Investigation of the Time of Flight estimation errors induced by neighboring signals

Investigation of the errors of Time of Flight (ToF) estimate of ultrasonic signals in case of multiple reflections environment is presented. Multiple signals environment induces neighboring signal energy leak into analyzed signal. This in turn introduces some errors in ToF estimate. Narrow signals like single pulse, should posses lower influence that CW burst or chirp signals. Then high energy signals (burst or chirp) will always be jeopardized in case of multiple reflections. New class of SS signals, trains of pulses of arbitrary pulse width and position (APWP), is expected to have properties similar to chirp (wide, controllable bandwidth) and the single pulse (low correlation sidelobes) signals. Goal of the investigation was to compare the multi-reflections performance in Time of Flight estimation for classical signals (rectangular pulse, step and CW burst) and spread spectrum signals (chirp and APWP). Signals from fixed delay line were recorded, aligned in time and averaged to produce noise-free reference signal which was used to simulate the plate thickness measurement and liquid velocity estimation with variable spacing of signals in time. Simulation and experimental investigation results are presented and possible problem solutions suggested.