scholarly journals Ultrasonic wave propagation in reticulated foams saturated by different gases: High frequency limit of the classical models

1996 ◽  
Vol 69 (18) ◽  
pp. 2641-2643 ◽  
Author(s):  
Ph. Leclaire ◽  
L. Kelders ◽  
W. Lauriks ◽  
J. F. Allard ◽  
C. Glorieux
Keyword(s):  
Wave Propagation ◽  
Ultrasonic Wave ◽  
High Frequency ◽  
Frequency Limit ◽  
Ultrasonic Wave Propagation ◽  
High Frequency Limit ◽  
Classical Models ◽  
Different Gases ◽  
Reticulated Foams

scholarly journals High Frequency Ultrasonic Wave Propagation in  Anisotropic Materials

2021 ◽  
Author(s):  
◽  
Andrew Paul Dawson
Keyword(s):  
Wave Propagation ◽  
Ultrasonic Wave ◽  
High Frequency ◽  
Guided Wave ◽  
Ultrasonic Waves ◽  
Tissue Characterisation ◽  
Ultrasonic Wave Propagation ◽  
Matching Layer ◽  
Fibrous Tissues ◽  
Wave Modes

<p>The influence of highly regular, anisotropic, microstructured materials on high frequency ultrasonic wave propagation was investigated in this work. Microstructure, often only treated as a source of scattering, significantly influences high frequency ultrasonic waves, resulting in unexpected guided wave modes. Tissues, such as skin or muscle, are treated as homogeneous by current medical ultrasound systems, but actually consist of highly anisotropic micron-sized fibres. As these systems increase towards 100 MHz, these fibres will significantly influence propagating waves leading to guided wave modes. The effect of these modes on image quality must be considered. However, before studies can be undertaken on fibrous tissues, wave propagation in more ideal structures must be first understood. After the construction of a suitable high frequency ultrasound experimental system, finite element modelling and experimental characterisation of high frequency (20-200 MHz) ultrasonic waves in ideal, collinear, nanostructured alumina was carried out. These results revealed interesting waveguiding phenomena, and also identified the potential and significant advantages of using a microstructured material as an alternative acoustic matching layer in ultrasonic transducer design. Tailorable acoustic impedances were achieved from 4-17 MRayl, covering the impedance range of 7-12 MRayl most commonly required by transducer matching layers. Attenuation coefficients as low as 3.5 dBmm-1 were measured at 100 MHz, which is excellent when compared with 500 dBmm-1 that was measured for a state of the art loaded epoxy matching layer at the same frequency. Reception of ultrasound without the restriction of critical angles was also achieved, and no dispersion was observed in these structures (unlike current matching layers) until at least 200 MHz. In addition, to make a significant step forward towards high frequency tissue characterisation, novel microstructured poly(vinyl alcohol) tissue-mimicking phantoms were also developed. These phantoms possessed acoustic and microstructural properties representative of fibrous tissues, much more realistic than currently used homogeneous phantoms. The attenuation coefficient measured along the direction of PVA alignment in an example phantom was 8 dBmm-1 at 30 MHz, in excellent agreement with healthy human myocardium. This method will allow the fabrication of more realistic and repeatable phantoms for future high frequency tissue characterisation studies.</p>

Correspondence between the low- and high-frequency limits for anisotropic parameters in a layered medium

Geophysics ◽  
2009 ◽  
Vol 74 (2) ◽  
pp. WA25-WA33 ◽  
Author(s):  
Mercia Betania Costa e Silva ◽  
Alexey Stovas
Keyword(s):  
Wave Propagation ◽  
Layer Thickness ◽  
High Frequency ◽  
Layered Medium ◽  
Homogeneous Medium ◽  
Low Frequency ◽  
Single Layer ◽  
Vertical Axis ◽  
Frequency Limit ◽  
High Frequency Limit

Wave propagation in a layered medium when the wavelength is much greater than each layer thickness (low frequency) produces a response equivalent to that of wave propagation in an equivalent single-layer medium. This equivalent medium is transversely isotropic with symmetry about a vertical axis (VTI), and the elastic parameters are computed with the Backus averaging technique. Conversely, when the wavelength is comparable to each layer thickness (high frequency), the directional dependence of the phase velocity in the transmission response also can be simulated by replacing the layered medium with a single homogeneous medium with properties derived from a time average. It then can be treated approximately as a VTI medium. To compute the medium parameters, a method based on fitting the traveltime parameters is used. We investigated the relationship between Thomsen’s anisotropic parameters [Formula: see text] and [Formula: see text] computed for the equivalent medium in the low-frequency limit and for the homogenized medium in the high-frequency limit. In our experiments, we used a medium in which layers of only two isotropic materials alternate repeatedly. For the high-frequency limit, we obtained solutions for PP- and SS-wave propagation.

scholarly journals High Frequency Ultrasonic Wave Propagation in  Anisotropic Materials

2021 ◽  
Author(s):  
◽  
Andrew Paul Dawson
Keyword(s):  
Wave Propagation ◽  
Ultrasonic Wave ◽  
High Frequency ◽  
Guided Wave ◽  
Ultrasonic Waves ◽  
Tissue Characterisation ◽  
Ultrasonic Wave Propagation ◽  
Matching Layer ◽  
Fibrous Tissues ◽  
Wave Modes

<p>The influence of highly regular, anisotropic, microstructured materials on high frequency ultrasonic wave propagation was investigated in this work. Microstructure, often only treated as a source of scattering, significantly influences high frequency ultrasonic waves, resulting in unexpected guided wave modes. Tissues, such as skin or muscle, are treated as homogeneous by current medical ultrasound systems, but actually consist of highly anisotropic micron-sized fibres. As these systems increase towards 100 MHz, these fibres will significantly influence propagating waves leading to guided wave modes. The effect of these modes on image quality must be considered. However, before studies can be undertaken on fibrous tissues, wave propagation in more ideal structures must be first understood. After the construction of a suitable high frequency ultrasound experimental system, finite element modelling and experimental characterisation of high frequency (20-200 MHz) ultrasonic waves in ideal, collinear, nanostructured alumina was carried out. These results revealed interesting waveguiding phenomena, and also identified the potential and significant advantages of using a microstructured material as an alternative acoustic matching layer in ultrasonic transducer design. Tailorable acoustic impedances were achieved from 4-17 MRayl, covering the impedance range of 7-12 MRayl most commonly required by transducer matching layers. Attenuation coefficients as low as 3.5 dBmm-1 were measured at 100 MHz, which is excellent when compared with 500 dBmm-1 that was measured for a state of the art loaded epoxy matching layer at the same frequency. Reception of ultrasound without the restriction of critical angles was also achieved, and no dispersion was observed in these structures (unlike current matching layers) until at least 200 MHz. In addition, to make a significant step forward towards high frequency tissue characterisation, novel microstructured poly(vinyl alcohol) tissue-mimicking phantoms were also developed. These phantoms possessed acoustic and microstructural properties representative of fibrous tissues, much more realistic than currently used homogeneous phantoms. The attenuation coefficient measured along the direction of PVA alignment in an example phantom was 8 dBmm-1 at 30 MHz, in excellent agreement with healthy human myocardium. This method will allow the fabrication of more realistic and repeatable phantoms for future high frequency tissue characterisation studies.</p>

Simulation study of axial ultrasonic wave propagation in heterogeneous bovine cortical bone

2016 ◽  
Vol 140 (5) ◽  
pp. 3710-3717 ◽  
Author(s):  
Toshiho Hata ◽  
Yoshiki Nagatani ◽  
Koki Takano ◽  
Mami Matsukawa
Keyword(s):  
Wave Propagation ◽  
Cortical Bone ◽  
Ultrasonic Wave ◽  
Simulation Study ◽  
Ultrasonic Wave Propagation
Sign in / Sign up

Export Citation Format

Share Document