Fabrication and characterization of flexible polymer iron oxide composite substrate for the imaging antennas of wearable head imaging systems

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 (FeO.Fe₂O₃ ) for wearable head imaging systems is presented. Micro-scale FeO.Fe₂O₃ 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 FeO.Fe₂O₃ 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.