Millimeter-resolution E-field probe for isotropic measurement in lossy media between 100 MHz and 20 GHz

Abstract

Currently, most advanced isotropic E-field probes for near-field measurements in lossy dielectric media have a tip diameter of typically 4-6 mm, housing three 2-3 mm long sensors. Although these probes are very well suited for many applications, their general use is constrained by several limitations: (1) upper frequency range of <4 GHz in tissue simulating liquids, (2) spatial resolution of a few millimeters, 3() unsuitable for measurements closer than 3-5 mm from any media boundary (boundary effects); and therefore (4) inapplicable for assessment of the induced field strengths in structures of a few millimeters. On the other hand, many current and future research projects require evaluation of the field distributions for frequencies larger than a few gigahertz, for measurements within small structures (e.g., in in vitro and in vivo experiments), for evaluations of special physical interactions such as strongly nonhomogeneous field distributions or characterization of larger probes, etc. A new probe has been developed which is applicable for frequencies well above 10 GHz in tissue-like media and provides a spatial resolution of at least 1 mm. Although it is a one sensor probe, it has been designed such that the isotropic measurement (spherical isotropy: <0.2 dB) can be obtained simply by taking three measurements each shifted by 1200 rotation around the probe's axis. The probe has been fully characterized and tested in various applications.