Ultrasonic range measurements on the human body

Ambulatory range estimation on the human body is important for the assessment of the performance of upper- and lower limb tasks outside a laboratory. In this paper an ultrasound sensor for estimating ranges on the human body is presented and validated during gait. The distance between the feet is estimated based on the time of flight and compared to an optical reference. The signal to noise ratio of the received signal is used as a measure for the uncertainty of the range estimate. For example when rejecting distance estimates with a signal to noise ratio smaller than 5, the mean absolute distance difference between the ultrasound sensor and an optical reference system is 7.0 mm (sd 7.1 mm) over six walking trials.