Acoustic Signal Propagation Research Articles

Speed and attenuation of acoustic waves in snow: Laboratory experiments and modeling with Biot's theory

Monitoring acoustic emissions (AE) prior to imminent failure is considered a promising technique for assessing snow slope instability. Gaps in elastic wave propagation characteristics in snow hinder quantitative interpretation of AE signals. Our study focuses on characterizing the propagation of acoustic reference signals in the ultrasonic range across cylindrical snow samples with varying density (240–450kgm−3). We deduced the acoustic attenuation coefficient within snow by performing experiments with different column lengths to eliminate possible influences of the snow-sensor coupling. The attenuation coefficient was measured for the entire burst signal and for single frequency components in the range of 8 to 35kHz. The acoustic wave propagation speed, calculated from the travel time of the acoustic signal, varied between 300ms−1 and 950ms−1, depending on the density and hardness of snow. From the sound speed we also estimated the Young's modulus of our snow samples; the values of the modulus ranged from 30 to 340MPa for densities between 240 and 450kgm−3. In addition, we modeled the sound propagation for our experimental setup using Biot's model for wave propagation in a porous medium. The model results were in good agreement with our experimental results and suggest that our acoustic signals consisted of Biot's slow and fast waves. Our results can be used to improve the identification and localization of acoustic emission sources within snow in view of assessing snow slope instability.

Low-Frequency Acoustic Signals Propagation in Buried Pipelines

The article deals with the issues concerning acoustic signals propagation in the large-diameter oil pipelines caused by mechanical action on the pipe body. Various mechanisms of signals attenuation are discussed. It is shown that the calculation of the attenuation caused only by internal energy loss, i.e, the presence of viscosity, thermal conductivity and liquid pipeline wall friction lead to low results. The results of experimental studies, carried out using the existing pipeline with a diameter of 1200 mm. are shown. It is experimentally proved that the main mechanism of signal attenuation is the energy emission into the environment. The numerical values of attenuation coefficients that are 0,14- 0.18 dB/m for the pipeline of 1200 mm in diameter, in the frequency range from 50 Hz to 500 Hz, are determined.

Array gain of conventional beamformer affected by structure of acoustic field in continental slope area

Conventional beamforming (CBF) is an important processing step in underwater array signal processing. Previous researches have shown that the sound field structure as manifested by amplitude nonhomogeneity and wave-front corrugation can reduce the array gain of CBF. The acoustic environment of the continental shelf slope area is very complex. For an underwater acoustic array in this area, the amplitude and phase of the received signals will be distortional seriously. Recently, the acoustic field correlation has been the focus of research on the array gain relations with the underwater acoustic filed. However, the attenuation of acoustic field correlation is not the only factor that induces the array gain to decline, and the analyses of the array gain in the shallow water based on normal-mode model are not applicable to the continental slope area. In this paper, the array gain relations with the structure of acoustic field in continental slop area are investigated based on the theory of underwater acoustic signal propagation. The effects of acoustic field on the signal and noise gains are considered respectively. The analytic expressions of the array gain of CBF in an isotropic noise field are derived from the primal definition of array gain, which indicates that acoustic field correlation and transmission loss in continental slope are the intrinsic factors that affect the array gain of CBF. A horizontal uniform linear array (ULA) with a wide aperture receiving signals from a source in the deep water region is considered in the upslope propagation condition. The RAM program is utilized in the numerical simulations to generate the sound field of this specific environment with given parameters. The array gains, the ATLs and the horizontal longitudinal correlation coefficients of the acoustic field corresponding to three different locations are compared. Conclusions can be drawn as follows. 1) The array gain of CBF is determined by acoustic field correlation and the acoustic average transmission loss (ATL), and its maximum is less than 10lg M as the signal waveform distortion. 2) when the ATLs corresponding to hydrophones at two different receiving locations are similar, the correlation of acoustic filed is higher, and the array gain of CBF is larger. 3) When the ATLs corresponding to hydrophones at two different receiving locations are greatly different, the relation between the array gain of CBF and the acoustic filed correlation is no longer positive. The simulation results verify the array gain of CBF relations with the acoustic filed correlation and the transmission loss in the continental slope area.

Operation of linear and ring arrays in shallow water

With the aim of unambiguously determining the direction to a tonal emission source, comparative analysis of the directed properties of sufficiently extended linear and ring horizontal arrays in shallow water was performed. An isovelocity waveguide with a homogeneous fluid bottom was used as the shallow water model, in which a multimode regime of acoustic signal propagation was achieved.

Acoustic emission location on aluminum alloy structure by using FBG sensors and PSO method

Acoustic emission location is important for finding the structural crack and ensuring the structural safety. In this paper, an acoustic emission location method by using fiber Bragg grating (FBG) sensors and particle swarm optimization (PSO) algorithm were investigated. Four FBG sensors were used to form a sensing network to detect the acoustic emission signals. According to the signals, the quadrilateral array location equations were established. By analyzing the acoustic emission signal propagation characteristics, the solution of location equations was converted to an optimization problem. Thus, acoustic emission location can be achieved by using an improved PSO algorithm, which was realized by using the information fusion of multiple standards PSO, to solve the optimization problem. Finally, acoustic emission location system was established and verified on an aluminum alloy plate. The experimental results showed that the average location error was 0.010 m. This paper provided a reliable method for aluminum alloy structural acoustic emission location.

Modal analysis of broadband signal arrival on Beaufort shelf

Using previously reported temperature and salinity data collected over the past decade, time evolving sound speed profiles were constructed and used (Prog. Oceanography, 127, pp.1-20, 2014) as input to a parabolic equation model. Modeling of broadband acoustic signal propagation in the Arctic shelf-basin region during ice free sea surface season was reported recently (J. Acoust. Soc. Am. 136(4), Pt. 2, 2317, 2014). It was shown that when broadband acoustic signals propagate from deep water to shallow water, the modal dispersion is changed. The change is mostly affected by the water thermocline behavior in time and space and by source depth. The modal arrival structure can be influenced by a number of factors including the degree of Pacific warm water intrusion, upwelling of the warm saline Atlantic water into the cold surface layer, the range-dependence of the water layers over the shelf break, and the depth of the source. In this paper, we analyze the range-dependent propagation in terms of adiabatic and coupled mode regimes in order to explain the model results. [Work supported by ONR.]

Wind turbine radiated acoustic signals—Propagation in a temporally and spatial variable marine meteorological boundary layer

The temporal and spatial properties of an acoustic field radiated from a wind turbine operating in a marine meteorological boundary layer and a spatial temporal variable impedance boundary will be quantified using paraxial equation based numerical simulations. A sound speed field will be constructed using wind field measurements made with a 915 MHZ radar wind speed sensor and local temperature and humidity measurements obtained from a meteorological tower. Temporally variable impedance boundary conditions for a tidal marine marsh will be included in the simulations.

Modeling of acoustic emission signal propagation in waveguides.

Acoustic emission (AE) testing is a widely used nondestructive testing (NDT) method to investigate material failure. When environmental conditions are harmful for the operation of the sensors, waveguides are typically mounted in between the inspected structure and the sensor. Such waveguides can be built from different materials or have different designs in accordance with the experimental needs. All these variations can cause changes in the acoustic emission signals in terms of modal conversion, additional attenuation or shift in frequency content. A finite element method (FEM) was used to model acoustic emission signal propagation in an aluminum plate with an attached waveguide and was validated against experimental data. The geometry of the waveguide is systematically changed by varying the radius and height to investigate the influence on the detected signals. Different waveguide materials were implemented and change of material properties as function of temperature were taken into account. Development of the option of modeling different waveguide options replaces the time consuming and expensive trial and error alternative of experiments. Thus, the aim of this research has important implications for those who use waveguides for AE testing.

Minimizing the Total Energy Consumption in Multi-hop UWASNs

This paper investigates the total energy consumption in multi-hop underwater acoustic sensor networks (UWASNs) for a given target signal to noise ratio (SNR) requirement. Specifically, our aim is to minimize the energy consumption along the route between source and destination and to find the optimal hop distance that result in minimum energy consumption, by taking into account the propagation characteristics of sound signals through the underwater acoustic medium. The proposed study will form the basis for the design of energy efficient routing protocols that select minimum energy route in UWASNs. The impact of various characteristics of underwater acoustic signal propagation such as attenuation, noise, and the dependence of usable bandwidth and transmit power on distance, are considered for the energy consumption analysis. Further, analysis is carried out for both shallow and deep water scenarios under the assumption that each node can adjust its transmission power for a link so that the signal reaches the destination node, satisfying a target received SNR. We observe that, a linear equidistant network consumes minimum energy for both shallow as well as deep water scenarios.

“Negative” acoustic signal propagation in a media with resonant density and compressibility response functions

The properties of acoustical double-negative media strongly depend on the frequency of a propagating wave. Particularly, the effective density and compressibility of a medium can be negative only at the certain frequency band. So it is very important to consider nonstationary processes in such media. The numerical simulations of the medium characterized by resonant-type density and compressibility response functions was performed in the article. It was based on the deduced matrix equation of a Lippmann-Shwinger type. The layer of “resonant” medium was placed inside an infinite background with constant density and compressibility. The incident impulse had a gauss form modulated by a certain carrier frequency. The effective density and compressibility of the layer change from both positive to both negative values while the impulse propagates through it. The phase velocity also becomes negative and the group velocity remains positive satisfying the causality principle. In the case of long enough impulse duration the layer behaves like it is made of a double-negative medium.

Development of a Comparison Method of Sonar Systems for Surface Platforms

This work sought to study the models of acoustic signal propagation in marine environments according toopen literature currently available, by interpreting the different effects occurring during their propagationand their characteristic principal parameters; identifying models of underwater acoustic propagation thatmay occur and its corresponding simulation for its understanding. Software, denominated BELLFAT,was developed in Matlab, which permits predicting, evaluating, and analyzing the capabilities of anactive sonar system. Such can function by taking depth, temperature, salinity in the sea of any referencearea and the characteristics of the sonar to evaluate. Thus, this computational tool is established to studymarine sonar systems sought to be developed or as a key piece to establish the characteristics active sonarmust have for the purposes of a surface platform.

A Study on the Characteristics of Underwater Sound Transmission by Short-term Variation of Sound Speed Profiles in Shallow-Water Channel with Thermocline

Underwater acoustic channel impulse responses (CIR) are influenced by sound speed profile (SSP), and the variation of CIR has significant effects on the performance of underwater acoustic communication systems. A significant change of SSP can occur within a short period, which must be considered during the design of underwater acoustic modems. This paper statistically analyzes the effect of the variation of SSP on the long-range acoustic signal propagation in shallow-water with thermocline using numerical modeling based on the data acquired from JACE13 experiment near Jeju island. The analysis result shows that CIR changes variously according to the SSP and the depth of the transmitter and receiver. We also found that when the transmitter and receiver are deeper, the variation of sound wave propagation pattern is smaller and signal level becomes higher. All CIR obtained in this study show that a series of bottom reflections due to downward refraction and small bottom loss in the shallow water with thermocline can be very important factor for long-range signal transmission and the performance of underwater acoustic communication system in time varying ocean environment can be very sensitive to the variation of SSP even for a short period of time.

Low-Frequency Hydroacoustic Experiments on the Shelf Using the Data of Geoacoustic Sediment Model

We present the results of hydroacoustic experiments carried out in 2010 in the Peter the Great Bay, the Sea of Japan, using low-frequency emitters (26 and 33 Hz). These studies are conducted in the waters where the information on geological conditions in the upper sediment layer have been obtained before and the geoacoustic sediment model has been built. An example of the influence of large inhomogeneities in bottom sediments on the acoustic signal propagation along the route is given.

Research on Doppler and Channel Estimation for Multicarrier Spread Spectrum Underwater Acoustic Communication System

Spreadspectrum orthogonal frequency-division multiplexing (SS-OFDM), which appliesspread spectrum technique into OFDM, performs robustly in severely multipathfading underwater channels. However, this technology is sensitive to thefrequency shift. Furthermore, communication in underwater acoustic (UWA)channels is more vulnerable to Doppler effect than other wireless channels dueto the low speed of acoustic signal propagation. It presents challenges forcommunication between underwater mobile nodes. Therefore, accurate Dopplerfrequency shift estimation and compensation is important. Aself-designed receiver structure for SS-OFDM system including a novel Dopplerscale estimation method and channel estimation via compressed sensing method isproposed. The simulation and experimental results offer strong proofs for ourscheme to be a viable option for acoustic communication between underwatermobile nodes and compressed sensing method outperforms the conventionalleast-squares (LS) method in channel estimation.

Spatial-temporal coherence of acoustic signals propagating in a refractive, turbulent atmosphere.

Propagation of acoustic signals above an impedance ground in a refractive, turbulent atmosphere with spatial-temporal fluctuations in temperature and wind velocity is considered. Starting from a parabolic equation, and using the Markov approximation and a locally frozen turbulence hypothesis, closed-form equations for the spatial-temporal statistical moments of arbitrary order of the sound-pressure field are derived. The general theory provides a basis for analysis of many statistical characteristics of broadband and narrowband acoustic signals for different geometries of propagation: line-of-sight propagation, multipath propagation in a refractive atmosphere above an impedance ground, and sound scattering into a refractive shadow zone. As an example of application of this theory, the spatial-temporal coherence of narrowband acoustic signals for line-of-sight propagation is calculated and analyzed. The coherence time of acoustic signals is studied numerically for meteorological conditions ranging from cloudy to sunny conditions, and with light, moderate, and strong wind. The results obtained are compared with available experimental data.

Statistical moments for wideband acoustic signal propagation through a turbulent atmosphere

Developing methods for managing noise propagation, sound localization, sound classification, and for designing novel acoustic remote sensing methods of the atmosphere requires a detailed understanding of the impact that atmospheric turbulence has on acoustic propagation. In particular, knowledge of the statistical moments of the sound field is needed. The first statistical moment corresponds to the coherent part of the sound field and it is need in beamforming applications. The second moment enables analysis of the mean intensity of a pulse in a turbulent atmosphere. Numerical solutions to a set of recently derived closed form equations for the first and second order statistical moments of a wideband acoustic signal propagating in a turbulent atmosphere with spatial fluctuations in the wind and temperature fields are presented for typical regimes of the atmospheric boundary layer.

Model Analysis of Underwater Acoustic Sensing with Hollow-Core Photonic Bandgap Fiber

Recently, using hollow-core photonic bandgap fiber (HC-PBF) for underwater acoustic sensing has been tested experimentally. Besides its unique characteristics and advantages over conventional single mode fiber (SMF), it provides higher responsivity to acoustic pressure. A robust deep water ray tracing model for multipath acoustic signals propagation and the elastic model of HC-PBF are both required to study the effects of underwater enviroment on the propagating acoustic signal for sensing with HC-PBF hydrophones. The combination of the two models allows studying the frequency response, sensitivity, detection range, and maximum operating depth of the HC-PBF hydrophones. The models analysis and simulations show the considerations that must be taken into account for the design and field operation of the HC-PBF hydrophones. In this paper, a complete package to study, design, optimize, and analyze the simulation results of the interferometric HC-PBF hydrophones is proposed.

When to CHEUS Contrast-Enhanced Endoscopic Ultrasound to Assess Gallbladder Wall Thickening

Gallbladder wall thickening identified on trans-abdominalultrasound is a relatively common finding that can be dueto common biliary pathologies such as cholecystitis, gall-bladder carcinoma, and adenomyomatosis, while systemicdisease and extracholecystic inflammation may also distortgallbladder morphology [1]. In many cases, ultrasoundimaging combined with the clinical history will suffice;however, for some patients, further imaging studies arerequired in order to accurately distinguish benign andmalignant pathologies. At the extremes, the patient with asuspected gallbladder cancer requires urgent referral to aspecialist hepatobiliary surgeon whereas the elderly, frailpatient with adenomyomatosis may simply be reassured.Cross-sectional imaging with computed tomography(CT) or magnetic resonance imaging (MRI) can providevaluable additional information concerning the etiology ofgallbladder wall thickening. However, there are surpris-ingly few studies that have addressed these modalities inthe context of gallbladder wall thickening [2–5], eventhough current cross-sectional imaging modalities canaccurately differentiate benign from malignant pathologiesin the majority of cases. When these techniques revealequivocal results, endoscopic ultrasound (EUS) may beconsidered. Despite its widespread use in the evaluation ofpancreatobiliary disease, it has not yet gained widespreaduse in evaluating the gallbladder [6, 7]. In the setting of athickened gallbladder wall, Kim and colleagues reported itto be of value with a wall thickness[10 mm and reducedinternal echogenicity being predictive of malignancy [8].In this issue of Digestive Diseases and Sciences, Imazuet al. [9] evaluated contrast-enhanced harmonic endoscopicultrasonography (CH-EUS) using a second-generation con-trast agent consisting of perfluorobutane microspheres(Sonazoid) in thediagnosis ofpatients exhibitinggallbladderwall thickening. The group examined 36 patients withequivocal conventional ultrasound and cross-sectional imag-ing in whom surgery was performed to provide histopatho-logic confirmation. The performance characteristics(sensitivity, specificity, accuracy, positive predictive value,negativepredictivevalue,andareaunderthereceiveroperatorcurve) of CH-EUS were 89.6, 98, 94.4, 97.7, 92.2, and 0.94,respectively, superior to conventional EUS in each case. Theauthors assessed inter-observer variation by comparingassessments made by an experienced endosonographer, atrainee EUS operator, and an experienced gastroenterologist,demonstrating an improvement in J score from 0.51 (mod-erate)to0.77(substantial)withtheadditionofSonazoid.TheyalsoidentifiedthataninhomogeneousenhancementpatternonCH-EUS,andawallthickness[12 mmwithoutcontrastwerestrongly predictive of a malignant etiology.CH-EUS is based on harmonic imaging, which exploitsthe nonlinear propagation of acoustic signals through bio-logical tissues, with secondary signals generated by thetissue creating high-resolution images. The use of contrastprovides the key advantage of enabling visualization of themicrovasculature in real time [9].Although this is the first series evaluating CH-EUS inassessing gallbladder wall thickness, the technique hasbeen used with success in the evaluation of gallbladder [10,11] polyps and pancreatic lesions [12].

UNDER WATER ACOUSTIC (UW-A) COMMUNICATION ARCHITECTURE AND THE KEY NOTIONS OF UW-A PROPAGATION

The study of the communication architecture for the underwater is very important due the wide applications based on these sensing devices. The more observed examples of applications are climate change monitoring, study of marine life, pollution control, and military purposes. It is observed the radio frequency (RF) electromagnetic waves [1], Optical electromagnetic waves, underwater Optical communication [2] waves all have been used for the underwater sensor networking. But these have shown with its slight disadvantages for the underwater related works. So this can be overcome by the usage of the acoustic communication as a means of transmission technology for the underwater networked system. It is also observed that the underwater acoustic signals are suffering from the some transmission loss, high propagation delay, limited bandwidth. So to eliminate these observed factors with respect to the underwater sensor networks the communication architecture has been developed to provide the point to point, having low data rate and high bandwidth signal and delay tolerant applications. Therefore this article has been written to give the details of how the communication architecture can be designed and for the underwater network and the key factors which relates to the propagation of underwater acoustic signals.

Long-Range Sound Transmission Characteristics in Shallow-Water Channel with Thermocline

본 논문은 수온약층이 존재하는 제주도 근처 천해역 환경에서 획득한 수중음향 실험 데이터를 이용하여 장거리 신호 전달에 수온약층이 미치는 영향을 분석한 결과를 제시한다. 제주도 인근 해역에 서 장기간 측정된 한국해양자료센터의 수온 및 염분 관측자료는 계절에 따라 수온약층이 형성되는 것을 보여주며, 수온약층이 형성되는 시기에는 음향 신호가 해저면 방향으로 굴절하며 전파되므로 해저면에서의 반사 손실이 장거리 전파에 매우 큰 영향을 가진다. 본 연구에서는 2013년 5월에 수행한 제주 음향 통신 실험 (JACE13) 데이터를 이용하여, 수온약층이 존재할 때의 해저면 반사 손실을 추정하였다. 추정된 반사 손실은 약 3 dB 미만의 손실 값을 가지는 것으로 나타났으며, 수신기의 수심이 깊을수록 수신 신호 준위가 높게 나타났다. 이는 수온약층이 형성되는 천해역 환경에서는 수온약층 아래의 음향 트랩핑이 장거리 신호 전달의 주요 경로가 될 수 있음을 보여준다. This paper analyzes the effect of a thermocline on the long-range acoustic signal propagation using the experimental data acquired in the shallow water near Jeju island. Temperature and salinity measurement data in Korea Oceanographic Data Center (KODC) show that the seasonal thermocline exists near Jeju island, and, under the thermocline, the bottom loss property strongly affects the long-range propagation of acoustic signal along the down-ward refractive paths. We estimate the bottom loss under the thermocline using experiment data obtained near Jeju island in May, 2013. The result shows that the estimated bottom losses are below 3 dB and the higher level signal is received at the deeper receiver depths. This shows that the acoustic trapping under the thermocline can be a viable long-range signal transmission channel in the shallow water with a thermocline.