| 摘要 |
The length of the polycrystalline silicon rod (100) is measured with a tape measure, then the polycrystalline silicon rod (100) is hit with a hammer (120), and this hammering sound is recorded in a recorder (140) through a microphone (130). Then, an acoustic signal of the hammering sound is subjected to a fast Fourier transform and a frequency distribution is displayed. Furthermore, a peak frequency f is detected which shows the largest sound volume in the frequency distribution obtained after the fast Fourier transform. The relationship between the length (L) of the polycrystalline silicon rod and the peak frequency f is obtained, and the firmness of the polycrystalline silicon rod is determined on the basis of whether or not the peak frequency f is in a range of f>=1,471/L (region A).
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