Near Field Microwave Radiometric Weighting Functions for Multilayered Materials

Abstract

A modal method is used for the determination of the near field weighting functions related to the power transmitted from a rectangular waveguide aperture towards a lossy material and, by reciprocity, to the corresponding radiometric signals created by the thermal noise emission. This method is applied to homogeneous or multilayered material, such as in microwave radiometry applied to medicine for non invasive thermometry of the subcutaneous tissues. From the knowledge of the weighting functions, we propose a new definition for the volume of material coupled with the probe, as radiometric measurement terms. We present examples of such coupled volumes, as a function of frequency or size of the probe.