Optimization of helical coil applicators for hyperthermia

Numerical solutions were used to optimize helical coil applicators to maximize the ratio of axial heating to surface heating within coaxial muscle cylinders. It is shown that this optimization requires significantly larger values of pitch angle and frequency than any previously specified for experimental applicators. The maximum ratio of axial to surface heating is obtained with a linear helix defined to have a pitch angle of 90°. Calculated ratios of axial/surface heating with a linear helix are as large as 2.54 (at 352 MHz) for a muscle cylinder with a radius of 4 cm, and 1.26 (at 82 MHz) for one with a radius of 8 cm. The relationship of the linear helix applicator to the annual phased-array applicator and to the resonant cylindrical cavity applicator is discussed