Alain Jungman

Diffraction of ultrasonic waves from periodically rough liquid–solid surface

Theoretical and experimental results concerning diffraction of ultrasonic waves on periodic liquid–elastic solid interfaces are presented. A general system of linear equations is established and solved numerically for triangular surfaces. Theoretical results are in good agreement with measurements obtained by a broadband pulse‐echo system in the region where the wavelength is of the same order of magnitude as the period and much greater than the depth of the grating. In the spectrum of the reflection coefficient frequency minima are identified as the surface waves excited along the periodic surface.

Ultrasonic anomalies in the spectrum of acoustic waves diffracted by periodic interfaces

The energy distribution of elastic waves reflected from corrugated periodic solid surfaces is investigated. Broadband pulse echo experiments using ultrasonic spectroscopy are carried out for surfaces with a triangular profile. Sharp discontinuities observed in the received spectrum are interpreted as anomalies first introduced by R. W. Wood [Philos. Mag. 4, 396 (1902)]. These minima are identified as the mode‐converted signals along the interface with bulk or surface wave velocities. The observed anomalies may be used to characterize interfaces and quality of bonding.

Reflection from a boundary with periodic roughness: Theory and experiment

Reflection of elastic waves from a traction‐free solid–air boundary of periodic sawtooth profile is investigated experimentally and analytically. For an incident plane wave the surface displacements on the profile are computed as the solution of a singular integral equation. The reflected field is subsequently obtained by using an integral representation for the reflected field. Experimental results are presented for the relative amplitude spectrum for reflection from brass–air, perspex–air, and steel–air boundaries. Both the theoretical and the experimental results show that surface resonances of the profile significantly affect the frequency spectrum of the reflected waves. It is shown that the existence of sharp dips in the amplitude spectra of reflected waves can be attributed to destructive interference between direct reflections and reradiation from surface‐resonance motions. Good agreement is obtained between calculated results and experimental data.

On the origin of the anomalies in the reflected ultrasonic spectra from periodic surfaces

This letter discusses the physical origin of the sharp minima observed in the reflection spectrum of normally incident ultrasonic waves from periodic free solid and solid–liquid interfaces. It is shown that Rayleigh wave generation along the surface does not necessarily produce a corresponding minimum in a reflected spectrum unless some mechanism of energy loss is involved as well.

Ultrasonic wave scattering from solids with periodic surfaces: Theory and experiment

The problem of an ultrasonic wave scattered from solids with periodic surfaces is formulated analytically. This analysis uses an integral representation of the scattered elastodynamic field in terms of the surface displacement of a suitable canonical problem. A digitized ultrasonic spectrum analysis system is used to measure the frequency components of broadband pulse backscattered from periodic surfaces of various solids. Features of the observed amplitude spectra are analyzed based on theoretical predictions.

Measurements of ultrasonic parameters in fluid‐filled porous metals with different grain size

Ultrasonic wave propagation in sintered metallic samples (immersed in fluid) was investigated. Samples made out of bronze and out of stainless steel materials with particle sizes ranging from 30–600 μ were used in this study. In order to correlate particle size with ultrasonic parameters, all samples were chosen with approximately the same volume porosity of 30%. Fast and slow compressional waves, surface wave velocities, as well as attenuation, were measured. The frequency dependence behavior of these ultrasonic parameters was studied from 1–20 MHz and correlated to particle size. [This work was supported by NATO Grant 0131/87 and by the National Science Foundation Grant INT‐8614592.]

Backscattering of leaky Lamb waves from fiber‐reinforced composite laminates

Fiber‐reinforced composite laminates were studied by analyzing the backscattered amplitude spectra of an incident broadband pulse. An extensive spatial averaging was carried out in the frequency domain to identify the coherent backscattering signals. For various angles of incidence the received signal was spectrum analyzed by using a digitized system. A set of curves were generated that clearly identified the source of backscattering as backscattered leaky Lamb waves. Results were generated by this method for different orientations of the fibers and compared to other ultrasonic techniques.

Theoretical and Experimental Developments in Ultrasonic Evaluation of Periodic Surfaces

Most ultrasonic NDE experiments and their theoretical models deal with perfectly smooth interfaces, but true materials generally exhibit rough interfaces. As an approach to include the ultrasonic scattering which occurs on the different interfaces along the beam path, the reflection factors of acoustic waves diffracted by periodic surfaces is investigated theoretically and experimentally by looking at the frequency dependence of the reflected signal. Mode conversion bulk and surface waves are shown to be the result of strong coupling between the incident wave and the geometry of the grating. As a consequence, the geometrical parameters of the interface can be obtained to within 5%.

Finite beam reflection from periodic surfaces

Analytical expressions are obtained for the reflection coefficient of a bonded ultrasonic beam from a periodic stress‐free solid surface. The frequency dependence of the reflection coefficient shows a sharp minimum at a frequency which corresponds to an apparent “displaced” beam coupled along the interface and “leaks” back to the solid. These leaky waves are produced by the periodically rough surface at the solid‐air boundary. These leaky waves are observed by an experimental setup using broadband ultrasonic pulses. The effects of finite beam on the reflected amplitude in the time and frequency domain will be discussed. Experimental results are in good agreement with theoretical prediction. [This work is supported by the National Science Foundation.]

Interaction of ultrasonic waves by periodically rough liquid‐solid interfaces

When a broadband ultrasonic wave interacts with periodically rough liquid‐solid interfaces at normal incidence the reflected spectrum contains several minima which are characteristics of the various parameters of the interface as reported earlier [J. Acoust. Soc. Am. Suppl. I 68, S81 (1980)]. An analytical approach to this problem will be discussed which uses general boundary conditions suggested by Poiree [Rev. Cethedec 39, 21–24 (1974); 48, 7–34 (1976)]. These boundary conditions are expressed in terms of continuity of functions involving velocity field v, and stress tensor Tij in liquid and solid, respectively, as: V1 ⋅ ∇φ = V2 ⋅ ∇φ and Σj = 13 Tij1(∇φ)j = Σj = 13 Tij2(∇φ)j, where φ(x,z) = f(x) − z defines the profile. The frequency dependence of the reflection coefficient is calculated for various surface parameters. Correlation between height of the irregularities and intensities of diffracted orders is shown to depend mainly on the characteristics of the solid. Theoretical results for the reflected ...