Papers by Keyword: Acoustic Microscopy

Abstract: Acoustic wave propagation in solids can carry valuable information on mechanical properties and is therefore used to determine Young, E, bulk, K and shear, G moduli which depend on longitudinal and transverse velocity VL and VT respectively. In this context acoustic microscopy can successfully be used in the investigations of porous materials. In micro-analysis, it directly determines the mechanical properties of materials via acoustic signature, V (z); this signature is obtained by recording the change in the reflected acoustic signal with the defocusing distance, z, as the sample is moved towards the acoustic lens. In this work, we simulate the porous alumina (PAl2O3) acoustic signature, V (z), as a function of porosity to evaluate the output signal attenuation at different operating frequencies. We continue our simulation by the determining of the propagating velocities as a function of porosity by the use of the fast Fourier transform (FFT). In a large part of this work, our interest concerns the study of the porous alumina microstructure by calculating the elastic constants. We compare then the obtained values of Young and bulk moduli to the published data given by various ultrasound methods.

Abstract: The determination of the characteristics and properties of thin films deposited on substrates is necessary in any device application in various fields. Adequate mechanical properties are highly required for the majority of surface waves and semiconductor devices. In this context, modelling the ultrasonic-material interaction, we present results of simulation curves of acoustic signatures for multiple thin film/substrate combinations. The results obtained on several structures (Al, SiO2, ZnO, Cu, AlN, SiC and Cr)/(Al2O3, Si, Cu or Quartz) showed a velocity dispersion of the Rayleigh wave as a function of layer thickness. The development of a theoretical calculation model based on the acoustic behaviour of these structures has enabled us to quantify the dispersive evolution (positive and negative) density. Thus, we have established a universal relationship describing the density-thickness variation. In addition, networks of dispersion curves, representing the evolution of elasticity modulus (Young and shear), were determined. These charts can be used to extract the influence of thickness of layers on the variation of elastic constants

Abstract: In this work, we study the microstructure of porous alumina Al₂O₃ through the acoustic signature behavior V(z). This function depends on the low porosity when annular lenses conditions at an operating frequency of 1 GHz are used. In non destructive control, this quantitative investigation which allows the determination of mechanical materials properties is of a great importance in the measurement of the surface waves attenuation in this type of biomaterials. Hence, we have numerically simulated the porous alumina acoustic signatures through variable occultation of generating rays at the lens center, in order to quantify the occultation limiting angle. Consequently, the evaluation of the equivalent Rayleigh velocity using the fast Fourier transform (F.F.T) spectra was achieved thanks to the suppression of the Rayleigh mode generation.