Abstract
In range-Doppler ultrasound applications, the velocity of a target can be measured by transmitting a mechanical wave, and by evaluating the Doppler shift present on the received echo. Unfortunately, detecting the Doppler shift from the received Doppler spectrum is not a trivial task, and several complex estimators, with different features and performance, have been proposed in the literature for achieving this goal. In several real-time applications, hundreds of thousands of velocity estimates must be produced per second, and not all of the proposed estimators are capable of performing at these high rates. In these challenging conditions, the most widely used approaches are the full centroid frequency estimate or the simple localization of the position of the spectrum peak. The first is more accurate, but the latter features a very quick and straightforward implementation. In this work, we propose an alternative Doppler frequency estimator that merges the advantages of the aforementioned approaches. It exploits the spectrum peak to get an approximate position of the Doppler frequency. Then, centered in this position, a centroid search is applied on a reduced frequency interval to refine the estimate. Doppler simulations are used to compare the accuracy and precision performance of the proposed algorithm with respect to current state of the art approaches. Finally, a Field Programmable Gate Array (FPGA) implementation is proposed that is capable of producing more than 200 k low noise estimates per second, which is suitable for the most demanding real-time applications.
Highlights
Doppler ultrasound is employed in several applications, like the monitoring of industrial processes [1,2], biomedical investigations [3], and non-destructive tests [4]
We propose an alternative Doppler frequency estimator that merges the advantages of the aforementioned approaches
It exploits the spectrum peak to get an approximate position of the Doppler frequency
Summary
Doppler ultrasound is employed in several applications, like the monitoring of industrial processes [1,2], biomedical investigations [3], and non-destructive tests [4]. Due to several phenomena like velocity broadening (in a fluid the adjacent particles move with slight different velocities), geometrical broadening (the ultrasound waves sourced by the finite transducer aperture reach the target with slight different angles θ [5]), or the transit-time broadening (the particle crosses the ultrasound beam in a finite time [6]), the Doppler spectrum is composed by a relatively large bandwidth instead of a single frequency tone. General details of the data processing employed in Pulse-Wave ultrasound can be found in several papers and books, for example References [3,10,11,12]. The phase rotation of echoes from subsequent PRIs corresponds to the frequency fv described quantitatively by the Doppler Equation (1)
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