wireless electricity

WiTricity is based on strong coupling betweenthe capture device.
electromagnetic resonant objects to transfer energyWORKING OF WITRICITY:
wirelessly between them. This differs from otherSTEP 1:
methods like simple induction, microwaves, or air 
ionization. The system consists of transmitters andA circuit [A] attached to the wall socket converts the
receivers that contain magnetic loop antennas criticallystandard 60-hertz current to 10 megahertz and feeds
tuned to the same frequency. Due to operating in theit to the transmitting coil [B]. The oscillating current inside
electromagnetic near field, the receiving devices mustthe transmitting coil causes the coil to emit a
be no more than about a quarter wavelength from the10-megahertz magnetic field.
transmitter 
Unlike the far field wireless power transmissionSTEP 2:
systems based on traveling electro-magnetic waves, 
WiTricity employs near field inductive coupling throughThe receiving coil [C] has the exact same dimensions
magnetic fields similar to those found in transformersas the sending coil and thus resonates at the same
except that the primary coil and secondary windingfrequency and, in a process called magnetic induction,
are physically separated, and tuned to resonate topicks up the energy of the first coil's magnetic field.
increase their magnetic coupling. These tuned magnetic 
fields generated by the primary coil can be arrangedSTEP 3:
to interact vigorously with matched secondary 
windings in distant equipment but far more weakly withThe energy of the oscillating magnetic field induces an
any surrounding objects or materials such as radioelectrical current in the receiving coil, lighting the bulb [D].
signals or biological tissue. 
In particular, WiTricity is based on usingWiTricity's technology is different than:
'strongly-coupled' resonances to achieve a highMagnetic Resonance Imaging(MRI):
power-transmission efficiency. Aristeidis Karalis, 
referring to the team's experimental demonstration,MRI machines use "magnetic resonance imaging" to
says that "the usual non-resonant magnetic inductionproduce diagnostic images of soft tissue.Many people
would be almost 1 million times less efficient in thisassume that WiTricity's "Resonant Magnetic Coupling"
particular system". Researchers attribute the delay tomust be similar to magnetic resonance imaging (MRI)
develop the technology to limitations of well-knowntechnology, however, the technologies are similar in
physical laws and a simple lack of need. Only recentlyname only.  MRI is, as its name suggests, a
have modern consumers obtained a high number oftechnology for using magnetism as a basis for
portable electronic devices which currently requirediagnostic imaging of soft tissue in the human body. It
batteries and plug-in chargersutilizes a strong DC magnet to orient the magnetic
Introduction to Witricity:fields of atoms within tissues, and radio frequency
Electricity is today a necessity of modern life. It isfields to manipulate those atoms in a selective way, so
difficult to imagine passing a day without electricity. Thethat tissues and structures can be imaged clearly. The
conventional use of electricity is made possible through"resonance" referred to in "MRI" refers to the
the use of wires. However researchers in MIT haveresonance of atomic structures. MRI is not considered
devised a means of providing electricity without anyto be a method for wireless power transfer.
wires.Tesla's Vision of a Wireless World
WiTricity, a portmanteau for wireless electricity, is aIn the late 1800's and early 1900's, at the dawn of the
term coined initially by Dave Gerding in 2005 and usedelectrification of the modern world, some scientists and
by an MIT research team led by Prof. Marinengineers believed that using wires to transfer
Soljačić in 2007. This principle of wireless electricityelectricity from every place it was generated to every
works on the principle of using coupled resonantplace that it could be used would be too expensive to
objects for the transference of electricity. The systembe practical. Nikola Tesla, one of the most well known
consists of WiTricity transmitters and receivers thatof these scientists, had a vision for a wireless world in
contain magnetic loop antennas critically tuned to thewhich wireless electric power and communications
same frequency. Wireless power transmission is not awould reach around the world, delivering information
new idea; Nikola Tesla demonstrated a "transmissionand power to ships at sea, factories, and every home
of electrical energy without wires" that depends uponon the planet.  Tesla contributed significantly to our
electrical conductivity as early as 1891.understanding of electricity and electrical systems and
The receiver works on the same principle as radiois credited with inventing three-phase AC power
receivers where the device has to be in the range ofsystems, induction motors, fluorescent lamps, radio
the transmitter. It is with the help of resonant magnetictransmission, and various modes of wireless electric
fields that witrecity produces electricity, while reducingpower transfer. WiTricity technology for power
the wastage of power. This is unlike the principletransfer is different than the technologies proposed by
adopted by Nikola Tesla in the later part of the 19thTesla, but his work is referenced and acknowledged in
century; where conduction based systems were used.the scientific articles published by WiTricity's founding
The present project on witricity aims at powertechnical team.
transmissions in the range of 100 watts. May be the 
products using WiTricity in future might be called WitricNikola Tesla's Wardenclyffe tower built on Long Island,
or Witric's.NY in 1904. This tower was intended to implement
So far the MIT researchers have been able to powerTesla's vision of transmitting power and information
a 60 watt light bulb from a power source that isaround the world.  The tower was destroyed in 1917.
located about seven feet away, while providing fortyNon-Radiative Energy Transfer is Safe for People and
percent efficiency. This was made possible using twoAnimals:
copper coils that were twenty inches in diameterWiTricity's technology is a non-radiative mode of
which were designed so that they resonated togetherenergy transfer, relying instead on the magnetic near
in the MHz range. One of these coils were connectedfield. Magnetic fields interact very weakly with biological
to a power source while the other, to a bulb. With thisorganisms people and animals and are scientifically
witricity setup, the bulb got powered even when theregarded to be safe. Professor Sir John Pendry of
coils were not in sight.Imperial College London, a world renowned physicist,
WiTricity Technology: The Basicsexplains:  "The body really responds strongly to
Understanding what WiTricity technology is transferringelectric fields, which is why you can cook a chicken in
electric energy or power over distance without wiresa microwave.  But it doesn't respond to magnetic
is quite simple. Understanding how it works is a bitfields. As far as we know the body has almost zero
more involved, but it doesn't require an engineeringresponse to magnetic fields in terms of the amount of
degree. We'll start with the basics of electricity andpower it absorbs."  Evidence of the safety of
magnetism, and work our way up to the WiTricitymagnetic fields is illustrated by the widespread
technology.acceptance and safety of household magnetic
Electricity: The flow of electrons (current) through ainduction cooktops.  Through proprietary design of
conductor (like a wire), or charges through thethe WiTricity source, electric fields are almost
atmosphere (like lightning).  A convenient way forcompletely contained within the source. This design
energy to get from one place to another.results in levels of electric and magnetic fields which
Magnetism: A fundamental force of nature, whichfall well within regulatory guidelines. Thus
causes certain types of materials to attract or repelWiTricitytechnology doesn't give rise to radio
each other. Permanent magnets, like the ones on yourfrequency emissions that interfere with other electronic
refrigerator and the earth's magnetic field, aredevices, and is not a source of electric and magnetic
examples of objects having constantmagnetic fields.field levels that pose a risk to people or animals.
Oscillating magnetic fields vary with time, and can beLimits for human exposure to magnetic fields are set
generated by alternating current (AC) flowing on aby regulatory bodies such as the FCC, ICNIRP, and are
wire. The strength, direction, and extent of magneticbased on broad scientific and medical consensus.
fields are often represented and visualized byWiTricitytechnology is being developed to be fully
drawings of the magnetic field lines.compliant with applicable regulations regarding
 magnetic fields and electromagnetic radiation.
As electric current, I, flows in a wire, it gives rise to aADVANTAGES OF WITRICITY:
magnetic field, B, which wraps around the wire. WhenMore Convenient:
the current reverses direction, the magnetic field also- No manual recharging or changing batteries.
reverses its direction.- Eliminate unsightly, unwieldy and costly power cords.
 More Reliable:
The blue lines represent the magnetic field that is- Never run out of battery power.
created when current flows through a coil. When the- Reduce product failure rates by fixing the
current reverses direction, the magnetic field also‘weakest link':  flexing wiring and   mechanical
reverses its direction.interconnects.
Electromagnetism: A term for the interdependence of- There is no need of having a line of sight.
time-varying electric and magnetic fields. For example,More Environmentally Friendly:
it turns out that an oscillating magnetic field produces- Reduce use of disposable batteries.
an electric field and an oscillating electric field produces- Use efficient electric ‘grid power' directly instead
a magnetic field.of inefficient battery charging.
Magnetic Induction: A loop or coil of conductive materialWiTricitytechnology can be used to provide:
like copper, carrying an alternating current (AC), is a- Direct Wireless Power—when all the power a
very efficient structure for generating or capturing adevice needs is provided wirelessly, and no batteries
magnetic field. If a conductive loop is connected to anare required. This mode is for a device that is always
AC power source, it will generate an oscillatingused within range of its WiTricity power source.
magnetic field in the vicinity of the loop.  A second- Automatic Wireless Charging—when a device with
conducting loop, brought close enough to the first, mayrechargeable batteries charges itself while still in use or
"capture" some portion of that oscillating magnetic field,at rest, without requiring a power cord or battery
which in turn, generates or induces an electric currentreplacement. This mode is for a mobile device that
in the second coil. The current generated in the secondmay be used both in and out of range of its WiTricity
coil may be used to power devices. This type ofpower source.
electrical power transfer from one loop or coil toWITRICITY IN FUTURE:
another is well known and referred to as magneticJust imagine the future, with witricity, where there will
induction. Some common examples of devices basedbe no need of power cables and batteries. The city
on magnetic induction are electric transformers andjust has to be covered with witricity hot spots wherein
electric generators.you can use your electric gadget battery and wire
Energy/Power Coupling: Energy coupling occurs whenfree making it more convenient to carry around and
an energy source has a means of transferring energymuch lighter. With witricity, there will be no need of
to another object. One simple example is a locomotivecharging batteries, or buying new batteries for your
pulling a train car the mechanical coupling between theelectrical gadgets.
two enables the locomotive to pull the train, and 
overcome the forces of friction and inertia that keepAPPLICATIONS:
the train still and, the train moves. Magnetic couplingConsumer Electronics:
occurs when the magnetic field of one object- Automatic wireless charging of mobile electronics
 (phones, laptops, game controllers, etc.) in home, car,
An electric transformer is a device that uses magneticoffice, Wi-Fi hotspots … while devices are in use and
induction to transfer energy from its primary winding tomobile.
its secondary winding, without the windings being- Direct wireless powering of stationary devices (flat
connected to each other. It is used to "transform" ACscreen TV's, digital picture frames, home theater
current at one voltage to AC current at a differentaccessories, wireless loud speakers, etc.) … eliminating
voltage.interacts with a second object and induces anexpensive custom wiring, unsightly cables and
electric current in or on that object. In this way, electric"wall-wart" power supplies.
energy can be transferred from a power source to a- Direct wireless powering of desktop PC peripherals:
powered device. In contrast to the example ofwireless mouse, keyboard, printer, speakers, display,
mechanical coupling given for the train, magneticetc… eliminating disposable batteries and awkward
coupling does not require any physical contactcabling.
between the object generating the energy and theIndustrial:
object receiving or capturing that energy.- Direct wireless power and communication
Resonance:interconnections across rotating and moving "joints"
This video shows how a wine glass captures sound(robots, packaging machinery, assembly machinery,
energy that ocillates at its natural resonant frequency,machine tools) … eliminating costly and failure-prone
converts it to mechanical energy that causes the glasswiring.
to deform at that same frequency and eventually- Direct wireless power and communication
causing it to shatter.interconnections at points of use in harsh environments
Resonance: Resonance is a property that exists in(drilling, mining, underwater, etc.) … where it is
many different physical systems. It can be thought ofimpractical or impossible to run wires.
as the natural frequency at which energy can mostTransportation:
efficiently be added to an oscillating system. A- Automatic wireless charging for future hybrid and
playground swing is an example of an oscillatingall-electric passenger and commercial vehicles, at
system involving potential energy and kinetic energy.home, in parking garages, at fleet depots, and at
The child swings back and forth at a rate that isremote kiosks.
determined by the length of the swing. The child can- Direct wireless power interconnections to replace
make the swing go higher if she properly coordinatescostly vehicle wiring harnesses and slip rings.
her arm and leg action with the motion of the swing.Other Applications:
The swing is oscillating at its resonant frequency and- Direct wireless power interconnections and automatic
the simple movements of the child efficiently transferwireless charging for implantable medical devices
energy to the system. The resonant frequency(ventricular assist devices, pacemaker, defibrilator, etc.).
depends on the size, shape and thickness of the- Automatic wireless charging and for high tech military
material.systems (battery powered mobile devices, covert
Resonant Magnetic Coupling: Magnetic coupling occurssensors, unmanned mobile robots and aircraft, etc.).
when two objects exchange energy through their- Direct wireless powering and automatic wireless
varying or oscillating magnetic fields. Resonant couplingcharging of smart cards.
occurs when the natural frequencies of the two- Direct wireless powering and automatic wireless
objects are approximately the same.charging of consumer appliances, mobile robots, etc.
  
Two idealized resonant magnetic coils, shown inConclusion:
yellow. The blue and red color bands illustrate theirWiTricity's technology is a non-radiative mode of
magnetic fields. The coupling of their respectiveenergy transfer, relying instead on the magnetic near
magnetic fields is indicated by the connection of thefield. Magnetic fields interact very weakly with biological
colorbands.organisms—people and animals—and are
WiTricity Technology: WiTricity power sources andscientifically regarded to be safe. WiTricity products
capture devices are specially designed magneticare being designed to comply with applicable safety
resonators that efficiently transfer power over largestandards and regulations. Hence witricity is technology
distances via the magnetic near-field. Thesesafe.witricity can transfer power depends on the
proprietary source and device designs and thesource and receivers. if it is relatively close to one
electronic systems that control them support efficientanother, and can exceed 95%.Efficiency is primarily
energy transfer over distances that are many timesdetermined by the distance between the power
the size of the sources/devices themselves.source and capture device, however, the shape may
 impact the efficiency. it can transfer the power through
The WiTricity power source, left, is connected to ACwalls also. Traditional magnetic induction requires that
power. The blue lines represent the magnetic near fieldthe power source and capture device be very close
induced by the power source. The yellow linesto one another usually within millimeters to transfer
represent the flow of energy from the source to thepower efficiently. WiTricitytechnology is based on
WiTicity capture coil, which is shown powering a lightsharply resonant strong coupling, and is able to transfer
bulb. Note that this diagram also shows how thepower efficiently even when the distances between
magnetic field (blue lines) can wrap around athe power source and capture device are several
conductive obstacle between the power source andtimes the size of the devices themselves.