Dielectric Properties of Materials Showing Constant-Phase-Element (CPE) Impedance Response

TLDR

Constant‑phase elements are commonly employed to model impedance spectra across diverse experimental systems. The study applied four distinct methods to translate CPE parameters of human skin and two metal oxides into characteristic frequencies and film thicknesses, then benchmarked the results against independent measurements. The Hirschorn power‑law model yielded the most reliable interpretations for normally distributed systems, while the CPE parameter Q should not be used as a capacitance estimate even when α exceeds 0.9.

Abstract

Constant-Phase Elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. Four approaches were used to interpret CPE parameters associated with the impedance response of human skin and two metal oxides in terms of characteristic frequencies and film thickness. The values obtained with each approach were compared against independent measurements. The power-law model developed recently by Hirschorn et al.1,2 provided the most reliable interpretation for systems with a normal distribution of properties. Readers are cautioned that the CPE parameter Q does not provide an accurate value for capacitance, even when the CPE exponent α is greater than 0.9.