WiTricity - Wireless Electricity

 ABSTRACT

             Don't you hate it when you forget to put your mobile phone on charge? Well, take heart - a new technology called WiTricity could mean never having to plug it in again. Welcome to the world of WiTricity. WiTricity, a portmanteau for wireless electricity, is a term which describes wireless energy transfer, the ability to provide electrical energy to remote objects without wires. The term was coined initially in 2005 by Dave Gerding and later used for the project of a MIT research team led by Prof. Marin Solijaci.

              The wireless electricity works on the principle of using coupled resonant objects for the transfer of electricity to objects without the use of any wires. This concept of witricity was made possible using resonance where an object vibrates with the application of a certain frequency of energy.  The MIT researchers have been able to power a 60 watt light bulb from a power source that is located about seven feet away. This was made possible using two copper coils that were twenty inches in diameter which were designed so that they resonated together in the MHz range. One of these coils were connected to a power source while the other, to a bulb. With this witricity setup, the bulb got powered even when the coils were not in sight.

              The main advantages of witricity are that it is omni directional; the mess of wires can also be avoided .Thus enabling us in easy recharging of our electronic gadgets likes mobiles and laptops. Also, interactions of the environmental objects with the magnetic fields are suppressed since there is no tendency of interaction with the common materials. Its discovery is different from all previous effort because it uses “magnetically coupled resonance", which means it will not only be safe but it will be fairly efficient.

             This technology is a big impediment to development in the retail sector right now. The wireless transfer of electricity has been a sci-fi dream up to this point, and truly, if electricity could simply be in the air, in the same way radio waves and wi-fi signals are, it would change the world.

INTRODUCTION

WiTricity, a portmanteau for wireless electricity, is a term which describes wireless energy transfer, the ability to provide electrical energy to remote objects without wires. The term was coined initially in 2005 by Dave Gerding and later used for the project of a MIT research team led by Prof. Marin Soljačić in 2007

Wireless power transmission is not a new idea, but to do so in an efficient way typically requires a directed beam like a laser or microwave. William C. Brown demonstrated in 1964 on the CBS Walter Cronkite news a microwave-powered model helicopter that received all the power needed for flight from a microwave beam (which requires the beam to be aimed at the aircraft as it flies). Between 1969 and 1975 Bill Brown was technical director of a JPL Raytheon program that beamed 30 kW over a distance of 1 mile between stationary points at 84% efficiency. Methods that don't require directed beams are typically very inefficient, as the energy is radiated in all directions (like a radio antenna) and only a small amount reaches the desired destination.

PRINCIPLE

The concept of wireless electricity works on the principle of using coupled resonant objects for the transfer of electricity to objects without the use of any wires. This concept of witricity was made possible using resonance where an object vibrates with the application of a certain frequency of energy. So two objects having similar resonance tend to exchange energy without causing any effects on the surrounding objects.

As WiTricity operates in the electromagnetic near-field, the receiving devices must be no more than about a quarter wavelength from the transmitter that is a few meters at the frequency of a few MHz used by the system. In the study of diffraction and antenna design the electromagnetic field (or EM field) is, where the radiation pattern and/or the energy level depends on the distance from the antenna. The near field is that part of the radiated field nearest to the antenna. Beyond the near field is the infinite far field. In their first paper, the group also simulated GHz dielectric resonators.

Unlike the far field wireless power transfer systems based on traveling EM waves, WiTricity employs near field inductive coupling through magnetic fields, which interact far more weakly with surrounding objects, including biological tissue. The WiTricity concept is fundamentally identical to the near field magnetically coupled Tesla coil resonators , WiTricity uses considerably lower and safer power levels and thus may be able to meet FCC and EMC regulations. Near-field technologies draw power from the transmitter when a receiver is nearby, but with far-field techniques, the source is always transmitting power in all directions, even if there is no receiver. Researchers attribute the non development of the concept to various reasons ranging from the limitations of well-known physical laws, to simply a lack of need. Only recently have modern consumers obtained a high number of portable electronic devices which currently require batteries and plug-in chargers.

Another example involves acoustic resonances: Imagine a room with 100 identical wine glasses, each filled with wine up to a different level, so they all have different resonant frequencies. If an opera singer sings a sufficiently loud single note inside the room, a glass of the corresponding frequency might accumulate sufficient energy to even explode, while not influencing the other glasses. In any system of coupled resonators there often exists a so-called "strongly coupled" regime of operation. If one ensures to operate in that regime in a given system, the energy transfer can be very efficient.

While these considerations are universal, applying to all kinds of resonances (e.g., acoustic, mechanical, electromagnetic, etc.), the MIT team focused on one particular type: magnetically coupled resonators. It might sound like magnetic induction, which is used in transformers to transmit power between two, very close but non touching coils, but the researchers note that such non resonant magnetic induction drops off very quickly as the coils are moved apart, and are about a "million times less efficient" than resonant

"Two coils with a matched resonance at the exact matching frequency on both ends = wireless power

INDETAIL ABOUT WIRELESS ELECTRICITY

INDUCTIVE COPLING

Inductive coupling uses magnetic fields that are a natural part of currents movement through wire. Any time electrical current moves through a wire,it create a circular magnetic magnetic field around the wire. Bending the wire into a coil amplifies the magnetic field. The more loops the coil makes, the bigger the field will be.

If you place a second coil of wire in the magnetic field you’ve created, the field can induce a current in the wire. This is essentially how a transformer works, and it is how a electric toothbrush charges.It takes three 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 as primary winding.

2. When you place a 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.

You can use the same principle to recharge several devices at once. For example, the Splashpower recharging mat and Edison Elctric Powerdesk both use coils to create same magnetic field. Electronic devices use corresponding built-in or plug-in receivers to recharge while resting on the mat. These receivers contain compatible coils the circulatory necessary to deliver electricity to device batteries.

                                         

ELECTRODYNAMIC INDUCTION

Research at MIT indicates that induction can take place little differently if the electromagnetic fields around the coils resonate at the same frequency. The theory uses a curved coil of wire as an inductor. A capacitance plate, which can hold a charge, attaches to end of the coil. A electricity travels through this coil, the coil begins to resonate. Its resonant frequency is a product of inductance of the coil and the capacitance between the plates.

As with an electric toothbrush, this system relies on two coils. Electricity, trvelling along an electromagnetic wave, can tunnel for one coil to the other as long as they both have the same resonant frequency. The effect is same as one vibrating trumpet can cause the other to vibrate.

As long as both coils are out of range of another, nothing will happen, since the fields around the coils aren’t strong enough to affect much around them. Similarly. If the two coils resonate at different frequencies, nothing will happen. But if two resonating coils with the same frequency get within a few meters of each other, stream of energy move from the transmitting coil to the receiving coil.According to this theory, one coil can send electricity to several receiving coils, as long as they all resonate at the same frequency. The researchers have named this non-radiative energy transfer since it involves stationary fields around the coil rather than fields that spread in all directions.

LONG RANGE WIRELESS POWER TRANSMISSION:

In 1980s, Canada’s Communications Research Centre created a small airplane that could run off power beamed from the Earth. The unnamed plane, called the Stationery High Altitude Relay Sharp could fl in circles two kilometers in diameter at an altitude of about 13kilometers(21 kilometers). Most importantly, the aircraft would 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 directcurrent (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.

Rectifying antennae are central to many wireless power transmission theories. They are usually made an array of dipole antennae, which have positive an negative poles. These antennae connect to semiconductors diodes. Here’s what happens : Microwave which is a part of the electromagnetic spectrum, reach the dipole antennae. The antennae collect the microwave energy and transmit it to the diodes. The diodes act like switches that are open or closed as well as turnstiles that let electrons flow in only one direction. They direct  that electrons to the rctenna’s circuitry.The circuitry routes the electrons to the parts and systems that need them.

THE NEED FOR A WIRELESS ENERGY TRANSMISSION SYSTEM:

A great concern has been voiced in recent years over the extensive use of energy, the limited supply of resources, and the pollution of the environment from the use of present energy conversion systems. Electrical power accounts for much of the energy consumed. Much of this power is wasted during transmission from power plant generators to the consumer. The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient.

A system of power distribution with little or no loss would conserve energy. It would reduce pollution and expenses resulting from the need to generate power to overcome and compensate for losses in the present grid system.

The proposed project would demonstrate a method of energy distribution calculated to be 90-94% efficient. An electrical distribution system, based on this method would eliminate the need for an inefficient, costly, and capital intensive grid of cables, towers, and substations. The system would reduce the cost of electrical energy used by the consumer and rid the landscape of wires, cables, and transmission towers.

There are areas of the world where the need for electrical power exists, yet there is no method for delivering power. Africa is in need of power to run pumps to tap into the vast resources of water under the Sahara Desert. Rural areas, such as those in China, require the electrical power necessary to bring them into the 20th century and to equal standing with western nations.

ADVANTAGES

• Unaffected by day or night cycle, weather or seasons.
• This is a ecofriendly system.
• No need for electric rooms or meter closets.
• Reduction in E-waste

DISADVANTAGES

The resonance condition should be satisfied or else an error exits and there is no possibility of power transfer.

If there is a possibility of strong ferromagnetic material presence causes low power transfer  due to radiation.

Replacing the old goods with new ones is costly affair.

APPLICATIONS

This technology can potentially be used in a large variety of applications, including consumer, industrial, medical and military. Its aim is to reduce our dependence on batteries.

Further applications for this technology include transmission of information — it would not interfere with radio waves and thus could be used as a cheap and efficient communication device without requiring a license or a government permit.

Some of these potential applications include the powering of cell phones, household robots, laptops and other devices that normally run with the help of batteries or with plugging in of wires. These witricity applications are expected to work on the gadgets that are in close proximity to a source of wireless power wherein the gadget charges automatically without necessarily having to get plugged in. There are no limitations in witricity power applications where anything and everything that used to run with batteries or electrical connections can be used using witricity.

COMPARITATIVE ADVANTAGES OF WITRICITY OVER OTHER RADIATION METHODS:

Various methods of transmitting power wirelessly have been known for centuries. Perhaps the best known example is electromagnetic radiation, such as radio waves. While such radiation is excellent for wireless transmission of information, it is not feasible to use it for power transmission. Since radiation spreads in all directions, a vast majority of power would end up being wasted into free space.

      One can envision using directed electromagnetic radiation, such as lasers, but this is      not very practical and can even be dangerous. It requires an uninterrupted line of sight between the source and the device, as well as a sophisticated tracking mechanism when the device is mobile.

Besides the wasteful nature of dispensing energy in a non-controlled direction (i.e. radio waves), there is also concern for safety. One property of WiTricity is that released energy remains within a magnetic field surrounding the source resonator until it is picked up by an object sharing the same frequency. As this technology will inevitably take off, it becomes the role of the designer to think of where these properties can appropriately be used, and to ensure that non-powered components within a facility don't share the same resonant frequencies; everything has a resonant frequency. This has also been achieved. It is realized that instead of irradiating the environment with electromagnetic waves, a power transmitter could fill the space around it with a "non-radiative" electromagnetic field. Essentially, energy would only be picked up by gadgets specified to "resonate" with the frequency. At any rate, Soljacic believes that the technology can be developed to be relatively safe, although working out the details will not necessarily be easy. Apart from this, 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. Magnetic coupling is particularly suitable for everyday applications because most common materials interact only very weakly with magnetic fields, so interactions with extraneous environmental objects are suppressed even further. The fact that magnetic fields interact so weakly with biological organisms is also important for safety considerations. Here they use extremely low frequency, thirty meter long electromagnetic waves, which are said to be harmless to humans

The main advantage of this system is that we can get electricity anywhere without wires. This will enable us to use our portable electronic gadgets everywhere without bothering about ending up in the charge of the batteries.

The nature of power delivery is omni directional i.e. in every direction.

Magnetic resonances are particularly suitable for everyday application because most of the common materials do not interact with magnetic fields, so interactions with environmental objects are suppressed even further.

DEVELOPMENTS MADE SO FAR

As witricity is in the developmental stage, lots of work is still to be done in improving it as it is  disclosed that witricity power applications operate at only 40% efficiency. However, Intel reproduced the MIT group's experiment by wirelessly powering a light bulb with 75% efficiency at a shorter distance.

Just as beneficial witricity may be, there are some contraindications to the concept, with debates if it is risky living next to power lines and having a low power witricity network running in the home. They wonder what happens if a glass of water is spilt in a witricity room. This has also been achieved.It is realized that instead of irradiating the environment with electromagnetic waves, a power transmitter could fill the space around it with a "non-radiative" electromagnetic field. Essentially, energy would only be picked up by gadgets specified to "resonate" with the frequency.

However despite these contraindications, witricity has a bright future with the many advantages it provides in terms of weight, convenience and portability of electrical appliances

CONCLUSION

This technology is a big impediment to development in the retail sector right now. Just imagine the future, with witricity, where there will be no need of power cables and batteries. The city just has to be covered with witricity hot spots wherein you can use your electric gadget battery and wire free making it more convenient to carry around and much lighter. With witricity, there will be no need of charging batteries, or buying new batteries for your electrical gadgetsThe wireless transfer of electricity has  been a sci-fi dream up to this point ,and truly, if electricity could simply be in the air, in the same way radio waves and wi-fi signals are, it would change the world.