Simulation of incoherent and coherent backscattered wave fields from cavities in a solid matrix

This article was published in the Journal of the Acoustical Society of America [© Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America]. The article may be found at: http://dx.doi.org/10.1121/1.4763985This paper reports a study of the backscattered ultrasonic signal from a solid layer containing spherical cavities, to determine the conditions in which an effective medium model is a valid description of the response. The work is motivated by the need to model the response of porous composite materials for ultrasonic non-destructive evaluation (NDE) techniques. The numerical simulation predicts the response of a layer containing cavities at a single set of random locations, and compares it to the predicted response from a homogeneous layer with ensemble-averaged material properties (effective medium model). The study investigates the conditions in which the coherent (ensembleaveraged) response is obtained even from a single configuration of scatterers. Simulations are carried out for a range of cavity sizes and volume fractions. The deviation of the response from effective medium behavior is modeled, along with the trends as a function of cavity radius, volume fraction, and frequency, in order to establish an acceptability criterion for application of an effective medium model

Ultrasonic spectrometry and modelling that verifies shear-wave reconversion in micro- and nano-fluids

Ultrasonic spectrometry and modelling that verifies shear-wave reconversion in micro- and nano-fluid

Experimental validation of shear-mediated contributions to multiple scattering in concentrated random dispersions of spherical particles

This conference abstract was also presented at the 171st Meeting of the Acoustical Society of America, Salt Lake City, Utah, USA, 23rd-27th May 2016. Copyright (2016) Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. The following article appeared in The Journal of the Acoustical Society of America, 139 (4), pp. 2184-2184 and may be found at https://doi.org/10.1121/1.4950499

Thermo-elastic multiple scattering in random dispersions of spherical scatterers

Copyright 2014 Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America. The following article appeared in the Journal of the Acoustical Society of America, 136 (6), 3008 and may be found at: http://scitation.aip.org/content/asa/journal/jasa/136/6/10.1121/1.4900566?aemail=authorUltrasonic monitoring of concentrated suspensions and emulsions is limited in concentration range due to the inaccuracy of the multiple scattering models currently used to interpret measurements. This paper presents the development of a model for the additional multiple scattering caused by mode conversion to/from thermal waves. These effects are believed to cause significant deviation from established models for emulsions at high concentration, or small particle size, at low frequency. The relevant additional scattering coefficients (transition factors) are developed, in numerical and analytical form, together with the modification to the effective wavenumber. Calculations have been carried out for a bromohexadecane-in-water emulsion to demonstrate the frequency-dependence of the scattering coefficients, and the effective speed and attenuation

A comparison of stochastic and effective medium approaches to the backscattered signal from a porous layer in a solid matrix

This article was published in the Journal of the Acoustical Society of America and is also available at: http://dx.doi.org/10.1121/1.3598461This paper reports a study of the backscattering behavior of a solid layer containing randomly spaced spherical cavities in the long wavelength limit. The motivation for the work arises from a need to model the responses of porous composite materials in ultrasonic NDE procedures. A comparison is made between models based on a summation over discrete scatterers, which show interesting emergent properties, and an integral formulation based on an ensemble average, and with a simple slab effective medium approximation. The similarities and differences between these three models are demonstrated. A simple quantitative criterion is established which sets the maximum frequency at which ensemble average or equivalent homogeneous medium models can represent echo signal generation in a porous layer for given interpore spacing, or equivalently, given pore size and concentration

Acoustic scattering by a spherical obstacle: Modification to the analytical long-wavelength solution for the zero-order coefficient

This article was published in the Journal of the Acoustical Society of America and is also available at: http://dx.doi.org/10.1121/1.3543967Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low kca (typically kca < 0.01) and above at kca > 0.1, where kc is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A0. It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately

Anomalous small angle x-ray scattering simulations: proof of concept for distance measurements for nanoparticle-labelled biomacromolecules in solution.

Anomalous small angle X-ray scattering can in principle be used to determine distances between metal label species on biological molecules. Previous experimental studies in the past were unable to distinguish the label-label scattering contribution from that of the molecule, because of the use of atomic labels; these labels contribute only a small proportion of the total scattering signal. However, with the development of nanocrystal labels (of 50-100 atoms) there is the possibility for a renewed attempt at applying anomalous small angle X-ray scattering for distance measurement. This is because the contribution to the scattered signal is necessarily considerably stronger than for atomic labels. Here we demonstrate through simulations, the feasibility of the technique to determine the end-to-end distances of labelled nucleic acid molecules as well as other internal distances mimicking a labelled DNA binding protein if the labels are dissimilar metal nanocrystals. Of crucial importance is the ratio of mass of the nanocrystals to that of the labelled macromolecule, as well as the level of statistical errors in the scattering intensity measurements. The mathematics behind the distance determination process is presented, along with a fitting routine than incorporates maximum entropy regularisation

Parameters for simulations.

<p><i>The parameters used in the calculations for each molecule type. (a) the </i><i>value at which the </i><i>function is truncated before inversion to obtain distance distributions. (b) the maximum inter-particle separation used for basis functions for inversion of </i><i> (c) the spacing between basis functions.</i></p><p><i>Set A: errors at 0.01% I(0) and energies of 11.6–12.4 keV at 200 eV intervals. Gold atom or nanocrystal labels.</i></p><p><i>Set B: errors at 0.1% I(0) and energies of 11.800, 11.912, 11.914, 11.916, 11.918, 11.920, 11.922, 12.000, 12.200 keV. Gold nanocrystal labels.</i></p><p><i>Set C: errors at 0.01% I(0) and energies of 11.6–12.4 eV at 100 eV intervals. Gold and platinum nanocrystal labels.</i></p

Probability distribution for the distance between nanocrystal centres for 50 base-pair DNA with gold nanocrystals at each end, and a platinum nanocrystal at some position between the ends.

<p>(a) Distribution for the gold-gold distance (b) distribution for the gold-platinum distance. In each case, each set of data is plotted shifted by 0.6 for clarity. The spacing between the Au-Pt nanocrystal coordinates are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095664#pone-0095664-t003" target="_blank">Table 3</a>, and the curves are plotted for spacings (i)–(v) from bottom curve to top curve. Simulated errors in intensity were at 0.01% <i>I</i>(0) (set C).</p