TEMkonseptet

TEMkonseptet refers to the concept of transverse electromagnetic (TEM) wave propagation in transmission lines. It describes a mode in which electric and magnetic fields are entirely transverse to the direction of travel, with no field component along the line. In a TEM mode, the electric field E and magnetic field H lie in the cross-sectional plane of the line, and energy is carried by the Poynting vector S = E × H.

Key properties include a propagation speed determined by the line’s material parameters, v = 1/√(μ ε) = c/√(ε_r μ_r). There is no cutoff frequency for TEM waves, meaning they can exist at arbitrarily low frequencies on suitable lines. The mode is supported by two-conductor transmission lines, such as coaxial cables or parallel-wire lines, where a well-defined characteristic impedance Z0 = √(L/C) exists. The per-unit-length inductance L and capacitance C depend on the line geometry and dielectric; these determine Z0 and the signal behavior along the line.

In practice, TEM is fundamental to many RF and electrical engineering applications, underpinning how signals are transmitted over cables in telecommunications, audio/video systems, and networking. Its straightforward field distribution and lack of cutoff make it desirable for wideband, impedance-controlled signaling.

Limitations include that TEM cannot exist in hollow single-conductor waveguides, where boundary conditions enforce TE and TM modes with nonzero cutoff frequencies. In such structures, higher-order modes may appear only above certain frequencies. The TEM concept thus sits alongside TE and TM descriptions as part of the broader theory of transmission-line and waveguide operation.