College Papers

Wireless may involve significant resists to human life.

Wireless Power Transmission
Using Microwaves



      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

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 method 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, in order 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.



In emergent this design, the PBG antenna, DGS LPF, and
rectifier circuits were every first fabricated, designed, and characterized

 The rectenna is
a passive element which contains antenna,a rectifying circuit with a resistor
and capacitor filter between the antenna and rectifying diode.Schottky Barrier
diodes(GaAs-W, Si, GaAs) are usually utilized
in the rectifying circuit due to the fast reverse recovery time and low forward
voltage drop and  RF characteristics.The
rectenna efficieny for various diodes at different frequency is shown in table



Measured Efficiency

Efficiency (%)













Table 1.1 
Rectenna Efficieny For Various Diodes at Different Frequency


            Figure 1.3 Rectenna Design


The figure 1.3 shows the rectenna used in the project.
Rectenna has divided two copper plates with Schottky diode which acts as a
resistor between two plates. Likewise, we have positioned 10 setups in parallel
such that we have placed 10 resistors in parallel which intone act as the
conductor with high absorption power since resistors in parallel act as a


Table 1. 2 Distance Covered Vs Voltage



















       In table 1.2 we have presented the
wireless power transmission which displays that increase in distance leads to
decrease in voltage. This decrease in voltage is due to distortion of microwaves
in the air medium.


                      Figure 1.8 Distance Vs Voltage Curve


         In figure 1.8, the graph is drawn between
the distance and voltage. If the rectenna is nearer to the transmitter, the
voltage level absorbed by the rectenna is high up to 32V.If the distance is
increased between the transmitter and receiver, the

         Voltage level decreased.



1.   Entirely eradicate the existing high-power
transmission line towers, cables etc…

2.   The transmission and distribution
cost become less

3.   Hence, the efficiency of this method
is very much higher than wired transmission.

4.   The power failure as a result of
short circuit and fault of cables would never be present.

5.   The power can be transmitted to the
places where the wired transmission is not a feasible.

6.   Capability to charge vehicles such as
industrial vehicles and golf carts.

and alter  to loads



  1.  Production and development is still under

2. It does not give sufficient
energy to charge enormous vehicles and types of equipment.

3.  Transmitting distance is unreliable

Heat energy is lost during the transmission.

5. Intervention of microwaves with a
present signal.




Used in cordless
tools, automatic wireless charging for mobile robots and instrument this
eliminates complex mechanism.

Easy and neat
Installation – there is no cable running here and there, just start up the
wireless device.

Mobility –
within the wireless range user device can be moved easily.

The ability of our technology to transfer
power efficiently, safely and over distance can improve products by making them
more reliable, convenient, and environmentally friendly.



 Wireless Power Transmission (WPT) was
successfully achieved up to the distance of 1 meter and beyond with the help of
the high power rectenna and proposed with higher lumens. It is difficult to
find inductors and capacitors that are capable of working at higher power
levels. However, safety is needed to be concern for the further extension of
the project and modification is required for higher end design. Configuration
on the cost factor and design constraints, including noise factor are to be
considered and suggested to concern for the further development.