Antennas for near-field radiothermometry

Abstract

The application of electrically-small antennas in the area of subsurface radiometry make possible measurements of the quasi-stationary field of thermal emission (evanescent modes at interface). New one-wavelength methods of non-invasive temperature sounding of absorbing media, such as water and living tissue, can be developed using such measurements. The quasi-stationary field component is formed in media in a different way compared to the ordinary used wave (propagating) component. Our theoretical analysis shows that the effective depth of the formation of the quasi-stationary component depends on the height of the antenna above the surface of a medium and on the antenna size. At the surface this skin-depth could be very small (for small antennas); it increases with antenna height, and at the height comparable to the wavelength in the medium it converges to skin-depth for the wave component of the thermal emission.