Technique for Calibrating Miniature Electric-Field Probes for Use in Microwave Bioeffects Studies at 2450 MHz: Evaluation and Calibration of BRH - NARDA Probes

摘要

A set of miniature probes for determining electric fields in tissue was evaluated and calibrated for use in microwave bioeffects studies at 2450 MHz. The calibrations in air and tissue-equivalent liquids were carried out using a new S-band waveguide technique. The air calibration using waveguide has an accuracy of + or - 10% compared to + or - 18% for our anechoic-chamber calibration. The average probe sensitivity in air is 1.0 mV/mW per sq cm for the five probes calibrated and varies slightly with power density and probe. To estimate probe sensitivity in tissue, a section of waveguide is filled with a tissue-equivalent liquid and is separated from the air-filled waveguide by a very thin (0.25 mm) planar spacer. The probe response is measured as a function of position on either side of the spacer and extrapolated to the interface. The ratio of probe sensitivity in air to that in test liquid is then determined using the continuity of tangential E field across the spacer. Liquids with dielectric properties simulating both wet and dry tissues were used. For the water-glycerol solution modelling wet tissue the probes are 3.0 + or - 0.6 times more sensitive to E superscript 2 than for air. When used in tissue the total calibration error is estimated to be + or - 30% for E superscript 2 and + or - 40% for the specific absorption rate at the site. One of the problems with this probe design, the mechanical weakness near the tip, has been eliminated in newer designs. The other problem, that the size of the probe tip (approximately 3 mm) is too large for optimal use in small-animal organs, is more difficult to solve. (Author)