Characteristics Of Acoustic Waves Research Articles

Tuning bandgaps in metastructured beams: numerical and experimental study

Tunable metastructures (including phononic crystals and metamaterials) have the unique advantage that one can change the operating frequency and acoustic wave characteristics as needed. In this paper, the bandgap characteristics and their controllability of a metastructured beam with mass-spring oscillators and under an axial force are investigated in depth both by the finite element method and by experiment. The experimental and numerical results indicate that there is one local resonance (LR) bandgap and multiple Bragg scattering (BS) bandgaps. The width and position of each bandgap can be tuned effectively by adjusting the axial force, lattice constant, and spring stiffness, and a super wide pseudo-gap can be obtained under suitable conditions. By integrating different mass-spring oscillators into one metastructured beam, the bandgap width can be broadened and pseudogap- like characteristics can be achieved. By changing the number of different oscillators, the propagating distance of elastic waves in the beam can also be controlled. It is further revealed that point defects have a large influence on the BS bandgaps but little effect on the LR bandgap. The present work provides an important reference for the optimal design of adjustable high-performance metastructures.

Surface Acoustic Wave Characteristics with a Layered Structure of IDT/θ° YX-LiTaO3/SiO2/AlN/diamond

A new layered surface acoustic wave (SAW) structure was proposed by Murata Co., Ltd recently. It was reported that such structure could achieve an incredible high performance including a higher quality factor Q and electromechanical coupling coefficient K2. For deeply understanding propagating characteristics and optimizing the performance of the SAWs in such structure, a layered structure of IDT/θ° YX-LiTaO3/SiO2/AlN/Diamond with different structural parameters were theoretically investigated by FEM method. The calculated admittance shows that four eigenmodes simultaneously exist in such layered structure including the main mode SH SAW. And compared with the Traditional SAW structure, the main mode could achieve a higher value of K2 with sacrificing its velocity a little. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With Au employed, the K2 of the main mode is a little larger resulting from better suppression of the spurious modes. The optimum thickness of electrode and piezoelectric layer are 0.2 and 0.02λ, respectively. In this case, the K2 for the SH SAW achieves its maximum value of 12.20% with a large phase velocity of 3608 m/s. Furthermore, the pure SH SAW can be obtained with the Y-cut Euler angle θ from 0° to 60°, where its K2 has a wide range of 8.70 to 13.69%. Consequently, the work provides a theoretical guide for designing SAW devices of different bandwidth and operation frequency with such structure.

Nonlinear dust acoustic waves in a self-gravitating and opposite-polarity complex plasma medium

The effects of the self-gravitational and the polarization forces on dust acoustic waves structure in a two-fluid complex plasma model are studied. The electrons and the ions obey the non-extensive distribution. The nonlinear dynamics of the massive positive and negative dust grains are considered. The reductive perturbation technique is applied to obtain a Zakharov-Kuznetsov equation. The nonlinear characteristics of the dust acoustic cnoidal (periodic) and solitary waves are investigated using the bifurcation theory. It is found that the dust acoustic wave properties depend strongly on the gravitational and the polarization parameters as well as the non-extensive indexes for electrons and ions. The possible applications of the present work to space plasma situations are discussed.

Analysis on Characteristics of ZnO Surface Acoustic Wave with and without Micro-Structures.

In this paper, we fabricate a surface acoustic wave (SAW) device with micro-structures on a zinc oxide (ZnO) thin film and measure its signal response. The manufacturing processes of the SAW device include the fabrication of micro-structures of a SAW element and its interdigital transducer by silicon micro-machining and the fabrication of a thin film of ZnO by RF magnetron sputtering. We, then, measure the SAW properties. This research investigates the properties of sputtered thin films for various amounts of O2/(Ar + O2) using Zn and ZnO targets. Regardless of target, the growth rate of the ZnO thin film decreases as the oxygen content increases. When the SAW is sputtered ZnO thin film using 30% oxygen, the digital signal of the SAW has better performance. The measurement signal of the SAW with micro-structures is similar to that without micro-structures.

Study of Dust Acoustic Wave Propagation in a Lorentzian Dusty Plasma in Presence of Secondary Electron Emission

In this paper, we have investigated the effect of secondary electron emission on the propagation characteristics of linear dust acoustic waves in dusty plasmas consisting of suprathermal inertialess primary electrons, secondary electrons, Boltzmann distributed ions, and negatively charged inertial dust grains. The suprathermal electrons are assumed to follow kappa velocity distribution. We have derived the linear dispersion relation and shown that real and imaginary frequencies of the waves are influenced by the strength of secondary electron emission as well as suprathermal electron population.

Interaction phenomena of ion acoustic solitary waves with singly charged cold ions and Boltzmann electrons

The linear features and phenomena concerning head-on collision between the two ion acoustic solitary waves are investigated considering the multi-component plasma system comprising singly charged cold positive and negative ions, and Boltzmann electrons. Linear characteristics of ion acoustic solitary waves are studied taking the dispersion relation into account. The two-sided Korteweg-de Vries (KdV) equations are derived to investigate the structures of the solitons and the phase shift of ion acoustic solitary waves due to collisions by the extended Poincaré-Lighthill-Kuo (ePLK) method. The linear analyses reveal that the densities of the ionic species and wave number modify the ion acoustic solitary wave frequency, and higher density of electrons changes the group velocity. It is found that a new wave is produced with high amplitude in the interaction region due to head-on collision between the waves. The compressive and rarefactive KdV solitons are produced due to the changes of density. The density ratios such as and modify the phase shift and nonlinear phase velocity after head-on collision.

Acoustic wave transmission channel based on phononic crystal line defect state

To generate directional transmission characteristics of acoustic waves, we constructed two abnormal transmission models based on the protocell. The simulation results showed that the band gap characteristic of the phononic crystal structure can be used to realize the directional transmission effect. We also found that the acoustic frequency has a great influence on the acoustic transmission characteristics of artificial acoustic structures. Because the artificial acoustic structure based on phononic crystals has the advantages of design flexibility, it can be customized according to the actual engineering application. Our results provided a new direction for engineering applications such as directional transmission of acoustic waves and acoustic diodes.

Effect of variable dust size, charge and mass on dust acoustic solitary waves in nonextensive magnetized plasma

Effects of variable dust size, mass and charge on the characteristics of nonlinear dust acoustic solitary waves (DASW) in a two-temperature ion dusty plasma have been studied analytically. Plasma ions are assumed to be Maxwellian while plasma electrons are nonextensively distributed. Mass and electrical charge of dust particles are assumed to be proportional to their size. Plasma is embedded in an external magnetic field with variable direction. The Zakharov–Kuznetsov equation was derived using reductive perturbation method, and its solitary answers were extracted. Dispersion relation of DASW shows that this wave may generate in plasma only if the nonextensivity coefficient, q, is positive. For all allowed magnitudes of c (the ratio of the largest dust radius to smallest dust radius) and q, only rarefactive solitons may be formed in plasma. Effect of variable dust size on the width and amplitude of DASW is noticeable when c is smaller than 3. Both the width and amplitude of DASW increase with increasing c, and with increasing the nonextensivity of plasma, effect of variable size increases. Results show that increasing the strength of external magnetic field leads to localization of DASW while both the width and amplitude of DASW are under the influence of the direction of the external magnetic field simultaneously.

Bulk Acoustic Wave Characteristics of Pseudo Lateral-Field-Excitation on LGT Single Crystal for Liquid Phase Sensing.

In the present study, pseudo lateral-field-excitation (LFE) bulk acoustic wave characteristics on LGT crystals are investigated to increase the sensitivity of LFE devices on the liquid characteristic variations. The cut orientation of LGT crystals for pseudo-LFE is investigated and verified experimentally. For an LFE device in the pseudo-LFE mode, the thickness shear mode wave is excited by the thickness field rather than the lateral field. The present work shows that when the (yxl) 13.8° LGT plate is excited by the electric field parallel to the crystallographic axis x, it operates in the pseudo-LFE mode. Moreover, characteristics of devices including the sensitivity and impedance are investigated. The present work shows that sensitivity of LFE devices to variation of the conductivity and permittivity of the aqueous solution are 9 and 3.2 times higher than those for AT-cut quartz crystal based devices, respectively. Furthermore, it has been found that the sensitivity of the LGT LFE sensor to liquid acoustic viscosity variations is 1.4 times higher than the one for the AT-cut quartz sensor. The results are a critical basis of designing high-performance liquid phase sensors by using pseudo-LFE devices.

ANALYSIS OF ACOUSTIC PATH TRANSMISSION FACTOR FOR ANGULAR VELOCITY SENSOR

The change in characteristics of ultrasonic waves’ transmittion in solid rotating media is the basis for the operation of acoustic angular velocity sensor. The transmission coefficient of the sensing element (SE) of the acoustic path deter-mines the level of angular velocity sensor informative signal based on detecting changes in characteristics of bulk acoustic waves in solid media. In this regard, the efforts aimed at obtaining maximum transmission coefficient are relevant and represent an important stage in the design of such devices. The sensitive element of the acoustic path consists of radiating and receiving plate piezoelectric transducers, propagation medium (acoustic duct), contact layers and electrical load. The coefficient is identical to the path of ultrasonic delay lines on bulk acoustic waves. Although, many sources present the theoretical analysis of the path of this type, they carry out the analysis in so-called one-dimensional approximation, i.e. they perform the analysis without taking into account the limited transverse dimensions, whereas the path of the sensing element should have limited lateral dimensions, which can affect the value of transmission coefficient. The above-mentioned sources do not present the results of experiments. Thus, it is necessary to conduct a complex of simulation and experiments to analyze the acoustic path transmission coefficient of the angular velocity sensor. Authors of the paper developed a pathmodeling program in Mathcad software to perform simulation. For implementation of the experiment, authors created the installation, as well as a number of proto-types with transducers made of piezoelectric quartz and piezoelectric ceramics. The results demonstrate that fundamental statements developed for one-dimensional approximation one can use to determine the transmission coefficient of the acoustic path with limited dimensions. Besides, the use of the matched electrical load gives the opportunity to increase the transmission coefficient. For example, in case of Y-cut piezoelectric quartz converter prototype the increase reached 20 dB.

Investigation of Characteristics of Dual-band Ladder-type Surface Acoustic Wave for High-power Durability Duplexer

Investigation of Characteristics of Dual-band Ladder-type Surface Acoustic Wave for High-power Durability Duplexer

Modeling the Propagation of Elastic Ultrasonic Waves in Isotropic and Anisotropic Materials when Excited by Various Sources

This work is devoted to the investigation of the characteristics of acoustic emission waves to establish their relations with the parameters of the fracture of the structure of the material. The paper presents the results of the analysis of acoustic emission signals recorded during the propagation of ultrasonic waves in metal sheet materials using piezoelectric sensors. The specimen was a rectangular aluminum plate. The piezoelectric sensor recorded acoustic emission signals generated by the Hsu-Nielsen source. The piezoelectric sensor is located in the center of the aluminum plate. Then sources are generated with different hardness to model various kinds of cracks at each specific location. To determine the informative component of a useful acoustic emission signal, the Morlet wavelet transformation was used. When excited by a fracture pencils of different hardness, the magnitude of the wavelet differ in the energy and intensity of the spectrogram.

AMPLITUDE ATTENUATION LAWS OF ACOUSTIC EMISSION WAVES IN PLATE STRUCTURES

Although acoustic emission technology has been used in the nondestructive testing of various plate structures, its further application and development remain limited because the laws governing the amplitude attenuation of acoustic emission waves in plate structures remain unclear. This study aimed to reveal the amplitude attenuation laws of acoustic emission waves in plate structures. Thus, in this study, the traditional model of amplitude attenuation, which is in the form of an exponential function, was improved in reference to cylindrical waves, and an amplitude attenuation model in the form of a power function suitable for plate structures was proposed. Moreover, an experimental system for the attenuation of acoustic emission waves in aluminum alloy plates was established to experimentally verify the proposed model. Finally, the amplitude attenuation laws of acoustic emission waves within the full field, near field, and far field of plate structures were discussed. Results show that the amplitude attenuation laws of acoustic emission waves within the full field, near field, and far field of plate structures all conform to the power function model and gradually reduce as propagation distance increases. In addition, the improved amplitude attenuation model better corresponds with the actual amplitude attenuation trend within the near-field range of the acoustic emission source than other forms of amplitude attenuation models. Specifically, the traditional model of amplitude attenuation model agrees with the actual attenuation laws of acoustic emission waves only within the far-field range of the acoustic emission source. The results of this study provide valuable references for the profound analysis of the propagation characteristics of acoustic emission waves in plate structures and will help promote the development and application of acoustic emission technology. Keywords: Acoustic emission waves, Amplitude, Attenuation, Laws, Plate

Directional Transmission Characteristics of Acoustic Waves Based on Artificial Periodic Structures

Acoustic artificial periodic structures, also known as phononic crystal, have been widely used in special acoustic problems such as low-frequency vibration reduction and noise reduction due to their bandgap characteristics. Different from previous researches, which focus on the bandgap characteristics, we designed a locally resonant artificial periodic structure, which can not only use the bandgap characteristics to design a directional transmission channel of acoustic waves, but also use its bandpass characteristics to generate multidirectional transmission of acoustic waves. The vibration mechanism of two-dimensional, three-components phononic crystal lattice structures was given, and a variety of directional transmission models of acoustic waves were constructed based on the unit cell. The simulation results showed that acoustic directional transmission characteristics were produced by the locally periodic resonance structure, and the transmission direction depends on the design of the structure. By taking advantage of the superposition properties of acoustic waves, the incident acoustic wave in the horizontal direction can be converted into the outgoing acoustic wave in the vertical direction without changing the position of the model, and this capability greatly expands the application range of the artificial periodic structure. In addition, the transmission characteristics of the directional transmission effect have a strong correlation with the frequency; that is, limited by the wavelength, the acoustic pressure distribution mode at different frequencies will be different. At the resonant frequency of the structure, the transmission efficiency of the acoustic wave will be highest. Moreover, similar to the traditional artificial periodic structure, the acoustic model proposed in this paper also has bandgap characteristics. Using bandgap characteristics, we designed an acoustic directional transmission channel to achieve uniform directional transmission of acoustic waves. These results greatly enrich the application space of artificial acoustic structures and provide new ideas for acoustic communication, acoustic detection, and acoustic stealth.

Acoustic Transmission Characteristics Based on H-Type Metamaterials

To achieve the artificial manipulation of the acoustic wave front, and to produce high-efficiency acoustic focusing effect, this paper designed an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -type locally resonant metamaterial structure based on a two-dimensional three-component local resonance unit. The transmission characteristics of acoustic waves in this model were analyzed by using COMSOL, which is a finite element simulation software. We found that the incident acoustic energy was absorbed by the model, and the transmission path was consistent with the model structure. We also found that in different frequencies, the transmission characteristics of acoustic waves were different. The acoustic transmission characteristics improved as the waves approached the resonant frequency. Because of the flexibility and controllability of metamaterials, the structure can be designed according to specific conditions in practical applications to meet the resonant frequency required for transmitting acoustic signals, thus, improving the acoustic transmission efficiency. In addition, if the point excitation source of spherical waves was replaced by the line excitation source of plane waves, a plane acoustic wave focusing phenomenon would occur, which further proved that the local resonance acoustic metamaterial has good focusing characteristics and manipulation characteristics. The result of our research provides a new direction for underwater acoustic imaging, acoustic communication, and acoustic detection.

A new power-based method to determine the first arrival information of an acoustic emission wave

Acoustic emission is a powerful experimental structural health monitoring technique for determining the location of cracks formed in a member. Pinpointing wave arrival time is essential for accurate source location. Conventional arrival detection technique’s accuracy deteriorates rapidly in low signal to noise ratio (5–40 dB) region, thus unsuitable for source location due to this inaccuracy. A new technique to pinpoint the arrival time based on the power of the wave is proposed. We have designed an adaptive filter based on the power characteristics of acoustic emission wave. After filtration of the acoustic emission wave, sliding window is employed to accurately identify the region of wave arrival based on the change in transmitted power. The results from various experimental and numerical arrival time detection experiments consistently show that the proposed methodology is stable and accurate for a wide range of signal to noise ratio values (5–100 dB). Particularly, in signal to noise ratio region (5–40 dB), the method is significantly more accurate as compared to the other methods described in the literature. The method was then employed to study the localized damage progression in a steel fiber–reinforced beam under four-point bending. The results suggest that calculated source location using the new method is consistent with that from visual inspection of the member at failure and more accurate than the localization results from existing method.

Realization of complex curved waveguide based on local resonant 3D metamaterial

To overcome the negative impact of diffraction effect on the transmission wave front at the bend and to improve the transmission efficiency of acoustic wave in the bend waveguide, the finite element method by COMSOL was used to simulate the propagation characteristics of acoustic wave in the structure of bending acoustic waveguide, based on local resonance acoustic metamaterials. Specifically, the vibration mechanism of three-dimensional (3D) component locally resonant phononic crystals was presented, and the acoustic metamaterial models of M-shaped, L-shaped and S-shaped bent waveguides were constructed on the basis of the protocells. The local resonance between the acoustic wave and the protocells in the waveguide model was investigated, in order to produce the nondestructive bending propagation effect of the acoustic wave. The results of finite element analysis show that the plane acoustic waves incident from the M-shaped, L-shaped and S-shaped bending waveguide model will propagate directionally along the model structure after being controlled at the resonance frequency. These results confirm the flexibility and feasibility of the bending acoustic waveguide model designed by the local resonance acoustic metamaterials. In addition, the acoustic waveguide model in long-distance special environment was designed and the low loss transmission of acoustic signal was implemented. This study provides a new solution for engineering applications, such as ultrasonic signal detection and underwater acoustic communication transmission.

Nonlinear ion acoustic waves in a relativistic degenerate plasma with Landau diamagnetism and electron trapping

We consider the effects of trapping in a relativistic degenerate plasma with quantizing magnetic field. The linear dispersion relation for such an ion acoustic wave is derived and the propagation characteristics of these waves are discussed. The Sagdeev potential for the formation of arbitrary amplitude solitary structures is obtained and it is seen that only compressive solitary structures are formed for the relativistic degenerate quantized magnetoplasma. The dependence of the linear and nonlinear propagation characteristics of ion acoustic waves on different plasma parameters is explored. A comparison is also made with the previous studies. The useful applications of the present investigation in dense astrophysical environments like white dwarf stars and neutron stars, in semiconductor physics, in high-energy density physics, in inertial confinement fusion and in next generation laser–plasma interaction experiments are pointed out.

Acoustic propagation characteristics of heteromorphic metamaterials

To explore the propagation characteristics of acoustic waves in heterogeneous acoustic materials, we studied the propagation of acoustic waves in resonant phononic crystals. We identified the vibration mechanism of two-dimensional three-component localized resonant phononic crystals. Using the finite element software COMSOL, an acoustic propagation model based on acoustic metamaterials was constructed and the local resonance characteristics of acoustic waves and the original cells were used to simulate multiple acoustic models based on triangular arrays. We found that the planar point-like and linear excitation sources incident from the bottom edge of the triangular array model converge to the focal point at the top corner after being controlled by the model. The low-loss movement effect of the point source could be achieved in a rectangular model with a triangular array. A reversal of the transmission of plane acoustic waves resulted when two or three identical triangular arrays were combined into a parallelogram or a trapezoid. This series of abnormal acoustic phenomena provides new directions for the detection of point sources, low-loss directional transmission of acoustic waves, and acoustic stealth.

An analytically based computer model for evaluating effective elastic properties of nitride nanowire-polymer compositions using laser-generated surface acoustic waves

The investigation of physical and mechanical properties of nitride nanowires (NWs) is a topical field of modern nanotechnological research due to a wide range of promising applications. Normally, the NWs are embedded in a host polymer (e.g., hydrogen silsesquioxane – HSQ), and it becomes necessary to determine the effective properties of polymer-NW compositions rather than of separate wires. The central idea of the present research is the evaluation of the effective elastic moduli of the anisotropic composite HSQ-NW material via the minimization of the goal function that specifies the discrepancy between the measured and calculated characteristics of laser-generated surface acoustic waves. The experimental data are obtained on the basis of transient grating spectroscopy while the theoretical dispersion curves are calculated using the analytically based computer model for elastic guided wave excitation and propagation in multilayered elastic anisotropic half-spaces. The numerical examples illustrate the validation of the developed computer model against the experimental data acquired for sandwich microstructures with known elastic moduli as well as demonstrate the restoration of the latter in the case of HSQ-NW compositions with unknown mechanical properties.