## 4 Discussion  
### Visualization of Heat Transfer  
After verifying and comparing the muscle numerical study and MWA data, the validity of the proposed model has been proved. Therefore, heat transfer of other similar biological tissues based on the physical field established by this model has a specific reference. Considering the complexity of fat and bone MWA experiments, which are single-component biological tissues, numerical models of fat and bone are established to discuss temperature distribution. Figure 3 records the temperature cloud map of muscle, fat, and bone at the 30 s, 60 s, 90 s, and 120 s, respectively. Although they are all 50 W/2.45 GHz microwave heating power during the heating process, the heat received by them differs due to the different biological characteristics of muscle, fat, and bone. It can be seen from the map at the 60 s that the high-temperature area of muscle is above the annular groove. Its heat spreads out from this position as the center, and the temperature distribution is in a droplet shape. For fat, the high-temperature area is much tinier than for muscle and bone, and its temperature distribution is similar to a vase shape. Compared with the muscle  
Figure 2: Temperature distribution at thermometric sequence near ablation antenna and MWA. temperature cloud map, the overall form of the fat temperature cloud map is slendererer. Its temperature distribution shifts downward. The microwave heating effect of bones is very significant. Its temperature exceeding 100 \({}^{\circ}\)C can be seen obviously. When heated to the 60 s, the high-temperature area continues to expand. The map shape also becomes more expansive. Except for some parts at the bottom, most areas experience a temperature increase. After the 60 s, no heating is allowed, so the temperature starts to drop gradually. The muscle temperature cloud map begins to contract; significantly the top retracts inward. The red high-temperature area disappears at 90 s. At 120 s, the map further retracts to a spherical shape, and the temperature domain position is close to the place during heating (the 30 s). At 60 s, the temperature of fat is not high, and its fall is also rapid. Temperature is already low at 90 s. The temperature domain center is near the slot at this time. At 120 s, the temperature has completely cooled down. After bone stops heating at 60 s, the high-temperature area in the original center begins to spread outward. A clear yellow edge can be seen to expand at 90 s. At this time, the shape of the high-temperature area above 100 \({}^{\circ}\)C begins to resemble the shape of the muscle temperature cloud map at the 60 s. After continuing to cool down, the top of the high-temperature area above 100 \({}^{\circ}\)C retracts, and outer edge temperature further diffuses. Even if heating is stopped for a while, there is still a high-temperature area inside the bone. The heating zone at the top of the bone shrinks inwardly after heating is stopped. Its influence on the adjacent temperature zone is significantly reduced, while the slot gradually becomes the center of the entire high-temperature area. Therefore, the shape of the temperature cloud map at the bone cooling period and muscle heating period is similar. Using a 2D view, a temperature cloud map of appropriate time was derived from observing the difference in the heating domain of three biological tissues. Figure 4 shows  
Figure 3: Temperature cloud map at 30 s, 60 s, 90 s, and 120 s. The 30 s and 60 s belong to the heating period, and 90 s and 120 s belong to the cooling period. (**a**) Temperature cloud map of muscle; (**b**) Temperature cloud map of fat; (**c**) Temperature cloud map of bone. muscles (at 60 s), fat (at 60 s), and bone (at 4 s). It can be seen that fat and bone have two warming regions near the annular slot and needle. High-temperature area of fat occurs near the ablation antenna needle. A high-temperature area near the needle of the bone is relatively large. Its high-temperature area occurs in the annular groove.