Towards Accurate Dielectric Property Retrieval of Biological Tissues for Blood Glucose Monitoring

Abstract

An analytical formulation for relative dielectric con- stant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, filling factor A and the effective length leff of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity .T he values of A and leff are determined for each phantom from the resulting S-parameter response, using Particle Swarm Op- timization. Multiple non-linear regression is applied to produce equations for A and leff, expressed as a function of frequency and the phantom's relative dielectric constant. These equations are combined to form a new non-linear analytical equation, which is then solved using the Newton-Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with a commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.