What is constant phase element?

A constant phase element (CPE) is an electrical circuit element used to model the behavior of a wide range of materials including porous electrodes, biological tissues, and electrochemical systems. The behavior of a CPE is characterized by a non-linear phase response across a range of frequencies. The impedance of a CPE can be described mathematically using a power law equation, rather than a simple resistor or capacitor.

A CPE can be used to model systems where the impedance is not purely resistive or capacitive, such as electrodes with adsorbed layers, and surfaces with roughness or porosity. The CPE is often used instead of a simple capacitor in equivalent circuit models of electrochemical systems, as it provides a more accurate representation of the system's impedance over a range of frequencies.

CPEs have applications in electrochemistry, corrosion studies, biosensors, and electrokinetics. They are often used in combination with other circuit elements to model complex, non-linear systems.