Human heel-contact and toe-off times measured with an in-air 40 kHz Doppler ultrasound

Abstract

In-air Doppler ultrasound is used to measure human gait parameters as a person walks in a hallway. Single element, 10 mm diameter transmit and receive transducers are used for a walk range from 2–10 m in a continuous wave mode at 40 kHz. The person’s foot heel-contact and toe-off times are needed to determine the leg’s swing phase and double stance times as well as asymmetries between the left and right legs. At the times, the foot velocity is zero, and the other body segments continue to move with non-zero velocities causing Doppler frequency shifts that mask the smaller foot velocity of interest. We currently use an algorithm to fit the measured foot velocity in the Doppler data to a model in order to estimate these times. This model was developed from simultaneously measured video motion capture and Doppler ultrasonic data for walking persons. Less than desirable results are achieved when the ultrasonic measured times are compared to those from commercially available pressure sensitive gait mats. We will present a comparison of the heel-contact and toe-off times measured using beamed transducer arrays and a foot plate sensor made from a pressure sensitive material.In-air Doppler ultrasound is used to measure human gait parameters as a person walks in a hallway. Single element, 10 mm diameter transmit and receive transducers are used for a walk range from 2–10 m in a continuous wave mode at 40 kHz. The person’s foot heel-contact and toe-off times are needed to determine the leg’s swing phase and double stance times as well as asymmetries between the left and right legs. At the times, the foot velocity is zero, and the other body segments continue to move with non-zero velocities causing Doppler frequency shifts that mask the smaller foot velocity of interest. We currently use an algorithm to fit the measured foot velocity in the Doppler data to a model in order to estimate these times. This model was developed from simultaneously measured video motion capture and Doppler ultrasonic data for walking persons. Less than desirable results are achieved when the ultrasonic measured times are compared to those from commercially available pressure sensitive gait mats. We wi...