Spectrum Of Acoustic Signal Research Articles

Beamformed Envelope Spectrum of acoustic signals for bearing diagnostics under varying speed conditions

Rolling element bearings are critical components in rotating machinery. Early damage detection methods are usually based on vibration signals from accelerometers. Microphones provide an interesting alternative, as they acquire system level information and could allow reducing the number of sensors. However, the bearing signature is mixed in these signals with noise coming from other nearby sources. Beamforming methods can enhance the targeted bearing signature while suppressing the contributions of other noise sources in the environment. The bearing impulses related to the localized surface defects are function of speed, and thus under varying speed conditions become nonstationary. Angular resampling based methods are therefore needed to compensate for the speed fluctuations in order to detect bearing damages. The goal of this paper is to propose a method for bearing diagnostics under varying speed conditions using an array of microphones and an encoder. The method is based on angular resampling of the microphone signals in function of the shaft speed and enhancing them using delay-sum beamforming based on the known positions of the microphones relative to the tested bearing. The method is validated on an experimental dataset acquired at a KU Leuven bearing test rig, under varying rotating speed conditions.

Effect of carbon and nitrogen diffusion zone on growth mechanism of boride layer produced on Q235 Steel

The purpose of this study was to indicate the effect of the presence of the carbon and nitrogen diffusion zone below the boride layers of Q235 low-carbon steel. The boride layers were produced by cathodic plasma electrolysis treatment (PET). Based on the results, the boride layer thickness on the treated samples at 260 V and 300 V varied from 10 μm to 22 μm. The XRD and GDOES analysis demonstrate that the boride layer on the treated samples mainly consists of single Fe 2 B phase, and the top loose layer mainly contain Fe 2 O 3 , Fe 3 C, Fe 4 N, and BN phases. The boride layers exhibited excellent scratch resistance compared to the bare Q235 steel. In addition, the plasma electron temperature was around 3000–4500 K, and the frequency spectra of acoustic signals were related to the voltage-time and current-time curves. At the high temperature and strong electric field, the decomposition reaction of electrolyte and the growth mechanism of the boride layers were discussed. Schematic of reactions in vapor gaseous envelope around the Q235 steel cathode during the plasma electrolysis process. • The boride layers on Q235 steel were produced by cathodic plasma electrolysis treatment. • The boride layers exhibited excellent scratch and adhesion resistance. • The OES and air acoustic spectra were measured. • Decomposition reactions of electrolyte and growth mechanism of boride layer were discussed.

Classification of oils by ECOC based multi-class SVM using spectral analysis of acoustic signals

Acoustic signals passing through a material gather a great deal of analytical information. Such information act as a signature for classification of the materials. Therefore, the paper proposes a novel method for classification of oils by extracting spectral features from acoustic signals. A developed acoustic resonance spectrometry system has been used for the acquisition of acoustic signals from different oils. The system has a quartz V-tube and two similar piezoelectric transducers, attached at the two ends of the tube. One of the transducer acts as a transmitter and the others as a receiver. The transmitter generates the vibrations with the excitation of white noise. The vibrations transmitted through the tube along with oil from the transmitter end to the receiver end. At the receiver end, vibrations translated into the acoustic signal that has been recorded and analyzed. The experiments were performed on six different oils samples namely: Castor, Mustard, Olive, D.Almond, Petrol, and Tarpin. The Burg spectral analysis was carried out on acoustic signals and eight resonance peaks frequency were recorded. The principal component analysis was done on the collected resonance frequencies datasets. The first three principal components were given as input to ECOC SVM classifier using radial basic function kernel in five different output coding schemes one versus one (1VS1), one versus all (1VSA), ordinal (ORD), and binary complete (BNC). The accuracies of SVM_1VS1, SVM_1VSA, SVM_ORD, and SVM_BNC are found to be 100% in classifying Castor, Mustard, Olive, and Tarpin. The best classifier in classifying D.Almond and Petrol is SVM_ORD that has accuracies of 96.75% and 91.47% respectively. The total classification accuracies of classifiers SVM_1VS1, SVM_1VSA, SVM_ORD, and SVM_BNC are 95.71%, 93.08%, 98.03%, and 95.47% respectively. Hence, the variation in resonant peaks in the Burg autoregressive spectrum of acoustic signals showed significant potential in classifying the oils.

Research on Reactor Condition Evaluation Method Based on Acoustic Vibration Characteristic Parameters and Weight Factors

Compared with the traditional reactor abnormal state detection method, the acoustic vibration detection method combines the advantages of acoustic detection and vibration detection, which has the advantages of simple installation, strong portability and good signal integrity, and has a broad application prospect. In this paper, the characteristic parameters of reactor acoustic vibration, including sound pressure level, sound power level, acoustic signal spectrum, vibration amplitude, vibration acceleration value, vibration signal spectrum, harmonic proportion and frequency complexity, are obtained to analyze the range and distribution rule of each characteristic parameter under long-term operation condition of reactor, and the weight factor of each characteristic parameter is determined by analytic hierarchy process On the basis of fuzzy reasoning, the state evaluation model of reactor is established.

Analysis of Acoustic Signals During the Optical Breakdown of Aqueous Solutions of Fe Nanoparticles

The study investigates the spectra of acoustic signals generating during the optical breakdown of colloidal solutions of iron nanoparticles. A characteristic form of the acoustic spectrum has been experimentally established, a distinctive feature of which is the presence of signals from an expanding and collapsing gas bubble. It is shown that the amplitude and area of these acoustic signals depend on the concentration of nanoparticles in the irradiated colloid. The effect of the concentration of nanoparticles on the bubble lifetime corresponding to the time interval between the acoustic spectrum signals corresponding to the birth and cavitation of a gas bubble has been studied.

An Experimental Setup for Acoustic Research of the Components of Fiber-Optic Measuring Systems

The results of theoretical calculations and experimental studies of the characteristics of an acoustic test signal when using an acoustic enclosure of the “open-shield” type are presented. The enrichment of the test acoustic signal spectrum due to the use of the developed enclosure was up to +30 dB in the frequency range of up to 500 Hz and from +4 to +20 dB in the frequency range of 1500–5000 Hz in comparison with the loudspeaker without an enclosure. The effect of room characteristics on the acoustic signal at the measurement point was studied and a method for compensation of this influence was proposed. As a result of applying it, the nonuniformity of the amplitude–frequency response of the acoustic signal at the measurement point decreased from 7 to 1.5 dB and the slopes of its spectral characteristic were eliminated.

Electromagnetic Sound Excitation and the Optoacoustic Effect in Magnetostrictive Materials

The effect a magnetic field has on the parameters of ultrasonic vibrations during laser excitation in magnetostrictive materials is studied. Dimensional effects and quasi-resonant dependence of the intensity of the acoustic response on the magnetic field strength are observed in films of iron–yttrium garnet. The effect domains and domain boundaries in manganese–zinc spinel plates and polycrystalline nickel films have on the characteristics of an acoustic response during laser sound excitation in the presence of a magnetic field is established. The effect the strength of the magnetic field has on the spectrum of acoustic signals in the investigated materials is examined.

Improvement of unmanned aerial vehicles detection method by spectral analysis of acoustic signals

The creation of algorithms for the detection of unmanned aerial vehicles (UAVs) based on the analysis of acoustic signals is an actual problem of the present. To solve such problem, it is necessary to correctly take into account the conditions for the propagation of acoustic signals in the atmosphere, as well as the characteristics of UAV flight, the height of which can vary up to several kilometers, and the speed can reach 200 km/h.The purpose of this study is to improve the UAV detection method by the results of spectral analysis of their acoustic signal. The investigations of the spectrum of acoustic signals from various types of UAV showed the presence of several characteristic harmonics in it. The criterion for a reliable detection of UAV is finding at least three characteristic harmonics in a received acoustic signal. The input values for this algorithm are samples of the input acoustic signal passing through the bandpass filter. To represent the signal in the frequency domain, the method of spectral estimation based on the periodogram without a window function has been selected.In this work the improved method and the complex layout for detection of unmanned aerial vehicles (UAV) based on the results of spectral analysis of acoustic signals are proposed. To implement the proposed algorithm, a specialized software and mathematical support for detecting an acoustic signal from the UAV were created. They allow with high reliability to detect an acoustic signal from the UAV at distances of about 1 kilometer. The efficiency of the proposed algorithm is verified using the layout of the acoustic detection complex in real conditions. Unmanned aerial systems "Fury" and "Leleka 100" were used in the experiment.Thus, it is shown that the acoustic signal created by UAV can be represented as the sum of harmonic components. The criterion for a reliable detection of UAV is finding at least three characteristic harmonics in a received acoustic signal.

Comparative analysis of options for applying spectral-acoustic method of gas-dynamic phenomena forecasting

The options of applying spectral-acoustic method of controlling stress state of a rock massif for preventing dynamic phenomena are analyzed in the paper. Two options are based on the dependence of relationship of high and low frequencies amplitudes of acoustic signal spectrum of operating equipment on a stress state of a massif in the area between the generator and the receiver of the sound. The difference between these two options is in choosing between high-frequency and low-frequency areas of a source sound spectrum. The drawback of both is in failure to use the whole spectrum of a sound that may cause the error in controlling stress state. To correct this drawback a modified option for applying the method based on the dependence of the median of amplitude and frequency characteristics of a sound on actual stresses is justified. The results of testing the method for controlling stress state of a working face space of a stope in the process of a hard roof directional hydraulic fracturing by hardwaresoftware complex based on RIPAS apparatus are introduced.

Investigation of acoustic properties of snow-covered sea ice

The paper presents results of field observations of hydroacoustic characteristics of snow-covered ice cover in shallow seas of the Arctic shelf. The purpose of the research was to determine the quantitative characteristics of the reflection and absorption coefficients of sound from the bottom of the drifting ice cover, as well as the Doppler broadening of the frequency spectrum of acoustic signals depending on the thickness of the ice, the structure of the reflecting surface, the thickness of the snow cover, and the ice drift speed. The objective of the research was to obtain the data necessary for choosing optimal parameters of specialized hydroacoustic equipment designed to monitor ice conditions in the areas of operation of offshore oil and gas platforms. Researches were conducted in areas of active construction of engineering marine constructions and carrying out the transport operations. The research methodology was based on the use of an autonomous measuring complex, which for a long period was installed on the bottom of the sea at depths of 50 to 130 m. The recording system consisted of the following components: upward looking pulse sonar of the IPS-5 type produced by the Canadian company ASL; the Doppler meter of the ice drift speed ADCP (the RDI firm); and a RSM-7 electromechanical current meter. All devices operated in continuous mode with a measurement cycle of 1s, the results were recorded in memory and processed after lifting the devices to the surface. The time delays of signals reflected from the ice cover, as well as the amplitudes and variations of the sound attenuation depending on the reflectance and absorption coefficients were recorded in the memory of the up-looking sonar. Variations of time delays were used to calculate a settlement of ice formations and to determine the shape of the reflective surface, including the angles of inclination of ice keels. Doppler shift of frequency of reflected acoustic signals and broadening of the frequency spectrum were calculated using values of the ice drift speed and changes of immersion depths of hummocks. Acoustic characteristics were measured repeatedly during several seasons of each year from 2010 to 2017. This investigation made possible to obtain statistical estimates of the distributions of the reflection coefficient of the sound and the quantitative values of broadening of the frequency spectrum of acoustic signals depending on the angle of incidence of the acoustic rays, the nature of the irregularities and the structure of the reflective surfaces of ice and snow cover thickness and the drift speed. The results obtained by this research allowed reasonable choosing and calculating the basic characteristics of the hydroacoustic equipment intended for runtime diagnostics of ice cover in zones of marine engineering structures.

RESEARCH OF MECHANOELECTRIC TRANSFORMATIONS IN ROCK WITH A SMALL DEGREE OF FLUID SATURATION

The paper describes an experimental plant and data processing technique for investigations of acoustoelectric transformations in rock samples with varying degrees of moistening. The results of investigations are presented for dry and moistened with kerosene core of Berea Grey sandstone under acoustic effect produced by linearly frequencymodulated signal in 0,7–10 kHz band. The was discovered a strong effect nonlinearity expressing itself in the second and third harmonics emerging, and an increase in the amplitude of the response of the electric signal. In the lower frequency band the amplitude of the second harmonic of the electric field intensity oscillations is comparable with the amplitude of the first one and can even exceed it. With the dropwise addition of kerosene, the power of the electrical signal varies at many times with a strong change in the shape of the signal spectrum. Therewith the shape of the acoustic signal spectrum is practically unchanged. The strong sensitivity of the coefficient of acoustoelectric transformation of rocks to moistening, which significantly changes the amplitude and phase of the response, is interesting from the point of view of developing remote methods for identifying the type of fluid saturation of rocks and methods for predicting geophysical catastrophes.

Passive acoustic measurement of bedload grain size distribution using self-generated noise

Abstract. Monitoring sediment transport processes in rivers is of particular interest to engineers and scientists to assess the stability of rivers and hydraulic structures. Various methods for sediment transport process description were proposed using conventional or surrogate measurement techniques. This paper addresses the topic of the passive acoustic monitoring of bedload transport in rivers and especially the estimation of the bedload grain size distribution from self-generated noise. It discusses the feasibility of linking the acoustic signal spectrum shape to bedload grain sizes involved in elastic impacts with the river bed treated as a massive slab. Bedload grain size distribution is estimated by a regularized algebraic inversion scheme fed with the power spectrum density of river noise estimated from one hydrophone. The inversion methodology relies upon a physical model that predicts the acoustic field generated by the collision between rigid bodies. Here we proposed an analytic model of the acoustic energy spectrum generated by the impacts between a sphere and a slab. The proposed model computes the power spectral density of bedload noise using a linear system of analytic energy spectra weighted by the grain size distribution. The algebraic system of equations is then solved by least square optimization and solution regularization methods. The result of inversion leads directly to the estimation of the bedload grain size distribution. The inversion method was applied to real acoustic data from passive acoustics experiments realized on the Isère River, in France. The inversion of in situ measured spectra reveals good estimations of grain size distribution, fairly close to what was estimated by physical sampling instruments. These results illustrate the potential of the hydrophone technique to be used as a standalone method that could ensure high spatial and temporal resolution measurements for sediment transport in rivers.

Underwater Cylindrical Object Detection Using the Spectral Features of Active Sonar Signals with Logistic Regression Models

The issue of detecting objects bottoming on the sea floor is significant in various fields including civilian and military areas. The objective of this study is to investigate the logistic regression model to discriminate the target from the clutter and to verify the possibility of applying the model trained by the simulated data generated by the mathematical model to the real experimental data because it is not easy to obtain sufficient data in the underwater field. In the first stage of this study, when the clutter signal energy is so strong that the detection of a target is difficult, the logistic regression model is employed to distinguish the strong clutter signal and the target signal. Previous studies have found that if the clutter energy is larger, false detection occurs even for the various existing detection schemes. For this reason, the discrete Fourier transform (DFT) magnitude spectrum of acoustic signals received by active sonar is applied to train the model to distinguish whether the received signal contains a target signal or not. The goodness of fit of the model is verified in terms of receiver operation characteristic (ROC), area under ROC curve (AUC), and classification table. The detection performance of the proposed model is evaluated in terms of detection rate according to target to clutter ratio (TCR). Furthermore, the real experimental data are employed to test the proposed approach. When using the experimental data to test the model, the logistic regression model is trained by the simulated data that are generated based on the mathematical model for the backscattering of the cylindrical object. The mathematical model is developed according to the size of the cylinder used in the experiment. Since the information on the experimental environment including the sound speed, the sediment type and such is not available, once simulated data are generated under various conditions, valid simulated data are selected using 70% of the experiment cylinder data. The selected simulated data are used to train the model. Randomly selected experiment cylinder data, which are 70% of the total experimental cylinder data, and the rock measurement data are used to test the model. This process is repeatedly carried out 1000 times. The results show that the proposed method is effective under the circumstance where experimental data are not sufficient and a mathematical model is available for a target.

Acoustic Spectrum Analysis of Genuine and Counterfeit Euro Coins

In this paper acoustic signal spectrum analysis using FFT and modal analysis based coin validation methods for authentic and counterfeit coins has been presented and investigated. For acoustical coin validation spectrum analysis has found to work well. Optimal parameters and methods for time-spectrum co-analysis has been estimated and discussed. In addition, the modal analysis for acoustic signals of coins has been implemented, the results of which has been presented and provide the authentication of the coin even with close acoustical signal spectrum. Proposed solutions has been implemented in Matlab and tested on real euro coins with denomination 50 cent, 1- and 2-euro, providing by first evaluations cost efficiency with high reasonable accuracy of described solutions. The counterfeited coins with domination of 2 euro have been tested with acoustical spectrum analysis and modal analysis evaluated in Matlab. The presented results provide the authentication of euro coins with high accuracy. DOI: http://dx.doi.org/10.5755/j01.eee.21.3.10384

Cavitation of two kinds of bubble mixtures

By solving the nonlinear wave equation coupled with the modified Rayleigh-Plesset equation, the characteristics of the acoustic field and bubble motion in cavitation environment can be described. In general, the cavitation cloud consists of many kinds of bubbles with different ambient radii. For simplicity, in this work the cavitation process of the mixture of two kinds of bubbles with different ambient radii is numerically simulated, and the ratio of the mixture is adjustable. Suppose that the cavitation in water contained in a cylindrical container is stimulated by ultrasonic horn. The dissipative absorption of the container wall is taken into account, which plays an important role in forming the stationary standing wave field, otherwise, the beat signal of acoustic pressure will appear which is absent in the observation. Based on the stationary acoustic wave field, for the case of the mixed-bubble cavitation, the interactions between bubbles and acoustic field, bubbles and bubbles, as well as the spectrum of acoustic signal are analyzed. We choose the cases that the ratio of two kinds of bubble species is varying, but the total density of bubble number is fixed to be 1/mm3, and find that those results are very different. For the case that the ambient radii of two bubble species are both a few micron, revealing that the interaction between bubbles and acoustic field is usually weak. As the proportion of bigger bubble increases, the change of the acoustic pressure and the averaged radius of bubble behave regularly; for the case that the ambient radius of one of bubble specie is relatively big, for example, the ambient radius is about a few tens of microns, the interactions between bubbles and acoustic field become stronger, and the nonlinearity is more apparent. We can observe the similar trends from the frequency spectrum. For the bubble of a few microns in size, the base frequency is dominant; in contrast, for the bubble of a few tens of microns in size, the components of harmonic frequencies are far beyond the base frequency component. The interesting phenomenon is that there is the cut off frequency and the cut of frequencies for different mixture of bubbles are almost the same.

Feature Extraction of the Small Leakage Diagnosis of Oil Pipeline Based on Acoustic Signal

This paper introduces the related theory of sound waves , we collect the data through the acoustic wave sensors of the pipeline fault diagnosis system platform, decompose the signals to five layers by Mallat algorithm and wavelet function db4, compare the normal waves and leakage acoustic signal spectrum, and then get the power spectrum estimation for the decomposed signal at each level, we can see the signals energy feature in different frequency band. Feature extraction method based on wavelet transform can make the category of signal characteristics fully displayed in the different resolution band, it has a good application prospect in the field of acoustic signal processing.

Characteristic Analysis and Origin Positioning of Acoustic Signals Produced by Partial Discharges in Insulation Oil

This paper dealt with the propagation characteristics of acoustic signals produced by partial discharges and the positioning of PD origin in insulation oil to develop insulation diagnostic techniques of oil-immerged transformers. Electrode systems such as needle to plane, plane to plane, and particle electrodes were fabricated to simulate some defects of power transformers. In addition, the frequency spectrum and propagation characteristics of acoustic signals with partial discharge (PD) in insulation oil were analyzed. Although there were differences based on the type of defect, the frequency spectra of the acoustic signals measured by wide and narrow band acoustic emission (AE) sensors were distributed in the range of 50 kHz-400 kHz. Therefore, a narrowband AE sensor is suitable for the diagnosis of oil-immersed power transformers. We could find the position of the PD source with an error margin of 10% in the experiments by calculating the position of the PD occurrence using the time difference of arrival measured by five AE sensors.

Genetic aspects of sexual behavior in malaria mosquitoes on the basis of specific acoustic signals at mating

Acoustic characteristics were studied in two species of the "Anopheles maculipennis" species complex, A. messeae and A. atroparvus. The species were found to clearly differ in sound frequencies, which was assumed to play a key role in species identification during mating in regions of their sympatric distribution. The sound spectrum in A. messeae was far more diverse than in A. atroparvus, which was associated with intraspecific inversion polymorphism of the former. Mosquitoes with the inversion combinations that were most common in populations of the central region of the A. messeae species area specifically differed in acoustic signal spectrum from each other. Hence, sound communication within the species was considered to be the main mechanism that is responsible for sexual partner selection and determines the chromosome associations observed earlier in individual karyotypes. Since males carrying different inversion combinations significantly differed in acoustic characteristics, females were assumed to play a main role in selecting the sexual partner.

Hydroacoustic observations of weak earthquakes in shallow waters of the Southern Kuril Islands

Results of hydroacoustic observations of signals from weak earthquakes in natural conditions in the region of the Southern Kuril Islands are presented. Some earthquakes were registered by the the Yuzhno-Kurilsk Seismic Station, other were only recorded by hydrophone stations. The observations were specific as seismic signals were recorded in shallow waters, i.e. in high noise level conditions. Hydrophones were installed in Lake Lagunnoe (Kunashir) and Khromovaya Bay (Shikotan). Our analysis of hydroacoustic records received from the hydrophone stations revealed no evident precursory response of the geological medium to weak distant events. This means that neither before the period of earthquake preparation nor during the earthquake preparation period, any geoacoustic emission was not detected. It is shown that despite the unfavourable noise level conditions, even distant weak earthquakes can be confidently registered by hydrophone stations, and pending application of proper signal processing techniques, it can be possible to determine arrival times of seismic waves and to measure parameters of seismic waves. It is also established that the frequency spectrum of acoustic signals from the weak earthquakes recordable by the hydrophone stations is continuous and of noise type in the frequency range up to 90–100 Hz. It is revealed that in some cases, weak earthquakes and microearthquakes may be forerun by low frequency signals.

Analysis of spectra of acoustic signals generated by high-power pulsed laser radiation propagating in the atmosphere. 2. Spectra of acoustic signals from laser sparks

Results of theoretical and experimental investigations into the spectra of acoustic signals generated by high-power pulsed laser radiation propagating in the atmosphere in the breakdown regime are presented. Results of analogous investigations for laser breakdown on a single aerosol particle and ensemble of monodispersed particles versus the particle material and size were published in [1]. In the present work, acoustic spectra of discrete laser sparks in the atmosphere are analyzed, and their special features in comparison with acoustic spectra of individual plasma formations, spectra of acoustic signals generated by pulsed laser radiation propagating in the atmosphere in thermooptical regime, and laboratory spectra of continuous laser sparks are discussed.