Coulomb coupling has been applied for imaging of bulk and guided acoustic waves propagating in a 0.5 mm thick, z cut
Lithium Niobate single-crystal. The excitation and detection of acoustic waves was performed by localized electrical
field probes. The developed scheme has been applied to imaging of the transport properties of skimming longitudinal and
guided acoustic waves. A short pulse of 20 ns has been used for the excitation of acoustic waves. Broadband coupling is
achieved since neither mechanical nor electrical resonances are involved. The attenuation of acoustic waves in piezoelectric
crystals is studied by this method. A thin film of conductive silver paint was deposited on the surface of the
crystal acting as an acoustic attenuator inducing also mass loading effects and shortening of electrical fields. The group
velocities of the propagating acoustic waves for both conditions, with and without the conductive silver paint film, are
determined from the propagation of the acoustic wave fronts.
The mechanical properties of cells reflect dynamic changes of cellular organization which occur during physiologic
activities like cell movement, cell volume regulation or cell division. Thus the study of cell mechanical properties
can yield important information for understanding these physiologic activities. Endothelial cells form the thin inner
lining of blood vessels in the cardiovascular system and are thus exposed to shear stress as well as tensile stress
caused by the pulsatile blood flow. Endothelial dysfunction might occur due to reduced resistance to mechanical
stress and is an initial step in the development of cardiovascular disease like, e.g., atherosclerosis. Therefore we
investigated the mechanical properties of primary human endothelial cells (HUVEC) of different age using scanning
acoustic microscopy at 1.2 GHz. The HUVECs are classified as young (tD < 90 h) and old (tD > 90 h) cells
depending upon the generation time for the population doubling of the culture (tD). Longitudinal sound velocity and
geometrical properties of cells (thickness) were determined using the material signature curve V(z) method for
variable culture condition along spatial coordinates. The plane wave technique with normal incidence is assumed to
solve two-dimensional wave equation. The size of the cells is modeled using multilayered (solid-fluid) system. The
propagation of transversal wave and surface acoustic wave are neglected in soft matter analysis. The biomechanical
properties of HUVEC cells are quantified in an age dependent manner.
Acoustic bulk waves were excited by local electric field probe in an anisotropic piezo-electric crystal Lithium Niobate
(X-cut). A narrow pulse with a width of 25 ns was used for excitation to obtain wide frequency content in the Fourier
domain. A wide spectrum ensures metamorphosis of bulk waves into Lamb waves for scan lengths comparable to the
involved wavelengths. The low frequency content experiences multiple reflections from the two surfaces of the plate and
disperses along the propagation direction. Acoustic bulk wave's evolution and transformation to Lamb waves are
illustrated and explained with the aid of the Lamb wave dispersion phenomenon. The holographic images in the Fourier
domain exemplify the metamorphosis of waves during propagation following the excitation at an approximate point
source.
The mechanical properties of blood vessel walls are important determinants of physiology and pathology of the
cardiovascular system. Acoustic imaging (B mode) is routinely used in a clinical setting to determine blood flow and wall
distensibility. In this study scanning acoustic microscopy in vitro is used to determine spatially resolved tissue elastic
properties. Broadband excitation of 30 MHz has been applied through scanning acoustic microscopy (SAM) for
topographical imaging of swine thoracic aorta in reflection mode. Three differently treated tissue samples were investigated
with SAM: a) treated with elastase to remove elastin, b) autoclaving for 5 hours to remove collagen and c) fresh controlled
untreated sample as control. Experimental investigations are conducted for studying the contribution of individual protein
components (elastin and collagen) to the material characteristics of the aortic wall. Conventional tensile testing has been
conducted on the tissue samples to study the mechanical behavior. The mechanical properties measured by SAM and tensile
testing show qualitative agreement.
Due to the dependence on a limited amount of parameters, the dispersion relations of Lamb waves can be presented in a generalized way. This is exemplified for the different established typical representations. Special attention is given to the representation of the momentum on energy, which is well suited to discuss basic features since energy as well as momentum is the properties which are strictly conserved in loss free homogeneous materials. Representations involving the phase and group velocity are discussed. Features related to level crossing of interacting modes and relations to basic mechanical properties especially relevant to Lamb waves are included in the presentation and discussion.
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