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Passive ultrasonic method for human footstep detection

Methods of human detection utilizing low-frequency seismic signals (typically below a few hundred Hertz) from footsteps are well known in the literature and in a practice. This frequency band is used for seismic detectors. Different walking styles (regular, soft, and stealthy) result in different vibration signatures in the low-frequency range that limit the maximum ranges for this method of footstep detection. For example, the stealthy walking style was undetectable even a few meters from a seismic detector. Human footsteps generate broadband frequency vibrations in the ground/floor and sound in the air from a few Hertz up to ultrasonic frequencies. The dynamic forces from footsteps that are normal to the ground/floor are the primary cause of the low-frequency component in these signals. Striking and sliding contacts between a foot and the ground/floor produce the high-frequency responses. The physical mechanisms involved in the generation of high frequency signals and the possibility of their application for human footstep detection were investigated by the authors [A. Ekimov, and J. M. Sabatier "Vibration and sound signatures of human footsteps in buildings," J. Acoust. Soc. Am., 120, 762-768 (2006)]. The present paper introduces an approach for human footstep detection using a passive ultrasonic method. The passive method employs an ultrasonic sensor that is sensitive to the sound from sliding contacts. Test results for the detection of a walking person indoors and outdoors are presented and discussed.