NFC Project report on Wirless Power Transmission.doc

LIST OF FIGURES FIGURE 1: Animated View of Resonant Coupling .......................................................5 FIGURE 2: Deliverable-Oriented Research plan............................................................10 FIGURE 3: Comparison between WIFI and WET system.............................................12 FIGURE 4: Wireless electricity could make this phenomenon a reality........................15 FIGURE 5: The 187-ft Wardenclyffe Tower (Tesla Tower) in 1903.............................17 FIGURE 6: Microwave Power Transmission.................................................................17 FIGURE 7: The Tran receiving circuit for wireless power transmission……...………19 FIGURE 8: System and method for wireless electrical power Transmission................20 FIGURE 9: Electric Power Transmission using LASER...............................................21 FIGURE 10: shows a unidirectional pattern..................................................................26 FIGURE 11: shows a bidirectional antenna pattern.......................................................27 FIGURE 12: Pattern of omni-direcrional antenna.........................................................29 FIGURE 13: Electric toothbrush battery charger..........................................................30 FIGURE 14: Induction Cooker Stovetop......................................................................30 FIGURE 15: Resonance Coupling between Coils........................................................32 FIGURE 16: LC switching circuit................................................................................36 FIGURE 17: Beginning of oscillations.........................................................................37 FIGURE 18: time 1/4t...................................................................................................37 FIGURE 19: time 1/2t...................................................................................................38 FIGURE 20: time 3/4t...................................................................................................38 FIGURE 21: Resonating circuit....................................................................................39 FIGURE 22: Impedance curves of R,L & C.................................................................40 FIGURE 23: Quality Factor at different values of R....................................................42 FIGURE 24: Capacitor charged: voltage at + peak, inductor discharged….………....43 FIGURE 25: Capacitor discharging voltage decreasing inductor charging………......43 FIGURE 26: Capacitor fully discharged and Inductor fully charged……….……......44 FIGURE 27: Capacitor charging with opposite polarity and inductor discharging......44 FIGURE 28: Capacitor fully charged (-) and inductor fully discharged…………......44 FIGURE 29: Capacitor discharging and inductor is charging……………………......45 FIGURE 30: Capacitor is fully discharged and inductor is fully charged (-)………...45 FIGURE 31: Capacitor charging and inductor is discharging…………………..........46 FIGURE 32: Capacitor fully charged (+) and inductor fully discharged…………….46 FIGURE 33: Pendulum Energy Transfer…………………………………………......47 FIGURE 34: Magnetic Loop Antenna..........................................................................50 FIGURE 35: Magnetic loop coil...................................................................................51 FIGURE 36: Schematic of the experimental setup.......................................................56 FIGURE 37: Flow Diagram of System.........................................................................59 FIGURE 38: AC to DC converter………………………………………………….....61 FIGURE 39: Inside SG3525A………………………………………………………..63 FIGURE 40: Transmitter Circuit…………………………………………………….. 64 FIGURE 41: Receiver Circuit ...…………………………………………………….. 67 FIGURE 42: Efficiency versus Distance……………………………………………...74 FIGURE 43: Efficiency versus Frequency……………………………………………74 FIGURE 44: Different Structures of coil……………………………………………...76

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LIST OF TABLES TABLE 1: Project Plan: Schedule/phasing…………………………………………9 TABLE 2: Impedances of R, L & C…………………………………......................40 TABLE 3: A comparison of different types of PWM ICs…………….....................62 TABLE 4: Transmitter Circuit Components List…………………….......................70 TABLE 5: Receiver Circuit Components List……………………………………...71 TABLE 6: Transmitter and Receiver Parameters…………………………………..73

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ABSTRACT

This thesis report explains the implementation of Wireless Electric Power Transmission System using Resonant Coupling. We have designed two circuit first circuit is called power sending circuit and second circuit is called receiving circuit. Both the circuits are working on resonant coupling system. In this way power is wirelessly transfer between two resonant coils. The device would plug into the wall and adjust the frequency of the wall voltage to the resonant frequency of the LC circuit (640 KHz) by rectifying and inverting the wall signal. After power is transmitted to the receiving LC circuit, this voltage will be transformed, rectified and filtered to produce around 220V to power up 22Watt energy saver bulbs at a contact less distance of 36 cm. The power is wirelessly transmitted even if any thick obstacle is placed between transmitter and receiver. All the block diagrams, equipment, circuit elements have been completely explained in the report.

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CHAPTER 1

PROJECT OVERVIEW

Objectives In this chapter, the main focus is on describing the general structure. This chapter is mainly concentrated on:

1.)

Goals and Objectives

2.)

Scope of the Project

3.)

Literature Review Summary

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Project Overview 1.1: Proposed Objective Our main objective is to develop a system for Wireless Electric Power Transfer. Today, portable technology is a part of every day life. Having your stereo, telephone or computer tied to a wall is a thing of the past. But from portability, emerges another challenge: energy. Almost all portable devices are battery powered, meaning that eventually, they all must be recharged–tying the user back to the wall he was trying to avoid.

Now imagine that instead of plugging in your cell phone, laptop or mp3 player to recharge it, it could receive its power wirelessly–quite literally, “out of thin air”. Sound like science fiction? It’s much closer to reality than you might think.

Wireless Electric Power Transmission is the process where electrical energy is transmitted from a power source to an electrical load, without interconnecting wires.

F1g. 1 Animated View of Resonant Coupling [1]

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The technique being used for Wireless Electric Power Transfer is “Resonant Coupling”. This technique introduces a concept called “Resonance” to the wireless energy equation. Similar to mutual induction, wherein electricity traveling along an electromagnetic wave moves between coils on the same frequency, Resonant Coupling functions on the concept that if you make both coils resonate at the same frequency, electricity can be passed between them at farther distances and without health dangers. Using this technique, one can even send electricity to multiple devices at once, as long as they all share the same resonance frequency.

Two objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with objects that have a different resonant frequency. In physics, resonance is the tendency of an object to oscillate at maximum amplitude at a certain frequency. If the object is excited with a different frequency, its oscillation will die down. Coupling is particularly suitable for everyday applications because most common materials interact only very weakly with electromagnetic fields, so interactions with extraneous environmental objects are suppressed even further. This makes it a safe design for people and other living creatures. The crucial advantage of using the non-radiative field lies in the fact that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost. Although the two coils are currently of identical dimensions, it is possible to make the device coil small enough to fit into portable devices without decreasing the efficiency. Using a non-radiative field means

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that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost.

1.2: Scope and Introduction of the Project (Abstract) We are trying to investigate whether, and to what extent, the physical phenomenon of long-life time resonant electromagnetic states with localized slowly-evanescent field patterns can be used to transfer energy efficiently over non-negligible distances, even in the presence of extraneous environmental objects. Via detailed theoretical and numerical analyses of typical real-world model-situations and realistic material parameters, we can establish that such a non-radiative scheme can lead to “strong coupling” between two medium-ranges distant such states and thus could indeed be practical for efficient medium-range wireless energy transfer.

We investigate the feasibility of using long-lived oscillatory resonant electromagnetic modes, with localized slowly-evanescent field patterns, for efficient wireless nonradiative mid-range energy transfer [8]. The proposed method is based on the well known principle of resonant coupling (the fact that two same-frequency resonant objects tend to couple, while interacting weakly with other off-resonant environmental objects) and, in particular, resonant evanescent coupling (where the coupling mechanism is mediated through the overlap of the non-radiative near-fields of the two objects). This well known physics leads trivially to the result that energy can be efficiently coupled between objects in the extremely near field (e.g. in optical waveguide or cavity couplers and in resonant inductive electric transformers). However, it is far from obvious how this

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same physics performs at mid-range distances and, to our knowledge, there is no work in the literature that demonstrates efficient energy transfer for distances a few times larger that the largest dimension of both objects involved in the transfer. In the present paper, our detailed theoretical and numerical analysis shows that such an efficient mid-range wireless energy-exchange can actually be achieved, while suffering only modest transfer and dissipation of energy into other off-resonant objects, provided the exchange system is carefully designed to operate in a regime of “strong coupling” compared to all intrinsic loss rates. The physics of “strong coupling” is also known but in very different areas, such as those of light-matter interactions. In this favorable operating regime, we quantitatively address the following questions: up to which distances can such a scheme be efficient and how sensitive is it to external perturbations? The omni directional but stationary (lossless) nature of the near field makes this mechanism suitable for mobile wireless receivers. It could therefore have a variety of possible applications including for example, placing a source (connected to the wired electricity network) on the ceiling of a factory room, while devices (robots, vehicles, computers, or similar) are roaming freely within the room..

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1.3: Project Plan: SCHEDULE/ PHASING

No.

Elapsed time from start (in months) of the project

Milestone

Deliverables

1 Months

Initial Literature Review

A comprehensive report on study and analysis of different methods of Electric Power Transmission

2.

3 Months

Study of “Coupling Mode Theory”

A Comprehensive Report on study of Coupling Mode Theory & Its Applications in Real Life & How it Can be Helpful in Our Project

3.

5 Months

Study of Resonant Coupling

1.

Hardware Designing 4.

5.

6.

6 Months

10 Months

11 Months

Hardware Implementations

Compilation and documentation of the experimental results and publication of research paper

Report on “ Resonant Coupling “ & its Biological Effects & effects on other Non-Resonating Objects Designing of “TransmitterReceiver” system for Wireless Transmission of Electric Power in 36cm range Implementation of a “TransmitterReceiver” system for Wireless Transmission of Electric Power in 36cm range Final Project Report and proposal For future work.

Table 1 Project Plan: Schedule / Phasing

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Fig. 2

[19]

1.4: Literature Review Summary In our present electricity generation system we waste more than half of its resources. Especially the transmission and distribution losses are the main concern of the present power technology. Much of this power is wasted during transmission from power plant generators to the consumer. The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient. We have to think of alternate state - of - art technology to transmit and distribute the electricity. Nowa- days global scenario has been changed a lot and there are tremendous development in every field. If we don’t keep pace with the development of new power technology we

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have to face a decreasing trend in the development of power sector. The transmission of power without wires may be one noble alternative for electricity transmission. In the early days of electromagnetism, before the electrical-wire grid was deployed, serious interest and effort was devoted (most notably by Nikola Tesla [1]) towards the development of schemes to transport energy over long distances without any carrier medium (e.g. wirelessly). These efforts appear to have met with little success. Radiative modes of omni-directional antennas (which work very well for information transfer) are not suitable for such energy transfer, because a vast majority of energy is wasted into free space. Directed radiation modes, using lasers or highly-directional antennas, can be efficiently used for energy transfer, even for long distances (transfer distance LTRANS»LDEV, where LDEV is the characteristic size of the device), but require existence of an uninterruptible line-of-sight and a complicated tracking system in the case of mobile objects. Rapid development of autonomous electronics of recent years (e.g. laptops, cellphones, house-hold robots, that all typically rely on chemical energy storage) justifies revisiting investigation of this issue. Today, we face a different challenge than Tesla: since the existing electrical-wire grid carries energy almost everywhere, even a mediumrange (LTRANS ≈ few∗LDEV) wireless energy transfer would be quite useful for many applications. There are several currently used schemes, which rely on non-radiative modes (magnetic induction), but they are restricted to very close-range (LTRANS«LDEV) or very low-power (~mW) energy transfers [2, 3, 4, 5, 6].

Getting around these issues is tricky. There have been a number of moderately successful efforts to make working systems, mostly based on near-contact (i.e., centimeter-range)

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power transfer. These use the sort of magnetic field induction found in a transformer or an induction motor, both of which rely on a non radiating “evanescent” field that reduces the power lost to radiation. But the power transfer falls off very steeply and the range is very short. The result is a powered pad on which a suitably enabled device can be placed to charge—wireless indeed, but not very mobile. These issues can be handled by making both the “sender” and the “receiver” of electrical power operate at the same frequency.

F1g. 3 Comparison between WIFI and WET system [2] With carefully chosen parameters, the two coils form a single coupled resonant structure and behave as though a “tunnel” was opened between them that can carry substantial power over ranges of several meters. The decay in the coupling between the source and receiver with increasing source receiver separation is still quite steep relative to sunlightstyle radiative transfer. However, this no longer translates directly into a decay of power transfer efficiency, because un-transferred power remains trapped around the source and all the power could still be transferred with ideal components. This technique cannot in reality extend the range indefinitely— for example, the power trapped around the source will tend to rise unacceptably, and imperfect real components will cause losses—but it does help a lot.

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And there is another likely benefit from the use of these resonances, which addresses the possible health concern. Unlike a freely propagating electromagnetic wave (such as sunlight), where the electric and magnetic components are always of similar intensity on average, these resonances are overwhelmingly magnetic in character. This could be extremely helpful in reducing the hazard to health, because most ordinary materials (including people) interact far more strongly with the electric than with the magnetic component of an electromagnetic wave [26], so the absorbed power can be much less for a given amount of power transferred. This helps efficiency but, far more important, it reduces the microwave oven–style heating within brain tissue that defines the known hazard limits for all radiofrequency devices such as mobile phones. This effect has not yet been proven by standard safety tests, but it looks very promising.

CHAPTER 2

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HISTORY

Objectives In this chapter, the need for a Wireless System of Energy Transmission and the various earlier technologies available so far for wireless transmission of electricity and is being discussed to find its possibility in actual practices, their advantages, disadvantages and economical consideration. This chapter is mainly concentrated on:

1.)

The most popular concept known as Tesla Theory.

2.)

The microwave power transmission (MPT) called solar power satellite.

3.)

The highly efficient fiber lasers for wireless power transmission.

HISTORY 2.1: INTRODUCTION 14

Today, portable technology is a part of every day life. Having your stereo, telephone or computer tied to a wall is a thing of the past. But from portability emerges another challenge: energy. Almost all portable devices are battery powered, meaning that eventually, they all must be recharged, tying the user back to the wall he was trying to avoid. Now imagine that instead of plugging in your cell phone, laptop or mp3 player to recharge it, it could receive its power wirelessly–quite literally, “out of thin air”. The power is wirelessly transmitted even if any thick obstacle is placed between transmitter and receiver.

Fig: 4 Wireless electricity could make this phenomenon a reality [3] In our present electricity generation system we waste more than half of its resources. Especially the transmission and distribution losses are the main concern of the present power technology. Much of this power is wasted during transmission from power plant generators to the consumer. The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient. We have to think of alternate state - of - art technology to transmit and

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distribute the electricity. Now- a- days global scenario has been changed a lot and there are tremendous development in every field. If we don’t keep pace with the development of new power technology we have to face a decreasing trend in the development of power sector. The transmission of power without wires may be one noble alternative for electricity transmission.

2.2: THE EXISTING TECHNOLOGIES AVAILABLE In this remarkable discovery of the "True Wireless" and the principles upon which transmission and reception, even in the present day systems, are based, Dr. Nikola Tesla shows us that he is indeed the "Father of the Wireless." The most well known and famous Wardenclyffe Tower (Tesla Tower) was designed and constructed mainly for wireless transmission of electrical power, rather than telegraphy. The most popular concept known is Tesla Theory in which it was firmly believed that Wardenclyffe (Fig.1) would permit wireless transmission and reception across large distances with negligible losses. In spite of this he had made numerous experiments of high quality to validate his claim of possibility of wireless transmission of electricity. But this was an unfortunate incidence that people of that century was not in a position to recognize his splendid work otherwise today we may transmit electricity wirelessly and will convert our mother earth a wonderful adobe full of electricity.

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Fig.5: The 187-ft Wardenclyffe Tower (Tesla Tower) in 1903. [4] The modern ideas are dominated by microwave power transmission (MPT, Figure 3) called Solar power satellite to be built in high earth orbit to collect sunlight and convert that energy into microwaves, then beamed to a very large antenna on earth, the microwaves would be converted into conventional electrical power.

William C. Brown [21], the leading authority on wireless power transmission technology, has loaned this demonstration unit to the Texas Space Grant Consortium to show how power can be transferred through free space by microwaves. A block diagram of the demonstration components is shown below. The primary components include a microwave source, a transmitting antenna, and a receiving antenna.

Fig.6: Microwave power transmission. [5] The microwave source consists of a microwave oven magnetron with electronics to control the output power. The output microwave power ranges from 50 W to 200 W at 2.45 GHz. A coaxial cable connects the output of the microwave source to a coax-to-waveguide adapter. This adapter is connected to a waveguide ferrite circulator which protects the microwave source from reflected power. The circulator is connected to a tuning waveguide section to match the waveguide impedance to the antenna input impedance. The slotted waveguide antenna consists of 8 waveguide sections with 8 slots on each section. These 64 slots radiate the power uniformly

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through free space to the antenna. The slotted waveguide rectenna is ideal for power transmission because of its high aperture efficiency (> 95%) and high power handling capability. A rectifying antenna called a rectenna receives the transmitted power and converts the microwave power to direct current (DC) power. This demonstration rectenna consists of 6 rows of dipoles antennas where 8 dipoles belong to each row. Each row is connected to a rectifying circuit which consists of low pass filters and a rectifier. The rectifier is a Ga As Schottky barrier diode that is impedance matched to the dipoles by a low pass filter. The 6 rectifying diodes are connected to light bulbs for indicating that the power is received. The light bulbs also dissipated the received power. This rectenna has a 25% collection and conversion efficiency, but rectennas have been tested with greater than 90% efficiency at 2.45 GHz[22]. The transmission of power without wires is not a theory or a mere possibility, it is now a reality. The electrical energy can be economically transmitted without wires to any terrestrial distance, many researchers have established in numerous observations, experiments and measurements, qualitative and quantitative. These have demonstrated that it is practicable to distribute power from a central plant in unlimited amounts, with a loss not exceeding a small fraction of one per cent, in the transmission, even to the greatest distance, twelve thousand miles - to the opposite end of the globe. This seemingly impossible feat can now be readily performed by electrical researchers familiar with the design and construction of my "high-potential magnifying transmitter," There were three popular theories present in the literature of the late 1800's and early 1900's. They were:

1. Transmission through or along the Earth, 2. Propagation as a result of terrestrial resonances, 3. Coupling to the ionosphere using propagation through electrified gases (Fig.4&5).

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Fig.7: The Trans receiving circuit for wireless power transmission [6] It has been proven that electrical energy can be propagated around the world between the surface of the Earth and the ionosphere at extreme low frequencies in what is known as the Schumann Cavity. Knowing that a resonant cavity can be excited and that power can be delivered to that cavity similar to the methods used in microwave ovens for home use, it should be possible to resonate and deliver power via the Schumann Cavity to any point on Earth. This will result in practical wireless transmission of electrical power. The intent of the experiments and the laboratory Tesla had constructed was to prove that wireless transmission of electrical power was possible. Although Tesla was not able to commercially market a system to transmit power around the globe, modern scientific theory [23] and mathematical calculations support his contention that the wireless propagation of electrical power is possible and a feasible alternative to the extensive and costly grid of electrical transmission lines used today for electrical power distribution.

Power transmission system using directional ultrasound for power transmission includes a transmitting device and a receiving device. The transmitting device has a set of ultrasound transducers forming an ultrasound transducer array, where in the array is a set of spaced individual transducers placed in the X-Y plane disposed to generate an[27] ultrasound beam in

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the Z direction (Fig.6). Another possibility is to use highly efficient fiber lasers for wireless power transmission where the possibilities are similar to microwaves concept but lasers emit energy at frequencies much higher that microwaves. For several years NASA, ENTECH, and UAH have been working on various aspects of collection of the laser radiation and conversion to electrical power for laser wireless power transmission.

Fig.8: System and method for wireless electrical power Transmission (directional ultrasound for power Transmission). [5] Laser technology can also be used to transmit electric power wirelessly over a long distance. This technology is used by NASA to transmit high electric power to their remote satellite or to their robots present on moon for the research work. [24] The only disadvantage of the Laser is that it works only in direct line of sight so it can be interrupted by obstacle.

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Fig. 9 Electric Power Transmission using LASER [7]

2.3: MERITS, DEMERITS & ECONOMICS OF EARLIER WIRELESS TECHNOLOGIES Merits An electrical distribution system, based on this method would eliminate the need for an inefficient, costly, and capital intensive grid of cables, towers, and substations. The system would reduce the cost of electrical energy used by the consumer and rid the landscape of wires, cables, and transmission towers [25]. There are areas of the world where the need for electrical power exists, yet there is no method for delivering power. Africa is in need of power to run pumps to tap into the vast resources of water under the Sahara Desert. Rural areas, such as those in China, require the electrical power necessary to bring them into the 20th century and to equal standing with western nations. The wireless transmission will solve many of these problems the electrical energy can be economically transmitted without wires to any terrestrial distance, so there will be no transmission and distribution loss. More efficient energy distribution systems and sources are needed by both developed and under developed nations. In regards to the new systems, the market for wireless power transmission is enormous. It has the potential to become a multi-billion

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dollar per year market. The increasing demand for electrical energy in industrial nations is well documented. If we include the demand of third [28] world nations, pushed by their increasing rate of growth, we could expect an even faster rise in the demand for electrical power in the near future. These systems can only meet these requirements with 90–94 %efficient transmission. High Transmission Integrity and Low Loss: To transmit wireless power to any distance without limit. It makes no difference what the distance is. The efficiency of the transmission can be as high as 96 or 97 per cent, and there are practically no losses.

Demerits Biological Impact One common criticism of the Tesla wireless power system is regarding its possible biological effects. Calculating the circulating reactive power, it was found that the frequency is very small and such a frequency is very biologically compatible.

2.4: Economic Impact The concept looks to be costly initially. The investment cost of Tesla Tower was $150,000 (1905). In terms of economic theory, many countries will benefit from this service. Only private, dispersed receiving stations will be needed. Just like television and radio, a single resonant energy receiver is required, which may eventually be built into appliances, so no power cord will be necessary! Monthly electric utility bills from old-fashioned, fossil-fuelled, loss prone electrified wire-grid delivery services will be optional, much like “cable TV” of today. In the 21st century, “Direct TV” is the rage, which is an exact parallel of Tesla’s “Direct Electricity.”

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CHAPTER 3

WIRELESS TECHNOLOGIES

Objectives In this chapter the reader may find a discussion of the issues involved so that one can make an informed decision on the antenna type as per need. And the various wireless technologies available so far for wireless transmission are being discussed. The chapter includes:

1.) Radiative Method



Uni- Directional



Omni Directional

2.) Non- Radiative Method



Resonant Coupling



Magnetic Induction

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WIRELESS TECHNOLOGIES 3.1: Introduction Concurrent with steadily increasing signal frequencies HF and microwave antennas get more and more important for applications such as broadband transmission links, radar remote sensing / navigation, and wireless transfer of high data rates. Most actual developments like satellite and mobile communications are strongly expanding all over the world. Miniaturized antenna sensor arrays support novel techniques of detection of earth resources, control of soil / water contamination, robotics, etc.

3.2: Antenna Characteristics The study of antennas involves the following terms with which we must become familiar:

3.2.1: Antenna Reciprocity The ability of an antenna to both transmit and receive electromagnetic energy is known as its reciprocity. Antenna reciprocity is possible because antenna characteristics are essentially the same for sending and receiving electromagnetic energy.

Even though an antenna can be used to transmit or receive, it cannot be used for both functions at the same time. The antenna must be connected to either a transmitter or a receiver. 3.2.2: Antenna Feed Point Feed point is the point on an antenna where the RF cable is attached. If the RF transmission line is attached to the base of an antenna, the antenna is end-fed. If the RF transmission line is connected at the center of an antenna, the antenna is mid-fed or center-fed.

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3.2.3: Directivity The directivity of an antenna refers to the width of the radiation beam pattern. A directional antenna concentrates its radiation in a relatively narrow beam. If the beam is narrow in either the horizontal or vertical plane, the antenna will have a high degree of directivity in that plane. An antenna can be highly directive in one plane only or in both planes, depending upon its use.

3.3- Radiative Method In general, we use three terms to describe the type of Radiative qualities associated with an antenna:

 



Omni- directional Bi- directional Uni- directional

Omni directional antennas radiate and receive equally well in all directions, except off the ends. Bidirectional antennas radiate or receive efficiently in only two directions. Unidirectional antennas radiate or receive efficiently in only one direction. Most antennas used in naval communications are either omni directional or unidirectional. Bidirectional antennas are rarely used.

3.3.1: Uni- Directional & Bi- Directional Method

Gain and directivity are intimately related in antennas. The directivity of an antenna is a statement of how the RF energy is focused in one or two directions. Because the amount of RF energy remains the same, but is distributed over less area, the apparent signal strength is higher. This apparent increase in signal strength is the antenna gain. The gain is measured in decibels over either a dipole (dBd) or a theoretical construct called an 25

isotropic radiator (dBi). The isotropic radiator is a spherical signal source that radiates equally well in all directions. One way to view the omni- directional pattern is that it is a slice taken horizontally through the three dimensional sphere.

Figure 10 [8] shows a unidirectional pattern such as found on Yagi and quad beams and certain other antennas. The main lobe is the direction of maximum radiation or reception. In addition to the main lobe, there are also sidelobes and backlobes. These lobes represent lost energy so good antenna designs attempt to minimize them. In the unidirectional antenna pattern, signals "A", "C" and "D" are suppressed, while signal "B" is maximized. The beam width of the antenna is a measure of its directivity. In the case of the pattern of Local installation factors can affect the radiation pattern. In "free space," i.e. the antenna is installed at great distance from the surface of the Earth, trees, houses, wiring and so forth, the pattern will be nearly perfect. But in practical situations, the two lobes might not be equal, or the minima might be less distinct.

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Fig. 11 [8] shows a bidirectional antenna pattern. This pattern is associated with half wavelength dipoles, quad loops, and a number of other antennas. There are two preferred directions (maxima) and two null directions (minima). In the half wavelength dipole the minima and maxima are positioned as shown. For receivers, signals arriving from the direction of the minima (Signal "A" and Signal "C") are suppressed because the antenna is not sensitive in that direction. The suppression is not complete, but it can be tremendous. The signals arriving from the direction of the maxima (Signal "B" and Signal "D") are received the loudest. For transmitters, the radiated signal is the lowest in the direction of the minima and greatest in the direction of the maxima. Again, the signal level radiated off the ends of the antenna, i.e. in the direction of the minima, is not zero, but is very low.

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It is common practice to mount unidirectional antennas in a manner that allows the main lobe to be positioned in any direction. This approach is easily achievable on the higher frequencies of the HF shortwave bands and throughout the VHF/UHF spectrum. At lower frequencies, however, the size of the antenna is usually too large. For example, the Yagi beam uses elements about half wavelength long, so at 15-MHz the elements are about 9.5- meters (31.2-feet) long. At 4 MHz, on the other hand, they are 36-meters (118-feet) long. For any given installation a decision has to be made on the mechanical aspects because the larger beams are also very expensive to install.

3.3.2: Omni- Directional Method The omni- directional antenna radiates or receives equally well in all directions. It is also called the "non-directional" antenna because it does not favor any particular direction. Figure 1 shows the pattern for an omni- directional antenna, with the four cardinal signals. This type of pattern is commonly associated with verticals, ground planes and other antenna types in which the radiator element is vertical with respect to the Earth's surface.

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Fig. 12 Pattern of omni-direcrional antenna [8] The key factor to note is that for receivers all four signals (or signals from any direction, for that matter) are received equally well. For transmitters, the radiated signal has the same strength in all directions. This pattern is useful for broadcasting a signal to all points of the compass (as when calling "CQ"), or when listening for signals from all points.

3.4: Non- Radiative Method In general, we use two terms to describe the type of Non- Radiative qualities associated with an antenna: 

Magnetic Induction



Resonant Coupling

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3.4.1: Magnetic Induction The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are electrically isolated from each other. The transfer of energy takes place by electroCoupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The electric toothbrush charger is an example of how this principle can be used. The main drawback to induction, however, is the short range. The receiver must be in very close proximity to the transmitter or induction unit in order to inductively couple with it.

Applications 

The electric toothbrush battery charger.

Fig. 13 Electric toothbrush battery charger [9]



The induction cooker stovetop.

Fig.14 Induction Cooker Stovetop [10]

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It can be argued the cookware part of an induction cooker is not a secondary in the strictest sense of the term. It is more accurately described as the non-laminated core of an alternating-current electromagnet, in which eddy currents are induced resulting in the heating effect. 

Artificial hearts and other surgically implanted devices.



Devices using induction to charge portable consumer electronics such as cell phones.

3.4.2: Resonance Coupling In 2006, the researchers at the Massachusetts Institute of Technology applied the near field behavior well known in electromagnetic theory to a wireless power transfer concept based on coupled resonators. In a short theoretical analysis they demonstrate that by sending electromagnetic waves around in a highly angular waveguide, evanescent waves are produced which carry no energy. If a proper resonantt waveguide is brought near the transmitter, the evanescent waves can allow the energy to tunnel (specifically evanescent wave coupling, the electromagnetic equivalent of tunneling) to the power drawing waveguide, where they can be rectified into DC power. Since the electromagnetic waves would tunnel, they would not propagate through the air to be absorbed or dissipated, and would not disrupt electronic devices or cause physical injury like microwave or radio wave transmission might. Researchers anticipate up to 5 meters of range for the initial device, and are currently working on a functional prototype.

"Resonant inductive coupling" has key implications in solving the two main problems associated with non-resonant inductive coupling and electromagnetic radiation, one of which is caused by the other; distance and efficiency. Electromagnetic induction works on the principle of a primary coil generating a predominantly magnetic field and a secondary coil being within that field so a current is induced within its coils. This causes the relatively short range due to the amount of power required to produce an electromagnetic field. Over greater distances the non-resonant induction method is inefficient and wastes much of the transmitted energy just to increase range.

31

This is where the resonance comes in and helps efficiency dramatically by "tunneling" the magnetic field to a receiver coil that resonates at the same frequency. Unlike the multiple-layer secondary of a non-resonant transformer, such receiving coils are single layer solenoids with closely spaced capacitor plates on each end, which in combination allow the coil to be tuned to the transmitter frequency thereby eliminating the wide energy wasting "wave problem" and allowing the energy used to focus in on a specific frequency increasing the range.

Fig. 15 Resonance Coupling between Coils [11]

32

CHAPTER 4

RESONANT COUPLING

Objectives In this chapter, we are focusing on “Resonant Coupling”, the Technique being used in our Project. This chapter is mainly concentrated on:

1.)

The idea of Resonance & its role in WET System.

2.)

Behavior of a Resonant Circuit.

3.)

Advantages of Resonant Coupling.

33

Resonant Coupling 4.1: Introduction Wireless Electric Power Transmission System is based on using coupled resonant objects. Two objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with objects that have a different resonant frequency. In physics, resonance is the tendency of an object to oscillate at maximum amplitude at a certain frequency. If the object is excited with a different frequency, its oscillation will die down. Think of a swing for example - a kid needs to pump his legs with the right rhythm in order to gain more momentum from it. Two objects with the same resonant frequency, allowing them to exchange energy efficiently, while not interacting strongly with extraneous off-resonant objects. Such strongly coupled systems have the ability of allowing relatively efficient energy transfer. Another example: we’ve all heard the myth about the opera singer breaking the glass with a high note, but has anyone ever seen it happening in real life? It’s not actually a myth, though - if the singer sings a sufficiently loud single note of the same frequency as the natural frequency of the glass, the latter will accumulate energy until it finally explodes. The example of a room with 100 identical water glasses each filled with water up to a different level, so they all have different resonant frequencies. If an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses.

34

While there are few different kinds of resonant systems, our team focused on one particular type: magnetically coupled resonators. We have explored a system of two electromagnetic resonators, each consist of a helical copper coil placed about 2.5-feets apart, coupled mostly through their electromagnetic fields. Using the mathematical theory, we calculated the optimal sizes of the coils in order to match their frequencies and maximize the energy transfer efficiency.

4.2: Resonance It's hard to grasp the idea that electric circuits can resonate because we can't see it happening. Still, it's one of the most useful and common forms of resonance. Resonance can occur in something called an RLC circuit. The letters stand for the different parts of the circuit. R is for resistor. These are devices which convert electrical energy into thermal energy. In other words, they remove energy from the circuit and convert it to heat. L stands for inductor. (How they came up with L for inductor is hard to understand.) Inductance in electric circuits is like mass or inertia in mechanical systems. It doesn't do much until you try to make a change. In mechanics the change is a change in velocity. In an electric circuit it is a change in current. When this happens inductance resists the change. C is for capacitors which are devices that store electrical energy in much the same way that springs store mechanical energy. An inductor concentrates and stores magnetic energy, while a capacitor concentrates charge and thereby stores electric energy.

35

4.2.1: Energy Flow in an Electric Circuit Of course, the first step in understanding resonance in any system is to find the system's natural frequency. Here the inductor (L) and the capacitor (C) are the key components. The resistor tends to damp oscillations because it removes energy from the circuit. For convenience, we'll temporarily ignore it, but remember, like friction in mechanical systems, resistance in circuits is impossible to eliminate.

(A)

(B) Fig. 16 LC switching circuit [12]

We can make a circuit oscillate at its natural frequency by first storing electrical energy or, in other words, charging its capacitor as shown in Figure 16 (A). When this is accomplished the switch is thrown to the position shown in Figure 16 (B).

At time = 0 all of the electrical energy is stored in the capacitor and the current is zero (see Figure 17). Notice that the top plate of the capacitor is charged positively and the bottom negatively. We can't see the electrons' oscillation in the circuit but we can measure

36

it using an ammeter and plot the current versus time to picture what the oscillation is like. Note that T on our graph is the time it takes to complete one oscillation.

Fig.17 [12]

Current flows in a clockwise direction (see Figure 18). The energy flows from the capacitor into the inductor. At first it may seem strange that the inductor contains energy but this is similar to the kinetic energy contained in a moving mass.

Fig. 18 [12]

Eventually the energy flows back into the capacitor, but note, the polarity of the capacitor is now reversed. In other words, the bottom plate now has the positive charge and the top plate the negative charge (see Figure 19).

37

Fig. 19 [12]

The current now reverses itself and the energy flows out of the capacitor back into the inductor (see Figure 20). Finally the energy fully returns to its starting point ready to begin the cycle all over again as shown in Figure 17.

Fig. 20 [12]

The frequency of the oscillation can be approximated as follows:

In real-world LC circuits there's always some resistance which causes the amplitude of the current to grow smaller with each cycle. After a few cycles the current diminishes to

38

zero. This is called a "damped sinusoidal" waveform. How fast the current damps to zero depends on the resistance in the circuit. However, the resistance does not alter the frequency of the sinusoidal wave. If the resistance is high enough, the current will not oscillate at all. Obviously, where there's a natural frequency there's a way to excite a resonance. We do this by hooking an alternating current (AC) power supply up to the circuit as shown in Figure 21. The term alternating means that the output of the power supply oscillates at a particular frequency. If the frequency of the AC power supply and the circuit it's connected to are the same, then resonance occurs. In this case we measure the amplitude or size of the oscillation by measuring current.

Fig. 21 [13]

Note in figure 21 that we have put a resistor back in the circuit. If there is no resistor in the circuit the current's amplitude will increase until the circuit burns up. Increasing resistance tends to decrease the maximum size of the current's amplitude but it does not change the resonant frequency. As a rule of thumb, a circuit will not oscillate unless the resistance (R) is low enough to meet the following condition:

39

4.2.1.1: Impedance of components Let's recap what we now know about voltage and current in linear components. The impedance is the general term for the ratio of voltage to current. Resistance is the special case of impedance when φ = 0, reactance the special case when φ = ± 90°. The table below summarizes the impedance of the different components. It is easy to remember that the voltage on the capacitor is behind the current, because the charge doesn't build up until after the current has been flowing for a while.

Table 2 Impedances of R, L & C [14]

The same information is given graphically below. It is easy to remember the frequency dependence by thinking of the DC (zero frequency) behavior: at DC, an inductance is a short circuit (a piece of wire) so its impedance is zero. At DC, a capacitor is an open circuit, as its circuit diagram shows, so its impedance goes to infinity.

Fig. 22 Impedance curves of R,L & C [14]

40

4.2.1.2: Selectivity and Quality Factor of a Circuit Resonant circuits are used to respond selectively to signals of a given frequency while discriminating against signals of different frequencies. If the response of the circuit is more narrowly peaked around the chosen frequency, we say that the circuit has higher "selectivity". A "quality factor" Q, as described below, is a measure of that selectivity, and we speak of a circuit having a "high Q" if it is more narrowly selective. An example of the application of resonant circuits is the selection of AM radio stations by the radio receiver. The selectivity of the tuning must be high enough to discriminate strongly against stations above and below in carrier frequency, but not so high as to discriminate against the sidebands created by the imposition of the signal by amplitude modulation. The selectivity of a circuit is dependent upon the amount of resistance in the circuit. The smaller the resistance, the higher the "Q" for given values of L and C. The parallel resonant circuit is more commonly used in electronics, but the algebra necessary to characterize the resonance is much more involved. Using the same circuit parameters, the illustration at left shows the power dissipated in the circuit as a function of frequency. Since this power depends upon the square of the current, these resonant curves appear steeper and narrower than the resonance peaks for current above. The quality factor Q is defined by

where Δω is the width of the resonant power curve at half maximum. Since that width turns out to be Δω =R/L, the value of Q can also be expressed as 41

The Q is a commonly used parameter in electronics, with values usually in the range of Q=10 to 100 for circuit applications.

Fig. 23 Quality Factor at different values of R [15]

4.2.2: An Electric Pendulum Capacitors store energy in the form of an electric field, and electrically manifest that stored energy as a potential: static voltage. Inductors store energy in the form of a magnetic field, and electrically manifest that stored energy as a kinetic motion of electrons: current. Capacitors and inductors are flip-sides of the same reactive coin, storing and releasing energy in complementary modes. When these two types of reactive components are directly connected together, their complementary tendencies to store energy will produce an unusual result. If either the capacitor or inductor starts out in a charged state, the two components will exchange energy between them, back and forth, creating their own AC voltage and

42

current cycles. If we assume that both components are subjected to a sudden application of voltage (say, from a momentarily connected battery), the capacitor will very quickly charge and the inductor will oppose change in current, leaving the capacitor in the charged state and the inductor in the discharged state: (Figure 24)

Fig . 24 Capacitor charged: voltage at (+) peak, inductor discharged [16]

The capacitor will begin to discharge, its voltage decreasing. Meanwhile, the inductor will begin to build up a “charge” in the form of a magnetic field as current increases in the circuit: (Figure 25)

Fig. 25 Capacitor discharging: voltage decreasing, Inductor charging [16]

The inductor, still charging, will keep electrons flowing in the circuit until the capacitor has been completely discharged, leaving zero voltage across it: (Figure 26)

43

Fig. 26 Capacitor fully discharged and Inductor fully charged [16] The inductor will maintain current flow even with no voltage applied. In fact, it will generate a voltage (like a battery) in order to keep current in the same direction. The capacitor, being the recipient of this current, will begin to accumulate a charge in the opposite polarity as before: (Figure 27)

Fig. 27 Capacitor charging: voltage with opposite polarity (-) and inductor discharging [16] When the inductor is finally depleted of its energy reserve and the electrons come to a halt, the capacitor will have reached full (voltage) charge in the opposite polarity as when it started: (Figure 28)

Fig. 28 Capacitor fully charged (-) and inductor fully discharged [16]

44

Now we're at a condition very similar to where we started: the capacitor at full charge and zero current in the circuit. The capacitor, as before, will begin to discharge through the inductor, causing an increase in current (in the opposite direction as before) and a decrease in voltage as it depletes its own energy reserve: (Figure 29)

Fig. 29 Capacitor discharging and inductor charging [16] Eventually the capacitor will discharge to zero volts, leaving the inductor fully charged with full current through it: (Figure 30)

Fig. 30 Capacitor fully discharged and inductor fully charged (-) [16] The inductor, desiring to maintain current in the same direction, will act like a source again, generating a voltage like a battery to continue the flow. In doing so, the capacitor will begin to charge up and the current will decrease in magnitude: (Figure 31)

45

Fig.31 Capacitor charging and inductor discharging [16]

Eventually the capacitor will become fully charged again as the inductor expends all of its energy reserves trying to maintain current. The voltage will once again be at its positive peak and the current at zero. This completes one full cycle of the energy exchange between the capacitor and inductor: (Figure 32)

Fig. 32 Capacitor fully charged (+) and inductor fully discharge [16] This oscillation will continue with steadily decreasing amplitude due to power losses from stray resistances in the circuit, until the process stops altogether. Overall, this behavior is akin to that of a pendulum: as the pendulum mass swings back and forth, there is a transformation of energy taking place from kinetic (motion) to potential (height), in a similar fashion to the way energy is transferred in the capacitor/inductor circuit back and forth in the alternating forms of current (kinetic motion of electrons) and voltage (potential electric energy). 46

At the peak height of each swing of a pendulum, the mass briefly stops and switches directions. It is at this point that potential energy (height) is at a maximum and kinetic energy (motion) is at zero. As the mass swings back the other way, it passes quickly through a point where the string is pointed straight down. At this point, potential energy (height) is at zero and kinetic energy (motion) is at maximum. Like the circuit, a pendulum's back-and-forth oscillation will continue with steadily dampened amplitude, the result of air friction (resistance) dissipating energy. Also like the circuit, the pendulum's position and velocity measurements trace two sine waves (90 degrees out of phase) over time: (Figure 33)

Fig. 33 Pendulum energy transfer [16] In physics, this kind of natural sine-wave oscillation for a mechanical system is called Simple Harmonic Motion (often abbreviated as “SHM”). The same underlying principles govern both the oscillation of a capacitor/inductor circuit and the action of a pendulum, hence the similarity in effect. It is an interesting property of any pendulum that its periodic time is governed by the length of the string holding the mass, and not the weight of the mass itself. That is why a pendulum will keep swinging at the same frequency as

47

the oscillations decrease in amplitude. The oscillation rate is independent of the amount of energy stored in it. The same is true for the capacitor/inductor circuit. The rate of oscillation is strictly dependent on the sizes of the capacitor and inductor, not on the amount of voltage (or current) at each respective peak in the waves. The ability for such a circuit to store energy in the form of oscillating voltage and current has earned it the name tank circuit. Its property of maintaining a single, natural frequency regardless of how much or little energy is actually being stored in it gives it special significance in electric circuit design. However, this tendency to oscillate, or resonate, at a particular frequency is not limited to circuits exclusively designed for that purpose. In fact, nearly any AC circuit with a combination of capacitance and inductance (commonly called an “LC circuit”) will tend to manifest unusual effects when the AC power source frequency approaches that natural frequency. This is true regardless of the circuit's intended purpose. If the power supply frequency for a circuit exactly matches the natural frequency of the circuit's LC combination, the circuit is said to be in a state of resonance. The unusual effects will reach maximum in this condition of resonance. For this reason, we need to be able to predict what the resonant frequency will be for various combinations of L and C, and be aware of what the effects of resonance are. REVIEW: 

A capacitor and inductor directly connected together form something called a tank circuit, which oscillates (or resonates) at one particular frequency. At that

48

frequency, energy is alternately shuffled between the capacitor and the inductor in the form of alternating voltage and current 90 degrees out of phase with each other. 

When the power supply frequency for an AC circuit exactly matches that circuit's natural oscillation frequency as set by the L and C components, a condition of resonance will have been reached.

4.2.3: Applications of Resonance Example 1: Magnetic Loop Antenna Magnetic loop antennas (also known as Small Transmitting/Receiving Loops) have a small antenna size compared to other antennas for the same wavelength. The antenna is typically smaller than 1/4 wavelength of the intended frequency of operation. Antennas for shortwave communication are typically very large, sometimes several hundred meters. The advantage of the magnetic loop is high efficiency despite its small size.

The technical mechanism uses a capacitor to "enlarge" the antenna and bring it to resonance. The disadvantage of this method is the low bandwidth of the antenna, also known as high Q, which limits efficient operation to a narrow frequency range. A high-Q can be advantageous, however. Since well-tuned magnetic loops function best within a narrow frequency range when tuned, they tend to reject harmonic noise from other RF sources. This keeps the level of unwanted noise down as compared with wider-bandwidth antennas.

49

Fig. 34 Magnetic Loop Antenna [17]

As a result of the narrow operating bandwidth of the antenna, if the frequency of operation is changed, the antenna needs to be retuned by changing the capacitive value of the antenna. Bandwidth is the usable frequency range of an antenna in relation to the area of desired operation. When the antenna is operated outside of its bandwidth, the energy from the transmitter is reflected back from the antenna, down through the feed line back to the transmitter. The term bandwidth relates to the concept of Standing Wave Ratio or SWR. When the reflected power exceeds a 2.5:1 power reflection ratio (too much energy being reflected from the antenna back into the feed line) the antenna will not maintain its performance characteristics. This type of condition relates specifically to the antenna's ability to transmit radio energy from the transmitter to the antenna.

The magnetic loop antenna is an old antenna; however, many military, commercial, and amateur radio operators still use them today. The Magnetic Loop was widely used in the Vietnam War due to its high portability.

50

Example 2: Application in Our System Our WET system relies on two coils. Electricity, traveling along an electromagnetic wave, can tunnel from one coil to the other as long as they both have the same resonant frequency. The effect is similar to the way one vibrating trumpet can cause another to vibrate.

Fig. 35 Magnetic loop coil [18] As long as both coils are out of range of one another, nothing will happen, since the fields around the coils aren't strong enough to affect much around them. Similarly, if the two coils resonate at different frequencies, nothing will happen. But if two resonating coils with the same frequency get within a few meters of each other, streams of energy move from the transmitting coil to the receiving coil. According to the theory, one coil can even send electricity to several receiving coils, as long as they all resonate at the same frequency. The researchers have named this non-radiative energy transfer since it involves stationary fields around the coils rather than fields that spread in all directions.

51

4.3: Advantages of Resonant Coupling Coupling is particularly suitable for everyday applications because most common materials interact only very weakly with electromagnetic fields, so interactions with extraneous environmental objects are suppressed even further. This makes it a safe design for people and other living creatures, and in order to prove it, the team released couple of photos with themselves standing between the coils while the system was operating. Here you can see that the system still works even when there’s an obstruction in the middle: The crucial advantage of using the non-radiative field lies in the fact that most of the power not picked up by the receiving coil remains bound to the vicinity of the sending unit, instead of being radiated into the environment and lost. Although the two coils are currently of identical dimensions, it is possible to make the device coil small enough to fit into portable devices without decreasing the efficiency. However, as the distance between the source and the device coils increases, the efficiency of transfer decreases. Still, for laptop-sized coils, power levels more than sufficient to run a laptop can be transferred across a room; as long as the laptop is in a room equipped with a source of such wireless power, it would charge automatically, without having to be plugged in.

52

CHAPTER 5

SYSTEM DESIGN

Objectives In this chapter, Hardware Design of WET System is being discussed. Different System Components and Parameters are described in detail. This chapter is mainly concentrated on:

1.)

System Components

2.)

Mathematical Work

3.)

Cost of Design

4.)

Circuit Diagrams

53

SYSTEM DESIGN 5.1: Development / Research Methodology Efficient mid-range power transfer occurs in particular regions of the parameter space describing resonant objects strongly coupled to one another. Using coupled-mode theory to describe this physical system, we obtain the following set of linear equations:

Where the indices denote the different resonant objects The variables am(t) are defined so that the energy contained in object m is |am(t)|2, resonant angular frequency of that isolated object, and

m

m

is the

is its intrinsic decay rate (e.g.,

due to absorption and radiated losses). In this framework, an uncoupled and undriven oscillator with parameters

0

and

0

would evolve in time as exp(i 0t – 0t). The

=

mn

nm

are coupling coefficients between the resonant objects indicated by the subscripts, and Fm(t) are driving terms. We limit the treatment to the case of two objects, denoted by source and device, such that the source (identified by the subscript S) is driven externally at a constant frequency, and the two objects have a coupling coefficient . Work is extracted from the device (subscript D) by means of a load (subscript W) that acts as a circuit resistance connected to the device, and has the effect of contributing an additional term object's decay rate

W

to the unloaded device

. The overall decay rate at the device is therefore 'D =

D

D

+

work extracted is determined by the power dissipated in the load, that is, 2

. The

W

|aD(t)|2.

W

54

Maximizing the efficiency of the transfer with respect to the loading

, given Eq., is

W

equivalent to solving an impedance-matching problem. One finds that the scheme works best when the source and the device are resonant, in which case the efficiency is

The efficiency is maximized when

/

W

to efficient energy transfer is to have

=[1+ ( 2/

D 2

/

S D

)]1/2. It is easy to show that the key

S D

>1. This is commonly referred to as the

strong coupling regime. Resonance plays an essential role in this power transfer mechanism, as the efficiency is improved by approximately

2

/

2 D

( 106 for typical

parameters) relative to the case of inductively coupled non resonant objects.

5.2 Theoretical model for self-resonant coils Our experimental realization of the scheme consists of two self-resonant coils. One coil (the source coil) is coupled inductively to an oscillating circuit; the other (the device coil) is coupled inductively to a resistive load (Fig. 1). Self-resonant coils rely on the interplay between distributed inductance and distributed capacitance to achieve resonance. The coils are made of an electrically conducting wire of total length l and cross-sectional radius a wound into a helix of n turns, radius r, and height h. To the best of our knowledge, there is no exact solution for a finite helix in the literature, and even in the

55

case of infinitely long coils, the solutions rely on assumptions that are inadequate for our system.

Fig. 36 [11]Schematic of the experimental setup. A is a single copper loop of radius 25 cm that is part of the driving circuit, which outputs a sine wave with frequency 500 KHz. S and D are respectively the source and device coils referred to in the text. B is a loop of wire attached to the load (light bulb). The various s represent direct couplings between the objects indicated by the arrows. The angle between coil D and the loop A is adjusted to ensure that their direct coupling is zero. Coils S and D are aligned coaxially. The direct couplings between B and A and between B and S are negligible

We start by observing that the current must be zero at the ends of the coil, and we make the educated guess that the resonant modes of the coil are well approximated by sinusoidal current profiles along the length of the conducting wire. We are interested in the lowest mode, so if we denote by s the parameterization coordinate along the length of the conductor, such that it runs from –l/2 to +l/2, then the time-dependent current profile has the form I0 cos( s/l) exp(i t). It follows from the continuity equation for charge that the linear charge density profile is of the form

0

sin( s/l) exp(i t), so that one-half of the

coil (when sliced perpendicularly to its axis) contains an oscillating total charge (of amplitude q0 =

l/ ) that is equal in magnitude but opposite in sign to the charge in the

0

other half.

56

As the coil is resonant, the current and charge density profiles are /2 out of phase from each other, meaning that the real part of one is maximum when the real part of the other is zero. Equivalently, the energy contained in the coil is at certain points in time completely due to the current, and at other points it is completely due to the charge. Using electromagnetic theory, we can define an effective inductance L and an effective capacitance C for each coil as follows:

where the spatial current J(r) and charge density (r) are obtained respectively from the current and charge densities along the isolated coil, in conjunction with the geometry of the object. As defined, L and C have the property that the energy U contained in the coil is given by

Given this relation and the equation of continuity, the resulting resonant frequency is f0 = 1/[2 (LC)1/2]. We can now treat this coil as a standard oscillator in coupled-mode theory by defining a(t)=[(L/2)1/2]I0(t).

57

We can estimate the power dissipated by noting that the sinusoidal profile of the current distribution implies that the spatial average of the peak current squared is |I0|2/2. For a coil with n turns and made of a material with conductivity , we modify the standard formulas for ohmic (Ro) and radiation (Rr) resistance accordingly:

The first term in Eq is a magnetic dipole radiation term (assuming r << 2 c/ , where c is the speed of light); the second term is due to the electric dipole of the coil and is smaller than the first term for our experimental parameters. The coupled-mode theory decay constant for the coil is therefore =(Ro + Rr)/2L, and its quality factor is Q = /2 . We find the coupling coefficient

DS

by looking at the power transferred from the source

to the device coil, assuming a steady-state solution in which currents and charge densities vary in time as exp(i t):

58

Where M is the effective mutual inductance, is the scalar potential, A is the vector potential, and the subscript S indicates that the electric field is due to the source. We then conclude from standard coupled-mode theory arguments that KDS = KSD = K=

M/

[2(LSLD1/2)]. When the distance D between the centers of the coils is much larger than their characteristic size, K scales with the D–3 dependence characteristic of dipole-dipole coupling. Both and are functions of the frequency, and / and the efficiency are maximized for a particular value of f, which is in the range 1 to 50 MHz for typical parameters of interest. Thus, picking an appropriate frequency for a given coil size, as we do in this experimental demonstration, plays a major role in optimizing the power transfer.

5.3 Flow Diagram of the System

Fig. 37 Flow Diagram of System [19]

59

5.3.1 AC to DC Converter "Electronic power converter" is the term that is used to refer to a power electronic circuit that converts voltage and current from one form to another”. These converters can be classified as: 

Rectifier converting an ac voltage to a dc voltage,



Inverter converting a dc voltage to an ac voltage,



Chopper or a switch-mode power supply that converts a dc voltage to another dc voltage, and



Cyclo-converter and cyclo-inverter converting an ac voltage to another ac voltage.

In our design, we can use an AC to DC converter that converts 220V AC supply into different DC values of 12V, 18V, 24V, 36V.

In this project we are using 14V / 2A because of the Power limitations of the Oscillator Circuit.

The Circuit Diagram of this AC to DC converter is given as follows:

60

Fig. 38 AC to DC converter (Proteus 7.6 sp4)

5.3.2 Oscillator Circuit

The Output of AC to DC converter is than applied to an Oscillator Circuit. The main component being used in Oscillator circuit is PWM IC. The PWM IC is used for:



Modulating the Width of the Pulse



Pulse-width modulation control works by switching the power supplied to the coil on and off very rapidly.



The DC voltage is converted to a square-wave signal, alternating between fully on and zero, giving the Transmitter, a series of power "kicks“.

61

A comparison of different types of PWM ICs is given in following table: Manufacturer

IC #

Normal use

Comment

SMPS

May operate at up to 100% duty cycle

SG1524 ST

SG3525A

PWM output only between 15% and 85%. Generates triangle & sine waves too.

Maxim

MAX038 Signal generation

Atmel

U2352B

PWM Generator for speed control of portable tools

Includes integrated current limiting circuitry for output MOSFETs.

TI

TL494

SMPS

Max 90% duty cycle

TI

UC2638

PWM generator for motor control

Provides many other features for DC motor speed control.

Table. 3 A comparison of different types of PWM ICs The PWM IC named as SG3525A is the IC of our choice due to its different characteristics as:



8 TO 35 V OPERATIONS



5.1 V REFERENCE TRIMMED TO ± 1 %



100 Hz TO 500 KHz OSCILLATOR RANGE



SEPARATE OSCILLATOR SYNC TERMINAL



ADJUSTABLE DEADTIME CONTROL

62



INTERNAL SOFT-START



PULSE-BY-PULSE SHUTDOWN



INPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS



LATCHING PWM TO PREVENT MULTIPLE PULSES



DUAL SOURCE/SINK OUTPUT DRIVERS

5.3.2.1: Inside SG3525A IC The block diagram of SG3525A [APPENDIX A] is as follows:

Fig. 39 Inside SG3525A [20]

63

Following are the details of Operation for PWM IC:



The speed demand signal is input at pin 2, the op-amp non-inverting input.



The demand signal is then applied to the PWM comparator.



This compares the demand level with the oscillator output.



The frequency of the oscillator, and therefore the PWM signal produced, is governed by the value of the resistor to ground on the RT pin.



The sync and osc out pins are not required for our purpose.



The soft start feature prevents the output from saturating at 100% ratio when the chip is powering up.



The Shutdown input is an active-high input that immediately shuts down the outputs, and resets the soft-start feature.

The Circuit Diagram for the Oscillator Circuit is given as follows:

64

Fig. 40 Transmitter Circuit (Proteus 7.6 sp4) 5.3.3: The Transmitter Circuit (Capacitors and Coil) The very basic equation governing our project work is:

fo = 1/ 2 π √L C

Inductance (L) of the coil :

L = 0.16 uH

Capacitance :

C = 390 nF

Resonant frequency (f0):

F0 = 640 KHz

Capacitive Reactance:

XC = 0.643022 Ω

Inductive Reactance:

XL = 0.643339 Ω

The Inductance (L) is measured By using eq.

65

L = μo N² R[ln(8R/a)-2]

On the transmission side LC circuit we connected capacitor with value of 390 nF. A coil with following parameters is used:

Outer coil: No. of Turns

N

= 100

Radius of Coil

R

= 143.75mm

Diameter of the coil

D

= 287.5mm

Wire radius

a

= 318um

Hence,

Value L = 11.18 mH

Middle coil: No. of Turns

N

= 42

Radius of Coil

R

= 81.25mm

Diameter of the coil

D

= 162.5mm

Wire radius

a

= 190.8um

66

Hence,

Value L = 1.104 mH

Inner coil: No. of Turns

N

= 20

Radius of Coil

R

= 56.25mm

Diameter of the coil

D

= 112.5mm

Wire radius

a

= 127.2um

Hence,

Value L = 0.2uH

Resultant Inductor Value:

L=0.16uH 5.3.4 The Receiver Circuit Now calculate inductance of each coil and then Using resonance frequency equation we calculate value of capacitors at resonance frequency of 640khz. Three capacitors with values of (aprox) 330uF on each receiving coil are connected.

67

Fig. 41 Receiver Circuit (Proteus 7.6 sp4) Outer coil: No. of Turns

N

= 100

Radius of Coil

R

= 143.75mm

Diameter of the coil

D

= 287.5mm

Wire radius

a

= 31.8um

Hence,

Value L = 15.34 mH

Middle coil: No. of Turns

N

= 210

Radius of Coil

R

= 81.25mm

68

Diameter of the coil

D

= 162.5mm

Wire radius

a

= 270.625um

Hence,

Value L = 26.043 mH

Inner coil: No. of Turns

N

= 110

Radius of Coil

R

= 56.25mm

Diameter of the coil

D

= 112.5mm

Wire radius

a

= 270.625um

Hence,

Value L = 4.632mH

Since both the Transmitter & Receiver are in the state of resonance, energy exchange will take place b/w two sides of the system. 5.3.5 Frequency Converter

69

Frequency Conversion is necessary to make the system compatible with any type of load. Since we are using a 22 Watt Energy Saver Bulb (Resistive Load), no Frequency Conversion Circuit was deployed. However, for charging a laptop or mobile phone, this conversion will be necessary.

5.4 Cost of the System The overall summary of the project cost is discussed in following summarized table, along with list of components being used in the system:

Component’s List

TRANSMITTER CIRCUIT PARTS

Sr. #

Component’s Name

Qty.

Unit Price (Rs.)

Total (Rs.)

2 3 4

POWER MOSFETS PWM GENERATOR IC SWITCHING TRANSISTORS MOSFET HEATSINK

20PCS 2 PCS 6 PCS 6 PCS

400 900 125 100

8000 1800 750 600

5 6 7 8 9

AC TO DC CONVERTER POWER CAPACITORS CIRCUIT BOARD RESISTORS AND CAPACITORS SOLDER WIRE

2 PCS 4 PCS 2 PCS

800 250 250 600

10

TRANSMITER LOOP WIRE

4000

4000

11 12 13

HI POWER RECTIFIERS HI FREQUENCY DIODES SURGE CAPACITORS

1 ROLL 1 LOOP 2 PCS 3 PCS 10 PCS

1600 1000 500 600 600

800 400 70

1600 1200 700

1

70

14 15 16 17 18 19 20 21 22

CHOPPER TRANSFORMER CHOPPER DRIVE CIRCUIT LOOP STAND LOOP CONNECTOR LOPP TAPE HI FREQ IC SOCKETS VOLTAGE VARIATION CKT VARIABLE RESISTORS SHOTKEY BARRIER DIODES

23

DIODES HEATSINK

24

HOOK UP WIRE

25

HI VOLTAGE CAPACITORS

26 27 28 29 30 31

CHOPPER STRIP VOLTAGE REGULATOR CIRCUIT HOLDING BASE CHOPPER WINDING WIRE VARNISH CAN MIXED COMPONENTS

2 PCS 2 PCS 1 PCS 2 PCS 1 PCS 2 PCS 1 PCS 5 PCS 10 PCS 10 PCS 10 FEET 14 PCS 2 PCS 2 PCS 2 PCS 2 PCS 1 PCS

550 600 610 150 350 15 1000 30 250

1100 1200 610 300 350 30 1000 150 2500

90

900

30

300

265

1060

250 50 250 650 250 1000

500 100 500 650 250 1000

Table 4: Transmitter Circuit Components List

RECEIVER CIRCUIT PARTS:

1 2 3 4 5

LOOP WIRE LOOP WIRE HOLDER VOLTAGE FILTER CAPACITORS LOOP TAPE RELAY

1 1 10 5 5

2000 1000 200 500 150

2000 1000 2000 2500 750

Table 5: Receiver Circuit Components List

Total Estimated Cost = Rs.

43,700 /-

71

CHAPTER 6

EXPERIMENTAL RESULTS

Objectives In this chapter, we are focusing on “EXPERIMENTAL RESULTS”, these results are as follows : 1.)

Efficiency versus Distance.

2.)

Efficiency versus Frequency. 72

6.1 Efficiency versus Distance In order to show Efficiency of the whole system with respect to the Distance. We calculate following parameters both at transmitter end and receiver end. Parameters at transmitter end remain constant but parameters at receiver end varied at different distances. TRANSMITTER PARAMETERS: Vs (V) 14

Is (A) 2

RECIEVER PARAMETERS: At distance 10cm Vr (V) Ir (mA) 230

104.3

V(trans) (V) 14

I(trans) (A) 1.8

Pr (Watt) 24

P(source)(W) P(trans)(W) 28 25.2

Coil efficiency (%) 95

Total efficiency (%) 85 Total efficiency (%) 82 Total efficiency

At distance 20cm Vr (V) Ir (mA)

Pr (Watt)

225

23.1

Coil efficiency (%) 91

Pr (Watt)

Coil efficiency

102.2

At distance 28cm Vr (V) Ir (mA)

73

(%) 220

100

(%)

22

87

78

At distance 35cm Vr (V) Ir (mA)

Pr (Watt)

200

19

Coil efficiency (%) 75

Total efficiency (%) 68

Coil efficiency (%) 69

Total efficiency (%) 58

Coil efficiency (%) 87 14.9 60 Table 6: Transmitter and Receiver Parameters

Total efficiency (%) 53

95

At distance 45cm Vr (V) Ir (mA)

Pr (Watt)

180

16.5

91

At distance 55cm Vr (V) Ir (mA) 171

Pr (Watt)

Fig. 42 Efficiency versus Distance (MS Excel 2003) 6.2 Efficiency versus Frequency Fig. 43 shows that the maximum efficiency of system is achieved approximately around 640 KHz 74

Fig. 43 Efficiency versus Frequency (MATLAB)

CHAPTER 7

ENHANCEMENTS AND APPLICATIONS

Objectives In this chapter, we are focusing on “ENHANCEMENTS AND APPLICATIONS” of project; following topics discussed in this chapter: 1.)

Enhancements.

2.)

Applications.

75

7.1 Enhancements Following enhancements can be made in this project:

7.1.1 Coils Structures By using different types of structures of coils some more enhanced results can be obtained. Different structures of coils can be:

 Circular  Rectangular  Square  Triangular  Spherical

76

 Etc…

Fig. 44 Different Structures of coil [29]

7.1.2 Material of coil wires By using different types of material in wires one can achieve more exact results. Every wire has to be chosen either by its gauge size or by its relative permeability.

7.1.3 Varying resonant frequency By choosing different values of resonant frequency, efficiency of system can be enhanced. The only thing which has main concern during variation in frequency is the saturation of coils which must be avoided.

7.1.4 Portability By reducing the size of receiver, the factor of portability can be achieved. If this system becomes portable then it can be tremendously in daily electronics or electrical equipments.

77

7.1.5 High Power Rating Components By using high power rating components, the efficiency of whole system can be increased. The only thing which should be kept in mind, the coil wiring must be according to that power rating.

7.2 Applications 

This project can be used in following applications:



Mobile devices wireless charging



Laptops, Cellular Phones, Music players



Household devices



Implanted medical devices



More efficient factories



Wireless energizing of pacemaker



Constant energy to factory robots



Electric railway systems

78

REFERENCES [1] http://blog.melvinpereira.com/2010/02/08/one-ring-to-rule-them-all-wirelesselectricity.html [2] www.linktostudy.blogspot.com [3] www.us.123rf.com [4] http://www.damninteresting.com/teslas-tower-of-power/ [5] www.veuphorik.wordpress.com [6] www.hubpages.com [7]http://www.thelivingmoon.com/46exuberant/03files/Laser_Power_Transmission_01.ht ml [8] www.wordpress.com [9] www.explainthatstuff.com

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[10] http://www.123rf.com/photo_4302903_hand-holding-one-glowing-light-bulbbetween-fingers.html [11] www.4hv.org [12] Fundamentals of electric circuits (Alexander Sadiku) [13] www.bibliotecapleyades.net [14] http://artsites.ucsc.edu/EMS/music/tech_background/Z/impedance.html [15] www.hyperphysics.phy-astr.gsu.edu [16] www.wps.prenhall.com [17] www.abitabout.com [18] http://www.noding.com [19] MS Paint [20] www.alldatasheet.com [21] Tesla, N. “Apparatus for transmitting electrical energy.” U.S. patent number 1,119,732, issued in December 1914. [22] Fernandez, J. M. and Borras, J. A. “Contactless battery charger with wireless control link.” U.S. patent number 6,184,651, issued in February 2001. [23] Ka-Lai, L., Hay, J. W. and Beart, P. G. W. “Contact-less power transfer.” U.S. patent number 7,042,196, issued in May 2006. (SplashPower Ltd., www.splashpower.com) [24] Esser, A. and Skudelny, H.-C. “A new approach to power supplies for robots.” IEEE Trans. on industry applications 27, 872 (1991). [25] Hirai, J., Kim, T.-W. and Kawamura, A. “Wireless transmission of power and information and information for cableless linear motor drive.” IEEE Trans. on power electronics 15, 21 (2000). [26] Scheible, G., Smailus, B., Klaus, M., Garrels, K. and Heinemann, L. “System for wirelessly supplying a large number of actuators of a machine with electrical power.” U.S. patent number 6,597,076, issued in July 2003. (ABB, www.abb.com)

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[27] Takao, A. et al. “Observation of strong coupling between one atom and a monolithic microresonator.”, Nature 443, 671 (2006). [28] Karalis, J. D. Joannopoulos, M. Soljačić, Ann. Phys., 10.1016/j.aop.2007.04.017 (2007). [29] http://www.technick.net/ [30] www.datasheetcatalog.com

APPENDIX A Data Sheet of SG3525 [30]

81

82

83

84

85

86

87

88