Wireless Charging Of Mobile Phones Using Microwaves

With mobile phones becoming a basic part of life, the recharging of mobile phone batteries has always been a problem. The mobile phones vary in their talk time and battery stand by according to their manufacturer and batteries. All these phones irrespective of their manufacturer and batteries have to be put to recharge after the battery has drained out.

INTRODUCTION :

THE ELECTROMAGNETIC SPECTRUM

When white light is shone through a prism it is separated out into all the colors of the rainbow; this is the visible spectrum. So white light is a mixture  of  all colors.  Black is NOT a color; it is what you get when all the light is taken away.  Some physicists pretend that light consists of tiny particles which they call photons. They travel at the speed of light. The speed of light is about 300,000,000 meters per second. When they hit something they might bounce off, go right through or get absorbed. What happens depends a bit on how much energy they have. If they bounce off something and then go into your eye you will "see" the thing they have bounced off. Some things like glass and Perspex will let them go through; these materials are transparent.

TRANSMITTER DESIGN

MAGNETRON:

Ø Magnetron is a high power microwave oscillator and it is used in microwave oven and radar transmitter.

Ø It is itself a special kind of vacum tube that has permanent magnet in its constructions.

Ø This magnet is setup to affect the path of travel of electrons that are in transit from cathode to the plate.

Ø Magnetron is capable to deliver more power than reflex klystron or gunn diode.

Ø It is a high power oscillator and has high efficiency of 50% to 80%.

RECEIVER DESIGN

The basic addition to the mobile phone is going to be the rectenna. A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a mesh pattern, giving it a distinct appearance from most antennae. A simple rectenna can be constructed from a Schottky diode placed between antenna dipoles. The diode rectifies the current induced in the antenna by the microwaves. Rectennae are highly efficient at converting microwave energy to electricity. In laboratory environments, efficiencies above 90% have been observed with regularity.

Inductive charging

Magne  Charge wall, handheld, and floor moun Inductive Charging. The primary coil in the charger induces a current in the secondary coil in the device being charged. Inductive charging uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device.

Induction chargers typically use an induction coil to create an alternating electromagnetic field from within a charging base station, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electrical current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.

Electric vehicles:

As mentioned above, Magne Charge inductive charging was employed by several types of electric vehicles around 1998, but was discontinued after the California Air Resources Board selected the SAE J1772-2001, or "Avcon", conductive charging interface for electric vehicles in California in June 2001.

In 2009, Evatran, a subsidiary of MTC Transformers, formally began development of Plugless Power, an inductive charging system they claim is the world’s first hands-free, plugless, proximity charging system for Electric Vehicles. With the participation of the local municipality and several businesses, field trials were begun in March 2010, on the system scheduled to be available in fourth quarter 2010.

Advantages:

Ø Lower risk of electrical shock or shorting out when wet because there are no exposed conductors as used with conductive wireless charging, for example toothbrushes and shavers, or outdoors.

Ø Protected connections - no corrosion when the electronics are all enclosed, away from water or oxygen in the atmosphere.

Ø Safer for medical implants - for embedded medical devices, allows recharging/powering through the skin rather than having wires penetrate the skin, which would increase the risk of infection.Convenience - rather than having to connect a power cable, the device can be placed on or close to a charge plate or stand.

Disadvantages

Ø Lower efficiency, waste heat - The main disadvantages of inductive charging are its lower efficiency and increased resistive heating in comparison to direct contact. Implementations using lower frequencies or older drive technologies charge more slowly and generate heat within most portable electronics.

Ø More costly - Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.

Ø Slower charging - due to the lower efficiency, devices can take longer to charge when supplied power is equal.

CONCLUSION :

Thus this paper successfully demonstrates a novel method of using the power of the microwave to charge the mobile phones without the use of wired chargers. Thus this method provides great advantage to the mobile phone users to carry their phones anywhere even if the place is devoid of facilities for charging. A novel use of the rectenna and a sensor in a mobile phone could provide a new dimension in the revelation of mobile phone.

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