Bulk Acoustic Wave Propagation Research Articles

Directional Acoustic Bulk Waves in a 2D Phononic Crystal

We used the transfer matrix method to investigate the conditions supporting the existence of directional bulk waves in a two-dimensional (2D) phononic crystal. The 2D crystal was a square lattice of unit cells composed of rectangular subunits constituted of two different isotropic continuous media. We established the conditions on the geometry of the phononic crystal and its constitutive media for the emergence of waves, which, for the same handedness, exhibited a non-zero amplitude in one direction within the crystal’s 2D Brillouin zone and zero amplitude in the opposite direction. Due to time-reversal symmetry, the crystal supported propagation in the reverse direction for the opposite handedness. These features may enable robust directional propagation of bulk acoustic waves and topological acoustic technology.

Design of a broadband acousto-optic filter using bulk acoustic wave beam steering with an interdigital transducer

Acousto-optic tunable filters are photonics devices whose operation is fundamentally based on crystal acoustics. One of the phenomena used to improve performances of bulk acousto-optic devices is acoustic beam steering. Here we present a complete analytical model, which covers bulk acoustic wave beam steering in crystals with phased-array excitation and Bragg phase matching of anisotropic acousto-optic diffraction. An interdigital phased-array transducer is proposed for laterally excited bulk acoustic wave generation enabling the effect of beam steering. The design of a paratellurite-based acousto-optic filter with extended transmitted optical wavelength range from 0.4 to 1.1μm is discussed and supported by numerical simulations.

Continuum Models for Bulk Viscosity and Relaxation in Polyatomic Gases

Bulk viscosity and acoustic wave propagation in polyatomic gases and their mixtures are studied in the frame of one-temperature and multi-temperature continuum models developed using the generalized Chapman–Enskog method. Governing equations and constitutive relations for both models are written, and the dispersion equations are derived. In the vibrationally nonequilibrium multi-component gas mixture, wave attenuation mechanisms include viscosity, thermal conductivity, bulk viscosity, diffusion, thermal diffusion, and vibrational relaxation; in the proposed approach these mechanisms are fully coupled contrarily to commonly used models based on the separation of classical Stokes–Kirchhoff attenuation and relaxation. Contributions of rotational and vibrational modes to the bulk viscosity coefficient are evaluated. In the one-temperature approach, artificial separation of rotational and vibrational modes causes great overestimation of bulk viscosity whereas using the effective internal energy relaxation time yields good agreement with experimental data and molecular-dynamic simulations. In the multi-temperature approach, the bulk viscosity is specified only by rotational modes. The developed two-temperature model provides excellent agreement of theoretical and experimental attenuation coefficients in polyatomic gases; both the location and the value of its maximum are predicted correctly. One-temperature dispersion relations do not reproduce the non-monotonic behavior of the attenuation coefficient; large bulk viscosity improves its accuracy only in the very limited frequency range. It is emphasized that implementing large bulk viscosity in the one-temperature Navier–Stokes–Fourier equations may lead to unphysical results.

Evaluation of bulk and surface acoustic waves propagation properties of (K,Na)NbO3 films deposited by hydrothermal synthesis or RF magnetron sputtering methods

In this study, the bulk and surface acoustic waves (BAW and SAW) propagation properties of (K,Na)NbO3 (KNN) films deposited by hydrothermal synthesis or RF magnetron sputtering methods were evaluated to investigate the applicability of such films to high-frequency devices. For the {100} c -oriented KNN epitaxial films deposited by the hydrothermal synthesis method, a BAW phase velocity of 6900 m s−1 and an electromechanical coupling coefficient k t 2 of 8.4% were obtained. From the measured Rayleigh-type SAW properties, a large electromechanical coupling coefficient K 2 of 4.0% in the 1st mode was obtained in the {110} c -oriented KNN epitaxial films. On the other hand, for the preferentially {100} c -oriented KNN film deposited on Pt(111) by RF magnetron sputtering, a BAW phase velocity of 7850 m s−1 and k t 2 of 7.4% were obtained. For the 0th mode of the Rayleigh-type SAW, a propagation loss of 0.13 dB/λ (λ: wavelength) at 440 MHz and a temperature coefficient of frequency of –42 ppm °C−1 were obtained for the {100} c -oriented KNN epitaxial film deposited on STO(100) by the RF magnetron sputtering method.

Methods of solving in‐band ripples and out‐of‐band suppression for yarn tension sensor based on surface acoustic wave

The two key problems of the in-band ripples and out-of-band suppression are proposed in the design of the SAW yarn tension sensor and the methods of decreasing them are achieved. The unbalanced split-electrode interdigital transducers (IDT) are designed so that the total phase of the regenerated reflection wave and mass load feedback is close to 180°, leading to an effective reduction of the in-band ripples effect characterised by the sensor frequency response. The engraved bi-directional slots on the back of the substrate can block the propagation path of the bulk acoustic wave (BAW) to a certain extent, reducing the influence of BAW propagation and suppressing the out-of-band suppression of the frequency response. The experimental results show that the SAW yarn tension sensor with the unbalanced split-electrode IDT can reduce the in-band ripples from 23.34 to 0.93 dB, and the engraved bi-directional slots can suppress the out-of-band suppression from 28.03 to 7.71 dB.

Effect of Bulk Acoustic Wave in Piezo Driven Nanomechanical Motion

Piezo actuation of mechanical resonators is widely adapted because of its simplicity and versatility. Piezo-driven atomic force microscopy cantilevers in air or liquid have a substantial drawback in that they produce spurious resonances that conceal the cantilever resonance peak. Bulk acoustic wave propagation via the piezo-shaker and device substrate causes these undesired peaks. Such restrictions of piezo actuation are rarely reported in nanomechanical resonant sensing. Because most NEMS (nanoelectromechanical systems) experiments are carried out at low pressure to achieve a higher quality factor ) and hence increased sensitivity, spurious resonances are frequently overlooked due to their insignificance. However, this piezo-driven issue may affect NEMS responses at higher pressures (lower Q) and must be addressed carefully. This study reveals spurious resonances from high vacuum to the atmosphere while investigating piezo-driven nanoscale doubly clamped beam responses. At all pressures, spurious peaks with a characteristic frequency span independent of air damping exist, and at higher pressures, they squeeze the mechanical peak. Such squeezing provides a larger derived from the driven phase responses by order of magnitude than the mechanical computed from the measured thermal noise spectra. Interestingly, the characteristic frequency span, not air damping, is revealed to dominate driven .

Measurement of the Second-Order Material Constants of Lanthanum-Gallium Tantalate (LGT) Through Ultrasound.

Lanthanum-gallium tantalate (LGT) is a member of the LGX crystal family (langasite, langanite, and langatate) known for high-quality factor and stability at higher temperatures. These characteristics enable filters and sensors for use in harsh environments. Accurate values for the second-order material constants are required for electromechanical modeling of such devices. A sufficient set of bulk acoustic wave (BAW) propagation velocities have been measured in cube-shaped samples to obtain the full set of second-order elastic and piezoelectric material constants along with the experimental uncertainties. The cross correlation method was used to accurately measure the time-of-flight (TOF) values between the first two back-wall echoes under a constant room-temperature environment. The calculated BAW velocities and extracted material constants show good agreement with earlier work.

Extreme acoustic anisotropy in crystals visualized by diffraction tensor

Anisotropic acoustic wave propagation in single crystals is a fundamental phenomenon enabling operation of various acoustic, acousto-electronic and acousto-optic devices. It provides a variety of device performances and application fields, but its role in pre-estimation of achievable device characteristics and location of crystal orientations with desired properties is often underestimated. A geometrical image of acoustic anisotropy can be an important tool in design of devices based on wave propagation in single crystals or combinations of anisotropic materials. We propose a fast and robust method for survey and visualization of acoustic anisotropy based on calculation of the eigenvalues of bulk acoustic wave (BAW) diffraction tensor (curvature of the slowness surface). The stereographic projection of these eigenvalues clearly reveals singular directions of BAW propagation (conical acoustic axes) in anisotropic media and areas with large and small BAW beam divergence. The method is illustrated by application to three crystals of different symmetry used in different types of acoustic devices: paratellurite, lithium niobate and potassium gadolinium tungstate. The specific features of acoustic anisotropy are discussed for each crystal in terms of their potential application in devices. In addition, we demonstrate that visualization of acoustic anisotropy of lithium niobate helps to find orientations supporting propagation of high-velocity surface acoustic waves.

The Sensitive Element of Acoustic Sensor on Circular Polarized Waves: From Theoretical Considerations towards Perspective Rotation Rate Sensors Design.

In this paper, the perspectives of using the features of acoustic wave propagation to design rotation rate sensors (RRS) are discussed. The possibility of developing the solid-state sensitive elements (SE) of RRS on acoustic waves of circular polarization is shown. The theoretical basis of bulk acoustic wave propagation under rotation is given. The direct excitation of circularly polarized acoustic wave (CPAW) is considered, the design of the CPAW emitting transducer is offered. The results of experimental studies that indicated the circular nature of the particle motions in the radiated wave are discussed. The principally new concept of the RRS SE design on CPAW, being able to operate under high vibration and acceleration, is proposed. The experimental results revealed a high correlation with theoretical and numerical predictions and confirmed RRS on CPAW operability.

Characteristics of Acoustic Waves upon Refraction at the Lithium Niobate–Pratellurite Interface in Acousto-Optic Devices

Results are prevented from studying the propagation and refraction patterns of bulk acoustic waves in acousto-optic crystals. The strong anisotropy of the elastic properties of the considered materials is responsible for new effects that cannot be achieved in isotropic media. Ways of using the acoustic anisotropy of crystals in acousto-optic devices are discussed, along with the advantages of such devices over similar ones in which this anisotropy is not crucial.

The Effect of a Rotating Medium on Bulk Acoustic Wave Polarization: From Theoretical Considerations to Perspective Angular Motion Sensor Design.

We study the effects of medium rotation on bulk acoustic wave (BAW) propagation. For a theoretical analysis of the BAW propagation characteristics, a motion equation for the plane harmonic waves propagating orthogonal to the rotation axis of the propagation medium was analytically resolved. We found that during medium rotation, the polarization of the waves becomes elliptical with the ratio of the polarization ellipse axes explicitly proportional to the angular velocity of the medium rotation, thereby opening the way for the design of sensitive elements (SE) for perspective angular motion sensors (AMS). Next, an analytical dependence of the SE informative parameter on the Poisson’s ratio of the acoustic duct material was obtained. The rotation effect on the dispersion of BAW propagation velocity was studied. Two approaches to the perspective SE design were proposed. An experimental study of a specially designed test assembly and SE model demonstrated high correlation with theoretical predictions and provided an estimate of a potential SE. Therefore, we believe that the study of acoustic wave propagation under nonclassical conditions is a promising direction for prospective solid-state AMS on based on BAW polarization effects design.

Remote Seismoacoustic Probing of the Bottom of a Sea Covered by Ice

The propagation of surface and bulk acoustic waves in a system consisting of the atmosphere, an ice cover, a water layer, and a seabed with inclusions is modeled numerically. It is shown that data on a fundamental surface wave recorded on ice can be used to probe the heterogeneous structure of the seabed. It is established that the use of an acoustic wave generated by a fundamental surface wave in the atmosphere allows the signal-to-noise ratio to be increased.

Raman Spectra of La3Ga5SiO14 Crystal Modulated by Bulk Acoustic Wave.

The influence of bulk acoustic wave excitation in langasite crystal on Raman spectra was studied. It was found that acoustic wave propagating in the crystal volume changes the intensity and position of the Raman scattering lines. Under bulk acoustic wave propagation conditions, Raman peak intensity changes less on 5% and peak position shifts on 0.5 cm-1. To detect such small changes, principal component analysis of Raman spectra was used.

Generation and Propagation of Superhigh-Frequency Bulk Acoustic Waves in GaAs

Coherent super-high-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We show that the electro-acoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the ZnO films. The BAWRs were then used for the study of the propagation properties of the LBAWs in GaAs in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We found that the intrinsic acoustic absorption of GaAs in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. At lower temperatures, in contrast, the intrinsic acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflection at the sample boundaries. We also demonstrate devices with high quality factor fabricated on top of acoustic Bragg-reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding GaAs-based nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs.

Numerical analysis of SAW propagation characteristics in Ca2Al2SiO7 crystal

The importance of surface acoustic wave (SAW) technology is to integrate signal processing with sensor functions. Recently, SAW sensors can operate at room temperature or around 100°C-200°C. The task associated with materials becomes relevant if it is necessary to increase the operating temperature of the device to 1000°C. A new piezoelectric calcium aluminate silicate (Ca2Al2SiO7) crystal of the tetragonal symmetry has stable piezoelectric properties up to the melting point temperature of 1500°C. The properties of surface acoustic waves a new Ca2Al2SiO7 single crystal are numerically modeled in the paper. The SAW velocity, the electromechanical coupling coefficient, and the power flow angle are modeled for various cuts of the Ca2Al2SiO7 crystal. The SAW has the maximal electromechanical coupling coefficient value (∼0.1%) on Z,X+45°-cut of the crystal. In the Z+63°, X-cut, the SAW electromechanical coupling coefficient is equal to 0.08%. Both of these crystal cuts show the absence of bulk acoustic wave generation by an interdigital transducer, and the Ca2Al2SiO7 crystal is a promising piezoelectric material for use in the SAW device applications.

A comparative study for two LiNbO3 cuts (Y-Z and Y-X) in detecting bulk acoustic microwaves using Probabilistic Neural Network

This work is mainly on the detection of the bulk acoustic waves (BAWs), where we have compared two Lithium Niobate cuts (Y-Z and Y-X), during the propagation of the acoustic microwaves in the piezoelectric LiNbO3-substrate. In this paper, we have used the classification by Probabilistic Neural Network (PNN) as a tool for numerical analysis in which we classify all the values of the real and imaginary parts of the attenuation coefficient for the propagation velocity. This analysis can allow us to demonstrate the best possibility in utilization for the BAW generation. This study will be very interesting in modeling and realization of acoustic wave devices (ultrasound) based on the propagation of acoustic microwaves.

Interaction of Rayleigh waves with 2D dipolar exciton gas: impact of Bose–Einstein condensation

The theory of the interaction of a two-dimensional gas of indirect dipolar excitons with Rayleigh surface elastic waves has been developed. The absorption and renormalization of the phase velocity of a surface wave, as well as the drag of excitons by the surface acoustic wave and the generation of bulk acoustic waves by a two dimensional gas of dipolar excitons irradiated by external electromagnetic radiation, have been considered. These effects have been studied both in a normal phase at high temperatures and in a condensed phase of the exciton gas. The calculations have been performed in the ballistic and diffusion limits for both phases.

Diamond’s third-order elastic constants: ab initio calculations and experimental investigation

In order to obtain more reliable values of diamond’s third-order elastic constants, experiments on bulk acoustic wave propagation under uniaxial stress application (up to 450 MPa) in pure IIa-type synthetic single-crystal diamond were carried out, and values of third-order elastic constants were calculated. We have also provided theoretical analysis using ab initio density functional theory approach which has shown close correspondence with the experimentally measured data. From ab initio calculations, the values of third-order elastic constants are (GPa): C 111 = −7611, C 112 = −1637, C 144 = −199, C 155 = −2799, C 123 = 604, C 456 = −1148, while experimental values are C 111 = −7750 ± 750, C 112 = −2220 ± 500, C 144 = −1780 ± 440, C 155 = −2800 ± 220, C 123 = 2100 ± 200, C 456 = −30 ± 150. The estimated values on diamond’s fourth-order elastic constants were obtained. The calculated stress–strain curves for different crystal orientations were investigated, including shear stress for [111] direction. From calculations for [100], [110], and [111] directions, the values of critical stress in case of the pure shear were estimated as 222, 113, and 84 GPa, respectively.

Influence of Initial Stresses and Piezoelectric Constants on the Propagation Bulk Acoustic Waves in an Anisotropic Smart Material (Aluminum Nitrite)

The aim of this paper is to illustrate the effect of initial stresses on the propagation of plane waves in a general anisotropic elastic medium. Therefore, an analytical analysis supported by numerical tests to calculate the bulk acoustic wave propagation in Aluminum Nitrite (AlN) as piezoelectric hexagonal elastic material has been presented. In addition, the Christoffel’s equation has been solved and the corresponding eigenvalues and eigenvectors have been obtained. Then, an explicit expressions of the waves propagation with three distinct phase velocities in anisotropic piezoelectric material including the effect of the initial stresses have been derived. The three velocities of bulk acoustic waves (BAW) which are called quasi-longitudinal, quasi-shear vertical and quasi-shear horizontal for Aluminum Nitrite are numerically calculated. The numerical examples are considered to illustrate graphically the effect of initial stresses on the variations of velocities of the BAW versus the angle of the propagation. The velocities of BAW change significantly with initial stresses as well as piezoelectric constants. This research is theoretically useful in signal processing, sound system, wireless communication and for the design of surface acoustic wave (SAW) devices with high performance.

Acoustic–excitonic effects in a two-dimensional gas of dipolar excitons

The theory of the interaction of a two-dimensional gas of indirect dipolar excitons with Rayleigh surface elastic waves has been developed. The absorption and renormalization of the phase velocity of a surface wave, as well as the drag of excitons by the surface acoustic wave and the generation of bulk acoustic waves by a twodimensional gas of dipolar excitons irradiated by external electromagnetic radiation, have been considered. These effects have been studied both in a normal phase at high temperatures and in a condensed phase of the exciton gas. The calculations have been performed in the ballistic and diffusion limits for both phases.