Near and far field

Summary

The near field and the far field are the regions close to and far from a radiating source, where the electromagnetic field behaves differently. In the far field, the field is a spherical wave: it falls off like $1/r$, is transverse, and carries energy outward. In the near field, terms falling off like $1/r^2$ and $1/r^3$ dominate. There much of the energy is stored and exchanged with the source rather than radiated. The distinction organizes antenna design, measurement and wireless power transfer.