Abstract: transmission technologies that use time varying electromagnetic


      Various new technologies are being
developed for transmitting power through wireless systems and one of the ways of
transmitting electricity without wire is through the microwave transmission.
The process of transmitting the power by using microwaves is called as Microwave
Power Transmission(MPT). This will cause reduction in the transmission and
distribution losses. Rectenna is a device used to convert the microwaves into
power for the MPT system. This paper will give the idea about impact on human
beings, advantages, disadvantages, & applications of wireless power

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Keywords: Wireless power transmission (WPT),

Microwave power transmission (MPT), Wireless Sensor network



        Wireless power transfer (WPT) is the
transmission of electrical power from a power source to a consuming device
without using manmade conductors. For long distance transmission without using wires
researchers have developed several techniques for moving electricity. There are
some exists only as theories or prototypes but others are already in use. This
paper provides the techniques used for wireless power transmission. It is a
generic term that refers to a number of different power transmission
technologies that use time varying electromagnetic fields.

Wireless transmission is useful to
power electrical devices in case where interconnecting wires are inconvenient,
hazardous, or are not possible. For example the life of WSN is its node which
consist of several device controllers, memory, sensors, actuators, transceivers
and battery and battery. The transceiver can operate in four states, i.e 1)
Transmit 2) Receive 3) Idle and 4) Sleep. The major energy problem of a
transmitter of a node is its receiving in idle state, as in this state it is
always being ready to receive, consuming great amount of power.

 However, the batter has a very short lifetime
and moreover in some developments owing to both practically and economically
infeasible or may involve significant resists to human life. That is why energy
harvesting for WSN in replacement of battery is the only and unique solution.
In wireless power transfer, a transmitter device source, such as the mains
power line, transmits power by electromagnetic fields across an intervening
space to one or more receiver devices, where it is converted  to electric power and then utilized.The goal
of the communication  is the transmission
of information, so the amount of power reaching the receiving antenna is
unimportant till  signal to noise ratio
is high enough so that the information can be received intelligibly. In wireless
communication technologies, generally, only little amounts of power reach the
receiver. By contrast the amount of power received is the important thing, so
the efficiency (fraction of transmitted power that is received) is the more
significant parameter.



Figure 1.1 Microwave Region of Electromagnetic

The figure 1.1 shows that the
microwaves are the radio signal which has the wavelength array of 1 mm to 1
meter and the frequency is 3000 MHZ to 300 GHZ. Microwaves contain wavelength
that preserves is calculated in centimeters microwaves are good quality for
transmitting information from one place to another place because microwave
energy be able to penetrate haze, snow, clouds, light rain, and smoke.
Microwave radiation is still connected with an energy level that is typically
nontoxic except for people with pacemakers.


 Possible methods of wireless transmission of
electrical power


Inductive coupling


Radio frequency



Inductive coupling

In this when
transmitting coil is excited then it generates flux and when receiver coil
receives this flux a potential difference is developed across its terminal.
This is the basic model and its efficiency is very poor hence cannot be used
for large distance transmission.


It is a device
which emits light based on the stimulated emission of electromagnetic
radiation. Power can be transmitted by means of converting electricity keen on
laser beam. But in this laser radiation is hazardous and conversion between
electricity and light is ineffective.

Radio frequency

Radio frequency
signals to direct current electrical current powered from either an
international or ambient power sources.



The figure 1.2 shows that the purposeful block diagram
of WPT consists of two sections: transmitting section and receiving section.

 In the
transmission section, the microwave power source generates microwave power
which is prohibited by the electronic control circuits. The waveguide
circulator protects the microwave resource from the reflected power, which is
connected through the co-ax waveguide adaptor. The tuner contests the impedance
between the microwave source and transmitting antenna. After that, based on the
signal broadcast direction, the  signals
are separated by using directional coupler. The transmitting antenna sends the
power frequently through open space to the receiving antenna.

 In the side of
receiver, the rectenna observes the  power that is transmitted and converts the  microwave power into DC power. The filter and impedance
matching circuit  is provided for
locating the harvest impedance of a signal source which is equivalent to
rectifying circuit. The circuit consists of Schottky barrier diodes that
converts the microwave power keen on DC power.


 A rectenna is a
rectangular antenna with rectifying circuit,It is a type of antenna that is
used to convert microwave energy into DC current. The elements are generally
arranged in a mesh type pattern,inorder to provide a unique appearance from other
antennae.A simple rectenna can be constructed using a Schottky diode placed
between antenna dipoles. The diode (a uni direction device)is used to rectify
the  current that is induced in the
antenna by the microwaves signals. Rectenna is very high efficient for
converting microwaves into electricity. In laboratory environments,
efficiencies above 90% have been observed. Scientists also tried to convert
electricity into microwave energy using inverse rectenna, but efficiencies are
very low. only in the area of 1%. With the advent of nanotechnology and MEMS
the size of rectenna elements can be brought down to molecular level. A
rectenna contains a mesh of dipoles and a mesh of diodes for absorbing
microwave energy from a transmitter and converting it into electric current.


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