## 3 Results and Discussion
### Performance Evaluation Result  
Based on the calculation results from Section 3.1, we developed a technique to blend flattened aerogel particles oriented against the thickness direction and fabricated aerogel particle-mixed non-woven fabric. Specifically, while producing thin non-woven fabrics using a carding machine, we laid flattened aerogel particles onto these thin fabrics and then laminated them to create non-woven fabrics with the particles aligned along the thickness direction. Figure 7 presents photographs of test specimens: PET non-woven fabric with a bulk density of 16.2 kg/m\({}^{3}\), PET non-woven fabric with a bulk density of 87.2 kg/m\({}^{3}\), and Thinsulate, a commonly used automotive sound-absorbing material composed of the fabricated non-woven fabric and the aerogel particle-mixed non-woven fabric. The particle content of the aerogel particle-mixed non-woven fabric was approximately 21.7 wt%, closely matching the 19.5 wt% particle content of particles A and B used in the calculation geometry. Figure 8 displays the results from the CT analysis of the internal structure of the PET non-woven fabric 1 and the aerogel particle-mixed non-woven fabric, examining fiber-to-fiber distances and particle size distribution. PET non-woven fabric 1, with a bulk density of 16.2 kg/m\({}^{3}\), showed a peak distribution of the distance between fibers at about 30 \(\upmu\)m. However, the aerogel particle-mixed non-woven fabric, with a bulk density of 87.2 kg/m\({}^{3}\), also showed a peak at 30 \(\upmu\)m but with fiber distances extending up to 180 \(\upmu\)m, indicating wider inter-fiber spacing in areas where particles are present. The median particle diameter, calculated from particle volume assuming a spherical shape, was about 240 \(\upmu\)m (particle volume: approximately 7.24 \(\times\) 10\({}^{6}\)\(\upmu\)m\({}^{3}\)). This volume is closely aligned with the volume of particles A and B used in the calculation geometry, which is 5.58 \(\times\) 10\({}^{6}\)\(\upmu\)m\({}^{3}\) (particle diameter: 220 \(\upmu\)m). Figure 6: Shape of mixed aerogel particles and tortuosity inside the porous material: (**a**) Spherical particles; (**b**) Elliptical flattened particles. Figure 7: External appearance of non-woven fabric: (**a**) polyethylene terephthalate (PET) non-woven fabric 1; (**b**) particle-mixed non-woven fabric; (**c**) Thinsulate. The measured sound absorption coefficients of PET non-woven 1 and PET non-woven 2, with bulk densities of 16.2 and 100.5 kg/m\({}^{3}\), respectively, and of aerogel particle-mixed non-woven fabric, with a bulk density of 87.2 kg/m\({}^{3}\), and of Thusulate are shown in Figure 9. PET non-woven fabric 2 demonstrated a higher sound absorption coefficient across a broader frequency range of 100-1600 Hz compared to PET non-woven fabric 1. Additionally, there was no reduction in sound absorption coefficient at higher frequencies up to 1600 Hz. From this, we conclude that PET non-woven fabric is effective in improving the sound absorption coefficient below 1600 Hz for bulk densities up to 100.5 kg/m\({}^{3}\). Conversely, the non-woven fabric mixed with aerogel particles demonstrates a higher sound absorption coefficient across most frequency bands of 100-1600 Hz than the PET non-woven fabric 2  
Figure 8: Distance between fibers of non-woven fabric and particle size distribution of mixed aerogel particles: (**a**) PET non-woven fabric 1; (**b**) particle-mixed non-woven fabric. Figure 9: Measured normal-incidence sound absorption coefficients of particle-mixed non-woven fabric. with a bulk density of 100.5 kg/m\({}^{3}\), despite having a lower bulk density of 87.2 kg/m\({}^{3}\). This indicates that the aerogel particles contribute to enhancing the sound absorption coefficient. Figure 10 displays the sound absorption coefficient measurements for a test specimen of the same shape, where a skin material with high airflow resistance was laminated on one side of the prepared non-woven fabric.