Summary
International Symposium on Antennas and Propagation
2012
Session Number:POS2
Session:
Number:POS2-15
Near-field Gain Measurement of Waterproofed Shielded Loop Antenna in Tissue-equivalent Liquid
Hidenori Toyoshima, Nozomu Ishii, Lira Hamada, Soichi Watanabe,
pp.-
Publication Date:2012/10/29
Online ISSN:2188-5079
Summary:
Recently, the methodology to evaluate SAR (Specific Absorption Rate) for the wireless energy transmission system which uses the phenomenon of magnetic-field resonance has been required. For the estimation of SAR for the mobile communication devices, electric-field probes can be used in the tissue-equivalent liquid. However, the magnetic-field is dominant at the frequencies which might be allocated for the wireless energy transmission. Therefore, the methodology to evaluate SAR with the magnetic-field probes should be developed. Also, the magnetic-field probe should be calibrated by relating its voltage to the magnetic-field intensity produced by reference antennas at those frequencies. According to our previous studies, the calibration of the electric-field probe is based on the extended Friis transmission formula and two-antenna method. In the case that the distance between two antennas is not so long that the far-field condition cannot be satisfied, the near-field gain should be introduced to find the behavior of the electric-field intensity near the reference antennas. In this paper, a waterproofed shielded loop antenna operated in the liquid at 30MHz as reference antenna is designed, and the near-field gain of this antenna is measured by our gain measurement system to calibrate the magnetic-field probe. As a result, we confirm that the theoretical curve of the near-field gain can be derived from the extended Friis transmission formula and the far-field gain can be estimated by use of curve fitting technique. Thus, it is found that our gain measurement method can apply to the shielded loop antenna in the liquid.