High speed non-contact acoustic inspection method using multi tone burst wave

• Published in: The Journal of the Acoustical Society of America 2016-10, Vol.140 (4), p.3212-3213
• Main Authors: Sugimoto, Tsuneyoshi, Sugimoto, Kazuko, Kosuge, Nobuaki, Kuroda, Chitose, Utagawa, Noriyuki
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4970116

The non-contact acoustic inspection method using an air-borne sound can detect the cavity defect and crack near the measurement surface by using flexural resonance. By this method using a single tone burst wave, the length of the measurement time of a two-dimensional scan was a practical problem. This is because only one frequency was used for one sound wave emission so that a high signal to noise (S/N) ratio could be obtained with the laser Doppler vibrometer (LDV) of a weak laser power (e.g., He-Ne 1mW). However, two or more frequency can be used at the time of one sound wave emission (multi tone burst wave) by taking into consideration the difference of the propagation velocity of a sound wave and laser light. That is, it becomes possible to perform high-speed measurement as compared with the conventional method, using effectively the time & frequency gate for raising a S/N ratio by terminating measurement before the reflective sound wave reaches a laser head from the measurement surface. The experiment using a concrete test object was carried out and the validity of this multi tone burst wave as high-speed measurement was confirmed from the experimental result.