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 (R in) increases by the permittivity (ε r) 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 ε r = 11.6, the R in value of 0.63 Ω at σ = 0 [S/m] is increased to the maximum value of R in = 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.

Increase of Input Resistance of a Normal-Mode Helical Antenna (NMHA) in Human Body Application

“…However, the effects of σ and εr as the key factors in the human body on the antenna input resistance are yet to be determined. In previous studies, it was already clarified through simulation that when the conductivity of dielectric material was increased, the input resistance also increased [19]. Another paper also presented that the σ and εr of human tissue are among the factors that have significant effects to the surface impedance, which has further affected the Rin of NMHAs in human tissue [35].…”

“…However, the implantable antennas face more difficulties and challenges than a wearable antenna for on-body communication due to the complex human tissue conditions. The human body is often referred to as a "lossy" medium due to the performance of antennas that is easily affected by the conductivity (σ) and permittivity (ε r ) inside the human body [18][19][20][21]. Due to the lossy characteristic of the human body, the radio wave degradation has been very severe.…”

Thermochromic Tissue Phantoms for Evaluating Temperature Distribution in Simulated Clinical Applications of Pulsed Electric Field Therapies

“…While tuned for liver tissue, the model could be further refined to match the tissue-specific electrical properties of various tissues through these parameters and the addition of nanomaterials such as carbon microcoils could be used to better recreate the frequency-dependent conductivity at higher frequencies if needed. 63 The model was fabricated as a two-part phantom, with a reusable large base and smaller plug inserted into a center base-void to allow plug removal for rapid evaluation of temperature fields in the volumes nearest to the applicator and continued use of the larger base. Use of this two-part system can help reduce costs of the phantom and studies, and the plug diameter can be modified based on predicted ablation size.…”

VHF/UHF wideband slim monopole antenna with meander line loading and slot-modified ground designed by characteristic mode analysis

“…But they have narrow bandwidths which are not suitable for current broadband applications. Normal-mode helical antennas [1,2,3,4] are with slim and short structures, while their bandwidths are also narrow. In addition, there are lots of wideband but not slim antennas.…”