We discuss the characterization of phantom materials that simulate the electromagnetic characteristics of various human tissues from 100 Hz to 10 MHz, and over a temperature range of 15 C to 40 C. The materials studied were: 1) a solution of potassium chloride in water, 2) a solution of propylene carbonate, ethylene carbonate, and salts, 3) a semi-solid material consisting of silicone and carbo...