Synthesis and use of bio-based dielectric substrate for implanted radio frequency antennas

Equipped with precision sensors/antenna modules combined with integrated processing and telemetry circuitry, wireless implants that are both biocompatible and biodegradable are important devices for monitoring patient's conditions and patient's safety. In this article we report on the development, design, and testing of a bio-based monopole radio frequency (RF) sensor/antenna module for potential use in human health applications. The module is built on a dielectric substrate biocomposite made of 0.5:1.0 ratio of polylactic acid (PLA) to sunflower carbon substrate (SCS) produced via pyrolysis of seeds shells. Findings for the SCS include optimized reactor yields around 7.9 wt.% at 500°C, a 0.27:1.0 fixed to elemental carbon content, dielectric constant near 3.4, loss factor between 0.0 and 0.4 measured in the 1 to 6 GHz frequency range. The PLA-SCS biocomposite exhibited comparable dielectric properties to those of pure SCS, a 17% elastic modulus increase, and over 500% increase in hardness. Numerical simulation of the designed sensor/antenna module agreed fairly well with the experimental validation results. Tests of the fabricated sensor/antenna module on water, soil and muscle tissue phantom, as well as implanted inside muscle tissue phantom, via the reflection coefficient (S) and in a communication link via the transmission coefficient (S) confirmed use and applicability of the developed antenna.