Excitation Of Ultrasonic Waves Research Articles

Determination of the elastic moduli of polymer films by a new ultrasonic reflection method

The development and first applications of a new ultrasonic reflection method for determination of the viscoelastic properties of polymer films are reported. The complex shear modulus G* and the complex longitudinal modulus L*=K*+4/3 G* of the samples are derived from the measured complex reflection coefficients of an ultrasonic shear and longitudinal wave, respectively. From G and L the Young's modulus E, the compression modulus K and the Poisson ratio v can be calculated for isotropic materials. A LiNbO 3 -transducer (10° rotated Y-cut) is used for the simultaneous excitation of longitudinal and transversal ultrasonic waves, which allows to determine different elastic constants by one measurement. A measuring cell with normal incidence of the ultrasonic waves is used. The equipment has been applied to study the time dependence of the moduli during film formation from an aqueous polymer dispersion and the isothermal curing of an epoxy resin. Furthermore, the temperature dependence of the elastic constants of a carbon-black filled rubber and during non-isothermal crystallization of a semi-crystalline polymer has been studied.

Characteristics of the excitation of ultrasonic waves by thin wafers of manganese zinc ferrite single crystals

It is suggested that thin wafers of a magnetostrictive material may be used as emitters of rf ultrasound. Single crystals of manganese zinc ferrite, which have high magnetostriction constants and low Foucault current losses, were used to investigate the orientational field dependences of the efficiency of excitation of acoustic waves having different polarizations. Some distinguishing features of the excitation of sound by single-crystal wafers compared with polycrystalline samples were observed, and the direction of propagation and polarization of the sound wave and its polarization relative to the crystallographic axes of manganese zinc ferrite with the highest conversion efficiency was identified.

Resonant electromagnetic excitation and detection of ultrasonic waves in thin sheets

A unified theory of the simultaneous electromagnetic excitation and detection of ultrasonic waves travelling in the through-thickness direction in conducting sheets in the presence of a static magnetic field is presented. What to our knowledge are the highest-frequency room-temperature measurements of this type are described for aluminium sheets of thickness as low as 20 μm for frequencies up to 120 MHz. Maxwell’s equations are solved for the geometry of a planar current sheet above a conducting sheet with sinusoidal time variation. It is shown how, from the solution of a single fourth-order differential equation for the magnetic vector potential, the coupled electromagnetic and elastic wave problem can be solved analytically. The effective transfer impedance is evaluated, a measure of the ultimate efficiency of the combined excitation and detection process. At acoustic resonance its amplitude is inversely proportional to the sum of the ultrasonic attenuation of the sample and the attenuation arising from the electromagnetic-elastic coupling. This high-frequency resonant method should open up a wide range of new applications for the nondestructive evaluation of thickness, ultrasonic attenuation, bonding, and delamination of thin sheets and coatings in the sub-10 μm to 1 mm thickness range.

The magnetic phase diagrams of dysprosium

The field dependence of the efficiency of electromagnetic-acoustic transformation in a Dy single crystal has been studied. Sharp changes of the transformation efficiency as a function of magnetic field H at different temperatures T, corresponding to different magnetic phase transitions, were found. In particular, intense excitation of longitudinal ultrasonic waves occurs in the regions of field-induced spin-reorientation transitions, which permit the construction of magnetic phase diagrams in the H - T plane for H along the two principal axes in the basal plane. The two diagrams were found to be somewhat different, and an explanation is presented.

Diffraction X-ray radiation from a relativistic oscillator in a crystal

Diffraction of X-rays in radiation from a relativistic oscillator formed by an external ultrasonic (laser) wave in a crystal is considered. Ultrasonic (laser) excitation, in the general case, leads not only to the formation of a transverse oscillator but also to the formation of a set of lattices by which the emitted photons are diffracted. It is shown that, in the particular case of a transverse ultrasonic wave excitation at tau .b<<1, the authors can neglect the ultrasonic wave influence on diffraction process. Just this situation is considered in detail in the present paper. The expressions for the angular and spectral distributions of considered radiation are derived. It is shown that the radiation spectrum, in this case, is more complicated than that of ordinary channelling radiation and its intensity in the vicinity of the Bragg frequency can be even higher than the intensity of the latter.

Low temperature magnetic phase diagrams of dysprosium and gadolinium

The field dependences of the efficiency of electromagnetic-acoustic transformation in Gd and Dy single crystals have been studied. The sharp peaks of the transformation efficiency corresponding to different magnetic phase transitions were found. In particular, intensive excitation of longitudinal ultrasonic waves occurs in the regions of field-induced spin-reorientation transitions. The data enables to construct H - T diagrams for Gd and Dy.

Ferroelectric crystals with periodic laminar domains as the micron superlattices for optic acoustic processes

Abstract The excitation and propagation of high frequency ultrasonic waves by the micron superlattices is cited as an example, the experimental results are compared with theoretical predictions. LiNbO3 and LiTaO3 crystals with periodic laminar domains with periods about several microns and several ten microns have been fabricated by Czochralski method of crystal growth with doped melts. These may be considered as the micron superlattices for optic and acoustic wave processes involving 3rd. rank tensor coefficients which change sign across the domain walls.

Reduction of threshold of acousto-optic effect in a nematic crystal subject to combined actions

Abstract The acousto-optic effect in a homeotropically aligned layer of a nematic liquid crystal was investigated subject to combined actions: 1, for coherent excitation of ultrasonic and viscous waves, 2, for ultrasonic action in an electric field near the Freedericksz transition. The acousto-optic effect threshold was reduced by two orders of magnitude. The experimental results are discussed using the facoustic streaming model. The theoretical analysis is supported by our experimental results.

An ultrasonic bridge for the study of viscoelastic properties of thin interface films

The method of elastic interface waves which is currently under development has proven effective in the investigation of viscoelastic properties of interfaces in solid bodies. The present paper is concerned with the development of a modified method of measurement, employing ultrasonic interface waves, which makes it possible to investigate the thermomechanical properties of thin interface layers. The effect of temperature variations in the substrates and transducers is eliminated by using a differential acoustic system. Comb transducers are used for excitation and reception of ultrasonic waves.

Excitation of ultrasonic Rayleigh leaky waves at liquid-solid interface for general angle incidence

Experimental results are presented to demonstrate the existence of ultrasonic leaky wave radiation from liquid-solid interface. This leaky wave is generated by a finite ultrasonic beam incident at any angle (not only at Rayleigh angle) to a liquid-solid interface and observed at the Rayleigh angle both forward and backward. It is suggested that the phenomena occurring at the Rayleigh angle incidence and producing (1) a complex reflected field and (2) a backscattered field are just two special cases of this general phenomenon.

Excitation of Ultrasonic Waves Due to Modulation of a Laser in a Magnetised Semiconductor

Excitation of Ultrasonic Waves Due to Modulation of a Laser in a Magnetised Semiconductor

Thermal interference-optical excitation of ultrasonic waves in condensed media

An investigation was made of an effective method for the excitation of ultrasonic waves in thin liquid films based on the pulsed heating of these films by an interference field of coherent radiation. The perturbations induced in the medium were measured from the diffraction of a cw laser beam. It is shown that the optimal conditions for the generation of monochromatic sound packets are achieved for exciting radiation having a pulse duration considerably shorter than the period of the acoustic waves. A method of determining the velocity and attenuation of the sound is proposed and the importance of edge effects in the relaxation processes of the perturbations is studied.

Investigation of piezoelectric properties of crystals using surface excitation of ultrasonic waves and some results for ferroelectric triglycine sulphate

The surface excitation of ultrasonic waves as a new method of investigation of piezoelectric properties of materials is suggested and experimental results specified to theZ-direction of a single crystal of triglycine sulphate (TGS) are reported. It has been found that the piezoelectric stress constant e23 of TGS depends on temperatureθ as:e23=K23(θc−θ)−1 whereK23=(31±0.5) As m−2 deg andθc=49.6°C.

Time and frequency behavior of sound waves thermally induced by modulated laser pulses

A temporally and spatially periodic light intensity distribution generates thermally in an absorbing sample a corresponding density variation which can be considered a standing sound wave. This thermal excitation of ultrasonic waves by modulated laser light has been investigated theoretically and experimentally. The sound waves were excited by two light beams of equal intensity derived from a mode-locked ruby laser. The amplitude, velocity, and damping of the sound waves were examined by Debye Sears diffraction of argon laser pulses.

Parametric excitaiton of ultrasonic waves in piezoelectric semiconductors

We have investigated the parametric excitation of ultrasonic waves in piezoelectric semiconductors by the application of a high-frequency electric field, near the electron-plasma frequency. The high-frequency field produces a nonlinear coupling between the ultrasonic waves and electron-plasma waves and leads to an instability when a critical value is exceeded.

Thermal excitation of ultrasonic waves by laser light

Thermal excitation of ultrasonic waves by laser light

Excitation of longitudinal ultrasonic waves in metals by ultra-high-frequency electric fields: Balkarei, Yu. I Soviet Physics—Solid State vol 11, no 6 (December 1969) p1300 (2063)

Excitation of longitudinal ultrasonic waves in metals by ultra-high-frequency electric fields: Balkarei, Yu. I Soviet Physics—Solid State vol 11, no 6 (December 1969) p1300 (2063)