OVERVIEWINTRODUCTIONMICROWAVESTRANSMITER DESIGNRECEIVER DESIGNWORKING PRINCIPLESENSOR CIRCUITRYCONCLUSIONBIBLIOGRAPHY

In this paper, we deal with the topic of automatic recharging of the mobile phones by use of microwaves.

The microwave signal is transmitted from the transmitter along with the message signal using slotted wave guide antenna at a frequency is 2.45 GHz.

There are minimal addition of a sensor, a “rectenna”, and a filter to the mobile handset.

The need for separate chargers for mobile phones is eliminated and makes charging universal.

THE ELECTROMAGNETIC SPECTRUM

Microwaves are electromagnetic wave with frequencies between 300 MHz (0.3 GHz) and 300 GHz

Shorter microwaves are used in remote sensing. These microwaves are used for radar like the Doppler radar used in weather forecasts.

Microwave radiation is still associated with energy levels that are usually considered harmless

Power transmission via radio waves can be made more directional, allowing longer distance power beaming .

A rectenna may be used to convert the microwave energy back into electricity.

A human safe power density of 1 mW/cm2 can be generated and distributed across a 10 km diameter area corresponds to 750 megawatts total power level.

THE MAGNETRON A microwave tube in which

electrons generated from a heated cathode are affected by magnetic and electric fields in such a way as to produce microwave radiation.

Magnetrons can produce continuous power outputs of more than 1 kW at a frequency of 1 GHz.

Cathode is indirectly heated& electrons are generated from a heated cathode, move under the combined force of a radial electric field and an axial magnetic field.

This causes moving electrons to interact synchronously with traveling-wave components of a microwave standing-wave pattern.

The open space between the plate and the cathode is called the INTERACTION SPACE. In this space the electric and magnetic fields interact to exert force upon the electrons.

CROSSED-ELECTRON and MAGNETIC fields are used in the magnetron to produce the high-power output required in radar and communications equipment.

A rectenna is a rectifying antenna, converts microwave energy into DC electricity.

The diode rectifies the current induced in the antenna by the microwaves.

“An antenna comprising a mesh of dipoles and diodes for absorbing microwave energy from a transmitter and converting it into electric power.”

Microwaves are received with about 85% efficiency at 2.45GHz

Rectennae have high efficiency converting microwave energy to electricity above 90%.With the advent of nanotechnology and MEMS the size of these devices can be brought down to molecular level called optical rectenna.

•This circuit is based on the optimization of the rectifier in order to have a good matching of the input impedance at desired frequency 2.45GHz and detection sensitivity at low levels of power.• Optimization of circuit is done by introducing the parasitic elements of the Schottky.

As our main objective is to charge the mobile phone with the transmitted microwave after rectifying it by the rectenna, the sensor plays an important role.

The sensor circuitry detects if the mobile phone receives any message signal.

The usage of simple F to V such as LM2907 converters would act as switches to trigger the rectenna circuit to on.

Fig shows F to V converter LM2907.It acts as a switch for triggering the rectenna circuitry.

Advantages

Charging of mobile phone battery is independent of the battery.

The recharging of the mobile phones is done automatically as you talk in your mobile phone.

The need for separate chargers for mobile phones is eliminated.

Microwave energy apparently has the potential to provide environmentally clean electric power.

The mobile phone users can carry their phones anywhere even if the place is devoid of facilities for charging.

Disadvantages

Rectenna is quite bulky , Further reduction in size is required.

Power level density desired for wireless power transmission may exceed the Human safe level.

The Mobile phone Battery is not standardized, hence design of receivers may vary.

The Magnetron at the Base transceiver station dissipates too much Heat. There is a requirement of heat sink.

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.. A novel use of the rectenna and a sensor in a mobile phone could provide a new dimension in the revelation of mobile phone.

Tae- Whan yoo and Kai Chang, " Theoretical and Experimental Development of 10 and 35 GHz rectennas" IEEE Transaction on microwave Theory and Techniques, vol. 40.NO.6.June.1992.

5 Hawkins, Joe, et al, "Wireless Space Power Experiment," in Proceedings of the 9th summer Conference of NASA/USRA Advanced Design Program and Advanced Space Design Program, June 14-18, 1993.

MW Medley Jr and MW Medley, 'Microwave and RF circuits: analysis, synthesis, and design', Artech House, Norwood, MA, 1993.

Falcone, Vincent J., "Atmospheric Attenuation of Microwave Power," Journal of microwave Power, 5(4), 1970.

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