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Estimation of layer thickness by the cost function optimization: phantom study

Tasinkiewicz J., Podhajecki J., Wojcik J., Falińska K., Litniewski J.

Hydroacoustics

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2015

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Vol. 18

161-166

EN

The aim of this work is to present preliminary results of the layer thickness assessment method based on optimization approach. The developed method is based on a multilayer model structure. The measured acoustic signal reflected from the layer is compared with a simulated signal on the basis of a multilayer model. The cost function is defined as the difference between the reflected signal measured using pulse echo approach and the simulated signal. The thickness of the solid layer is the parameter which minimizes the cost function yielding desired solution. Minimization of the cost function is performed with the simulated annealing algorithm. The results obtained with the developed method using measurement data of a custom design model are compared with the reference value and the accuracy of the method is checked. The relative error of the thickness estimation is 1.44%.

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Pulsed Focused Nonlinear Acoustic Fields from Clinically Relevant Therapeutic Sources in Layered Media: Experimental Data and Numerical Prediction Results

Kujawska T.

Archives of Acoustics

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2012

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Vol. 37, No. 3

269-278

EN

In many therapeutic applications of a pulsed focused ultrasound with various intensities the finite- amplitude acoustic waves propagate in water before penetrating into tissues and their local heating. Water is used as the matching, cooling and harmonics generating medium. In order to design ultrasonic probes for various therapeutic applications based on the local tissue heating induced in selected organs as well as to plan ultrasonic regimes of treatment a knowledge of pressure variations in pulsed focused nonlinear acoustic beams produced in layered media is necessary. The main objective of this work was to verify experimentally the applicability of the recently developed numerical model based on the Time- Averaged Wave Envelope (TAWE) approach (Wójcik et al., 2006) as an effective research tool for predicting the pulsed focused nonlinear fields produced in two-layer media comprising of water and tested materials (with attenuation arbitrarily dependent on frequency) by clinically relevant axially-symmetric therapeutic sources. First, the model was verified in water as a reference medium with known linear and nonlinear acoustic properties. The measurements in water were carried out at a 25.C temperature using a 2.25 MHz circular focused (f/3.0) transducer with an effective diameter of 29 mm. The measurement results obtained for 8-cycle tone bursts with three different initial pressure amplitudes varied between 37 kPa and 113 kPa were compared with the numerical predictions obtained for the source boundary condition parameters determined experimentally. The comparison of the experimental results with those simulated numerically has shown that the model based on the TAWE approach predicts well both the spatial-peak and spatial-spectral pressure variations in the pulsed focused nonlinear beams produced by the transducer used in water for all excitation levels complying with the condition corresponding to weak or moderate source-pressure levels. Quantitative analysis of the simulated nonlinear beams from circular transducers with ka ť 1 allowed to show that the axial distance at which sudden accretion of the 2nd or higher harmonics amplitude appears is specific for this transducer regardless of the excitation level providing weak to moderate nonlinear fields. For the transducer used, the axial distance at which the 2nd harmonics amplitude suddenly begins to grow was found to be equal to 60 mm. Then, the model was verified experimentally for two-layer parallel media comprising of a 60-mm water layer and a 60-mm layer of 1.3-butanediol (99%, Sigma-Aldrich Chemie GmbH, Steinheim, Germany). This medium was selected because of its tissue-mimicking acoustic properties and known nonlinearity parameter B/A. The measurements of both, the peak- and harmonic-pressure variations in the pulsed nonlinear acoustic beams produced in two-layer media (water/1.3-butanediol) were performed for the same source boundary conditions as in water. The measurement results were compared with those simulated numerically. The good agreement between the measured data and numerical calculations has shown that the model based on the TAWE approach is well suited to predict both the peak and harmonic pressure variations in the pulsed focused nonlinear sound beams produced in layered media by clinically relevant therapeutic sources. Finally, the pulsed focused nonlinear fields from the transducer used in two-layer media: water/castor oil, water/silicone oil (Dow Corning Ltd., Coventry, UK), water/human brain and water/pig liver were predicted for various values of the nonlinearity parameter of tested media.

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Zastosowanie teorii linii transmisyjnych do modelowania własności odbiciowych ośrodka geologicznego

Pasternak M.

Przegląd Elektrotechniczny

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2009

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R. 85, nr 11

139-141

PL

W artykule omówione zostało zastosowanie modelu linii transmisyjnej w przypadku ośrodka geologicznego tj. medium o słabo zdefiniowanej geometrii przestrzennej. Model taki okazuje się przydatny w symulacyjnych badaniach elektrycznych własności wierzchnich warstw gruntu. Tego typu podejście, posiłkując się parametrami stosunkowo łatwymi do zmierzenia, może okazać się przydatne w technice radarowego rozpoznania obiektów znajdujących się pod ziemią, bądź w ogólności za nieprzeźroczystymi przeszkodami.

EN

The transmission line model application for geological multilayer medium has been described in the paper. The approach seems to be useful for analyse of electrical reflectivity of soil subsurface structures. Such analyse is helpful to ground penetrating radar signal propagation modeling. The necessary model parameters can be measured in relatively easy way. The approach may be also useful for modeling of the radar through the wall detection process.

4

Interface inclusion problems in laminated medium

Rogowski B., Pawlik M.

Journal of Theoretical and Applied Mechanics

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2001

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Vol. 39 nr 3

621-635

EN

A moduli perturbation method is to used to construct the solution for the contact stiffness in the inclusion problem of a composite laminate under a state of torsional deformation. The inclusion is considered to be embedded at the interface of the laminate. The following solutions have been obtained: (i) the exact solution for the inclusion in a medium consisting of two layers and two half- spaces, (ii) a first-order accurate solution for a layered medium consisting of (n+m) constituents, (iii) an approximative solution for a physically inhomogeneous medium as the limiting case of the layered medium.

PL

Zagadnienia miedzypowierzchniowej inkluzji w ośrodkach warstwowych. Za pomocą metody perturbacji modułów znaleziono rozwiązania określające kontaktową sztywność w zagadnieniach inkluzji umieszczonej na powierzchni "sklejenia" warstwowego kompozytu będącego w stanie skrętnej deformacji. Otrzymano następujące rozwiązania: (i) dokładne rozwiązanie dla inkluzji w ośrodku składającym się z dwóch warstw i dwóch półprzestrzeni, (ii) rozwiązanie o dokładności pierwszego rzędu dla ośrodka (n+m)- warstwowego, (iii) przybliżone rozwiązanie dla ośrodka fizycznie niejednorodnego z modułami ścinania zmieniającymi się w sposób ciągły, otrzymane jako przejście graniczne w rozwiązaniu dla ośrodka warstwowego.