The Impedance of an Electrode Coated by a Resistive Film with a Graded Thickness

The impedance of a rectangular electrode coated by a resistive film, the local thickness of which varies along the electrode length, is calculated considering a local capacity of each surface element inversely proportional to local film thickness and different cases for film resistance. Experimental model systems are obtained by anodizing niobium or tantalum rectangular sheets. The impedance of the coated electrode, in agreement with the calculations, shows a minimum in the plot of the ohmic resistance corrected phase angle vs frequency and cannot be accurately modeled by a constant phase element.