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# Electromagnetic Spectrum

## Discussion

### introduction

A good, general sequence to remember is radio waves, microwaves, infrared, light, ultraviolet, x-rays, gamma rays

table-spectrum.shtml

### micropulsations

• small, almost sinusoidal fluctuations of the geomagnetic field, usually with durations of seconds to minutes

### radio waves

• oscillating, electric circuits
• discovered in 1888
• micropulsations, electric power transmission, analog audio signals, radio transmission, microwaves
• ELF, SLF, ULF, VLF, LF, MF, HF, VHF, UHF, SHF, EHF
Radio Frequency Bands 1 International Telecommunication Union * The ITU actually assigns the designation ELF to everything below VLF. Thus ELF on the table above is ELF1, SLF is ELF2, and ULF is ELF3.  The middle bands are sometimes identified by their relative wavelengths. Thus low frequency (LF) is also called long wave (LW), medium frequency (MF) is also called medium wave (MW), and high frequency (HF) is also called short wave (SW).  This designation is not official, but I like it. The "t" in tremendous matches the "t" in terahertz (the geometric center of the band), matches the "t" in twelve (1 THz = 1012 Hz), matches the "t" in trillion (1012 is also known as a trillion).
name ITU1 number frequency wavelength
extremely low frequency (ELF)* 1 (~1001 Hz) 3 30 Hz 100,000 10,000 km
super low frequency (SLF)* 2 (~1002 Hz) 30 300 Hz 10,000 1,000 km
ultra low frequency (ULF)* 3 (~1003 Hz) 300 3000 Hz 1000 100 km
very low frequency (VLF) 4 (~1004 Hz) 3 30 kHz 100 10 km
low frequency (LF) 5 (~1005 Hz) 30 300 kHz 10 1 km
medium frequency (MF) 6 (~1006 Hz) 300 3000 kHz 1000 100 m
high frequency (HF) 7 (~1007 Hz) 3 30 MHz 100 10 m
very high frequency (VHF) 8 (~1008 Hz) 30 300 MHz 10 1 m
ultra high frequency (UHF) 9 (~1009 Hz) 300 3000 MHz 1000 100 mm
super high frequency (SHF) 10 (~1010 Hz) 3 30 GHz 100 10 mm
extremely high frequency (EHF) 11 (~1011 Hz) 30 300 GHz 10 1 mm
tremendously high frequency (THF) 12 (~1012 Hz) 0.3 3 THz 1 0.1 mm
• microwaves
• radiation which has a wavelength between 1 mm and 30 cm and frequencies between 1 GHz and 300 GHz
• rotating polar molecules
• cavity resonator magnetron
• cosmic background radiation
• radio detection and ranging (RADAR)
• microwave oven

Equivalent Circuit Diagram

Magnify

Diagram from Percy Spencer's 1945 US patent for the microwave oven. Note the popcorn kernel labeled "Food to be Cooked".

• radar
• The traditional band names originated as code-names during World War II and are still in military and aviation use throughout the world in the 21st century. They have been adopted in the United States by the IEEE, and internationally by the ITU.

Military radar band nomenclature (L, S, C, X, Ku, K and Ka bands) originated during World War II as a secret code so scientists and engineers could talk about frequencies without divulging them. After the war the codes were declassified, millimeter (mm) was added, and the designations were eventually adopted by the IEEE — Institute of Electric and Electronic Engineers. Military radar band nomenclature is widely used today in radar, satellite and terrestrial communications, and electronic countermeasure applications, both military and commercial.
Radar frequency bands 1 Institute of Electrical and Electronics Engineers 2 International Telecommunication Union 3 International Organization for Standardization * Space radiocommunication  Unconfirmed  German for short
frequency range (GHz)
band IEEE1 ITU2 ISO3
P previous             0.225 0.39
L long 1 2 1.215
1.525

1.400
1.710*
0.39 1.55
S short 2 4 2.300
2.500
2.700

2.500
2.690*
3.400
1.55 5.20
C compromise 4 8 3.400
4.500
5.250
5.850

4.200*
4.800*
5.850
7.075*
3.90 6.20
X crosshair 8 12 8.500 10.50 5.20 10.9
uKu kurze under 12 18 10.70
13.40
14.00
15.30

13.25*
14.00
14.50*
17.30

K kurze 18 27 17.70
24.05
24.65

20.20*
24.25
24.75
10.9 36
aKa kurze above 27 40 27.50
33.40

30.00*
36.00

Q               36 46
V   40 75 37.50
47.20
59.00

42.50*
50.20*
64.00
46 56
W   75 110 76.00
92.00

81.00
100.0
56 100
mm millimeter 110 310 126.0
144.0
231.0
238.0

142.0
149.0
235.0
248.0

Earth Exploration-Satellite Services (Active) Reserved Frequencies Source: ITU
frequency (GHz) required bandwith
scatterometer altimeter synthetic aperture radar precipitation radar cloud profiling radar
0.432–0.438     6 MHz
1.215–1.300 5–500 kHz   20–085 MHz
3.100–3.300   200 MHz 20–200 MHz
5.250–5.570 5–500 kHz 320 MHz 20–320 MHz
8.550–8.650 5–500 kHz 100 MHz 20–100 MHz
9.300–9.900 5–500 kHz 300 MHz 20–600 MHz
13.25–13.75 5–500 kHz 500 MHz   0.6–14 MHz
17.20–17.30 5–500 kHz     0.6–14 MHz
24.05–24.25       0.6–14 MHz
35.50–36.00 5–500 kHz 500 MHz   0.6–14 MHz
78.00–79.00         0.3–10 MHz
94.00–94.10         0.3–10 MHz
133.5–134.0         0.3–10 MHz
237.9–238.0         0.3–10 MHz
Radio Astronomy Service (Passive) Reserved Frequencies Source: International Telecommunication Union and National Academy of Sciences Hat Creek, CA; Goldstone, CA; Arecibo, PR; Socorro, NM; Green Bank, WV; Pie Town, NM; Kitt Peak, AZ; Los Alamos, NM; Fort Davis, TX; North Liberty, IA; Brewster, WA; Owens Valley, CA; Saint Croix, VI; Mauna Kea, HI; Hancock, NH
frequency range (GHz) notes
1.350 1.400 protected at 15 geographic areas in the US*
1.400 1.427 H (1.420406 GHz)
1.718.8 1722.2 protected at 15 geographic areas in the US*
2.690 2.700
4.590 4.990 protected at 15 geographic areas in the US*
10.68 10.70
15.35 15.40
23.60 24.00 NH3 (23.6946 GHz, 23.7236 GHz, 23.8706 GHz)
31.30 31.50
31.50 31.80
48.94 49.04
50.20 50.40
52.60 54.25
86.00 92.00 clouds, oil spills, ice, snow; HCN (88.632 GHz)
100.00 102.00 NO (100.49 GHz)
109.50 111.80 CO (109.782 GHz, 110.201 GHz, 112.35 GHz), O3 (110.8 GHz)
114.25 116.00 CO (115.221 GHz, 115.271 GHz)
148.50 151.50 surface, water vapor, cloud parameters; NO (150.74 GHz)
164.00 167.00 Cloud water, rain, ice; ClO (164.38 GHz, 167.2 GHz)
182.00 185.00 H2O (183.31 GHz), O3 (184.75 GHz)
190.00 191.80 three-dimensional sounding for water vapor
200.00 209.00 NO (200.98 GHz)
226.00 231.50 CN (226.600 GHz, 226.800 GHz), CO (230.538 GHz)
250.00 252.00 NO (250.62 GHz, 51.21 GHz)

### infrared (a.k.a. "infrared light")

• "below" red
• a pigment of the imagination
• radiation in the wavelength range 0.7 micrometer to 1 millimeter
• discovered in 1800 by William Herschel (1738–1822) in the sun's spectrum
• vibrating molecules
• atoms in solids vibrating about their lattice positions
• Humans usually perceive infrared radiation as heat.
• "not so hot" stuff
• thermal infrared radiation which has a wavelength between 30 μm and 200 μm. At normal environmental temperatures objects emit infrared between these wavelengths; hotter objects, such as fires, emit infrared at wavelengths shorter than thermal infrared.
• far-infrared a.k.a. terahertz waves
• terahertz radiation is estimated to account for 98% of all the photons that have been emitted since the big bang — P.H. Siegel, IEEE Transactions Microwave Theory Technology, 30, 910 (2002)
• 0.8–4 THz known as the terahertz gap, frequencies just below the reach of optical technologies and just above the reach of electronics
• mid-infrared Infrared radiation which has a wavelength between 5 μm and 30 μm
• near-infrared Infrared radiation which has a wavelength between 0.7 μm and 5 μm. Near-infrared is further subdivided into
• short-wave infrared (1 μm-5 μm).
• very-near infrared (0.7 μm-1 μm) Photographic films respond to wavelengths between 0.7 μm and 1.0 μm, hence very-near infrared is also known as photographic infrared. Glass is opaque to infrared radiation of wavelength longer than 2 μm and other materials, such as germanium, quartz, and polyethylene, have to be used to make lenses and prisms.
• "not so excited" electrons in atoms, molecules, and semiconductors

### light (a.k.a."visible light")

• roughly 400 - 700 nm
• a good, general sequence to remember is red, orange, yellow, green, blue, violet
• "hot" stuff
• "excited" electrons in atoms, molecules, and semiconductors

### ultraviolet (a.k.a. "ultraviolet light")

• "beyond" violet
• a pigment of the imagination
• "very hot" stuff
• "very excited" electrons in in atoms, molecules, and (are we there yet?) semiconductors
• discovered in 1801
• moderately energetic, accelerated electric charges (just under ten to thousands of electronvolts)
• classification I (ISO 21348)
• NUV, near ultraviolet (300–400 nm)
• MUV, middle ultraviolet (200–300 nm)
The ozone layer of the atmosphere absorbs all wavelengths shorter than 290 nm.
• FUV, far ultraviolet (122–200 nm)
• EUV, extreme ultraviolet (10–121 nm)
It should really be XUV since the word extreme is alliterative with the letter x — as in x-rays. Extreme ultraviolet radiation is verging on x-rays.
• VUV, vacuum ultraviolet (10–200 nm)
Absorption by the oxygen in air makes the use of evacuated apparatus essential when working with FUV and EUV radiation.
• classification II (ISO 21348), according to its effects on the skin, Photobiological designations of the Commission Internationale de l'Eclairage (International Commission on Illumination), cited in IARC 1992.
• UVA (315–400 nm)
UVA is the dominant tanning ray and plays a major part in skin aging and wrinkling (photoaging). "Most of us are exposed to large amounts of UVA throughout our lifetime. UVA rays account for up to 95 percent of the UV radiation reaching the Earth's surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass." Black light. Maximum Permissible Exposure (MPE) 1000 µW/cm2 8 hours. Suntans are related to UVA exposure. They do not cause sunburns because of their lower energy than UVB or UVC. Since UVA penetrate deeper they damage collagen fibers and destroy vitamin A. Some skin problems (psoriasis, for example) can be treated with UV light. For a treatment known as PUVA, a drug called a psoralen is given first. The drug collects in the skin and makes it more sensitive to UV. Then the patient is treated with UVA radiation. Another treatment option is the use of UVB alone (without a drug).
• UVB (280–315 nm)
The tanning and cancer-causing rays. Erythemal — the chief cause of skin reddening and sunburn. MPE 500 µW/cm2 1 minute. Photokeratitis, Welder's Flash, or Arc Eye is literally burning of the cornea by intense exposure to UVB. Cataracts, pterygia, pinguecula. One positive affect of moderate doses of UVB is that in induces the production of vitamin D and vitamin K. Used clinically in the treatment of certain skin complaints (such as psoriasis) and to induce vitamin D formation in patients that are deficient. Acne, psoriasis, neonatal high levels of bilirubin, and daylight deprivation depression are some of the ailments treated with UVB.
• UVC (100–280 nm)
This radiation band is entirely absorbed by the ozone layer in the atmosphere and does not reach the Earth's surface. Germicidal. MPE 100 µW/cm2 1 minute.

### x-rays

• range of wavelengths is 10−11 m to 10−9 m
• discovered in 1895
• energetic, accelerated electric charges (thousands to millions of electronvolts)
• bremsstrahlung — braking acceleration
• synchrotron — centripetal acceleration
• extreme electron transitions to replace electrons dislodged from deep shells near the nucleus (bombardment of atoms by high-quantum-energy particles)
• soft x-rays, hard x-rays

### gamma rays

• ranges in energy from about 10−15 to 10−10 joule (10 keV to 10 MeV) corresponding to a wavelength range of about 10−10 to 10−14 meter
• discovered in 1900
• very energetic, accelerated electric charges (millions to billions of electronvolts and higher)
• usually extraterrestrial in origin. High-energy particles that fall on the Earth from space. Primary cosmic rays consist of nuclei of the most abundant elements, with protons (hydrogen nuclei) forming by far the highest proportion; electrons, positrons, neutrinos, and gamma ray photons are also present. The particle energies range from 10−11 J to 101 J (108 to 1020 eV) and as they enter the Earth's atmosphere they collide with oxygen and nitrogen nuclei producing secondary cosmic rays. The secondary rays consist of elementary particles and gamma -ray photons. A single high-energy primary particle can produce a large shower of secondary particles. The sources of the primary radiation are not all known, although the sun is believed to be the principal source of particles with energies up to about 1010 eV. It is believed that all particles with energies of less than 1018 eV originate within the Galaxy.
• nuclear reactions; excited nuclei returning to their ground state
• usually terrestrial in origin