New Coded Sequences for Accurate Time-of-Flight Measurements with Resonant Ultrasonic Sensors

Air-coupled piezoelectric ultrasonic transducers are usually designed around resonant frequencies of the piezoelectric and matching layers, to partially compensate for the huge acoustic impedance mismatch between sensor and gas medium. However, such resonant or narrow-band sensors pose difficulties for an accurate measurement of the time-of-flight. By using an optimal pair consisting of a coded sequence as excitation and a mismatched FIR filter, we are able not only to improve the signal-to-noise ratio but also to shape the received pulse envelope for a better determination of the ToF. We apply these new coded sequences in a virtual experiment for ToF measurements using a simulated transducer response and compare them to Golay complementary pairs and pseudo-random codes.