Effects of Flexible Induction Coil Pitch on the Heating Performance of Thermotherapy Needles

This article presents a newly developed flexible laminated copper (FLC) coil for electromagnetic thermotherapy that has several advantages over traditional hard copper coils. We study the effect of pitch (the distance between coil turns) on the heating performance of the proposed FLC coil. The flexible coil can be wound into different shapes for various purposes. However, the output power of the heating system can be substantiality affected by the coil inductance. This study is aimed at reducing coil inductance by changing the original flexible coil diameter and pitch in order to enhance the output power of a high-frequency machine, improve treatment, and meet the actual heating requirements. The results of the experiments show that the temperature is six times better when using the flexible coil compared with when using the traditional hard copper coil, where adjusting the coil pitch can increase the needle temperature by a maximum of 48.3 °C in pork liver tissue. In addition, this study simulates the distribution of the magnetic field of the flexible coil via a finite element analysis and explores the coil design and heating effect of metal needle heating and liver tissue ablation. The improved features of this proposed method are threefold: 1) the flexible coil can be used to treat different zones of the human body; 2) the flexible coil exhibits better heating performance than a hard copper coil; and 3) the coil inductance is lowered, and the power is improved, which, in turn, leads to better treatment and meets the actual heating requirements.