The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (High Intensity Focused Ultrasound) applications. In addition to the development and validation of a novel, 100 MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10 μm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about ±12% (±1 dB) up to 40 MHz, ±20% (±1.5 dB) from 40 to 60 MHz and ±25% (±2 dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth.

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Evaporation of a single droplet of a binary mixture of ethanol/iso-octane was numerically studied. Liquid/gas interface was tracked using VOF multiphase model. As ethanol and iso-octane form a highly non-ideal mixture, vapour-liquid-equilibrium (VLE) calculations were made using UNIFAC group contribution method. Source terms arising due to interfacial mass transfer are implemented in the continuity, momentum, energy and species equations. In this study, commercial CFD solver, Ansys Fluent 12.1 was used. VLE calculations and the source terms were implemented using user defined functions. A non-isothermal flow condition with droplet and surrounding medium at different temperatures was studied. Time history of temperature, evaporation rate, droplet size and shape were studied and reported. A parametric study of droplet composition and Reynolds number has been performed and reported in this study.

The primary objective of this research was to develop and optimize the calibration techniques for ultrasonic hydrophone probes in acoustic field measurements up to 100 MHz. Dependable, 100 MHz calibration method was necessary to examine behavior of the sub-millimeter fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also of interest was to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (High Intensity Focused Ultrasound) applications. The innovative elements of this research include implementation of a prototype FO sensor with an active diameter of about 10 µm that exhibits uniform frequency range and does not require any spatial averaging correction procedure up to about 75 MHz. The sensor is also sufficiently robust to measure fields generated by HIFU transducers. Accordingly, to test the FO probe behavior a novel 100 MHz bandwidth calibration technique was developed. This technique provided the sensitivity of conventional, finite aperture piezoelectric hydrophone probes as a virtually continuous function of frequency and allowed the verification of the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined initially to be about ±12% up to 40 MHz, ±20% up to 60 MHz and ±25% up to 100 MHz. Comparison of these data with those obtained from an independent laboratory is presented and a possibility of using the FO sensor as a reference tool to determine the phase response of finite aperture hydrophones is briefly discussed. Finally, the attempt is made to answer the question posed in the title. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will form an important breakthrough in acoustic measurements of both diagnostic and therapeutic fields.

Broadband fiber optic hydrophone probes are an attractive solution for characterization of ultrasound fields with sub-millimeter resolution up to 100MHz frequency range without need for complicated spatial averaging corrections. In this work, optical hydrophone sensors based on single mode straightcleaved fibers and down-tapered coated fibers with sensitive dimensions of less than 10μm have been reported. Thinly gold coated optical fiber sensors demonstrated a higher sensitivity and bandwidth performance than straight cleaved uncoated and down-tapered uncoated. The statistical analysis clearly indicates that the gold coated fibers with thickness of 30 nm provide a 26 dB improvement in sensitivity over that of the uncoated straight cleaved fibers, raising the overall sensitivity of the fiber optic hydrophone sensor to a value of -245 dB re 1V /μPa (unprecedented 0.56 V/ MPa). Broadband testing of these sensors with a 10MHz acoustic tone burst further indicates that the bandwidth of gold coated fiber sensor is as high as 60 MHz. Amplified optical source intensity noise limits the current intensity detection system up to 60MHz.