A Model for Impedance Determinations and Power Deposition Characterization in Three-Electrode Configurations for Capacitive Radio Frequency Hyperthermia-Part A: Impedance Determinations

By means of simplifying assumptions, a 2-D rectangular model for three-electrode radio frequency hyperthermia systems is established. The validity of these assumptions is discussed. The electric behavior of the model is characterized by a three-port equivalent network. The three resistances in the network are determined by means of conformal mappings. The process is applied to devices exhibiting a plane of symmetry but provisions exist for a generalization to asymmetrical systems. The set of five design elements completing the description of the system comprises a resistance and a balance factor as the two electrical parameters, and electrode sizes and spacings as the three geometrical parameters. For practical purposes the links between these parameters, figured out by computations, are mapped into block diagrams and into a chart. The block diagrams show that the electrode sizes and spacings have almost uncorrelated effects upon the electrical parameters. When the values of any three among the five parameters have been chosen, the chart gives the two unknown parameter values by direct reading or through interpolations. The use of complementary systems widens the chart range to almost any practical system values, and it allows the two-electrode system relation between resistance and capacitance to be generalized to any three-electrode system.