Wi-tricity

Made By Manish Kumar, Minaam Abbas, Murtaza Tunio, Mustafa Rashid and Saad Hirani

Contents:-

1. Introduction 2. History of Wireless Electricity 3. Our Model 4. Advantages 5. Feasibility 6. Wireless Electricity and the Future 7. Applications 8. Reference Photographs

Introduction Wireless electricity is one of the most emerging solutions to the global power crisis. It is defined as the transfer of wireless electricity or power from a source to a load without the use of any artificial interconnecting conductors such as wires. Wireless electricity is being used primarily on the basis that at times, wires can be inefficient (power is lost as wires transmit electricity over long distances), inconvenient (in terms of cost and labor) and sometimes hazardous (many people may be electrocuted or put in some sort of danger). The transmission of wireless energy/ electricity is different from that of telecommunications such as radios. KGS Group A has paid attention to two different forms of wireless energy transfer- the first is through resonant inductive coupling, whereby energy supplied to a coil is transferred to a similar parallel coil without the use of any wires in order to provide enough electricity to light LED’s (Light Emitting Diodes). The second is through the use of a laser that reflects onto a solar panel attached to a capacitor that stores the energy converted by the solar panel, and transmits it to an LED placed at a distance. This time, the LED is connected through wires as the laser already shows the transfer of wireless energy. Other forms of wireless electricity transfer not looked at include the use of microwaves etc. The basic purpose and motivation for this project stems from the fact that in the modern world, power has become short in supply and its demand excessive. The costs of maintaining power and equating it to the increasing demand for fossil fuels makes the production of electricity a difficult task. With the reserves of fossil fuels in the world set to end within the first half of the 21st century, now is the best time to explore alternative forms of electricity for usage around the world. Sunlight, water and wind have already been used for powering houses, but these are also resources of nature and considering the fact that we live in a biosphere with limited resources it would be foolish to chase something natural to replace another. Thus the production of electricity by resonant inductive coupling and through lasers seems a useful alternative to the power crisis. The project not only demonstrates on a small scale the way in which such electricity is produced, but also explores throughout the course of this experiment, whether or not wireless power is a viable source of energy. By looking at various advantages and disadvantages we will be able to determine to what extent in the future, wireless electricity will and can be used to

human advantage. The project was inspired from MIT visionaries who wished to use this method of producing electricity following the discoveries of Tesla to benefit power producers around the world and ease production burden and alleviate running costs.

History of Wireless Transmission

Wireless power transmission is not a new idea. Nicola Tesla demonstrated transmission of electrical energy without wires in early 19th century. Tesla used electromagnetic induction systems. Tesla discovered that electrical energy could be transmitted through the earth and the atmosphere. In the course of his research he successfully lit lamps at moderate distances and was able to detect the transmitted energy at much greater distances. The Wardenclyffe Tower project was a commercial venture for trans-Atlantic wireless telephony and proof-of-concept demonstrations of global wireless power transmission. The facility was not completed because of insufficient funding. Earth is a naturally conducting body and forms one conductor of the system. A second path is established through the upper troposphere and lower stratosphere starting at an elevation of approximately 4.5 miles.

A global system for "the transmission of electrical energy without wires" called the World Wireless System, dependent upon the high electrical conductivity of plasma and the high electrical conductivity of the earth, was proposed as early as 1904 Following World War II, which saw the development of high-power microwave emitters known as cavity magnetrons, the idea of using microwaves to transmit power was researched. William C Brown demonstrated a microwave powered model helicopter in 1964. This receives all the power needed for flight from a microwave beam. In 1975 Bill Brown transmitted 30kW power over a distance of 1 mile at 84% efficiency without using cables. Japanese researcher Hidetsugu Yagi also investigated wireless energy transmission using a directional array antenna that he designed. In February 1926, Yagi and Uda published their first paper on the tuned high-gain directional array now known as the Yagi antenna. While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout the broadcasting and wireless telecommunications industries due to its excellent performance characteristics. In 2006, more recent breakthroughs were made; using electrodynamics induction a physics research group, led by Prof. Marin Soljacic, at MIT, wirelessly power a 60W light bulb with 40% efficiency at a 2 meters distance with two 60 cm-diameter coils. Researchers developed several techniques for moving electricity over long distance without wires. Some exist only as theories or prototypes, but others are already in use.

Means of Transmission The most common form of wireless power transmission is carried out using direct induction followed by resonant magnetic induction. Other methods under consideration include electromagnetic radiation in the form of microwaves or lasers.

Inductive Coupling

This is the first method used for wireless power transfer. The simplest example for wireless energy transfer using this method is the electrical transformer. In this the primary and secondary circuits are electrically isolated from each other. The transfer of energy takes place by electromagnetic coupling through mutual induction. Coupling must be tight in order to achieve high efficiency. As the distance from the primary is increased, more and more of the magnetic field misses the secondary. The main drawback of this method is the short range. For efficient working of a system, which uses this method, the receiver must be in very close proximity to the-transmitter. A larger, stronger field can be used for energy transfer over large distances, but this process is extremely inefficient, since the magnetic field spreads in all direction, wasting energy. Mobile and electric tooth brush battery chargers, and electrical power distribution transformers are examples of how this principle is used.

Resonant Induction (Evanescent Wave Coupling) In 2006 MIT researchers discovered an efficient method to transfer power between coils separated by few meters. They extend the distance between coils in inductive coupling system by adding resonance. They demonstrated this by sending electromagnetic waves in a highly angular waveguide, producing evanescent waves, which carry no energy. An evanescent wave is a near field standing wave exhibiting exponential decay with distance. Evanescent waves are always associated with matter, and are most intense within one-third wavelength from any radio antenna. If a proper resonant waveguide is brought near the transmitter, the evanescent waves can allow the energy to tunnel to the power drawing wave-guide. 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 waves transmission. In resonant induction method, induction can take place a little differently if the electromagnetic fields around the coils resonate at the same frequency. In this a curved coil of wire is used as an inductor. A capacitance plate, which can hold charges, is attached to each end of the coil. As electricity travels through this coil the coil begins to resonate. Its resonant frequency is a product of the inductance of the coil and the capacitance of the plate. When resonant coupling is used, performance can be further improved by modifying the drive current from a sinusoidal to a non-sinusoidal transient waveform. Pulse power transfer occurs over multiple cycles. In this way significant power may be transmitted between two mutually attuned LC circuits having a relatively low coefficient of coupling. Transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitors, which, in combination, allow the receiving element to be tuned to the transmitter frequency. Resonance is used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal

wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi wireless charging standard. It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters.

Electromagnetic Radiation Regardless of resonance incorporation, induction generally sends wireless power over relatively short distance. For very long distance power transmission radio and microwaves are used. Japanese researcher Yagi developed a directional array antenna known as YAGI antenna for wireless energy transmission. It is widely used for broadcasting and wireless telecommunications industries. Whilst it did not prove to be particularly useful for power transmission, power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna is a rectifying antenna, an antenna used to convert microwaves into DC power. An antenna refers to any type of device that converts electromagnetic waves into electricity or vice versa. A rectenna is simply a microwave antenna. Inverse rectennas convert electricity into microwave beams; rectennas suitable for receiving energy beamed from solar panels in geocentric orbit would need to be several miles across. Although power densities of such an arrangement would be low enough to avoid any damage to people or the environment. Rectifying antennae are usually made an array of dipole antennae, which have positive and negative poles. These antennae connect to semiconductor diodes. Rectenna conversion has an efficiency of about 95%. In the 1980s, Canada's Communications Research Centre created a small airplane that could run off power beamed from the Earth. The unmanned plane, called the Stationary High Altitude Relay Platform (SHARP), was designed as a communications relay. Rather flying from point to point, the SHARP could fly in circles two kilometers in diameter at an altitude of about 13 miles. Most importantly, the aircraft could fly for months at a time. The secret to the SHARP'S long flight time was a large, ground-based microwave transmitter. The SHARP'S circular flight path kept it in range of this transmitter. A large, disc-shaped rectifying antenna, or rectenna, just behind the plane's wings changed the microwave energy from the transmitter into direct-current (DC) electricity. Because of the microwaves interaction with the rectenna, the SHARP had a constant power supply as long as it was in range of a functioning microwave array. This arrangement functions according to the following procedure.

1. Microwaves, which are part of the electromagnetic spectrum, reach the dipole antennae. 2. The antennae collect the microwave energy and transmit it to the diodes. 3. The diodes act like switches that are open or closed as well as turnstiles that let electrons flow in

only one direction. They direct the electrons to the rectenna's circuitry. 4. The circuitry routes the electrons to the parts and systems that need them. 5. A human safe power density of 1 mW/cm2 distributed across a 10 km diameter area

corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants.

The size of the components may be dictated by the distance from transmitter to receiver, the wavelength and the Rayleigh criterion or diffraction limit, used in standard radio frequency antenna design, which also applies to lasers. In addition to the Rayleigh criterion Airy's diffraction limit is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture. The Rayleigh criterion dictates that any radio wave, microwave or laser beam will spread and become weaker and diffuse over distance; the larger the transmitter antenna or laser aperture compared to the wavelength of radiation, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobes. However, the concept of laser aperture considerably differs from an antenna. Typically, a laser aperture much larger than the wavelength induces multi-moded radiation and mostly collimators are used before emitted radiation couples into a fiber or into space.

Microwave power beaming can be more efficient than lasers, and is less prone to atmospheric attenuation caused by dust or water vapor losing atmosphere to vaporize the water in contact. Microwave power transmission has some drawbacks: The project would require solar stations on the moon. The solar power stations on the moon would require supervision and maintenance. In other words, the project would require sustainable, manned moon bases.

Only part of the earth has a direct line of sight to the moon at any given time. To make sure the whole planet had a steady power supply, a network of satellites would have to re-direct the microwave energy. Many people would resist the idea of being constantly bathed in microwaves from space, even if the risk were relatively low.

Laser Laser beams can be used for wireless power transmission. In the case of electromagnetic radiation closer to visible region of spectrum (10s of microns (um) to 10s of nm), power can be transmitted by converting electricity into a laser beam that is then pointed at a solar cell receiver. This mechanism is generally known as "power-beaming" because the power is beamed at a receiver that can convert it to usable electrical energy. Advantages of laser based energy transfer compared with other wireless methods are:

1. Collimated monochromatic wave front propagation allows narrow beam cross-section area for energy transmission over large ranges.

2. Compact size of solid-state lasers-photovoltaic semiconductor diodes fit into small products.

3. No radio-frequency interference to existing radio communication such as Wi-Fi and cell phones.

4. Control of access; only receivers illuminated by the laser receive power.

But it has many drawbacks:

1. Conversion to light, such as with a laser, is moderately inefficient 2. Conversion back into electricity is moderately inefficient, with photovoltaic cells achieving 40%-

50% efficiency 3. Atmospheric absorption causes losses. 4. This method requires a direct line of sight with the target. 5. The laser "power-beaming" technology has been mostly explored in military weapons and

aerospace applications and is now being developed for commercial and consumer electronics Low-Power applications.

Electrical Conduction Single wire with Earth return electrical power transmission systems rely on current flowing through the earth plus a single wire insulated from the earth to complete the circuit. In emergencies high-voltage direct current power transmission systems can also operate in the 'single wire with earth return' mode. Elimination of the raised insulated wire and transmission of high-potential, high-frequency alternating current through the earth with an atmospheric return circuit has been investigated as a method of wireless electrical power transmission. Transmission of electrical energy through the earth alone, eliminating the second conductor is also being investigated. Low frequency alternating current can be transmitted through the inhomogeneous earth with low loss because the net resistance between earth antipodes is considerably less than 1 ohm. The electrical displacement takes place predominantly by electrical conduction through the oceans, and metallic ore bodies and similar subsurface structures. The electrical displacement is also by means of electrostatic induction through the more dielectric regions such as quartz deposits and other non-conducting minerals.

Our Model

1. Space Harvesting

Our model consists of ‘satellite’, which emits a laser, and a solar cell, placed on ‘earth’, designed absorbs the energy from that laser. This model demonstrates the concept of energy harvesting from space. The world today relies heavily on oil to fulfill its energy requirements; however, oil will not last long enough to sustain us for long. The US Department of Energy in the Hirsch report indicates that “The problems associated with world oil production peaking will not be temporary, and past “energy crisis” experience will provide relatively little guidance.” Moreover, the increasing demand for energy all over the world does not make the situation any better. Therefore scientists have proposed many radical solutions.

One of the proposed solutions is to place an array of solar panels in space and beam the energy generated down to earth by means of microwaves or lasers. Such a system has many benefits:

1. Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of atmospheric gasses. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth's surface.

2. Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar radiation, generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most.[1]

3. Elimination of weather concerns, since the collecting satellite would reside well outside of any atmospheric gasses, cloud cover, wind, and other weather events.

4. Elimination of plant and wildlife interference. 5. Re-directable power transmission: A collecting satellite could possibly direct power on

demand to different surface locations based on geographical baseload or peak load power needs.

Our main focus here is to demonstrate the application of the laser as one of the modes of wireless transfer of energy, it effectively transfers the potential difference generated on the solar panels in space to receiving station on the ground, from where it can be regulated and utilized.

2. Resonant Inductive Coupling

Our model here demonstrates that electricity can be effeiciently transmitted over large distances using inductive coupling. It consists of a two coils which have been ‘inductively coupled’, that is, the magnetic feild generated in one coil induces a magnetic feild in the other coil. However the point that differenciates this from an ordinary ‘transformer’ type setup is the fact the magnetic flux in these coils has been made to vibrate at a specific frequency witht the help of a capacitor. This enables the two coils to transfer energy effectively evem over large distances!

Our focus here was to show that electricity can be effeicently transferred over couple of Inches with the use of resonant inductive coupling. With usage of higher frequencies and a more powerful output such a device could be be used to eliminate the need for power cords or extension cables.

Range & Rate of Coupling

Using Coupled Mode Theory (CMT), we can give some frame work to the system. The field system of the two resonant objects 1, 2 is

F(r,t)=a1(t)F1(r)+a2(t)F2(r)

Where F1,2(r) are the resonating modes of 1 and 2 alone, and then the field amplitudes a1(t)

and a2(t).The lower order representation of the system is given by :

Here, ω1, 2 are the individual frequencies, Γ1, 2 are the Resonance widths (Decay rates) due to the objects’ intrinsic (absorption, radiation etc.) losses, and ‘κ’ is the coupling coefficient.

The solution of the equation show that at exact resonance at ω1=ω2 and Γ1=Γ2 the normal modes of the combined system are split by 2κ. The energy exchange between the two objects takes place in time Pi/κ and is nearly perfect, apart for losses, which are minimal when the coupling rate is much faster than all loss rates (κ>> Γ1, 2). It is exactly this ratio {κ /sqrt (Γ1, 2)} shows that, it will set as figure-of-merit for any system under consideration for wireless energy-transfer, along with the distance over which this ratio can be achieved. The desired optimal regime {κ/sqrt (Γ1,2)>>1} is called “Strong-Coupling” regime. There is No change in Energy, unless κ/Γ>>1 is true.

Advantages:

There are several advantages for this new mode of energy transfer.

1. Highly Resonant Strong Coupling Provides High Efficiency Over Distance This mode of wireless power transfer is highly efficient over distances ranging from centimeters to several meters. We define efficiency as the amount of usable electrical energy created from a source. This mode of transfer can assure a high rate of efficiency due to its design.

2. Energy Transfer via Magnetic Near Field Can Penetrate and Wrap Around Obstacles

The magnetic near field has several properties that make it an excellent means of transferring energy in a typical consumer, commercial, or industrial environment. Most common building and furnishing materials, such as wood, gypsum wall board, plastics, textiles, glass, brick, and

concrete are essentially “transparent” to magnetic fields—enabling this technology to efficiently transfer power through them. In addition, the magnetic near field has the ability to “wrap around” many metallic obstacles that might otherwise block the magnetic fields.

3. Non-Radiative Energy Transfer is Safe for People and Animals WiTricity’s technology is a non-Radiative mode of energy transfer, relying instead on the magnetic near field. Magnetic fields interact very weakly with biological organisms—people and animals—and are scientifically regarded to be safe. Professor Sir John Pendry of Imperial College London, a world renowned physicist, explains: “The body really responds strongly to electric fields, which is why you can cook a chicken in a microwave. But it doesn't respond to magnetic fields. As far as we know the body has almost zero response to magnetic fields in terms of the amount of power it absorbs."

4. Scalable Design Enables Solutions from Milli watts to Kilowatts

This system can be designed to handle a broad range of power levels. The benefits of highly efficient energy transfer over distance can be achieved at power levels ranging from Milli watts to several kilowatts. This enables the technology to be used in applications as diverse as

powering a wireless mouse or keyboard (milliwatts) to recharging an electric passenger vehicle (kilowatts).

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 body.

Wireless Electricity and the future: -

More Convenient:

1. No manual recharging or changing batteries. 2. Eliminate unsightly, unwieldy and costly power cords.

More Reliable:

1. Never run out of battery power. 2. Reduce product failure rates by fixing the ‘weakest link’: flexing wiring and mechanical

interconnects.

More Environmentally Friendly:

1. Reduce use of disposable batteries. 2. Use efficient electric ‘grid power’ directly instead of inefficient battery charging.

Applications: -

Consumer Electronics

Automatic wireless charging of mobile electronics (phones, laptops, game controllers, etc.) in home, car, office, Wi-Fi hotspots

… while devices are in use and mobile.

Direct wireless powering of stationary devices (flat screen TV’s, digital picture frames, home theater accessories, wireless loud

speakers, etc.) … eliminating expensive custom wiring, unsightly cables and “wall-wart” power supplies.

Direct wireless powering of desktop PC peripherals: wireless mouse, keyboard, printer, speakers, display, etc… eliminating

disposable batteries and awkward cabling.

Industrial

Direct wireless power and communication interconnections across rotating and moving “joints” (robots, packaging machinery,

assembly machinery, machine tools) … eliminating costly and failure-prone wiring.

Direct wireless power and communication interconnections at points of use in harsh environments (drilling, mining,

underwater, etc.) … where it is impractical or impossible to run wires.

Direct wireless power for wireless sensors and actuators, eliminating the need for expensive power wiring or battery

replacement and disposal.

Automatic wireless charging for mobile robots, automatic guided vehicles, cordless tools and instruments…eliminating complex

docking mechanisms, and labor intensive manual recharging and battery replacement.

Transportation

Automatic wireless charging for existing electric vehicle classes: golf carts, industrial vehicles.

Automatic wireless charging for future hybrid and all-electric passenger and commercial vehicles, at home, in parking garages,

at fleet depots, and at remote kiosks.

Direct wireless power interconnections to replace costly vehicle wiring harnesses and slip rings.

Other Applications

Direct wireless power interconnections and automatic wireless charging for implantable medical devices (ventricular assist

devices, pacemaker, defibrillator, etc.).

Automatic wireless charging and for high tech military systems (battery powered mobile devices, covert sensors, unmanned

mobile robots and aircraft, etc.).

Direct wireless powering and automatic wireless charging of smart cards.

Direct wireless powering and automatic wireless charging of consumer appliances, mobile robots, etc.

Reference Photographs:-