Effects of the permittivity and conductivity of human body for normal-mode helical antenna performance

Abstract

In the capsule endoscope application, a coil type antenna namely a normal-mode helical antenna was used because of suitable shape to deploy in a cylindrical capsule. In antenna design, many human tissue conditions such as a stomach, fat and skin should be taken into account. Here, losses of human tissues are changed depending on personal differences and basic feature of the antenna in numerical simulation. At some tissue examples, antenna input resistance (Rin) increases by the permittivity (εr) and conductivity (σ) effect were shown. In order to establish antenna design method, physical mechanism of antenna input resistance increases should be clarified. In this paper, input resistance increases are numerically clarified for all changing conditions of permittivity and conductivity through electromagnetic simulations. As for an antenna, self-resonant normal-mode helical antenna of 0.2 wavelength is designed at 402 MHz. In the case of εr = 11.6, the Rin value of 0.63 Ω at σ = 0 [S/m] is increased to the maximum value of Rin = 35 Ω at σ = 0.3 [S/m]. For understanding input resistance increases mechanism, electric field distributions around antenna are also shown. To ensure simulation adequateness, a measured result of input resistance is compared with simulated result.