## 2 Materials and Methods
### Insulated Monopole Antenna Fabrication  
The two different experiments conducted in this study (PTFE thermal expansion characterisation and the ablation experiments) required fabrication of an insulated monopole antenna. In both cases, an antenna was used once and discarded following an experiment to avoid cumulative degradation errors.  
The antennas used for the ablation experiments were constructed from an RG405 coaxial cable cut as indicated in Section 2.2. An SMA connector was soldered to one end for the annealed and non-annealed versions. The design and development of the uncooled insulated monopole are comprehensively described in [35], wherein two primary dimensions of significance during the antenna development process are detailed: the quarter-wavelength monopole length (D) and the antenna's immersion length (E) (refer to Figure 1). Length (D) was achieved by exposing the PTFE solely by cutting the outer conductor. This was accomplished by cutting the outer conductor in an annular motion and limiting the cutting depth using a modified copper tube cutter (W127, WIGAM, Arezzo,  
Figure 2: The annealing process of the RG405 coaxial cable utilising a thermal chamber.  
Italy). This produced a repeatable and neat cut. The cut outer conductor was slid away to expose around 20 mm of the PTFE underneath. The length (D) was cut to 12.8 mm using a hand-driven 3D-printed rotary guillotine. This resulted in an immersion length (E) of 140 mm, excluding the SMA connector. Every antenna was assigned a unique identifier and underwent validation. The validation process utilised a Vector Network Analyser (VNA) ZNA50 (Rhode and Schwarz, Munich, Germany). The antennas were immersed in minced porcine liver, which was contained in a cylindrical plastic vessel sufficiently large to approximate a quasi-semi-infinite medium. This was achieved by adjusting the container size until no further changes were detected in the reflection coefficient. The return loss was measured at between 1.1 GHz and 3.8 GHz with 301 points, and the complete return loss profile was confirmed. A needle file was used for fine adjustments to improve the matching condition. It was ensured that the measured return loss was above 25 dB at 2.45 GHz; otherwise, the antenna was rejected.  
Unlike the ablation experiments, the antennas intended for the PTFE thermal expansion characterisation experiments were neither energised nor matched with the surrounding medium (peanut oil). Thus, the antennas required no soldered SMA connector and equally no matching validation. In these cases, 70 mm pieces of RG405 coaxial cables were used. The length (D) was developed using the same copper tube cutter and hand-driven 3D-printed rotary guillotine as the antennas developed for the ablation experiments. However, the antennas meant for the PTFE thermal expansion characterisation experiments had a shorter length (E) of 50 mm to reduce cable waste, as the constricted PTFE below the outer conductor had no significant impact on the monopole's matching condition during ablation. The antennas meant for the PTFE thermal expansion characterisation experiments had their dimensions/lengths measured and recorded using a toolmaker's microscope (Maxtascan 2000, Graticules Optics Ltd, Tonbridge Kent, UK). All antennas were rigorously fabricated to ensure matching dimensions, resulting in a mean length (D) of 12.95 mm and a standard deviation of 0.1 mm. The process was equivalent for both annealed and non-treated antennas.