Surgical diathermy

The principle behind the use of surgical diathermy is that of current density. When a current is applied over a small area, the current density is high and heating may occur. If the same current is applied over a suitably large area then the current density is low and no heating occurs. For unipolar diathermy, the apparatus utilizes a small surface area at the instrument end and a large area on the diathermy plate to allow current to flow but to confine heating to the instrument alone. Bipolar diathermy does not utilize a plate as current flows directly between two points on the instrument. 

Esser, A.T., Smith, K.C., Gowiishankar, T.R., Weaver, J.C., 2007. Towards solid tumor treatment hy irreversible electroporation intrinsic redistribution of fields and currents in tissue. Technol. Cancer Res. Treat 6, 261—274. Etter, H.S., Pudenz, R.H., Gersh, I., 1947. The effects of diathermy on tissues contiguous to implanted surgical materials. Arch. Phys. Med. Rehab. 28, 333—344. 

---