand

attention: Energy is transferred from the source capacitor to only after (t) has reached

the sum of the load voltage (t) and 2 and after the diode bridge begins to conduct. With

29 | P a g e

each current pulse from the source capacitor , the voltage across the capacitor will rise

quickly to the sum of (t) and 2 , and remain there for the remainder of the current pulse.

Due to the relationship Q=CV holds for both source and bucket capacitors, Q is fixed

for each current pulse and the ratio between and is necessarily high ( / = ~103), the

voltage across rises (over the same period) at one thousandth of the rate at which the

voltage across would have risen were it not loaded. These observations lead to a general

conclusion that the direct-discharge method clamps the source voltage quite low in

comparison to the natural tendency of a piezoelectric source. [12]

Now, given that the energy delivered to during each current pulse is Q=VI, and the

total charge Q liberated during each current pulse is fixed and relatively constant, clamping

the voltage is equivalent to clamping the energy over a cycle, or the power, transferred to the

load stage. Even if the capacitors perfectly matched, only one quarter of the original energy

can be transferred from one capacitor to another, and half of the total energy lost, if no other

energy storage elements are placed in between.

Moreover, the most efficient way to transfer energy off of a charging capacitor is by

allowing it reach a maximum voltage and then leak off the charge through exponential voltage

decay. That is what happens during an RC decay and, in a sense, is why supplementing a

capacitive load with a matched inductance is advantageous in ac systems.

To further illustrate this point and to quantify the inefficiency of such a system, the

following mathematical model is derived. Using the equivalent circuit in Fig 3.1, and

assuming an average load voltage < > over the charge/discharge cycle:

30 | P a g e

(3.1)

where:

and

The previous equations describe the source and load voltages during the brief period

before the rectifier diodes turn ON. The charge source is assumed to ramp linearly with each

footfall and subsequent heel lift, thereby providing an approximately square pulse of current

to and . The magnitude of this pulse is , which has length L and period T in the

following derivation.

The next series of equations result in a function describing load voltage throughout

a current pulse cycle: pulse cycle:

31 | P a g e

Now in the Laplace domain,

solving for , and letting = + and Re = || ,

Or

32 | P a g e

At the end of the current pulse, the charge across is nearly drained, so it is assumed that

negligible charge leaks through the diodes and onto the bucket capacitor after t = a.

Moreover, the voltage (t) begins to decay though , or:

Where

And

Now, the energy transferred to the load is found using the following equation:

Or

And, integrating the previous expression,

33 | P a g e

34 | P a g e

4.3 Equations/Simulations/General Circuits

4.3.1 AC/DC converter [12]

Figure 4.2: Bridge rectifier circuit

35 | P a g e

4.3.2 Capacitor charging/discharging

Figure 4.3: Voltage and current simulation on a capacitor : 15V, : 2.3A, and :

25A.

Power from one capacitor Power from power source

P=I*V P=I*V

P= 4.6A*5V P=2.3A*12V

P=23W P=27.6W

Efficiency of capacitor = Output power/Input power *100%

= 23W/27.6W *100%

= 83.33%

From simulation it is shown to be very efficient to use 10000µF in the project circuit.

36 | P a g e

CHAPTER 5

5.1 Conclusion and Recommendation

Although the theory developed in this report justifies the use of switching techniques

in efficiently converting that energy to a usable form, there are obviously some practical

limitations to the systems presented. Measurements of source current into the primary and

load current transferred from the secondary reveal that very little current gain truly occurs

between the input and output ports of the switch in the forward converter hybrid. Further,

similar results were encountered when one examines the energy transferred through the series

switch and inductor in the buck converter.

In addition, based on the results gathered in this investigation, the final prototype

design does fulfill the objective of generating electricity from piezoelectric disk. Due to the

low cost design of the piezoelectric system it is a practical product which could increase the

operating period of most common products. The data collected is capable of extending the

operational lifespan per charge of portable electronic devices.

5.2 Limitations and Assumptions

In the process of testing the viability of using piezoelectricity as a human generated

source of electricity, there were several assumption that were made. Steps were taken to

control the consistency of isolation data collected. There was care taken to ensure that the

data collected from voltage tests carried out on the piezoelectric material was reliable by

maintaining a consistent mass being applied on the piezoelectric material and the

piezoelectric disk was also fixed to a wooden plank to prevent slip and unintended voltage

spikes due to secondary impulses. Precautions taken to preserve consistency of footstep data

include the data from multiple individuals being compared and an equal number of lead up

steps up to the force plate. By comparing different footsteps against each other, it is possible

to make more generalizable conclusions by getting a wider sample size.

37 | P a g e

The final product does assume that real world conditions are accurately mimicked by

test conditions. When electrical data was collected from the output terminal the environment

and walking circumstances were made to be as similar to real life applications as possible.

5.3 Recommendation

Through testing of the final prototype, several issues became evident that needed

rectification before the production unit. In addtion, investigation into the use of more

sustainable or recycled materials should be considered if possible. Availability of material

may be an issue too, but it is more feasible at large scale. White crystalline LEDs were used

due to their brightness.

In conjunction,seals between tiles may be necessary to prevent debris or water from

entering. In fact,doubling the height of the piezoelectric stack will double the performance of

the tile, so maximizing the amount of piezoelectric material per unit area is critical during the

final sourcing of components. The lower the lost, the more feasible it is to implement more

per tile.

38 | P a g e

REFERENCES

1) Piezoelectric effect.

http://seminarprojects.com/Thread-project-on-piezoelectric-car#ixzz2QoCxRi2y,

accessed on 15th January 2013.

2) What is piezoelectricity? 2003 – 2013.

http://www.wisegeek.com/what-is-piezoelectricity.htm, accessed on 15th

January

2013.

3) Piezoelectricity.

http://en.wikipedia.org/wiki/Piezoelectricity, accessed on 16th

February, 2013.

4) Fundamentals of piezoelectricity. 2012.

http://www.piezo.ws/piezoelectric_actuator_tutorial/Piezo_Design_part2.php,

accessed on 20th

February, 2013.

5) Uses of Piezoelectric sensor. 2012.

http://answers.yahoo.com/question/index?qid=20071212185616AAEAZMV, accessed

on 22nd

February,2013.

6) Piezoelectric. APC International Limited. 2013.

http://www.americanpiezo.com/product-service/custom-piezoelectric-

elements/shapes-sizes.html, accessed on 25th

February,2013.

7) Piezoelectric ceramics. 2013. IIT-EXELIS.

http://www.exelisinc.com/capabilities/piezoelectrics/Pages/default.aspx, accessed on

25th

February,2013.

8) Series and parallel circuits.

http://en.wikipedia.org/wiki/Series_and_parallel_circuits, accessed on 26th

February,

2013.

9) Piezoresistive effect-Impedance. 2013.

39 | P a g e

http://www.ionizationx.com/index.php?topic=1232.0, accessed on 26th

February,

2013.

10) Pavegen-Pioneer in piezoelectricity.

http://www.pavegen.com/, accessed on 26th

February, 2013.

11) MOSFETs. 2013.

http://www.fairchildsemi.com/products/mosfets/, accessed on 22nd

February,2013.

12) Ramadass, Y.K., and A.P. Chandrakasan. “An Efficient Piezoelectric Energy

Harvesting Interface Circuit Using a Bias-Flip Rectifier and Shared Inductor.” Solid-

State Circuits, IEEE Journal Of 45.1 (2010)

40 | P a g e

Appendix 1 – Orthographic Projection View

41 | P a g e

Appendix 2 – Dimension Drawing

42 | P a g e

Appendix 3- Schematic Diagram