E. Le Clezio

Full tensorial characterization of PZN-12%PT single crystal by resonant ultrasound spectroscopy

An experimental setup based on the electrical excitation of a piezoelectric sample is proposed for resonant ultrasound spectroscopy measurements. The detection of the mechanical vibrations is performed by means of a laser interferometer. At the same time, the free vibrations of piezoelectric parallelepipeds of tetragonal and hexagonal symmetries are modeled taking into account the effect of the sample metalization. The paper presents the full elastic, piezoelectric and dielectric tensors of two PMN-34.5%PT ceramic and PZN-12%PT single crystal cubes.

Transmission of acoustic waves through piezoelectric plates: modeling and experiment

The transmission of acoustic waves through a piezoelectric plate is dealt with theoretically and experimentally. The analytical treatment engages the octet formalism of anisotropic piezoacoustics. A specific version of the plate admittance matrix is introduced, which incorporates the electric boundary conditions for a non-metallized or metallized plate. In consequence, expressions for the reflection and transmission coefficients are reduced to explicitly the same form as in the case of pure elasticity. This theoretical model is then applied for material characterization. Material constants of a Pz27 plate are inferred from the numerical simulations and the experimental results of ultrasonic-transmission measurements. Good agreement is observed with another method based on electrical-impedance measurements. The impact of electrical boundary conditions is visualized by presenting the numerical and experimental transmission spectra through the Pz27 plate with non-metallized and metallized faces.

Acoustic wave transmission through piezoelectric structured materials

This paper deals with the transmission of acoustic waves through multilayered piezoelectric materials. It is modeled in an octet formalism via the hybrid matrix of the structure. The theoretical evolution with the angle and frequency of the transmission coefficients of ultrasonic plane waves propagating through a partially depoled PZT plate is compared to finite element calculations showing that both methods are in very good agreement. The model is then used to study a periodic stack of 0.65 PMN-0.35 PT/0.90 PMN-0.10 PT layers. The transmission spectra are interpreted in terms of a dispersive behavior of the critical angles of longitudinal and transverse waves, and band gap structures are analysed. Transmission measurements confirm the theoretical calculations and deliver an experimental validation of the model.

Wood elastic characterization from a single sample by resonant ultrasound spectroscopy

The goal of this paper is to propose an experimental method allowing the identification of the complete elastic tensor of anisotropic biological materials such as wood using only one sample. To do so, two complementary methods are used. First, the wood eigen-directions are defined from a sample of spherical shape that is then cut into a cube in a way to perform resonant ultrasound spectroscopy (RUS). The method is successfully applied on a reference beech sample with known orthotropic directions. A comparison of the identified elastic constants with those from the literature and some inferred from ultrasonic transmission measurements is given.

Electromagnetic Surface Wave Attenuation Caused by Acoustic Wave Radiation

Abstract In theoretically studying electromagnetic surface wave propagation in crystals possessing piezoelectric properties, we found that, if the frequency is smaller than typical phonon frequencies (not exceeding 1012–1013 Hz), then electric fields are able to generate elastic vibrations because of the piezoelectric effect. In this case, an electromagnetic surface wave is coupled with bulk acoustic modes propagating from the interface to the interior of the structure. As a result, the surface wave attenuates because of the radiation of acoustic waves. The attenuation factor is proportional to the parameter τ2 va/vel, where τ is the electromechanical coupling coefficient, and va and vel are typical speeds of acoustic and electromagnetic waves in the crystal, respectively.

Moisture content characterization in composite materials based on ultrasonic transmission measurements

Moisture absorption is known to alter many of the mechanical properties of polymer-based composites. This study presents ultrasonic characterization of moisture content based on the transmission of acoustic waves through composite plates. The elastic constants of 14 plates with different controlled water contents are obtained. The redundancy of the results allows to validate the characterization process and the assumption made on the sample symmetry. The sensitivity of the process to moisture content is then discussed.

Acoustic waves in the vicinity of the normal to the surface of piezoelectric crystals

The acoustic wave propagation in the vicinity of the normal to the plane surface confining a piezoelectric crystal of arbitrary symmetry is theoretically studied. An octet formalism arid a perturbation theory have been put forward to describe the wave fields in the region of concern. The developed mathematical approach has been applied to several problems. Specifically, the derivation of the transfer matrix for the normal direction to the surface has been discussed. Furthermore, we have discussed how to estimate the electric potential induced outside the piezoelectric material by a normally incident wave. In addition, an analytical expression has been derived for the numerical factor in the function describing the asymptotic behavior of quasielectrostatic Greens function for half-infinite piezoelectric substrates at small values of the wave vector

Relations between single-domain and multidomain piezoelastic properties in single crystals

This paper presents a new method to compute the piezoelastic properties of multidomain single crystals from the single-domain constants. Based on a quasi static assumption, a PMN-xPT multidomain is defined as a periodic medium with a lattice composed of layers of two domains in a twin structure. Such a structure is assumed to have charged domain walls that imply specific lattice media and boundary conditions. A numerical computation has been performed for a PMN-33PT single crystal in the rhombohedral phase. The effective elastic, piezoelectric, and dielectric constants of the macroscopic structure have been calculated, as well as the wave velocities in different configurations of domain patterns

Elastic characterization of wood by Resonant Ultrasound Spectroscopy (RUS): a comprehensive study

The main principle of Resonant Ultrasound Spectroscopy (RUS) measurement method is to excite a sample and to deduce its elastic constants from its free mechanical resonant frequencies. The goal of this paper is to propose an application of RUS in the case of wood cubic samples by: (1) using frequencies and mode shapes (or vibration patterns) of the free resonant modes in an iterative numerical procedure to solve the inverse problem for identifying components of the stiffness tensor of the sample’s material, (2) finding the limits and optimizing the robustness of the identification procedure in the case of wood and (3) applying it to a large density range of wood samples. Specific continuous waves have been used as excitation signal in order to experimentally determine the free resonant frequencies and mode shapes of the sample in a faster way by means of Scanning Doppler Vibrometer measurements. Afterward, the stiffness tensor was derived by solving iteratively an inverse problem. The gain of using the mode shapes in the inverse identification procedure is demonstrated to be particularly necessary for wood, especially for pairing each measured frequency with its corresponding theoretically predicted one, as viscoelastic damping causes the resonant peaks to overlap and/or disappear. A sensitivity analysis of each elastic constant on the measured resonant frequencies has thus been performed. It shows that, in its current state of development, not all of the elastic constants can be identified robustly and a modified identification procedure is thus proposed. This modified procedure has been applied successfully to wood samples with a large density range, including softwood and hardwood, and particularly non-homogeneous wood species or with specific anatomical features.

Piezoelectric material characterization by acoustic methods

Two characterization methods of piezoelectric materials based on acoustic measurements are presented. Their main objective is to identify the entire set of electromechanical properties of piezoelectric materials from a single sample. In order to characterize new materials like single-crystals with small dimensions, the first section of the paper presents an identiffication protocol based on the study of the resonance spectra of parallelepipeds. The second characterization method is performed by means of the measurement of the transmission coefficients of plane waves propagating through an immersed plate. It is is suitable for the determination of the properties of bulk piezoelectric ceramics.