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The fiber optic ultrasonic sensor's discrete light diffraction orders are not produced if the width of the light beam is of the order on ultrasonic wavelength or less. This implies that any model based on the Raman-Nath theory concerning ultrasound and light beam parameters is applicable only under certain conditions. Thus, for any 'excellent spatial resolution' a tomographic approach is required. The approach that could be adopted for the purpose is reported.

The authors Wu et al. failed to resolve the problems associated with the position-dependent changes in sensor sensitivity for fiber optic ultrasonic sensors. According to them, the effects of the ultrasound on the light beam ranges from light deflection, through Raman-Nath regime, to the transition regime approaching Bragg diffraction for ranges of 3-15 MHz. The reason of its fallout is discussed.

Based on a numerical solution to the Burger's equation, a computational model is developed to describe the propagation of an initially sinusoidal ultrasonic bounded beam. The propagation algorithm fully describes the combined effects of nonlinearity and attenuation mechanisms, which are responsible for the predicted growth and depletion of higher harmonics in a liquid medium. The model also incorporates reflection of the bounded beam from a solid plate immersed in the liquid and continues the propagation description after reflection. The important features of the computer model are presented and representative results are given for a 2.98-MHz, 2.0-cm-diam beam. [ABSTRACT FROM AUTHOR]

Low-MHz, continuous ultrasonic waves traveling in a transparent medium cause light to be diffracted into discrete diffraction orders when light and sound propagation directions are normal to each other. When pulsed ultrasonic waves are used the diffraction orders split into secondary orders which are asymmetric with respect to the central diffraction order. This splitting is derived and a general expression provided for the intensity as a function of the ultrasonic pulse Fourier spectra. Examples are provided which demonstrate the degree of asymmetry for an exponential driving pulse and the convergence to the classic Raman-Nath results when the pulse approaches a continuous wave. [ABSTRACT FROM AUTHOR]

A numerical integration method is devoloped to calculate the intensity profile of an ultrasonic beam reflected from a liquid-solid interface. This numerical treatment is used to calculate nonspecular reflectivity at a range of angles of incidence near and at the Rayleigh angle. Calculations for a water-stainless steel interface are compared to a known approximate analysis for various beamwidths and frequencies. The theoretical predictions of the reflected beam profile near the Rayleigh angle of incidence are compared to experimental results. [ABSTRACT FROM AUTHOR]

Poles of the infinite plane-wave reflection coefficient are used to show a correspondence between Rayleigh and Lamb modes of vibration. It is demonstrated that a Rayleigh vibrational mode is a special type of Lamb mode of vibration. Further, it is shown that it should be expected that one vibrational mode for a thick plate should be similar to the theoretically predicted vibrational mode of an infinite half space, a Rayleigh mode. Thus, it is consistent to use a thick plate as an approximation to an infinite half space and expect results predicted by Rayleigh-wave analysis. Subject Classification: [43]35.54; [43]40.24. [ABSTRACT FROM AUTHOR]

Schlieren techniques are used to show that bounded beam reflection effects occur at liquid/solid-plate/liquid (L/SP/L) interfaces which are analogous to the bounded beam reflection effects reported previously at liquid/solid (L/S) interfaces. At L/SP/L interfaces, nongeometric effects are shown to be present in both the reflected and transmitted beams when the incident angle of an ultrasonic beam corresponds to the Lamb angle. In addition, similarities between wave phenomena at L/SP/L interfaces and L/S interfaces are presented which suggest that the description of bounded beam reflection derived by Bertoni and Tamir for a L/S interface can be qualitatively applied to the L/SP/L interface case. This theory is shown to account for the lateral extent to which a leaky Lamb surface wave, excited by mode conversion, propagates. Subject Classification: [43]35.54; [43]20.40, [43]20.30. [ABSTRACT FROM AUTHOR]

Reflectivities are calculated as functions of sonic incidence angle, densities, and sonic velocities. The resulting sets of curves are used to determine under which conditions reflectivity measurements can or cannot yield information about the values of sonic velocities and density of sea ice. Subject Classification: 30.25, 30.30. [ABSTRACT FROM AUTHOR]

The diffraction of monochromatic light by reflection off a single-frequency ultrasonic surface wave of arbitrary standing-wave ratio is analyzed theoretically, with the assumption that the light and sound beams share a direction of symmetry. The diffraction integral is solved for the case in which the surface illumination has a uniform intensity cross section, and also for a Gaussian intensity cross section. The dependences of the diffracted light intensities in the limiting case of small sound-beam intensity are examined in detail for varying standing-wave ratios. [ABSTRACT FROM AUTHOR]

Three optical methods, formerly only used for isotropic media, are applied to find the ultrasonic velocities in sapphire. From the results the elastic constants are calculated for this crystal. The elastic moduli are determined from measurements of ultrasonic velocities in different crystallographic directions, and Young's modulus is plotted as function of these directions. [ABSTRACT FROM AUTHOR]

A numerical integration method for the description of acoustic bounded beams is used to calculate possible backscattering strength from a smooth liquid-solid interface. It is shown that the backscattering strength is maximum for Rayleigh angle incidence. The influence of beam shape and beamwidth on the backscattering strength near the maximum is demonstrated. [ABSTRACT FROM AUTHOR]

Schlieren techniques are used to show that a bounded ultrasonic beam impinging on a liquid-single-crystal-copper interface, and generating generalized surface and pseudo surface waves, can produce reradiation fields which result in changes in the reflected beam similar to effects observed at liquid-isotropic-solid interfaces when Rayleigh waves are generated. The existence of these reflected beam effects at water-single-crystal-copper interfaces is attributed to the component of the particle displacement ellipse of the generated surface wave which is perpendicular to the crystal surface. A parameter β, characteristic of this perpendicular particle motion, is introduced and its value calculated from existing surface-wave particle-motion data. Observed reflected beam effects are described in terms of the parameter β. [ABSTRACT FROM AUTHOR]

A novel insonification system, intended for the verification of the existence and assessment of single-frequency, nonthermal vibrational effects of ultrasound on biological targets, is described. The induction of vibration-triggered damage was made possible by insonifying suitable targets immersed in liquid nitrogen with continuous-wave ultrasound at approximately 3, 5, and 7 MHz, while monitoring the ultrasonic intensities (2-24 mW/cm²) by acoustic and acousto-optic methods. The extent and nature of vibration-induced damage in recovered samples may then be assessed by a variety of analytical procedures. [ABSTRACT FROM AUTHOR]

The actual phase modulation introduced in a light beam by reflection off a surface corrugated in an arbitrary manner is calculated. The forms of the light intensity distribution in the reflection of a uniform- or Gaussian-intensity monochromatic circular light beam from a sinusoidal cylindrically corrugated surface are given. [ABSTRACT FROM AUTHOR]

Optical techniques are employed to investigate reradiation patterns of ultrasonic waves incident on flat liquid-solid interfaces. It is shown that, for Rayleigh-angle incidence, reflection takes place into a cone rather than only into the forward direction. The apex angle of the cone is found to be twice the Rayleigh angle. [ABSTRACT FROM AUTHOR]

The intensity distribution in the orders of a light-diffraction pattern produced by the interaction of a progressive ultrasonic surface wave and a monochromatic light beam is calculated. The amplitude of the surface wave is determined from the light-intensity distribution in the diffraction pattern. The spacing of the diffraction orders is related to the surface wave velocity and the angle of light incidence. [ABSTRACT FROM AUTHOR]

The diffraction of light by progressive, sinusoidal ultrasonic waves in water is investigated experimentally for conditions where Raman-Nath diffraction or Bragg reflections might occur. Results are given for frequencies between 3 and 12.3 Mc/sec and for angles between the direction of sound and light propagation within ±1° of normal incidence. [ABSTRACT FROM AUTHOR]

Light-diffraction patterns produced by wide ultrasonic beams of 5.235 and 8.786 Mc/sec are investigated for normal and slightly nonnormal incidence. A method for the correct alignment of the transducer is described. The results are discussed regarding agreement between experiment and theory. [ABSTRACT FROM AUTHOR]

A simple method, based on the total reflection of a sound beam from a liquid-solid boundary at the critical angles, is described. With this method, it is possible to measure the velocity of longitudinal and shear waves in the solid by locating the angles of maximum reflection in the liquid. [ABSTRACT FROM AUTHOR]