Loic Martinez

Lamb Wave Sensor for Viscous Fluids Characterization

This paper is a study of a new sensor for fluid characterization. This sensor is composed of a stainless steel plate in contact with a viscous material. The aim is to characterize the material viscosity by using reflected Lamb waves at the boundary interface. In order to identify the effects on the Lamb reflected modes by the viscous material, a complete study of the propagation wave in the alone plate is first presented. The propagation modes of the loaded plate are then investigated. By monitoring the mechanical impedance, the viscosity of the material in contact is extracted. In order to validate the experimental setup, the mechanical impedance variation is measured for different water-glycerol mixtures. Results are in good agreement with those obtained by other techniques in the literature.

Surface acoustic wave depth profiling of a functionally graded material

The potential and limitations of Rayleigh wave spectroscopy to characterize the elastic depth profile of heterogeneous functional gradient materials are investigated by comparing simulations of the surface acoustic wave dispersion curves of different profile-spectrum pairs. This inverse problem is shown to be quite ill posed. The method is then applied to extract information on the depth structure of a glass-ceramic (alumina) functionally graded material from experimental data. The surface acoustic wave analysis suggests the presence of a uniform coating region consisting of a mixture of Al2O3 and glass, with a sharp transition between the coating and the substrate. This is confirmed by scanning electron microscope with energy dispersive x-ray analysis.

Study of the bending modes in circular quartz resonators

An experimental and theoretical study of bending modes in a partially electroded circular piezoelectric quartz (AT-cut) with free edge is presented. The quartz is excited by a voltage pulse applied on the electrodes, and its surface is scanned by a laser vibrometer that measures the out-of-plane displacements. The classical theory of bending of thin disks is used to describe the flexural modes at frequencies lower than the first thickness shear resonance (6 MHz). A fairly good agreement is found between experimental and theoretical results for the forced mode shapes and for the resonance frequencies. However, it appears that the two springs used to maintain the disk in position introduce extra clamping conditions. Several source shapes were studied, among which a collection of an arbitrary number of forces is particularly useful. The two-dimensional wavenumber representation shows the presence of anisotropy related to the crystallographic axes at higher frequencies, which is not predicted by the model. The experimental phase velocities are compared to those given by the classical theory of disks and to those of Lamb A0 mode. This study confirms the correspondence at low frequencies between the A0 mode and the bending eigenmodes of a disk with finite size

Transient space-time surface waves characterization using Gabor analysis

Laser ultrasonics allow the observation of transient surface waves along their propagation media and their interaction with encountered objects like cracks, holes, borders. In order to characterize and localize these transient aspects in the Space-Time-Wave number-Frequency domains, the 1D, 2D and 3D Gabor transforms are presented. The Gabor transform enables the identification of several properties of the local wavefronts such as their shape, wavelength, frequency, attenuation, group velocity and the full conversion sequence along propagation. The ability of local properties identification by Gabor transform is illustrated by two experimental studies: Lamb waves generated by an annular source on a circular quartz and Lamb wave interaction with a fluid droplet. In both cases, results obtained with Gabor transform enable ones to identify the observed local waves.

New RF EMUS Transducer for Complex Fluid Characterization

Real-time measurements are of the outmost importance for developing industrial “on line” effective monitoring techniques for the elaboration of new soft materials. In this paper, we will show a new radio frequency (RF) electromagnetic ultrasonic (EMUS) transducer design and technique for remotely sensing the micro-rheological properties of complex fluids in hidden places. The new sensor consists in a single electrode loop deposited on the surfaces of an AT-cut quartz substrate magnetically coupled with a high quality RF antenna. This sensor is inductively excited by a loosely coupling with a transmitter/receiver (T/R) circular probe. A suitable electrical model of the probe/loaded EMUS transducer is proposed in order to extract the mechanical and electrical properties of a complex fluid in contact. Various tabulated Newtonian liquids (made from water-glycerol mixtures) are then studied to validate the capability of this technique to monitor their viscosity. These results show that this technique allows the online monitoring of hidden complex fluids.

2D Finite Impulse Response filters for surface wave identification

Elliptical areas transfer function Finite Impulse Response filters are investigated (E-FIR). The main axis of the elliptical area is oriented along the selected surface wave dispersion curve. The advantage of such areas is the analytical formulas of the impulse responses as a function of the frequencies bandwidths parameters, k and ω, without the need to use Inverse Fourier transform. E-FIR filters are tested on experimental space-time signals corresponding to the propagation of Lamb waves generated by a pulse and observed by classic transducers on a cylindrical shell and by laser Doppler on a plate. E-FIR filters exhibit their potential to extract Lamb modes and their direction of propagation, even in noisy datasets. Due to their natural round shape energy distribution in k-ω space, E-FIR filtering adds few artefacts to the filtered signals. By using wide k-bandwidth and narrow ω-bandwidth E-FIR filter, Gabor like analysis is also reached.

Gelation monitoring by quartz microbalance in pulse mode

Classical viscoelastic measurement setup with a quartz crystal microbalance uses a steady state input signal in order to measure the complex equivalent electrical parameters. Using a network analyzer, this method enables the measurement of the equivalent impedance around the first resonance peak of the quartz within a tiny frequency range (typically 10 kHz around a 6 MHz resonance frequency). However, due to the network analyzer acquisition time, such a setup cannot make two successive acquisitions in less than 15 s for one resonance peak. We excite the quartz by a short pulse and record its time impulse response. This kind of excitation allows us to record higher resonance peaks (up to the 11th order) and to reduce drastically the acquisition time, enabling up to 100 acquisitions per second.

Phonon localization methods through time and space: Experimental SAW phonon aspects on a cylindrical shell

A transient experimental study of Surface Acoustic Wave (SAW) propagation along a 1D medium as a function of time leads to a 2D space–time signal collection. Previous studies have shown that 3D space‐wave number–frequency representation S(x,k,f) allows the characterization of the space transient aspects of SAW generation [L. Martinez, J. Acoust. Soc. Am. 105, 952 (1999)]. In order to analyze the time transient aspect of phonon propagation, the 3D time–wave Number‐Frequency representation Z(t,k,f) is proposed. The Z(t,k,f) matrix is obtained by short time Fourier transforming each time signal of the 2D time–wave number representation. The Z(t,k,f) representation is used to experimentally investigate SAW generation and propagation around a cylindrical shell (the relative thickness is equal to 0.03) surrounded by water and excited by a pulse (0.1 s duration). For the air filled shell, the Z(t,k,f=const) slices show the time sequence of the continuous flow of incident phonons striking the insonified side of t...

Gel formation monitoring by acoustic spectroscopy

An acoustic technique in the audible range has been developed to characterize the sol–gel process. Resonances appear at the sol to gel transition of a sol–gel matrix when submitted to an acoustic wave. The range of the associated resonance frequencies leads to a very low propagation speed of sound (about 20 m/s). The resonance frequencies versus time curves, corresponding to the harmonic propagation modes, converge to a unique intersection point with the time axis corresponding to the gelation time tg. The temporal evolution of the resonance frequencies features the formation of the network. Actually, the evolution of the matrix is independent of the initial conditions (precursor concentration, hydrolysis rate). Depicting the ‘‘reduced frequency’’ fi/fi(∞) [fi(∞) is the long‐term resonance frequency for the harmonic mode i] versus the ‘‘reduced time’’ t/tg for various Si concentrations and hydrolysis rates results in a unique curve, revealing the insensitivity of the matrix formation process to the input ...

Slant-Stack analysis for the estimation of a marble degradation profile

Ultrasonic techniques are increasingly used in various fields such as mining, geotechnical, civil engineering, because they are non-destructive and easy to apply. These techniques are usually employed both in situ and in laboratory conditions to characterize and determine the dynamic and physical properties of rocks. In cultural heritage, the characterization of marble statue by acoustic wave is a wellknown non-destructive method. This paper undertakes a study of the Carrara marble that composes the statues exposed in the Château de Versailles gardens, in order to better understand the processes of deterioration affecting them. For this, a plate of Carrara marble is artificially aged through heating/cooling thermal cycles performed on one face of the samples. A Rayleigh wave is generated by a 1 MHz central frequency contact transducer exited by a voltage pulse. A laser vibrometry method is used to detect the Rayleigh wave propagation on the depth sample. In order to understand how the degradation and nonhomogeneity and Rayleigh velocity vary through depth, Slant Stack (SS) transform was used. This analysis is a particular case of the Radon Transform (TR). The results show a uniform vibration behavior of non-degraded sample and highlight three zones with different state of degradation in the altered marble sample. The extraction of relevant parameters using this analysis is promising for the characterization of marble and following up its weathering.