Anne-Christine Hladky

Propagation of Lamb waves in a plate with a periodic grating: Interpretation by phonon

In this paper the propagation of Lamb waves in an aluminium plate with a periodic grating containing triangular grooves is studied. Numerical simulations (FEM) are performed. A single incident mode is excited on a flat area and the interaction with the periodic grating is studied. Reflected converted waves are observed when the incident Lamb wave passes through the grating. At the entrance of the periodic grating, a phonon relation is written between the incident signal, the converted mode, and the phonon related to the grating. An experimental verification of the phonon relation is carried out.

Tunability of Bragg band gaps in one-dimensional piezoelectric phononic crystals using external capacitances

A one-dimensional stack of identical piezoelectric rods is investigated. The device exhibits a band gap related to electrical boundary condition. A separate control of the central frequency and of the width of the band gap is performed by an electrical boundary condition involving two different variable capacitances. Because the capacitances are grounded, a specific model has been developed and validated. Finally, experiments unambiguously confirmed previous theoretical observations.

Design and characterisation of 1-3 ultrasonic composites using ATILA and ultra fast laser measurements (20 MHz)

Further progress in ultrasonic technology is expected by using custom shape, high-quality, low-cost ultrasonic transducers. Therefore, 1-3 ultrasonic composites based on piezoceramic fibers have been developed. In order to make use of all advantages of piezo composites effective design and characterization tools are necessary. Here we report on the combined use of ATILA and a newly developed ultra fast scanning laser measurement system (vibrometer) such as provided by Polytec. ATILA is a finite element software tool, which is able to simulate coupled piezoelectric, electromechanical and acoustic field problems. The laser vibrometer allows to measure in-plane movements as well as sound field. The present paper is focused on 1-3 composites based on piezoceramic fibers. First simulated and measured data, e.g. spectrum, resonant frequency and anti-resonant frequency as well as the mode shapes for different frequencies have been collected. The modeled and measured data agree completely. Furthermore new effects of lateral waves of 1-3 composites have been measured and are discussed in the paper. Keywords-piezoceramic fiber; 1-3 composites; ultrasonic; FE-

Highly tunable Fabry-Perot resonators using piezoelectric phononic crystals

Theoretical and experimental analyses of piezoelectric stacks submitted to periodical electrical boundary conditions via electrodes, are conducted. These structures are shown to exhibit Bragg band gaps which are switched on or off by setting electrodes in short or open circuit. Band gap frequency width is determined by electromechanical coupling coefficient. This property is used to design a Fabry-Perot cavity the length of which is delimited by two periodical piezoelectrical stacks. Tunability of cavity resonance is obtained by varying cavity length i.e. by shifting spatially short circuit boundary conditions in the stacks. 36% tuning of resonance and antiresonance frequencies with almost constant resonator electromechanical coupling coefficient of 40% are theoretically predicted for PZT.

Band gaps in a phononic crystal constituted by cylindrical dots on a homogeneous plate

Using the finite difference time domain (FDTD) and the finite element (FE) methods, we investigate theoretically the band structure of a phononic crystal constituted by a periodic array of cylindrical dots deposited on a thin homogeneous plate. We demonstrate that such a structure can exhibit a very low frequency absolute band gap as compared to the wavelength in the constituent materials. The occurrence of this gap requires an appropriate choice of the geometrical parameters and, in particular, of the thickness of the plate as compared to the period or to the height of the cylinders. However, the same behavior can be obtained for various combinations of the materials constituting the homogeneous plate and the dots. We study in detail the width of this band gap as a function of the geometrical and physical parameters of the structure. On the other hand, the structure can also exhibit one or more higher gaps whose numbers can be increased by increasing the height of the cylinders.

Development of a suitable PML for an harmonic study of a finite 1D phononic crystal

This paper deals with the interaction of ultrasonic Lamb waves with a 1D phononic crystal. The studied structure is a finite plate with a periodic corrugated surface. Two types of forbidden bands arise in the Lamb wave dispersion curves. The first one is located at the limit of the first Brillouin zone, the second one exists at the crossing of dispersion curves of two different Lamb modes. These forbidden bands lead to conversion phenomena. In order to study accuratly the conversion phenomena in the band gaps, harmonic finite element analysis are performed. Perfect matching layers (PML) on both sides of the plate are then necessary to avoid stationnary waves. PML, adapted for Lamb modes involved at a given frequency, must be designed. By using these PML, the attenuation of Lamb waves propagating in the phononic crystal is clearly shown and is related to the existence of the forbidden band.

Damping of a device with piezoelectric materials and negative capacitance electrical circuits

In this paper, the damping of a device is obtained by a transfer of the vibratory energy into electrical energy and then into thermal energy (dissipation in an electrical resistance). The transfer is carried out by using piezoelectric materials (PZT piezoelectric plates, macro fibre composite MFC) and it is improved by charging the piezoelectric materials by an electrical circuit having a negative capacitance impedance. Two devices are considered: a clamped plate, witch is a academic case, and a large aluminium plate (0.85m×0.78m×2mm). The optimal position and the geometry of the ceramics are determined using an analytical method and a numerical method with the help of the ATILA finite element code. The equivalent electrical circuit of the device is conceived. Damping of the device charged by the electrical circuits is measured using a laser vibrometer. Damping can be performed on a given frequency range, covering several bending modes, by using several ceramics on the plate and several external electrica...

Propagation of Lamb Waves on Rough Plates : Analysis of the Beam Section

This work is a study of Lamb waves propagating on one‐side rough plates : it deals with the analysis of the energy repartition in the perpendicular direction of propagation. An experimental work is performed involving an optical interferometer (YAG laser). The energy repartition is the result of the transducer diffraction and the roughness diffusion. The roughness diffusion manifests itself first as an increase of the beam spreading and in a second time, depending to the distance of propagation, as an apparent focusing.