Rhythm analysis of orthogonal signals from human walking

In physical terms, periodic movements of a human body resulting from walking produce a pulse sequence with repetition time T 1 (instant cadence frequency, 1/ T 1 ) and duration time T 2 . Footstep forces generate periodic T 1 broadband seismic and sound signals due to the dynamic forces between the foot and the ground/floor with duration time T 2 , which is equal to the time interval for a single footstep from heel strike to toe slap and weight transfer. In a human gait study (for normal speeds of walking), T 1 was detected as 0.5-0.69 s and double limb support takes up about 12% of the gait cycle (2 T 1 ), so T 2 is greater than 0.12-0.17 s. Short range (of about 50 m) signatures for 30 humans were recorded simultaneously by four orthogonal sensor types at two locations. The sensor types were active Doppler sonar/radar and passive seismic/acoustics. Analysis of signals from these four sensors collected for walking humans showed temporal synchronization and stability of the cadence frequencies, and the cadence frequency from each sensor was equivalent. The time delay between signals from these sensors due to the differences in speeds of propagation for seismic, sound, and electromagnetic waves allows calculation of the distance from a walker to the sensor suite.