Ultrasonic wave generation due to human footsteps on the ground.

Human footsteps generate broadband frequency vibrations in the ground/floor and sound in the air from a few Hertz up to ultrasonic frequencies due to striking and sliding contacts between a foot and the ground/floor. The high-frequency (above 1 kHz) vibrations from footsteps were detected on a building floor, but were not detected on the outdoor ground, even at 1 m from a walker. This paper presents results of ultrasound registration from footsteps on the ground at greater distances. Results are based on sound measurements in air, since the sound absorption in air is less than vibration absorption in the ground.