Holographic Passive Sonar

A system to detect a car by measuring an automobile sound is introduced. The time difference between the signals taken from plural microphones is measured by using a specially-designed microphone array. The sound source location is estimated based on the calculation of the cross-correlation, and a particular car is identified. The measurement was tested in different noisy environments for the practical use, and fair results were obtained.

Automobile identification based on the measurement of car sounds

Near field determination of the complex radiation efficiency and acoustic intensity distribution for a resonality vibrating surface

If machines or apparatuses radiate partially coherent sound waves, locating their sources can be performed by the reconstruction of an acoustical hologram produced by the waves themselves. Since the practical spectrum of the sound fluctuates, a time average of the hologram signals can be taken, and a lock-in amplifier is used for the purpose. Using rotating gears as a test object, an experiment based on this principle has been successfully carried out to obtain the distribution of radiation sources at a frequency of 9·9 kHz.

Makoto Fujinami

Papers

Mapping of noiselike sound sources with acoustical holography.

Imaging of Acoustic Radiation Sources with Acoustical Holography