From SEG Wiki
Jump to navigation Jump to search

{{#category_index:N|near-field}} The field near a source. Relationships near a source involve effects that attenuate rapidly with distance as well as those that attenuate more slowly (such as spherical divergence). At large distances many near-field phenomena are relatively unimportant. If the distance from the source is R and the wavelength is λ, near-field implies R<λ. In the near-field zone of an antenna, fields vary predominantly as the inverse cube of the distance. With EM methods, near-field implies receiver-transmitter separation less than three skin depths (q.v.). Compare far field. See Sheriff and Geldart (1995, 48).