Conference Paper

Hybrid surface-bulk mode in periodic gratings

Moscow Steel & Alloys Inst.
DOI: 10.1109/ULTSYM.2001.991618 Conference: Ultrasonics Symposium, 2001 IEEE, Volume: 1
Source: IEEE Xplore

ABSTRACT We report on a SAW/BAW hybrid mode (SBH), which arises from
surface skimming bulk wave due to the trapping of its energy by a
counter-propagating surface wave (SAW) or leaky surface wave (LSAW), in
periodic grating structures. The SBH is the result of an interaction
between surface and bulk waves and exists within limited frequency
region, outside which it is decomposed into counterpropagating SAW and
BAW. Different examples of SBH mode illustrate interactions of BAW with
pure SAW, leaky and high-velocity leaky waves. The behavior of the SBH
mode was numerically investigated using the harmonic admittance
function. Calculation of velocity dispersion revealed the existence of
an additional branch of the dispersion curve, which refers to the SBH
mode. A stopband occurs due to SAW/BAW interaction and manifests itself
by a resonance of harmonic admittance at its lower edge, which can be
considered as the cut-off frequency of bulk wave radiation

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    ABSTRACT: It is shown that effective permittivity function in the complex plane of slowness for 36-42 degrees rotated lithium tantalate substrates apart from the well-known LSAW exhibits an additional singular point. The pole is located between "fast shear" and "longitudinal" branch points and can be numerically found out when appropriate branch line is drawn from the "fast shear" branch point. The effective propagation velocity of this leaky mode on 36 degrees rotated lithium tantalate equals 4723 m/s that is 1.1 times larger than the velocity of fast shear SSBW propagating in the same direction. The intrinsic attenuation of this mode is extremely high and equal to 6.93 dB/wavelength. The previously reported PSAW-like mode in periodic system of metal electrodes is associated with this new mode.
    Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE; 11/2002
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    ABSTRACT: We report on a study of the effect produced by the surface-bulk hybrid (SBH) mode on the performance of resonators built on 42°YX and 48°YX cuts of LiTaO<sub>3</sub>(LT). An approximation was suggested for SBH mode effect on harmonic admittance, and the main parameters of this mode were extracted from numerically found admittance, as functions of electrode thickness, metalization ratio and detuning factor. In both orientations, effective electromechanical coupling of SBH mode reduces with electrode thickness and increases with metalization ratio. Maximum coupling occurs when the detuning from synchronous resonance is about (0.4-0.6)%. In 48°YX-LT, SBH mode is much stronger attenuated than in 42°YX-LT and its effect on strip admittance is less apparent. The simulated behavior of SBH mode shows good agreement with experimental data.
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    ABSTRACT: We suggest an approximation of the effect of the surface skimming bulk wave (SSBW) on harmonic admittance of periodic grating. The approximation is valid on both sides of cut-off frequency and predicts the existence of surface-bulk hybrid mode (SBH), if such mode occurs in the grating due to SAW/SSBW interaction. As an example, parameters of approximating function were calculated for 36°X, Y+90° cut of quartz with Al grating and plotted versus metalization ratio a/p. They revealed the existence of SBH mode for a/p >0.685. The resonance frequency of additional resonance of harmonic admittance, which corresponds to this mode, was predicted with high accuracy from approximation of harmonic admittance around the cut-off frequency.
    Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE; 11/2002

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