lähikenttää

Lähikenttä is a Finnish term that translates to "near field" or "close field" in English. It refers to a specific region or area of interest, often in a scientific or technical context, that is located close to a point of origin or measurement. The concept of a lähikenttä is commonly encountered in fields such as electromagnetism, acoustics, and optics.

In electromagnetism, the lähikenttä describes the region of electromagnetic radiation close to an antenna or a radiating source. Within this region, the electric and magnetic fields are strongly coupled and vary rapidly with distance. The behavior of electromagnetic waves in the lähikenttä is significantly different from that in the far field, where the radiation is more coherent and can be described by plane waves. Understanding the lähikenttä is crucial for designing and analyzing antennas and other radiating systems.

Similarly, in acoustics, the lähikenttä relates to the sound pressure levels and particle velocity close to a sound source. The acoustic field in this region is complex, with significant spatial variations. Measurements in the lähikenttä can provide detailed information about the source's directivity and emission characteristics.

In optics, the term can be applied to the region near a lens or aperture where diffraction effects are pronounced. The wave propagation in the lähikenttä is governed by Fresnel diffraction, which differs from the Fraunhofer diffraction observed in the far field. The lähikenttä concept helps in understanding how light behaves immediately after interacting with optical elements.

The specific characteristics and importance of the lähikenttä depend heavily on the physical phenomenon being studied and the nature of the source. It represents the immediate environment around a phenomenon before its more distant and predictable behavior becomes dominant.