V. M. Levin

Principles of local sound velocity and attenuation measurements using transmission acoustic microscope

Fundamentals of transmission acoustic microscopy as applied to measurements of sound velocities and attenuation in thin specimens and films are discussed. The method is based on measuring the output signal A as a function of a distance z between the radiating and the receiving lenses in the two-lens focusing system of the transmission microscope. It is proposed to measure the A(z) dependence twice: initially without a specimen, and then in the presence of it. When a specimen is absent, maximum of the A(z)-curve arises in the confocal position of the lenses. In the presence of an object, the main peak of the curve is shifted, and its magnitude diminishes. Measuring the changes makes it possible to determine local values of sound velocities and attenuation. For data interpretation a theory of formation of the output signal in the two-lens focusing system was developed. The relationship between the peak shift and the ratio of sound velocities in a specimen and a couplant contains a correction depending on beam angle aperture.

The use of acoustic microscopy for biological tissue characterization

A system of transmission raster acoustic microscope with an ultrasound frequency of 450 MHz has been designed to investigate biological tissues and comparative analysis of their optical and acoustic images. The possibility of obtaining the contrast acoustic images of nonfixed, nonstained biological tissues and viscoelasticity measurements in microscale was demonstrated.

High-resolution ultrasonic ultrasound methods: Microstructure visualization and diagnostics of elastic properties of modern materials (Review)

High-resolution ultrasonic methods are briefly reviewed. Special attention is paid to the principles underlying acoustic microscopy, since exactly they provide the high resolution necessary for modern technologies. Examples of acoustic images of fullerite ceramics, metals, and carbon materials are given.

Scanning acoustic microscopy study of superhard C60-based polimerized fullerites

Abstract Ultrahard and superhard fullerites are a new class of the carbon materials produced recently by bulk polymerization of C60 and C70 fullerenes under high-pressure-high-temperature treatment. We applied the acoustic microscopy technique to measuring longitudinal and shear sound velocities and determinating elastic constants of the super- and ultra-hard polimerized fullerites. Bulk elastic modulus of ultrahard fullerites is essentially higher than diamonds one, while the shear modulus and the Young modulus are less. The acoustic microscopy images reflected microstructure of fullerite speciments were obtained.

Elastic properties of ultrahard fullerites

The elastic properties of C60 fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (cL=17–26 km/s) and transverse (cT=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond.

Microstructure, elastic and electromagnetic properties of epoxy-graphite composites

A set of epoxy resin-based composites filled with 0.25 – 2.0 wt.% of commercially available exfoliated graphite (EG) and thick graphene (TG), prepared by suspending EG particles in cyclohexane, and submitting the suspension to a series of grinding and ultrasonic dispersion steps, was produced. The microstructure of such epoxy-graphite composites has been studied by the impulse acoustic microscopy technique. According to acoustic microscopy data, exfoliated graphite microparticles have been well dispersed in the epoxy matrix. TG nanoflakes demonstrated persistent tendency to clustering and formation of agglomerates. The addition of graphite particles in small amount (0.25 – 2.0 wt.%) did not influence the bulk elastic properties of epoxy-graphite composite materials. Being extremely lightweight, 0.003 g cm−3, EG had a lower percolation threshold than TG, at the level of 1-1.5 wt.% against 2.1-3.2 wt.%, respectively. As a result, epoxy composites filled with 1.0-2.0 wt.% EG provided high electromagnetic (EM) interference shielding both at microwave and THz frequencies. In contrast, no significant influence of TG loading was observed at low weight fraction (up to 2 wt.%) on the EM performance of epoxy composites.

Observation of ultrasound velocity gradient in fullerene ceramics by acoustic microscopy

A scanning acoustic microscope is used to study the distribution of elastic properties in small samples (O 3 x 2 mm3) of new hard phases of C60. The specimens under investigation were synthesized from pure C60 powder under pressure P = 8 GPa in the temperature range 500-1650 K. The time-of-flight mode was used for bulk sound wave velocity determination in a direction parallel to the cylinders axis. Longitudinal sound wave velocities greater than 10,000 m/s were found for all specimens treated at temperatures higher than 1000 K. Using the B-scan mode allowed us to observe the velocity gradient in the samples periphery. The heterogeneous internal structure of the specimen is visualized in the images formed in C- and B-scan modes.

Internal friction and elastic properties of the high pressure-induced phases of solid C60

Abstract Solid C 60 is a new promising material made from giant high-symmetric carbon clusters. Though C 60 molecules are extremely stable at ambient conditions, heat treatment under high pressures induces transformations to other phases, in which some weak van der Waal-type bonding between C 60 molecules is replaced with covalent sp 3 bonds. Many new C 60 high pressure phases (HP) demonstrate a set of unique physical properties including mechanical and elastic ones. This paper is an analytic review of the experimental measurements of the elastic and dissipative properties of solid C 60 (from C 60 single crystal to C 60 ultrahard phase).

Integral and Local Elastic Properties of C60 Single Crystals

Elastie properties of the f.c.c. phase of solid C 60 have been determined experimentally on the base of sound velocity measurements in single crystalline specimens of different crystallographic orientations. Integral elastic properties were measured by the echo-pulse method at 5 MHz and local elastic parameters were measured by the acoustic microscopy technique. The local values obtained have confirmed with a good accuracy the results from measurements of integral elastic properties in single crystals of solid C 60 . From these experimental data the magnitudes of elastic stiffncss constants for the f.c.c. phase of solid C 60 were calculated. The results obtained are in good agreement with the theoretical estimations of elastic moduli made in terms of existing models of intermolecular interaction in C 60 .

Structure and elastic properties of immiscible LDPE-PP blends: dependence on composition

Abstract : Local elastic properties and microstructural features of low-density polyethylene-polypropylene (LDPE-PP) blends have been studied by microacoustical technique, differential scanning calorimetry and infrared spectroscopy. Focused ultrasonic beam of acoustic microscope has been employed to measure elastic wave velocities, bulk and shear elastic moduli and Poisson ratio, The experiments show that the mechanical properties of immiscible LDPE-PP blends are non-additively changeable in relation to ones of primary gomopolymers. Maximum of the moduli values is achieved with small addition of LDPE to PP. Additional drawing of bipolymer shows essential increasing of orientation ability for PP chains in 5/95 - 10/90% LDPE-PP compositions. DSC curves show no significant deviations in melting temperature and crystallinity degree for different compositions of PP and LDPE phases. Internal microstructure has been imaged for the blends by acoustic microscopy technique. It allows revealing dispersivity of components over the blend body.