Effects of floating sleeve geometry on thermal selectivity in dual-slot microwave coaxial antennas for microwave ablation

Microwave ablation (MWA) is widely used as a local tumor treatment, and its therapeutic outcome is strongly affected by antenna configuration and operating power. In the present work, a dual-slot microwave coaxial antenna (MCA) equipped with a floating sleeve was examined to clarify how sleeve-related design parameters influence ablation performance. Numerical simulations were carried out by varying the floating sleeve length, the separation distance between the slot and the sleeve, and the applied input power. The electromagnetic response inside tissue and the subsequent heat transfer behavior were predicted using coupled electromagnetic and bioheat analyses, and tissue damage was assessed quantitatively with the Arrhenius damage model. The results confirmed that both the extent and spatial pattern of tumor damage changed noticeably according to floating sleeve geometry, even at identical power levels. In addition, the antenna design altered the power required to induce sufficient tumor necrosis, which in turn affected the degree of unwanted thermal damage in adjacent normal tissue. A floating sleeve length of 15 mm combined with a slot-to-sleeve distance of 6 mm achieved complete tumor damage at 13 W while suppressing collateral damage to surrounding tissue. These results indicate that careful adjustment of floating sleeve geometry can improve ablation efficiency and thermal selectivity, offering a practical basis for antenna optimization in MWA applications.