Wireless Power Transmision Review

  

    In the late 19th century, the realization that electricity could be coaxed to light up a bulb prompted a mad dash to determine the best way to distribute it. At the head of the pack was inventor Nikola Tesla, who had a grand scheme to beam elec­tricity around the world. Having difficulty imagining a vast infrastructure of wires extending into every city, building, and room, Tesla figured that wireless was the way to go. He drew up plans for a tower, about 57 meters tall, that he claimed would transmit power to points kilometers away, and even started to build one on Long Island. Though his team did some tests, funding ran out before the tower was completed. The promise of airborne power faded rapidly as the industrial world proved willing to wire up. 

    Then, a few years ago, Marin Soljačić, an assistant professor of physics at MIT, was dragged out of bed by the insistent beeping of a cell phone. "This one didn't want to stop until you plugged it in for charging," says Soljačić. In his exhausted state, he wished the phone would just begin charging itself as soon as it was brought into the house.

   So Soljačić started searching for ways to transmit power wirelessly. Instead of pursuing a long-distance scheme like Tesla's, he decided to look for midrange power transmission methods that could charge--or even power--portabl­e devices such as cell phones, PDAs, and laptops. He considered using radio waves, which effectively send information through the air, but found that most of their energy would be lost in space. More-targeted methods like lasers require a clear line of sight--and could have harmful effects on anything in their way. So Soljačić sought a method that was both efficient--able to directly power receivers without dissipating energy to the surrounding­s--and safe.

 

   Most of us at home maybe using multi-plug to connect all the electronic devices with power cords. You may have even got confused to get the right cord for unplugging it among the other cords that lead to the same outlet.

   At last you pull one out and hope that it is the right one. This is one of the main problems with electric connections. Though it makes the life of people simpler, it can also cause more clutter in the method. It may not be a big problem for us. But think about the electric stations where hundreds of wires run from the same outlet. For them, it is a problem.

   As a part of the upgrade in technology and also the above reasons, researchers have started developing methods to transmit electricity to devices wirelessly. Though the method may sound completely new, the basic idea behind this theory was first proposed by Nicola Tesla in the early 1900′s. He was also able to release a prototype by transmitting power to lights that were kept in the ground at his Colorado Springs experiment station.

Though the first prototype received wide applause, the method was not practical enough for a higher range of its application. After years of research, many theories about this matter were discussed and some prototypes were also released. Some of them were not recognized while some of them are already in use. The best example for such a device is the electric toothbrush.

There are many types of wireless data transferring mediums in this world. Some of the most common ones are infrared, radio waves, bluetooth, and so on. In all these technologies, the signals will be scattered into space before they are received by the corresponding devices. The same method cannot be used for transferring electricity as it is power consuming and dangerous.

The main principle that is used in electric toothbrush is called Inductive Coupling. The basic idea is that a magnetic field is induced when an electric current flows through a wire. The magnetic field will be circular in shape and will flow around the wire. When another coil is placed in the same magnetic field, a current will be induced in the wire. This is the same principle that is used in a transformer and also in the electric brush. A magnetic field is created inside the brush through the current that moves through the coil inside the charger. When the brush is connected to the charger, another current will be produced in another coil, due to the magnetic field. This current is supplied to the battery which is the input for the brush.

   But this method is not practical when it comes to transmitting energy to longer distances. For such a method, it is necessary that the coils are close enough to each other so that the small magnetic field is produced. When it comes to longer distance transmission, a very big magnetic field is to be produced and the coil turnings should be multiple. Counter measures should be taken to save the energy wasted due to the flow of magnetic field in different directions. This is practically impossible. A much better method and its explanation are given below.

Long distance wireless transmission
 

   The first experiment for long distance wireless power transmission was carried out by the Communications Research Centre in Canada during the year 1980. They designed an unmanned plane by the name Stationary High Altitude Relay Platform (SHARP). This plane could not only fly from one point to another, but could also fly in circles at a height if 21 kilometres away from the ground with a radius of 1 kilometre. It was also designed to fly without rest or battery backup for months.

Stationary High Altitude Relay Platform (SHARP)

   The main idea behind the SHARP technology is a large ground-based microwave transmitter. The plane will fly only in the range of the transmitter. The signal from the transmitter will be received by a disc-shaped rectifying antenna called the rectenna, which is placed behind the wings of the plane. This signal will then be converted into DC current. The antenna is usually of the dipole type, that is, it has positive as well as negative poles. When the signal hits the antenna, they will be transferred to a series of diodes. These diodes behave like switches and allow the electrons to flow in unidirection. These electrons are then passed onto the rectenna’s circuitry. The electrons are then shifted to the other parts of the plane.