Статьи журнала - Техническая акустика
Все статьи: 276
Localization in a HRTF-based minimum-audible-angle listening test for guib applications
Статья научная
Listening tests were carried out for investigating the localization judgments of 40 untrained subjects through equalized headphones and with HRTF (Head-Related Transfer Function) synthesis. The investigation was made on the basis of the former GUIB. (Graphical User Interface for Blind Persons) project in order to determine the possibilities of a 2D virtual sound screen and headphone playback. Results are presented about the minimum, maximum and average values of discrimination skills. The measurement method includes a special 3-categoryforced- choice Minimum Audible Angle report on a screen-like rectangle virtual auditory surface in front of the listener. Average spatial resolution of 7-11° and 15-24° were measured in the horizontal plane and median plane respectively dependent of spectral content of the noise signal excitation. Accessory signal processing is suggested to enhance poor vertical localization performance.
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Low cost virtual instrumentation using pc printer port for ultrasonic velocity measurements
Статья научная
The most popular and effective technique for ultrasonic velocity measurements is the pulse technique. In the present work, PC based single-pulse sender/receiver system is developed using indigenous components and the bi-directional printer port. A program written in C, under the DOS/WINDOWS environment, controls the pulse generation, detection and travel time measurement. A radio frequency burst of 2 MHz of 5 µs width is obtained from an external source. This pulse is amplified and sent to the transmitting transducer. The received pulse is detected and is used to stop the counter. The number of pulses is counted using a 32 MHz external crystal source. The count is read by printer port and is further used in determining the travel time and to display the ultrasonic velocity of propagation in the medium on the computer screen. The system developed has been tested for ultrasonic velocity measurements in standard liquids. It has been found that the ultrasonic velocity measurement results obtained using the above system match well with those reported in the literature.
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Modeling of a nonlinear control method applied to an advanced static var compensator
Статья научная
The paper deals with the modeling and control of an advanced static VAR (Volt Amperes Reactive) compensator (ASVC) system with self controlled DC bus which employs a three phase Pulse Width Modulation (PWM) voltage source inverter. The ASVC system is modeled using the d-q transform and employs a programmed PWM voltage wave shaping pattern stored in an EPROM to simplify the logic software and hardware requirements. The inverter system can compensate leading and lagging reactive power supplied by the load connected to the supply. This model is used to design an efficient control strategy based on the control of the phase angle of the switching pattern. Simulated results obtained with Matlab are also presented and discussed to validate the model.
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Modeling of gallium arsenide surface acoustic wave devices
Статья научная
A Surface-Acoustic Wave (SAW) device has been modeled employing a secondorder Lagrangian finite-element method. The model is able to describe SAW response variations with arbitrary orientation of the unit crystal cell as compared to the macroscopic device geometry and hence allows for fast SAW design optimization. The model is used to determine the resonance frequency of different SAW device structures. The finite-element results are compared with independent analytical results obtained for two configurations of the applied electrode voltages. In order to obtain significant excitation of SAWs, it is preferable to have the electrode fingers oriented along the [110] crystal axis direction, which is the direction along the x=y line with z constant. Indeed, characteristics of normal displacement amplitudes as a function of rotation angle between the crystal axes and the electrode fingers at a fixed frequency albeit independent of the frequency verify that strong SAW excitations take place for rotation angles near 45 degrees corresponding to the [110] direction. Computations of various eigenmodes of both Rayleigh and Lamb type are discussed.
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Natural frequency automatic variation in seismic isolation system
Статья научная
The proposed system is based on the following operations: 1. interruption of the continuity between the building and the foundation-soil complex; 2. self-centring of the building after an earthquake. By means of its own elastic deformation each bearing can automatically compensate the rigid deflection variation relative to support due to the horizontal component of the motion. The building remains motionless with respect to the foundation-soil complex, which moves. The vertical motion, due to the sub-undulatory shock, varies the building behaviour only partially. It remains stationary with respect to the horizontal translation, but it is subject to a low vertical translation and to a resonance possibility. In order to prevent the resonance danger, the vertical natural frequency variability takes place because of auxiliary springs which automatically increase the action of one or more main springs during an emergency, characterised by an interval of vertical seismic frequencies including the resonance one.
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On compact Green's functions and asymptotic expansions for flow-induced sound predictions
Статья научная
Both compact Green's functions and asymptotic expansions are widely used to analytically predict sound generated by low Mach number ( 1 M ) fluid-dynamic sources, where the acoustic compactness of the source region is satisfied. By mathematically investigating the detailed assumptions involved in each of the two methods and by using two classical examples of flow noise problems, it is shown that the applicability of compact Green's function is restricted to a receiver location, r, at the acoustic far-field with ωr / c0 ЃЁ Ѓ‡where ω is the frequency and c0 is the speed of sound, and that the solution from matched asymptotic expansions can be applied less restrictively starting at ωr / c0 ~ 1. Significant differences between the two solutions are shown when ωr / c0 ~ 1. In the acoustic far-field, the solutions from the two methods are analytically proved identical.
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On the fresnel zones of a circular transducer
Статья научная
In classic acoustics one differs two areas around the acoustic source - near field and far field. There is a third area, called very near field, but it is mostly the subject of researches in the field of vibration mechanics. The near and the far field are often called Fresnel zones and Fraunhofer zone. In this work a criterion for determining the borders of Fresnel zones is proposed. The criterion is based on multiple examinations, researches and measurements of the spatial parameters and characteristics and some of the electrical parameters and characteristics of circular transducers (loudspeakers)
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Optimal control of booster phase shifters using HVSO pulse width modulation
Статья научная
Pulse width modulation (PWM) phase shifters allow smooth control of power flow in transmission lines. Previous publications present a multimodal structure based on PWM control of GTO to achieve high-voltage and high speed switching. A new control scheme based on the high voltage sub optimal PWM modulation is proposed for semiconductor-controlled static phase shifters and its performance is compared with SPWM and optimal regular-sampled PWM techniques. This paper proposed a new single-module; six- switch structure based on high voltage sub optimal (HVSO) PWM technique with high voltage and limited harmonic injection. Simulations and comparisons of different PWM techniques for semiconductorcontrolled static phase shifter (SPS) are used to illustrate the advantages and fine performance of the proposed structure.
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Optimal low noise amplifier for ultrasonic receptor
Статья научная
The paper describes a detailed investigation of the noise generated by an ultrasonic chain of reception carried out on a piezoelectric receiver of standard characteristics amplified by an LNA (Low Noise Amplifier) of optimum design. The objective is to provide the conditions which will allow the best signal-to-noise ratio of the entire chain. The noise chain factor is studied theoretically. It is shown that the noise factor is minimal if the noise characteristics of the LNA and the gain resistance of the first amplification stage are jointly matched to the transducer's internal resistance. A two-stage 56 dB amplifier optimized for transducers with a resonant frequency between 1 and 10 MHz and with an internal resistance of approximately 390. is designed. Measurements show a low noise factor (1.46). This advantage reveals the direct correlation between noise PSD of the chain and the real part of the transducer impedance.
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Optimization on constrained single-layer absorbers by simulated annealing
Статья научная
As the thickness of sound absorber is often confined by the necessity of worker's maintenance and access in the practical engineering work, the consideration of maximal sound absorption on the sound absorber with limited thickness becomes important and essential. In this paper, by using the simulated annealing (SA), a stochastic relaxation technique based on the analogy of the physical process of annealing metal, a single-layer absorber, including (1) one layer of perforated plate; (2) one layer of acoustic fiber; (3) one layer of air space; and (4) a rigid-backing wall, is optimized under the thickness constraints. A numerical case in dealing with pure tone noise of 350 Hz was exemplified. Before optimization, a sample was tested and compared with the experimental data for accuracy check of mathematical model. Results proved that SA optimization provides a quick and efficient approach on the design of single-layer sound absorbers under fixed thickness.
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Статья научная
This paper analyzes the effect of the speaker feature vector characteristics, in the performance of speaker recognition systems (SRS) based on the Gaussian Mixture Model (GMM). To this end, the performance of the SRS is analized using speaker features derived from: a) linear predictive cepstral coefficients (LPCepstral) extracted from the whole speech frame, b) LPCepstral derived from the voiced parts of the speech frame, c) LPCepstral extracted from voiced segments of speech frame together with the pitch information, d) LPCepstral extracted from voiced segments of each frame normalized using a Cepstral Mean Normalization (CMN). Evaluation results, using phrases of 2.5-3 second of telephone speech utterances in Japanese language, show that a fairly good performance of GMM-based SRS is achieved with most speaker features vectors with both, close test as well as with open-test, although the features vector providing the best recognition performance closely depends on each particular speaker.
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Performance analysis of wide band MC-CDMA
Статья научная
Multicarrier (MC) systems are being proposed and tested for wireless data transmission in applications such as broadband wireless networking and digital broadcasting of audio and television. The combination of multicarrier modulation and code-division multiple access (CDMA) is seen as a very promising technique for the development of high-capacity wireless indoor communications. However, this scheme is very sensitive to multi-user interference. In this work, we consider the classical MC-CDMA architecture modified by the introduction of sequence chip modulation on each subcarrier. The introduced orthogonal sequences, with suitable arrangement for each user, will show multi-user interference cancellation and increase the bandwidth required for each sub-carrier, enhancing by that the system performance. The results are given in terms of bit error rate (BER) obtained by an analytical approach for additive white Gaussian noise (AWGN) in Rayleigh fading channel.
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Piezoceramic ring loaded on each face: a three-dimensional approach
Статья научная
An approximated 3D matrix model of piezoceramic ring loaded on each face is proposed. Ring is treated as a three-dimensional structure whose vibrations can be described by two coupled differential equations. Solution of this system are two orthogonal wave functions which depend only on one axis, corresponding to the propagation direction, and which satisfy the boundary conditions only in an integral form. With this model, which describes both the thickness and the radial modes, and the coupling between them, the piezoceramic element is schematized as a five-port system, with one electrical and four mechanical ports, one for each surface. The electrical impedance of the sample can also be easily computed. Also, the computed and experimental results are compared. Compared with numerical methods, the computation is time-saving.
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Power systems harmonics and inter-harmonics identification: a power quality issue
Статья научная
The discrete Hartley transform (DHT) is a real-valued transform and is closely related to the familiar Fourier transform (FT). This paper presents the application of DHT for power system harmonics and inter-harmonics identification and measurements. Unlike the DFT, DHT can identify these harmonics without any restriction on the frequency of the harmonic to be identified. Also DHT can easily identify the harmonics and inter-harmonics directly without any mathematical models for any one of them. The proposed algorithm uses directly the samples of the voltage or current waveform at the location where the power quality criteria are to meet. In this paper, the convolution property of the DHT is used in the identification and measurement process. Because the Hartley transform is a real transform, it is more computationally efficient than the Fourier and Laplace transforms. Different examples are presented. Effects of critical parameters on the performance of the proposed algorithm are discussed.
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Pulse echo method for nonlinear ultrasound parameter measurement
Статья научная
Pulse echo method for nonlinear ultrasound measurement attracts the interest of the scientific community because it can be used for non destructive evaluation and in vivo measurement. Also, it can be useful in quantitative harmonic imaging. The technique is based on the measurement of the reflected harmonics from an interface separating two mediums. The use of this method for nonlinear ultrasound parameter measurement was suggested. However the mathematical model derived was based on the plane wave theory ignoring diffraction phenomenon. An analytical model taking into account diffraction is proposed in this paper. Using a decomposition of the source function in terms of Gaussian beams, analytical expressions are obtained for the fundamental and second harmonic reflected. For the experimental study a ring transducer is used for transmission allowing machining a tube to insert the hydrophone. The hydrophone is a PZT with 0.4 mm in diameter. The harmonics reflected from two interfaces (ethanol/water and water/glycerol) are measured. Comparing the measured values to the theoretical results allow to deduce the nonlinear parameter for water and ethanol. The results obtained agree with the value find in the literature and show the validity of the model.
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Rayleigh waves in a rotating transversely isotropic materials
Статья научная
Rayleigh wave speed in a rotating transversely isotropic material is studied. Speed in some transversely isotropic materials is calculated by choosing an angular velocity. Rayleigh wave speed is also calculated in non-rotating medium. It is observed that rotational effect plays a significant role and increases the speed of Rayleigh waves.
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Reconfigurable vlsi architecture design for real time image stabilization
Статья научная
This paper proposes reconfigurable VLSI (Very Large Scale Integration) architecture design of real time image stabilization to remove the unwanted displacement due to camera motion and the displacement of the target. This is based on image preprocessing, based many steps (namely light compensation, thresholding, scaling and offset, histogram equalization, LUT operator), followed by sub image phase correlation for motion estimation and kalman filtering for motion correction and stabilization. For the implementation into VLSI, FPGA (Field Programmable Gate Arrays) board consisting 3Ч2 array of vertex 2 as processing element (PEs) is interfaced with PCI port of the PC and the camcorder is connected to USB port of the FPGA board for capturing, visualization and testing of the image if any. Image preprocessing techniques are applied on input image before actual processing to suppress the unwanted distortion or to enhance some image features, which is important for further processing. Global motion is estimated from the local motion vector (LMV) and the average of two maximum peak amplitudes from the block of LMV decides its global motion vector, thereby accumulating motion vector for panning. The kalman filtering based motion correction system stabilizes image caused by unwanted movement or camera vibration. This proposed system design is expected to achieve a target frame rate of 30 fps, integration time 3.33 ms per frame producing 7.5 mbps image data when pixel is converted to 8 bit digital value for 320Ч240 QVGA input image. The proposed design algorithms has been implemented and verified with Frame grabber board (Matrox Meteor-II Mil-lite software) that is interfaced with camcorder and PC. Similarly, the same design has also been tested using ARM Emulator and DM320 Board (ARM9TDMI core, DSP core).
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Sampling rate error in acoustic measurements
Статья научная
Two aspects of data collection and analysis are considered in the paper: the transfer function of the detector and the sampling method used on the data the detector reports. Following a brief look at transfer function theory, a simple model is constructed which shows the effect of sampling time dependent functions (acoustic or otherwise) at different rates. The average value of a time dependent parameter (pressure for example) is calculated to illustrate the analysis method. Four different type functions were chosen to represent the parameter: sinusoidal, pseudo-sinusoidal, asymmetric triangular, and random. The results illustrate the important role played by sampling rate when analyzing time dependent data.
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Scattering of a distribution of encapsulated gas bubbles, a computer model
Статья научная
The interest in using suspensions of polymeric encapsulated microbubbles as contrast agents in medical ultrasound imaging has increased during the last few years. Most of the knowledge on the non-linear mechanical and acoustical behaviour of encapsulated microbubbles is the result of empirical measurements, while the theoretical study of these phenomena, in particular the echo of a bubble distribution, is still an open research area. This paper presents a computer simulation program that calculates the global echo of a bubble distribution according to a modified Rayleigh-Plesset model for each bubble and by summing the contribution of each bubble to highlight the higher harmonics. Thanks to this approach, the study of the effects of the parameters of both the bubble and transmitted acoustic impulse on the higher harmonics contained in the echo is simplified. The results of this study are fundamental to the design of the microbubble or the echographic system.
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Shape optimization on constrained linearly expanded tubes by using genetic algorithm
Статья научная
One of the most important practical considerations in muffler design is the constrain problems in a confined place. In addition, to release the pressure drop in a muffler system, a new silencer of linearly expanded tube is proposed and investigated in this paper. The genetic algorithm (GA), a stochastic algorithm, is used as an optimizer by mimicking the genetic drift and Darwinian strife for survival. To approach this study effectively, the linearly inclined tube is divided into several segments of straight tube with different diameters. Four-pole transfer matrix is then in use, accordingly. Not only the theoretical derivation in sound transmission loss (STL) but also the GA searching technique is discussed. Additionally, a numerical case on the expanded tube is introduced. To achieve the best optimization in terms of STL of a muffler, the GA parameters are on trial in various values. Results show that when the divided elements of the tube are more than sixteen segments, the modeled segmental tube is similar to the linearly expanded tube. In addition, the STL in muffler becomes to be stable.
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