I. ACOUSTIC SURFACE WAVES: EXPERIMENT AND ANALYSIS, II. TIME-FREQUENCY ANALYSIS OF PHOTONIC DOPPLER VELOCIMETRY DATA

Heather A. Moon

This thesis is arranged into two parts: Underwater acoustic experiments and analysis and Photonic doppler velocimetry time-frequency analysis. Part I: Underwater acoustic experiments were performed on targets of varied shape and material. Solid spheres in water illuminated by ultrasound can display enhanced backscattering due to an axially focused scattering contribution. One of the mechanisms for producing the needed outgoing toroidal wavefront is the launching and guiding of a leaky Rayleigh-like wave around the surface of the sphere [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 78, 722-728 (1985)]. A related backscattering enhancement was also demonstrated for spherical shells [S. G. Kargl and P. L. Marston, J. Acoust. Soc. Am. 85, 1014-1028 (1989)]. The present research demonstrates that a similar backscattering enhancement is detectable for axisymmetric ultrasonic illumination of a solid prolate brass spheroid. By using short tone burst illumination, the axially focused contribution to the scattering is distinguishable from the specular reflection and other contributions to the scattering. The evidence for the Rayleigh wave mechanism is seen in the timing of this contribution and bistatic measurements: experimental and theoretical predictions are supportive. This research supports surface-guided ray theory for variable curvature objects in water. Part II: Photonic Doppler Velocimetry (PDV)[D. Dolan, Rev. Sci. Inst. 81 (5) (2010)] is a technique used for measuring high velocities in shock physics experiments. Typical time-frequency analysis techniques include spectrogram analysis and short-time Fourier transform methods. These techniques are limited by a so-called uncertainty method that is said to prohibit one from obtaining both velocity and time precision in the same analysis of PDV data [B. Jensen, J. Appl. Phys, 101(1) (2007)]. To overcome this uncertainty principle, the bispectrum of Cohen [L. Cohen, Proc. IEEE 77(7) 941-981 (1989). L. Cohen, {\it Time-frequency analysis} Princeton Hall PTR 778 (1995)] and synchro-squeezed wavelets of Daubechies et al. [I. Daubechies et al. Appl. Comp. Harm. Analysis 30 (2) 243-261 (2011). I. Daubechies and S. Maes {\it Wavelets in Medicine} Routledge 527-546 (2017)] and Thakur et al. [G. Thakur, Excursions Harm. Analysis, 4 397-406 (2015)]\cite{thakur2015synchrosqueezing} are applied to PDV data. Results for obtaining velocity profiles are compared to typical methods showing that, indeed, the uncertainty principle does not apply after the measurement is made.

I. ACOUSTIC SURFACE WAVES: EXPERIMENT AND ANALYSIS, II. TIME-FREQUENCY ANALYSIS OF PHOTONIC DOPPLER VELOCIMETRY DATA

Files and links (1)

Abstract

Metrics

Details