Localization of moving periodic impulsive source in a noisy environment

Sound generated from a machine often carries information on the condition of the machine. For example, the faults in the rotating part of a machine generate impulsive sound. This means that by visualizing the radiation pattern from a moving machine, the condition of the machine: where the fault is, can be examined. The moving frame acoustic holography method [H.-S. Kwon, Y.-H. Kim, Moving frame technique for planar acoustic holography, Journal of the Acoustical Society of America 103(4) (1998) 1734–1741.] enables us to visualize sound field from a moving source of pure tone or narrow band signal. This method cannot be applied directly, however, to the moving periodic impulsive sound because the impulsive signal is obviously different from the pure tone or narrow band signal. In this paper, we propose a means to use the method to localize moving periodic impulsive source that is embedded by noise. Moving periodic impulsive signal can be regarded as the combination of moving several discrete pure tones. This enables us to visualize the sound field at each frequency component. We also found that the signal to noise ratio can be readily improved by averaging several holograms. This is because periodic impulsive noise has several discrete frequency components.