• Muhammad Umer Shehzad• Jawad Fakhir

• Sir Haissam Sattar

Introduction to MicrowavesProperties of MicrowavesAdvantages/Disadvantages of MicrowavesWaveguideApplications of MicrowavesMicrowave ovenRadarWireless Mobile ChargingOthers Applications

In physics, a wave is disturbance or oscillation that travels through matter or space, accompanied by a transfer of

energy.

There are two main types of waves.

Mechanical WavesElectromagnetic

Waves

• Radio waves• Microwaves• Infrared radiation• Visible light• Ultraviolet radiation

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Microwaves are electromagnetic waves

Frequency range 300MHz-300Ghz

Wavelengths range in air

100cm-1mm

The word microwave means “very short wave”

Microwaves is the shortest wavelength region of the radio

spectrum and a part of the

electromagnetic spectrum

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Microwaves Frequency Bands

Properties of Microwaves

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1.Electromagnetic radiation of short

wavelength

2.Can reflect by conducting surface like optical waves.

3.M.W current flows through outer layer

of conductor

4.Microwaves are easily attenuated

5.They are not reflected by ionosphere

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Microwaves have large bandwidths

Improved Directive properties.Can be

focused in a specified direction

Fading effect and reliability.

Due to LOS and high frequency fading effect is

very low

Transmitter/Receiver power requirements are pretty low at microwave

frequencies

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Microwave band ranging from 300MHz-10GHz are capable of freely propagating through atmosphere

This helps in astronomical research of space in the study of microwave radiations from

the sun and stars

Because of high frequency, more data can be sent.

High bandwidth,higher speeds

Because of their short wavelength,microwaves use

smaller antennas

Smaller antennas produce a

more focused beam

Functional Block Diagram of a Communication System

Input signal

(Audio, Video, Data)

Input TransducerTransmitter

Output TransducerReceiver

Output signal

(Audio, Video, Data)

Channel

Electrical System

Wire

or

Wireless

Antenna and Wave Propagation

Surface Wave

Direct Wave

Sky Wave

Satellitecommunication

Microwave & Millimeter Wave

Earth

Ionsphere

Transmitting Antenna

Receiving Antenna

Repeaters(Terrestrial communication)

50Km@25fts antenna

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A Hollow metallic tube of uniform cross section for transmitting

electromagnetic waves by successive reflections from the inner walls of the

tube is called waveguide.

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Electromagnetic waves at frequencies greater than

3GHz; transmission through cables becomes difficult.

Reason

This is due to losses in the solid cable and the

dielectric use to support the cable.

So, we use waveguide which is a hollow

metallic

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Waveguides are used to carry energy from one equipment to

another

e.g. In Antennas transmitter power

to antenna and microwave signal from antenna to

receiver

Waveguides are made from copper, aluminum or brass

The metals are extruded into long

rectangular or circular pipes

The energy to be transmitted is injected from one end of the waveguide through probes

The electric and magnetic field of

signals bounce off the walls back and

forth.

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EM field configuration can be determined from Maxwell’s equation.

There are number of configurations and each configuration is known as mode.

Possible modes

TransverseElectromag

netic

Transverse Electric

Transverse Magnetic

Hybrid

Components of Electric and Magnetic Field Intensities in an EM wave

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O

X

Y

Z

Ex , Hx

Ez, Hz

E y,H y

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2. Transverse Electric (TE) wave: Here only the electric field is

purely transverse to the direction of propagation and the magnetic

field is not purely transverse. (i.e.) E z = 0, Hz ≠ 0

1.Transverse Electro Magnetic (TEM) wave:Here both electric and magnetic

fields are directed components.(i.e.) Ez=0 and Hz=0

2.Transverse Electric (TE) wave:The electric field component is

purely transverse to the direction of propagation.(i.e.) Ez=0 and Hz≠0

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3.Transverse Magnetic (TM) wave:The magnetic field component is

purely transverse to the direction of propagation.(i.e.) Ez≠0 and Hz=0

4.Hybrid (HE) wave:Here neither electric nor magnetic fields are

purely transverse to the direction of propagation.(i.e.) Ez≠0 and Hz≠0

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Rectangular Waveguides

Any shape of cross section of a waveguide can support electromagnetic waves of which rectangular and circular waveguides have become more common.

A waveguide having rectangular cross section is known as Rectangular waveguide

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Rectangular waveguide

Dimensions of the waveguide which determines the operating

frequency range

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1.The size of the waveguide determines its operating frequency

2.The frequency of operation is determined by dimension ‘a’ which is usually made one half the wavelength at lowest frequency of

operation.

3.At cutoff frequency and below, the waveguide will not transmit energy.

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Wave paths in a waveguide at various frequencies

Angle of incidence(A) Angle of reflection (B)

(A = B) (a) At high

frequency

(b) At medium

frequency

( c ) At low frequency

(d) At cutoff

frequency

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Wave propagation

When a probe launches energy into the waveguide, the electromagnetic fields bounce off the side walls of the waveguide as shown in the above diagram.

The angles of incidence and reflection depend upon the operating frequency. At high frequencies, the angles are large and therefore, the path between the opposite walls is relatively long as shown in Fig.

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At lower frequency, the angles decrease and the path between the sides

shortens.

When the operating frequency is reaches the cutoff frequency of the

waveguide, the signal simply bounces back and forth directly between the side

walls of the waveguide and has no forward motion.

At cut off frequency and below, no energy will propagate.

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• It is used for bends, twists or in applications where certain criteria may not be fulfilled by normal waveguides.

• Figure below shows some of the flexible waveguides:

How a Microwave Oven Works?

History

Invented Accidentally By Dr. Percy Lebaron Spencer.

Working Principle

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Microwave radiations generated by a magnetron pass through the exposed food, create dielectric heating within the food, this is the basic principle on which a microwave oven works.

Dielectric Heating

How the Oven Works

Electricity from the wall outlet travels through the power cord and enters the

microwave oven through a series of fuse and safety protection circuits

When the oven door is closed, an electrical path is also established through a series

of safety interlock switches

Sensing That All Systems Are Set To Go, The Signal Activates Triac Producing A Voltage Path

To The High-voltage Transformer.

The High-voltage Transformer Along With A Special Diode And Capacitor Arrangement

Increases The Typical Household Voltage From ~220 Volts To ~3000 Volts

The magnetron converts the high voltage into the microwave frequency for cooking.

The microwave energy is transmitted into a waveguide.

The waveguide feeds the energy to the stirrer blade and into the cooking area.

When the door is opened, or the timer reaches zero, the microwave energy stops.

How Foods Get Cooked

The microwaves that penetrate the food have an electric field that oscillates 2.45

billion times a second, a frequency that is well absorbed by polar liquid molecules

such as water, sugars, fats and other food molecules.

Water interacts with the microwave:

flipping its orientation back and forth very rapidly

bumping into one another and producing heat, cooking the food.

Radar

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Introduction

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Radar Radio Detection and Ranging

A System For Detecting The Presence, Direction, Distance, And Speed Of Aircraft, Ships, And Other Objects, By Sending Out Pulses Of Radio Waves Which Are Reflected Off The Object Back To The Source.

The Time Delay Between The Transmitted Pulse And The Received Echo Can Be Used To Determine The Distance To The Target .

Basic Principle and Operation Of Radar

RADAR FUNCTIONS

TRANSMITTER:

Generate radio waves

Perform modulation

Amplification to high power

RECIEVER:

High sensitivity

Very low noise

Ability to discern a received signal from background noise

PROCESSING & CONTROL:

It regulates the rate at which pulses are sent (PRF). Synchronizes the function between Transmitter, Receiver,

display, duplexer etc.

DUPLEXER:

A switch to alternatively connect Tx and Rx to antenna.

ANTENNA:

Takes radar pulses from transmitter and puts into the air.

Focuses energy into the well designed beam.

Antenna is of two types

1) Physically moving

2) Electronically steered

DISPLAY:

Display received information to the operator. It is of two types

1) PPI

Used for surface search and navigation

2) A-Scan

Used for gunfire control

MAIN TYPES OF RADAR

There are two main types of radar:

1)Primary Radar

Continuous wave Radar

Pulse Radar

2)Secondary Radar SSR

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1)CONTINUOS WAVE RADAR:

Employs continual RADAR transmission

Separate transmit and receive antennas

Relies on the “DOPPLER SHIFT”

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2)PULSE RADAR:

The PULSE radar is the more conventional radar, which transmits a burst of radar energy and then waits for the energy (or echo) to be reflected back to the antenna.

Since radar waves travel at the speed of light, range from the return can be calculated.

Applications of Radar

MILITARY

Target Detection, Target Tracking & Weapon Control

Tracks The Targets, Directs The Weapon To An Intercept And Assess The Effectiveness Of Engagement

Weather Observation

Planetary Observation

Below Ground Probing

REMOTE SENSING

Used To Safely Control Air Traffic In The Vicinity Of The Airports.

Mapping Of Regions Of Rain In The Vicinity Of Airports & Weather.

AIR TRAFFIC CONTROL

Radar Speed Meters Are Used By Police For Enforcing Speed Limit.

LAW ENFORCEMENT & HIGHWAY SAFETY

• Airborne Weather Avoidance Radar Outlines The Regions Of Precipitation & Dangerous Wind Shear

• Low Flying Military Aircrafts Rely On Terrain Avoidance & Terrain Following Radars To Avoid Collision With High Terrain & Obstructions

AIRCRAFT SAFETY & NAVIGATION

• Radar Is Found On Ships & Boats For Collision Avoidance & To Observe Navigation Buoys, When The Visibility Is Poor

• Shore Based Radars Are Used For Surveillance Of Harbours & River Traffic

SHIP SAFETY

• Space Vehicles Have Used Radar For Landing On The Moon And Other Planets.

• Used For Planetary Exploration

• Ground Based Radars Are Used For Detection & Tracking Of Satellites & Other Space Objects

• Used For Radio Astronomy

SPACE

MINE INSPECTION

LOCATING UNDER GROUND PIPES

Wireless Charging of Mobile Phones Using Microwaves

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INTRODUCTION Objective—to Recharge Any Mobile Phone Independent Of Particular Mobile

Charger.

Mobile Phones Becoming Basic Part Of Life

Recharging Of Mobile Phones Is A Big Problem

More You Talk More The Mobile Get Charged!

No Separate Mobile Charger

Additives To Mobile Handsets:

Sensor

Rectenna

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Microwave region of electromagnetic spectrum

We choose s –band of microwave region(2-4GHz)

We Use License free 2.45 GHz Industrial, Scientific and Medical (ISM)

radio bands

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Designation Frequency range

L Band 1 to 2 GHz

S Band 2 to 4 GHz

C Band 4 to 8 GHz

X Band 8 to 12 GHz

Ku Band 12 to 18 GHz

K Band 18 to 26 GHz

Ka Band 26 to 40 GHz

Q Band 30 to 50 GHz

U Band 40 to 60 GHz

Principle of Operation &

Block Diagram

Transmitting station with the

microwave transmitter

sensor

Rectenna

RF cable

circulator

waveguide

Slotted waveguideAntenna

mobile signal

Microwave signal is transmitted from transmitter along with message signal using slotted waveguide antenna at frequency 2.45 GHZ.

The sensor search for the mobile signal , in addition it has a “RECTENNA”.

Rectenna receives the transmitted power and converts the microwave power to DC power.

TRANSMITTER SECTION

Consists of two parts

Magnetron

Slotted waveguide antenna

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MAGNETRON

• Magnetron is a vacuum tube oscillator that generates

high-power electromagnetic signals in the microwave

frequency range.

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Working Principle

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When a charge/charge particle accelerates in space, it generates electromagnetic waves.

This statement is the derivation of Maxwell’s law which says that a classical electromagnetic radiation is ultimately generated when a charged particle is accelerated through space.

Working

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Slotted waveguide antenna

It is an Omni-directional Antenna.

It is used as ideal power transmitter

(because of its high aperture efficiency

>95%) .

It has high power handling capacity .

RECEIVER SECTION

Basic additions to mobile phone

Sensor

Rectenna

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SENSOR Simple circuit which detects whether the user is making a call

Simple F to V converter, this would serve our purpose

Operating frequency of mobile phone operators for GSM system for mobile

communication in Pakistan is 900MHZ to 1800MHZ

Simple yet powerful F to V converter is LM2907

On the reception of the microwave signal ,the sensor circuitry directs rectenna circuit to

ON

Rectenna circuit converts microwave energy to dc output

Mobile phone begins to charge using the microwave power as long as the user talks over

cell phone.

RECTENNA A rectifying antenna called a rectenna receives the transmitted power

and converts the microwave power to direct current (DC) power.

The Schottky diode rectifies the AC current induced in the antenna by the microwaves, to produce DC power, which powers a load connected across the diode.

Schottky diodes are usually used because they have the lowest voltage drop and highest speed and therefore have the lowest power losses due to conduction and switching.

Circuit Design

Implementation

Recently NOKIA has launched this wireless charging technology

in its new recent mobile model “ NOKIA LUMIA 1020”.

Advantages

The need of different types of chargers by different

manufacturers is totally eliminated

Lower risk of ELECTRICAL SHOCK or shorting.

Convenience.

Get Charged as we make call.

Only one microwave transmitter can serve to all the

service providers in that area.

Disadvantages

Wireless transmission of the energy causes some

drastic effects to human body, because of its radiation.

Process is of high cost.

Network Traffic may Cause Problem in charging

Other Applications Of Microwaves

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Homeland Security Applications

Potential Security Applications

Detection of hidden weapons and explosives

Detecting non-metallic weapons

Postal screening of envelopes for bacteria

Chem/bio detection

Security screening wand

Explosives

Stand-off detection

Postal screening

Envelope

Terahertz Images Can Reveal Objects Concealed Under Cloth, Paper, Tape, Even Behind Walls

Objects Concealed Under clothes Knife Wrapped in Newspaper

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