Shields

Shields or Shielding is the general term used for some type or form of protection.
==Radiation protection==
Radiation protection is a general term used in relation with nuclear radiation. Shielding is typically provided by physical means in form of layers of matter according to the half-value layer. As particle radiation is easily stopped in comparison to photons they are usually ignored. Amount of radiation by a source and the energetic value of the photons determine the actual half-value. Lead shielding is most effective.
Photon Energy(keV)	HVL (cm) 	HVL (cm) 	HVL (cm) 	HVL (cm) 	HVL (cm)	HVL (cm)
Photon Energy(keV)	lead(11.35 g/cm3)	iron(7.86 g/cm3)	aluminum(2.70 g/cm3)	concrete(2.4g/cm3)	air 	water(1.0 g/cm3)
100 	0.014 	- 	1.7 	- 	3.6×103 	4.1
500 	(0.38) 0.41 	1.0 	3.0 	3.3 	5.9×103 	(7.2) 7.3
1000 	0.88 	1.5 	4.3 	4.5 	8.3×103 	(9.8) 9.9
1500 	1.2 	1.8 	- 	5.6 	- 	12.0
2000 	1.36 	2.1 	5.7 	6.4 	13.4×103	(14.0) 17.3
3000 	1.5 	2.4 	- 	7.9 	- 	17.5
5000 	1.46 	- 	9.5 	- 	21.5×103	21.7
==Electromagnetic shielding==
Electromagnetic shielding covers a broad range of fields and purposes. The majority of shielding used is for protecting equipment, appliances or people against Electromagnetic interference or physical harm like cables, computers or a microwave oven.
===Electromagnetic pulse (EMP)===
An electromagnetic pulse is a pulse created by any kind of ionization or similar energetic flux. 
EMP is categorized into three groups: 
*high-frequency (E1 EMP)
*medium-frequency (E2 EMP)
*low-frequency (E3 EMP)
It can be natural phenomenon (coronal mass ejection, Geomagnetic storm, lightning) or artificial like a nuclear electromagnetic pulse. In an atmosphere the NEMP from a high-altitude nuclear explosion (HEMP) is very strong, "longer living" (microseconds), and far reaching due to compton scattering. In the vacuum of space the NEMP is very short lived (nanoseconds) due to the short half life and the quick dispersion of the relatively small mass of the bomb. Visual protection from a nuclear detonation is required even from a distance of one light second or more as has been researched in Project A119.
An EMP can also be created by an electromagnetic bomb (e-bomb). One method is the explosively pumped coaxial flux compression generator (FCG) or (explosive-driven ferromagnetic generator (EDFMG)) or simply flux generator. Another method is by Pulsed High-Power Microwave (HPM) created in the virtual cathode oscillator or vircator. It can be transported by a delivery system (CHAMP). An EMP effect can be caused by a powerful radar, or a microwave cannon (directed-energy weapon (DEW)). 
EMP protection is achieved by using the Faraday cage. In practice and the military, multiple meshes are sandwiched within high magnetic permeability metal alloy plating. These must be grounded to direct the energy away. However, in space, starships are threaten by space charge caused by thermionic emission, the low orbit plasma, a photovoltaic system, the magnetic induction process, and the interaction with the high energy electrons in the polar regions. The only way to deal with it is bleeding plasma, ion or electron by a thermionic cathode (TC) or a Field Emitter Array Cathode (FEAC).
===Electronic warfare (EW)===
Another form of warfare is Electronic warfare (EW) which typically refers to interference with electronic devices or disrupting communications e.g. Dembuth ECM or radio jamming or radar jamming, laser jamming against LIDAR or optical communication and IR jamming. ECM can be detected and countered by ECCM, Laser Irradiance Detector or LWS. Weaponized systems are dazzler, blinding laser, wikipedia:Pulsed energy projectile. EW also includes intelligence gathering (ELINT, SIGINT, COMINT). Information manipulation is also part of the game. For example, spoofing Global Positioning System (GPS), hence, misdirecting enemy forces or tying their movement altogether. Vessels with celestial navigation aren't affected of course. For a time, the Inertial Navigation System (INS) and Integrated GPS Anti-Jam System (IGAS) were solutions until the introduction of the paracompass. Protection against ELINT/SIGINT/COMINT is achieved by TEMPEST certification, encryption, and by following operations security. These are very vital measures in current Network-centric warfare (NCW).
===Magnetic shielding===
Physical magnetic shielding is used for shielding strong magnetic fields from magnets, speakers, small transformers and motors. For example for a sensitive circuit breaker or against corona discharge. However, strong magnetic fields are harder to shield because they tend to "saturate" the shielding material. 
In a fusion reactor, high power magnets keep hot fusion plasma from touching the reactor's surfaces.
magnetosphere
Flat/Bubble shield
*electrodynamic (ED) tethers
*plasma both works ways
*Radio frequency (RF) shielding
Alternatively, radio frequency (RF) shielding can be used against RF, ions and plasma.
Abh magnetic shield
==Cloak==
Cloaking or low observable or stealth refers to a different kind of protection in which the asset is removed from enemy awareness or influence. The simplest of all methods is using radio silence or EM emission control (EMCON).
===Acoustic===
acoustic quieting is usually applied to systems working within a medium such as an atmosphere or ocean. One approach is using insulation material like Anechoic tile or reducing vibration by using springs for footing. Another approach is to mitigate the sonic boom by reducing drag with a spike or reshaping it altogether.
===Magnetic===
Magnetic shielding can be used against magnetic mines or to avoid detection by a magnetic anomaly detector (MAD).
===IR===
Infrared (IR) cloaking can be achieved by lowering the asset's temperature or by spoofing thermography. Lowering termperature is done by using a coolant such as air or liquid or a material. A ceramic matrix could be used to absorb and irradiate in a different spectra. Electromagnetic radiation absorbent/shielding materials are commonly used in electromagnetic capability/electromagnetic interference (EMC/EMI).
Active IR cloaking can be achieved by projecting or adjusting the asset's thermal radiation such as the ADAPTIV system which uses the peltier_effect for thermoelectric cooling (TEC) and heating.
This type of cloaking could be exposed by multispectral imaging and hyperspectral imaging.
===Visual/Optical===
Passive camouflage employs a fixed pattern which makes recognition difficult from a distance. Other means gilley
Active camouflage employs phased-array optics (PSO) or realtime scanning and projection techniques to blend into the environment or projected adabtive pattern.
This type of cloaking could be exposed by multispectral imaging and hyperspectral imaging.
===Plasmonic cover===
This type is based on plasmonic metamaterial which uses a sort of surface polarisation effect known as surface plasmon polariton (SPP).
Another technique relies on electromagnetic metamaterials to bend electromagnetic waves such as microwaves (radar). However, the materials have a limited range within the electromagnetic spectrum.
This type of cloaking could be exposed by multispectral imaging and hyperspectral imaging.
===Gamma radiation===
Using radiation protection gamma radiation could be reduced. However, it's not economic to completely cloak an anti-matter drive.
===Ultraviolet===
Ultraviolet (UV) was a highly sought after technology such that its secrets remain obscured. It's supposedly achieved by quantum dots (QD) emitting scattering UV. UV seekers, especially of the UV-III spectra, have been feared for their ability to distinguish between materials and had been used since the early days of the legendary Hellfire and Stinger.
===Space-time cloaking (Event cloaking)===
This type can be achieved by using metamaterial to manipulate electromagnetic radiation in space and time in such a way that a certain collection of happenings, or events, is concealed from distant observers. 
===Radar===
Radar cloaking mostly relies on decreasing the radar cross-section (RCS). 
One approach is to absorb radar energy, hence, reducing reflection, by using Radar absorbing material (RAM). RAM could be 
*a coating incorporating iron particles in a resin
*radar-absorbent paint made from both ferrofluidic and nonmagnetic substances
*insulating material or tile such as neoprene polymer sheets with ferrite grains or conductive carbon black (nano-) particles embedded in the polymer matrix
The performance of these, particularly those using spherical particles, is dependent upon how closely the spheres are packed together. The RAM's high attenuation level and broad frequency range are important, therefore, to improve broad band coverage multiple layers are used. They are separated by some kind of a band pass filter. 
Similarly, reducing reflection can be achieved by using composite material such as carbon fiber reinforced polymer in the construction.
Another approach is reflecting radar energy away from the radar source/receiver based on Petr Ufimtsev's theory and Huygens–Fresnel principle. This can be done by shaping the outer surface such that the reflecting angle is always different and area with similar angles are minimized. To further mitigate electromagnetic radiation reflection the internal structure could be designed to trap, redirect, and reflect radar energy elsewhere.
Other measures aim to reduce operational emission of sensors and communication systems by using low probability of intercept signals
This type of cloaking could be exposed by phased array, infra-red search and track (IRST) and by more ellaborate radar imaging such as passive covert radar (PSR) MASINT.
It's also possible to mark a target with endohedral metallofullerene radiotracers.DAWSON W. CAGLE, et al., In vivo studies of fullerene-based materials using endohedral metallofullerene radiotracers, 1998
==Impact shield==
whipple shield
==Heat shield==
==Gravitational shielding==
passive, not to be mistaken with active antigravity systems like the repulsor etc.
===Gravitic shield===
==Subspace shield==
==Null space==
==References==
Category: Technology