Acoustic Velocity Measurements in the Air by Means of Laser Doppler Velocimetry: Dynamic and Frequency Range Limitations and Signal Processing Improvements

Characterization of an acoustic liner by means of Laser Doppler Velocimetry in a subsonic flow

“…Some attempts to measure the Eulerian perturbation of velocity, also called the acoustic velocity, in a quiescent medium were first performed about 30 years ago by Taylor [24], demonstrating the ability of LDV to detect sound. Recent studies have been carried out concerning the measurement noise [28] and the specific signal processing [21,23,27]. The latter relies on time/frequency analysis.…”

Use of Frequency Trackers in Laser Doppler Velocimetry for Sound Field Measurement: Comparative Study of Two Estimators

“…The estimation of the velocity amplitude was then based on the analysis of the averaged density spectrum of the signal [5], but this approach led to high variance estimates and appeared to be strongly dependent on the seeding conditions. Recently, a "rst experiment has been carried out in the laboratory in order to test this technique over a large range of acoustic levels and frequencies, with promising results [6], and current work aims to carefully assess and improve the accuracy of the technique for acoustic applications [7]. It was pointed out that as velocity variations due to an acoustic "eld lead to temporal variations of the frequency of the Doppler signals, the instantaneous frequency (IF) introduced by Ville [8] and Gabor [9] is a very relevant quantity to consider, as it is simply proportional to velocity variations.…”

“…Previous studies have shown the abilities and limitations of time}frequency analysis for Doppler signal IF estimation in the context of LDV measurement [6,10]. A model of the signal has been established which makes possible the use of parametric methods to estimate the IF law; in a recent study [11], such a method, the Kalman "ltering, was shown to give promising results.…”

Digital Calibration Procedure for Laser Doppler Velocimetry in Acoustics

“…Its principle is based on laser velocity with low sampling frequency. Then, digital signal interferometry [1]: Two coherent laser beams, crossed and processing methods consist in estimate the acoustic parameters focused, define a measuring volume in which an interference from the phase 9o(k) obtained thanks to the transformation pattern, made of bright and dark fringes, appear. These fringes are then shifted by means of a Bragg cell working at FB = 40 MHz.…”