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
**********************************************************************************.
Many
example of International Telecommunication Union’s bands
Band name |
Abbrev. |
ITU band # |
Frequency and Wavelength |
Example Uses |
|
ELF |
1 |
3–30 Hz |
|||
SLF |
2 |
30–300 Hz |
Comm. with submarines |
||
ULF |
3 |
300–3,000 Hz |
Submarine Comm., Comm.
within mines |
||
VLF |
4 |
3–30 kHz |
Navigation, time
signals, submarine Comm., wireless heart rate monitors, geophysics |
||
LF |
5 |
30–300 kHz |
Navigation, time
signals, AM longwave broadcasting (Europe and parts of Asia), RFID, amateur
radio |
||
MF |
6 |
300–3,000 kHz |
AM (medium-wave)
broadcasts, amateur radio, avalanche beacons |
||
HF |
7 |
3–30 MHz |
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 |
||
VHF |
8 |
30–300 MHz |
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 |
||
UHF |
9 |
300–3,000 MHz |
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 |
||
SHF |
10 |
3–30 GHz |
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 |
||
EHF |
11 |
30–300 GHz |
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 |
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:
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.
Alt + {8704 :∀ ;
8707 :∃ ;
8708 :∄ ;
8709 :∅ ;
8743 :∧ ;
8744 :∨ ;
8712 :∈ ;
8713 :∉ ;
8800 :≠ ; 8776 :≈ }
Alt + {9833 :♩; 9834 :♪ ; 9835 :♫; 9836 :♬ ; 9837 :♭ ; 9838 :♮ ; 9839 :♯ ; 127929 :🎹 ; }
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