Study on wave localization in disordered periodic layered piezoelectric composite structures

Acoustic waves in solid and fluid layered materials

This work presents the design, construction and characterization of air-coupled piezoelectric transducers using 1–3 connectivity piezocomposite disks with a stack of matching layers being the outer one an active quarter wavelength layer made of polypropylene foam ferroelectret film. This kind of material has shown a stable piezoelectric response together with a very low acoustic impedance (<0.1 MRayl). These features make them a suitable candidate for the dual use or function proposed here: impedance matching layer and active material for air-coupled transduction. The transducer centre frequency is determined by the λ/4 resonance of the polypropylene foam ferroelectret film (0.35 MHz), then, the rest of the transducer components (piezocomposite disk and passive intermediate matching layers) are all tuned to this frequency. The transducer has been tested in several working modes including pulse-echo and pitch-catch as well as wide and narrow band excitation. The performance of the proposed novel transducer is compared with that of a conventional air-coupled transducers operating in a similar frequency range.

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Air-coupled piezoelectric transducers with active polypropylene foam matching layers.

Review of the use of air-coupled ultrasonic technologies for nondestructive testing of wood and wood products

Effects of initial stress on the reflection and transmission waves at the interface between two piezoelectric half spaces

Dispersion relations for SH wave in magneto-electro-elastic heterostructures

Air-coupled wideband ultrasonic piezoelectric transducers are used in the frequency range 0.3 to 1.3 MHz to excite and sense first-order thickness resonances in the leaves of four different tree species at different levels of hydration. The phase and magnitude spectra of these resonances are measured, and the inverse problem solved; that is, leaf thickness and density, ultrasound velocity, and the attenuation coefficient are obtained. The elastic constant in the thickness direction (c33) is then determined from density and velocity data. The paper focuses on the study of c33, which provides a unique, fast, and noninvasive ultrasonic method to determine leaf elasticity and leaf water content.

Air-coupled ultrasonic resonant spectroscopy for the study of the relationship between plant leaves' elasticity and their water content

Noncontact ultrasonic spectroscopy (NCUS) is used to excite and sense thickness resonances in films of polypropylene ferroelectrets. From the comparison of these measurements with theoretical calculations it is possible to extract some material properties: film thickness and density, velocity, and attenuation of ultrasounds and variation in these two magnitudes with the frequency. Hence elastic compliance and acoustic impedance are worked out. Observed variation in the attenuation with the frequency exhibits classical viscoelastic behavior which can be used to investigate the underlaying physical mechanism. In addition, the influence of the metallization on the film response is studied. A modification of the NCUS method is proposed on the basis of the piezoelectric response of these films, which give rise to an alternative characterization method. Consistency of both methods is verified.

Noncontact ultrasonic spectroscopy applied to the study of polypropylene ferroelectrets

Acoustic field modeling for physiotherapy ultrasound applicators by using approximated functions of measured non-uniform radiation distributions

Surface and shear horizontal waves in piezoelectric composite media consisting of piezoelectric layers of hexagonal $6mm$ symmetry are studied. We consider finite and infinite systems. For the finite case we study ``periodic'' and two types of nonperiodic structures: Fibonacci sequences and systems with a linear perturbation in the piezoelectric parameters which give rise to resonances of Stark-Ladder type. For the infinite case we only consider periodic systems. The transmission, dispersion relation, angular dispersion relation, and eigenmodes of vibration of the composites are analyzed. We discuss in detail the effect of surface waves on these properties. We use the transfer matrix formalisms of $4\ifmmode\times\else\texttimes\fi{}4$ and $2\ifmmode\times\else\texttimes\fi{}2$ dimensions to study the system in the exact approach and in the approximation where the surface waves are neglected, respectively. Numerical results are also presented.

H. Calas

Papers

Dispersion relations for SH wave in magneto-electro-elastic heterostructures

Air-coupled ultrasonic resonant spectroscopy for the study of the relationship between plant leaves' elasticity and their water content

Noncontact ultrasonic spectroscopy applied to the study of polypropylene ferroelectrets

Acoustic field modeling for physiotherapy ultrasound applicators by using approximated functions of measured non-uniform radiation distributions

Surface and shear horizontal waves in piezoelectric composites