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

This work proposes a 2.45GHz non-invasive microwave lipolysis system, aimed at addressing two critical challenges in current microwave lipolysis technology: low coupling efficiency caused by strong reflection at the skin interface, and electromagnetic loss introduced by the cooling front end. The system employs a side-fed tangentially radiating waveguide antenna combined with an integrated gradient-index cooling lens (I-GRIN). By suppressing the normal electric-field component, the specific absorption rate peak is concentrated at the skin-adipose interface, reducing off-target energy deposition in deeper tissues. Compared with conventional microwave lipolysis, this approach achieves higher precision in ablating the targeted tissue. The antenna is miniaturized using metamaterial loading and is integrated with the I-GRIN lens. The lens is fabricated using polymethyl methacrylate as the scaffold, with internally graded water-filled cavities to achieve dual functionality: providing low-temperature surface cooling via circulating deionized water, and optimizing impedance matching between the antenna and the skin, thereby enhancing near-field focusing. This design significantly reduces the electromagnetic loss associated with the addition of a cooling front end in conventional microwave lipolysis systems. Simulation and experimental results demonstrate that, under an input power of 10 W, the system can generate a nearly uniform thermal region of approximately 50 °C at a depth of 10 mm in subcutaneous adipose tissue within 5 min.