Near-Field Antenna for Noninvasive Human Head Microwave Thermometry

Microwave radiometry is an emerging technology for noninvasive measurement of internal body temperature. This technique relies on the use of a near-field antenna placed on the skin that receives black body radiation from the tissues under it. Even for a well-matched antenna, mismatch is introduced from variations in the tissue layer properties and/or imperfect characterization of the dielectrics used for antenna assembly. This work demonstrates a design of a receiving antenna element for a human head-specific tissue stack, and a tuning procedure to improve impedance match. Measurements of a fabricated antenna against the forehead indicate that inaccurate characterization of the materials used for antenna assembly more significantly contribute to antenna mismatch than variations in the tissue properties of the forehead. Therefore, proper modeling of assembly materials, in addition to reasonably accurate tissue stack modeling, is crucial for near-field antenna design.