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|Very low frequency (VLF)||105–104||3x103–3x104||electronic circuitry|
|Low frequency (LF)||104–103||3x104–3x105||electronic circuitry|
|Medium frequency (MF)||103–102||3x105–3x106||electronic circuitry|
|High frequency (HF)||102–101||3x106–3x107||electronic circuitry|
|Very high frequency (VHF)||101–100||3x107–3x108||electronic circuitry|
|Ultra high frequency (UHF)||100–10-1||3x108–3x109||electronic circuitry|
|Super high frequency (SHF, microwave)||10-1–10-2||3x109–3x1010||electronic circuitry|
|Extremely high frequency (EHF, microwave)||10-2–10-3||3x1010–3x1011||electronic circuitry|
|Far infrared (FIR)||3x10-5–3x10-6||1013–1014||incandescent, fluorescent, laser|
|Near infrared (NIR)||3x10-6–7x10-7||1014–4x1014||incandescent, fluorescent, laser|
|Visible light||7x10-7–4x10-7||4x1014–7x1014||incandescent, fluorescent, laser|
|Near ultra-violet (UV I)||4x10-7–10-8||7x1014–3x1016||incandescent, fluorescent, laser|
|Deep ultra-violet (UV II)||10-8–10-9||3x1016–3x1017||incandescent, fluorescent, laser|
|Soft X-rays||10-9–10-10||3x1017–3x1018||cathode ray bombardment, laser|
|Hard X-rays||10-10–10-11||3x1018–3x1019||cathode ray bombardment|
|Soft Gamma-rays||10-11–10-12||3x1019–3x1020||nuclear decay|
|Hard Gamma-rays||10-12–10-13||3x1020–3x1021||nuclear decay|
|Cosmic rays||10-13–||3x1021–||extra terrestial|
Electromagnetic shielding generally means shielding against microwave and radio frequency radiation. Shielding against infrared, light, ultraviolet and X-ray radiation technically ought to be included, and often is, albeit inadvertently (inasmuch that a metal box designed to shield against the first two will probably shield against all the others as well, with the possible exception of X-rays).
Similarly, the metal box can also be made to shield against electric fields on their own, and depending on the choice of metal for the box, against magnetic fields, too.
These topics are briefly discussed, next.
A conductive layer to shield against EMI will also greatly protect against electrostatic fields (acting as a Faraday cage) and hence against the concerns of electrostatic discharge (ESD), but it needs to be connected to ground, which EMI protection does not necessarily need. Also, the operatives on the production line might need to be earthed (using mats and wrist-straps), and to use equipment, materials and clothing that do not generate static electric fields. Indeed, one major difference is that EMI is a concern during the running of the equipment, while ESD tends to be a concern during its fabrication.
Equipment that is designed to work at 12V might need protection on its power supply leads, and data lines, from any voltages that go well above this voltage. This would protect it against inadvertent connection of faulty power supplies (over voltage protection); it might also provide protection against transient voltage surges (TVS), and from static electricity and lightning strikes. Thus, this, too, overlaps with the concerns for ESD protection.
This includes the concerns of protecting the outside world from internally generated magnetic fields: from motor windings, for example. It also includes the concerns of protecting the sensitive contents from externally generated magnetic fields: magnetic "short-circuits" to protect sensitive equipment and data-storage media.
Just as a metal box provides a short circuit for an electrostatic field, so a box made of a suitable metal (notably iron, with nickel and cobalt as more exotic alternatives) provides a short circuit for a magnetic field. The field lines strike the box at the given incident angle, bend to follow the contours of the box, and leave on the other side of the box at roughly the same angle as they had entered. By following the contours of the box, the inside of the box is turned into a protected island, free from external field lines.
This includes the concerns of protecting the outside world from internally generated radiation (from switch-contacts, motor commutators and arc-welders that each generate UV, cathode-ray tubes that generate X-rays, and nuclear sources that generate gamma-rays). It also includes the concerns of protecting the sensitive contents from externally generated radiation (such as from arc-welding, a nearby medical scanner, solar exposure and cosmic rays).
In general, the amount of matter in the shield is important (or rather the thickness and the density), for the given wavelength of radiation. A box with a metal coating should be enough to block the passage of visible light, and near ultraviolet, but a solid metal box might be needed for the even shorter wavelengths. For X-rays, the box would need to be thick, and made of lead (Pb), say, in preference to aluminium (Al).
For cosmic rays, and radiation from nuclear sources, the incident particles are so energetic, and able to knock out new particles, that the complexity of the atoms in the shielding starts to become important, too. It is all very well that lead would be good at stopping the primary radiation, but it would generate so many secondary rays that it often cannot be used (in the case of nuclear sources, the gamma rays might be accompanied by fast moving neutrons, for which this is even more relevent). The ideal substance then becomes the lightest, namely hydrogen, and hence needs to be deployed in extremely thick walls, in enormous quantities. Consequently, hydrogen-rich substances, such as water, become the shielding materials of choice.
As before, this includes the dual concerns of protecting the outside world from internally generated radiation, and protecting the sensitive contents from externally generated radiation. There is also the problem of protecting against heat conduction and convection, which, of course, overlaps with the issues of thermal shielding and thermal insulation.