Active damping for enhanced time resolution in measurement with narrowband transducers

Narrowband ultrasonic or acoustic transducers typically exhibit extended ringing in their vibration response when driven by temporally short excitation voltages. In common measurement processes the generated pressure waveform from a narrowband transmitter is received by a separate narrowband transducer that is closely matched in resonant frequency. In these cases, the incident pressure waves can create significant ringing of the receiving transducer, irrespective of how short the envelope of the incident waves are. The principle of active damping in reception can be utilised in such systems by engineering a pressure wave from the transmitter that is used to damp the resonant ringing in the receiver, rather than the more usual approach of trying to damp vibrations of the generating transducer. This can improve the measurement accuracy of the system when attempting to distinguish multiple wave arrivals, improving the time resolution for detection. This study examines the key measurement strategies required to tailor an appropriate electrical input to perform active damping in reception with the specific system of transducers used, including methods to numerically simulate the transducer system in the input optimisation process, and recommendations for various potential applications discussed. Experimental measurements are performed using a transmit-receive system of flexural ultrasonic transducers (FUTs), a class of fluid-coupled, narrowband transducers, demonstrating that the time duration of the received signal can be reduced by nearly 80% when compared to no applied damping methods, without a significant compromise in received signal amplitude. The results show the suitability of active damping in reception as a novel and highly effective method of obtaining measurements with increased time-resolution for lightly damped ultrasonic or acoustic transducers.