Influence of the conductivity of radiofrequency conducting medium on the temperature gradient of bipolar radiofrequency based on finite element analysis

Bipolar radiofrequency (RF) heats the deeper layers of the skin to denature collagen. This treatment will tighten the skin and reduce the appearance of wrinkles. However, due to the high electrical impedance in the epidermis, RF energy transmission requires the application of a conducting medium to the surface of the skin to increase electrical conductivity. In this study, the finite element analysis is used to investigate the influence of the conductivity of the RF conducting medium on the heating performance of the bipolar RF technique, which has acquired the optimal conductivity of the conduction medium used in household RF beauty instruments. For bipolar RF, the thermal conduction equation of the four-layer skin tissue with a surface conducting medium is firstly derived, and then a finite element model of bipolar RF skin is established by COMSOL Multiphysics to simulate tissue heating with a conducting medium which has a conductivity of 900-2500 μs/cm. The results showed that the highest temperature range in the target area was 41.22-42.23 ℃. Compared to the case without the conducting medium, the temperature increased by approximately 2.4-5.1%, and the heating rate increased by 2.51-10.42%. Taking into account the safety and effectiveness of RF treatment, for a household RF beauty instrument with an output frequency of 1 MHz and a peak-to-peak voltage of 110 V, the conducting medium with an optimal conductivity of 900 μS/cm was more suitable.