Lionel Haumesser

Negative refraction of acoustic waves using a foam-like metallic structure

A phononic crystal (PC) slab made of a single metallic phase is shown, theoretically and experimentally, to display perfect negative index matching and focusing capability when surrounded with water. The proposed PC slab is a centimeter scale hollow metallic foam-like structure in which acoustic energy is mediated via the metal lattice. The negative index property arises from an isolated branch of the dispersion curves corresponding to a mode that can be coupled to incident acoustic waves in surrounding water. This band also intercepts the water sound line at a frequency in the ultrasonic range. The metallic structure is consequently a candidate for the negative refraction of incident longitudinal waves.

Investigation of damage mechanisms of composite materials: Multivariable analysis based on temporal and wavelet features extracted from acoustic emission signals

Identification methods of nonlinear parameters are developed to characterize solid materials and soft tissues. In the frame of classical parametric interaction methods, the parameter evaluation is based on the measurement of quantities related to the acoustic wave propagation medium. They appear at frequencies combinations and/or multiple harmonic of primary wave frequencies, and are generally weak in comparison to the amplitudes of the sources. Hence, the use of experimental devices excited at high amplitude levels is required. One problem in the identification of nonlinear parameters is that the ultrasonic device itself is not exempt of nonlinearity. Generally speaking the problem is to ensure, for each specific configuration, that the involved instrumentation (waveform generator, voltage amplifier, transducer), the coupling medium, mutual interactions between many sources… do not perturb the evaluation of the investigated nonlinear effects.

Tunable phononic crystals based on piezoelectric composites with 1-3 connectivity.

Phononic crystals made of piezoelectric composites with 1-3 connectivity are studied theoretically and experimentally. It is shown that they present Bragg band gaps that depend on the periodic electrical boundary conditions. These structures have improved properties compared to phononic crystals composed of bulk piezoelectric elements, especially the existence of larger band gaps and the fact that they do not require severe constraints on their aspect ratios. Experimental results present an overall agreement with the theoretical predictions and clearly show that the pass bands and stop bands of the device under study are easily tunable by only changing the electrical boundary conditions applied on each piezocomposite layer.

Negative refraction of elastic waves in 2D phononic crystals: Contribution of resonant transmissions to the construction of the image of a point source

Negative refraction properties of a two-dimensional phononic crystal (PC), made of a triangular lattice of steel rods embedded in epoxy are investigated both experimentally and numerically. First, experiments have been carried out on a prism shaped PC immersed in water. Then, for focusing purposes, a flat lens is considered and the construction of the image of a point source is analyzed in details, when indices are matched between the PC and the surrounding fluid medium, whereas acoustic impedances are mismatched. Optimal conditions for focusing longitudinal elastic waves by such PC flat lens are then discussed.

Modelling nonlinearity in piezoceramic transducers: From equations to nonlinear equivalent circuits

Quadratic nonlinear equations of a piezoelectric element under the assumptions of 1D vibration and weak nonlinearity are derived by the perturbation theory. It is shown that the nonlinear response can be represented by controlled sources that are added to the classical hexapole used to model piezoelectric ultrasonic transducers. As a consequence, equivalent electrical circuits can be used to predict the nonlinear response of a transducer taking into account the acoustic loads on the rear and front faces. A generalisation of nonlinear equivalent electrical circuits to cases including passive layers and propagation media is then proposed. Experimental results, in terms of second harmonic generation, on a coupled resonator are compared to theoretical calculations from the proposed model.

Nonlinear constant evaluation in a piezoelectric rod from analysis of second harmonic generation

The design of transducers requires a clear understanding of their electromechanical behavior. This involves precise linear modeling as well as characterization. With the development of novel techniques such as harmonic imaging as well as high-power applications, nonlinear aspects must also be taken into account. In this study, harmonic generation in the mechanical displacement of a piezoceramic rod under high sinusoidal electric fields was measured. Theoretically, the nonlinearity can come from various sources: dielectric, mechanical, and electromechanical. The nonlinearity coming from external sources being eliminated or taken into account, it is shown here that the analysis, over a wide frequency range, of 2 parameters related to the harmonic distortion enables the respective identification of these sources and, at the same time, the evaluation of third-order constants of the material.

P2I-4 Experimental Study of the Non Linearity from Ultrasonic Transducers

The quantitative evaluation of the non linearity from a material is a characterization method currently used in various applications such as NDE or medicine. Such a measurement must be performed using a set of devices exempted of non linearity themselves. The purpose of the present work is to investigate the non linear behavior of transducers. A measurement method is proposed to evaluate the second harmonic generation in an ultrasonic transducer submitted to a high electrical excitation. Displacement at the surface of the transducer is measured by a laser probe, while the real electrical excitation is acquired. The method is based on measurement of fundamental and harmonic quantities on the acoustical axis of the transducer for aluminum samples of various thicknesses. The experimental set up includes a high power filter to avoid second harmonic electrical excitation. However, the possibility to take into account the presence of component at twice the fundamental frequency is considered in the proposed method. Then the second harmonic generation due to the loaded transducer itself is compared to the generation in a solid sample

Ultrasonic self-calibrated method applied to monitoring of sol–gel transition

In many industrial processes where online control is necessary such as in the food industry, the real time monitoring of visco-elastic properties is essential to ensure the quantity of production. Acoustic methods have shown that reliable properties could be obtained from measurements of velocity and attenuation. This paper proposes a simple, real time ultrasound method for monitoring linear medium properties (phase velocity and attenuation) that vary in time. The method is based on a pulse echo measurement and is self-calibrated. Results on a silica gel are reported and the importance of taking into account the changes of the mechanical loading on the front face of the transducer will be shown. This is done through a modification of the emission and reception transfer parameters. The simultaneous measurement of the input and output currents and voltages enables these parameters to be calculated during the reaction. The variations of the transfer parameters are in the order of 6% and predominate other effects. The evolution of the ultrasonic longitudinal wave phase velocity and attenuation as a function of time allows the characteristic times of the chemical reaction to be determined. The results are well correlated with the gelation time measured by rheological method at low frequency.

Experimental exploration of imaging properties of a two-dimensional flat lens made of phononic crystals

We investigate negative refraction of acoustic waves in a two-dimensional phononic crystal (PC) made of stainless steel rods arranged in a triangular lattice filled with methanol. The theoretical dispersion curves of this PC exhibit a branch with group and phase velocities with opposite signs yielding to negative refraction. Moreover, in the frequency range of interest, the equi-frequency contours are circular around the high symmetry point T leading to a negative effective refractive index (ERI) constant at a given frequency whatever the incident angle. An experimental study is performed in a way to evaluate the ultrasonic beam deviation when the wave is transmitted through a slab of PC. This allows the determination of the experimental ERI as a function of the frequency. Furthermore, the transmission coefficients are obtained versus the incident angles. Finally, the property of All-Angle-Negative-Refraction (AANR) of the required PC for imaging is discussed.

Linear and nonlinear acoustic parameters measurements in plates with various moisture contents

Variation of the moisture content is known to modify many of the mechanical properties of solids. For this reason, the estimation of the absorbed quantity of water is a subject of growing interest in characterization of materials. In this work, the water content in phenolic resin plates, placed under variable relative moisture conditions, is investigated through linear and nonlinear acoustic parameter measurements. Linear measurements are performed using an insertion/substitution spectroscopy technique. Nonlinear measurements consist of an evaluation of the phase modulation obtained by a collinear interaction between a high frequency tone burst and a low frequency wave. Results show that many of the studied parameters have a good sensitivity to the absorbed water content.