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The near field refers to places nearby the antenna conductors, or inside any polarizable media surrounding it, where the generation and emission of electromagnetic waves can be interfered with while the field lines remain electrically attached to the antenna, hence absorption of radiation in the near field by adjacent conducting objects detectably affects the loading on the signal generator ...
A changing electromagnetic field which is physically close to currents and charges (see near and far field for a definition of "close") will have a dipole characteristic that is dominated by either a changing electric dipole, or a changing magnetic dipole. This type of dipole field near sources is called an electromagnetic near-field.
The near field has strong effects its source, with any energy withdrawn by a receiver causing increased load (decreased electrical reactance) on the source. The near field does not propagate freely into space, carrying energy away without a distance limit, but rather oscillates, returning its energy to the transmitter if it is not absorbed by a ...
Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-field pattern or Fresnel pattern. [4] This refers to the positional dependence of the electromagnetic field in the near field , or Fresnel region of the source.
The near field is the region around a source where the electromagnetic field can be evaluated quasi-statically. If target distance from the multipole origin r = ‖ x ‖ 2 {\displaystyle r=\|\mathbf {x} \|_{2}} is much smaller than the radiation wavelength λ = 2 π / k {\displaystyle \lambda =2\pi /k} , then k r ≪ 1 {\displaystyle kr\ll 1} .
Some observed electromagnetic phenomena cannot be explained with Maxwell's equations if the source of the electromagnetic fields are the classical distributions of charge and current. These include photon–photon scattering and many other phenomena related to photons or virtual photons , " nonclassical light " and quantum entanglement of ...
Very weak electromagnetic fields disrupt the magnetic compass used by European robins and other songbirds, which use the Earth's magnetic field to navigate. Neither power lines nor cellphone signals are to blame for the electromagnetic field effect on the birds; [ 89 ] instead, the culprits have frequencies between 2 kHz and 5 MHz.
A near-field magnetic induction (NFMI) communication system is a short range wireless physical layer that communicates by coupling a tight, low-power, non-propagating magnetic field between devices. The concept is for a transmitter coil in one device to modulate a magnetic field which is measured by means of a receiver coil in another device.