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ABSTRACT:
A non-radiative energy transfer, commonly referred as WiTricity and based on ‘strong coupling’ between two coils which are separated physically by medium-range distances, is proposed to realize efficient wireless energy transfer. WiTricity idea is spear-headed by MIT researcher Marin Soljacic, which describes the ability to provide electricity to remote objects without wires. The advent of WiTricity technology is though old of 1899, explored by Nikola Tesla, but has founded its grip in recent years with numerous gadgets and there snaking cables around us. The technology is in turn expels E-waste and will free us from the power cords. WiTricity depends upon strong coupled resonance between transmitter and receiver coils. The transmitter emits a non-radiative magnetic field resonating at MHz frequencies and the receiving unit load resonates in that field. Thin film WiTricitycells, consisting of a tape coil on one layer, which is separated by an insulation layer to conductive strips on another layer, are fabricated. These cells are light, compact, and flexible provide convenience and flexibility in the design of wireless devices. Experiments are conducted to showcase the performance of this energy transfer system.
INTRODUCTION :
In the 1890’s wireless energy transmission was demonstrated by Nikola Tesla using his demonstration on resonant transformers called Tesla coils. Since these coils had undesirable electric fields which radiated energy in all directions, the efforts made by Tesla made little success. Various technologies for wireless power transfer like capacitive coupling, microwave and laser method have been proposed involving far fields. However it is the technology using magnetic resonance coupling has been found to be a viable technology for midrange energy transfer. Further, this means of energy transfer uses non-radiative mode of transmission and offers the use of connector free devices and is an alternative to the use of hazardous disposable batteries. Wireless energy transfer or WiTricity is currently extending its applications to medical implants saving patients from undergoing operations to replace the lithium ion batteries used for pacemakers. Magnetic resonance is also being used for charging of electric vehicles while driving on a highway. Since this technology can work even in water, powering of under- water cameras can be done reliably.
Thanks to the advent in power electronics, inductive charging, also known as wireless charging, has found much successes and is now receiving increasing attention by virtue of its simplicity and efficiency. The most important distinctive structural difference between contactless transformers and conventional transformers is that the two ‘coils’ in the former are separated by a large air gap. Compared with plug and socket (i.e., conductive) charging, the primary advantage of the inductive charging approach is that the system can work with no exposed conductors, no interlocks and no connectors, allowing the system to work with far lower risk of electric shock hazards.
This paper reports the study on a topical mode of energy transmission using resonant technique, commonly known as WiTricity (short form of wireless electricity) [4]. Detailed theoretical and numerical analyses reveal that WiTricity is efficient and practical for mid-range wireless energy exchange. Unlike conventional inductive coupling methods, there are only very small energy dissipations in off-resonant objects for systems working on WiTricity principle.
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A. Brief History
• Nikola Telsa – Experimented in 1899
• Imagined a global wireless power distribution system
• William Brown
• Established microwave to electricity conversion
• Invention of the Solar Panel
• First NASA solar powered satellite 1958
• Oil Crisis
• NASA program
• Marine Soijacic and team – Experimented in 2007
• 60- watt light bulb from a power source 7 feet away without wires.
• Currently looking for WiTricity in the range of 100 watts.
Near Field Transfer (Non-Radiative): These are wireless transmission techniques over distances comparable to, or a few times the diameter of the device(s).
a) Inductive Coupling: Inductive coupling is the action of electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are not directly connected. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. The receiver must be very close to the transmitter or induction unit in order to inductively couple with it.
b) Resonance Coupling: The idea of such mid-range induction was given by Marin Soljacic for efficient wireless transfer. The reason behind it is that, if two such resonant objects are brought in mid-range proximity, their near fields (consisting of so-called 'evanescent waves') and can allow the energy to transfer from one object to the other within times much shorter than all loss times, which were designed to be long, and thus with the maximum possible energy-transfer efficiency. Electromagnetic resonance 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, when both of these are made to resonate at same frequency they become much efficient.
2) Far Field Transfer (Radiative): Far Field transfer refers to methods achieving longer range transfers, often multiple kilometre ranges, where the distance is much greater than the diameter of the device(s).
Laser/Microwave Transmission: Such power transmissions can be made effective at long range power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna may be used to convert the microwave energy back into electricity. These provide 95% efficiency. A new company, Powercast introduced wireless power transfer technology using RF energy this system is applicable for a number of devices with low power requirements. Currently, it achieves a maximum output of 6 volts for a little over one meter.
Energy Transmission via laser is an efficient way for long range, except for it requires a proper line of sight for power beaming. In the case of light, power can be transmitted by converting electricity into a laser beam that is then fired at a solar cell receiver. With such laser beam efficiencies it is planned to build a solar panel grid in space & transferring the solar energy to earth receivers via laser methods.
BENEFITS OF DESIGN :
1) More Convenient
a) No manual recharging or changing batteries.
b) Unaffected by the day night cycle, weather or seasons.
c) Eliminate unsightly, unwieldy and costly power cords.
2) More Reliable
a) Never run out of battery power.
b) Reduce product failure rates by fixing the weakest link: flexing wiring and mechanical interconnects.
3) More Eco Friendly
a) Reduce use of disposable batteries.
b) Use efficient electric grid power directly instead of inefficient battery charging.
LIMITATIONS OF DESIGN :
• The resonance condition should be satisfied and if any error exists, there is no possibility of power transfer.
• If there is any possibility of Very Strong ferromagnetic material presence, then there may be a possibility of low power transfer due to radiation.
APPLICATIONS OF WITRICITY:
WiTricity wireless power transfer technology can be applied in a wide variety of applications and environments. The ability of our technology to transfer power safely, efficiently, and over distance can improve products by making them more convenient, reliable, and environmentally friendly. WiTricity technology can be used to provide:
1) Automatic Wireless Power Charging: When all the power a device needs is provided wirelessly, and no batteries are required. This mode is for a device that is always used within range of its WiTricity power source. When a device with rechargeable batteries charges itself while still in use or at rest, without requiring a power cord or battery replacement. This mode is for a mobile device that may be used both in and out of range of its WiTricity Consumer Electronics
a) 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.
b) Direct wireless powering of stationary devices (flat screen TV‘s, digital picture frames, home theatre accessories, wireless loud speakers, etc.) eliminating expensive custom wiring, unsightly cables and wall-wart power supplies.
c) Direct wireless powering of desktop PC peripherals: wireless mouse, keyboard, printer, speakers, display, etc.
Eliminating disposable batteries and awkward cabling power source.
2) Industrial :
a) Direct wireless power and communication interconnections across rotating and moving joints (robots, packaging machinery, assembly machinery, machine tools) eliminating costly and failure-prone wiring.
b) Direct wireless power for wireless sensors and actuators, eliminating the need for expensive power wiring or battery replacement and disposal.
3) Transportation :
a) Automatic wireless charging for existing electric vehicle classes: golf carts, industrial vehicles.
b) 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.
c) Direct wireless power interconnections to replace costly vehicle wiring harnesses and slip rings.
4) Medical Application: Wireless charging systems are being developed for implanted medical devices including Left ventricular assist device (LVAD) heart assist pumps, pacemakers, and infusion pumps. Using highly resonant wireless power transfer, such devices can be efficiently powered through the skin and over distances much greater than the thickness of the skin, so that power can be supplied to devices deeply implanted within the human body. The HR-WPT technique eliminates the need for drive lines that penetrate the human body, and for surgical replacement of primary batteries.
5) Military Application: Designers of defence systems are able to utilize wireless charging to improve the reliability, ergonomics, and safety of electronic devices. The Talon Tele-operated robot shown in Figure 9 is being equipped with wireless charging so that it can be recharged while it is being transported by truck from site to site. Helmet mounted electronics, including night vision and radio devices can be powered wirelessly from a battery pack carried in the soldier’s vest, eliminating the need for disposable batteries or a power cord connecting the helmet to the vest mounted battery pack.
CONCLUSIONS AND FUTURE WORK:
• This provides mid-range non-radiative energy transfer scheme based on strongly-coupled resonances. Even very simple design has promising performance and provides better efficiency with respect to distance. As a powerful concept, it could enable a wide range of applications. We can call WiTricity as future technology of Electricity transmission for power consumer.
• MIT's WiTricity is only 40 to 45% efficient and according to Soljacic, they have to be twice as efficient to compete with the traditional chemical batteries. The team's next aim is to get a robotic vacuum or a laptop working, charging devices placed anywhere in the room and even robots on factory floors.