EMR carries energy — sometimes called radiant energy — through space continuously away from the source ( this is not true of the near-field part of the EM field ).

This is in contrast to dipole parts of the EM field close to the source ( the near-field ), which varies in power according to an inverse cube power law, and thus does not transport a conserved amount of energy over distances, but instead dies away rapidly with distance, with its energy ( as noted ) either rapidly returning to the transmitter, or else absorbed by a nearby receiver ( such as a transformer secondary coil ).

Whereas the magnetic part of the near-field is due to currents in the source, the magnetic field in EMR is due only to the local change in the electric field.

In a similar way, while the electric field in the near-field is due directly to the charges and charge-separation in the source, the electric field in EMR is due to a change in the local magnetic field.

Both of these processes for producing electric and magnetic EMR fields have a different dependence on distance than do near-field dipole electric and magnetic fields, and that is why the EMR type of EM field becomes dominant in power “ far ” from sources.

A common misconception is that the E and B fields in electromagnetic radiation are out of phase because a change in one produces the other, and this would produce a phase difference between them as sinusoidal functions ( as indeed happens in electromagnetic induction, and in the near-field close to antennas ).

The Huygens – Fresnel principle ( named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel ) is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction.

The use of shorter wavelengths of light, such as the ultraviolet, is one way to improve the spatial resolution of the optical microscope, as are devices such as the near-field scanning optical microscope. Sarfus, a recent optical technique increases the sensitivity of standard optical microscope to a point it becomes possible to directly visualize nanometric films ( down to 0. 3 nanometre ) and isolated nano-objects ( down to 2 nm-diameter ).

A part of the " near-field " close to the transmitter, is part of the changing electromagnetic field, but does not count as electromagnetic radiation.

For an optical fiber, the effective mode volume is the square of the product of the diameter of the near-field pattern and the sine of the radiation angle of the far-field pattern.

The diameter of the near-field radiation pattern is defined here as the full width at half maximum and the radiation angle at half maximum radiant intensity.

Inductive ( magnetic ) and capacitive ( electric ) field strengths are near-field effects, and are only important if the device under test ( DUT ) is designed for location close to other electrical equipment.

Intermediate-field region: For an antenna, the transition region -- lying between the near-field region and the far-field region -- in which the field strength of an electromagnetic wave is dependent upon the inverse distance, inverse square of the distance, and the inverse cube of the distance from the antenna.

The near-field pattern is most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical surface enclosing it.

This allows the use of near field speckle analysis to detect the scattering distribution ; this is the so-called near-field scattering

In order to derive the intensity behind the circular obstacle using this integral one assumes that the experimental parameters fulfill the requirements of the near-field diffraction regime ( the size of the circular obstacle is large compared to the wavelength and small compared to the distances g = P < sub > 0 </ sub > C and b = CP < sub > 1 </ sub >).

However, lower-frequency dielectric heating, as described in the aforementioned patent, is ( like induction heating ) an electromagnetic heating effect, which itself is the result of the so-called near-field effects that exist in an electromagnetic cavity that is small compared with the wavelength of the electromagnetic field.

Other flavors include reflection EELS ( including reflection high-energy electron energy-loss spectroscopy ( RHEELS ), typically at 10 to 30 keV ) and aloof EELS ( sometimes called near-field EELS, in which the electron beam does not in fact strike the sample but instead interacts with it via the long-ranged Coulomb interaction ; aloof EELS is particularly sensitive to surface properties but is limited to very small energy losses such as those associated with surface plasmons or direct interband transitions ).

For example, although far-field thermal radiation at distances from surfaces of more than one wavelength is generally not coherent to any extent, near-field thermal radiation ( i. e., radiation at distances of a fraction of various radiation wavelengths ) may exhibit a degree of both temporal and spatial coherence.

* near-field ( mathematics ), an algebraic structure

an antenna has a static charge, it cannot contribute to the electrical near-field in any way that varies in time, and the same is true for any constant currents that may flow in an antenna.

The term " near-field region " ( also known as the " near-field " or " near-zone ") has the following meanings with respect to different telecommunications technologies:

Also, in the part of the near-field closest to the antenna ( called the " reactive near-field ", see below ), absorption of electromagnetic power in the region by a second device has effects that feed-back to the transmitter, increasing the load on the transmitter that feeds the antenna by decreasing the antenna impedance that the transmitter " sees ".

Thus, the transmitter can sense that power has been absorbed from the closest near-field zone, but if this power is not absorbed by another antenna, the transmitter does not supply as much power to the antenna, nor does it draw as much from its own power supply.

In this reactive region, not only is an electromagnetic wave being radiated outward into far-space but there is a " reactive " component to the electromagnetic field, meaning that the nature of the field around the antenna is sensitive to, and reacts to, EM absorption in this region ( this is not true for absorption far from the antenna, which has no effect on the transmitter or antenna near-field ).

It has been claimed that Stubblefield invented the radio before either Nikola Tesla or Guglielmo Marconi, but his devices seem to have worked by audio frequency induction or, later, audio frequency earth conduction ( creating disturbances in the near-field region ) rather than by radio frequency radiation for radio transmission telecommunications.

The diffraction horn has been popular in monitor designs and for near-field public address applications which benefit from its wide horizontal dispersion pattern.

As distance from the antenna grows, the near-field effects ( as dipole fields ) die out more quickly, and only the " radiative " effects that are due to real photons remain as important effects.

Although electric charges do exist and may create static electric fields, the oscillating electric part of EM near-fields that is created by an electric potential in the radiator always shows a dipole nature, because the source of the electric part of the EM near-field is created from an electrical neutral conductor only in a way that temporarily creates a dipole or multipole.

In a sense, the near-field offers energy that is available to a receiver only if the energy is tapped, and this is sensed by the transmitter by means of answering electromagnetic near-fields emanating from the receiver.

In electrical engineering, evanescent waves are found in the near-field region within one third of a wavelength of any radio antenna.

The " transition zone " between these near and far field regions, extending over the distance from one to two wavelengths from the antenna, is the intermediate region in which both near-field and far-field effects are important.

The " near-field ", which is inside about one wavelength distance from the antenna, is a region in which there are strong inductive and capacitative effects from the currents and charges in the antenna that cause electromagnetic components that do not behave like far-field radiation.

However, these boundary regions are a fraction of one wavelength within the near-field.

The radiative near-field ( also called the " Fresnel region ") covers the remainder of the near-field region, from λ / 2π out to λ ( one full wavelength ).

Further out into the radiative near-field ( one half wavelength to 1 wavelength from the source ), the E and H field relationship is more predictable, but the E to H relationship is still complex.

As an example of such an effect, power is transferred across space in a common transformer or metal detector by means of near-field phenomena ( in this case inductive coupling ), in a strictly " short-range " effect ( i. e., the range within one wavelength of the signal ).

As one gets closer and closer to the source ( smaller r ), approaching the near-field, other powers of r become significant.

Rather, in the near-field, it is sometimes useful to express the contributions as a sum of radiating fields combined with evanescent fields, where the latter are exponentially decaying with r. And in the source itself, or as soon as one enters a region of inhomogeneous materials, the multipole expansion is no longer valid and the full solution of Maxwell's equations is generally required.

* As with proximity card technology, near-field communication uses magnetic induction between two loop antennas located within each other's near field, effectively forming an air-core transformer.

Charges and currents directly produce the near-field.

A part of the " near-field " close to the transmitter, forms part of the changing electromagnetic field, but does not count as electromagnetic radiation.

Both of these fields make up the near-field near the EMR source.

The far-field ( EMR ) depends on a different mechanism for its production than the near-field, and upon different terms in Maxwell ’ s equations.

dynamic collisional quenching, near-field dipole-dipole interaction ( or resonance energy transfer ), internal conversion, and intersystem crossing.

Circuits and materials close to the inductor will have near-field coupling to the inductor's magnetic field, which may cause additional energy loss.

Two types of diffraction are distinguished, depending upon the separation between the source and the screen: Fraunhofer diffraction or far-field diffraction at large separations and Fresnel diffraction or near-field diffraction at close separations.

For this demonstration they employed a near-field Talbot Lau interferometer.

Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern, or near-field radiation pattern, may also be used as a synonym for the near-field pattern or Fresnel pattern.

This refers to the positional dependence of the electromagnetic field in the near-field, or Fresnel region of the source.

The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation.