“Piezoelectric Energy Harvester”
Visvesvaraya Technological University Belgaum-590018
Project Report – 8th Semester (2014-15)
“PIEZOELECTRIC ENERGY HARVESTER”
Submitted in partial fulfillment of the requirement for the award of the degree
Bachelor of Engineering In Electrical and Electronics Engineering
Submitted by NAME USN NO 1) GAYATHRI MENON 1NH11EE014 2) HARSHKUNJ P CHOKHAWALA 1NH11EE017 3) R. NARMADHA RANI 1NH11EE044 4) RENJINI MOHAN 1NH11EE050
June 2015 Under the guidance of Lithesh J Assistant professor
NEW HORIZON COLLEGE OF ENGINEERING Department of Electrical and Electronics Engineering Permanent affiliated to VTU, Approved by AICTE and ISO9001:2008 certified A Recipient of Prestigious State Award 2012 conferred by the Government of Karnataka Marathahalli Ring Road, Bellandur Post, Bangalore – 560 103
New Horizon College of Engineering (A Recipient of Prestigious State Award 2012 by the Government of Karnataka) (Accredited by NBA, Permanent affiliation by VTU) Ring Road, Kadubisanahalli, Bellandur Post, Near Marathahalli. Bangalore – 560 103 Department of Electrical and Electronics
CERTIFICATE
Certified that the project work entitled “PIEZOELECTRIC ENERGY HARVESTER” is a bonafide work carried out by GAYATHRI MENON (1NH11EE014), HARSHKUNJ PRASHANT CHOKAWALA (1NH11EE017), R. NARMADHA RANI (1NH11EE044), RENJINI MOHAN(1NH11EE050) in partial fulfillment for the award of the degree of Bachelor of Engineering in Electrical and Electronics of the Visvesvaraya Technological University, Belgaum during the year 2014-2015. It is certified that all corrections / suggestions indicated for internal assessment have been incorporated in the report deposited in the departmental Library. The project report has been approved as it satisfies the academic requirements in the respect of project work prescribed for the Bachelor of Engineering Degree.
Lithesh J Prof. Mahesh.K Dr. Manjunatha Assistant professor HOD -EEE PRINCIPAL
Submitted by NAME USN NO 1) GAYATHRI MENON 1NH11EE014 2) HARSHKUNJ P CHOKHAWALA 1NH11EE017 3) R. NARMADHA RANI 1NH11EE044 4) RENJINI MOHAN 1NH11EE050
Name of the Examiners Signature with date
PIEZOELECTRIC ENERGY HARVESTER
ACKNOWLEDGEMENT
I have taken maximum effort in doing this project report on piezoelectric energy harvesting. However, it would not have been possible without the kind support and help of many individuals .I would like to extend my sincere thanks to all of them. First and foremost I would like to give credit to our beloved chairman of New Horizon Educational institutions Dr. Mohan Manghnani for providing world class infrastructure and education facilities. Secondly our respected college Principal Dr. Manjunatha for providing continues support in all aspects throughout my engineering degree I would like to express my gratitude to our HOD Prof. Mahesh. K. Gowda(EEE dept.)for his constant support and encouragement throughout the semester and for providing us the right ambience for carrying out our project and seminar work. I am highly indebted to our internal guide. Prof.Lithesh J , for his guidance and constant supervision as well as for providing necessary information regarding the project & also for his support and complete help in completing the project. I would like to express my gratitude towards all the staff members of our Department, for the valuable information provided by them in their respective fields. I would like to express my gratitude towards my parents for their kind co- operation and encouragement which help me in completion of this project. Last but not the least I would like to thank my friends for their support and encouragement.
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ABSTRACT
The demand for energy is ever increasing and our project aims at harnessing the waste mechanical energy that is expelled while walking, into useful electrical energy using a piezoelectric model. This project also aims at determining the best combination of piezoelectric crystals that will produce an optimum output which can further be used for various applications.
A spring model is used in the project so as to optimize the effectiveness of the vibrations and increase the output from each crystal. The spring model also ensures that the pressure on the model is evenly distributed.
Various ways of increasing the output from one crystal and a combination of crystals resulted in using a bridge rectifier in series with each crystal. The bridge rectifier is a uni- directional current controlling device. The positive and negative peak of the output was rectified, giving a higher voltage.
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CONTENTS CHAPTER 1
INTRODUCTION 5 CHAPTER 2
PIEZOELECTRICITY
2.1 Piezoelectric effect 6
2.2 Temperature influence 7
2.3 History of piezoelectricity 8
2.4 Working of piezo ceramic 9
2.4 Different types of piezoelectric materials 10
2.5 Reversibility process 16
2.6 Summary of piezoelectric processes 17 CHAPTER 3
PZT CRYSTAL
3.1 How the crystals are made 18
3.2 Piezoelectric crystal 20 CHAPTER 4
4.1 Limitations 23
4.2 Comparison 25
4.3 Literature review 26 CHAPTER 5
APPLICATIONS
5.1 Pressure applications 30
5.2 Vibration applications 35
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5.3 Sensing applications 36
5.4 Industrial applications 38
5.5 Miscellaneous 39 CHAPTER 6 OUR MODEL
6.1 Mechanical part 40
6.2 Electrical part 44
6.3 Materials cost 47
6.4 Combinations 49 CHAPTER 7
7.1 Applications of piezoelectric energy harvesting 56
7.2 Future scope 60 CHAPTER 8 Conclusion 62
REFERENCES
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LIST OF FIGURES
Figure Figure name Page no. no. 2.1.1 Piezoelectric mechanism 6 2.2.1 Effect of temperature 8 2.3.1 Modes of operation od piezo crystal 10 2.4.1 Quartz 11 2.4.2 Rochelle salt 11 2.4.3 Tourmaline Crystal 12 2.4.4 Bone 12 2.4.5 Gallium Orthophosphate 16 2.4.6 langasite 2.4.7 Graph: Dielectric Constant Vs Temperature 2.5.1 Reversibility Process 2.6.1 Deformation of crystal 17 2.6.2 Change in deformation 18 3.1.1 Crystalline structure 19 3.1.2 Polarization in piezo ceramic 19 3.2.1 PZT Crystal 19 3.2.2 Crystal structure 21 5.1.1 Cigarette lighter 31 5.1.2 Keyboard 31 5.1.3 Wireless keyboard 32 5.1.4 Tennis Racquet 32 5.1.5 Treadmill 32 5.1.6 Vehicles utilizing vibration 33 5.1.7 Laser 33 5.1.8 Microphone 33 5.1.9 Escalator 34 5.1.10 Transient pressure application 34 5.2.1 Stepper motor 35 5.2.2 Auto focus camera 36 5.3.1 Ultrasonic Sensor 37
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5.3.2 Scientific instruments 38 5.3.3 Pumping and dozing 38 5.3.4 Medical technology 39 5.3.5 Energy Harvesting 40 6.1.1 Baseboard 41 6.1.2 Stopper 42 6.1.3 Stopper with bushing 43 6.1.4 Stopper board 44 6.1.5 Connection board 44 6.2.1 Dot board 45 6..4.1 Simple series connection 47 6..4.2 Simple parallel connection 48 6..4.3 Series parallel combination 49 6..4.4 Parallel combination on series w 50 6..4.5 Single crystal with diode 51 6..4.6 Series combination ending with diode 51 6..4.7 Series connection with each crystal connected to the 52 diode 52 6..4.8 Single crystal with germanium diode 53 6..4.9 Crystals in parallel with each one with diode 53 6..4.10 Crystal series with one diode each 54 6..4.11 Single crystal connected to bridge rectifier 57 7.1.1 Flooring tiles 57 7.1.2 Street lighting 57 7.1.3 Steet lighting 58 7.1.4 Dance floors 59 7.1.5 Foot Wear 59
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CHAPTER 1 INTRODUCTION
Nowadays, a lot of research is being done to develop energy sources that are of the future. They need to be sustainable and reliable sources as all the oil resources have been tapped and are bound to be exhausted in the near future. Piezoelectric materials have the scope of becoming a reliable source and more research needs to be directed to this field as they have many interesting properties that need more exploration.
Piezoelectricity, also called the piezoelectric effect, is the ability of certain materials to generate an AC (alternating current) voltage when subjected to mechanical stress or vibration, or to vibrate when subjected to an AC voltage, or both. This form of harnessing energy is highly advantageous as it uses waste energy to produce electrical energy.
Piezoelectric transducers are common in ultrasonic applications, such as intrusion detectors and alarms. Piezoelectric devices are employed at AF (audio frequencies) as pickups, microphones, earphones, beepers, and buzzers. In wireless applications, piezoelectricity makes it possible to use crystals and ceramics as oscillator that generate predictable and stable signals at RF (radio frequencies).
The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry.
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CHAPTER 2
PIEZOELCTRICITY
2.1 PIEZOELECTRIC EFFECT
To understand the piezoelectric effect we need to look into its molecular level. Each molecule within the crystalline material has a dipole polarisation, with one end of the molecule positively charged and the other end negatively charged. In a monocrystalline material, all of these dipoles are aligned in the same direction so the crystal can be described as being symmetrical. When the material is polycrystalline, these dipoles are orientated in different directions and the material is thus asymmetrical. Applying an electric field, as represented in figure 2.1.1 below, to heat the piezoelectric material imparts enough energy to drive reorganisation of the dipoles such that they all face in the same direction, and the material is now symmetrical.
Figure 2.1.1 Piezoelectric mechanism
The first image shows the material in its initial, non-polarised state, composed of cells of arbitrary direction. The middle image shows it after being polarised by the application of a strong DC electric field. The last image shows the remnant polarity, which it retains even when the electric field has been removed, and it can now be used as a piezoelectric material.
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2.2 TEMPERATURE INFLUENCE
Temperature plays an important part of the behaviour of piezoelectric materials. These materials have a characteristic temperature, known as the Curie temperature. Above this Curie point, each micro crystal into the overall macro material reverts to a cubic orientation with a loss of polarisation as there is no longer any dipole moment present and enter a state where they are referred to as being paraelectric or “depoled”. At temperatures below the Curie point, each crystal has a tetragonal or rhombohedral symmetry and a dipole moment.
The Curie temperature of Quartz is 573°C, but for PZT is only 250°C and significant performance degradation can be seen even when temperatures of only 150°C are reached. PZT will not self-re-polarise at room temperature after heating above its Curie temperature, but can be repolarised through the original polling mechanism by re- application of a strong electric field.
Figure 2.2.1 Effect of temperature
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2.3 HISTORY OF PIEZOELECTRICITY
Piezoelectrics are a family of materials that exhibit a very special property – when the material is deformed by either squeezing or stretching; an electric charge is created by what is known as the “piezoelectric effect”. Pierre and Jacques Curie were the first to discover the piezoelectric effect in 1880 by measuring surface charges which were demonstrated on specially arranged crystalline salts of naturally occurring materials such as cane sugar, Rochelle salt and quartz. The term “piezoelectricity” was subsequently coined by the German mathematician Hermann Hankel, coming from the Greek word “piezen” which means “to press”.
One important aspect of the Curie brother‟s work was that not only had they chosen specific materials which they believed would show the piezoelectric phenomenon, but also they realised that the crystalline orientation of those materials was just as important in creating the conditions for electricity to be created from mechanical deformation of the material. One thing that they did not realise was the reciprocal nature of the phenomenon and the importance of the inverse (or converse) piezoelectric effect - that of creating a stress in the material by the application of a voltage this was later proved mathematically from thermodynamic principals by Gabriel Lippman in 1881 and experimentally confirmed by the Curies in practice one year later.
In 1920 W. G. Cady filed the patent for the piezoelectric resonator, realising the radio frequency applications of piezoelectric crystals oscillating near their resonant frequency. In 1935 the piezoelectric effect was demonstrated in potassium di-hydrogen phosphate (KDP), which was the first major “family” of commercially viable piezoelectric and ferroelectric materials to be discovered. The onset of World War II saw increased research by both the US, USSR and Japan which led to the post-war creation of artificial piezoelectric materials such as barium titanate and lead zirconatetitanate which were first synthesised in the 1950‟s by sintering metallic oxide powders, with synthetic quartz becoming available for the first time in 1958 by the use of the autoclaved hydrothermal process.
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2.4 WORKING OF PIEZO CERAMIC
Mechanical compression or tension on a poled piezoelectric ceramic changes the dipole moment, creating a voltage. Compression along the direction of polarization, or tension perpendicular to the direction of polarization, generates voltage of the same polarity as the poling voltage (figure ). 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 ). These actions are generator actions, the ceramic element converts the mechanical energy of compression or tension into electrical energy. This behaviour is used in fuel-ignition devices, solid state batteries, force-sensing devices, and other products. 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.
If a voltage of 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 2.3.1 ). If a voltage of polarity opposite that of the poling voltage is applied, the element will become shorter and broader (figure 2.3.1 ). If an alternating voltage is applied, the element will lengthen and shorten cyclically, at the frequency of the applied voltage. This is motor action- electrical energy is converted into mechanical energy. The principle is adapted to piezoelectric motors, sound or ultrasound generating devices, and many other products.
Figure 2.3.1 Modes of operation of piezoelectric disc
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2.5 DIFFERENT TYPES OF PIEZOELECTRIC MATERIALS
Piezoelectric materials
Natural crystals Synthetic crystals Synthetic ceramics Polymers
Piezoelectric materials may be divided into the categories of Natural Crystals, Synthetic Crystals, Synthetic Ceramics and Polymers. Since a piezoceramic is at the micro scale composed of a random grain structure of multiple-orientated crystals which have a majority of aligned dipoles, in the strictest sense they should be referred to as exhibiting a “polarised electro effect”, as technically a material should be composed of a single monolithic crystal to be a classic piezoelectric.
1.) Natural Crystals: Quartz, Rochelle salt, Topaz, Tourmaline Group Minerals, Berlinite (AlPO4), cane sugar, and dry bone (apatite crystals) i.) Quartz: Quartz is one of the original piezoelectric materials and has many advantages – it can be readily produced synthetically, can withstand temperatures up to 400°C and can be cut in pre-determined crystalline planes to maximise its sensitivity to incoming pressure or shear forces. They can be oscillated at high frequencies but demonstrate low magnitudes of deflection. A subsection of quartz is calcium gallogermanate isotopes, which can withstand temperatures up to 1300°C and are also highly sensitive, making them ideal for use in applications such as sensors and actuators for engines, however their cost is extremely high.
Figure 2.4.1 Quartz crystal
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ii.) Rochelle salt: Rochelle salt (chemical name Potassium sodium tartrate) is named after the French seaside town where it was first synthesised by chemist Pierre Seignette in 1675. Potassium sodium tartrate and the similar monopotassium phosphate were amongst the earliest materials known to display the phenomenon of piezoelectricity.
Figure 2.4.2 Rochelle salt iii.) Tourmaline group: Tourmaline is not a single mineral, but a group of several closely related minerals. The three most well-known members are Elbaite, Schor, and Dravite. Other lesser known members include Uvite, Liddicoatite and Buergerite. -
Figure 2.4.3 Tourmaline crystal iv.) Bone: Bone is a rigid organ that constitutes part of the vertebral skeleton. Bones support and protect the various organs of the body, produce red and white blood cells, store minerals and also enable mobility. Bone tissue is a type of dense connective tissue. Bones come in a variety of shapes and sizes and have a complex internal and external structure. They are lightweight yet
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strong and hard, and serve multiple functions. Mineralized osseous tissue or bone tissue, is of two types – cortical and cancellous and gives it rigidity and a coral-like three-dimensional internal structureals:
Figure 2.4.4 Bone
2.) Synthetic crystals
i.) Gallium orthophosphate (GaPO4): Galliumphosphate (GaPO4 or gallium orthophosphate) is a colourlesstrigonal crystal with a hardness of 5.5 on the
Mohs scale. GaPO4 is isotypic with quartz, possessing very similar properties, but the silicon atoms are alternately substituted with gallium and phosphorus,
thereby doubling the piezoelectric effect. GaPO4 has many advantages over quartz for technical applications, like a higher electromechanical coupling
coefficient in resonators, due to this doubling. Contrary to quartz, GaPO4 is not found in nature. Therefore, a hydrothermal process must be used to synthesize the crystal.
Figure 2.4.5 Gallium orthophosphate
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ii.) Langasite (La3Ga5SiO14): Lanthanum gallium silicate (referred to as LGS in this article), also known as langasite, has a chemical formula of the form
A3BC3D2O14, where A, B, C and D indicate particular cation sites. LGS is a piezoelectric material, with no phase transitions up to its melting point of 1470 °C. Single crystal LGS can be grown via the Czochralski method, in which crystallization is initiated on a rotating seed crystal lowered into the melt followed by pulling from the melt. The growth atmosphere is usually argon or nitrogen with up to 5% of oxygen.
Figure 2.4.6 Langasite crystal
iii.) Zinc oxide (ZnO): Zinc Oxide is familiar as an insoluble white powder widely used as an additive in a huge array of manufactured goods; but as a material it is its properties as a wide bandgap III-VI material that appeals to us for application in piezoelectrics. This has seen ZnO used in LCD and LED technology as well as an energy saving thin film. In 2006 Wang and Song demonstrated that an array of ZnO nanowires, could be used to harvest mechanical energy and to power devices at the nano scale, with the power generated by the strain field created by coupling of the semiconducting and piezoelectric characteristics of the ZnO array as a result of its deformation and the establishment of a persistent Schottky barrier between the metal wires and the ZnO substrate. The potential for energy harvesting using this system is estimated at approximately 10pW/µm² with an efficiency of between 17 and 30%, although this may be an underestimate depending on if any further gains can be made by approaching the resonating frequency of the ZnO pillars
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3.) Synthetic ceramics: Lead titanate (PbTiO3), Lead zirconatetitanate (Pb[ZrxTi1- x]O3 0
Below the Curie temperature of 120°C, the octahedral lattice geometry changes to cubic to tetrahedral arrangement and the titanate ion becomes non-symmetrical, giving rise to a strong dipole moment.
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4.) Polymers: Polyvinylidene fluoride (PVDF) i.)Polyvinylidene fluoride (PVDF): PVDF, or Polyvinylidene fluoride, (C2H2F2) is a highly reactive fluoropolymer which is formed by controlled polymerisation of vinylidenedifluoride. It is naturally semi-crystalline and adopts one of four different molecular forms based upon composition and processing temperature. Polling of the material by thermal or electrical means leads to a permanent polarisation due to dipole orientation and it is this which gives it it‟s piezoelectric properties. It is medium cost, easily fabricated and highly formable into diverse shapes and form factors.Its advantages as a robust, light weight and flexible material allow it to be used where other more brittle piezoelectric materials would not be suitable, however this is achieved at the cost of its intrinsically lower coupling factor between mechanical and electrical energy.
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2.5 REVERSIBILTY PROCESS
Figure 2.5.1 Reversibility process
The piezoelectric effect is the electromechanical relationship that allows certain materials such as crystals and synthetic ceramics to produce an output power due to a mechanical stress as well as produce a mechanical force as a result of an electric input. This concept was first demonstrated by Pierre and Jacques Curie in 1880. These brothers found the mechanical to electrical process of piezoelectricity, but they were unaware of its reversibility. This reversibility was found mathematically in 1881, where the Curie brothers quickly confirmed these thermodynamic calculations experimentally.
One of the reasons piezoelectrics are so interesting is because their functionality can be reversed. Piezoelectric materials can be used in a mechanical to electrical process or the reverse, electrical to mechanical. This is particularly interesting when comparing with other processes, as this reversibility is not a possibility. Electricity can be passed through piezoelectric materials which will cause a physical deformation of the material. Additionally, mechanical energy can be used to deform the material and therefore produce an output current. This reversibility is one attribute of piezoelectric materials that makes them interestingly unique.
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2.6 SUMMARY OF PIEZOELECTRIC PROCESSES i.) A deformation of the crystal structure (eg: squeezing or pressing it) will result in an electrical current.
Figure 2.6.1 ii.) Changing the direction of deformation (eg: pulling it) will reverse the direction of the current.
Figure 2.6.2 iii.) If the crystal structure is placed into an electrical field, it will deform by an amount proportional to the strength of the field. iv.) If the same structure is placed into an electrical field with the direction of the field reversed, the deformation will be opposite.
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CHAPTER 3
PZT CRYSTALS
3.1 HOW THE CRYSTALS ARE MADE
Piezoelectric materials can be natural or man-made. The most common natural piezoelectric material is quartz, but man-made piezoelectric materials are more efficient and mostly ceramics. Due to their complex crystalline structure, the process with which they are made is very precise and has to follow very specific steps. To prepare a piezoelectric ceramic, fine PZT powders of the component metal oxides are mixed in specific proportions, and then heated to form a uniform powder. The piezo powder ismixed with an organic binder and is formed into structural elements having the desired shape (discs, rods, plates, etc.). The elements are fired according to a specific time and temperature program, during which the piezo powder particles sinter and the material attains a dense crystalline structure. The elements are cooled, then shaped or trimmed to specifications, and electrodes are applied to appropriate surfaces.
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Figure 3.1.1: Crystalline structure
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However, piezoelectric material exhibits an electric behaviour and acts as a dipole only below a certain temperature called Curie temperature. Above the Curie point, the crystalline structure will have a simple cubic symmetry so no dipole moment (figure 3.1.1 left side). On the contrary, below the Curie point, the crystal will have tetragonal or rhombohedra symmetry hence a dipole moment (figure3.1.1 right side). Adjoining dipoles from regions called Weiss domains and exhibit a larger dipole moment as every dipole in the domain has roughly the same direction, thus a net polarization.
The change of direction of polarization between two neighbouring domains is random, making the whole material neutral with no overall polarization (figure 3.1.2)
Figure 3.1.2 Polarization in a piezo ceramic
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3.2 PIEZOELECTRIC CRYSTAL
Piezoelectricity is the ability of some materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) to generate an electric field or electric potential in response to applied mechanical strain. The effect is closely related to a change of polarization density within the material's volume. The most common piezoelectric transducer comprises a "crystal" sandwiched between two metal plates. When a sound wave strikes one or both of the plates, the plates vibrate. The crystal picks up this vibration, which it translates into a weak AC voltage. Therefore, an AC voltage arises between the two metal plates, with a waveform similar to that of the sound waves. Conversely, if an AC signal is applied to the plates, it causes the crystal to vibrate in sync with the signal voltage. As a result, the metal plates vibrate also, producing an acoustic disturbance.
Figure 3.2.1 PZT crystal If the material is not short-circuited, the applied stress/strain induces a voltage across the material. However, if the circuit is closed the energy will be quickly released. So in order to run an electric load (such as a light bulb) on a piezoelectric device, the applied mechanical stress must oscillate back and forth. For example, if you had such a device in your shoes you could charge your cell phone while walking but not while standing.
The crystal is made up of lead zirconate titanate (PZT PbZnTiO3). It is currently the world‟s most widely-used piezoelectric material. In its native form as a white insoluble solid, it has a crystal structure shown in figure 3.2.2 below which resembles that of
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perovskite, and where the unit cell is composed of a small tetravalent metal ion (usually titanium or zirconium) sitting within a lattice of large divalent metal ions (normally lead).
Figure 3.2.2 – The crystal structure of Piezo crystal. This type of atomic orientation is very amenable to doping due to the large spaces available in the lattice for elemental substitution, meaning there is a large range of possible oxide materials which can be tailored from this parent structure.
Industrial PZT is normally termed either “Hard” or “Soft” depending on the type of doping that has been used – the presence of an excess of acceptors creates anion (ions with a net - negative charge) vacancies in the lattice and gives rise to the hard variant, whilst the soft type is the result of donor doping and cations (ions with a net + positive charge) vacancies.
Soft flavours of PZT, characteristic features are comparably high domain mobility and resulting „soft ferroelectric‟behaviour, i.e. it is relatively easy to polarize. The advantages of the soft PZT materials are their large piezoelectric charge coefficient, moderate permittivity‟s and high coupling factors. Even though they have higher piezoelectric constant but this is not seen externally due to the larger internal losses in the material due to internal friction effects.
Important fields of application for “soft“ piezo ceramics are actuators for micro - positioning and nanopositioning, sensors such as conventional vibration pickups, ultrasonic transmitters and receivers for flow or level measurement, for example, object identification or monitoring as well as electro-acoustic applications as sound transducers and microphones, through to their use as sound pickups on musical instruments.
Hard PZTs have lower internal losses as any motion in the domain wall is pinned by the higher impurity levels, but they have an intrinsically lower piezoelectric constant to begin
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with. Hard PZT materials can be subjected to high electrical and mechanical stresses. Their properties change only little under these conditions and this makes them particularly ideal for high-power applications.
Important fields of application of hard piezoceramics are ultrasonic cleaning (typically kHz frequency range), machining of materials (ultrasonic welding,bonding, drilling, etc.), ultrasonic processors (e.g. to disperse liquid media), medical field (ultrasonic tartar removal, surgical instruments etc.) and also in sonar technology.
The advantages of these PZT materials are :
i. Moderate permittivity ii. Large piezo electric coupling factors iii. High quality iv. Very good stability under high mechanical loads and operating fields. v. Low dielectric losses facilitate their continuous use in resonance mode with only low intrinsic warming of the component. vi. Cost effective vii. Operation is time independent viii. Simple working ix. Easy to use
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CHAPTER 4
4.1 LIMITATIONS
1.) STABILITY
Most properties of a piezoelectric ceramic element erodes gradually, in a logarithmic relationship with time after polarization. Exact rates of aging depend on the composition of the ceramic element and the manufacturing process used to prepare it. Mishandling the element by exceeding its electrical, mechanical, or thermal limitations can accelerate this inherent process.
2.) ELECTRICAL LIMITATIONS
Exposure to a strong electric field, of polarity opposite to that of the polarizing field, will depolarize a piezoelectric material. The degree of depolarization depends on the grade of material, the exposure time, the temperature, and other factors, but fields off 200-500 V/mm or greater typically have a significant depolarizing effect. An alternating current will have a depolarizing effect during each half cycle in which polarity is opposite that of the polarizing field.
3.) MECHANICAL LIMITATIONS
Mechanical stress sufficient to disturb the orientation of the domains in a piezoelectric material can destroy the alignment of the dipoles. Like susceptibility to electrical depolarization, the ability to withstand mechanical stress differs among the various grades and brands of piezoelectric materials.
4.) THERMAL LIMITATIONS
If a piezoelectric ceramic material is heated to its Curie point,the domains will become disordered and the material will be depolarized. The recommended upper operating temperature for a ceramic usually is approximately half-way between degree Celsius and the Curie point. Within the recommended operating temperature range, temperature- associated changes can create charge displacements and electric fields. Also, sudden temperature fluctuations can generate relatively high voltages, capable of depolarizing the
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ceramic element. A capacitor can be incorporated into the system to accept the superfluous electrical energy.
For a particular ceramic material, the pyroelectric charge constant – the change in the polarity for a given change in temperature – and the pyroelectric field strength constant- the change in electric field for a given change in temperature- are indicators of the vulnerability of the material to pyroelectric effects. A high piezoelectric charge constant: pyroelectric charge constant ratio or piezoelectric voltage constant: pyroelectric field strength constant ratio indicates good resistance to pyroelectric effects.
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4.2 COMPARISON
Advantages of piezoelectricity over other form of energy sources are:
Cheaper than photovoltaic cells. Available all through the day, year. The only process where reversibility is present. Mostly ambient energy is harnessed and thus does not depend on any other source like solar rays. Renewable Relatively new and developing concept. Can be used for any form of energy harnessing which has a force like rain, wind, water, man power, animal power, etc. Power generated is free of cost.
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4.3 LITERATURE REVIEW
1.) PAPER I: BASE PAPER Paper title: Footstep Power Generation Using Piezo Electric Transducers Publication: International Journal of Engineering and Innovative Technology (IJEIT) Volume 3, Issue 10, April 2014 Author name: Kiran Boby, Aleena Paul K, Anumol.C.V, Josnie Ann Thomas, Nimisha K.
Idea: A piezo tile capable of generating 40V has been devised. Comparison between various piezo electric material shows that PZT is superior in characteristics. Also, by comparison it was found that series- parallel combination connection is more suitable. The weight applied on the tile and corresponding voltage generated is studied and they are found to have linear relation. It is especially suited for implementation in crowded areas. This can be used in street lighting without use of long power lines. It can also be used as charging ports, lighting of pavement side buildings.
2.) PAPER II
Paper title: Charging an Electronic Gadget using Piezoelectricity Publication: Indian Journal of Science and Technology, Vol 7(7), 945–948, July 2014 Author name: J. John Livingston* and M. Hemalatha Idea: The necessary voltage required for charging a mobile phone battery is successfully generated and the output is shown in the picture. The output current that is generated from the piezoelectric sensor may be less, which may increase the time taken for charging a battery. But it can be used for charging an electronic device battery for emergency purpose where there is no direct source of electricity. This can be used as an efficient source for portable electric powerfor portable devices. This work is a low cost approach to demonstrate the application of piezoelectric sensor to meet the need for portable electric power
3.)PAPER III
Paper title: Piezoelectric Energy Harvesting.
Author names: Paul Aheren
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Idea: A short history of piezoelectric materials has been presented and the different mechanisms of their piezoelectric, ferroelectric and electrostrictive responses have been discussed. When compared to other types of renewable energy technologies, piezoelectric energy harvesters offer very high efficiency and power density in comparison to their small footprint and low total cost of ownership. While admittedly still in its infancy, it is hoped that the potential of these novel materials and devices can be appreciated in the context of providing a viable, alternative battery-free energy source for a host of low power micro- and nano-electronic devices in the future. Niche applications such as bio-medical military and robotics have the potential to drive the fundamental materials research and development which should ultimately provide beneficial mainstream uses for energy harvesting technologies; leading us all to eventually benefit from the harvesting of “good vibrations”.
4.) PAPER IV
Paper title: Electrical Power Generation Using Piezoelectric Crystal . Publication: International Journal of Scientific & Engineering Research Volume 2, Issue 5,May-2011 Author names: Anil Kumar
Idea: As the results show, using double actuators in parallel we can reduce the charging time of the battery and increase the power generated by the piezoelectric device. In the second research, a piezoelectric generator was put to the test and it generated some 2,000 watt-hours of electricity. The setup consists of a ten-meter strip of asphalt, with generators lying underneath, and batteries in the road‟s proximity. So that it is clear by using parallel combination we can overcome the problems like of impedance matching and low power generation. The results clearly show that piezoelectric materials are the future of electric power generation.
5.) PAPER V
Paper title: A Unique Step towards Generation of Electricity via New Methodology. Publication: International Journal of Advanced Research in Computer and Communication Engineering Vol. 3, Issue 10, October 2014. Author names: ItikaTandon, AlokKumar
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Idea: This statement of Albert Einstein is true “Energy can neither be created nor be destroyed it can be transferred from one form to another.” This method of generating electricity by the use of piezoelectric material has already being started in many countries viz Japan, Israel, Netherlands. Use of piezo-electric material is eco-friendly causes no pollution. It is an inexpensive way of generating electricity and is easy to install. In future this method will be a promising method for generating eco-friendly electricity. We also contribute this method at common places like home entrance gates, parking area, bus stands etc. This method will exploits different areas of electricity generation.
6.) PAPER VI
Paper title: Comparison between four piezoelectric energy harvesting circuits. Publication: Research work(Front. Mech. Eng. China 2009, 4(2): 153–159) . Author names: Jinhao QIU, Hao JIANG, Hongli JI, Kongjun ZHU
Idea: Four vibration powered piezoelectric energy harvesting interfaces, two of which use the synchronous switching technique, have been investigated and compared. A simple source-less trigger circuit used to control the synchronized switch has been proposed and two interface circuits of energy harvesting systems have been designed based on the trigger circuit. The effectiveness of the proposedcircuits was validated by the experimental results of energy harvesting systems based on a vibrating beam. The power levels of the four interfaces are different. According to the experimental results, the synchronized switch harvesting on the inductor interface increases the power of harvested energy by a factor of 7, and the synchronous charge extraction interface has the resistance adaptation capability of the terminal electric load. The synchronized switching technique brings significant improvements to vibration-based piezoelectric energy harvesting systems, thus showing promising possibility of applications in standalone systems and long lifespan intelligent power sources.
7.) PAPER VII
Paper title: Generating electricity using piezoelectric material.
Author name‟s: JedolDayou, Man-Sang,C. , Dalimin, M. N. & Wang, S Publication: BORNEO SCIENCE 24: MARCH 2009
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Idea: In this paper, a theoretical model on the generation mechanisms of electricity by piezoelectric material attached to a flexible structure has been developed and tested experimentally. The Euler-Bernoulli method was proven to be the most appropriate model in reference to the experimental data and its practicality. The piezo-host configuration was then optimized with huge increment in the voltage output. With the configuration optimised, the voltage and current density from the piezoelectric were made high enough to be stored in a 1.2V-2500 mAh nickel metal hybrid battery for later applications.
8.) PAPER VIII
Paper title: Application of piezoelectric materials in transportation industry.
Publication: Global Symposium on Innovative Solutions for the Advancement of the Transport Industry, 4.-6. October 2006, San Sebastian, Spain
Idea: The present paper gives an overview on actual developments in the application of piezoelectric components in transportation industry. During the past decades, piezoelectric materials made huge progress in entering commercial mass markets in all branches, where piezoelectrics are used as the basis materials for actuators as well as sensors. Especially in transportation industry, they found numerous fields of applications. The development of piezoelectric actuators for fuel injection systems is a popular application of the near past, active noise and vibration reduction is a current activity, and the use of piezoelectric materials for energy harvesting in vibrating structures is one possible future trend.
Recent developments in ceramic processing and possibilities in tailoring of special properties will be shown as well as latest developments in manufacturing of piezoelectric actuator and sensor components. Another part of the paper is the aspect of reliability and performance degradation of piezo-based active systems, as well as new concepts of structural health monitoring.
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CHAPTER 5 APPLICATIONS OF PIEZOELECTRICITY
Both the direct and indirect piezoelectric effects have industrial applications. They are used in various fields like medical engineering, biotechnology, mechanical engineering, production technology, semiconductor technology etc.
5.1 DIRECT PIEZOELECTRIC APPLICATIONS:
The piezo element converts mechanical quantities such as pressure, strain or acceleration into a measureable electric voltage.
They can be classified into different fields based on the type of input- pressure, strain, acceleration, stress etc.
1) Pressure applications:
a.) Electric cigarette lighter: Pressing the button of the lighter causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high voltage that electric current flows across a small spark gap, thus heating and igniting the gas.
Figure 5.1.1 Cigarette lighter
b.) Mobile Keypads and keyboards: Crystals are laid down under keys of mobile unit and keyboard. For every key pressed, vibrations are created. These vibrations can be used for charging purposes. .
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Figure 5.1.2: A simple keyboard where the slots are occupied by piezoelectric crystals
Piezoelectric materials can very efficiently be used in wireless keyboards. Such keyboards then can be self-charging which will eliminate the frequent charging requirement of such keyboards
Figure 5.1.3: Wireless keyboard employing piezoelectric system
2) Vibration applications
a.) Tennis racquet: Piezoelectric materials are installed in tennis racquet to reduce the shock wave which is produced when a player hits the ball. Figure 5.1.4 Tennis racquet
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b.) Gyms: Vibrations caused from machines in the gym can be laid with piezoelectric crystals to generate electricity. Example: Treadmill. Figure 5.1.5 Treadmill
c.) Vehicles: Utilizing the vibrations in the vehicle like clutches, gears etc. Figure 5.1.6
d.) Lasers: Piezoelectric elements can be used in laser mirror alignment, where their ability to move a large mass (the mirror mount) over microscopic distances is exploited. By electronically vibrating the mirror it gives the light reflected off it a Doppler shift to fine tune the laser's frequency. Figure 5.1.7
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3) Sensing applications:
a.) Microphones: Detection of pressure variations in the form of sound is the most common sensor application, e.g. piezoelectric microphones. Sound waves bend the piezoelectric material, creating a changing voltage.
Figure 5.1.8 Microphone
b.) Sensing applications: Piezoelectric materials are used to sense human presence in automatic doors, escalators and other sensing applications. Figure 5.1.9 Escalator
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c.) Transient pressure measurement to study explosives, internal combustion engines (knock sensors), and any other vibrations, accelerations, or impacts. Figure 5.1.10
Various other applications are:
Acoustic Emission Spectroscopy In detection of imbalances on rotating machine parts or crash detectors in the automotive field. Passive damping Noise analysis Level and flow rate measurements
5.2 INDIRECT PIEZOELECTRIC APPLICATIONS
The piezo element deforms when an electric voltage is applied; mechanical motions or oscillations are generated. i.) Motor applications: a.) Stepper motors: The piezo motor is viewed as a high-precision replacement for the stepper motor.
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Figure 5.2.1 Stepper motor
ii.) Travelling-wave motors used for auto-focus in cameras.
Figure 5.2.2 auto focus camera
The other applications are :
Micro- and nano-positioning. Laser Tuning Vibration damping Micro-pumps Pneumatic valves Signal generator (buzzer) High-voltage sources / transformers Delay lines High-powered ultrasonic generators: Cleaning, welding, atomization, etc. Level measurement Flow rate measurement
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Object recognition and monitoring Medical diagnostics High-resolution materials testing Sonar and echo sounders Adaptive structures
5.3 INDUSTRIAL APPLICATIONS OF DIRECT AND INDIRECT PIEZOELECTRICITY
i.) Metrology
Ultrasonic sensors emit high-frequency sound pulses beyond the human hearing threshold and receive signals reflected from objects. The time the echo signals take to arrive is processed electronically and can be used for a wide range of applications in metrology.
Figure 5.3.1
a) Noncontact Ultrasonic Flow Metering b) Detection of Gas Bubbles c) Level Measurement d) Piezo Force Sensors e) Ultrasonic Proximity Sensors as Park Distance Control f) Noncontact Measurement with Air Ultrasound g) Haptic feedback h) Structural Health Monitoring (SHM)
ii.) Ultrasonic Technology
Piezoceramics can be used to generate ultrasonic waves in the frequency range of power ultrasound (20 to 800 kHz). They can be used in different diagnostic and therapeutic
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applications, for example in tartar removal or lithotripsy, but also in ultrasonic technology.
a) Industrial Ultrasonic Cleaning b) Ultrasonic Piezomotors c) Shock Wave Lithotripsy d) Sonar Technology and Hydroacoustics e) Ultrasonic surgery f) Ultrasonic welding g) Tartar removal h) Ultrasound therapy i) Materials processing
iii.) Scientific Instrumentation
Piezo components have become firmly established in modern science as drives and ultrasonic transducers. They work reliably even under extreme conditions such as magnetic fields, cryogenic temperatures or ultrahigh vacuum, which they have proven worldwide in many applications in space, in laboratories and in large-scale research installations such as synchrotrons. High-precision measurement and testing systems in industry also rely on piezo components as drives.
Figure 5.3.2
a) Mineralogical Analyses in NASA's Mars Rover b) Cryogenic Applications in the German Electron Synchrotron (DESY) c) Scanning Probe Microscopy d) Laser tuning e) Components for piezomotors f) Active vibration damping
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iv.) Pumping and Dosing
Piezo elements pump and meter small liquid or gas volumes reliably and precisely in the range of a few hundred milliliters to a few nanoliters. Different types of pumps, such as membrane or peristaltic hose pumps, are actuated by different drive principles. The piezo elements can be adapted perfectly to each specific application environment, for example miniaturized lab-on-a-chip solutions for mobile analytical instruments.
Figure 5.3.3
a) Metering with Piezo Valves b) Aerosol Production c) Piezo Micro-pumps d) Drug Metering Pumps (Implantable Medical Devices) e) Printing technology
v.) Medical Technology
Medical technology and related life-science disciplines require drive components that have to be fast, reliable and energy-saving. In these fields as well, progress goes hand in hand with increasing miniaturization. Piezoceramic drives combine exactly these characteristics. The piezo components and piezo actuators used are as different as their applications. Ultrasonic applications that use simple disks are in use, for example, in cosmetics, but also in medical tooth cleaning and for metering tasks.
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Figure 5.3.4
a) Shock Wave Lithotripsy b) Detection of Gas Bubbles c) Aerosol Production d) Piezo Micropumps e) Implantable Medical Devices f) Tartar removal g) Ultrasonic surgery h) Medical diagnostics: Imaging i) Cosmetics
vi.) Energy Harvesting
The term "energy harvesting" refers to the generation of energy from sources such as ambient temperature, vibration or air flow. Converting the available energy from the environment allows a self-sufficient energy supply for small electric loads such as sensors or radio transmitters.
Figure 5.3.5
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CHAPTER 6 OUR MODEL
A spring model is created such that when a user walks, two plates are pressed together which cause rods to impact and physically deform the piezoelectric transducers, therefore creating an electrical output via the piezoelectric effect.
The model can be described istwo parts, that is the mechanical part of the model and the electrical part of the model.
6.1 MECHANICAL PART
1) BASE BOARD:
The base board is a board where the crystals are mounted. In our project, we are using 25 crystals of size 2.5cm diameter. The crystals are placed in a square having five rows and columns, hence the dimension of board is cm x cm .The base board is made out of acrylic material ,instead of wood or plastic as it is stronger and more flexible. The board is also drilled with four holes at the corner which is provided with the screws for inserting the stopper board. A spring system is also included to facilitate movement of the stopper board when pressure is applied. These springs ensure that the crystals are not damaged due to excessive pressure.
Picture of base board: Figure 6.1.1
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2) STOPPERS:
Stoppers are the plastic bushes mounted on the stopper board for hitting the crystals placed in the base board. The dimension of the stoppers is same as that of the crystals 2.5cm in diameter. The stoppers are stuck to the stopper board with the help of araldite and they are placed exactly above the crystals.
Since the stoppers have a flat surface, a small bushing of 10mm is stuck on each stopper sin such a way that the crystals are hit efficiently.
Picture of stopper: Figure 6.1.2
Picture of stopper with bushing: Figure 6.1.3
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2) STOPPER BOARD:
Stopper board is the upper board or the board to be placed on top of the base board. It consists of 25 stoppers, which are made out of thick plastic. This board is also made out of acrylic material, same as that of base board and its dimension is also the same as base board that is cm x cm. This board also has four holes drilled in it, exactly at the same location as the holes on the base board, so that it can be inserted over the base board through the screws.
Picture of stopper board: Figure 6.1.4
3) PLACEMENT OF CRYSTALS :
The crystals are stuck onto a plastic board with the help of double sided tape on the edges so as to provide a cushioning effect for the crystals. The plastic board, in turn is stuck on the base board with the help of double side tape on the edges. The idea of using double sided tape to stick the crystals on the board is mainly to achieve maximum vibration of the crystals as it more effective than vibrations achieved in the absence of the tape.
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4) CONNECTION BOARD :
In order to try different combinations of connections of the crystals conveniently, the terminals of the crystals are taken out, and connected to another plastic board with banana pins. For this, the terminals (positive and negative) of the crystals are soldered to wires which are in turn, soldered to red and black banana pins. The pins are placed (bolted) on a board by making small holes and screwing the pins in them. This is called the connection board.
Figure 6.1.5
6.2 ELECTRICAL PART :
1) DOT BOARD :
The crystals produce an ac output, thus the output of each crystal has to be rectified in order to add the outputs of all the crystals. 5 small dot boards are used and each has 5 bridge rectifiers. The crystals of each column (5 crystals) were connected to the input banana connectors (green colour in the diagram below) which are internally soldered to the ac terminals of the bridge rectifiers. The dc terminals of the bridge rectifiers are soldered to the output banana connectors (green colour in diagram below), from where wires go to the terminals of the connections board. Thus the connection board consists of positive and negative terminals of each crystal, in dc form.
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Picture:
Figure 6.2.1
Figure 6.2.2
2) SOLDERING:
The terminals of the crystals are soldered with single strand wires, thus 50 wires are soldered for 25 crystals. The dot boards are soldered with bridge rectifiers and banana
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connectors. A total of 50 probes were soldered with banana pins for making connections on the connection board.
6.3MATERIALS USED
SLNO. MATERIAL QUANTITY COST per unit Total cost 1.) Piezoelectric crystal 25 10 250 2.) Mechanical model 1 1300 1300 3.) Single strand wire 40metres 3 120 4.) Multi strand wire 30metres 4 120 5.) Sleeve 30metres 3 90 6.) Double side tape 4 roles 30 120 7.) Insulation tape 1 role 25 25 8.) Soldering iron 1 260 260 9.) Soldering iron stand 1 65 65 10.) Soldering tin 2 roles 50 100 11.) Small dot boards 5 6 30 12.) Banana pins 50(25B ,25R) 11 550 13.) Bolts of banana pins 50(25B ,25R) 4 200 14.) Banana pin connector 50 3 150 15.) Bridge rectifier 25 12 300 16.) Silicon diodes 0.5 20 1 17.) Germanium diodes 4 20 80 TOTAL 2496
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6.4 COMBINATIONS
Various combinations of the 25 crystals were tried and the output in each case was measured. Though a lot of them failed to give desired results, they were helpful in concluding about the behaviour of crystals in different combinations.
The load in each case was a capacitor and the output was measured across it using a mutlimeter.
SET A:
1.) Simple series connection of crystals without rectification :
Circuit diagram: Figure 6.4.1
Output: The voltage measured was almost nil.
Conclusion: It was clearly understandable that since the crystals produce ac output, when connected in series the voltage of positive polarity cancels the opposite polarity voltage produced at the same time by two different crystals. Thus it is confirmed that the crystals produce ac output.
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2.) Simple parallel connection of crystals without rectification :
Circuit diagram: Figure 6.4.2
Output: The voltage measured for 3 crystals in series was approximately 80mV and the capacitor kept charging as the crystal was getting deformed and a maximum voltage of V was achieved. The discharging time of the capacitor was greater than the charging time .
Conclusion: Although the crystals produce ac output, the voltage measured across them will have a value since the voltage follows KVL. As in parallel connection the current should increase, no such increase in current was achieved, and the current was almost zero.
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3.) Series parallel combination:
a.) Two crystals in series were connected in parallel to another set of two crystals in series : Circuit diagram: Figure 6.4.3
Output: The voltage measured was =
Conclusion: The same principle of ac output was justified.
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b.)Two crystals connected in parallel were connected in series to two crystals in parallel :
Circuit diagram: Figure 6.4.4
Output: The voltage measured was almost nil.
Conclusion: The voltage of the connection failed to be present at the capacitor terminals again because there was cancellation of voltage of opposite polarity at the same instant.
Thus from experiments 1, 2 and 3 it was clearly visible that the output voltage should be rectified.
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SET B:
1.) Single crystal connected with a Si diode :
Circuit diagram: Figure 6.4.5
Output: Voltage = 1.5V
Conclusion: A comparatively good voltage was obtained and a way to add the voltage from each crystal was to be found.
2.) Crystals connected in series with a only one Si diode at the output :
Circuitdiagram: Figure 6.4.6
Output Voltage= NIL
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Conclusion: Each crystal voltage must be rectified else it gets cancelled.
3.) Crystals connected in series with one Si diode for each crystal :
Circuit diagram: Figure 6.4.7
Output voltage = almost nil
Conclusion: The voltage drop of each silicon diode is greater than produced by the crystal thus the output voltage is almost nil. Thus it was concluded to use germanium diodes instead of silicon diodes.
SET C:
1.) Single crystal with Ge diode:
Circuit diagram: Figure 6.4.8
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Output voltage = 1.9 – 2V
Conclusion: The loss due to breakdown voltage of Si diode is overcome in case of Ge diodes.
2.) Crystals connected in parallel with one diode for each crystal:
Circuit diagram: Figure 6.4.9
Output: Voltage approximately 1.5 to 1.9 V achieved at a fast charging time, almost within 60 seconds.
Conclusion: The Ge diodes rectify the output of each crystal and hence they seem to be more effective than Si diodes.
3.) Crystals connected in series with one Ge diode for each crystal:
Circuit diagram: Figure 6.4.10
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Output: A voltage fluctuating between positive and negative is obtained across the capacitor.
Conclusion: Since the same diodes were used, the breakdown of diodes has occurred, and the voltage is not rectified. Thus it is concluded that though the knee voltage of Ge is less than Si ,it cannot be used since it breakdown voltage is also lesser than Si and hence the diodes may have to be replaced before each time. Thus the idea of Ge diodes was given up and the thought of full wave bridge rectifiers emerged.
SET D:
1.) Single crystal connected to bridge rectifier : Figure 6.4.11
Output voltage = 30 – 40 V was achieved.
Conclusion: High voltage was obtained compared to half wave rectifiers. Thus it was found that full wave bridge rectifier is suitable for piezoelectric crystals.
2.) Each crystal connected to bridge rectifier and then connected in parallel :
For 5 crystals:
Output: Voltage of about 40- 50V is obtained.
Conclusion: In parallel connection, the current is found to increase but not voltage.
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3.) Each crystal connected to bridge rectifier and then connected in series :
For 5 crystals:
Output: 300V is obtained.
Conclusion: Series connection was seen to be the best among the various combinations tested and very high voltages can be obtained when 25 crystals are connected in series as their voltages get added up.
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CHAPTER 7
7.1 APPLICATIONS OF ENERGY HARVESTING VIA PIEZOELECTRIC MATERIAL
Flooring Tiles
The flooring tiles are made up of rubber which can absorb the vibration and under these the piezoelectric materials are placed so as when the movement is felt by the material they can generate the electricity. When these kind of tiles are installed in locations where large crowd movements are expected such as in Railway station ,Bus stations, Airports, Malls, footpaths etc, and when a person steps on them, then by piezoelectric effect small charge is built up. So the energy generated by one human would be too less but if number of steps on these kind of tiles increase then energy produced by it would increase too. When a person steps on such tiles piezoelectric crystal under the tiles would experience some mechanical stress which makes electric charge to built up on crystal‟s surface which can be collected by use of electrodes. This kind of energy can be stored in capacitors and power can be transfer to energy deficient regions. Japan has already started experimenting use of piezoelectric effect for energy generation by installing special flooring tiles at its capitals‟ two busiest stations. Tiles are installed in front of ticket turnstiles. Thus every time a passenger steps on mats, they trigger a small vibration that can be stored as energy.
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Figure 7.1.1
B. Road side to Power street lights
The present invention relates generally to methods of electrical power generation and more particularly is a method and device to generate electricity by using traffic on existing roadways to drive an electrical generator.
Figure 7.1.2
The idea of constructing the special types of roads which generate the electricity is a unique application in power harvesting methodology. This system works by embedding tiny piezoelectric crystals into the road.
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The first layer is laid with fine graval and sand content.Then a thin layer of asphalt is laid which acts like a strong base for the generators.Piezoelectric generators are placed in
quick drying concrete as per design and left for 30min.
Then all the generators are wired in series to get collective output. A bitumen sheet is used to cover all the generators to provide better adhesion of concrete to asphalt. Finally a thick layer of asphalt is laid which finishes the construction.
Harvesting mechanism: Generators harvest the mechanical energy of the vehicles and converts to electrical energy. Electricity energy is transferred and stored via harvesting module. Then it is charged into the battery on one side of the road. From there it is distributed.
Yield: For one km of piezoelectric road of one lane, we can generate 44000 KW·h/yr.
When automobiles or vehicles drive over through this road then the piezoelectric crystals sense the force and pressure which generates the small electrical charge. Though small charge is generated by single car but 1 km stretch of such road could generate around 400kW-enough to run eight small cars. Such experimenting have already started in Israel.
C. Dance Floors
Apart from roads and railway stations, piezoelectric effect is also being in use in the dance floors. In Europe, certain nightclubs have already begun to power their night clubs, strobes and stereos by use of piezoelectric crystals
These floors are using the piezoelectric effect. As the floor is compressed by the dancers feet the piezoelectric material makes contact and generate the electricity around 2-20
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watts. It depends on the impact of the feet. The constant compression of piezoelectric crystals causes a huge amount of energy to be generated, which can comfortably drive the remotely placed low power consuming devices
Figure 7.1.4
3.4. Inside the Footwear heel
Apart from tiles, roads, dance floors, attempts are made to harvest energy from our daily movements by installing piezoelectric crystals in the shoes also. These shoes would have piezoelectric crystals at the rear end or near heel. Thus with each step piezoelectric crystal would go through pressure and force which in turn can generate enough energy to power cell phones, mp3 players etc. If these such shoes undergo through movements daily then these will be able to generate electricity enough to charge up the small electronic devices or gadgets. Often we can do that with a piezoelectric transducer, a transducer is simply a device that converts small amount of energy from one kind to another for instance converting light, sound or mechanical pressure into electrical signals.
Figure 7.1.5
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7.2 FUTURE SCOPE
A. Roads and Highways
The traffic is more in day than the night and sometimes traffic run 24hrsand the traffic varies throughout the day. The total force exerted by moving automobiles on the road surface can be calculated by considering the average number of vehicles passing through certain point, for a certain time period. In a survey Israel is putting PEG 6cm under the road level and at a distance of 30cm apart. From this trial, it has been seen that a vehicle weighing at around 5 tons can generate 2000V, and a 1Km cluster of such generator can generate 400Kwh energy. If 600 vehicles are allowed to go through this road for an hour, it can power up to 600-800 homes.
B. Power Generating from Footpaths
Footpath is most common place on where we embed the piezoelectric tiles to produce the small amount of energy by utilizing the human footstep over it. The produced charge is stored in battery and then that stored charge can be use for charging low power electronic devices.
C. Power Generating Railway Tracks
The railway tracks are the important place which is responsible for generation of large energy as the huge amount of pressure is exerted by trains on the railway tracks. The embedded piezoelectric crystals at the railway tracks where wheels make contact with the tracks and these materials get excessive pressure and force, because of this greater amount of energy is stored.
D. Power Generating Airport Runway
In large amount of pressure is exerted on runways, when the aircraft takes off or lands. If we place the piezoelectric clusters here then we can convert this mechanical energy. The efficiency of system can be improved by placing the stacked structure which is consist of several layers of piezoelectric clusters and have the capacity to handle the huge amount of
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pressure.. The maximum takeoffweight for the airbus aircraft (A380) is 560 tones, which can produce 224 KV, so if one considers the total number of landing in the runway a large amount of energy could be produced. Nearly 8138 kWh energy could be produced which can power up to 12207-16276 homes.
E. Schools, Colleges, Shopping Malls and Gyms
Having the flooring of piezoelectric material will cause to produce the more energy in the malls and schools. We can embed the piezoelectric tiles at the entrance of the malls and schools. The idea of utilizing the vibrations caused by the machines in the gym, and at workplaces also, while sitting on the chair this energy can be stored in the batteries by putting the piezoelectric crystals in the chair.
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CHAPTER 8 CONCLUSION
A high voltage of about 400V was obtained by using just 25 crystals. Even though there are various projects that generate electricity using piezoelectric crystals, the aim of this project was to determine the combination of crystals that will produce optimum output, which is still under research. We have concluded with a series connection for all 25 crystals since we have added the voltage from each crystal and did not go for series- parallel combination because the current obtained in any type of parallel or series-parallel combination is very low; of the order of 1 microampere and lesser.
So far from this project, we have understood that, the piezoelectric crystals are capable of generating high voltages when mechanical stress is applied to it. The voltage keeps increasing as the stress increases. Further the type of mechanical stress applied to the crystal is very important. Normal pressing of the crystal will not produce any strain in the crystal lattice, but enough strain is created when the crystal is vibrated. More than hitting the crystals with a lot of force, the crystals should be made to vibrate with a high frequency. The crystal has a resonating frequency, as it produces ac output, so if the crystal is made to vibrate at its resonating frequency then it will produce maximum output.
Further, it was found that the crystal produces very less current, in micro ampere range. The reason for this, according to our knowledge is, each crystal has a reactance in the mega ohm range thus the current obtained is in microampere. So if the crystals are used as power source, a method to decrease the reactance of the power source must be found. As reactance is inversely proportional to frequency, if the crystals are made to vibrate at a very high frequency then the reactance of the crystal will decrease and the current will increase.
Department of EEE,NHCE Page 63
PIEZOELECTRIC ENERGY HARVESTER
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Energy Scavenging with Piezoelectric Transducers
Rain water used to generate electricity
Piezoelectric energy harvester
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American piezo company,USA#www.americanpiezo.com
Kannampilly, Ammu(bracket 2008/07-11).”How to Save the World One Dance at a Time”,ABC.
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