Effect of fat thickness on subcutaneous temperature field under monopolar radiofrequency

Background Monopolar Radiofrequency uses high-frequency waves to generate heat for skin tightening and tissue repair. However, individual fat layer thickness variation causes uneven radiofrequency (RF) penetration and heat thresholds, compromising personalized results. Objective The purpose of this study is to analyze the temperature distribution of tissues with different fat thickness after radio frequency treatment and the experimental temperature distribution and tissue changes of pork tissues in vitro by finite element analysis and in vitro experiment verification, so as to achieve appropriate energy parameters for different individuals. Methods A two-dimensional bio-thermal model including epidermis, dermis and subcutaneous tissue was developed in COMSOL Multiphysics 6.2. Four fat thicknesses (2, 4, 6, and 8 mm) were simulated to assess their impact on dermal temperature distribution during 6.78 MHz, 120 W radiofrequency exposure. The electromagnetic-thermal coupling effects were validated through in vitro experiments. Results Experimental results validate the simulations, demonstrating consistent thermal trends across fat thicknesses (2–8 mm). Post-treatment intratissue temperatures reached 69 °C (2 mm), 60 °C (4 mm), 55 °C (6 mm), and 45 °C (8 mm), all within epidermal safety limits. Conclusion The results show that the energy parameters need to be adjusted according to the thickness of adipose tissue during radiofrequency therapy, and higher energy or longer treatment time may be needed for the treatment site with thicker adipose tissue to achieve the expected effect.