Electromagnetic Field

(redirected from EM field)
Also found in: Dictionary, Medical.
Related to EM field: electromagnetic

Electromagnetic field

A changing magnetic field always produces an electric field, and conversely, a changing electric field always produces a magnetic field. This interaction of electric and magnetic forces gives rise to a condition in space known as an electromagnetic field. The characteristics of an electromagnetic field are expressed mathematically by Maxwell's equation. See Electric field, Electromagnetic radiation, Electromagnetic wave

Electromagnetic Field


a special form of matter that mediates the interaction between charged particles (seeFIELD).

In a vacuum, an electromagnetic field is characterized by the electric field strength E and the magnetic flux density B, which determine the forces exerted by the field on stationary or moving charged particles. In addition to the vectors E and B, which are measured directly, an electromagnetic field may be characterized by a scalar potential φ and a vector potential A. The potentials are not uniquely determined, a gauge transformation being required.

In a medium, an electromagnetic field is also characterized by the following two auxiliary vector quantities: the magnetic field strength H and the electric flux density D (seeINDUCTION, ELECTRICAL AND MAGNETIC).

The behavior of electromagnetic fields is a subject of classical electrodynamics. In an arbitrary medium, the behavior of such fields is described by Maxwell’s equations. The equations make it possible to determine the fields as a function of the distributions of charge and current.

Microscopic electromagnetic fields, which are produced by individual elementary particles, are characterized by the strengths of the microscopic electric field (e) and the microscopic magnetic field (h). The mean values of the microscopic field strengths are related to the macroscopic characteristics of an electromagnetic field in the following way: ē = E and h̄ = B. Microscopic fields satisfy the Lorentz-Maxwell equations.

The electromagnetic field of stationary charged particles or of charged particles moving with constant velocity is inseparably bound to the particles. When particles are accelerated, their electromagnetic field is “torn away” and exists independently in the form of electromagnetic waves.

The generation of an electromagnetic field by an alternating magnetic field and the generation of a magnetic field by an AC electric field show that alternating electric and magnetic fields do not exist separately, that is, are not independent of one another. According to the theory of relativity, the components of the vectors that characterize an electromagnetic field form a single physical quantity called the electromagnetic field tensor. The components of the tensor are transformed upon a transition from one inertial reference frame to another, in accordance with the Lorentz transformations.

At high field frequencies, the quantum properties of an electromagnetic field become important. In this case, classical electrodynamics is not applicable and an electromagnetic field is described by quantum electrodynamics.


Tamm, I. E. Osnovy teorii elektrichestva, 9th ed. Moscow, 1976.
Kalashnikov, S. G. Elektrichestvo, 4th ed. Moscow, 1977. (Obshchii kurs fiziki, vol. 2.)
Feynman, R., R. Leighton, and M. Sands. Feinmanovskie leklsii po fizike, vols. 5–7. Moscow, 1966–67.
Landau, L. D., and E. M. Lifshits. Teoriia polia, 6th ed. Moscow, 1973. (Teoreticheskaia fizika, vol. 2.)
Landau, L. D., and E. M. Lifshits. Elektrodinamika sploshnykh sred. Moscow, 1959.


electromagnetic field

[i¦lek·trō·mag′ned·ik ′fēld]
An electric or magnetic field, or a combination of the two, as in an electromagnetic wave.
References in periodicals archive ?
The frequency dependence of a response function for a given observation site can be estimated through spectrum analysis (7) of obtained time series data for the EM field components.
Application of the SPM method on (3) and (4) above leads to the following analytic expressions for the EM field in the higher half space (x > 0) [10], [11]
As argued above, this method developed in this paper is realized thanks to the combination of a calculation method enabling to determine the EM fields disturbing the wiring systems independently to the evaluation method of the susceptibility.
The EM field is modeled by a damped harmonic oscillator at frequencies around the lossless resonant frequency [[omega].
The first step is to develop technology that can detect the EM field of the human body remotely.
The existence of an EM field includes both electric and magnetic fields.
The EM field results, which will be presented, reflect the following two activities:
In the case of a microstrip transmission line, the EM field exists both in the air above and the dielectric substrate below the microstrip line.
The model is based on a long-range interaction of the water molecule dipoles and local EM field resulting in a coherent emission of photon pulses propagating via tunneling.
Advantages that may be gained by coupling advanced EM field solvers with high frequency circuit simulation for LTCC design were demonstrated.