Spectrum Of Acoustic Waves Research Articles

Development and evaluation of laser acoustic measurement system for supersonic jet noise

Acoustic measurements in the near field are significant to suppress the noise generated by a supersonic jet. The microphone measurement is commonly used to measure noise, but it is not appropriate for the jet noise measurement in the near field, because it may be broken or disturb the sound field. In this study, we propose an optical acoustic measurement method using a laser and a 2-D position sensitive detector. This system can measure the propagating direction and the spectra of acoustic waves by detecting the angle and direction of laser path deflection by acoustic wave passing. To evaluate this laser measurement method, it was applied to various supersonic jet noise phenomena, such as Mach waves and screech tones, and then the results were compared with those of microphone measurements. The spectra measured by the laser measurement show good agreement with those by microphone measurements, and the difference in OASPL was less than 0.7 dB. As for the propagating direction, it is calculated using the principal component analysis in the laser measurement, and its results also show good agreement with those of acoustic intensity vector measurement.

Toward streaked collective Thomson scattering measurements on an extreme ultraviolet plasma light source

We show through forward modeling calculations that streaked collective Thomson scattering measurements are feasible on laser-produced tin plasmas generated under conditions relevant for extreme ultraviolet lithography. Using a 532 nm probe laser beam, the feasibility of simultaneous measurements of electron plasma wave (EPW) and ion acoustic wave (IAW) spectra is investigated. Absolute photon counts for laser scattering off both waves are calculated. Probe laser electron heating and bremsstrahlung background radiation effects are accounted for. While a large spatiotemporal region can be successfully probed based on the IAW feature, only one measurement location can be accessed through the EPW as a result of the low signal to noise ratio. A portable/traveling tabletop system is proposed.

(Digital Presentation) Lifetime Prediction of SiC Power Module By Using Time-Series Analysis of Acoustic Emission during Power Cycling Test

Acoustic emission (AE) based condition monitoring is a popular method to inspect a material health condition in many areas[1]. It monitors irreversible structure changes of material through radiation of acoustic waves. Typically, the structure change generates a typical spectrum of acoustic waves starting at 1 kHz, and falling off at several MHz, which can be detected and analyzed via an AE system. Meanwhile, AE signals convey massive information such as rise time, AE energy, AE peak frequency, which are expressive of the failure process. AE based condition monitoring technology exhibits excellent capability of detecting, positioning, and characterizing damage and has been wildly used in monitoring of inner structure changes in bridges, pressure containers, and pipeline systems. In the last decade, the AE technology has been applied to condition monitoring of power modules and shows a promising application scenario in the power electronics field, which help us acquire accurate failure information and making precise perdition of a failure in the power module[2].In this work, we firstly combined the AE monitoring and a deep learning model - Gated Recurrent Unit (GRU) to monitor and predict the failure of power module as shown in Figure 1[3]. The proposed method integrally analyzes and summarizes the patterns from the time-series data obtained during power cycle tests of power modules and predicts the failures. Specifically, the time-series data consisting of junction temperature, electric power, thermal resistance, and several AE parameters were obtained from AE sensor data and power cycling test. The proposed method (a) automatically extracts common or different time-series patterns among devices and estimates device states, and (b) effectively predicts failures by switching prediction models according to changes in device states.By time-series analysis of AE sensor data, it was confirmed that the AE parameters obtained from the AE sensor data capture the progression and signs of failures. In addition, by verifying the effectiveness of the time-series pattern detection, it was confirmed that the proposed method can accurately extract the timeseries patterns during normal conditions, the time-series patterns that show signs of failure, and the time-series patterns after failure. Furthermore, by verifying the prediction accuracy and learning efficiency, it was showed that the proposed method is capable of faster learning while retaining the same or better performance compared to existing methods. Reference [1] A. Nair and C. Cai, "Acoustic emission monitoring of bridges: Review and case studies," Eng Struct, vol. 32, no. 6, pp. 1704-1714, 2010.[2] S. Müller, C. Drechsler, U. Heinkel, and C. Herold, "Acoustic emission for state-of-health determination in power modules," in 2016 13th International Multi-Conference on Systems, Signals & Devices (SSD), 2016: IEEE, pp. 468-471.[3] R. Dey and F. M. Salem, "Gate-variants of gated recurrent unit (GRU) neural networks," in 2017 IEEE 60th international midwest symposium on circuits and systems (MWSCAS), 2017: IEEE, pp. 1597-1600.

Modeling of acoustic and gravity wave interactions, coupling, and observables above meteorological systems

Meteorology, especially strong tropospheric convection, is widely appreciated to generate broad spectra of acoustic and gravity waves (AWs and GWs or, together, AGWs). These include GWs with scales of tens to hundreds of kilometers and periods of ∼5 min to hours, that readily propagate upward, reach high altitudes (often to the lower-thermosphere), and grow to large amplitudes so that they may evolve nonlinearly prior to being overcome by dissipation. Strong convective dynamics, e.g., thunderstorms and tornadoes, are also known to radiate AWs at very low infrasonic frequencies (e.g., 0.1 Hz down to ∼4 mHz) that reach high altitudes and may be detectable in fluctuations of the atmosphere and ionosphere [e.g., Nishioka et al. (2013); Heale et al. (2019)]. The breaking of strong GW fields may also generate secondary AWs and, more generally, AGWs [Snively (2017); Heale et al. (2021)]. Together, convection and secondary AGW processes contribute to a broad spectrum of AWs with ∼mHz periods that are readily detectable at high altitudes and in pressure signals also measured at ground. Although AWs are excluded from traditional numerical weather prediction models, we report on models and simulation experiments designed to capture AW/AGW evolutions and their resulting observable signatures. In particular, we review and highlight scenarios by which ∼mHz AWs may reveal source processes of interest, as well as the opportunities to use atmospheric and ionospheric signals of AWs/AGWs as complement to ground-based infrasound recordings.

Primary Versus Secondary Gravity Wave Responses at F‐Region Heights Generated by a Convective Source

AbstractA 2D nonlinear, compressible model is used to simulate the acoustic‐gravity wave (AGW, i.e., encompassing the spectrum of acoustic and gravity waves) response to a thunderstorm squall‐line type source. We investigate the primary and secondary neutral AGW response in the thermosphere, consistent with waves that can couple to the F‐region ionospheric plasma, and manifest as Traveling Ionospheric Disturbances (TIDs). We find that primary waves at z = 240 km altitude have wavelengths and phase speeds in the range 170–270 km, and 180–320 m/s, respectively. The secondary waves generated have wavelengths ranging from ∼100 to 600 km, and phase speeds from 300 to 630 m/s. While there is overlap in the wave spectra, we find that the secondary waves (i.e., those that have been nonlinearly transformed or generated secondarily/subsequently from the primary wave) generally have faster phases than the primary waves. We also assess the notion that waves with fast phase speeds (that exceed proposed theoretical upper limits on passing from the mesosphere to thermosphere) observed at F‐region heights must be secondary waves, for example, those generated in situ by wave breaking in the lower thermosphere, rather than directly propagating primary waves from their sources. We find that primary waves with phase speeds greater than this proposed upper limit can tunnel through a deep portion of the lower/middle atmosphere and emerge as propagating waves in the thermosphere. Therefore, comparing a TID's/GWs phase speed with this upper limit is not a robust method of identifying whether an observed TID originates from a primary versus secondary AGW.

Correlation and spectrum of dust acoustic waves in a radio-frequency plasma using PK-4 on the International Space Station

Dust acoustic waves were investigated in an experiment under microgravity conditions, using the European Space Agency-Roscosmos facility PK-4 on the International Space Station. A three-dimensional dust cloud was confined in a glow-discharge plasma powered by a radio-frequency coil in low-pressure neon gas. Low-frequency dust acoustic waves (DAWs) were spontaneously excited due to the flowing ions in the plasma. Dust motion was imaged using video cameras, yielding the position for individual dust particles. Besides these particle-level measurements, the dust was also measured as a fluid continuum to obtain its velocity and density fluctuations. A space–time diagram of the dust-fluid velocity reveals that the waves changed properties as they propagated across the dust cloud, in the direction of the ion flow. Density fluctuations were characterized by a wave spectrum, indicating the emergence of collective vibration modes in a broad range of wave numbers. The decay of the modes was characterized by density correlation functions. Fitting the correlation functions to an analytical model yields an experimental measurement of the dispersion relation for DAWs, which is compared to that of linear theory.

Symmetric and asymmetric spectra of acoustic waves resonantly transmitted through a slab in a fluid

We theoretically studied the resonant transmission of acoustic waves through a slab in a fluid. When acoustic waves are incident on the interface perpendicularly, Bright–Wigner type resonances occur, whereas Fano resonances are observed when acoustic waves are obliquely incident. We examine various resonance peaks in transmission using analytical expressions for the transmittance. In particular, we show that an antiresonance occurs when two types of resonance overlap at the same frequency.

Determination of Ethanol Content in Fuels with Phononic Crystal Sensor

Introduction. In-line analysis of ethanol content in gasoline blends is currently one of the urgent needs of fuel industry. Developing safe and secure approaches is critical for real applications. A phononic crystal sensor have been introduced as an innovative approach to high performance gasoline sensing. Distinguishing feature of proposed sensor is the absence of any electrical contact with analysed gasoline blend, which allows the use of sensors directly in pipelines without the risk of explosion in an emergency.Aim. Investigation of the possibilities of using phononic sensor structures to determine the ethanol content in liquid hydrocarbons.Materials and methods. A theoretical analysis of sensor structure was carried out on the basis of numerical simulation using COMSOL Multiphysics software. For measurement, substances of ordinary gasoline and gasoline 63–80 with ethanol concentrations in the range of 1–10 % by volume in increments of 2 % were prepared. The phononic crystal sensor was designed as a stainless steel plate with cylindrical holes and a resonant cavity, formed as a running across the wave propagation path slit between two lattices.Results. In-line analysis of measuring the concentration of ethanol in alcohol-containing fuels on a phononic crystal structure with a resonant cavity was carried out. Using the Agilent4395A admittance meter, the transmission spectra of longitudinal acoustic waves through the gasoline-filled sensor structure with were obtained. The non-linear correlation between the composition and the speed of sound of the blend is presented in the article is due to the ability to reduce the speed of sound of the mixture with an increase in ethanol concentration in the range of 0–10 % by volume.Conclusion. A measurement structure on the basis of phononic crystal was created. The measurements of various gasoline-ethanol mixtures show that the sensor has significant sensitivity (0.91 kHz/ms−1 ) with quality factor of 200) to distinguish between regular fuels, gasoline based blends and the presence of additives in standard fuels. The sensor has prospects for in-line analyzes the composition of liquid hydrocarbons.

Locally Resonant Phononic Crystals at Low frequencies Based on Porous SiC Multilayer

In this work, a one-dimensional porous silicon carbide phononic crystal (1D-PSiC PnC) sandwiched between two rubber layers is introduced to obtain low frequency band gaps for the audible frequencies. The novelty of the proposed multilayer 1D-PnCs arises from the coupling between the soft rubber, unique mechanical properties of porous SiC materials and the local resonance phenomenon. The proposed structure could be considered as a 1D acoustic Metamaterial with a size smaller than the relevant 1D-PnC structures for the same frequencies. To the best of our knowledge, it is the first time to use PSiC materials in a 1D PnC structure for the problem of low frequency phononic band gaps. Also, the porosities and thicknesses of the PSiC layers were chosen to obtain the fundamental band gaps within the bandwidth of the acoustic transducers and sound suppression devices. The transmission spectrum of acoustic waves is calculated by using the transfer matrix method (TMM). The results revealed that surprising low band gaps appeared in the transmission spectra of the 1D-PSiC PnC at the audible range, which are lower than the expected ones by Bragg’s scattering theory. The frequency at the center of the first band gap was at the value 7957 Hz, which is 118 times smaller than the relevant frequency of other 1D structures with the same thickness. A comparison between the phononic band gaps of binary and ternary 1D-PSiC PnC structures sandwiched between two rubber layers at the micro-scale was performed and discussed. Also, the band gap frequency is controlled by varying the layers porosity, number and the thickness of each layer. The simulated results are promising in many applications such as low frequency band gaps, sound suppression devices, switches and filters.

Study on the low-frequency forbidden transmission properties of one-dimensional ternary solid-fluid sonic crystals by FEM

Based on the finite element method (FEM), an acoustic transmission model of onedimensional ternary solid-fluid sonic crystals under the condition of oblique incidence is established. Transmission spectra of acoustic waves with different incident angles and frequencies in sonic crystals are calculated. The results show that two broadband forbidden band gaps exist in the low frequency range within two separated incident angle ranges for the ternary structure, which has one more band gap than the binary solid-fluid structure. By adjusting the solid filling fraction, period and lattice constant of the ternary structure, the angle widths of these two band gaps can be effectively regulated. This work will be of great significance to the design of underwater low-frequency acoustic filters.

1J3-3 Symmetric and asymmetric spectra of acoustic waves resonantly transmitted through a slab in a fluid

1J3-3 Symmetric and asymmetric spectra of acoustic waves resonantly transmitted through a slab in a fluid

Refraction behavior investigation and focusing control of phononic crystals under external magnetic fields

The refraction and focusing behaviors of two-dimensional phononic crystals (PCs) tuned by external magnetic fields are investigated systematically. The PCs are constructed by inserting ferromagnetic shape memory alloys (FSMAs) between tungsten cylinders and water matrix. Under the magnetic field, material parameters of FSMAs will vary, which furthermore changes the frequency spectrum and equi-frequency surfaces of acoustic waves in sonic crystals. It is revealed that the refraction angle can be tuned from a positive value to a negative one when the PC slab suffers from continuous magnetic fields. Moreover, the focusing behavior can be achieved and controlled artificially by applying a proper magnetic field. These interesting phenomena of the tunable sonic crystals with FSMAs can provide us guidance for the design and application of novel acoustic devices, as well as the active control of acoustic waves.

Acoustic Wood anomaly in transmitted diffraction field

In acoustics, the term Wood anomaly, in analogy to the Wood anomaly in optics, has so far referred to the anomalies observed in the specular reflection spectra of acoustic waves perpendicularly incident on periodic surfaces. Inspired by the pioneering work of Jungman et al. on the study of the transmission field of a solid-fluid periodic interface, this work attempts to provide a complete experimental investigation of the transmission fields of a broadband sound pulse transmitted through a periodic liquid-solid interface as well as a periodic solid-liquid interface. At different frequencies, two types of anomalies are observed: a spectral tip and a spectral dip, which correspond, respectively, to the brighter band and the darker band in optical Wood anomalies. The search for their physical origin suggests that the type and location of the observed spectral anomalies are strongly related to the generation and the diffraction of pseudosurface waves on the interface having superimposed periodic corrugations and time-domain windowing in spectral analysis. To compare with the surface waves on a plane surface, the properties of the pseudosurface waves are also investigated through examining their phase and by comparing their amplitudes.

Finite element analysis of surface modes in phononic crystal waveguides

The study of surface modes in phononic crystal waveguides in the hypersonic regime is a burgeoning field with a large number of possible applications. By using the finite element method, the band structure and the corresponding transmission spectrum of surface acoustic waves in phononic crystal waveguides generated by line defects in a silicon pillar-substrate system were calculated and investigated. The bandgaps are caused by the hybridization effect of band branches induced by local resonances and propagating modes in the substrate. By changing the sizes of selected pillars in the phononic crystal waveguides, the corresponding bands shift and localized modes emerge due to the local resonance effect induced by the pillars. This effect offers further possibilities for tailoring the propagation and filtering of elastic waves. The presented results have implications for the engineering of phonon dynamics in phononic nanostructures.

Mean spectral characteristics of acoustic gravity waves in the thermosphere‐ionosphere determined from Dynasonde data

AbstractWave‐like disturbances have been observed in the ionospheric plasma for several decades using a wide range of remote sensing techniques. In this paper, the use of Dynasonde‐derived ionospheric “tilt” measurements is demonstrated to determine the dominant features of the underlying acoustic gravity wave spectrum and its height variation. The diurnal ionospheric variability introduces data gaps of varying length and distribution at any constant height level. This excludes the use of conventional fast Fourier transform techniques for spectral calculations. To obtain a complete and accurate image of the height variability of the wave activity in the thermosphere‐ionosphere, a method is required that would provide physically comparable results at all altitudes, regardless of the variations in sampling. In addition, the true geophysical variability should be distinguished from overlapping noise. The proposed solution is a combination of the well‐known Lomb‐Scargle and Welch methods, with the dataset of interest being divided into several overlapping subintervals and the mean spectrum calculated using results for those subintervals for which the power spectral density integral equals the time domain variance within a preset tolerance. The choice of the tolerance value is justified by means of numerical simulations using synthetic data similar to the tilt measurements. The proposed method is verified using a 10 day long dataset obtained with the Wallops Island Dynasonde. Results obtained with this method are compared in this paper with those obtained with a basic implementation and with a filtering method based on the amount of available data. A considerable reduction in the number of artifacts is observed with the use of this innovative approach, allowing reliable conclusions to be derived regarding the acoustic gravity wave spectrum and its height variability.

Seismic Sounding of Convection in the Sun

Thermal convection is the dominant mechanism of energy transport in the outer envelope of the Sun (one-third by radius). It drives global fluid circulations and magnetic fields observed on the solar surface. Vigorous surface convection excites a broadband spectrum of acoustic waves that propagate within the interior and set up modal resonances. These acoustic waves, also called seismic waves in this context, are observed at the surface of the Sun by space- and ground-based telescopes. Seismic sounding, the study of these seismic waves to infer the internal properties of the Sun, constitutes helioseismology. Here we review our knowledge of solar convection, especially that obtained through seismic inference. Several characteristics of solar convection, such as differential rotation, anisotropic Reynolds stresses, the influence of rotation on convection, and supergranulation, are considered. On larger scales, several inferences suggest that convective velocities are substantially smaller than those predicted by theory and simulations. This discrepancy challenges the models of internal differential rotation that rely on convective stresses as a driving mechanism and provide an important benchmark for numerical simulations.

RETRACTED: Monitoring and Analyzing Volatile Organic Compounds in Fabs by Gas Chromatograph/Surface Acoustic Wave sensors

The continuous trend toward smaller structures and thinner layers in semiconductor and TFT/LCD manufacturing directs attention more and more toward yield-affecting influences from the clean room air. Not only particle be a factor that is not easy to control but also so-called airborne molecular contamination (AMC) is a problem. VOCs are typical AMCs in Fabs. In this thesis, field monitoring and analyzing on concentration of various VOCs of the so-called Red, Green,and Bule areas of a Color Filter Fab were conducted. The results show that the Trap, Column and SAQ sensor can be block-off due to deposition VOCs, such as NMP and HMDS, which have high molecular weight. IPA and Acetone has approximate Retention Time to water vapor, creating reading error. Nevertheless, the SAW exhibits excellent real time monitoring function for other VOCs such as Toluene, Xylene, PGME, and PGMEA. Keyword:VOC(Volatile Organic Compounds)、GC(Gas Chromatograph)、 SAW(Surface Acoustic Wave Spectrum)

Characterization of mechanical properties of materials using ultrasound broadband spectroscopy

This article explores the characterization of homogenous materials (metals, alloys, glass and polymers) by a simple broadband ultrasonic interrogation method. The novelty lies in the use of ultrasound in a continuous way with very low input power (0dBm or less) and analysis of the transmitted acoustic wave spectrum for material property characterization like speed of sound, density and dimensions of a material. Measurements were conducted on various thicknesses of samples immersed in liquid where continuous-wave, frequency swept ultrasonic energy was incident normal to the sample surface. The electro-acoustic transmission response is analyzed in the frequency domain with respect to a specifically constructed multi-layered analytical model. From the acoustic signature of the sample materials, material properties such as speed of sound and acoustic impedance can be calculated with experimentally derived values found to be in general agreement with the literature and with pulse-echo technique establishing the basis for a non-contact and non-destructive technique for material characterization. Further, by looking at the frequency spacing of the peaks of water when the sample is immersed, the thickness of the sample can be calculated independently from the acoustic response. This technique can prove to be an effective non-contact, non-destructive and fast material characterization technique for a wide variety of materials.

Theoretical basal Ca ii and Mg ii fluxes for late-type stars: results from acoustic wave spectra with time-dependent ionization and multilevel radiation treatments

Theoretical basal Ca ii and Mg ii fluxes for late-type stars: results from acoustic wave spectra with time-dependent ionization and multilevel radiation treatments

Study of Laser-Array-Source-Generated Narrow-Band Acoustic Waves Interacting with Surface-Breaking Cracks Using Finite Element Method

Based on the classical theory of laser ultrasound generation in the thermoelastic regime, the generation of ultrasound by the irradiation of a laser array source is simulated by the finite element method. The interaction of ultrasound with a surface-breaking crack is studied. By changing the space distribution of a simultaneously triggered laser array source, narrow-band acoustic waves can be obtained. The characteristics of the narrow-band acoustic waves in the frequency domain are analyzed. By comparing with the spectrum of wide-band reflected acoustic waves generated by a single laser source, the mechanism of the interaction of a surface-breaking crack on the reflected narrow-band acoustic waves is studied. According to the variation of a reflected narrow-band acoustic wave spectrum on cracks with different depths, the influence of the crack-depth variation on different components of the narrow-band acoustic waves is obtained. Results suggest that the narrow-band acoustic waves could also be sensitive to the variation of the crack depth so that it can provide an alternative option for crack-depth gaging using all-optical methods.