Electromagnetic waves and Applications Part III:

Electromagnetic waves and Applications Part III:
Microwave Fundamentals

Electromagnetic spectrum
Millimeter waves 300 MHz 3 GHz 30 GHz 300 GHz 3 THz 30 THz 300 THz Photonic devices Electronic devices Microwaves THz gap visible Radio waves UV Infrared Microwave bands Band P L S C X Ku K Ka Freq (GHz) 0.23-1 1-2 2-4 4-8 8-12.5

Microwave applications
Wireless communications (cell phones, WLAN,…) Global positioning system (GPS) Computer engineering (bus systems, CPU, …) Microwave antennas (radar, communication, remote sensing, …) Other applications (microwave heating, power transfer, imaging, biological effect and safety)

Syllabus Chapter 1: Transmission line theory
Chapter 2: Transmission lines and waveguides Chapter 3: Microwave network analysis Chapter 4: Microwave resonators Reference books： David M. Pozar, Microwave Engineering, third edition (Wiley, 2005) Robert E. Collin, Foundations for microwave engineering, second edition (Wiley, 2007) J. A. Kong，Electromagnetic theory (EMW, 2000)

Chapter 1: Transmission line theory
1.1 Why from lumped to distributed theory? 1.2 Examples of transmission lines 1.3 Distributed network for a transmission line 1.4 Field analysis of transmission lines 1.5 The terminated lossless transmission line 1.6 Sourced and loaded transmission lines 1.7 Introduction of the Smith chart

Transmission line theory
R = series resistance per unit length, for both conductors, in /m; L = series inductance per unit length, for both conductors, in H/m; G = parallel conductance per unit length, in S/m; C = parallel capacitance per unit length, in F/m. Loss: R (due to the infinite conductivity) + G (due to the dielectric loss)

Transmission line theory
Bridges the gap between field analysis and basic circuit theory Extension from lumped to distributed theory A specialization of Maxwell’s equations Significant importance in microwave network analysis The key difference between circuit theory and transmission line theory is electrical size. Circuit analysis assumes that the physical dimensions of a network are much smaller than the electrical wavelength, while transmission lines may be a considerable fraction of a wavelength, or many wavelengths, in size. Thus a transmission line is a distributed-parameter network, where voltages and currents can vary in magnitude and phase over its length.

1.1 Why from lumped to distributed theory?

1.2 Examples of transmission lines
(2) Coaxial line (1)Two-wire line Magnetic field (dashed lines) Electric field (solid lines) (3) Microstrip line

Review: Kerchhoff’s law
1.3 Distributed network for a transmission line Review: Kerchhoff’s law KCL: KVL:

1.3 Distributed network for a transmission line

(Telegrapher equations)

Impedance, wavelength and phase velocity TL current: Characteristic impedance: Voltage in the time domain: Wavelength: Phase velocity:

Propagation constant: Characteristic impedance: Wavelength: (what happens if exchange L and C ?) Phase velocity:

Electromagnetic Waves
Section 1 slides 3- 31 What are electromagnetic waves? Section 2 slides 32-59 The Electromagnetic Spectrum Section 3 slides Radio Communication

What are electromagnetic waves?
How electromagnetic waves are formed How electric charges produce electromagnetic waves Properties of electromagnetic waves

Electromagnetic Waves…
Do not need matter to transfer energy.

Electromagnetic Waves…
Do not need matter to transfer energy. Are made by vibrating electric charges and can travel through space by transferring energy between vibrating electric and magnetic fields.

How do moving charges create magnetic fields?
Any moving electric charge is surrounded by an electric field and a magnetic field.

What happens when electric and magnetic fields change?
A changing magnetic field creates a changing electric field.

A changing magnetic field creates a changing electric field. One example of this is a transformer which transfers electric energy from one circuit to another circuit.

A changing magnetic field creates a changing electric field. One example of this is a transformer which transfers electric energy from one circuit to another circuit. In the main coil changing electric current produces a changing magnetic field Which then creates a changing electric field in another coil producing an electric current The reverse is also true.

This page was copied from Nick Strobel's Astronomy Notes
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.

Making Electromagnetic Waves
When an electric charge vibrates, the electric field around it changes creating a changing magnetic field.

The magnetic and electric fields create each other again and again.

An EM wave travels in all directions. The figure only shows a wave traveling in one direction.

The electric and magnetic fields vibrate at right angles to the direction the wave travels so it is a transverse wave.

Properties of EM Waves All matter contains charged particles that are always moving; therefore, all objects emit EM waves.

Properties of EM Waves All matter contains charged particles that are always moving; therefore, all objects emit EM waves. The wavelengths become shorter as the temperature of the material increases.

Properties of EM Waves All matter contains charged particles that are always moving; therefore, all objects emit EM waves. The wavelengths become shorter as the temperature of the material increases. EM waves carry radiant energy.

What is the speed of EM waves?
All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!)

What is the speed of EM waves?
All EM waves travel 300,000 km/sec in space. (speed of light-nature’s limit!) EM waves usually travel slowest in solids and fastest in gases. Material Speed (km/s) Vacuum 300,000 Air <300,000 Water 226,000 Glass 200,000 Diamond 124,000

What is the wavelength & frequency of an EM wave?
Wavelength= distance from crest to crest.

Wavelength= distance from crest to crest. Frequency= number of wavelengths that pass a given point in 1 s.

Wavelength= distance from crest to crest. Frequency= number of wavelengths that pass a given point in 1 s. As frequency increases, wavelength becomes….

Wavelength= distance from crest to crest. Frequency= number of wavelengths that pass a given point in 1 s. As frequency increases, wavelength becomes smaller.

Can a wave be a particle? In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected.

Can a wave be a particle? In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected. Whether or not electrons were ejected depended upon frequency not the amplitude of the light! Remember energy depends on amplitude.

Can a wave be a particle? Years later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves.

Can a particle be a wave? Electrons fired at two slits actually form an interference pattern similar to patterns made by waves

What did Young’s experiment show?

How they are formed Kind of wave Sometimes behave as

How they are formed Waves made by vibrating electric charges that can travel through space where there is no matter Kind of wave Transverse with alternating electric and magnetic fields Sometimes behave as Waves or as Particles (photons)

Section 2 The Electromagnetic Spectrum

The whole range of EM wave…
Frequencies is called the electromagnetic spectrum.

Frequencies is called the electromagnetic spectrum. Different parts interact with matter in different ways.

Frequencies is called the electromagnetic spectrum. Different parts interact with matter in different ways. The ones humans can see are called visible light, a small part of the whole spectrum.

As wavelength decreases, frequency increases…

Devices detect other frequencies:
Antennae of a radio detects radio waves.

Antennae of a radio detects radio waves. Radio waves are low frequency EM waves with wavelengths longer than 1mm.

Antennae of a radio detects radio waves. Radio waves are low frequency EM waves with wavelengths longer than 1mm. These waves must be turned into sound waves by a radio before you can hear them.

What are microwaves? Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength.

What are microwaves? Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength. Cell phones and satellites use microwaves between 1 cm & 20 cm for communication.

What are microwaves? Microwaves are radio waves with wavelengths less than 30 cm and higher frequency & shorter wavelength. Cell phones and satellites use microwaves between 1 cm & 20 cm for communication. In microwave ovens, a vibrating electric field causes water molecules to rotate billions of times per second causing friction, creating TE which heats the food.

How does radar work? Radio Detecting And Ranging or radar is used to find position and speed of objects by bouncing radio waves off the object.

What is magnetic resonance imaging?
MRI was developed in the 1980s to use radio waves to diagnose illnesses with a strong magnet and a radio wave emitter and a receiver. Protons in H atoms of the body act like magnets lining up with the field. This releases energy which the receiver detects and creates a map of the body’s tissues.

Infrared Waves EM with wavelengths between 1mm & 750 billionths of a meter. Used daily in remote controls, to read CD-ROMs Every objects gives off infrared waves; hotter objects give off more than cooler ones. Satellites can ID types of plants growing in a region with infrared detectors

Visible Light Range of EM humans can see from 750 billionths to 00 billionths of a meter. You see different wavelengths as colors. Blue has shortest Red is the longest Light looks white if all colors are present

A range of frequencies In order of increasing frequency and decreasing wavelength, the EM spectrum consists of: very long wave radio, used for communication with submarines; long, medium and short wave radio (used for AM broadcasting); FM radio, television and radar; infra-red (heat) radiation, which is recorded in the Earth photographs taken by survey satellites; visible light; ultraviolet light, which, while invisible, stimulates fluorescence in some materials; x rays & gamma rays used in medicine and released in radioactive decay

Ultraviolet Waves EM waves with wavelengths from about 400 billionths to 10 billionths of a meter. Have enough energy to enter skin cells Longer wavelengths – UVA Shorter wavelengths – UVB rays Both can cause skin cancer

Can UV radiation be useful?
Helps body make vitamin D for healthy bones and teeth Used to sterilize medical supplies & equip Detectives use fluorescent powder (absorbs UV & glows) to find fingerprints

What is the ozone layer? 20-50 km above earth Molecule of 3 O atoms
Absorbs Sun’s harmful UV rays Ozone layer decreasing due to CFCs in AC, refrigerators, & cleaning fluids

What could happen to humans…
And other life on Earth if the ozone layer is destroyed?

X Rays and Gamma Rays EM waves with shortest wavelength & highest frequency High Energy- go through skin & muscle High level exposure causes cancer

X Rays and Gamma Rays EM with wavelengths shorter than 10 trillionths of a meter. Highest energy, can travel through several centimeters of lead. Both can be used in radiation therapy to kill diseased cells. The composite image shows the all sky gamma ray background.

Identify which statement is not true:
A. Gamma rays are low frequency waves. B. X rays are high-energy waves. C. Gamma rays are used to treat diseases.

Why do you think MRIs cause ...
Less harm than X rays?

F Fill in the boxes with the waves of the EM spectrum.

Chp. 12 Section 3 Radio Communication

Radio Transmission Radio stations change sound to EM waves & then your radio receiver changes the EM waves back to sound waves again.

How does a radio receive different stations?
Each station broadcasts at a certain frequency which you tune in by choosing their frequency. Carrier wave- the frequency of the EM wave that a station uses Microphones convert sound waves to a changing electric current or electronic signal containing the words & music.

Microphones convert sound waves to a changing electric current or electronic signal containing the words & music. The modified carrier wave vibrates electrons in the station’s antennae creating a radio wave that travels out in all directions at the speed of light to your radio antennae.

The modified carrier wave vibrates electrons in the station’s antennae creating a radio wave that travels out in all directions at the speed of light to your radio antennae. The vibrating electrons produce a changing electric current which your radio separates the carrier wave from the signal to make the speakers vibrate creating sound waves….

What is AM radio? In AM amplitude changes but frequency does not. AM frequencies range from 540,000 Hz to 1,6000,000 Hz usually listed in kHz.

What is FM radio? In FM radio stations transmit broadcast information by changing the frequency of the carrier wave. The strength of FM waves is always the same and is in megahertz. Mega=million

Television Uses radio waves to send electronic signals in a carrier wave. Sound is sent by FM; color and brightness is sent at the same time by AM signals.

What is a cathode-ray tube?
Many TVs and computer monitors display images on a CRT, a sealed vacuum tube in which beams of electrons are produced. Color TV produces 3 electron beams inside the CRT which strike the inside of the screen that is covered with more than 100,000 rectangular spots.

What is a cathode-ray tube?
There are 3 types of spots, red, green and blue. The electron beams move back and forth across the screen. The signal from the TV station controls how bright each spot is. Three spots together can form any color. You see a full color image on the TV.

Telephones Sound waves microphone electric signal radio waves transmitted to and from microwave tower  receiver electric signal  speaker sound wave Mobile Phone BTS Base Transceiver Station BSC Base Station Controller MSC Mobile services Switching Centre VLR Visitor Location Register HLR Home Location Register

How do cordless phones work?
Cell phones and cordless telephones are transceivers, device that transmits one signal & receives another radio signal from a base unit. You can talk and listen at the same time because the two signals are at different frequencies.

How do pagers work? A pager is a small radio receiver with a phone number. A caller leaves a message at a terminal with a call-back number. At the terminal, the message is turned into an electronic signal transmitted by radio waves. Newer pagers can send and receive messages.

Communications Satellites
Thousands of satellites orbit Earth. A radio or TV station sends microwave signals to the satellite which amplifies the signal and sends it back to a different place on Earth. Satellite uses dif freq to send & receive.

Global Positioning System
GPS is a system of 24 satellites, ground monitoring stations and portable receivers that determine your exact location on Earth. GPS receiver measures the time it takes for radio waves to travel from 4 different satellites to the receiver. The system is owned and operated by the US Dept of Defense, but the microwaves can be used by anyone.

Objectives: After completing this module, you should be able to:
Explain and discuss with appropriate diagrams the general properties of all electromagnetic waves. Discuss and apply the mathematical relationship between the electric E and magnetic B components of an EM wave. Define and apply the concepts of energy density, intensity, and pressure due to EM waves. This module is OPTIONAL: check with instructor. Much of this material is NOT in Tippens Textbook

Maxwell’s Theory Electromagnetic theory developed by James Maxwell (1831 – 1879) is based on four concepts: 1. Electric fields E begin on positive charges and end on negative charges and Coulomb’s law can be used to find the field E and the force on a given charge. + - q1 q2

Maxwell’s Theory (Cont.)
2. Magnetic field lines F do not begin or end, but rather consist of entirely closed loops.

3. A changing magnetic field DB induces an emf and therefore an electric field E (Faraday’s Law). Faraday’s Law: A change in flux DF can occur by a change in area or by a change in the B-field: DF = B DA DF = A DB

4. Moving charges (or an electric current) induce a magnetic field B. R Inductance L l B Solenoid Current I induces B field B I Lenz’s law x

Production of an Electric Wave
Consider two metal rods connected to an ac source with sinusoidal current and voltage. - + Arrows show field vectors (E) + - - + + - E Wave Vertical transverse sinusoidal E-waves.

An Alternating Magnetic Field
The ac sinusoidal current also generates a magnetic wave alternating in and out of paper. + - X + - X • - + • - + B I r Inward B X In B I r Outward B • Out r

A Magnetic Wave Generation
The generation of a magnetic wave due to an oscillating ac current. Arrows show magnetic field vectors (B) I + - I r + - B I r + - B I r B - + B - Wave Horizontal transverse sinusoidal B-waves.

An Electromagnetic Wave
An electromagnetic wave consists of combination of a transverse electric field and a transverse magnetic field perpendicular to each other. + - Arrows show field vectors EM wave propagation in space

Transmitting and Receiving
An ac current generates an EM wave which then generates an ac signal at receiving antenna.

A B-field Moves Past a Charge
Relativity tells us that there is no preferred frame of reference. Consider that a magnetic field B moves at the speed of light c past a stationary charge q: Charge q experiences a magnetic force F N S c B Stationary positive charge q But electric field E = F/q: Substitution shows:

An E-field Moves Past a Point
A length of wire l moves at velocity c past point A: A current I is simulated. A r c E In time t, a length of wire l = ct passes point A Wire moves at velocity c past A Charge density: In time t: q = l ct Thus, the current I is: Simulated current I:

Moving E-field (Cont.) A B-field is created by the A E r
c E simulated current: A B-field is created by the Eliminating l from these two equations gives: Recall from Gauss’ law:

The Speed of an EM Wave For EM waves, we have seen: A E r c
c E Substituting E = cB into latter equation gives: EM-waves travel at the speed of light, which is: c = 3.00 x 108 m/s

Important Properties for All Electromagnetic Waves
EM waves are transverse waves. Both E and B are perpendicular to wave velocity c. The ratio of the E-field to the B-field is constant and equal to the velocity c.

Energy Density for an E-field
Energy density u is the energy per unit volume (J/m3) carried by an EM wave. Consider u for the electric field E of a capacitor as given below: Energy density u for an E-field: A d Energy density u:

Energy Density for a B-field
Earlier we defined the energy density u for a B-field using the example of a solenoid of inductance L: R l A Energy density for B-field:

Energy Density for EM Wave
The energy of an EM wave is shared equally by the electric and magnetic fields, so that the total energy density of the wave is given by: Total energy density: Or, since energy is shared equally:

Average Energy Density
The E and B-fields fluctuate between their maximum values Em and Bm. An average value of the energy density can be found from the root-mean-square values of the fields: The average energy density uavg is therefore: or

Example 1: The maximum amplitude of an E-field from sunlight is 1010 V/m. What is the root-mean-square value of the B-field? EM wave Earth What is the average energy density of the wave? Note that the total energy density is twice this value.

Wave Intensity I ct Area A
The intensity of an EM wave is defined as the power per unit area (W/m2). Area A EM wave moves distance ct through area A as shown below: Total energy = density x volume Total energy = u(ctA) ct A Total intensity: And Since u = eoE2

Calculating Intensity of Wave
In calculating intensity, you must distinguish between average values and total values: Area A Since E = cB, we can also express I in terms of B:

Example 2: A signal received from a radio station has Em = 0. 0180 V/m
Example 2: A signal received from a radio station has Em = V/m. What is the average intensity at that point? The average intensity is: Note that intensity is power per unit area. The power of the source remains constant, but the intensity decreases with the square of distance.

Wave Intensity and Distance
The intensity I at a distance r from an isotropic source: The average power of the source can be found from the intensity at a distance r : A For power falling on surface of area A: For isotropic conditions: P = Iavg A

Example 3: In Example 2, an average intensity of 4
Example 3: In Example 2, an average intensity of 4.30 x 10-7 W/m2 was observed at a point. If the location is 90 km (r = 90,000 m) from the isotropic radio source, what is the average power emitted by the source? 90 km P = (4pr2)(4.30 x 10-7 W/m2) P = 4p(90,000 m)2(4.30 x 10-7 W/m2) Average power of transmitter: P = 43.8 kW This assumes isotropic propagation, which is not likely.

Radiation Pressure Radiation Pressure
EM-waves not only carry energy, but also carry momentum and exert pressure when absorbed or reflected from objects. A Radiation Pressure Recall that Power = F v The pressure is due to the transfer of momentum. The above relation gives the pressure for a completely absorbing surface.

Radiation Pressure (Cont.)
The change in momentum for a fully reflected wave is twice that for an absorbed wave, so that the radiation pressures are as follows: A Radiation Pressure Absorbed wave: A Radiation Pressure Reflected wave:

Example 4: The average intensity of direct sunlight is around 1400 W/m2. What is the average force on a fully absorbing surface of area 2.00 m2? A Radiation Pressure Absorbed wave: For absorbing surface: F = 9.33 x 10-6 N

The Radiometer A radiometer is a device which demonstrates the existence of radiation pressure: Radiometer One side of the panels is black (totally absorbing) and the other white (totally reflecting). The panels spin under light due to the pressure differences.

Summary EM waves are transverse waves. Both E and B are perpendicular to wave velocity c. The ratio of the E-field to the B-field is constant and equal to the velocity c. Electromagnetic waves carry both energy and momentum and can exert pressure on surfaces.

Summary (Cont.) EM-waves travel at the speed of light, which is:
c = 3.00 x 108 m/s Total Energy Density:

Summary (Cont.) Totally Absorbing Totally Reflecting
The average energy density: or Intensity and Distance Totally Absorbing Totally Reflecting

In the above diagram the white line represents the position of the medium when no wave is present.

http://id. mind. net/~zona/mstm/physics/waves/partsOfAWave/waveParts

Radio Waves Are produced by feeding an electric signal to the mast or antenna of a transmitter.

Radio Waves Radio waves have the longest wavelengths in the electromagnetic spectrum. These waves can be longer than a football field or as short as a football.

Radio Waves The signal makes the electrons in the metal atoms of the mast or antenna change energy levels and emit light rays.

RAY’S TV reception uses radio_ waves
The SATELITE_ at Ray’s TV – receives movies via radio waves from a satellite TAXI_ - Car radio receives radio wave signals TAXI_ - Driver receives instructions on a CB radio which uses radio waves. RADIO TOWER - broadcast’s radio signals LARGE SATELITE _ dish in field – receives radio waves from distant stars

3 8 5 100,000 m 1 m

3 1000 m 8 m 5 100,000 m 1 m

Microwaves Microwaves have wavelengths that can be measured in centimeters The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven Images from:

Microwaves Microwaves are good for transmitting information from one place to another because microwave energy can penetrate haze, light rain and snow, clouds, and smoke. Images from:

Microwaves Shorter microwaves are used for radar like the doppler radar used in weather forecasts. Microwaves, used for radar, are just a few inches long. Images from:

MICROWAVES in Wavesgrill – uses microwave to cook food. Antennas on tower they send microwave communications

9 8 -2

9 m 8 m -2 0.01 m

Infrared Waves The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic. Images from:

Infrared Waves The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared. Shorter wavelengths are the ones used by your TV's remote control. Images from:

Infrared Waves Satellites like GOES 6 and Landsat 7 look at the Earth. Special sensors, like those aboard the Landsat 7 satellite, record data about the amount of infrared light reflected or emitted from the Earth's surface. Images from:

Infrared lights above food in Wavesgrill – use infrared waves to keep food hot
Infrared remotes - Remote controls use infrared waves to communicate with the TV Trees, brashes, crops, and short vegetation reflects short infrared waves Astronomers study thermal infrared (long infrared waves) from stars

11 12 -3

11 m 12 m -3 0.001 m

Visible Spectrum Cones in our eyes are receivers for these tiny visible light waves. The Sun is a natural source for visible light waves and our eyes see the reflection of this sunlight off the objects around us. Images from:

Visible Spectrum The color of an object that we see is the color of light reflected. All other colors are absorbed. Light bulbs are another source of visible light waves. Images from:

VISIBLE LIGHT Water droplets cause white light to break apart into seven colors (Visible Light). Portrait photographers use film sensitive to visible light Astronomers look at visible light from planets and stars

14 15 -6

14 m 15 m -6 m

Ultraviolet Waves Astronomers have to put ultraviolet telescopes on satellites to measure the ultraviolet light from stars and galaxies - and even closer things like the Sun Images from:

A tanning booth uses ultraviolet waves to tan our skin
ultraviolet waves - sunglasses protect our eyes from the ultraviolet waves Sunblocks - protects our skin from ultraviolet waves ultraviolet waves astronomers see some ultraviolet radiation from planets and stars

15 17 -8

15 m 17 m -8 m

X-Rays X-ray light tends to act more like a particle than a wave. X-ray detectors collect actual photons of X-ray light. The Earth's atmosphere is thick enough that virtually no X-rays are able to penetrate from outer space all the way to the Earth's surface. Images from:

X-Rays X-ray telescopes and detectors are placed on satellites. We cannot do X-ray astronomy from the ground can not be done from Earth comets emit X-rays The Sun also emits X- rays Many things in deep space give off X-rays Images from:

17 19 -10

17 m 19 m -10 m

At EMS, Dr. Bob uses X-ray detectors collect actual photons of X-ray light in his Clinic.
Nuclear Medicine is used to treat cancer. Gamma radiation kills sick cells.

Gamma Rays Gamma-rays are generated by radioactive atoms and in nuclear explosions They can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.

Gamma Rays .Gamma-rays travel to us across vast distances of the universe, Instruments aboard high-altitude balloons and satellites like the Compton Observatory provide our only view of the gamma-ray sky

19 23 -12

19 m 23 m -12 m

Coaxial cable

Electromagnetic radiation is in the form of waves called photons
Electromagnetic radiation is in the form of waves called photons. The important characteristics of the photons—their energy E, wavelength λ, and frequency ν—are related by the equation

Electromagnetic applications
Electromagnetic interference (EMI) shielding Low observability (Stealth) Electromagnetic transparency (radomes)

Electromagnetic shielding applications
Electronic enclosures (e.g., computers, pacemaker leads, rooms, aircraft, etc.) Radiation source enclosures (e.g., telephone receivers) Cell-phone proof buildings Deterring electromagnetic form of spying

Electromagnetic applications
Electronic pollution Telecommunication Microwave electronics Microwave processing Lateral guidance

Coaxial cable method of electromagnetic testing

Fraction of energy of the electromagnetic radiation that is reflected
Reflectivity R Fraction of energy of the electromagnetic radiation that is reflected

Absorptivity A Fraction of the energy of the electromagnetic radiation that is absorbed

Transmissivity T Fraction of the energy of the electromagnetic radiation that is transmitted

R + A + T = 1 The transmitted portion is the portion that has not been absorbed or reflected.

The attenuation in decibels (dB) is defined as
Attenuation (dB) = 20 log10 (Ei/E), where Ei is the incident field and E is the transmitted or reflected field. Note that Ei > E.

Mechanisms of interaction of electromagnetic radiation with materials
Reflection Absorption Multiple reflection

Reflection Mainly due to interaction of electromagnetic radiation with the electrons in the solid

Skin Effect Phenomenon in which high frequency electromagnetic radiation interacts with only the near surface region of an electrical conductor

Skin depth () where f = frequency,  = magnetic permeability = 0r, r = relative magnetic permeability, 0 = 4 x 10-7 H/m, and  = electrical conductivity in -1m-1.

Absorption Due to interaction of electromagnetic radiation with the electric/magnetic dipoles, electrons and phonons in the solid

Material attributes that help shielding
Electrical conductivity Magnetization Electrical polarization Small unit size Large surface area

Superpermalloy (at 1 kHz)
Table Electrical conductivity relative to copper (r) and relative magnetic permeability (r) of selected materials. Material r r rr r/r Silver 1.05 1 Copper Gold 0.7 Aluminum 0.61 Brass 0.26 Bronze 0.18 Tin 0.15 Lead 0.08 Nickel 0.2 100 20 2 x 10-3 Stainless steel (430) 0.02 500 10 4 x 10-5 Mumetal (at 1 kHz) 0.03 20,000 600 1.5 x 10-6 Superpermalloy (at 1 kHz) 100,000 3,000 3 x 10-7

Electromagnetic shielding materials
Nanofiber is more effective than fiber, due to small diameter and the skin effect. Thermoplastic matrix: nanofiber (19 vol.%) gives shielding 74 dB at 1 GHz, whereas fiber (20 vol.%, 3000 microns long) gives 46 dB. Cement matrix: nanofiber (0.5 vol.%) gives 26 dB, whereas fiber (0.8 vol.%) gives 15 dB.

Nanofiber inferior to the following fillers for shielding
Carbon fiber (400 microns long) Nickel fibers (2 and 20 microns diameter) Aluminum flakes

Nickel coated carbon nanofiber
Diameter: 0.4 micron Carbon core diameter: 0.1 micron Nickel by electroplating 87 dB at 7 vol.% (thermoplastic matrix) Much better than uncoated carbon nanofiber and nickel fibers.

EMI shielding effectiveness (dB)
Table 1. Electromagnetic interference shielding effectiveness at 1-2 GHz of PES-matrix composites with various fillers Filler Vol. % EMI shielding effectiveness (dB) Al flakes (15 x 15 x 0.5 m) 20 26 Steel fibers (1.6 m dia. x 30 ~ 56 m) 42 Carbon fibers (10 m dia. x 400 m) 19 Ni particles (1~5 m dia.) 9.4 23 Ni fibers (20 m dia. x 1 mm) 5 Ni fibers (2 m dia. x 2 mm) 7 58 Carbon filaments (0.1 m dia. x > 100 m) 32 Ni filaments (0.4 m dia. x > 100 m) 87

Cement pastes (with 1 vol
Cement pastes (with 1 vol. % conductive admixture) for EMI shielding at 1 GHz Steel fiber (8 microns) dB Carbon fiber (15 microns) dB Carbon nanofiber (0.1 micron) dB Graphite powder (0.7 micron) dB Coke powder (less than 75 microns) 47 dB

Cement pastes (with 1 vol.% conductive admixture)
Steel fiber (8 microns) ohm.cm Carbon fiber (15 microns) ohm.cm Carbon nanofiber (0.1 micron) ,000 ohm.cm Graphite powder (0.7 micron) ,000 ohm.cm Coke powder (less than 75 microns) 38,000 ohm.cm

EMI gaskets Shielding effectiveness Resiliency

EMI gasket materials Metal coated elastomers
Elastomers filled with conductive particles Flexible graphite

High specific surface area Resilience Conductive
Reasons for outstanding performance of flexible graphite (130 dB at 1 GHz) High specific surface area Resilience Conductive

Shielding effectiveness at 0.3 MHz – 1.5 GHz (dB) Thickness
Table 1 EMI Shielding effectiveness and DC electrical resistivity of various EMI Gasket materials Material Shielding effectiveness at 0.3 MHz – 1.5 GHz (dB) Thickness (mm,  0.02) Resistivity (.m) Flexible graphite A Flexible graphite B Silicone/Ag-Cu Silicone/Ag-glass Silicone/Ni-C Silicone/carbon black Silicone/oriented wire 125.4  5.1 125.4  6.5 122.6  8.9 120.6  7.0 120.4  9.5 116.0  12.6 93.7  14.1 14.92  0.56 0.31  0.13 3.10 1.60 0.79 1.14 3.00 2.74 1.59 (7.5  0.2) x 10-6 (7.5  0.8) x 10-6 (7.10  0.03) x 10-6 (1.6  0.3) x 10-5 (7.5  1.4) x 10-4 (9.8  0.7) x 10-4 (1.17  0.13) x 10-3 (4.46  0.15) x 10-3 (1.07  0.17) x 103

Carbon materials for EMI shielding
Flexible graphite (130 dB at 1 GHz) Nickel coated carbon nanofiber (7 vol. %) polymer-matrix composite (87 dB at 1 GHz) Coke particle (1 vol. %) cement-matrix composite (47 dB at 1 GHz)

Attenuation upon transmission (dB) Attenuation upon reflection (dB)
Table 1 Attenuation upon transmission, attenuation upon reflection and transverse electrical resistivity of carbon fiber epoxy-matrix composites at 1.0 – 1.5 GHz. Fiber type Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.mm) As-received 29.6  0.9 1.3  0.2 20.7  2.4 Epoxy coated 23.8  0.8 1.7  0.2 70.9  3.8

Elongation at break (%)
Table 2 Tensile properties of carbon fiber epoxy-matrix composites. Standard deviations are shown in parentheses Fiber type Strength (MPa) Modulus (GPa) Elongation at break (%) As-received 718 (11) 85.5 (3.8) 0.84 (0.03) Epoxy coated 626 (21) 73.5 (4.4) 0.85 (0.03)

Table 1 Attenuation under transmission and under reflection of carbon fiber composites.
Fiber type Attenuation upon transmission (dB) reflection (dB) As-received 29.6  0.9 1.3  0.2 Activated 38.8  0.8 1.2  0.2

Table 2 Tensile properties of carbon fibers before and after activation. Standard deviations are shown in parentheses. Fiber type Strength (MPa) Modulus (GPa) As-receiveda 665 (87) 126 (7) Activatedb 727 (151) 138 (15) a Six specimens tested b Eight specimens tested

(ratio of ingredients by volume) Attenuation upon transmission (dB)
Table 1 EMI shielding effectiveness (attenuation upon transmission), attenuation upon reflection and electrical resistivity. Row No. Material on Mylar (ratio of ingredients by volume) Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.cm) 1 None 0.7  0.1 21.6  0.8 1018 a 2 Base paint 1.3  0.2 16.8  0.9 1014 3 Base paint + mumetal (100 : 2) 3.2  0.3 15.9  0.8 33.0  1.6 4 Base paint + mumetal (100 : 5) 5.3  0.4 8.9  0.6 27.8  0.9 5 Base paint + mumetal (100 : 10)b 6.9  0.3 6.4  0.4 25.4  0.8 a From DuPont’s datasheet for Mylar. b Maximum possible filler content.

Table 1 EMI shielding effectiveness (attenuation upon transmission), attenuation upon reflection and electrical resistivity (cont’d). Row No. Material on Mylar (ratio of ingredients by volume) Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.cm) 6 Base paint + graphite flake (100 : 10)b 8.5  0.4 5.6  0.5 22.0  1.0 7 + mumetal (100 : 10 : 2) 8.8  0.5 5.7  0.5 22.5  0.8 a From DuPont’s datasheet for Mylar. b Maximum possible filler content.

Table 1 EMI shielding effectiveness (attenuation upon transmission), attenuation upon reflection and electrical resistivity (cont’d). Row No. Material on Mylar (ratio of ingredients by volume) Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.cm) 8 Base paint + nickel powder I (100 : 10)b 5.8  0.4 7.7  0.5 23.5  1.2 9 Base paint + nickel powder I + mumetal (100 : 10 : 2) 5.6  0.3 7.9  0.4 25.3  0.9 a From DuPont’s datasheet for Mylar. b Maximum possible filler content.

Table 1 EMI shielding effectiveness (attenuation upon transmission), attenuation upon reflection and electrical resistivity (cont’d). Row No. Material on Mylar (ratio of ingredients by volume) Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.cm) 10 Base paint + nickel powder II (100 : 10) 16.2  0.5 3.9  0.1 8.3  0.3 11 (100 : 20)b 26.2  0.6 1.8  0.1 4.7  0.3 12 + mumetal (100 : 20 : 2) 29.3  0.5 1.9  0.1 4.9  0.4 a From DuPont’s datasheet for Mylar. b Maximum possible filler content.

Table 1 EMI shielding effectiveness (attenuation upon transmission), attenuation upon reflection and electrical resistivity. (cont’d) Row No. Material on Mylar (ratio of ingredients by volume) Attenuation upon transmission (dB) Attenuation upon reflection (dB) Resistivity (.cm) 13 Base paint + nickel flake (100 : 10) 25.7  0.6 2.6  0.2 4.3  0.3 14 (100 : 20)b 32.4  0.5 1.5  0.1 3.4  0.2 15 Base paint + nickel flake + mumetal (100 : 20 : 2) 38.5  0.7 1.6  0.1 3.5  0.3 a From DuPont’s datasheet for Mylar. b Maximum possible filler content.

Design an aircraft that cannot be detected by radar.
We might make the aircraft from materials that are transparent to radar. Many polymers, polymer-matrix composites, and ceramics satisfy this requirement. We might design the aircraft so that the radar signal is reflected at severe angles from the source. The internal structure of the air craft also can be made to absorb the radar. For example, use of a honeycomb material in the wings may cause the radar waves to be repeatedly reflected within the material. We might make the aircraft less visible by selecting materials that have electronic transitions of the same energy as the radar.

Absolute thermoelectric power (V/C)a
Table 5.1 Electrical resistivity (DC), absolute thermoelectric power (20-65C) and EMI shielding effectiveness (1 GHz, coaxial cable method) of cement pastes containing various electrically conductive admixtures. Conductive admixture Vol.% Resistivity (.cm) Absolute thermoelectric power (V/C)a EMI shielding effectiveness (dB) None 6.1  105 -2.0 4 None, but with graphite powder (<1 m) coating / 14 Steel fiber43 (8 m diameter) 0.09 4.5  103 19 Steel fiber44 (60 m diameter) 0.10 5.6  104 -57 0.18 1.4  103 +5b 28 0.20 3.2  104 -68 0.27 9.4  102 38 0.28 8.7  103 Carbon fiber37 (10 m diameter) (crystalline, intercalated) 0.31 6.7  103 +12 0.36 57 52 0.40 1.7  103 +20 12b

Carbon fiber37 (10 m diameter)
(crystalline, pristine) 0.36 1.3  104 -0.5 / Steel fiber43 (8 m diameter) 0.54 23 Steel fiber44 (60 m diameter) 0.50 1.4  103 +26 Carbon fiber37 (15 m diameter) (amorphous, pristine) 0.48 1.5  104 -0.9 Carbon filament24 (0.1 m diameter) 0.5 30 Graphite powder73 (<1 m) 0.46 2.3  105 10 Coke powder33 (< 75 m) 0.51 6.9  104 44 0.72 16 59 0.90 40 58 1.0 8.3  102 +0.5 15c (crystalline, intercalated) 7.1  102 +17 1.2  104 35 0.92 1.6  105 22

Graphite powder30 (< 45 m) 37 4.8  102 +20
Coke powder33 (< 75 m) 1.0 3.8  104 / 47 Steel dust (0.55 mm) 6.6 5b Graphite powder30 (< 45 m) 37 4.8  102 +20 a Seebeck coefficient (with copper as the reference) minus the absolute thermoelectric power of copper. The Seebeck coefficient (with copper as the reference) is the voltage difference (hot minus cold) divided by the temperature difference (hot minus cold). b Ref. 72. c 0.84 vol.% carbon fiber in cement mortar at 1.5 GHz74.

Electromagnetic waves and Applications Part III:

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