Polarization manipulation of surface acoustic waves by metallization patterns on a piezoelectric substrate

Surface acoustic waves (SAWs) with large normal (vertical) surface displacement at the surface are commonly utilized in microfluidic actuators in order to provide the desired momentum transfer to the fluid. We present an alternative concept using a SAW with comparatively small vertical displacement. Such a SAW passes underneath the microfluidic vessel walls with minimum losses but it needs to be converted inside the vessel into surface vibrations with large vertical displacements. The principal operability of the above idea is illustrated by experimental and numerical studies of the polarization conversion of a leaky SAW on 64° rotated Y-cut of lithium niobate owing to the partial metallization of the substrate surface. In particular, it is found that vertical displacements on the metallized surface can be up to 3.5 times higher as compared to their values on the free surface. Results of computations agree reasonably well with measurements carried out with a laser Doppler vibrometer and allow the clarification of some specific features of this polarization conversion by means of spatial frequency analysis. © 2020 Author(s)

Surface acoustic waves on one-dimensional phononic crystals of general anisotropy: Existence considerations

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Surface acoustic waves in one-dimensional piezoelectric phononic crystals with a symmetric unit cell

International audienceThe paper studies the existence of surface acoustic waves in half-infinite one-dimensional piezoelectric phononic crystals consisting of perfectly bonded layers, which are arranged so that the unit cell is symmetric, i.e., is invariant with respect to inversion about its midplane. An example is a bilayered structure with exterior layer being half thinner than the interior layers of the same material. The layers may be generally anisotropic. The maximum possible number of surface acoustoelectric waves referred to a fixed wave number and a given full stop band is established for different types of electric boundary conditions at the mechanically free or clamped surface. In particular, it is proved that the phononic crystal-vacuum interface can support two surface waves in any full stop band. The same statement holds true in the case of a metallized surface of the crystal. This number is greater than that in a purely elastic case. In the presence of crystallographic symmetry, which decouples the sagittally and horizontally polarized surface waves, their separate admissible numbers are obtained. It is shown that the propagation along the normal to the surface is a special case, where the maximum number of surface waves is less than that along oblique directions

Interfacial acoustic waves in one-dimensional anisotropic phononic bicrystals with a symmetric unit cell

International audienceThe paper is concerned with the interfacial acoustic waves localized at the internal boundary of two different perfectly bonded semi-infinite onedimensional phononic crystals represented by periodically layered or functionally graded elastic structures. The unit cell is assumed symmetric relative to its midplane, whereas the constituent materials may be of arbitrary anisotropy. The issue of the maximum possible number of interfacial waves per full stop band of a phononic bicrystal is investigated. It is proved that, given a fixed tangential wavenumber, the lowest stop band admits at most one interfacial wave, while an upper stop band admits up to three interfacial waves. The results obtained for the case of generally anisotropic bicrystals are specialized for the case of a symmetric sagittal plane

Non-leaky surface acoustic waves in the passbands of one-dimensional phononic crystals

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Acoustic wave degeneracies in two-dimensional phononic crystals

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The role of electromagnetic waves in the reflection of acoustic waves in piezoelectric crystals

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Stoneley-type waves in anisotropic periodic superlattices

The paper investigates the existence of interfacial (Stoneley-type) acoustic waves localised at the internal boundary between two semi-infinite superlattices which are adjoined with each other to form one-dimensional phononic bicrystal. Each superlattice is a periodic sequence of perfectly bonded homogeneous and/or functionally graded layers of general anisotropy. Given any asymmetric arrangement of unit cells (periods) of superlattices, it is found that the maximum number of interfacial waves, which can emerge at a fixed tangential wavenumber for the frequency varying within a stopband, is three for the lowest stopband and six for any upper stopband. Moreover, we show that this number of three or six waves in the lowest or upper stopband, is actually the maximum for the number of waves occurring per stopband in a given bicrystal plus their number in the “complementary” bicrystal, which is obtained by swapping upper and lower superlattices of the initial one (so that both bicrystals have the same band structure). An example is provided demonstrating attainability of this upper bound, i.e. the existence of six interfacial waves in a stopband. The results obtained under no assumptions regarding the material anisotropy are also specified to the case of monoclinic symmetry leading to acoustic mode decoupling