Phase-Coded Modulation-Based Time-of-Flight Measurement Improvement for Piezoelectric Ceramic Transducers

Ultrasonic time-of-flight (ToF) measurement is commonly used in a variety of scenarios when using small bandwidth ultrasonic transducers with 40-kHz central frequency. With these transducers, the threshold detection technique is commonly implemented, but the small bandwidth can cause inaccurate results. This article proposes a variant of correlation method for the improvement of the ToF measurement accuracy and stability with these transducers. Barker 13 and derived codes are proposed for this purpose, together with the selected code band narrowing techniques. The performance of these codes was evaluated experimentally, where 1000 measurements of each code and modulation schemes took place in several fixed transmitter-receiver settings. As the main criterion for comparison of the performance of the codes and the threshold detection technique, a sample standard deviation (SSD) was selected, showing the stability of the measured results. The best results were produced by quadriphase codes and codes with implemented fluent phase change technique, where the measured SSD was smaller than 20% of the SSD of the threshold detection techniques with all the used codes and was also smaller than 10% for the best-recorded cases.