## 3 Results
### Thermal Safety Evaluation  
The simulation was conducted in two stages: first, analyzing temperature changes when only the temporal bone was present, and then when the SCC was included. This approach was designed to assess the thermal effects by considering the physical properties of both media. The temporal bone has a low specific heat and high attenuation coefficient [41; 42], which results in significant localized temperature increases as it absorbs a substantial amount of ultrasound energy. In contrast, the endolymph has a higher specific heat and lower attenuation coefficient [40; 41], allowing the absorbed heat to disperse over a broader area, resulting in a relatively smaller temperature rise. This demonstrates that evaluating the temperature increase in the temporal bone alone is critical for assessing thermal safety for this ultrasound stimulation. Figure 9 presents the heat transfer results at different frequencies when only the temporal bone is present. The simulation evaluated temperature increases during and after 1 second of ultrasound exposure, with a total simulation time of 5 seconds. Figure 9a shows the temperature distribution along the axial distance at the end of the 1-second exposure,  
Figure 8: Three-dimensional visualization of cupula displacement caused by acoustic streaming in the endolymph at three different frequencies: (**a**) 400 kHz, (**b**) 600 kHz, and (**c**) 800 kHz. The displacement results are shown on the surface of the cupula, with the center of the cupula positioned at (0, 0). analyzing temperature changes near the cupula at x = 3 mm. At 400 kHz, the maximum temperature increase was 0.42 \({}^{\circ}\)C at 35.2 mm, occurring at a shorter distance than the focal length calculated for water (40.616 mm). At 600 kHz, the maximum temperature increase was 0.57 \({}^{\circ}\)C at 37.1 mm, and at 800 kHz, it was 0.81 \({}^{\circ}\)C at 39.4 mm. This indicates that as the frequency increases, the location of the maximum temperature shifts further from the transducer, although still shorter than the calculated focal length. Nonetheless, higher frequencies lead to greater temperature increases. Additionally, the temperature distribution narrows as the frequency increases, with 800 kHz showing the narrowest distribution, suggesting that higher frequencies cause more localized heating. Figure 9b illustrates the temperature changes over 5 seconds at the location where the maximum temperature was recorded for each frequency. At 800 kHz, the temperature decreased from 0.81 \({}^{\circ}\)C to about 0.3 \({}^{\circ}\)C after 4 seconds. At 600 kHz, it decreased from 0.57 \({}^{\circ}\)C to 0.25 \({}^{\circ}\)C, and at 400 kHz, it decreased from 0.42 \({}^{\circ}\)C to 0.2 \({}^{\circ}\)C. These results show that higher frequencies not only lead to greater initial temperature increases but also cause faster heat dissipation. As shown in the previous results, z = 39.4 mm (Temporal bone domain) is the point where the highest temperature increase occurs in the absence of the SCC, while z = 42 mm (endolymph domain) is the designed focal point. Through this result, we investigated the effect of the presence of the SCC on the temperature change in the temporal bone domain, along with the temperature change in the endolymph region inside the SCC. Figure 10 compares temperature changes at 800 kHz when the SCC is present and when it is absent. The graph shows temperature changes at the same point in the temporal bone for both cases, as well as at a point in the endolymph region. Without the SCC, the maximum temperature was 0.81 \({}^{\circ}\)C, while with the SCC, it decreased to 0.74 \({}^{\circ}\)C in the same location. This reduction is due to the presence of endolymph, which has a higher specific heat and lower attenuation coefficient compared to the temporal bone [40; 41]; this results in a smaller temperature increase for the same amount of absorbed energy.