Fabrication and Characterization of Flexible Polymer Iron Oxide Composite Substrate for the Imaging Antennas of Wearable Head Imaging Systems

Abstract

Given the increased interest in wearable electromagnetic imaging systems, developing a low-cost, lightweight, flexible, and conformal customized substrate to accommodate the imaging antenna array is essential. The characterization and assessment of a custom-made composite substrate using a flexible polymer poly-di-methyl-siloxane (PDMS) and magnetite iron oxide ( ${\text{FeO.Fe}}_{2}{\text{O}}_{3}$ ) for wearable head imaging systems is presented. Micro-scale ${\text{FeO.Fe}}_{2}{\text{O}}_{3}$ particles are homogeneously combined with PDMS in different ratios to build the flexible engineered magneto-dielectric (MD) composite substrate. Besides the low cost, fabrication simplicity, and durability, the magnetite ${\text{FeO.Fe}}_{2}{\text{O}}_{3}$ particles can be used to control the relative permittivity and permeability over a wide range of values to suit the proposed application. The permittivity, permeability, and losses of the developed substrate are extracted using a custom-made two-port multilayer microstrip transmission line test fixture with the help of conformal mapping algorithms. The characterization is performed across the microwave frequency range 1.2–4 GHz, which is widely adopted for head imaging. The extracted permittivity is successfully verified by using a Keysight 85070E dielectric slim probe kit.