Defect images in plate-like structures can be obtained using a scanning laser source technique. In the imaging technique, a laser for generating elastic waves is scanned over a plate-like structure and the signals of elastic waves are detected at a fixed position with a laser Doppler vibrometer (LDV). This imaging technique is expected in inspecting large structures such as pipes and bridges because it can be implemented from a distance like 5 meters and 10 meters. However, large structures are usually swinging at a displacement of about millimeter or sub-millimeter order, and therefore the LDV detection is often unstable during the imaging measurements.

In this study, considering that the imaging technique was implemented in the low frequency range of audible sound, we used acoustic MEMS microphones to detect the surface vibration instead of LDVs to avoid the unstable measurements. The acoustic microphones located close to the surface of the object, say 10 mm away from the surface, were able to detect the surface vibration that leaks into the air and reaches the MEMS microphones. Using the signals, the defect images in a pipe and a thin plate were obtained. Moreover, we fabricated the wireless devices equipped with a Bluetooth transmitter, a solar panel, and a battery as well as the acoustic microphones to implement remote imaging. The solar panel enable us to implemente the imaging by supplying energy at a remote distance with a laser or a floodlight projector. Once the wireless microphone devices are installed on a structure, we can measure the acoustic signals on a surface whenever light is supplied from a distance.


Remote Defect Imaging Using a Wireless Microphone Unit With an Optical Power Feeding Device

No proceedings papers in 2020. Video only.

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