High-Resolution Pulse-Echo Detection by Means of Wideband Airborne Ultrasonic Signals

The resolution capabilities of a time-of-flight sensing system based on a highly damped electrostatic ultrasound transducer (termed L-CMUT) and a commercial MEMS microphone are tested in this work. The combination of these two components results in a high-bandwidth frequency response function that enables the transmission of chirps in the range of 30-60 kHz. With this bandwidth, the cross-correlation between the transmitted and received signal results in a sharp peak and is capable of detecting echoes below the noise level. A resolution of 11 μm (in distance) and of 0.04° (in relative angle) were measured with this system. This opens possibilities for wideband time delay estimation in air, previously limited to the SONAR field.