WITRICITY: A WORLD WITHOUT WIRESSUBMITTED BY: SUBMITTED TO: SATYAJIT MOHANTY Dr. ABHIMANYU MAHAPATRA Regd. no- 0901106207 Dr. RANJAN KU JENA
TOPICS TO BE DISUSSED :• WIRELESS POWER TRANSFER•CONCEPT OF ELECTROMAGNETIC WAVE•EVIDENCE FROM HISTORY•MODES OF WPT TRANSMISSION•WHAT IS WITRICITY HOW IT IS DEVELOPEDRESONACE COUPLING (COUPLING RESONATOR)COMPARISON WITH OTHER TECHNOLOGIESAPPLICATIONSADVANTAGES & DIS ADVANTAGES
WHAT IS WIRELESS POWER TRANSFER : Efficient transmission of electric power from onepoint to another through vacuum or without the use ofwire or any other substance. This is used forapplications wherecontinuous delivery of energy is needed, butconventional wires are inconvenient, expensive orimpossible.The power can be transmitted usingelectromagnetic waves like microwaves, radio wavesor lasers.
CONCEPT OF ELECTROMAGNETIC WAVE:When an electric current passes through a wire, thereis an electric field & magnetic field in the dielectricsurrounding the conductor .The electric field of a circuit over which energy flowshas three main axes at right angles with leach other:a. The magnetic field, concentric with the conductor.b. The lines of electric force, radial to the conductor.c. The power gradient, parallel to the conductor.
In a direct current circuit, the current is continuous &the fields are constant . There is a condition of stressin the space surrounding the conductor, whichrepresents stored electric and magnetic energy, justas a compressed spring or a moving mass representsstored energy.In an alternating current circuit, the fields arealternate; that is, with every half wave of current andof voltage, the magnetic and the electric field start atthe conductor(primary) and run outwards into spacewith the speed of light. Where these alternating fieldsimpinge on another conductor(secondary) & voltageand current are induced. This is calledElectromagnetic induction.
Electromagnetic induction is proportional to theintensity of the current and voltage in conductor &frequency of field. The higher the frequency themore is the inductive effects.A high frequency current does not pass for longdistances along a conductor but rapidly transfersits energy by induction to adjacentconductors. The more rapidly the energydecreases and the current dies down along thecircuit. in electromagnetic wave radiation , flow ofelectric energy comprises -phenomena inside ofthe conductor and phenomena in the spaceoutside of the conductor .
SOME EXAMPLES FROM HISTORY
Maxwells theory of electromagnetism, publishedin 1865 mentions electromagnetic waves moving atthe speed of light.In 1886 Hertz performed a successfulexperiment with pulsed wireless energy transfer.He produced an apparatus that produced anddetected microwaves in the UHF region.
Tesla’s experiment : TESLA COIL In1894 Nikola Tesla used resonant inductivecoupling, also known as "electro-dynamicinduction" to wirelessly light up phosphorescentand incandescent lamps at the 35 South FifthAvenue laboratory.1897 he patented a device calledhigh-voltage resonance transformer or "Tesla coil” capable of producing very high voltagesat high frequency.In 1899 using pulsed wireless energymanaged to light 200 lamps, without wires, from 40kilometers away by using an aerial tower callledWardenclyffe tower, which was meant to be a pilotplant for his “World Wireless System” to broadcastenergy around the globe. The core facility wasnever fully operational and was not completed dueto economic problems .
DIFFERENT MODES OF WPT
1.Electrostatic induction or capacitive coupling2.Electromagnetic radiation-beam powered antenna,microwave radiation , laser radiation3.Electrodynamic induction method or resonantinductive coupling or witricity
Electrostatic induction: It is the passage of electrical energy through adielectric. Here insulated terminals or platesare elevated over a conducting ground plane.The electric field is created by charging theplates with a high potential, high frequency acpower supply. The capacitance between twoterminals and a powered device form a voltagedivider . The electric energy transmitted by thisis utilized by wireless lamp.
MICROWAVE POWER TRANSMISSION:power transmission through microwave is called farfield power transmission . It is accomplished by 3 stages:1. The electrical energy is transmitted towards receiver by transmitting antenna which is supplied by a dc energy2. Propagating medium3. Rectenna : the energy sent was received by a a special designed antenna called Rectenna. “An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.” Microwaves radiation: 85% efficiency around 5kmacross (3.1 miles) ,95% of the beam will fall on the Rectenna.
Demonstration of microwave power transmission using solar energy
Recent development has shown that power can be transmitted by laser waveMicrowave vs. Laser transmission Microwave Laser More developed Recently High efficiency up developed to 85% solid state lasers Beams is far below allow efficient the lethal levels of transfer of power concentration even Range of 10% to for a prolonged 20% efficiency exposure within a few years Cause interference Conform to limits with satellite on eye and skin communication damage industry as 2.45 ghz.
WITRICITYWiTricity ,is used for "wireless electricity” in whichwireless energy transfer includes resonant energytransfer , the ability to provide electrical energy toremote objects without wires using oscillatingmagnetic fields. The term WiTricity was used for aproject that took place at MIT, led by Marin Soljačićin 2007.
Inductive Coupling: It uses magnetic fields that is produced due tocurrents movement through- wire. Bending the wireinto a coil amplifies the magnetic field. The moreloops the coil makes, the bigger the field will be. This is the principle how a transformer works.Using it an electric toothbrush recharged. It takesthree basic steps:1. Current from the wall outlet flows through a coil inside the charger, creating a magnetic field. In a transformer, this coil is called the primary winding.2. When you place your toothbrush in the charger, the magnetic field induces a current in another coil, or secondary winding, which connects to the battery.3. This current recharges the battery.
Need of Resonant couplingNon-resonant coupled inductors(transformers,)workon the principle of inductive coupling is of short rangepower transfer & requires a magnetic core. Over greaterdistances the NRI Method is highly inefficient andwastes the majority of the energy in resistive losses ofthe primary coil.Hence concept of resonant coupling comes wheretwo coils are tuned to a particular frequency calledresonating frequency & absorb optimal energy.
CONCEPT OF COUPLED RESONATOR :For resonance coupling coupled resonator is used.Here Two resonant objects of the same resonantfrequency tend to exchange energy efficiently, whileinteracting weakly with extraneous off-resonant objects.Coupled resonators operate in a strongly coupledregime where energy transfer rate is substantially higherthan the rate at which they lose energy due to materialabsorption and radiation. So energy transfer can be veryefficient.This is use for wireless charging of devices(mobile/laptop)
WiTricity Technology is BornExperimental demonstration : Two copper coils, each a self-resonant system. resonant source &resonant capture device, connected to a 60 watt light bulb. The coils aresuspended in mid-air with nylon thread, at distances that ranged from afew centimeters to over 2.5 meters (8.2 ft).Not only was the light bulb illuminated, but the theoretical predictions ofhigh efficiency over distance were proven experimentally. By placingvarious objects between the source and capture device, the teamdemonstrated how the magnetic near field can transfer power throughcertain materials and around metallic obstacles.
Block diagram of the setup
general principle:If an ac is applied to a primary coil which iscapacitively loaded, the coil will ring, and form anoscillating magnetic field. The energy will transfer backand forth between the magnetic field in the inductor andthe electric field across the capacitor at the resonantfrequency. This oscillation will die away at a ratedetermined by the gain-bandwidth (Q factor), mainly dueto resistive and radiative losses. However secondarycoil has to cut most of the field before loss, then most ofthe energy can be transferred.The primary coil forms a series RLC circuit, andthe Q factor for such a coil is: For R=10 ohm,C=1 micro farad and L=10 mH, Q is given as 10. Because the Q factor can be very high, (1000 with air cored coils) only a small percentage of the field has to be coupled from one coil to the other to achieve high efficiency.
Transmitter coils and circuitryUnlike the multiple-layer secondary of anon-resonant transformer, coils for thispurpose are single layer solenoids (tominimize skin effect and giveimproved Q) in parallel with a suitablecapacitor. Insulation absent, with spacersof low permittivity, low loss materialssuch as silk to minimize dielectric losses.To progressively feed energy/power intothe primary coil with each cycle, Colpittsoscillator is used
Receiver coils and circuitryIn receiver coil is connected to amicrochip. It provides capacitanceto give resonance & regulators toprovide suitable voltage.The secondary receiver coil is ofsame design & same tuningfrequency like primary . so offersless impedance. So energy isoptimally absorbed. To remove energy from thesecondary coil, different methods Receiver of a smartcardcan be used, the AC can be useddirectly or rectified and a regulatorcircuit can be used to generate DCvoltage.
FEATURES OF THIS COUPLING:It is a near field effect . the wireless powertransmission concept based on strongly-coupledresonator.Time taken for energy transfer is less than the time ofloss . So high efficiency. Since the resonant wavelengthis much larger than the resonators, the field cancircumvent extraneous objects in the vicinity and noneed of line-of-sight.This method is safe, since magnetic fields interactweakly with living organisms.
Coupling coefficient:The coupling coefficient is the fraction of the flux ofthe primary that cuts the secondary coil, and is afunction of the geometry of the system. The couplingcoefficient is between 0 and 1.a. Tight coupling coupling coefficient ~1 as with conventional iron-core transformers.b. Over coupling :secondary coil is so close that it tends to collapse the primarys field . Critical coupling is when the transfer in the pass band is optimal.c. Loose coupling coils are distant from each other, most of the flux misses the secondary.In Tesla CC=0.2 . At greater distances, for inductivewireless power transmission, it may be < 0.01.
Comparison with other technologies:In conventional transformers, for inductive transferefficiency around 80% at short range in witricity tightly coupled conventional transformershas efficiency around 90-95% .In addition, where batteries need periodicmaintenance and replacement, resonant energytransfer can be used instead. So pollution due toBatteries during their construction and their disposal islargely avoided.
Regulations and safety: Shock prevention unlike wired connection causeno direct connection.The coupling is due to predominantly magneticfield. so technology is safe up to <10 mhzaccording to Safety standards and guidelines forelectromagnetic field exposures . This alsodepends on transmitted power .Deployed systems already generate magneticfields, for example inductioncookers and contactless smart card readers . Butthey are proved not to be harmful.
APPLICATION:Contactless smart cardHigh voltage (one million volt) sources for X-ray productionTesla coilsSome Passports recharging mobiles or computers ,tooth brush etc.