Pulse Shaping to Mitigate Ringing of Ultrasound Transducers with Admittance-Based System Identification

Ringing of piezoelectric transducers complicates time-domain ultrasound measurements by increasing pulse length, narrowing bandwidth, and producing a 'dead zone' in the pulse envelope that obscures near-field measurements. This leads to decreased axial resolution, and a reduction of the region over which the ultrasound measurements are sensitive. Ringing is caused by resonant behavior of the transmitter, but can also occur from resonances within or between test objects, the receiver, and/or other components. This paper focuses on transducer ringing caused by radial modes of disc-shaped transmitters, but the techniques described are generalizable to other transmitter geometries. We eliminate ringing by making careful adjustments to the excitation pulse, and we call this 'pulse shaping'. We bring concepts from control systems and system identification theory, especially areas concerning feedforward control and input shaping. We implement a procedure that identifies a mechanical systems model from the electrical admittance spectrum of the transmitter, and then computes pulse shaping filters that are capable of canceling multiple ringing modes simultaneously. We include an in-depth review of previous work, an overview of applicable techniques, and experimental results section for various filter designs.