Статьи журнала - Техническая акустика
Все статьи: 276
Статья научная
In this paper, adaptive filtering, wavelets, and lossy image compression are considered. Performances of the subband adaptive digital filter are discussed. We propose a transform coding method in which the low pass filters in the wavelets decomposition tree are time-varying. The idea is to decompose a digital image using an adaptive FIR (Finite Impulse Response) filter in each low frequency subband and compare it with an invariant filter of Daubechies. We employ a framework that includes the main comparison parameters. It is clearly shown here that it provides better performances than invariant filters in most applications. This work consists of applying an adaptive FIR filter by the ADFFLS (Adaptive Digital Filter with Fast Least Square) algorithm to digital images. The filter performances on the different stages of the data image compression chain are then valued and compared with an invariant and biorthogonal filter of Daubechies. This is done studying of the main parameters, namely the covariance matrix, the subband coding gain, the concentration of energy in the low frequency subband, the signal to noise ratio, the correlation, the bit allocation, and the compression ratio. This study resides in the meticulous choice of comparison parameters, and the different stages of comparison. Results show that the PSNR (Pic Signal Noise Ratio), the correlation between original and reconstructed images, and the compression ratio are better with the adaptive filter for different lengths, quantifiers, and quantification levels.
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A method of ultrasonic study of materials
Статья научная
An improved ultrasonic method for non-destructive testing of materials is proposed in the paper. Тhe method is capable of determining material structure and mechanical properties, whereas subsequent measuring devices are designed. Moreover, the method is tested by studying the structure and physico-mechanical properties of specimens and products made of steel, cast iron and aluminum alloys. A correlation between the ultrasonic velocity and attenuation is found, on one hand, and material structure, strength and elastic characteristics are analyzed, on the other hand.
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A model for the conduction in polycrystalline silicon thin film transistors
Статья научная
The aim of this paper is the analysis, prediction and optimisation of polysilicon thin film transistors (TFTs) in both « on » and « off » states. We have established a physical model which accounts for the grain, the grain surface and grain boundaries. The conduction mechanisms and the exchange between electron and hole populations are explicitly considered. Field effects are included through the influence of carrier velocity saturation, impact ionisation and interband tunnel effect. A fair agreement between experimental characteristics and simulated results is obtained, and the simulations allow a good insight into the main mechanisms controlling the TFT operation modes. Keywords: Polysilicon, dangling bonds, band tail states, TFT, simulation, generation-recombination, impact ionisation, interband tunnel effect
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Статья научная
The analytical solution, which gives the dependence between strain and displacement of beam free end at first eigen mode in cantilever, stepped beam was yielded. The dependence can be used as a basis for calibration of PVDF reusable strain gauges in practice. A value of calibrational accuracy for reusable PVDF strain gauges using conventional vibrational equipment was estimated and proofed. The characteristics of rig were obtained, reported and certified.
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A preliminary study of sound absorption using multi-layer coconut coir fibers
Статья научная
Acoustic treatment using absorbing materials are widely used to reduce reverberation properties of closed spaces and to increase the transmission loss properties of multi-layer sound absorption panels. Natural fibers such as coconut coir fiber have high potential to be used as acoustic materials. As the natural fibers are agriculture waste, manufacturing natural product is therefore an economic and interesting option. This paper discusses the sound absorption using multi-layer coconut fiber as absorbing material component. The effect of microperforated plate and airspaces layers towards the sound absorption of the multi-layer construction was also investigated in this paper. Acoustic absorption coefficient is the main parameter to be estimated in this research. Computer simulation using WinFLAGTM program was done to calculate the acoustic absorption coefficients. Simulation indicated that multi-layer coconut coir fibers and airspaces could increase the acoustic absorption coefficient. All simulation results obtained are based on diffused sound incidence situation.
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A survey of the acoustic quality for speech in auditoriums
Статья научная
A sample of auditoriums in the city of São Paulo was surveyed in terms of the acoustic quality for speech. The sample was selected based on interviews with well-known actors and actresses of the Brazilian drama community, and with other professionals of the scenic arts as well. Sound decays, the strength and objective measures of speech intelligibility were measured throughout the auditoriums, which were then ranked based on position-averaged values. The variations in the values of the measured parameters with the measuring position are discussed and correlations between them are established. An attempt was made to validate the Objective Support (ST1-Gade) as an objective measure of support to actors on stage. The preliminary diagnosing results with ray tracing simulations are presented. A guideline of less than 5 cubic meters per seat, to achieve reverberation times of less than 1 s in auditoriums for drama has emerged from the results of the measurements.
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Статья научная
In this paper, first, a methodological principle trial for the quantitative evaluation of the correlative and/or cumulative effect on indoor high-technology pollution has been proposed under an absolutely inseparable relationship between utility and risk at the same time and in the same ring. Then, the effectiveness of the proposed method is partly confirmed through some principle experiment between sound (served for utility) and leaked magnetic field (served for risk) especially before and after attachment of a magnetic oscillator called Tecno AO (CE mark, ISO sanction).
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Acquire real-time RF digital ultrasound data from a commercial scanner
Статья научная
Although new ultrasound signal processing can be designed from simulation data or recorded data, the development and prototyping of new medical ultrasound imaging tools is essentially based on processing the radio frequency (RF) data, which is the signal generated by the ultrasound probe. Unfortunately, the diversity and technological level of knowledge required for implementing a whole ultrasound scanner from scratches are usually found in the companies that manufacture such engines. The implementation of the new methods in the laboratories is then tributary to the interest and good will of those companies, and the lack of such experience makes technological transfers even more difficult. But another approach of the problem can be chosen: the direct acquisition of the real time RF data in a commercial scanner. This approach takes advantage of the high technological level of the transceiver of the commercial ultrasound scanners and frees the researcher from the post processing applied by each company. The side effects of such approach are resumed to the difficulty of interfering with the scanner's electronic systems, but this problem is simplified by the high technological level of the modern engines. Indeed, their digital conception makes the electronic signals easier to understand and the manual operations safer, and the impact of an unfortunate manipulation is essentially reduced to a distortion of the scanner's display. In this paper, the general approach of RF derivation in a commercial digital scanner is exposed. Then it is demonstrated on a commercial scanner, the Kretztechnic 530D, equipped with a volumic probe. This system allowed us to implement one of our current subjects of research, that is the Parallel Integral Projection for the localization of a micro needle in soft tissues, and to conclude on its performances on real data, including a minimum gain of 5.
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Active noise cancellation: air conditioner and transformer case study
Статья научная
Two cases of active noise cancellation technique are discussed in the paper. A feedforward control systems for both cases were used. FxLMS (Filtered Least Mean Square) algorithm for noise reduction of air conditioner is implemented whilst sub band LMS utilized in transformer case. To provide a good quality of the reference signal the special method of flow isolation for reference and error microphones is proposed. The noise reduction efficiency of 15 and 10 decibels at frequencies 90 and 240 Hz is provided using proposed configuration of the system. Three tonal components 120, 240 and 360 Hz are dominated in transformer noise spectrum. Implementation of sub band FxLMS algorithm for transformer case has shown the high efficiency of proposed technique within local area for tonal component 120 and 340 Hz. The most wide silent zone at frequency 240 Hz is revealed during study.
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Active noise control and noise reduction: practical examples
Статья научная
The practical examples of ANC (active noise control) systems are shown and discussed in the paper. Examples shown for active noise reduction headsets, noise cancellation in the duct system, general noise reduction using adaptive algorithm are discussed. The efficiency of the active noise control is 1020 dB for the all cases except of transformer where much more control channels have to be implemented in order to obtain the global reduction of three transformer harmonics. It was shown that global reduction for transformer case could be achieved using anti noise loudspeaker and error microphones separated with one half of wavelength.
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Aeolian vibrations of the overhead cables
Статья научная
Wind induced vibrations (Aeolian vibrations) of overhead transmission lines and resulting conductors fatigue breakages constitute a problem for utility companies in maintaining uninterrupted supply of electrical energy. The aim is the study of Aeolian vibrations of overhead transmission lines conductors. The fractures caused by the wind vibrations often appear in front of the points of attachment, and with the junctions of the conductors. To this end one tried to give a mathematical model of the forces acting on the cables, as well as a mathematical model of the cable. This model permits to have curves of the amplitude according to the speed of the wind and the frequency. A simplified analysis of the partial differential equation describing these vibrations is presented using the concept of characteristic length as a single quantity describing the mechanical properties of a conductor.
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Статья научная
Recent mate choice investigations reveal that females often prefer to mate with males that produce acoustic loud, long, and/or leading acoustic signals. However, only a limited number of studies have examined within population variation in these temporal components. Even fewer studies have estimated their heritabilities. Work has been hindered by the time and personnel required to quantify the variation. A design for building an efficient and inexpensive electronic acoustic recorder (EAR), that enables hypothesis testing of temporal signaling behavior in most acoustically signaling insects, is described. The EAR is attached to a personal computer and samples the acoustic environment of up to 128 individuals, 10 times per second, for unlimited time periods. It compares microphone sound pressure level to a pre-set level and stores signaling/non-signaling data on the computer's hard drive. The EAR monitors when individuals signal temporally, how much time they spend signaling, how loud they signal, duration of signaling bouts, duration of breaks, and when they produce their signaling bouts in relation to their neighbors. The capabilities of the recorder are illustrated with the Texas field cricket, Gryllus texensis.
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Application of Crocco - Wang equation to the Blasius problem
Статья научная
Navier-Stokes problem for a boundary layer can be transformed, by a similarity transformation, into the Blasius problem which is governed by a non-linear ordinary differential equation of order three. Since it is simpler to solve an ordinary differential equation, this transformation leads to an easy evaluation of physical parameters such as the drag and the thickness of the boundary layer. Crocco and independently Wang further transformed this problem to one which is governed by a second order differential equation. In this paper this problem is solved by a classical method and the solution is used to derive two sequences, the first an increasing sequence and the second a decreasing sequence, both converging to the unknown second derivative, at the origin, of the solution to the Blasius equation. Also an asymptotic expression for the solution is obtained.
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Статья научная
Premature ventricular contraction (PVC) is a cardiac arrhythmia that can result in sudden death. Understanding and treatment of this disorder would be improved if patterns of electrical activation could be accurately identified and studied during its occurrence. In this paper, we shall review three feature extractions algorithms of the electrocardiogram (ECG) signal, Fourier transform, linear prediction coding (LPC) technique and principal component analysis (PCA) method, with aim of generating the most appropriate input vector for a neural classifier. The performance measures of the classifier rate, sensitivity and specificity of these algorithms will also be presented using as training and testing data sets from the MIT-BIH (Massachusetts Institute Technology Beth Israel Hospital) database.
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Audibility of temporal smearing and time misalignment of acoustic signals
Статья научная
Misalignment in timing between drivers in a speaker system and temporal smearing of signals in components and cables has long been alleged to cause degradation of fidelity in audio reproduction. It has also been noted that listeners prefer higher sampling rates (e.g., 96 kHz) than the 44.1 kHz of the digital compact disk, even though the 22 kHz Nyquist frequency of the latter already exceeds the nominal single-tone high-frequency hearing limit fmax ~18 kHz. These qualitative and anecdotal observations point to the possibility that human hearing may be sensitive to temporal errors, τ, that are shorter than the reciprocal of the limiting angular frequency [2 π fmax]-1≈ 9µs, thus necessitating bandwidths in audio equipment that are much higher than fmax in order to preserve fidelity. The blind trials of the present work provide quantitative proof of this by assessing the discernability of time misalignment between signals from spatially displaced speakers. The experiment found a displacement threshold of d ≈ 2mm corresponding to a delay discrimination of τ ≈ 9µs.
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Статья научная
In dental surgery, a great number of pathologies (cysts, granuloma ) presents clinical, radiological and evolutionary aspects considerably polymorphic. Medical imagery and particularly oral imagery, by the means of the digitized images and the image analysis algorithms, constitutes an essential element which leads to a precise presumptive diagnosis. The technique of retiming per subtraction can be thus used to recognize in two-dimensional images evolution of the pathological zones (lesions, tumours). From this point of view, a method of automatic retiming was developed by genetic algorithm to follow the evolution of the pathological zones after parodental treatment. In this article the traditional technique of retiming by specifying its disadvantages for our application and then an automatic model of retiming, which offers promising results, are presented. This tool will make it possible to distinguish, identify, and visualize automatically the form of the pathological structures and their evolution in time. An analysis of form and texture of these structures will allow the identification type of pathology.
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Статья научная
Commercial ultrasound power meters based on the radiation force technique are ubiquitously used in both the clinic and in laboratory settings for calibrating therapeutic ultrasound transducers. Despite their popularity, these devices are inherently inaccurate in that they do not compensate for the effects of acoustic cavitation and acoustic streaming. These factors can alter the displacement generated on the meter’s target, and hence the power being sensed. In the present study we built a low cost power meter comprised of a non-reflecting target suspended from an analytical balance in a water tank. Investigations in to the effects of cavitation and streaming were performed, where the former was shown to significantly lower the measured power and the latter was shown to increase it. Both effects were found to be proportional to the applied power as predicted by theory. A modified device was then constructed, where an acoustic permeable membrane was positioned directly over the target and shown to effectively eliminate the streaming effect. For the effects of cavitation, a pair of ultrasound transmitting and receiving transducers was positioned across the beam path, and custom software automatically calculated the attenuation coefficient of the water in the beam column. This was then used to correct for the attenuating effect of cavitation on the power being measured. In addition to correcting for sources of error associated with commercial devices, the setup can easily be constructed for a much lower cost using existing, off-the-shelve components found typically in the laboratory environment. The system may also be employed for research on the effects of water borne phenomena associated with the application of ultrasound in a fluid medium.
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Computer assisted evaluation of traffic noise level
Статья научная
This article presents the main aspects concerning the traffic noise as well as the elements that generate it. Starting with a study on several street profiles, the paper takes into account the variability of modelling parameters (height of buildings, distance between the faзades of buildings, green zones, composition of traffic etc) and then, analyzes the influence of these factors on the traffic noise level. At the same time, it proposes a comparative study of the equivalent noise level, calculated and measured "in situ", in several boulevards of the Romanian capital city, Bucharest.
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Correcting distortion in acoustic sense lines
Статья научная
Pressure sense lines, as employed in the measurement of rocket engine test firings, can propagate the time-domain pressure signal out of hostile regions, which allows the use of instrumentation with fragile pressure transducers. In such applications, it is necessary to correct the data to account for attenuation and resonance due to the sense line. One technique for doing this involves the application of Fourier transform theory to obtain the transfer function of the sense line. Various techniques for obtaining the transfer function are explored, including the use of Gaussian noise, single frequency sweeps, and impulse signals as input functions. The transfer function thus obtained is then mathematically fit, scaled, and validated against a related rocket engine test.
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Статья научная
Prediction of the fluid-structure vibration and acoustic radiation from a submerged submarine is a key problem in the naval engineering. In this paper, for a simulated submarine power cabin with ring-stiffened double shell, the fluid-structure coupling model is built by finite element software ANSYS. The vibrating transfer function inside the cabin, vibration velocity of the outer hull and radiated acoustic power are calculated by FEM/BEM for different parameters of the floating-raft isolating systems, i. e. (1) stiffness of two-stage elastic mounts; (2) raft mass ratio; (3) raft stiffness. This computational procedure can be further used to perform acoustic design of a real submarine.
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