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PROJECT REPORT

ON

“ENERGY SCAVENGING FROM VIBRATIONS”

Submitted for partial fulfillment of the award of

BACHELOR OF TECHNOLOGY

DEGREE

SESSION 2010-11

In

ELECTRICAL AND ELECTRONICS ENGINEERING

By

1. VIPUL KUMAR 3.BHRAMIT AGARWAL

2. RAHUL SHARMA

Under the guidance of:- Mrs. Mona Sharma Mr. Gulshan Dubey

IMS ENGINEERING COLLEGE, GHAZIABAD

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(U.P. Technical University, Lucknow (U.P.)

CERTIFICATE

We hereby declare that the work being presented in this report entitled “Energy Scavenging from Vibrations” is an authentic record of our own work carried out under the supervision of Mrs. Mona Sharma.

The matter embodied in this report has not been submitted by us for the award of any other degree.

DATED NAME OF STUDENTS VIPUL KUMAR RAHUL SHARMA

BHRAMIT AGARWAL (Electrical and Electronics )

This is to certify that the above statement made by the candidates is correct to the best my knowledge

Mrs. Annu Govind Mrs. Mona Sharma (H.O.D.) (SUPERVISOR) Asst. ProfessorDate- (Electrical & Electronics)

Date-

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ACKNOWLEDGEMENT

The successful completion of any project and also the report is the endeavor of all the people who support, help and faster doer of the process, without which the project remains a daunting player whose might is difficult to comprehend. I would like to thank the Department of Electrical and Electronics Engg. providing a path to explore my knowledge.

We would like to express my deep sense of gratitude to Mrs. Annu Govind, HOD EN Department for giving me full support and guidance in completing the project.

Moreover we wish to take this opportunity to express our sincere thanks and gratitude to Mrs. Mona Sharma (Asst. professor) from The department of Electrical and Electronics Engineering and Mr. Gulshan Dubey(Asst. Professor) from the Electronics and Communication Engineering Dept., who is so generous in sharing his ideas and time, with extend beyond the duty of his department.

VIPUL KUMAR RAHUL SHARMA BHRAMIT AGARWAL

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ABSTRACT

The process of acquiring the energy surrounding a system and converting it into usable electrical energy is termed as power harvesting ,With piezoelectric materials ,it is possible to harvest from vibrating system .It has been proven that micro to mill watts of power can be generated from vibrating systems .

The project targets the transformation of mechanical vibration into electrical energy using piezoelectric material .The modeling and design of MEMS –scale piezoelectric based vibration energy harvester are presented. The work is motivated by the need for pervasive and limitless power for wireless sensor nodes. In some mining application, ex: water jet drilling; large high frequency vibration may be present. If successfully harvested this energy could be used to eliminate batteries in wireless sensors .This project presents a model of a piezoelectric transducer; a mechanical Vibration spectrum, the simulation of the model and prototype of power scavenging circuit.

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Contents

1. Introduction

1.1 Distributed Wireless Sensor Network

1.2 Power generation Sources

2. Objective

2.1 Background

2.2 Mechanical Vibrating System Design and Construction

2.3 Battery Charging Circuitry

3. Methodology

3.1 Vibration Energy Harvesting

3.2 Vibration Powered Generator

3.2.1 Electrostatic

3.2.2 Electromagnetic

3.2.3 Piezoelectric

3.3 Piezoelectric Generator Power

3.4 Improving Power output

3.5 Piezoelectric Energy Harvester Model

3.6 The Piezoelectric Effect

3.7 Discovery of Piezoelectric Effect

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3.8 Mathematical Description

3.9 Hooke’s Law

3.10 Materials

3.10.1 Naturally Occurring

3.10.2 Man made

4. Details of project work

4.1 Background

4.2 Principle Of operation

4.3 Micro Electrical Mechanical System (MEMS)

4.3.1 Materials for MEMS manufacturing

4.3.1.1 Silicon

4.3.1.2 Polymer

4.3.1.3 Metals

4.3.2 MEMS manufacturing Tech.

4.3.2.1 Bulk Micro mining

4.3.2.2 Surface Micro mining

4.3.2.3 HAR Silicon Micro mining

4.3.3 Application

4.4 Piezo-Electric Sensors

4.4.1 Principle of Operation

4.4.2 Electrical Properties

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4.4.3 Sensor Design

4.4.4 Sensing Material

4.5 Piezoelectric Buzzer

4.6 Super Capacitor

4.7 Zener Diode

4.8 Full Wave Rectifier

4.9 Charging Circuit

4.10 Micro Power Module

5. Result and discussion

5.1 The Future of Power Harvesting

5.2 Current Scenario

5.3 Scope

5.4 Energy Harvesting Application

6. Conclusion

6.1 Contribution from Project

6.2 Recommendation

7. References

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LIST OF FIGURES

FIGURE PAGE

1. Basic construction of vibration scavenger ………………………….15

2. Types of vibration power generation………………………………..17

3. Schematic of an electrostatic scavenger with electrets……………...18

4. Schematic of electromagnetic scavenger ……………………………18

5. Schematic of piezoelectric scavenger……………………………

6. Piezo electric effect 22

7. Inverse piezo electric effect 23

8. Piezoelectricity 33

9. Schematic symbol and electronic model of piezo sensor 35

10. Frequency response of piezo electric sensor 36

11. Spectrum of piezo device 38

12.Basic capacitor construction 39

13. Construction of different types of capacitor 40

14. EDLC charge storage mechanism 41

15. Typical configuration of EDLC cell 42

16. Zener diode 43

17. Transfer characteristics of zener 44

18. Full wave register 45

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19. Working of diode bridge 46

20. Energy harvesting circuit 46

21. Charging circuit 47

22. Micro power module 48

23. Time vs. voltage curve 48

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LIST OF SYMBOLS

Cp is the elastic constant of the piezo electric cermic. K31 is the piezo electric coupling coefficient. W is the frequency of driving vibrations. Wn the resonance frequency of generator. tc is the thickness of one layer of of the piezo electric ceramic. K2 is a geometric constant that relates average piezo electric material

strain. € is dielectric constant of piezo electric material. R is the load resistance. V is the voltage across load resistance. Cb is the capicatance of piezoelectric bimorph. D is the electrical charge density displacement. ε is permittivity . E is the electric field strength. S is strain, s is stiffness and T is stress.

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Chapter-1

Introduction

Vibration powered electronic devices have been applied in several commercial project, Such as kinetic wristwatches, smart tennis racquet and smart sport shoes. In recent years, the rapid development of micro sensors for various applications including remote environmental monitoring, automotive sensors and biomedical sensors require a miniaturized integrated distributed power supply to reduce potential problems. In many of these micro sensors, power supplies from chemical energy sources are undesirable due to limited shelf life and replacement accessibility. To solve this power supply problem, the conversion of electrical energy from a vibrating source to a renewable storage device, Such as rechargeable batteries or super capacitors can be a potential and promising alternative solution. The electrical energy stored in the storage device can be readily used for low-power ICs or integrated distributed micro sensors.

1.1 Distributed Wireless Sensor Network

Distributed wireless micro sensor network have been described as a system of ubiquitous, low cost, self organizing agent (or nodes) that work in a collaborative manner to solve complex problem. A node can be defined as “A single physical device consisting of as sensor, a transceiver, and supporting electronics, and which is connected to a larger wireless network. Advances in low power DSP’s (Digital Signal Processors) and trends in VLSI (Very Large Scale Integration) have reduced power requirement for the individual nodes. Power consumption of tens to hundreds of Micro watts is predicted. This lowered power requirement has made self powered sensors nodes a possibility. Power solution envisioned for these self powered nodes will convert ambient energy into usable electrical energy.

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1.2 Power Generation Sources

Ambient energy can be defined as energy that is not stored explicitly, but is available in the device surroundings. Various sources of ambient energy have been explored, and are discussed in following section. These sources have the advantages that they are essentially free, their conversion mechanism are clean (there is no pollution associated with the conversion process), and the source has a potentially infinite lifespan. Source types and harvesting technologies include solar, thermoelectric, acoustic energy harvesting, the axial-flow micro-turbine generator, and mechanical

vibration energy harvesting. Solar energy harvesting is the most common mechanism of energy harvesting. Solar panels consist of photovoltaic cells and can generate up to 15, 000 μW/cm2 indirect sunlight. However, their

performance rapidly reduces to 150 μW/Cm2 on a cloudy day. Thermoelectric energy harvesting devices generate electricity when placed in a temperature gradient. This is the same principle (the Seebeck effect) upon which a thermocouple works. Some published results include: 2.2 μW/cm2 is generated for Temperature difference = 5 K and 8.6 μW/cm2 for Temperature difference = 10 K.

The final mechanism of energy harvesting to be discussed, and the focus of the current research, is mechanical vibration energy harvesting. Low-level mechanical vibrations occur pervasively in the environment and high levels occur on machinery and vehicles (e.g., an automobile or aircraft).These devices can be divided into two groups :

1. Non-resonant Energy Harvester2. Resonant Energy harvester

These devices are most effective in different vibration regimes and are thus not competing, but rather complimentary configurations. The non-resonant energy harvester is more efficient where the input contains very low frequency (< 10 Hz), irregular vibrations with amplitudes larger than the

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device critical dimensions. Irregular vibrations are defined as inconsistent or discontinuous motions (such as the movements of a body).

This configuration finds application in human movement energy harvesters (for example with wearable computing applications). On the other hand, the resonant energy harvester finds application where the input vibrations are regular, frequencies are higher (> 100 Hz), and the input vibration amplitude is smaller than the device critical dimensions. Regular vibrations are continuous with stable and well defined vibration spectra, such as vibrations generated by an unbalanced machine. Resonant energy harvesters are the focus of the current Project.

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Chapter-2

Objective

2.1 Background:

Energy harvesting or the process of acquiring energy from the surrounding environment has been a continuous human endeavor throughout history, e.g. the use of watermills in ancient Greece, and of sailboats by Phoenicians and Egyptians, circa 4000 B.C. These days there is an increasing interest to harvest energy at a much smaller scale, i.e. energy scavenging. For applications such as the ones found in many embedded systems the power requirements are often small (less than 100 mW). Piezoelectric materials are great candidates for energy scavenging using vibrations from the surrounding environment, e.g. vibrations generated by the traffic through bridges, or the motions of people as they walk. Piezoelectric materials become electrically polarized when subjected to mechanical strain and the degree of polarization is proportional to the applied strain.

The project objective is to design a prototype of energy harvesting system using piezoelectric effect. The design of the prototype can be broke into following steps:-

1. The design and construction of a mechanical vibrating system2. The experimental measurements, data acquisition and analysis3. The use of an energy harvesting circuitry to charge a battery.

2.2 Mechanical vibrating system design and construction

The design component of this project is the construction of a vibrating system that will be used with experiments on energy harvesting using a

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piezo buzzer. Design a test station that generates vibrations of different amplitudes and frequencies. A gear train needs to be designed to for the vibrating system to match as closely as possible the given resonant frequency of a piezo buzzer.

2.3 Battery charging circuitry

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Chapter-3 Methodology

3.1 Vibration Energy harvesting

In order to able to convert Vibration energy into electrical energy there has to be a movement between the mechanical parts of the generator. The vibrations consist of travelling waves and it is often not possible to find a relative movement within the reach of a small generator.The most common approach to couple the mechanical movement to the generator is to an inertial system, having a spring connected to theVibrating frame and a mass suspended by the spring (Fig 1). This way, the motion of the mass with respect to the frame can be converted to power by the electromechanical generator. The generated power will be delivered to an external load.

There are three different kinds of generators that can be used:1. Electrostatic 2. Electromagnetic3. Piezoelectric

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Fig 1: Basic construction of a vibration scavenger

Below is an explanation of how the different generators work.

3.2 Vibration Powered generators

1. Electrostatic 2. Electromagnetic 3. Piezoelectric

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Fig 2: Types of Vibration power generator

3.2.1. Electrostatic

An electrostatic generator (Fig 3) consists of a variable capacitor with fin type plates and an electret1. The fins of one side of the capacitor are attached to a suspended proof mass and move with vibrations while the other side of the capacitor is fixed to the glass wafer. The electrets provides a polarization voltage, which is needed to initiallyCharge the electrodes.

Fig 3: schematic of an electrostatic scavenger with electrets

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The capacitor has a value that changes as a function of displacementas the device resonates with the vibration, the total electrical energy Stored in the capacitor increases. This redistribution of charge makes a current flow through the load, given by:

I = dQ/dt = d(C(z)V)/dt

As the plates move further apart, capacitance increases, causing an increase in current. This is harvested, stored, and as the plates contract again, the cycle is repeated. One of the main advantages of electrostatic energy converters is that their technology is compatible with CMOS technology. However, the Generators need an advanced control system in order to regulate the power switches. Also, high voltages can be generated which may harm the switches or the microelectronics.

3.2.2. Electromagnetic

The electromagnetic working principle is based on the relative motionof a magnetic mass and a coil.

Fig 4 : Schematic Of electromagnetic scavenger

An electro-motive force (e.m.f.) is induced across a coil if the magnetic flux coupled to the inductor changes as a function of time. The e.m.f. is proportional to the coil’s total number of turns, the magnetic field density and the velocity of the motion. The relationship between the e.m.f. and the displacement of the mass depends on the design of the system.

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Electromagnetic conversion has some advantages and disadvantages compared to electrostatic conversion. Its advantages are that it doesn’t need an external voltage source or electret, nor does it need controlling or sensing electronics to manage the power switches. The only thing needed to regulate the e.m.f. is a diode bridge. Its disadvantages, on the other hand, are that its fabrication techniques are not compatible with CMOS technology and the converters generate relatively low e.m.f.

3.3.3.Piezoelectric

This type of scavenger makes use of the fact that a piezoelectric materialgenerates an electric field when it is stressed mechanically.This electric field is related to stress by the materials “g” coefficients, whose units are[V/m]/[ N/m2].

g = Open circuit electric field/ applied mechanical stress

Output voltage is calculated by multiplying the electric field by the thickness of ceramic between electrodes. The piezoelectric layer is polarized by applying a field through the electro- -des after heating it up to 150°C. It is necessary to polarize both sides at once since heating one side will result in heating of the other side. It is not possible to connect the piezoceramic element directly between the mass and the frame because it is a stiff material and would result in having a generator with a very high resonance frequency. That’s why the generator is often mounted on a long thin cantilever beam: as the beam/mass structure oscillates, the piezoelectric layer adhered to the surface of the beam deforms and causes a charge to be displaced across the capacitor electrodes positioned on the top and bottom surfaces of the piezoelectric elements. A voltage then appears across the capacitor and a current will flow through the load. Roundy and colleagues have shown that piezoelectric scavengers produce highest level of practical power output.

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Fig 5: schematic Of piezoelectric scavenger

3.3 Piezoelectric Generator Power

When a resistor is connected across the device electrodes, the relationship for power output as a function of input vibration amplitude and frequency is:

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Power output is maximized when the driving frequency is operating at the resonance frequency of the generator. That frequency depends on the stiffness and the mass of the beam according to:

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3.4 Improving power Output

There are three basic approaches to improving power output from aPiezoelectric cantilever scavenger:-

The first is to modify the cantilever geometry to produce more strain. This can be accomplished by making a cantilever beam which is longer and narrower or by increasing the proof mass. But because of the brittle nature of piezoelectric ceramics, too much strain will damage them. Second approach is to increase the width/thickness of the piezoelectric material, but this stiffens the beam, reducing overall strain and increasing resonant frequency. Most biomedical applications target frequencies in the 10s of Hz, so a low resonant frequency is essential.The third approach seems to be the most viable: tuning the resonant frequency of the device to match the frequency of excitation. In cases where the excitation frequency changes (which is true in most practical applications— particularly biomedical), this calls for either wide-bandwidth designs which are optimized for a wider range of frequencies or adaptive self-tuning mechanisms which can detect excitation frequencies and adjust the cantilever’s resonant frequency to match. The only practical wide-bandwidth design approach involves multiple cantilevers with different resonant frequencies. The obvious problem with this approach is that it increases size and decreases the power-to-volume ratio. Since size is of utmost importance in a biomedical application, we are left with adaptive Self tuning. There are two methods of self tuning, which Roundy calls “active” and “passive”. Active tuning mechanisms run continuously to match the cantilever’s resonant frequency to the excitation frequency. Electronic springs are an example. Passive tuning mechanisms tune the cantilever and then turn off. In other words, no power is required to maintain the desired resonant frequency once it has been set. An example would be a variable/moveable proof mass or a mechanism that adjusts the length of the beam. It has been mathematically shown that active tuning mechanisms will never be practical because the power gains they provide will never be enough to offset the power they require to operate . Therefore, passive tuning is the only viable approach.

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3.5 Piezoelectric Energy Harvester Model

This project represent the design and fabrication of piezoelectric power generator to be used as a power source for MEMS(Micro Electrical Mechanical Systems).The system scavenges environmental vibrations and convert it into electrical power through a piezoelectric transduction. Coupled electromechanical models are developed for design and performance prediction of a micro-scale piezoelectric energy harvester and for validation to macro-scale harvester experiments.

3.6 The Piezoelectric Effect

Piezoelectricity is the ability of certain materials to produce a voltage when subjected to a mechanical stress .When these materials are subjected to a mechanical force, their crystal become electrically polarized. The polarities for the tensile and compressive forces are opposite and the polarity is proportional to the applied force. The converse relationship is also true: When the crystalline material is subjected to an electric field it lengthens or shortens according to the polarity of the electric field. The latter is known as the inverse piezoelectric effect. Materials with crystals that have a dipole are termed piezoelectric materials.

Fig 6 : Piezoelectric Effect

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Fig 7 : Inverse Piezoelectric Effect

3.7 Discovery of Piezoelectric Effect

The effect known as piezoelectricity was Discovered by brothers Pierre and Jacques Curie when they were 21 and 24 years old in 1880. Pierre Curie (15 May 1859 – 19 April1906) was a French physicist who received a Nobel prize in Physics in 1903. Piezoelectric effect can be understood as the linear electro mechnical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. Piezoelectricity is found in useful applications such as the production and

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detection of sound, generation of high voltages, electronic frequency generation, microbalances, and ultrafine focusing of optical assemblies. It is also the basis of a number of scientific instrumental techniques with atomic resolution.

3.8 Mathematical Description

Piezoelectricity is the combined effect of the electrical behavior of the material

Where D is the electrical charge density displacement, ε is permittivity and E is the electric field strength.

3.9 Hooke’s Law

Where S is strain, s is stiffness and T is stress.

These may be combined into so called coupled equations, of which the strain charge form is

where [d] is the matrix for the direct piezoelectric effect and [dt] is the matrix for the converse piezoelectric effect. The superscript E indicates a zero, or constant, electric field; the superscript T indicates a zero, or constant, stress field; and the subscript t stands for transposition of a matrix.

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3.10 Materials

Many material both natural and man made , Exhibit piezoelectricity

3.10.1 Naturally-occurring crystals

Berlinite  (AlPO4), a rare phosphate mineral that is structurally identical to quartz

Cane sugar Quartz Rochelle salt Topaz Tourmaline-group minerals

3.10.2 Man-made crystals

Gallium orthophosphate  (GaPO4), a quartz analogic crystal Langasite  (La3Ga5SiO14), a quartz analogic crystal

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Chapter-4

Details of Project report work

4.1 Background

Energy harvesting or the process of acquiring energy from the surrounding environment has been a continuous human endeavor throughout history, e.g. the use of watermills in ancient Greece, and of sailboats by Phoenicians and Egyptians, circa 4000 B.C. These days there is an increasing interest to harvest energy at a much smaller scale, i.e. energy scavenging. For applications such as the ones found in many embedded systems the power requirements are often small (less than 100 mW). Piezoelectric materials are great candidates for energy scavenging using vibrations from the surrounding environment, e.g. vibrations generated by the traffic through bridges, or the motions of people as they walk. Piezoelectric materials become electrically polarized when subjected to mechanical strain and the degree of polarization is proportional to the applied strain.

4.2 Project Overview and Design Content

The design process can be broke into following steps:-

1. The design and construction of a mechanical vibrating system.

2. The experimental measurements.

3. The use of an energy harvesting circuitry to charge a battery.

4.2 Principle of Operation

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Any vibration based energy harvester can be primarily divided into three parts. The first part consists of the power generator module which converts the ambient mechanical energy into an electrical equivalent energy. The second part is the power processor module that effectively processes the converted energy into a form of DC power. The final module is the power storage architecture which stores the generated power into a battery or a capacitor efficiently for application specific end use. The fundamental concept for piezoelectric energy harvesting involves a piezoelectric layer attached to a vibrating mechanical structure that converts the strain energy into induced electric charge. Joule Thief TM is made up of a composite beam that consists of a cantilever shim with an attached piezoelectric layer and a proof mass at its end. The device when directly attached to a vibrating surface, places the whole structure in an accelerating frame of reference. The proof mass essentially converts the input base acceleration into an effective inertial force at the tip that deflects the beam, thereby inducing mechanical strain in the piezoelectric layer. This strain produces an effective voltage in the layer that is converted into usable power with the help of a power processor.

The cantilever configuration is chosen over other designs such as circular plate/membrane configurations or fixed-fixed plate/beam designs. The primary reason for this choice is based on the goal to maximize the stress/strain in the piezoelectric layer for a given fixed vibration input. Since the ambient surroundings have a definite amount of energy in amplitude and frequencies, the fundamental optimization in the mechanical device would be to generate maximum power for a given source. Consequently, the need to maximize the strain the piezoelectric layer is essential as the voltage generated in the piezoceramic is proportional to the strain induced.

AdaptivEnergy’s Joule-Thief™ achieves exactly the same requirement using their core RLP® technology. AdaptivEnergy has spent years of research in developing a lamination technique for producing stress biased piezoelectric composites in various sizes and shapes. The stress biasing technique effectively places the piezoceramic element in the device under compression. Therefore, the operation range and strain limits for failure for

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the piezoelectric layer is extended further. Consequently, the device exceeds in performance and reliability resulting in a robust product that can survive harsh environments for extended periods of time. This unique feature of RLP® products provides a great advantage over other systems.

4.3 Micro Electrical Mechanical Systems (MEMS)

Micro Electro-mechanical systems (MEMS) (also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems) is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines (in Japan), or Micro Systems Technology - MST (in Europe).MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micrometers in size (i.e. 0.001 to 0.1 mm) and MEMS devices generally range in size from 20 micrometers (20 millionths of a metre) to a millimeter. They usually consist of a central unit that processes data, the microprocessor and several components that interact with the outside such as micro sensors. At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate volume effects such as inertia or thermal mass.

4.3.1 Materials for MEMS manufacturing

4.3.1.1 Silicon

Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS

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applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking. The basic techniques for producing all silicon based MEMS devices are deposition of material layers, patterning of these layers by photolithography and then etching to produce the required shapes.

4.3.1.2 Polymers

Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to produce. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding, embossing or stereo lithography and are especially well suited to micro fluidic applications such as disposable blood testing cartridges.

4.3.1.3 Metals

Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability.

Metals can be deposited by electroplating, evaporation, and sputtering processes.Commonly used metals include gold, nickel, aluminum, copper, chromium, titanium, tungsten, platinum, and silver.

4.3.2 MEMS manufacturing Technologies

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4.3.2.1 Bulk micromachining

Bulk micromachining is the oldest paradigm of silicon based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures. Silicon is machined using various etching processes. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that have changed the shape of the sensor industry in the 80's and 90's.

4.3.2.2 Surface micromachining

Surface micromachining uses layers deposited on the surface of a substrate as the structural materials, rather than using the substrate itself. Surface micromachining was created in the late 1980s to render micromachining of silicon more compatible with planar integrated circuit technology, with the goal of combining MEMS and integrated circuits on the same silicon wafer. The original surface micromachining concept was based on thin polycrystalline silicon layers patterned as movable mechanical structures and released by sacrificial etching of the underlying oxide layer. Interdigital comb electrodes were used to produce in-plane forces and to detect in-plane movement capacitively. This MEMS paradigm has enabled the manufacturing of low cost accelerometers for e.g. automotive air-bag systems and other applications where low performance and/or high g-ranges are sufficient. Analog Devices have pioneered the industrialization of surface micromachining and have realized the co-integration of MEMS and integrated circuits.

4.3.2.3 High aspect ratio (HAR) silicon micromachining

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Both bulk and surface silicon micromachining are used in the industrial production of sensors, ink-jet nozzles, and other devices. But in many cases the distinction between these two has diminished. A new etching technology, deep reactive-ion etching, has made it possible to combine good performance typical of bulk micromachining with comb structures and in-plane operation typical of surface micromachining. While it is common in surface micromachining to have structural layer thickness in the range of 2 µm, in HAR silicon micromachining the thickness can be from 10 to 100 µm. The materials commonly used in HAR silicon micromachining are thick polycrystalline silicon, known as epi-poly, and bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also have been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining. The consensus of the industry at the moment seems to be that the flexibility and reduced process complexity obtained by having the two functions separated far outweighs the small penalty in packaging. A comparison of different high-aspect-ratio microstructure technologies can be found in the HARMST article.

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4.3.3 Applications

In one viewpoint MEMS application is categorized by type of use.

Sensor

Actuator

Structure

In another view point MEMS applications are categorized by the field of application (commercial applications include):

Inkjet printers, which use piezoelectric or thermal bubble ejection to deposit ink on paper.

Accelerometers in modern cars for a large number of purposes including airbag deployment in collisions.

Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone, various Nokia mobile phone models, various HTC PDA models)[11] and a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs to park the hard disk head when free-fall is detected, to prevent damage and data loss.

MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger dynamic stability control[12]

Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors

Displays e.g., the DMD chip in a projector based on DLP technology, which has a surface with several hundred thousand micro mirrors

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Optical switching technology, which is used for switching technology and alignment for data communications

Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemo sensor)

Interferometric modulator display (IMOD) applications in consumer electronics (primarily displays for mobile devices), used to create interferometric modulation - reflective display technology as found in mirasol displays.

4.4 Piezoelectric Sensors

Piezoelectric sensor is a device that uses the piezoelectric effect to measure pressure, acceleration, Strain or force by converting them to an electrical signal. In this project we are using a Piezo buzzer to convert Vibration present in the environment to electricity.

Fig 8 : Piezoelectricity

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4.4.1 Principle of Operation

Depending on how a piezoelectric material is cut, three main modes of operation can be distinguished:transverse, longitudinal, and shear.

1. Transverse EffectA force is applied along a neutral axis (y) and the charges are generated along the (x) direction, perpendicular to the line of force. The amount of charge depends on the geometrical dimensions of the respective piezoelectric element. When dimensions a,b,c apply, Cx = dxyFyb / a,where a is the dimension in line with the neutral axis, b is in line with the charge generating axis and d is the corresponding piezoelectric coefficient

2. Longitudinal EffectThe amount of charge produced is strictly proportional to the applied force and is independent of size and shape of the piezoelectric element. Using several elements that are mechanically in series and electrically in parallel is the only way to increase the charge output. The resulting charge is Cx = dxxFxn,where dxx is the piezoelectric coefficient for a charge in x-direction released by forces applied along x-direction (in pC/N). Fx is the applied Force in x-direction [N] and n corresponds to the number of stacked elements .

3. Shear EffectAgain, the charges produced are strictly proportional to the applied forces and are independent of the element’s size and shape. For n elements mechanically in series and electrically in parallel the charge is Cx = 2dxxFxn.In contrast to the longitudinal and shear effects, the transverse effect opens the possibility to fine-tune sensitivity on the force applied and the element dimension.

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4.4.2 Electrical Properties

A piezoelectric transducer has very high DC output impedance and can be modeled as a proportional voltage source and filter network. The voltage V at the source is directly proportional to the applied force, pressure, or strain. The output signal is then related to this mechanical force as if it had passed through the equivalent circuit. The inductance Lm is due to the seismic mass and inertia of the sensor itself. Ce is inversely proportional to the mechanical elasticity of the sensor. C0 represents the static capacitance of the transducer, resulting from an inertial mass of infinite size. I is the insulation leakage resistance of the transducer element. If the sensor is connected to a load resistance, this also acts in parallel with the insulation resistance, both increasing the high-pass cutoff frequency.For use as a sensor, the flat region of the frequency response plot is typically used, between the high-pass cutoff and the resonant peak. The load and leakage resistance need to be large enough that low frequencies of interest are not lost. A simplified equivalent circuit model can be used in this region, in which Cs represents the capacitance of the sensor surface itself, determined by the standard formula for capacitance of parallel plates. It can also be modeled as a charge source in parallel with the source capacitance, with the charge directly proportional to the applied force.

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Fig 9 : schematic symbol and electronic model of a piezoelectric sensor4.4.3 Sensor Design

Based on piezoelectric technology various physical quantities can be measured; the most common are pressure and acceleration. For pressure sensors, a thin membrane and a massive base is used, ensuring that an applied pressure specifically loads the elements in one direction. For accelerometers, a seismic mass is attached to the crystal elements. When the accelerometer experiences a motion, the invariant seismic mass loads the elements according to Newton’s second law of motion F = ma. The main difference in the working principle between these two cases is the way forces are applied to the sensing elements. In a pressure sensor a thin membrane is used to transfer the force to the elements, while in accelerometers the forces are applied by an attached seismic mass. Sensors often tend to be sensitive to more than one physical quantity. Pressure sensors show false signal when they are exposed to vibrations. Sophisticated pressure sensors therefore use acceleration compensation elements in addition to the pressure sensing elements. By carefully matching those elements, the acceleration signal (released from the compensation element) is subtracted from the combined signal of pressure and acceleration to derive the true pressure information.Vibration sensors can be used to harvest otherwise wasted energy from mechanical

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vibrations. This is accomplished by using piezoelectric materials to convert mechanical strain into usable electrical energy.

Fig 10: Frequency response of a piezoelectric sensor

4.4.4 Sensing Material

Two main groups of materials are used for piezoelectric sensors:

1.Piezoelectric ceramics 2.Single crystal materials

The ceramic materials (such as PZT ceramic) have a piezoelectric constant sensitivity that is roughly two orders of magnitude higher than those of single crystal materials and can be produced by inexpensive sintering processes. The piezoeffect in piezoceramics is "trained", so unfortunately their high sensitivity degrades over time. The degradation is highly correlated with temperature. The less sensitive crystal materials (gallium phosphate, quartz, tourmaline) have a much higher – when carefully handled, almost infinite – long term stability

4.5 Piezoelectric Buzzer

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A Piezo buzzer is made from two conductors that are separated by Piezo crystals. When a voltage is applied to these crystals, they push on one conductor and pull on the other. The result of this push and pull is a sound wave. These buzzers can be used for many things, like signaling when a period of time is up or making a sound when a particular button has been pushed. The process can also be reversed to use as a guitar pickup. When a sound wave is passed, they create an electric signal that is passed on to an audio amplifier.In this project a vibrating Module interact with the Piezo buzzer and it convert Mechanical Vibrations into Electricity.

Electrical Specifications:• Sound Pressure Level: 97dB min. / 30cm / 9VDC• Oscillating Frequency: abt. 2.9 or 3.05KHz / 9VDC• Current Consumption: 20mA max. / 9VDC• Operating Voltage: 5 to 20VDC.

Mechancial Specifications:• Operating Temperature: -20°C to +70°C• Storage Temperature: -40°C to +85°C

Materials:• Case: PC (UL 94V-2)• Lead Wire: UL 1007 26AWG• Weight: 15.0 gms• Tone: Dual

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Fig 11 : Spectrum of a piezo device

The time signal shows the voltage output when the piezo device is subjected to motion with a vibrator built by the instructors. The frequency

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signal (the spectrum) shows the frequency components or content of the time signal.

4.6 Super Capacitor

Capacitor is a device that can store electrical charge.In a capacitor equal amount of positive and negative charges are stored on two separate conductors.

Fig 12 : Basic capacitor construction

In this project we are using a super capacitor for Charge storage.

Capacitors have two main application:- One of which is a function to charge or discharge electricity. Other function is to block the flow of DC.

Super capacitor or Electric double layer capacitor (EDLC), where the electric charge stored at a metal/electrolyte interface is exploited to construct a storage device. The interface can store a Electric charge in

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order of ~1000000 farad. They are complementary to batteries as they deliver high power density and low energy density. They also have longer cycle life than batteries and possess higher energy density as compared to conventional capacitors. This has led to new concepts of the so-called hybrid charge storage devices in which electrochemical capacitor is interfaced with a fuel cell or a battery. These capacitors using carbon as the main electrode material for both anode and cathode with organic and aqueous electrolytes are commercialized and used in day to-day applications the main electrode material for both anode and cathode with organic and aqueous electrolytes are commercialized and used in day to-day applications.

Fig 13 : Construction of Different type of capacitors

Electric/electrochemical double layer capacitor (EDLC) is a unique electrical storage device, which can store much more energy than conventional capacitors and offer much higher power density than batteries. EDLCs fill up the gap between the batteries and the conventional capacitor, allowing applications for various power and energy requirements i.e., backup power sources for electronic devices, load-leveling, engine start or acceleration for hybrid vehicles and electricity storage generated from solar or wind energy. EDLC works on the principle of double-layer capacitance at the electrode/electrolyte interface where electric charges are accumulated on the electrode surfaces and ions of opposite charge are arranged on the electrolyte side.

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Fig 14 : EDLC charge storage mechanism

There are two main types of double layer capacitors as classified by the charge storage mechanism: (1) Electrical double-layer capacitor(2) Electrochemical double layer capacitor or super/pseudo-capacitor

An EDLC stores energy in the double-layer at the electrode/electrolyte interface, whereas the super capacitor sustains a Faradic reaction between the electrode and the electrolyte in a suitable potential window. Thus the electrode material used for the construction of the cell for the former is mainly carbon material while for the latter, the electrode material consist of either transition metal oxides or mixtures of carbon and metal oxides/polymers. The electrolytes can be either aqueous or Non-aqueous depending on the mode of construction of EDLC cell.

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Fig 15 : Typical configuration of an EDLC cell

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4.7 ZENER Diode

A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage". The device was named after Clarence Zener, who discovered this electrical property.A conventional solid-state diode will not allow significant current if it is reverse-biased below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. In case of large forward bias (current in the direction of the arrow), the diode exhibits a voltage drop due to its junction built-in voltage and internal resistance. The amount of the voltage drop depends on the semiconductor material and the doping concentrations.A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage. By contrast with the conventional device, a reverse-biased Zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the Zener diode close to the Zener breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2 V will exhibit a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The Zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.

Fig 16 : Zener Diode

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Fig : 17 Transfer characteristic Of zener DiodeCurrent-voltage characteristic of a Zener diode with a breakdown voltage of 17 volts. In the project we are using a ZENER Diode in the Energy harvesting Circuit For the protection of Super Capacitor. It is connected in parallel with the super capacitor.

4.8 Full Wave RectifierA rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which is in only one direction, a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components. A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center tapped transformer, four diodes are required

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instead of the one needed for half-wave rectification.Four diodes arranged this way are called a diode bridge or bridge rectifier

Fig 18 : Full wave Rectifier

The average and root-mean-square output voltages of an ideal single phase full wave rectifier can be calculated as:

Fig 19: Working of Diode Bridge

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Energy generated from the piezo buzzer is A.C.But for the Charging of battery we need DC energy.So a Diode bridge is used to convert DC from AC.

4.9 Charging Circuit

Fig 20:Energy harvesting Circuit

A super capacitor (0.47F 5.5v) is used to store electric Charge.A Zener diode (BZX85‐C5V6) is used to protect the super capacitor .

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Fig 21 : Charging Circuit

4.10 Micro power Module

Consists of the piezoelectric scavenger and an energy storage system composed of a super capacitor and a rechargeable battery . The AC/DC converter consists of a rectifier built with diodes.

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Fig 22 : Micro Power Module

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Chapter-5

Result and Discussion

The goal of this project was to build an energy harvesting device that would charge a battery over a period of a half hour. We realized that our design would both have to produce a charge and hold together for a half hour while getting vibrated the whole timeDifferent voltages are given to Vibrating structure to change the Vibrating Frequency. Once we found out which voltage did best with both of our designs, it was time to see which of the two would charge the battery best.

0 5 10 15 20 25 30 350

0.2

0.4

0.6

0.8

1

1.2

1.4

Time V.S. Volts

Time(Min)

Volts

(V)

Fig 23 : Time Vs Voltage curve

The graphs below show the data points of the battery’s charge every 5 minutes till we reached the half hour mark.

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5.1 The Future of Power Harvesting

The idea of carrying electronic devices such as a portable radio and never worrying about when the batteries will need to be replaced could be far closer than one would think. This thought has caused the desire for self powered electronics to grow quickly, leaving only one limitation before these devices can become a reality. The one issue that still needs to be resolved is a method to generate sufficient energy to power the necessary electronics. However, with the advances in power harvesting that have been outlined in this paper the ability to obtain and accumulate the necessary amount of energy to power such devices is clearly possible. The major limitations facing researchers in the field of power harvesting revolve around the fact that the power generated by piezoelectric materials is far too small to power most electronics. Therefore, methods of increasing the amount of energy generated by the power harvesting device or developing new and innovative methods of accumulating the energy are the key technologies that will allow power harvesting to become a source of power for portable electronics and wireless sensors. One recent advance that shows great promise for power harvesting is the use of rechargeable batteries as a means of accumulating the energy generated during power harvesting. Much of the early research into power harvesting looked to the capacitor as a method of storing energy and powering electronics. However, the capacitor has poor power storage characteristics due to its quick discharge time, causing the electrical output of such circuitry to switch on and off as the capacitor charges and discharges. This aspect of the capacitor is not suitable for powering computational electronics. However, the rechargeable battery can be charged and then used to run any number of electronic devices for an extended period of time while being continuously charged by ambient motion. Innovations in power storage such as the use of rechargeable batteries with piezoelectric materials must be discovered before power harvesting technology will see widespread use.Furthermore, the efficiency of the power harvesting circuitry must be maximized to allow the full amount of energy generated to be transferred to the storage medium. The continuous advances that are being made in low power electronics must be studied and utilized to both optimize power flow from the piezoelectric and minimize circuit losses. Gains in this area are a necessity for the successful use of piezoelectric materials as power harvesting devices.

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Additionally, the intended location of the power harvesting system must be identified so that its placement can be optimized and the excitation range realized to allow for tuning of the power harvesting device. By tuning the power harvesting medium with the structure the excitation can be made to maximize the strain of the piezoelectric material using the concept of resonance.Finally, practical applications for power harvesting systems such as wireless sensors and self-power damage detection units must be clearly identified to encourage growth in this area of research, thus allowing the contributions and in flow of ideas to increase. With the advances in wireless technology and low power electronics, power harvesting is the missing link for completely self-power systems.

5.2 Current ScenarioOrganizations active in either carrying out research on Energy Harvesting technologies or in developing energy harvesting products and integrating energy harvesting into sensing element.

University of Southampton: school of electronics and computer scienceThis university has a long record in energy harvesting research and one of the largest team in the world .The team has investigated various energy harvesting techniques and made a number of break through .The group developed a generator, which is 10 times more powerful than any other similar device and is less than 1 cm3 in size.

Imperial college London,Dept. of electrical and electronics engg.The control and power group at imperial college covered several areas, including MEMS, integrated circuits and multi domain system modeling. The group have demonstrated the first working electrostatic and also invented a type of generator architect that is insensitive to frequency and presented a unified analytic framework.

Commercial Organizations:-

Perpetuum Ltd.Perpetuum is a world-leading vibration energy harvesting company funded in 2004.The products use electromagnetic energy harvesting techniques offering a good combination of simplicity ,low cost and reliable operation. Examples include installation at shell gas plant in Norway.

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WEB : www.perpetuum.com

Piezotag Ltd.(Conventry, UK)Piezotag has developed a tyre pressure Monitoring system that is based on the piezoelectric effect-energy is harvested from the roatation of the tyre.The system transmits RF signals from the wheels to a receiver every 6s advising the driver of the current temperature and pressure of the tyres.

5.3 ScopeEnergy harvesting technologies such as piezoelectric, thermoelectric and others will have potential applications in wireless sensor networks and low-power devices. Although micro-level energy harvesting technologies are very new compared to batteries, they can initially be used to recharge batteries and gradually replace them as self-sufficient devices, By replacing batteries, these devices eliminate toxic waste from disposed batteries and provide the perfect solution to many countries that are implementing stringent rules to monitor power consumption and environmental waste." As energy harvesting technologies harness ambient and renewable sources of energy, growing awareness among consumers to use environmental friendly technology further strengthens demand. Low output power and below-par efficiency of energy harvesting systems currently limit the application scope of energy harvesting technology. It faces difficulty in penetrating the market as it is still in the early prototyping or early commercialization stage, as opposed to battery technology, which is well established. Along with developments in materials and control electronics, researchers and manufacturers concentrate their efforts on the exploration of various kinds of energy sources and improve the performance characteristics. Starting with low-power sensor applications, they can be gradually used to power portable devices and utilized in buildings for lighting and temperature control. Additionally, improvements in energy harvesting technologies would allow these devices to provide reliable and constant power for industrial, automotive, aerospace, defense and medical applications. Although the future looks promising for these emerging eco-friendly energy harvesting technologies, their acceptance in the market depends on many factors such as performance metrics, consumer awareness of harnessing ambient energy, funding for R&D and collaboration between manufacturers and technology developers. Energy

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harvesting technology will be able to establish itself in the market place on dealing with most of these aspects.

5.4 Energy harvesting Application

Advances in low power technology are making it easier to create wireless sensor networks in a wide range of applications, from remote sensing to HVAC monitoring, asset tracking and industrial automation. The problem is that even wireless sensors require batteries that must be regularly replaced—a costly and cumbersome maintenance project. A better wireless power solution would be to harvest ambient mechanical, thermal or electromagnetic energy from the sensor’s local environment.

The vibration of the helicopter structure can be used to power low-power wireless electronic systems used in the HUMS modules. Health and Usage Monitoring Systems (HUMS)contain sensors for monitoring the external state of helicopters.

DARPA(Defense advanced research project agency) program concerns power MEMS designed to harvest vibration energy from the movement of wings. The main driver of this program is to eliminate the size and weight issues caused by the battery.

Piezoelectric Energy harvesting can be used for Bio-Mems devices as a Biomechanical Energy Harvester.

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Fig 24 : Biomedical Energy Harvester

Self powered Wireless Sensors.

Fig 25 : Self Powered Wireless sensors

Wireless corrosion monitoring System

Fig 26 : Corrosion Monitoring system

vibrating structure

frequency

Acc

el. P

SD

mechanical energy

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Chapter-6

Conclusion

There is little doubt that the field of vibration energy harvesting continues to expand apace. With the predicted proliferation of wireless sensor networks, an alternative (or at least complementary) approach to battery power is required. If there are sufficient ambient vibrations available, then it is possible to generate an electrical supply by using a micro-generator to harvest the mechanical excitation. There are three main approaches that can be used to implement a vibration-powered generator. Each of the technologies described in this review has their own advantages and disadvantages and these are now summarized.

Piezoelectric GeneratorThese offer the simplest approach, whereby structural vibrations are directly converted into a voltage output by using an electrode piezoelectric material. There is no requirement for having complex geometries and numerous additional components. Piezoelectric generators are the simplest type of generator to fabricate and can be used in force and impact coupled harvesting applications. There is a wide range of piezoelectric materials available for different application environments. One major advantage is that this transduction principle is particularly well suited to micro engineering, since several processes exist for depositing piezoelectric films (thin and thick). The piezoelectric method is capable of producing relatively high output voltages but only at low electrical currents. The piezoelectric materials are required to be strained directly and therefore their mechanical properties will limit overall performance and lifetime. Also the transduction efficiency is ultimately limited by piezoelectric properties of materials employed. The output impedance of piezoelectric generators is typically very high (>100 k).

Electromagnetic GeneratorThese offer a well-established technique of electrical power generation and the effect has been used for many years in a variety of electrical generators. There is a wide variety of spring/mass configurations that can be used with various types of material that arewell suited and proven in cyclically stressed applications. Comparatively high output current levels are

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achievable at the expense of low voltages (typically <1 V). High-performance bulk magnets and multi-turn, macro-scale coils are readily available.Wafer-scale systems, however, are quite difficult to achieve owing to the relatively poor properties of planar magnets, the limitations on the number of turns achievable with planar coils and the restricted amplitude of vibration (hence magnet/coil velocity). Inevitably, there are also problems associated with the assembly and alignment of sub-millimetre scale electromagnetic systems.

Electro-Static Generator

The electrostatic concept is easily realizable as a MEMS and much processing know-how exists on the realization of inplane and out-of-plane capacitors. Energy density of the generator can be increased by decreasing the capacitor spacing, facilitating miniaturization. The energy density, however, is also decreased by reducing the capacitor surface area. High transduction damping, at low frequencies, is achievable by incorporating small capacitor gaps and high voltages.Unfortunately, electrostatic generators require an initial polarizing voltage or charge. This is not an issue in applications that use the generator to charge a battery, as this can be used to provide the necessary initial excitation level. Electrostatic generators can utilize electrets to provide the initial charge and these are capable of storing charge for many years. The output impedance of the devices is often very high and this makes them less suitable as a power supply. The output voltage produced by the devices is relatively high (>100 V) and often results in a limited current-supplying implementation.The three main techniques of harvesting energy from ambient vibrations have been shown to be capable of generating output power levels in the range of μW to mW. A few years ago, such energy levels would have been considered as ‘unusable’. Modern-day VLSI circuit designs, however, are being built with low-power operation in mind and many commercial circuits can now be used with energy harvesting solutions. Take, as an example, the electronic calculator whose early form required several ‘AA’ sized cells, but are now capable of running wholly off solar power. Vibration-powered wireless sensor systems can be used in numerous scenarios and several research groups across the world are addressing possible uses in ambient intelligence, medical implants and smart clothing. Wireless, battery-less industrial condition monitoring systems are already close to commercialization.

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6.1 Contribution from this project

Ambient vibration sources were measured and it was found that vibration levels Suitable for harvesting exist in the frequency range below 300 Hz. A simple dissipative model was developed to interpret the vibration spectra. Based on the dominant damping terms of the structure, optimal input vibration frequencies(operating points) are identified (for maximum power harvesting), to which the resonant energy harvester resonance frequencies are aligned. Damping dependency on frequency is carefully considered. The selected operating point will depend on the device size (micro- vs. macro scale) and the operating environment (e.g., vacuum or atmospheric), since the dominant damping components differ for these conditions.Only piezoelectric material properties that affect the maximum power generated are the elastic stiffness and density. Since these properties vary little for typical piezoelectric ceramics, the choice of material will have little affect on the maximum power extracted. Furthermore, the piezoelectric mode of operation has negligible effect on the maximum power extracted. However, the electrical response (voltage and current) is dependent on the piezoelectric coupling. The piezoelectric material choice and mode of operation will have a significant effect on the voltage/current performance and need to be considered once application-specific electrical requirements are imposed.

6.2 Recommendations

Low-level, low-frequency vibrations in the ambient have been targeted for harvesting in this project. The resonant frequencies of the harvester need to be aligned to this low frequency. High quality factors are achievable with MEMS resonators. However, for high quality factors, very narrow response peaks are obtained, which need to be aligned with the dominant frequency component of the vibration source. Given the variability of ambient sources and micro fabrication processes, it is likely desirable to incorporate a frequency-tuning mechanism into the harvester design.

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This Project has focused on the design and modeling of a single harvester, which is a component of the power sub-system of the wireless node. The next step is to implement the harvester design with the rest of the power sub-system, consisting of conditioning circuitry and a storage device (battery), among others.

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Chapter-7 References

1.M. Raju, “Energy Harvesting, ULP meets energy harvesting: A game-changing combination for design engineers,” Texas Instrument White Paper, Nov. 2008

2.R.J.M. Vullers, V. Leonov, T. Sterken, A. Schmitz, “Energy Scavengers For Wireless Intelligent Microsystems,” Special Report in Microsystems & Nanosystems, OnBoard Technology, June 2006

3.Imec, “Design for analog and RF technologies and systems,” www.imec.be

4.Imec, “Micropower generation and storage,” www.imec.be

5.F. Whetten, “Energy Harvesting Sensor Systems – A Proposed Application for 802.15.4f, ” DOC: IEEE802.15-09/0074-00-004f

6.C. Cossio, “Harvest energy using a piezoelectric buzzer,” EDN, pg.94-96, March 20, 2008

7.“Vibration Scavenger” http://www.powermems.be/scavenger.html

8.M. S. M. Soliman, E. F. El-Saadany, Raafat R. Mansour. “Electromagnetic and Electrostatic Micro-Power Generators; an Overview”. IEEE Proc. of Intl. Conf onMechatronics and Automation. 2005.

9. Sterken T, Baert K.1, Van Hoof C, Puers R, Borghs G, Fiorini P. “Comparative Modeling for Vibration Scavengers”. IEEE Proc. of Sensors. 2004.

10. “Piezoelectric Terminology” http://www.piezo.com/tech1terms.html 11.Roundy, S.; Leland, E.S.; Baker, J.; Carleton, E.; Reilly, E.; Lai, E.; Otis, B.;

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Rabaey, J.M.; Wright, P.K.; Sundararajan, V. “Improving Power Output forVibration-Based Energy Scavengers”. IEEE Pervasive Computing. 2005.

12.R.J.M. Vullers, V. Leonov, T. Sterken, A. Schmitz. “Energy Scavengers for Wireless Intelligent Microsystems”. OnBoardTechnology Magazine.

13.“Electret” http://www.wikipedia.org/Electret14. S. Roundy, P. Wright, J. Rabaey. “Energy Scavenging for Wirelss Sensor Networks: with Special Focus on Vibrations”.