Notes about the Electromagnetic Spectrum

 

 

Electromagnetic Spectrum

The electromagnetic spectrum (EMS) is the general name given to the known range of electromagnetic radiation. Wavelengths increase from approximately 10-18 m to 100 km, and this corresponds to frequencies decreasing from 3 × 1026 Hz to 3 ×103 Hz.

 

The image below shows the names given to different regions of the EMS. Note that the visible part of the spectrum, the only type of electromagnetic radiation that we can detect with our eyes, makes up only a tiny fraction of the EMS.

 

 

In a vacuum, all electromagnetic waves travel at the speed of light: c = 299,792,458 m/s. An energy ( E ) can be associated with each region of the EMS using the equation:

 

 E = hf

 

where f is the frequency and h is Planck’s constant which has the value:

 

 h = 6.6260693(11) x 10-34 Js

 

The table below lists typical wavelengths, frequencies and energies for different regions of the EMS.

 

Region

Wavelength

Frequency

Energy

Hard gamma

1 × 10-9 nm

3 × 1026 Hz

1.2 × 1012 eV

Gamma

1 × 10-6 nm

3 × 1023 Hz

1.2 GeV

Gamma/X-ray

0.001 nm

3 × 1019 Hz

12 MeV

X-ray

1 nm

3 × 1017 Hz

120 keV

X-ray/Ultraviolet

10 nm

3 × 1016 Hz

12 keV

Ultraviolet

100 nm

3 × 1015 Hz

1.2 keV

Visible (blue)

400 nm

7.5 × 1014 Hz

3.1 eV

Visible (red)

700 nm

4.3 × 1014 Hz

1.8 eV

Infrared

10000 nm

3 × 1013 Hz

0.12 eV

Microwave

1 cm

30 GHz

1.2 × 10-4 eV

Microwave/Radio

10 cm

3GHz

1.2 × 10-5 eV

Radio

100 m

3 MHz

1.2 × 10-8 eV

Radio

100 km

3 kHz

1.2 × 10-11 eV

 

 

Source : astronomy.swin.edu.au

 

 

July 2018

 

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Many example of International Telecommunication Union’s bands

 

Band name

Abbrev.

ITU

band #

Frequency and

Wavelength

Example Uses

Extremely low frequency

ELF

1

3–30 Hz
100,000–10,000 km

Comm. with submarines

Super low frequency

SLF

2

30–300 Hz
10,000–1,000 km

Comm. with submarines

Ultra low frequency

ULF

3

300–3,000 Hz
1,000–100 km

Submarine Comm., Comm. within mines

Very low frequency

VLF

4

3–30 kHz
100–10 km

Navigation, time signals, submarine Comm., wireless heart rate monitors, geophysics

Low frequency

LF

5

30–300 kHz
10–1 km

Navigation, time signals, AM longwave broadcasting (Europe and parts of Asia), RFID, amateur radio

Medium frequency

MF

6

300–3,000 kHz
1,000–100 m

AM (medium-wave) broadcasts, amateur radio, avalanche beacons

High frequency

HF

7

3–30 MHz
100–10 m

Shortwave broadcasts, citizens band radio, amateur radio and over-the-horizon aviation Comm.s, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio Comm.s, marine and mobile radio telephony

Very high frequency

VHF

8

30–300 MHz
10–1 m

FM, television broadcasts, line-of-sight ground-to-aircraft and aircraft-to-aircraft Comm.s, land mobile and maritime mobile Comm.s, amateur radio, weather radio

Ultra high frequency

UHF

9

300–3,000 MHz
1–0.1 m

Television broadcasts, microwave oven, microwave devices/Comm.s, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as land mobile, FRS and GMRS radios, amateur radio, satellite radio, Remote control Systems, ADSB

Super high frequency

SHF

10

3–30 GHz
100–10 mm

Radio astronomy, microwave devices/Comm.s, wireless LAN, DSRC, most modern radars, Comm.s satellites, cable and satellite television broadcasting, DBS, amateur radio, satellite radio

Extremely high frequency

EHF

11

30–300 GHz
10–1 mm

Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner, wireless LAN (802.11ad)

Terahertz or Tremendously high frequency

THz or THF

12

300–3,000 GHz
1–0.1 mm

Experimental medical imaging to replace X-rays, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/Comm.s, remote sensing, amateur radio

Band 9 /

GMRS : General Mobile Radio Service, short-distance comm.

ADSB : Automatic Dependent Surveillance-Broadcast

ZigBee and Z-Wave, low energy consumption

 

Band 10 /

DSRC : Dedicated short-range communications short-range to medium-range wireless communication

 

 

 

 

 

 


 

 

 

Wireless technologies

 

Network definition

Standard

Public name

  M/S

Max M/S

Wireless personal area network (WPAN)

IEEE 802.15.1

Bluetooth

>=24

24 (V4)

Low-rate WPAN (LRWPAN)

IEEE 802.15.4

ZigBee

>=250 kb

250 kb

Wireless local area network (WLAN)

IEEE 802.11b

WiFi

>=10

11

Wireless local area network (WLAN)

IEEE 802.11g

WiFi

>=10

54

Wireless local area network (WLAN)

IEEE 802.11ac/n

WiFi

>=100

1 Gb

Wireless metropolitan area network (WMAN)

IEEE 802.16

WiMAX

>=100

134

Long Term Evolution (LTE)

IMT-Advaced / 3GPP

LTE Advanced DL

>=100

3 Gb

Long Term Evolution (LTE)

IMT-Advaced / 3GPP

LTE Advanced UL

>=100

1.5 Gb

 

ISM (Industrial, Scientific and Medical) frequency bands:

900 MHz band (902 … 928 MHz)

2.4 GHz band (2.4 … 2.4835 GHz)

5.8 GHz band (5.725 … 5.850 GHz)

60 GHz band

 

ISM frequency band at 2.4 Ghz

Transmitters using FH (Frequency Hopping) technology Transmitters using DSSS technology.

 

Multiplexing / multiple access / duplexing

Multiplexing / multiple access

Signals to/from different users share a common channel using time division methods (TDMA), Frequency Division Methods (FDMA), Code Division Methods (CDMA), or

Random Access Methods (CSMA).

 

 

Duplexing:

The signals moving between two elements in opposite directions can be separated using Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD). In the case of CSMA, duplexing is not relevant.

 

Wireless Fidelity (WiFi) @ 100m

 

The WiFi certification program of the Wireless Ethernet Compatibility Alliance (WECA) addresses compatibility of IEEE 802.11 equipment.

 

802.11 Medium Access Control (MAC) CSMA / CA

802.11 PHY

802.11ac PHY

802.11b PHY

802.11g PHY

 

WiFi ensures interoperability of equipment from different vendors.

 

 


Electromagnetic spectrum

 

 

James Clerk Maxwell (1831–1879) was able to come up with a single theory that explained both electricity and magnetism. Maxwell summed up everything people had discovered in four simple equations to produce a superb theory of electromagnetism, which he published in 1873. He realized that electromagnetism could travel in the form of waves, at the speed of light, and concluded that light itself had to be a kind of electromagnetic wave.

 

About a decade after Maxwell's death, a brilliant German physicist named Heinrich Hertz (1857–1894) became the first person to produce electromagnetic waves in a laboratory. That piece of work led to the development of radio, television, and wireless Internet.

 

 

Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays.

 

Gamma rays, x-rays, and some ultraviolet waves are “ionizing,” meaning these waves have such a high energy that they can knock electrons out of atoms.

 

Object

Length

As

Radio waves | AM radio

10^2m

Football field

Radio waves | FM radio

10m

 

Cell phone+WiFi

10^-1m

Baseball width

Microwave oven

10^-1m

Baseball width

Human radiate heat

10^-4m

Thickness of paper

Infrared | telecommand

10^-6m

 

Intrared | visible light

10^15hz

 

Ultraviolet | Sunburn

[10^-7 to -8]m

 

X-rays | Medical X-rays

10^-10m

 

Gamma waves | Nuclear Power

10^-12m

 

 

The three terms: Light, Electromagnetic Waves, and Radiation, refer to the same physical phenomenon: electromagnetic energy, which can be described by :

 

 

 

Unit

Wave

f

Frequency

Hertz

Radio and Microwaves

l

Wavelength

Meters

Infrared and Visible Light

E

Energy

Electron volts (eV)

X-Rays and Gamma Rays

1eV=1.6×10−19 joules (symbol J) in SI units

It is the amount of energy, gained or lost, by the charge of a single electron, moving across an electric potential difference of one volt.

 

The Hertz is the derived unit of frequency in SI, defined as one cycle per second.

 

Electromagnetic waves are typically described by any of the following three physical properties: the frequency f, wavelength λ, or photon energy E.

Frequencies observed in astronomy range from 2.4 ×1023 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency, so gamma rays have very short wavelengths that are fractions of the size of atoms, whereas wavelengths on the opposite end of the spectrum can be as long as the universe.

 

Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts), while radio wave photons have very low energy (around a femtoelectronvolt). These relations are

illustrated by the following equations:

 

, or , or   

 

where:

c = 299 792 458 m/s is the speed of light in a vacuum

h = 6.626 068 96(33) × 10−34 J·s = 4.135 667 33(10) × 10−15 eV·s is Planck's constant.

 

 

Electromagnetic radiation interaction with matter

 

Region of the spectrum

Main interactions with matter

Radio

Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillatory travels of the electrons in an antenna.

Microwave through far infrared

Plasma oscillation, molecular rotation

Near infrared

Molecular vibration, plasma oscillation (in metals only)

Visible

Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only)

Ultraviolet

Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect)

X-rays

Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers)

Gamma rays

Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei

High-energy gamma rays

Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high-energy particles and antiparticles upon interaction with matter.

 

X-rays | Gamma-rays

 

Distinction between X-rays and Gamma rays :

Gamma Rays = Photons generated from nuclear decay.

X-Rays =  Electronic transitions involving highly energetic inner atomic electrons.

 

 

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