Effect of frequency and conductivity on field penetration of electromagnetic hyperthermia applicators

The field penetration of electromagnetic hyperthermia applicators in 2.5-29 g l-1 saline (NaCl) solutions over a range of frequencies is investigated. Calculated field penetration based on the current-element method agrees well with measurement at frequencies above about 100 MHz, but at lower frequencies measured field penetration becomes progressively less than calculated as conductivity is reduced. Experimental results and finite-difference time-domain (FDTD) method modelling show that the electromagnetic field produces circulating currents. The effect of these circulating currents on the heating pattern of the applicators should be considered when planning hyperthermia treatment.