# Phase Compensation Technique for Effective Heat Focusing in Microwave Hyperthermia Systems
## 4 Thermal Experiment Results  
To verify the thermal effects, the temperature measurement setup and block diagram of the temperature measuring system are presented in Figure 11a,b, respectively. At the boundaries of the phantom in simulation, the initial temperature was set to 0 \({}^{\circ}\)C for a clear comparison of the measured temperature increase. The thermal experiments consisted of four stages of radio frequency (RF) signal generation and amplification, RF energy excitation, an experiment on the fabricated phantom, an experiment on the thermal effect, and an evaluation of the effects of the temperature rise [19]. The thermal effects on tumor necrosis were verified by analyzing the effective treatment area (ETA) [8], which was regarded as a region in which the tumor satisfies the temperature increase requirement of 7-10 \({}^{\circ}\)C.  
To verify the heating effect on both a single tumor and on multiple tumors, the thermal measurements were conducted as follows: two for single tumor cases and one for a double tumor case. The first and second cases were conducted on a single tumor located at (0,0) mm and (20,0) mm, respectively, and the third case was conducted on two tumors located at (15,10) mm and (\(-\)15,10) mm. The phases of each antenna array were applied to the delay lines based on the calculated input phases. The thermal increase that occurred inside the cylindrical breast phantom was measured using a multi-channel thermometer with 12 probes and a data logger to manage the real time temperature data. The probe was set to detect the middle of the cylindrical phantom in the vertical axis. The simulated and measured results of the thermal effects on a single tumor cell and two tumor cells are shown in Figure 12a-f. The target positions of the tumor cells are marked with a black circle. To achieve an optimum temperature increase during a 1-h period heating, the total input powers of the array antenna were decided by the bio-heat equation supported by the CST Studio Suite [27]. The total input powers for the single tumor cells at (0,0) mm and (20,0) mm were 7.1 W and 6 W, respectively. The simulated and measured maximum temperature increases were 8.4 \({}^{\circ}\)C and 8.3 \({}^{\circ}\)C for the single tumor cell at (0,0) mm, and 8.5 \({}^{\circ}\)C and 8.3 \({}^{\circ}\)C for the single tumor cell at (20,0) mm, respectively. The target therapeutic areas of the multifocal breast cancer were at (15,10) mm and (\(-\)15,\(-\)10) mm, as shown in Figure 12e,f. To provide a heating effect on two targets simultaneously, phase compensation was applied in sub-array #2, and the input phases were controlled with delay lines. The induced total RF power was 7.1 W for 1-h treatment. The simulated and measured maximum temperature increases were 7.8 \({}^{\circ}\)C and 7.7 \({}^{\circ}\)C, respectively. The temperature transient distribution over time and the simulation and measurement results are shown in Figure 12a-c, where a single tumor was present at (0,0) mm and (20,0) mm, and two tumors at (10,15) mm and (\(-\)10,\(-\)15) mm. All the temperature results were post-processed using MATLAB. As shown in Figure 13, the temperature increased gradually  
Figure 11: (a) Configuration of the temperature measurement setup, and (b) block diagram of the temperature measuring system [25]. over time. When comparing the simulation and measurement results, the hot spots were well-formed, and the results were well-matched. Moreover, the ETAs covered the target tumor cell positions and areas, thereby leading to effective thermal therapeutic effects. The inducing power, simulated SAR, and thermal effects achieved with the proposed TSA antenna array are summarized in Table 5.  
Figure 12: The 2D sections of temperature distribution after the 1-h heating on a single tumor at (0,0) mm: (**a**) simulation result and (**b**) measurement result. Temperature distribution after 1-h heating on a single tumor at (20,0) mm: (**c**) simulation result and (**d**) measurement result.