An ultrafast broadband digital signal processing approach to pulse echo measurements

Abstract

Pulse-Echo (PE) measurements are commonly used to determine the sound velocity in a sample of known length. In PE measurements, the interface between the transducer and buffer rod, and that between the buffer rod and sample, introduces a total phase shift, Φ, to the acoustic wave that must be accounted for if high accuracy in the velocity is desired. The appropriate time correction, τ=Φ/ω, is traditionally determined by measuring the time-of-flight of multiple acoustic waves with different angular frequencies, ω. A single PE measurement can take several minutes, depending on experimental details such as the number of frequencies measured and the amount of signal averaging performed. Several minutes of data acquisition is tolerable for static experiments, but it is too long for many dynamic processes of interest in biology, pulsed magnetic fields, or any other rapidly changing system. This work describes an approach to PE in which a single broadband signal is collected and later processed offline using standard digital signal processing techniques. We demonstrate that a single captured waveform can be processed to yield the same information as 80 separate waveforms collected over an 80 MHz span, enabling accurate PE measurements on sub-second time scales.