Longitudinal Acoustic Waves Research Articles

Phonon transfer in silicon-diamond films: Influence of thermal boundary resistance on acoustic phonon intensities

Thermal energy transfer across two-dimensional silicon and diamond thin films are considered and the influence of the thermal boundary resistance, due to mismatching of properties, on the acoustic phonon transport characteristics is studied. The transient form of the Boltzmann equation with frequency dependency of phonons is incorporated simulating the phonon transport. Thermal boundary resistance is considered incorporating mismatches of interface conditions of films, namely cut-off and diffusive models. The ratios of longitudinal and transverse acoustic phonon wave intensities because mismatch models (cut-off and diffusive mismatches) are predicted for temperature oscillating boundary condition at the silicon edge. It is found that the ratio of the longitudinal acoustic phonon intensities ratio because of mismatch models (cut-off over diffusive) does not behave exactly the oscillation of temperature at the edge of the silicon film due to scattering of phonons in the films. The same arguments are applicable for the ratio of transverse acoustic phonon intensities because of the interfacial mismatch models (cut-off over diffusive). The consideration of the phonon frequencies cut-off results in the ballistic phonon transfer in between films, which lowers the interfacial thermal resistance.

Controlling the electromagnetic density of modes in one-dimensional photonic crystal with defect using acoustic wave

We have theoretically analyzed the effect of acoustic parameters on the electromagnetic density of modes (DOM) in a one-dimensional photonic crystal featuring a defect mode. The whole structure is modulated by a longitudinal acoustic wave. The transfer matrix method and Wigner time approach are used to calculate the transmittance and electromagnetic DOM, respectively. The results show that the electromagnetic DOM is dynamically controlled by the acoustic amplitude. A sharp peak in DOM is found at the defect site whose magnitude decreases with the increase in acoustic amplitude and shows periodic swing with fractional change in time period of acoustic wave. Furthermore, the result of polarization of electromagnetic wave is also discussed and it is found that the location of the defect mode can be modulated in a large frequency rage without changing the structure of the photonic crystal.

Influence of long-range interatomic and interlayer interactions on dispersion of acoustic waves by multilayer graphene

In this study, effects of the long-range interatomic and interlayer interactions on the dispersion of acoustic waves by multilayer graphene are investigated. A hybrid model that accounts for the long-range interatomic and interlayer interactions is developed. In the context of this model, the interatomic interactions are modeled based on the general nonlocal theory. The general nonlocal theory effectively models the dispersions of acoustic waves where it defines two independent nonlocal fields for the longitudinal and transverse acoustic waves. Interlayer interactions are defined to model the van der Waals interaction between the graphene layers. A new approach is proposed to determine the mechanical properties and the equivalent thickness of a single-layer graphene. The Young's modulus and Poisson's ratio of a single-layer graphene is obtained by ∼345MPa and ∼0.08, respectively. The equivalent thickness of a graphene sheet is determined by ∼0.057nm. An experimental validation for the dispersions of four-layer graphene is carried out where a good assent is observed. A parametric study is then presented to demonstrate the significant influence of the long-rang interatomic and interlayer interactions on the dispersion of incident acoustic waves by multilayer graphene.

Generation of coherent phonons by coherent extreme ultraviolet radiation in a transient grating experiment

We investigate the excitation of coherent acoustic and optical phonons by ultrashort extreme ultraviolet (EUV) pulses produced by a free electron laser. Two crossed femtosecond EUV (wavelength 12.7 nm) pulses are used to excite coherent phonons at a wavelength of 280 nm, which are detected via diffraction of an optical probe beam. Longitudinal and surface acoustic waves are measured in BK-7 glass, diamond, and Bi4Ge3O12; in the latter material, the excitation of a coherent optical phonon mode is also observed. We discuss probing different acoustic modes in reflection and transmission geometries and frequency mixing of surface and bulk acoustic waves in the signal. The use of extreme ultraviolet radiation will allow the creation of tunable GHz to THz acoustic sources in any material without the need to fabricate transducer structures.

Thermal properties of one-dimensional piezoelectric phononic crystal

By using the transfer matrix method, we theoretically studied the propagation of a longitudinal acoustic wave in a one-dimensional phononic crystal (PnC) that contains a piezoelectric material as a defect layer. A pass band can be generated and controlled in the middle of the band gap. The pass band position is tuned by applying an external electric field. The position of the pass band inside the band gap is tuned by the changing of temperature. We introduce a comparison between temperature effects on two piezoelectric materials, PZT-5H and 0.7 PMN-0.3PT inside a PnC structure. Moreover, the pass band is shifted towards high or low frequencies by temperature decrement or increment, respectively. The simulated results provide a valuable guidance for PnC applications such as acoustic switch and temperature sensor.

Metaparticles of Pulsed Wave Fields

Properties of elementary particles of pulsed (localized) electromagnetic and acoustic wave fields directionally radiated by aperture sources (antennas, lasers, acoustic diaphragms) in free space and homogeneous isotropic media, for which the term metaparticle is used, are considered. The structure of the wave field and the energy transferred by the metaparticles are presented. The results obtained for the presented scalar theory of metaparticles of pulsed transverse electromagnetic (TEM) waves and longitudinal elastic acoustic waves can be extended to vector pulsed wave modes guided by layered inhomogeneous guiding media and guiding technical devices (waveguides).

Acoustic Modes at the Twist Boundary in Piezoelectric Crystals

The transformations of the shear (SH and SV) and longitudinal (L) acoustic waves at the twist boundary in piezoelectrics of 62m and 42m the and classes have been investigated. This boundary is formed at a hard contact between two identical crystal half-spaces rotated relative to each other around the Z||6||4 axis by an angle 2ϕ. Propagation occurs along the bisector of this angle (х axis) in the (x, y) twist plane. Situations have been established in which the shear modes are localized at the twist boundary exclusively due to the combination of the piezoelectric effect and half-space rotation, as well as the joint effect of the elastic anisotropy and rotation. The cases of independence of a bulk wave of the half-space rotation and occurrence of leaky waves are described.

3.5 GHz longitudinal leaky surface acoustic wave resonator using a multilayered waveguide structure for high acoustic energy confinement

In this paper, the use of a structure comprising a thin LiNbO3 plate and a multilayered acoustic mirror composed of SiO2 and Pt for high-performance longitudinal leaky surface acoustic wave (LLSAW) device is proposed. The mirror is expected to offer a much higher reflectivity than that composed of SiO2 and AlN, which the authors proposed previously. The field distribution of these structures is calculated by using a finite element method. It is shown that the acoustic wave energy of the proposed structure is well confined in the vicinity of the top surface, and that leakage to the substrate is reduced. A one-port resonator is fabricated on the structure and its performance characteristics are evaluated. Owing to a high phase velocity of 6,035 m/s, which is about 1.5 times higher than that of conventional SAWs, a large impedance ratio of 71 dB was achieved at 3.5 GHz in addition to a large fractional bandwidth of 9.5%.

Piezo-, elasto- and acousto-optic properties of Tl3AsS4 crystals.

Complete matrices of piezo-optic and elasto-optic tensors are experimentally determined for Tl3AsS4 crystals. It is revealed that the piezo-optic coefficients are very high, ∼10-11 N/m2 in the order of magnitude. This implies that Tl3AsS4 can be referred to the best piezo-optic materials. The same concerns the elasto-optic coefficients, of which absolute values are in the interval 0.28-0.54. It is also found that, at the anisotropic and isotropic interactions with the slowest transverse and longitudinal acoustic waves, the acousto-optic figure of merit reaches extremely high values (1.99×10-12 s3/kg and 9.45×10-13 s3/kg, respectively). In other words, the Tl3AsS4 crystals can be referred to as one of the best acousto-optic materials for the visible and infrared spectral ranges.

Short‐Period Nonlinear Viscoelastic Memory of Rocks Revealed by Copropagating Longitudinal Acoustic Waves

AbstractWe describe a new sensitive acoustic method to measure nonlinear viscoelastic properties of rocks directly in the time domain. Unlike static stress‐strain measurements, or dynamic acousto‐elastic methods that use steady state resonance to load a strain field into a rock, our method uses two copropagating longitudinal acoustic waves, one to perturb the strain in the sample and the other to probe the effect of that strain. Experiments on Crab Orchard Sandstone and Lucite samples are presented. We evaluate the time‐dependent nonlinear effects and find strong evidence that rocks have a short‐period nonlinear viscoelastic memory that is a function of the time history of the loaded strain. We develop a phenomenological model to describe both this nonlinear viscoelastic memory and the nonlinear elastic behavior of rock. Our model shows that the viscoelastic memory is controlled by both the traditional nonlinear elastic coefficients and a memory strength parameter. These new observations and methods have significance for quantifying changes in microstructure. This short‐term memory effect, on the order of a small fraction of a cycle, is shown to be related through viscoelasticity to absorption in the sample.

Acoustic Wave Sensor Based on Piezomagnetic Phononic Crystal

The propagation of longitudinal acoustic waves in a 1D phononic crystal (PnC) contains a piezomagnetic material (Terfenol-D) as a defect layer is analyzed and discussed theoretically. A resonant mode was generated inside the phononic band gap when the piezomagnetic material thickness becomes around its half wavelength. The present results revealed that the frequency of the generated resonant mode can be controlled by applying an external magnetic field. In addition, the resonant mode is shifted towards higher and lower frequencies by applying an external pressure on the PnC structure. The simulated results are very valuable in the application of sensors measuring magnetic fields and in the early detection of building cracks.

Acousto-optic Bragg diffraction using longitudinal leaky surface acoustic wave

In this study, to increase the amount of frequency shift by adopting a longitudinal leaky surface acoustic wave (LLSAW) with a higher phase velocity than a Rayleigh-type SAW to a waveguide-type acousto-optic Bragg deflector, a Ti-diffused optical waveguide was fabricated on an X-cut 36°Y-propagating LiNbO3 substrate with a high electromechanical coupling factor for the LLSAW and its diffraction properties were evaluated. The diffraction of the guided light by the LLSAW was observed for the first time. The diffraction efficiency in the TE0 mode was approximately 50% for an optical wavelength of 0.633 µm.

Effect of Nonthermal Electrons and Ions on Longitudinal Dust Acoustic Solitary Waves in a Strongly Coupled Dusty Plasma

The propagation properties of longitudinal dust acoustic waves (LDAWs) have been investigated in a strongly coupled dusty plasma containing negatively charged dust fluid, and nonthermal electrons and ions using the generalized hydrodynamic model in “kinetic regime.” The nonlinear dynamics of the system are shown to be governed by a modified KdV equation in the presence of viscoelastic forces. The modified KdV equation so obtained is found to possess a nonlinear force term and a linear damping term. The effects of various physical parameters on the phase velocity and coefficients of modified KdV equation have been analyzed. Furthermore, the effect of nonthermality of electrons and ions is realized in the numerical solution of the equation so obtained to study the time evolution of LDAWs under the influence of dust correlation forces.

Acoustically driven degradation in single crystalline silicon solar cell

The influence of ultrasound on current–voltage characteristics of crystalline silicon solar sell was investigated experimentally. The transverse and longitudinal acoustic waves were used over a temperature range of 290–340 K. It was found that the ultrasound loading leads to the reversible decrease in the photogenerated current, open–circuit voltage, fill factor, carrier lifetime, and shunt resistance as well as the increase in the ideality factor. The experimental results were described by using the models of coupled defect level recombination, Shockley–Read–Hall recombination, and dislocation–induced impedance. The contribution of the boron-oxygen related defects, iron-–boron pairs, and oxide precipitates to both the carrier recombination and acousto–defect interaction was discussed. The experimentally observed phenomena are associated with the increase in the distance between coupled defects as well as the extension of the carrier capture coefficient of complex point defects and dislocations.

Dielectric Nonlinearity and the Velocity of Ultrasonics in the Region of the Structural Phase Transition in (K0.5Na0.5)(Nb1 – xTa x )O3 Ceramics

Properties of the dielectric response of (K0.5Na0.5)(Nb1 – xTa x )O3 + 0.5 mol % MnO2 (KNN-xTa) ferroelectric ceramics at temperatures including that of the structural phase transition (SPT) from the orthorhombic phase to tetragonal is studied and compared to the behavior of elastic properties in this region of temperatures. The character is determined of the concentration dependences of such anomalies as the temperature of the maximum of permittivity Tmax(x) in the SPT region and temperature Textr at which the maximum increment of permittivity upon specimen heating in the SPT region occurs. It is found temperature Textr coincides with the one at which minimum v(T) of the velocity of a longitudinal acoustic wave is observed at SPT. Features of a nonlinear dielectric response associated with the coexistence of different types of domain boundaries in the region of a smeared structural transition in KNN-xTa ceramics are determined in studying the temperature behavior of polarization loops.

Experimental investigation of the hypersonic boundary layer transition on a 7° straight cone

In this paper, the experiments about the boundary layer transition on a 7° half-angle straight cone are carried out in a Mach 6 low-noise wind tunnel. The wall fluctuation pressure is measured by the transducer with megahertz response frequency, and the development process of the disturbance in the hypersonic boundary layer is investigated. The peaks in power spectrum density of the fluctuation pressure are related to the second mode wave, which is indicated through verifying the existence of the longitudinal acoustic second mode waves reflected between the relative sonic line and the solid wall by the flow visualization result. The wavelength and the characteristic frequency of the second mode wave in the hypersonic boundary layer are found to be greatly influenced by Reynolds number. The characteristic frequency of the second mode wave changes from 55 kHz to about 226 kHz when the Reynolds number increases from 2×106 m-1 to 8×106 m-1. The second mode wave appears at the position closer to the upstream with a higher disturbance growth speed under higher unit Reynolds number. As the second mode wave propagates downstream, its characteristic frequency gradually decreases. The freestream noise level also has a great influence on the development of the disturbance wave. The characteristic frequency of the second mode wave decreases significantly in a relatively quiet environment. The cross-correlation analysis results show that the propagation velocity of the second mode wave in the boundary layer is about 0.8-0.9 times the local mainstream velocity. The wavelength of the second mode wave is about 5.01 mm at the location from X=380 mm to X=440 mm when the unit Reynolds number is 5×106 m-1. At 1° angle of attack, the development of the boundary layer on the windward side and the leeward side of the cone are significantly different. The characteristic frequency of the second mode wave in the leeward surface is almost the same as the result at zero angle of attack under the same unit Reynolds number. However, the position of the second mode wave is greatly advanced. Results show that the disturbance development in the boundary layer of the leeward surface is accelerated, and the second mode wave appears at the position closer to the upstream. The velocity of the second mode wave in the leeward surface rapidly increases when it propagates downstream. While on the windward side, the disturbance development is inhibited and the second mode wave has a higher characteristic frequency. The wavelength of second mode wave also decreases obviously.

Investigation of deep defects in nanocrystalline-Si/Si interfaces using acoustic spectroscopy

Abstract A set of structures with nanocrystalline-Si/Si interfaces formed on p-type Si substrate appropriated for photovoltaic application was prepared. The Acoustic DLTS technique based on the acoustoelectric response signal produced by the structure when a longitudinal acoustic wave propagates through the structure was used together with electric characterization to determine deep defects and the role of both individual layers. Several kinds of interface deep centers with activation energies typical for dangling bonds, oxygen participated Si or point defects were observed as well as a particular influence of individual layers on the interface states. The obtained results are analyzed, discussed and subsequently compared.

Photoelastic and acousto-optic effects in 65GeS2-25Ga2S3-10CsCl glass

The peculiarities of photoelastic and acousto-optic effects are first tested in chalcohalide 65GeS2-25Ga2S3-10CsCl glass exploring the interferometry method. The determined piezo-optic coefficients occur to be (in Br) π11=2.8±0.6, π12=6.0±0.9 and π44=−3.2±1.1. In respect to maximal acousto-optic figure of merit М2=55.6·10−15s3/kg proper for longitudinal acoustic wave propagation and polarization along X2 (і=2) direction, this glass seems more perspective for photoelastic and acousto-optic modulation in visible and near IR ranges, than many alternative candidates, such as crystalline quartz, LiNbO3, CaWO4, PbMoO4, β-BaB2O4, etc. For the first time it has been shown that piezo-optic effect of isotropic solids is anisotropic, and the degree of anisotropy is the difference of π11–π12 coefficients.

Viscoelasticity of amyloid plaques in transgenic mouse brain studied by Brillouin microspectroscopy and correlative Raman analysis.

Amyloidopathy is one of the most prominent hallmarks of Alzheimer's disease (AD), the leading cause of dementia worldwide, and is characterized by the accumulation of amyloid plaques in the brain parenchyma. The plaques consist of abnormal deposits mainly composed of an aggregation-prone protein fragment, β-amyloid 1-40/1-42, into the extracellular matrix. Brillouin microspectroscopy is an all-optical contactless technique that is based on the interaction between visible light and longitudinal acoustic waves or phonons, giving access to the viscoelasticity of a sample on a subcellular scale. Here, we describe the first application of micromechanical mapping based on Brillouin scattering spectroscopy to probe the stiffness of individual amyloid plaques in the hippocampal part of the brain of a β-amyloid overexpressing transgenic mouse. Correlative analysis based on Brillouin and Raman microspectroscopy showed that amyloid plaques have a complex structure with a rigid core of β-pleated sheet conformation (β-amyloid) protein surrounded by a softer ring-shaped region richer in lipids and other protein conformations. These preliminary results give a new insight into the plaque biophysics and biomechanics, and a valuable contrast mechanism for the study and diagnosis of amyloidopathy.

Peculiarities of energy trapping of the UHF elastic waves in diamond-based piezoelectric layered structure. I. Waveguide criterion

Finite Element Modeling of the peculiarities of the trapping energy phenomenon in application to the piezoelectric layered structure (PLS) “Al/(0 0 1) AlN/Mo/(1 0 0) diamond” has been fulfilled. The resonant properties of longitudinal bulk acoustic waves (BAW) as well as frequency dependence of impedance within the 1 – 6 GHz band have been studied. The investigation of distribution of elastic energy flow and elastic displacements in a PLS cross-section allowed us to obtain an important information on energy trapping (ET) in PLS.Experimentally and as a result of modeling, it has been found that Q minimums are observed in PLS at quarter-wave resonance in the thin-film piezoelectric transducer (TFPT). Maximal Q value was observed at half-wave resonance in TFPT.It has been established that the ET-effect depends considerably on the mutual location of the n-th overtone’s antiresonant frequency fa,n and cut-off frequencies of substrate fs,n−k−1 and fs,n−k where fs,n−k−1<fa,n<fs,n−k, and k=0, 1,2,… is the number of half-length waves to be stowed on the thickness of TFPT. The total violation of the ET-effect will be arisen at the condition f >fs,n−k, when the BAW energy excites the symmetrical or antisymmetrical Lamb waves.