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Wireless SYSTEM

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Today large number of new technologies depends on electrical supply system, so complexity of ...

Today large number of new technologies depends on electrical supply system, so complexity of
wires is very high. In this project, as requirement of wireless electrical power system, project
team present an analysis the concept of cable less transmission i.e. Power without the usage of
any kind of the electrical conductor or wires. Transmission or distribution of 50 or 60 Hz
electrical energy from the generation point to the consumers end without any physical wire has
yet to mature as a familiar and viable technology.
Our team chose to project the feasibility of wireless power transmission through
inductive coupling. This consists of using a transmission and receiving coils as the coupling
antennas. Although the coils do not have to be solenoid they must be in the form of closed loops
to both transmit and receive power. To transmit power an alternating current must be passed
through a closed loop coil. The alternating current will create a time varying magnetic field. The
flux generated by the time varying magnetic field will then induce a voltage on a receiving coil
closed loop system. This seemingly simple system outlines the major principle that our research
investigated. The primary benefits to using inductive coupling are the simplicity of the
transmission and receiving antennas, additionally for small power transmission this is a much
safer means of conveyance. To demonstrate the success of our the teams we created a receiving
circuit to maximize the amount of received power and light an LED at a distance up to two feet.
We were able to create both transmission and receiving circuits capable of transmitting the
necessary power to light an LED in a pulsed mode. On average with transmitting one watt of
power the receiving circuit was able to receive 100 micro-watts of power. While the efficiency of
the system is extremely low, approximately 0.01% with some improvements we feel certain the
efficiency could be greatly improved. Furthermore, as the transmission distance is decreased the
efficiency of any system using inductive coupling improves exponentially.

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Wireless SYSTEM Wireless SYSTEM Document Transcript

  • A Project Report On WIRELESS ELECTRICAL POWER SYSTEM Submitted In partial fulfillment For the award of the Degree of Bachelor of Technology (B.TECH) In Department of Electrical Engineering 2009-2013 Submitted To Submitted By Mr. Neeraj Garg Radhey Shyam Meena (09EEJEE037) H.O.D. Electrical Engineering B.Tech Final Year (2009-2013) DEPT. OF ELECTRICAL ENGINEERING GOVT ENGINEERING COLLEGE JHALAWAR RAJASTAN TECHNICAL UNIVERSITY KOTA (RAJASTHAN)
  • PREFACE OF PROJECT Today large number of new technologies depends on electrical supply system, so complexity of wires is very high. In this project, as requirement of wireless electrical power system, project team present an analysis the concept of cable less transmission i.e. Power without the usage of any kind of the electrical conductor or wires. Transmission or distribution of 50 or 60 Hz electrical energy from the generation point to the consumers end without any physical wire has yet to mature as a familiar and viable technology. Our team chose to project the feasibility of wireless power transmission through inductive coupling. This consists of using a transmission and receiving coils as the coupling antennas. Although the coils do not have to be solenoid they must be in the form of closed loops to both transmit and receive power. To transmit power an alternating current must be passed through a closed loop coil. The alternating current will create a time varying magnetic field. The flux generated by the time varying magnetic field will then induce a voltage on a receiving coil closed loop system. This seemingly simple system outlines the major principle that our research investigated. The primary benefits to using inductive coupling are the simplicity of the transmission and receiving antennas, additionally for small power transmission this is a much safer means of conveyance. To demonstrate the success of our the teams we created a receiving circuit to maximize the amount of received power and light an LED at a distance up to two feet. We were able to create both transmission and receiving circuits capable of transmitting the necessary power to light an LED in a pulsed mode. On average with transmitting one watt of power the receiving circuit was able to receive 100 micro-watts of power. While the efficiency of the system is extremely low, approximately 0.01% with some improvements we feel certain the efficiency could be greatly improved. Furthermore, as the transmission distance is decreased the efficiency of any system using inductive coupling improves exponentially.
  • ACKNOWLEDGEMENT “Every good work requires the guidance of some experts.” Many lives & destinies are destroyed due to the lack of proper guidance, directions & opportunities. It is in this respect we feel that we are in much better condition today due to continuous process of motivation & focus provided by our parents & teachers in general. The process of completion of this project was a tedious job & requires care & support at all stages. We would like to highlight the role played by individuals towards this. We oblige to acknowledge my heartiest gratitude to all honorable people who helped us during our project on “WIRELESS ELECTRICAL POWER SYSTEM.” We want to express our thanks to Mr. Neeraj Garg (H.O.D., EE) for granting us the permission for doing this project and to give their valuable time and kind co-operation. We would like to thanks Mr. Raju sir (TCS Ltd.), & Mr. Raman sir (Operation Engineer ,BGR Energy System) for providing us the knowledge about the wireless work and giving their valuable guidance during our project period. We would like to thanks Mr. Sunil Kumar (Electronics Lab Technician) for providing us knowledge and guidance about our project. We Would Co-Heartedly Thank and Use This Opportunity to Express Gratitude and Debtness to Mr.M.M.Sharma (Principal), Govt Engineering College Jhalawar We are also thanks a lot to other staff members of Electronics and Electrical Dept. and also staff of labs for their further co-operation to gain the better knowledge about the project. Radhey Shyam Meena & Rakesh Kumar Deepa Sharma & Samta Meena Kanwar Lal & Teena Garg B.Tech 4th Year Electrical Engineering
  • TABLE OF CONTENTS Table of Contents.....................................................................................................................................i List of Figures........................................................................................................................................ii Chapter-01 Basic of Wireless Electrical Power System 1.1 Executive Summary........................................................................................................................02 1.2 Introduction.....................................................................................................................................03 1.3 Problem Statement..........................................................................................................................04 1.4 Research..........................................................................................................................................05 1.5 Possible Solutions...........................................................................................................................06 Chapter-02 Operating Frequency and Design 2.1 Operating Frequency......................................................................................................................07 2.2 Design Choice................................................................................................................................09 2.3 Theoretical Background.................................................................................................................10 2.4 Safety and FCC regulations............................................................................................................11 2.5 Division of Work............................................................................................................................12 Chapter-03 Wireless System Design 3.1 System Design................................................................................................................................14 3.2 Power Supply..................................................................................................................................14 3.3 Oscillator.........................................................................................................................................16 3.4 Power Amplifier.............................................................................................................................19 3.5 Transmitter and Receiver Design...................................................................................................23 3.6 Booster/rectifier..............................................................................................................................28 3.7 LED Flasher....................................................................................................................................31 Chapter-04 Hard Ware Design …………………………………………………………...…...32 Chapter-05 Future Use 5.1Feasibility........................................................................................................................................35 5.2 Future Improvements.....................................................................................................................36 Chapter-06 Reference References..................................................................................................37 Appendices Appendix A.Detailed specifications…………………………………………………………………38 Appendix B.fcc regulations……………………………………………………………………….. 40
  • LIST OF FIGURES Figure 1: An Ideal Transformer............................................................................................................10 Figure 2: Entire System Block Diagram...............................................................................................14 Figure 3: Power Supply Schematic.......................................................................................................15 Figure 4: Colpitts oscillator schematic.................................................................................................16 Figure 5: Oscillator system schematic..................................................................................................17 Figure 6: Output of oscillator system...................................................................................................17 Figure 7: Class B Amplifier..................................................................................................................19 Figure 8: Preamplifier and Power Amp................................................................................................20 Figure 9: Power Amplifier Final Design..............................................................................................21 Figure 10: Power Amplifier FFT.........................................................................................................22 Figure 11: Flux density in a solenoid...................................................................................................23 Figure 12: Bigger Transmitter and Smaller Receiver Coil..................................................................24 Figure 13: Transmitter and bigger Receiver Coil …………………………………………….……...25 Figure 14: coupling circuit …………………………………………………………………..……….27 Figure 15: Output of the Pspice Simulation for Received power.........................................................27 Figure 16: Schematic of the Voltage Booster.......................................................................................28 Figure 17: Schematic of the LED Flasher circuit.................................................................................30 Figure 18: Picture of the Transmitter System Enclosure......................................................................33 Figure 19: Picture of the Receiver System...........................................................................................34 Figure 20: Alternate design for the Transmitter coil............................................................................36
  • CHAPTER-01 BASIC OF WIRELESS ELECTRICAL POWER SYSTEM 1.1 EXECUTIVE SUMMARY
  • Wireless power transmission is the means to power devices without a built in power source such as a battery. There are multiple needs and uses for such technology. One initial use of such technology is found in powering small devices where much of the size of the device is in the battery itself. By eliminating the battery in a small device it would be possible to compact the device even further. Furthermore, on a larger scale as consumable energy sources on the planet are dwindling in number it remains an important task to look to the future. If it was possible to transmit power wirelessly it would be economical to retrieve power from outer space and simply transmit it back to the planet’s surface as an endless power source. In our initial research about this project we discovered many have looked into the feasibility of wireless power transmission and there are many solutions that all offer promise. Our team chose to project the feasibility of wireless power transmission through inductive coupling. This consists of using a transmission and receiving coils as the coupling antennas. Although the coils do not have to be solenoid they must be in the form of closed loops to both transmit and receive power. To transmit power an alternating current must be passed through a closed loop coil. The alternating current will create a time varying magnetic field. The flux generated by the time varying magnetic field will then induce a voltage on a receiving coil closed loop system. This seemingly simple system outlines the major principle that our research investigated. The primary benefits to using inductive coupling are the simplicity of the transmission and receiving antennas, additionally for small power transmission this is a much safer means of conveyance. To demonstrate the success of our the teams we created a receiving circuit to maximize the amount of received power and light an LED at a distance up to two feet. Within a few months of research as part time workers we were able to create both transmission and receiving circuits capable of transmitting the necessary power to light an LED in a pulsed mode. On average with transmitting one watt of power the receiving circuit was able to receive 100 micro-watts of power. While the efficiency of the system is extremely low, approximately 0.01% with some improvements we feel certain the efficiency could be greatly improved. Furthermore, as the transmission distance is decreased the efficiency of any system using inductive coupling improves exponentially.
  • 1.2 INTRODUCTION This document will detail the need and usefulness of wireless power transmission and furthermore the feasibility of using inductive coupling as the means for wireless power transmission. The subject matter of the report will be directed towards the knowledge level of an electrical engineer. Thus some points about general circuits may not be explicitly stated as they have been taken as common knowledge for the intended audience. However, it is intended that anyone with an interest in electrical circuits and more importantantly transformer theory or electromagnetic fields would be able to understand and follow the subject matter outlined in the following document. The report will outline our teams design process and the logical steps we took in our experimentation and design of the final unit. The first section of the document will explicitly illustrate the problem and what the group intended to accomplish. With the complexity of the problem in mind and what we must accomplish our team then began research on the available means to transmit power without a physical connection. Once the initial background research was accomplished it was necessary to layout the advantages and disadvantages of all the available means for wireless power transmission. Once all the necessary criteria for each system were known we chose the best solution for the problem. After our team had chosen upon using inductive coupling we all began to review the major theories that would determine the constraints of the system and what pieces of hardware must be designed to achieve the transmission of wireless power. Furthermore because we are transmitting power through the surrounding area we had to be sure that our system would not endanger others and be FCC compliant. Once the basic system components were known our team divided up the work load, set the necessary deadlines, and began designing the following circuits and hardware: power supply, oscillator, transmission coil, receiving coil, voltage booster/rectifier, and LED flashing circuit. After the entire system was integrated into a working unit it was time to determine how well the system operated and the feasibility of wireless power transfer through inductive coupling. Additionally, future improvements that could greatly improve the overall system will be discussed. Finally, the cost of producing the system, any references our team used, and extra calculations will be presented in the appendices.
  • 1.3 PROBLEM STATEMENT For the completion of this project, we were asked to wirelessly transfer the power of an AC oscillating waveform into a DC voltage on the receiving end which will be used to light an LED to demonstrate the instantaneous power transfer. The frequency of oscillation of the AC signal must not exceed 100MHz. The power transfer needs to be done over a two feet distance or greater. The transferred AC power needs to be converted to DC power and boosted up enough to drive a low power display design, such as an LED in continuous or pulsed mode.
  • 1.4 RESEARCH Nikolai Tesla Nikolai Tesla was the first to develop the designs for wireless power transmission. Tesla was famed for his work in the research and work with alternating current. His wireless research began with his original transformer design and though a series of experiments that separated the primary and the secondary coils of a transformer. Tesla performed many wireless power transmission experiments near Colorado Springs. In Tesla’s experimentation, Tesla was able to light a filament with only a single connection to earth. Tesla’s findings lead him to design the Wardenclyffe plant as a giant mushroom shaped wireless power transmitter. Tesla was never able to complete construction of this project. Space Satellite System The concept of wireless power transmission has been an area of research that the U.S. Department of Energy (D.O.E.) and the National Aeronautical Space Administration (NASA) have been working to develop. NASA has been looking into research to develop a collection of satellites with the capability to collect solar energy and transmit the power to earth. The current design for project by NASA and DOE is to use microwaves to transfer power to rectifying antennas on earths. Similar to this system, NASA and DOE have put research into using laser technology to beam power to earth. Japan’s National Space Development Agency (NASDA) has also been performing this variety of research to use satellite and laser technology to beam power to earth. Japan is expected to have the laser technology developed by 2025. The use of laser technology would theoretically eliminate many of the problems that could occur with the use of microwaves. This laser satellite system is unlikely to be devolved by the United States due to current treaties with Russia preventing either nation from having satellites with high power laser technology. This treaty was created to prevent either nation from completing President Regan’s “Star Wars” project. Microsystem and Microsensor Power Supply Currently, the use of inductive coupling is in development and research phases. There several different projects that use inductive coupling to create alternatives for batteries. One developed at the Tokyo Institute of Technology is to develop a power supply for a medical sensor while it is left inside the human body. In this system, power was transmitted by both electromagnetic waves when at close distance to the transmitter an also by magnetic flux when at farther distances. The receiver portion utilizes a cascade voltage booster to charge capacitors within the device to provide the necessary power to the system. Another similar project, done at Louisiana State University in Baton Rouge, uses inductive coupling in a similar method recharge an internal small battery in a small bio-implanted microsystem.
  • 1.5 POSSIBLE SOLUTIONS In this project, as well as practical knowledge, we knew of three possibilities to design a device. There are the use of antennas, inductive coupling, and laser power transfer. In addition, we had to be aware of how antennas and inductive coupling would be affected by the frequency we select. ANTENNA Antennas are the traditional means of signal transmission and would likely work. In initial research, it appears that system utilizing antennas can receive power gains based upon the shape and design of the antenna. This would allow more power actually being sent and received while also have a small input power. The difficulty comes in the trade off of antenna size versus frequency. In attempting to stay in a lower frequency, one would be require using antennas of very large size. INDUCTIVE COUPLING Inductive coupling does not have the need for large structures transfer power signals. Rather, inductive coupling makes use of inductive coils to transfer the power signals. Due to the use of coils rather than the antenna, the size of the actual transmitter and receiver can be made to fit the situation better. The tradeoff is for the benefit of custom size, there will be a poor gain on the solenoid transmitter and receiver. LASER POWER TRANSMISSION The concept of laser power transmission is addressed in the research of NASA and NASDA solar programs. Lasers would allow for a very concentrated stream of power to be transferred from one point to another. Based upon available research material, it appears that this solution would be more practical for space to upper atmosphere or terrestrial power transmission. This option would not be valid to accomplish our tasks because light wavelengths are higher than the specified allowable operational frequencies.
  • CHAPTER-02 OPERATING FREQUENCY AND DESIGN
  • 2.1-FREQUENCY Very High And Greater Frequency Range- High High frequency transmissions are common in several devices including cell phones and other wireless communications. Higher frequencies can be made to transmit in very specific directions. In addition, these antennas can be rather small. This set of frequency ranges includes microwave frequency bands. Very High Frequencies to Extremely High frequencies are described as being in the range of 30 MHz to 300 GHz and Microwave frequencies are described as being the range of 3 GHz to 300 GHz. The safety issues of using the high end of the spectrum are not completely known. There is currently research looking into the safety of microwave and higher frequencies. However, many of the devices in this frequency range are not permissible due to the frequency limitations placed,on our Very Low to Extremely Low Frequency Range- Antennas of these frequencies would need to be of sizes that are very impractical to build and would be better suited for power transmission over wire. Several of these frequencies are specifically used for submarine communication transmission. Extremely low frequencies and possibly other frequencies in the band up to 3 KHz have the uncertain risk of being potentially hazardous the humans and the environment. There is still on going research on the dangers on very low to extremely low range frequencies. Low, Medium, and High Frequency Range- Radio Frequencies in these bands seem to have few hazardous concerns given by the FCC. In addition, these frequencies are commonly used as the primary frequency bands of radio transmission. The high frequency band is typically used in short range communications due to the ease of the reflection of these waves off the ionosphere. This range is described as being from 3 MHz to 30 MHz. In addition, this frequency range includes two experimental frequency bands. The major disadvantage of working in this frequency range is the inability to properly test in the design phase due to effects parasitic capacitance in breadboards. Medium Frequency includes the AM broadcast band. Medium frequencies are described as being from 300 KHz to 3 MHz. This band includes one band used for testing purposes. The Low frequency band is primarily used for aircraft, navigation, information and weather systems. In addition, this frequency includes a band commonly used for testing purposes. The low frequency band is described as being from 30 KHz to 300 KHz.
  • 2.2 DESIGN CHOICE After reviewing the possible solutions, inductive coupling was chosen as the best alternative. Our team believes that inductive coupling based system will meet most of the design criteria in the designated time given to us. We also felt that our background and knowledge of electromagnetic fields and transformer theory would help us resolve any problems encountered during the design process. Inductive coupling also offers several advantages over other options that are as follows: SIMPLE DESIGN – The design is very simple in theory as well as the physical implementation. The circuits built are not complex and the component count is very low too. LOWER FREQUENCY OPERATION – The operating frequency range is in the kilohertz range. This attribute makes it easy to experiment and test in breadboard. Furthermore there is low risk of radiation in the LF band. LOW COST – The entire system is designed with discrete components that are readily available. No special parts or custom order parts were necessary for the design. Thus we were able to keep the cost of the entire system very low. PRACTICAL FOR SHORT DISTANCE – The designed system is very practical for short distance as long as the coupling coefficient is optimumized. The design also offers the flexibility of making the receiver much smaller for practical applications. Inductive coupling also has some shortcomings that need to be addressed. HIGH POWER LOSS – Due its air core design the flux leakage is very high. This results in a high power loss and low efficiency. NON-DIRECTIONALITY – The current design creates uniform flux density and isn’t very directional. Apart from the power loss, it also could be dangerous where higher power transfers are necessary.
  • 2.3 THEORETICAL BACKGROUND Our power transmission system utilizes the concepts of transformer theory. In a basic single phase transformer as shown in figure, when the primary coil is connected to an AC source, a time varying flux is produced in the core. This flux is confined within the magnetic core. If another coil is added on the same core, the flux links the second coil inducing voltage at its terminals given by the equation . where N is the number of turns of the secondary coil and φ is the flux generated. Furthermore if a load is connected across the terminals of the coil, current flows across the load. V = -N (∂φ/∂t) Figure 1: An Ideal Transformer Our system follows the same concepts of Faraday’s law of electromagnetic induction, but with two major differences. Our system is an air core transformer i.e. there is no solid magnetic core that confines the flux produced at the primary. This means that there is high flux leakage and only a portion of the flux generated induces an emf across the secondary coil. Moreover in our system the primary and secondary coils are two feet apart, which results in low flux linkage, low coupling, and even lower power transfer. Therefore the biggest challenge in this project is to maximize the flux linkage between the primary and secondary coils to be able to transfer enough power to light an LED at the given distance.
  • 2.4 SAFETY AND FCC REGULATIONS One of the key factors in our device was to be aware of FCC (Federal Communications Commission) regulations. The FCC regulations are put in place first to limit the use of particular frequency bandwidths. In doing so, the FCC prevents multiple users from occupying the same frequency band and interfering with one another. In addition, the FCC also regulates power emissions of a variety of different devices. Due to the nature of our project, we will be affected by FCC regulations. Our project is an intentional radiator as well as working with radio frequency (RF) energy. The FCC defines an intentional radiator as: A device that intentionally generates and emits radio frequency energy by radiation or induction. The FCC defines radio frequency energy as: Electromagnetic energy at any frequency in the radio spectrum between 9 kHz and 3,000,000 MHz For this project, the frequency band of 160-190 KHz was selected. The frequency of 160-190 KHz is an open test band that does not require any special permission to work in the frequency range. This frequency range contains three limiting factors. The limitations of this frequency are the following: • Total input power into the final radio frequency stage shall not exceed 1 watt. • The total length of transmission line, antenna, and ground lead shall not exceed 15 meters. • All emissions below 160 kHz and above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier. For the complete FCC code, refer to Appendix B. Radiation in the frequency band of 160 KHz to 190 KHz does not seem particularly hazardous at such low power levels. In general, it is suggested to remain a distance radius of 6 inches away from the transmitter and not standing in the direction of transmission. Additionally avoid exposure to children under a body weight of 50 lbs. During the testing procedure, radiation from the transmitter did not affect cell phones, calculators, and digital watches. Direct effects of the radiation of the system on medical devices, such as pace makers, are unknown. It is recommended that people with medical implants remain a distance of 1 meter away from the transmitter as a precaution.
  • 2.5 DIVISION OF WORK In order for our team to be productive every team member was given very specific goals and deadlines to meet. Furthermore for all design components everyone worked with another team member to ensure success. We felt that because many did not possess a technical background in certain necessary fields having the assistance of another engineer would prove to be an invaluable resource. Every team member and their major responsibilities are listed below. Samta Meena – Oscillator, Deepa Sharma- Power Amplifier Radhey Shyam Meena – FCC Regulations and Safety and Transmitte Rakesh Kumar – Receiver Coil & power supply Teena Garg –, Voltage Booster/Rectifier Kanwar lal - LED Flashing Circuit team members were tasked with other various responsibilities not directly related to the design process, but to ensure the cooperation of all team members. These positions were designed to create order in team meetings and the design environment.
  • CHAPTER-03 WIRELESS SYSTEM DESIGN
  • 3.1 SYSTEM DESIGN With all the necessary background research completed it became clear what basic design components the entire system would require. First we needed a method to power the transmission side of the system. The power supply would then power an oscillator which would provide the carrier signal with which to transmit the power. Oscillators are not generally designed to deliver power, thus it was necessary to create a power amplifier to amplify the oscillating signal. The power amplifier would then transfer the output power to the transmission coil. Next, a receiver coil would be constructed to receive the transmitted power. However, the received power would have an alternating current which is undesirable for lighting a LED. Thus, a voltage booster and rectifier would be needed to increase the received voltage while outputting a clean DC voltage. Finally, a LED flasher circuit would be constructed to flash the LED when enough power had been received to light the LED. The entire system can be seen in the figure. Figure 2: Entire System Block Diagram 3.2 POWER SUPPLY The main design aspects our team wanted to incorporate in the power supply was that it could use the 120 V AC voltage found in any basic wall outlet, and use that voltage to power any necessary circuits to the system. Initially, 120 volts is too large for our small circuits so we incorporated a small transformer to step down the voltage. Furthermore for any basic electrical components it would be necessary to have a DC power supply available, thus the stepped down AC voltage converted to DC by a full-wave bridge rectifier. The full-wave bridge rectifier is the KBU4D which can be easily found at any Radioshack store. Large capacitors were then connected to the output of the full-wave bridge rectifier to ensure that a steady DC voltage could be maintained. The power supply schematic can be seen in figure
  • Fig-03 Power Supply The center tap on the secondary side of the transformer serves as the ground for the entire circuit. Thus, all additional circuits connected to the power supply will use the center tap of the transformer for the ground plane. The secondary on the transformer is rated at 25 volts but with loading from additional circuits the steady state voltage reduces to 18 volts. The design for the power supply is extremely compact and very simple to implement. Furthermore, the voltage is more than sufficient for the necessary circuits that will be connected to it. The layout of the power supply is shown in Appendix F. One of the major drawbacks of the transformer is the two amp output, but due to FCC regulations the maximum power that could be delivered to the transmission coil would be one watt. A two amp output is more than sufficient to supply one watt of power. As stated earlier the only real drawback to the power supply design would be the current output. If it was possible to transmit more than one watt of power to the transmission coil a more robust power supply capable of supplying more current would be better suited. Although no tough design challenges were present in creating the power supply, it was necessary that the system operate well because of a good design. The key points in creating a DC power supply are the voltage, current, and removing ripple in the DC components. All three of these key points were known and addressed in the design process.
  • 3.2 OSCILLATOR There are two popular types of oscillators: the Colpitts and the Hartley oscillator. The Colpitts is somewhat similar to the shunt fed Hartley with the exception that instead of utilizing a tapped inductor like the Hartley oscillator does, it uses two series capacitors in its LC circuit. The connection between these two capacitors is used as the center tap for the circuit. The schematic of such oscillator is shown in figure Fig-04 .Colpitts Oscillator DESIGN In designing the Colpitts oscillator shown in figure, a general purpose 2N2222A type bipolar junction transistor was used . The two biasing resistors connected to the base of the transistor are used to limit the voltage and current going in the base of the transistor for proper operation. They need to be in the tens of kilo ohms range for low base current. The capacitor connected to the base of the transistor is used to keep the base voltage constant. The bias resistor at the emitter of the transistor which can be replaced by a large inductor is used to prevent the capacitors C4 and C5 to be short circuited. The other components in figure not mentioned above (L1, C1, C4 and C5) are frequency dependent. They are found using the following equation: F osc= 1/ (2π√(L C eq)) The capacitor C5 is tunable and is used to adjust the frequency of oscillation. One oscillation cycle is produced by the charging and discharging of the capacitor and inductor respectively. The oscillating frequency of the circuit shown in fig. is 175 kHz.
  • ADVANTAGES AND DISADVANTAGES The advantage in using the Colpitts oscillator is that is does not require the use of a center tapped inductor, a variable inductor. Such inductors are heavy, costly and hard to work with as they generate electromagnetic waves that will alter the frequency of oscillation. Such an oscillator has limited frequency range because so many fixed value components are used. Figure 05: Oscillator system schematic Figure 06: Output of oscillator system
  • DESIGN,CHALLENGES- The designed oscillator worked as expected as a stand alone system but its output was very sensitive to loading. To rectify that problem, a buffer that uses the high frequency power amplifier, AD711jn was integrated. Also the output of the oscillator is directly fed to the power amplifier. The power amplifier has a 0.7V input amplitude limitation. Due to the 2V DC input supplied to the oscillator, its oscillation is done at 2V level instead of 0V. A DC bias offset problem was then encountered. To correct that problem a difference amplifier to subtract the 2V DC from the output signal of the oscillator was implemented. Finally in order to conform with the higher harmonic distortion rule set by the FCC regulation, a low pass filter with cutoff frequency at 190kHz was added to the output of the buffer. The higher harmonics are thus filtered out. The complete schematic of the oscillator is shown is figure
  • 3.4 POWER AMPLIFIER DESIGN In order to generate the maximum amount of flux which will induce the largest voltage on a receiving coil, a large amount of current must be transferred into the transmitting coil. The oscillator is not capable of supplying the necessary current, thus the output signal from the oscillator will then be passed through a power amplifier to produce the necessary current. The key design aspects of the power amplifier are generating enough current while producing a clean output signal without large harmonic distortions. If the output from the amplifier was not clean with harmonic distortions the system would cease to be FCC compliant. A simple amplifier design capable of yielding high current for an alternating waveform is the class B amplifier. A diagram of this amplifier can be seen below Figure 07: Class B Amplifier The main design challenge with class B amplifiers occurs when the signal alternates polarity and more importantly rather quickly which is the case with our 175 kHz carrier frequency. The problem arises when one BJT is turned off and the other on, this creates crossover distortions. These crossover distortions would create higher order harmonics which are very undesirable. To compensate for these distortions a feedback control loop is desirable. Furthermore this feedback would offer control over the output voltage level. To create this feedback loop a preamplifier was added to the design. An operational amplifier was used as the preamplifier and the feedback control loop. This design can be seen in the figure
  • Figure 08: Preamplifier and Power Amp It can be noted that the diodes connected the output of the operational amplifier and the BJT bases have been removed as voltage biasing was not necessary. Furthermore, there are no resistors connected to the emitters of each BJT because we are trying to deliver the most current possible to the load. Thus limiting the current with resistors is not desirable. The input vs. output file can be seen below. The OPA134 operational amplifier was chosen for this project because it is an acoustic amplifier that is made for high switching frequencies with minimal distortions. The OPA134 has a bandwidth up to 8 MHz which is more than sufficient for the carrier frequency of 175 kHz. Furthermore at 175 kHz the OPA134 offers up to 40 dB gain, but for our needs the operational amplifier will only have a gain of 20 dB. For the npn transistor the TIP31 was chosen and for the pnp transistor the TIP42 was chosen. Both transistors can operate up to 1 MHz which is more than enough to operate at 175 kHz. Furthermore, they can both support a collector current up to 3 amps, while the power supply can only output 2 amps maximum this will be sufficient to supply the necessary current to the transmission coil. POWER AMPLIFIER OUTPUT In this the larger waveform represents the output signal while the input signal is the smaller signal. It can easily be seen how the signal has been greatly amplified. Finally the harmonic distortions may also be viewed according to the simulation. POWER AMPLIFIER HARMONICS Again it is possible to see the amplification however here one will notice the presence of the harmonic distortions found in the larger waveform. Due to the presence of the feedback loop connected to the emitters of the BJTs the harmonics are minimal. ADVANTAGES AND DISADVANTAGES The overall advantages to the amplifier are quite apparent, this system is capable of greatly increasing the power transmitted to a given load. Furthermore, by using a variable resistor in place of R5 the 5 KOhm resistor it would be possible to implement an amplifier with variable Gain.
  • this would be extremely useful when the transmission coil resistance could vary upon future design aspects. This would allow the gain of the amplifier to be adjusted as necessary, yet at the same time always comply with the FCC regulations and transmit less than the one watt. The power amplifier performs as it was designed too, if it was necessary to improve upon it ideally more current output would be desired. Furthermore, to really ensure FCC regulations a class AB amplifier could be designed which would further minimize the harmonic distortions. Figure 11 is the output from the power amplifier using FFT (Fast Fourier Transfer). The final production model of the power amplifier was improved by adding a variable resistor to change the overall amplifier gain. Furthermore, it became apparent that a large variable capacitor would be needed in series with the transmission coil. The need for this capacitor will be discussed in the following section. Thus the system was modeled accordingly below. Figure 09: Power Amplifier Final Design
  • Fig -10 Power amplifier FFT The input to the power amplifier was the oscillator and above is the harmonic components of the output signal. It can easily be seen the largest point is at 175 kHz the carrier frequency, and the next largest point is 21.2 dB below the main signal this ensures that the FCC regulations have been met according to the harmonic content below 160 kHz and beyond 190 kHz. DESIGN CHALLENGES The major design challenges that occurred in creating the power amplifier was maximizing the power transfer to the coil and minimizing the harmonic distortions. The impedance matching network was the most substantial design upgrade in improving the current flow which will be explained in detail in later sections. Initially we transferred 70 mA to the coil however with the impedance matching we were easily transferring 200 mA while staying under the one watt power limitation. Finally, the feedback control through the preamplifier allowed the class B amplifier to work for our project even with the transition distortions.
  • 3.5 TRANSMITTER AND RECEIVER DESIGN The transmitter and receiver circuit combined can be called the coupling circuit. It is the heart of the entire system as the actual wireless power transfer is carried out here. The efficiency of the coupling circuit determines the amount of power available for the receiver system as well as how far the LED can be from its actual power source. SOLENOID DESIGN A solenoid configuration was used for the design of the transmitter and receiver. A solenoid is a long cylinder upon which wire is wound in helical geometry as shown in figure. The magnetic field at the center of the solenoid is very uniform. Usually, the length of a solenoid is several times of its diameter. The longer the solenoid the more uniform the magnetic field at the middle. In this way a solenoid is a very practical way to generate a uniform controlled magnetic field. Figure 11: Flux density in a solenoid The magnetic flux density in a solenoid can be approximated by the following equation: B = μ0 nI where B is the magnetic flux density, μ 0 is the permeability of free space, n is number of turns of wire per unit length and I is the current flowing through the wire. To maximize the flux linked to the receiver coil, it is imperative to increase the magnetic flux density as much as possible.
  • The equation shows that one of the ways to increase B is to increase the current (I) going into the wire. Since all wires have some resistance, this process requires increase in the voltage put across the wires which can result in more heating in the coil. B can also be increased by increasing n. This can be accomplished by decreasing the wire size or winding wires closely. Winding wires closely can increase the overall resistance of the coil and thus increase the heating in the coil. Another way of increasing n is by winding several layers of wire which can cause insulations problems as well as decrease the diameter to length ratio. It is apparent that there are several parameters that we have to manipulate to select the appropriate tradeoff that might fit our system’s needs. As the input power to our transmitter is limited to 1W, it certainly limits the amount of current that can be pushed through the transmitter coil. Thus one of the design goals of the team was to keep the resistance low to maximize the current. In addition to that, we also strived to increase the number of turns per unit length without drastically increasing the resistance. Initially our team was using shielded wire for the coils. A major advancement was made in decreasing wire size by replacing it with magnetic wires. This wire is common copper wire but rather than having a thick insulation over the copper, it is simply coated in enamel which keeps the overall diameter of the wire much thinner compared to shielded wire. Magnetic wires also has low resistance and therefore can carry much higher current. We also utilized two complete layers of wires for the transmitter coil to increase the number of turns even more. These steps improved the performance of our system to a great extent. INITIAL EXPERIMENTATION In addition to the solenoid parameters, it was also necessary to determine certain parameters such as relative size of the transmitter and receiver coil, the orientation of the coils, the turns ratio as well as the operating frequency. To establish these parameters, we conducted few experiments. For our experiments we made two handmade inductive coils of different diameters (approximately 1.5 ft and 6 inches), but with equal turns (N=10). First we tried supplying the large diameter coil with a 7 volt 21 kHz sine waveform to act as the transmitter and the small diameter coil was placed next to it at various distances and the resulting voltage received was measured. Figure 12: Bigger Transmitter and Smaller Receiver Coil
  • BIG LOOPS FOR TRANCEIVER SMALL LOOPS FOR RECEIVER Separation distance MEASURED VOLTAGES 0inch 7V 43mV 2inches 7V 18mV 5inches 7V 8mV Quickly we realized that it was best to orient the coils such that they were directed along the same axis. Next, we wanted to verify which was best to have has the receiver the larger diameter coils or the smaller diameter coils while being oriented in the following manner. Fig. 13 receiver coil bigger then transmitter coil Under this arrangement the following data was collected. BIG LOOPS = receiver SMALL LOOPS = transmitter Separation distance MEASURED VOLTAGES 3 inches 40mV 7V This proved that it was better to have the receiver diameter larger than the transmitter. Next, we varied the frequency and the number of turns to determine how these factors affected the received power allowing for the following date to be collected. BIG LOOPS SMALL LOOPS Nature/ N value(turn) observations Nature/N value(turn) observations Receiver N=10turns V=400mV at 3inches Transmitter N=10turns 7V amplitude AC signal at 210kHz
  • Signal completely dies out at 2 feet Transmitter N= 10 turns 7V amplitude AC signal at 210kHz Receiver N=10 turns V= 150mV at 3inches The wave dies out at 2feets Transmitter N=10 turns 7V amplitude AC signal at 210kHz receiver N=5turns V=300mV at 3in Receiver N=10turns V > 400mV at 3in Transmitter N=5turns 7V amplitude AC signal at 210kHz IMPEDANCE MATCHING One of the major improvements made to the coupling circuit was accomplished by impedance matching. When a capacitor is put in series with the transmitter coil and it is tuned to its resonant frequency, then the phase differences of the capacitor and inductor are equal and opposite. jwL =-1/jwC When this occurs the load will appear purely resistive and the maximum amount of real power will be transferred into the transmission coil as voltage and current are in phase. This maximum power transfer to the transmitter will ensure the maximum amount of current which will produce the most magnetic flux. At the receiver circuit we utilized the same concepts of impedance matching to tune the receiver circuit to the same resonant frequency as of the transmitter. This ensures that the maximum power is transmitted to the receiver coil. A parallel resonance circuit was used to maximize voltage output to the load at the receiving end. COUPLING COEFFICIENT The entire system was also modeled using coupling coefficient. A coupling coefficient is a number that expresses the amount of electrical coupling that takes exists between two circuits. The coupling coefficient is calculated as the ratio of the mutual inductance to the square root of the product of the self-inductance of the coupled circuits as shown in the equation below k = M/√(L1* L2) where M is the mutual inductance and L1 and L2 self inductances of the transmitter and receiver coils approximately. This number determines how much power is transfer between coupled circuits and is the range between 0 and 1. The coupling coefficient is directly dependent on the
  • spatial relationship of the coils as well their sizes. We made some theoretical calculations as to the estimated value of our coupling coefficient of our system. We utilized this number to model the theoretical power that we should be receiving in Pspice. The schematic diagram of our coupling circuit using coupling coefficient is shown in the figure 19 where R2 represents our effective load at the receiver. Fig 14 .Coupling Circuit The average power received at the load is around 400uW as shown in figure 20. Our system outputs 100uW approximately. Thus we can see that our actual system follows the model reasonably well. Fig. 15: Output Simulation for Received power
  • 3.6 BOOSTER/RECTIFIER DESIGN The booster/rectifier was based on the cascaded voltage booster circuit in [3]. Their design was used to feed a capacitor which powered the control circuitry. Our original design was to use a full wave rectifier and then feed the DC signal to a DC-DC converter to obtain the proper output voltage. Using one circuit to accomplish both goals effectively reduces the complexity of the design of the receiver circuit. The voltage multiplier works by rectifying an AC signal and charging half of the capacitors during the positive cycle. During the negative cycle, the capacitors charged during the positive cycle are an effective “open circuit” while the other half of the capacitors are being charged. When the circuit is viewed over the output of the voltage multiplier, the total voltage of all the capacitors is added up. Fig.16 : Schematic of the Voltage Booster The finalized design utilizes 3 multiplication stages. The final design uses 6 Vishay 1n5711 schottky diodes and 6 10uf tantalum capacitors. These were selected due to their low current leakage characteristics. ADVANTAGES AND DISADVANTAGES This circuit is simple to design, test, and build. The device does the duty of both rectifying an AC voltage and multiplying it. It is easy to increase the number of multiplication stages in the design. The design yields a large reduction of current on its output. This reduction makes the circuit good for charging capacitors.
  • DESIGN CHALLENGES This portion had three primary design challenges. The first was to increase voltage gain. The next stage was to reduce any time constant of the booster to provide near instantaneous power on the output. The next phase was to create an optimum voltage to current ratio to the next stage of the receiver. And finally the last task was to reduce overall power dissipation in the circuit. All aspects of these challenges are related to the selection of parts. In diodes, we need a low current dissipation as well as low forward current and high speed switch capability. We need capacitors that are low power dissipating and of the proper size. High value capacitors create a longer charge time. In addition, higher value capacitors also seem to reduce the available voltage gain as seen in on the output.
  • 3.7-LED-FLASHER DESIGN The LED flasher operates as a voltage control switch. The switching of the transistors is controlled by the capacitor C1 in figure above. It uses general purpose pnp and npn bipolar junction transistors. The capacitor C1 controls the switching of the transistor as well as the flash duration and frequency of the LED D1. The system generates negative pulses at the collector of the npn transistor. Initially there is no voltage drop across the LED D1. That is because the values selected for the resistors R4, R5 and R2 make the base voltage of the pnp transistor to be almost 0V. Both transistors are turned off. At that time the capacitor C1 gets charged. When fully charged, C1 starts discharging in the base of the pnp transistor and switches it on. The pnp’s collector voltage switches on the npn transistor which drops its initial collector voltage. A voltage drop is therefore generated across the LED D1 and current flowing through it that makes it flash. The larger the value of C1, the lower the flashing frequency of the LED becomes, additionally the LED is lit longer during its pulsed mode. Figure 17 Schematic of the LED Flasher circuit ADVANTAGE AND DISADVANTAGE The flasher system is a low power system. It only requires 1.2uW for its operation.
  • CHAPTER-04 HARDWARE DESIGN
  • BASIC – The Enclosure designs are relatively simple. The transmitter was designed as a box large enough to carry most components on the bottom of the box and screw them to the base. In addition, there is sufficient room for additional circuits if necessary. External Width = 8 ¼ inches Internal Width = 7 7/8 inches External Length = 10 ¾ inches Internal Length = 10 1/8 inches External Height = 6 ¼ inches internal Height = 5 1/8 inches Base Height = ¾ inch
  • The construction of the box included space for an extension cord to exit the box and to be close to the transformer and a switch to turn on the system. The side exiting to the receiver included connection lines to the transmitter coil. On one of the long sides closest to the power amplifier circuit, test point connections were made to measure voltage and current, with a switch to activate current measurement. This side also included a connection point to tune the receiver coil and an adjust the gain of the power amplifier. The receiver enclosure was a radio shack 5x2.5x2 inch box. Initially, 4 holes were drilled for a tunable capacitor on the receiver side, wire connections to the receiving coil, and for 2 LEDs to be seen from the top. The capacitor was removed from the box to allow measurement connection points outside of the box. Additional pieces of material were made and fitted into the receiver box to hold the circuitry close enough to the top of the box and to hold the circuits steady. The material is a non conducting,material. fig. 18 transmitter circuit
  • Figure 19: Picture of the Receiver System
  • CHAPTER-05-FUTURE- 5.1-FEASIBILITY- The feasibility of wireless power transfer is a definite reality as our project has demonstrated. The major point of the research was to evaluate whether or not inductive coupling was a feasible solution. While it is possible to transmit and receive power using inductive coupling it has some definite drawbacks. For our team’s project the goal distance was two feet, at such a large distance inductive coupling is far too inefficient in its current state. However the following graph shows that the efficiency between power transmitted and power received increases exponentially as the distance decreases, the data taken for the graph was compiled using the design project. Inductive coupling still has a definite future in the short range transmission distance. This particularly has medical implementations to transmit a few inches to power a remote sensor implanted in the human
  • 5.2 FUTURE IMPROVEMENTS There are several improvements that can be made to the system to increase its overall performance. The oscillator output wasn’t a very clean sine wave signal which increased the harmonic distortion of the signal. A pure sine wave can be generated by using better filters at the output. Currently our system is powered by a transformer that provides +18V/-18V volt rails. Our system can work with lower power. Thus one of the future improvements could be an implementation of a solar cell array to make our system more mobile. The coupling circuit can be made more efficient by altering the design in several ways. Increasing the input current to the transmitter coil would definitely enhance its performance. We can also make the signals more directional in the z direction by using a conical coil as a transmitter instead of the solenoid coil as shown in figure Figure20 : Alternate design for the Transmitter coil Future design improvements in the booster/rectifier circuit would include additional testing on different values of capacitance around 10 uF and seeing the effect of combining fast charging capacitors (Ex. mica capacitors) along with slower voltage holding capacitors (Ex. tantalum capacitors). Additional future improvements would utilize surface mount parts, particularly for diodes. There are wider variety of surface mount schottky diodes available than compared to available through hole components. Available surface mount components have lower current losses as well as smaller forward currents.
  • CHAPTER-06 REFERENCES [1] G. L. Peterson, “THE WIRELESS TRANSMISSION OF ELECTRICAL ENERGY,” [online document], 2004, [cited 12/10/04], http://www.tfcbooks.com/articles/tws8c.htm [2] U.S. Department of Energy, “Energy Savers: Solar Power Satellites,” [online document] rev 2004 June 17, [cited 12/10/04], http://www.eere.energy.gov/consumerinfo/factsheets/l123.html [3] S. Kopparthi, Pratul K. Ajmera, "Power delivery for remotely located Microsystems," Proc. of IEEE Region 5, 2004 Annual Tech. Conference, 2004 April 2, pp. 31-39. [4] Tomohiro Yamada, Hirotaka Sugawara, Kenichi Okada, Kazuya Masu, Akio Oki and Yasuhiro Horiike,"Battery-less Wireless Communication System through Human Body for in- vivo Healthcare Chip,"IEEE Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, pp. 322-325, Sept. 2004. [10] All Data Sheets, “AD711JN Operational Amplifier”, November 2004, http://www.alldatasheet.com/datasheet-pdf/view/AD/AD711JN.html. [11] ”2.3 Class B” September 2004, http://www.st- andrews.ac.uk/~www_pa/Scots_Guide/audio/part2/page2.html. [12] Texas Insturments, “OPA13442 Operational Amplifier”, September 2004, http://focus.ti.com/lit/ds/sbos058/sbos058.pdf. [13] Digikey, “TIP31 BJT”, http://rocky.digikey.com/WebLib/On- Semi/Web%20Data/TIP31_A_B_C,%20TIP32_A_B_C.pdf. [17] “The Spark Transmitter. 2. Maximising Power, part 1. “ November 2004, http://home.freeuk.net/dunckx/wireless/maxpower1/maxpower1.html [18] R. Victor Jones, “Diode Applications,” [Online Document], 2001 Oct 25, [cited 2004 Dec 11], http://people.deas.harvard.edu/~jones/es154/lectures/lecture_2/diode_circuits/diode_appl.html [19] Central Semiconductor Corp, “PNP Silicon Transistor”, November 2004, http://www.semiconductors.philips.com/acrobat_download/datasheets/2N2222_CNV_2.pdf.
  • APPENDICES APPENDIX A Detailed specifications: In many electronic devices the size is not limited by the electronic circuit, but by the battery; such as pacemaker and many micro-sensors. The size of these devices can be reduced significantly if the battery can be removed. However, the power must be supplied externally by means of wireless transmission. The basic principle of this project is to convert the energy of an AC oscillation into a DC voltage, which can be used to charge a capacitor or battery. In order to avoid the complexity of RF/MW circuit, the system will operate at a lower frequency (< 100 MHz range). This project is consisted of the following components: • Convert AC signal to DC signal • DC-DC converter (increase the DC voltage) • Oscillator design • Coupling system design • Low power display design • Solar cell implementation The project will be carried out in three phases: Phase I: Convert an AC signal from a function generator into a DC signal, and raise the DC voltage by a DC-DC converter so that it can charge a battery. The battery will be used to drive a low power display. Phase II: Design an oscillator and coupling circuit. The oscillator is used as a power transmitter, and it is powered by a DC power supply. The coupled circuit can collects part of the power transmitted, and output an AC signal. In this way, the wireless power transmission is achieved. Phase III: Use a solar cell to replace the DC power supply in the transmitter circuit. In this way, the whole system is battery free. At the same time, the system is optimized in order to increase the distance between the transmitter and receiver, as well as higher power transfer. Specification: 1) The power delivered in this way should be able to light up an LED, either in pulsed mode or CW mode. 2) The distance between the transmitter and the receiver should be no less than 1 meter.
  • APPENDIX B FCC Regulation: [Code of Federal Regulations] [Title 47, Volume 1] [CITE: 47CFR15.217] [Page 743] TITLE 47--TELECOMMUNICATION CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION PART 15--RADIO FREQUENCY DEVICES-- Subpart C--Intentional Radiators Sec. 15.217 Operation in the band 160-190 kHz. (a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed one watt. (b) The total length of the transmission line, antenna, and ground lead (if used) shall not exceed 15 meters. (c) All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification may be based on measurements at the intentional radiator's antenna output terminal unless the intentional radiator uses a permanently attached antenna, in which case compliance shall be demonstrated by measuring the radiated