Alain Tinel

Experimental demonstration of the negative refraction of a transverse elastic wave in a two-dimensional solid phononic crystal

The negative refraction of transverse elastic waves is demonstrated experimentally in a two-dimensional phononic crystal (PC) made of a square lattice of cylindrical air cavities in an aluminum matrix. Dispersion curves of elastic waves in this PC exhibit a unique branch with phase and group velocities of opposite signs in a broad frequency range. Measurement of refraction angles through prismatic PC included in an aluminum block demonstrates negative refraction of elastic transverse wave.

Numerical description of the edge mode at the beveled extremity of a plate

This paper deals with the reflection of a two-dimensional harmonic Lamb wave at the beveled end of a plate. The existence of a resonant edge mode is described by a numerical model. It is proved that the edge mode is the resonance of different complex modes. The behavior of this mode as a function of the bevel angle is studied. Its amplitude decreases and its resonance frequency shifts as the bevel angle decreases from 90 to 85 deg. An unexpected strong variation of the repartition of the reflected energy is linked to this phenomenon.

Estimating frame bulk and shear moduli of two double porosity layers by ultrasound transmission

The acoustic plane wave transmission by water saturated double porosity media is investigated. Two samples of double porosity media assumed to obey Berryman and Wang (BW) extension (Berryman and Wang, 1995, 2000) of Biots theory in the low frequency regime are under consideration: ROBU® (pure binder-free borosilicate glass 3.3 manufactured to form the individual grains) and Tobermorite 11Å (the individual porous cement grains show irregular shapes). The de facto gap existing between theoretical and experimental data can be minimized by modifying adequately two of the parameters estimated from triaxial tests: the frame bulk and shear moduli. The frequency dependent imaginary parts that follow necessary from the minimization are in relation with the energy losses due to contact relaxation and friction between grains.

Coupling of Lamb waves at a tee junction

Lamb wave propagation in an infinite plate is well known. In this experimental study, propagation in a limited plate and a rib-stiffened plate are investigated. Conversion phenomena, distribution of energy among converted Lamb wave and energy conservation are evaluated.

Band gap structures in underwater screens of periodically spaced porous plates.

Acoustic properties of different periodic structures composed of alternating fluid and fluid-saturated porous layers obeying Biots theory are investigated. At first, the network of modes and the transmission coefficients of finite structures of six plates are studied in the frequency-angle of incidence plane. It is shown that the network of modes concentrates in localized domains of the plane where the transmission coefficients will take the greatest values. With this minimum of six plates, the structures exhibit the main features as for structures containing more plates, especially those with an infinite number of plates. Then, considering infinite structures the band gap calculations are led using the Bloch-Floquet theorem. The evanescent and propagative zones in the frequency-angle of incidence plane are determined. What is proposed here is a class of underwater porous screens that exhibits band gaps extending over great angular domains and enlarging in the frequency domain when the pores at the interfaces of the porous plates are sealed. The effect of porosity on the band gaps is also investigated.

Space‐wave number representation of transient waves. Experimental determination of the space location origin of Lamb waves on cylindrical shells

A new space‐frequency‐wave number representation is introduced. This representation is obtained by space‐sliding window FFT of the space‐frequency representation. This new method is used to experimentally define the space origin of the pulse‐generated Lamb wave on an air‐filled cylindrical shell immersed in water (relative thickness is equal to 0.03). The space‐wave number slices also allow the measurement of the Lamb‐wave complex wave numbers and their propagation direction (reduced frequencies range from 20 to 1000). The reflected field is experimentally separated from multiple propagating Lamb waves. This efficient method is complementary to the surface wave analysis method (S.W.A.M.) [Martinez et al., 16th ICA and 135th ASA Congress, II, 1359–1360 (1998)]. In particular, the space‐wave number representations are not limited by space windowing. The experimental results confirm the theoretical computations performed on waves propagating on a plane plate.

Scholte wave propagation and diffraction on a fluid-solid periodic rough surface

Experimental results concerning propagation and diffraction of a Scholte wave on periodic liquid-elastic solid interface are presented. We describe the behaviour of the Scholte wave when it meets the grating. Thus, to give a complete description of the phenomena observed, one must account for three effects: (1) Scholte conversion into Rayleigh waves, (2) diffraction along the grating in the liquid and in the solid, and (3) restoration of the Scholte wave at the end of the grating

Negatively refracted transverse waves : study of the ultrasonic field at the exit of an elastic phononic crystal

A two-dimensional phononic crystal (PC) with square lattices composed of air holes in aluminum matrix is studied. The band structure of the PC exhibits some properties which allow the negative refraction of transverse wave transmitted through the PC. The left-handed behaviour of the PC is verified numerically with an emphasis on the process of refracted beam construction near the exit surface of the PC.

Negative refraction of transverse waves in an elastic phononic crystal

This paper reports numerical and experimental analyses of negative refraction process using a phononic crystal, made of a periodic arrangement of holes in aluminium. Dispersion curves are discussed and conditions for which negative refraction can appear are identified. Negative refraction is clearly obtained for transverse waves. Experiments confirm numerical predictions.

Scholte Wave Diffraction by a Periodically Rough Surface

Bulk wave reflection and diffraction in an infinite medium or plate have been studied for a long time. In a liquid medium, a bulk wave impinging on a plate, with velocity Cf, may generate Rayleigh or Lamb waves. A wave with phase velocity c may be generated, under an angle β (with the normal to the interface) only if the equation (1) Cf = c·sin(β) is satisfied; so the Scholte-Stoneley wave whose velocity is slightly less then Cf for usual solid mediums, may not be generated. However if engraved by a periodical grating a solid substrate may generate waves not satisfying equation (1); on thick substrates [1] and plates [2] part of the incident wave energy is considered to be converted in a Scholte-Stoneley wave, though such a wave has never been observed.