  We are aiming to identify the thin insulating inhomogeneities and small
conductive inhomogeneities inside an electrically conducting medium by using
multi-frequency electrical impedance tomography (mfEIT). The thin insulating
inhomogeneities are considered in the form of tubular neighborhood of a curve
and small conductive inhomogeneities are regarded as circular disks. Taking
advantage of the frequency dependent behavior of insulating objects, we give a
rigorous derivation of the potential along thin insulating objects at various
frequencies. Asymptotic formula is given to analyze relationship between
inhomogeneities and boundary potential at different frequencies. In numerical
simulations, spectroscopic images are provided to visualize the reconstructed
admittivity at various frequencies. For the view of both kinds of
inhomogeneities, an integrated reconstructed image based on principle component
analysis (PCA) is provided. Phantom experiments are performed by using Swisstom
EIT-Pioneer Set.
