Analysis and Verification of a Proposed Antenna Design for an Implantable Rfid at 915 Mhz

Abstract

This work focused on design and analysis of an antenna to be used with an RFID tag that is implanted in human brain tissue. The goal is to maximize the power transferred between the external RFID measurement system and the implanted RFID tag while minimizing the power dissipated within the surrounding tissue. The commercial computational electromagnetics software package COMSOL, based on finite element method (FEM) has been used for design process. The COMSOL models have been validated against additional simulations using the FEKO commercial package based on method of moments (MOM) as well as against measurement of test antenna structures radiating in bulk homogeneous medium. The proposed antenna geometry is compatible with the human tissue and viable for use in implantable RFID Tag. The proposed antenna is a planar folded dipole made from a gold conductor that acts as a biocompatible material. The metal thickness is 1 micrometer and the overall antenna dimensions are 22 mm 3.5 mm. The antenna structure also includes a dielectric substrate and an acrylic coating. The antenna impedance is 28+j201.5 ohms at 915 MHz. The inductive reactance is high enough to compensate the capacitive reactance of RFID tag and the antenna resistance is close to effective chip resistance providing a conjugate match. This antenna fulfills the criteria for minimizing the power dissipation within the human tissue. Also, a radiation efficiency of 87% is achieved with this antenna at 915 MHz. The quality factor of greater than 10 is achieved which is sufficient to turn on the diodes in the electronic circuit of the RFID tag due to the high D.C voltage obtained.