Defect Characterization in Gel Phantom Using Ac Impedance Spectroscopy

Abstract

Gel phantoms are useful materials for medical diagnostics and impact testing. The gel phantoms can be tailored to suit various tissues from the bulk, microscopic and molecular components. These components have responses under an AC electric field. In this work, a gel phantom was prepared using a commercially-available gel powder. Cylindrical samples with varying degrees of defects were cut from the prepared gel phantom and tested using an AC impedance analyzer. The defects were created by piercing a needle along the center plane of the sample and the degree of defects was varied by increasing the number of piercings in the sample. The conductivity of the sample at lower frequencies was influenced by the mechanism involved in water leakage due to piercing while the conductivity at higher frequencies was dominantly affected by space charge relaxation and structural conductivity barriers. The Nyquist plots obtained were seen to exhibit modified Randles-type behavior. Equivalent circuit fittings showed the parameters to be distinct with varying degrees of defects.