Broad frequency acoustic response of ground/floor to human footsteps

Abstract

The human footstep is one of several signatures that can serve as a useful parameter for human detection. In early research, the force of footsteps was measured on load cells and the input energy from multiple footsteps was detected in the frequency range of 1-4 Hz. Cress investigated the seismic velocity response of outdoor ground sites to individuals that were crawling, walking, and running. In his work, the seismic velocity response was shown to be site-specific and the characteristic frequency range was 20-90 Hz. The current paper will present vibration and sound pressure responses of human footsteps in a broad frequency range. The vibration and sound in the low-frequency band are well known in the literature and generated by the force component normal to the ground/floor. This force is a function of person's weight and a manner of motion (e.g. walking, running, etc). Forces tangential to the ground/floor from a footstep and the ground reaction generate the high frequency responses. The interactions of foot and the ground/floor produce sliding contacts and the result is a friction signal. The parameters of this friction signal, such as frequency band and vibration and sound magnitudes as functions of human walking styles, were studied. The results of tests are presented and discussed.

Design and Development of an Ultrasonic Motion Detector

“…Each method has advantages and disadvantages. Motion detectors can be categorized into two major types [2][3] these are namely: (1) Passive detectors, and (2) Active detectors.…”

Ultrasonic wave generation due to human footsteps on the ground

“…Indoor tests have demonstrated such high-frequency bands in the vibration and sound responses from human footsteps, 1,2 while outdoor tests have shown only the low-frequency vibration responses ͑below 1 kHz͒. 2 In buildings, footstep vibration magnitudes in the high-frequency range are comparable and independent of walking styles ͑regular, soft, and stealthy͒ 1 at distances close to the detector ͑1 m͒. However, on the ground/ floor surfaces, different walking styles result in different vibration signatures in the lowfrequency range that limit the maximum ranges for the seismic method of footstep detection.…”

“…For example, the stealthy walking style is undetectable on the ground even a few meters from a seismic detector. 2,3 Sound measurements can provide the high-frequency response of footsteps on the ground, but previous experiments have not measured sound responses from human footsteps in outdoor environments.…”

“…1, 2 The first frequency band is generated by a force normal to the supporting surface and is concentrated in a low-frequency range below 500 Hz. The second frequency band is generated by the tangential ͑friction͒ force and is located in a high-frequency range, above 1 kHz up to ultrasonic frequencies.…”