Metamaterial-loaded waveguide antenna with integrated gradient-index cooling lens for abdominal subcutaneous adipose ablation

This paper presents a noninvasive microwave lipolysis system operating at 2.45 GHz, designed to overcome two critical challenges: poor coupling efficiency due to strong reflection at the skin interface, and electromagnetic loss introduced by the cooling front end. The proposed solution integrates a side-fed, tangentially radiating waveguide antenna with an integrated gradient-index cooling lens (I-GRIN). The antenna is miniaturized using metamaterial loading, and the side-fed configuration suppresses the normal electric-field component, steering the specific absorption rate (SAR) maximum toward the skin-adipose interface. This reduces off-target power deposition in deeper tissues. The I-GRIN lens, fabricated from a PMMA scaffold with graded water-filled cavities, provides dual functionality: low-temperature surface cooling via circulating deionized water and improved impedance matching at the antenna-skin interface, which enhances near-field focusing. Both simulation and experimental results demonstrate that, with 10 W of input power, the proposed system can generate a relatively uniform thermal region of approximately 50 °C at a depth of 10 mm in subcutaneous adipose tissue within 5 minutes.