Holographic diagnosis: Basic principles and applications

Abstract

Acoustic signals achieved from a machine often have information on condition of the machine. This means that the location of faults can be found by using acoustic signal. Location of sound source can be found by using techniques such as MFAH (moving frame acoustic holography), which is applicable for pure tone noise and good signal‐to‐noise ratio, and beamforming, which basically assumes no reflected wave. Faults due to breakdown of rotating parts in a moving vehicle, however, make the above method hard to be directly applicable. The difficulty stems from three characteristics in the fault detection of the moving vehicle. First, the sound source radiates periodic impulsive noise. Second, there exist reflected waves from the ground since the array microphones should be settled between the vehicle and the ground to monitor the bottom side of the vehicle. Last, for the measurement problem, there exists noise due to other parts and wind for the moving vehicle, which degrades coherence among measured signals. In this research, holographic diagnosis, a machine diagnosis technique based on holographic approach, is introduced to find the position of faults effectively. The modified version of beamforming that models the moving periodic impulsive noise as a scan function is introduced.