Showing papers in "Technical Acoustics in 2010"

Frequency offset estimation and synchronization of underwater acoustic communication with hyperbolic frequency modulation signal

Abstract: Due to the band-limited underwater acoustic(UWA) channels, it is a good way to make use of band-width-efficient modulation techniques for high-speed communicationOrthogonal Frequency Division Multiplexing(OFDM) modulation, in which the overlap of subcarriers is allowed, has very good application prospectBut demodu-lation of OFDM is very sensitive to frequency offset and synchronization;the former is often severe in UWA commu-nication because of Doppler phenomenonEmploying hyperbolic frequency modulation signal as a pilot makes it possible to calculate the frequency offset accurately and achieve synchronization

The design and establishment of a Chinese whispered speech emotion database

Abstract: In order to study the new issue of emotion recognition of whispered speech,the construction flow and standards are developed,and the whispered speech emotion database,which includes 4000 words,5000 sentences and 600 paragraphs,is designed and established.With the concepts of Membership Function and Analytic Hierarchy Process in fuzzy math,the validity of each sentence has been checked out to obtain a qualified database with which a preliminary experiment of whispered speech emotion recognition is carried out.It is concluded that the parameters such as sound length and sound power,which are suitable for normal speech emotion recognition,are still useful in whispered speech,while the other parameters related to pitch are not suitable for whispered speech emotion recognition.So the old parameters should be improved or new parameters would be extracted.

Mathematic model of multi-path ultrasonic gas flowmeter

Abstract: There are many factors to cause the measurement error in the practical application of ultrasonic flowmeter,and the flow velocity profile is a very important factor.Using the multi-path ultrasonic flowmeter is an effective method to decrease the measurement error.However,the flow velocity is not the same at different point(along the radius direc-tion) in the pipe cross-section because of fluid viscosity.So the average flow velocity measured by the multi-path flow-meter is still different from the actual average flow velocity.The mathematic model of multi-path ultrasonic gas flow-meter is studied in this paper.The average linear flow velocity could be converted into the average cross-sectional flow velocity via the dynamic calibration factor and weight coefficient,which are calculated by the mathematic model.So the measurement accuracy could be improved.The software of the mathematic model is applied in the four-path ultra-sonic flowmeter for comparison experiment.

Design and establishment of practical speech emotion database

Abstract: An elicited speech emotion database is designed and established for practical speech emotion research.Based on Scherer’s stimulus evaluation checks,the experiments of inducing emotional speech with a computer game are de-signed.A Chinese practical speech emotion database is established for the first time.Three practical speech emotions including impatience,nervousness and happiness are induced.And four categories of emotional data,including the neutral state,are collected,and emotional data are evaluated in a listening perception test.The results show that the method of emotional speech elicitation with a computer game is a reasonable and effective way of collecting high quality practical speech emotion data,which is a necessary support to feature analysis and recognition of practical speech emotion.

Improved passive time reversal array processing in underwater communication

Abstract: Irrespective of environmental condition,time reversal approach can self-adaptively compress multi-path and selectively focus on a target,reduce inter-symbol interference(ISI) and co-channel interference(CI) of multi-user com-munications,so it is widely used in underwater acoustic communications.Based on the passive time reversal approach,an offset term is added to vertical receiving array processing,which can restrain one user’s receiving signal amplitude to achieve communication with another pointed one.The computer simulation shows that this method can reduce half of bit error rate(BER) as compared with only using time reversal processing.The sea-trial data analysis is generally con-sistent with the simulation.

A method for ship propeller blade-number recognition based on template matching

Abstract: The existing algorithm of ship propeller blade-number recognition is based on mathematical model or expert system.The result of blade-number recognition is usually instable and inaccurate, in the case of DEMON line spectrum of ship radiated noise at low signal-to-noise ratio(SNR).This paper proposed a method for ship propeller blade-number recognition based on template matching.This method establishes a template library, which is independent of samples.Template Matching algorithm and confidence factor algorithm are designed.This method can resolve the problem of inaccurate mathematical model, incomplete rules and samples in existing algorithm.Practical experiments prove that the error rate of propeller blade-number recognition is reduced distinctly, and the result of target classification goes toward stability.

Modeling and analysis of ultrasonic anemometer

Abstract: The ultrasonic characteristics in air are analyzed in this paper,and a theoretical model of ultrasonic anemo-meter is given based on propagation time and amplitude,which describes the basic principle of ultrasonic anemometer from transmitting time and acoustic intensity.An experiment result in various wind speeds and directions is in accord with the theoretical model.This paper provides a basis of developing ultrasonic anemometer.

Unequally spaced linear array beamforming

Abstract: This paper introduces an analyzing method and principle of unequally spaced linear arrays beamforming,caculates unequally spaced array beamforming of 10 elements,16 and elements,32 elements.By using z-transform,this paper tries to reveal the relationship between the equally spaced beamforming with weighted amplitudes and unequally spaced beamforming,and gives the fomulae of weighted amplitudes transformed to unequally spaced beamforming.Simulation shows that the method can reduce the first and second sidelobes,and doesn't widen the mainlobe.

Effects of L-type matching network on characteristics of ultrasonic transducers

Abstract: The effects of L-type matching network on resonant frequency and vibration characteristics of ultrasonic transducers are studied.The relationship between the L-type matching network and the electromechanical coupling coefficient is derived by theoretical analysis and experiment.The effective electromechanical coupling coefficient of the ultrasonic transducer with a series inductor,a parallel inductor or an L-type matching network is analyzed,and the result show that using L-type matching network is better,the effective electromechanical coupling coefficient can be improved by properly electing the network parameters.

Study of thickness-vibrating transducers with matching layers

Abstract: With the development of signal processing in underwater acoustics,the demand for broadband signal is arising increasingly.The broadband transducer is the basis of making use of broadband signal.Matching layer technology is the most effective method to broaden the frequency bandwidth of thickness-vibrating transducers.Study is introduced on how to design thickness-vibrating transducers with multiple matching layers.The equivalent circuit model is built on the basis of complex coefficients.The relation of matching layers parameters and transducers response is simulated.It is pointed out that there are some limits to broaden the bandwidth of transducers with single or double matching layers,and the proper thickness of matching layer is not exactly the quarter of wavelength.Samples of thickness-vibrating transducers with single and double matching layers are developed to validate the simulation results.The tested results are in good agreement with the simulation results.

The separability of active sonar signals in the presence of reverberation

Abstract: The separability of active sonar signals is the important factor for the application of blind source separation(BSS) to the signal detection in the presence of reverberation.Based on the sonar data model and the analysis of the source correlation function,a rule has been presented for judging the separability of the sonar data.It has been described that the reverberation data is separable when the sources have small correlation coefficient in most of time delays.The simulation data and trial data with two classical transmitting signals(CW and LFM) are used to verify the rule,and the result says that the separation of the reverberation data is possible when the LFM is the transmitting signal.

A study of underwater acoustic communication based on the joint processing of passive time reversal and adaptive equalization

Abstract: Passive time reversal processing only needs one-way propagation so that it can be implemented more easily.While its spatial focusing can mitigates channel fading and its temporal focusing reduces intersymbol interference(ISI),there always is some residual ISI depending on the complexity of the channel.Therefore a decision feedback equalizer based on recursive least squares algorithm is used to reduce the residual ISI after passive time reversal processing.The complex experimental waveguide results show that(1) the number of error symbols can be reduced to zero by this joint processing while it's impossible for the passive time reversal processing;(2) the number of taps of adaptive equalization after passive time reversal processing is reduced largely so that the complexity of computation is also reduced.This demonstrates that this joint processing of passive time reversal and adaptive equalization is not only reliable but also effective in phase coherent underwater communication.

A modified method in calculating attenuation spectra for particle system

Abstract: By analyzing the difficulties of ultrasonic attenuation calculation with directly solving method for the ECAH model in particulate two-phase systems,a novel approach to constructing new variants involved in Bessel(Hankel) function is put forward,which can significantly decrease the condition number,and avoid numerical overflow to enlarges the available evaluation range to frequency 100MHz for particles of millimeters size.A comparison with BLBL scattering method validates the effectiveness of the modified algorithm proposed in this paper.

Research on MC-CDMA in underwater acoustic communication

Abstract: Multi-Carrier Code Division Multiple Access(MC-CDMA) is a combination of Orthogonal Frequency Di-vision Multiplexing(OFDM) and Code Division Multiple Access(CDMA),and has their both advantages.In under-water acoustic communication,there is serious multipath interference,marine environment noise,and space-time va-rying properties,which make the underwater acoustic signals attenuated greatly.MC-CDMA is used in underwater acoustic communication for its high-speed data transmission and reliable performance.In the paper the basic principle of MC-CDMA is analyzed,and it is tested that MC-CDMA has better performance in underwater acoustic communi-cation than OFDM via the simulation for MC-CDMA and OFDM and the experiment in pool.

Research on FFH/MFSK long range deep-water acoustic communication technique

Abstract: The FFH/MFSK communication scheme is proposed for long range deep-water acoustic communication.The scheme employs fast frequency hopping(FFH) to suppress severe multipaths interference effectively and reduce bit error rate.Using the characters of the deep-water acoustic channel and putting the communication modems at the depth corresponding to the minimal sound velocity value can improve the range of communication efficiently.The results of simulation and experiment show that proposed method has outstanding advantage in performance of bit error rate(BER).

Application of Cadna/A software in prediction and assessment of railway noise

Abstract: Cadna/A(Computer Aided Noise Abatement) is the simulation software based on RLS90 in Germany for calculation, presentation, assessment and prediction of environmental noise.By utilizing the software-program, Cad-na/A designed by Germany Data Kustik Gmbh, the influence of railway traffic noise on environment are simulated and predicted.The measure of controlling environmental noise pollution is also put forward in this paper.

Effects of absorbing wall on acoustical property of micro-perforated panel absorbers

Abstract: With placing absorbing material on the side wall of cavity in a micro-perforated panel absorber,the acoustic compliance of cavity increases,and the acoustic resistance of cavity appears,thereby the acostic property of the mi-cro-perforated panel absorber is improved.Compared with an absorber structure with rigid wall,the resonant frequency of the structure with absorbing wall is lower,the absorption coefficient frequency response curve tends to flat,and the difference between peak and valley in the curve deceases.Its acoustical characteristics are basically the same as that of the structure filled up with absorbing material.Two theoretical calculation formulas has been derived and supported by an example.Pithier than three-dimensional formula,one-dimensional formula only requires normal incidence absorp-tion coefficient and can meet engineer accuracy except for higher resonance frequency.

An active noise control algorithm without secondary path identification

Abstract: Most available active noise control(ANC) requires the identification of the secondary path using offline or online secondary path identification technique.By means of analyzing the FXLMS Algorithm’s vector map and its geometric characteristics of algorithm convergence,the model free ANC can be realized.Sub-band technology is that the signal through different filter banks is decomposed into different sub-band frequency bands,so that each sub-band signal can be separately dealt with accordingly,and reduce the processing time.In this paper,combining the two technologies,an ANC algorithm is proposed without secondary path identification based on the over-sampled non-delay sub-band architecture.

Research on DOA estimation of vector-sensor array with time-frequency MUSIC algorithm

Abstract: Time-frequency MUSIC algorithm utilizes signal’s time-frequency distribution to construct spatial time-frequency distribution matrix instead of the conventional covariance matrix to estimate direction of arrival of the signals.It has been shown that using the spatial time-frequency distribution can restrain both noise and disturbance ef-ficiently,and the robustness of the algorithm can also be improved.Time-frequency subspace algorithm is not restricted by the number of sources unlike the traditional subspace estimation algorithm.Time-frequency-space information is contained by time-frequency points which can be used to establish the array manifold matrix.As for a wideband signal,the algorithm avoids to search in frequency domain,so the calculation amount can be reduced.In this paper,time-frequency MUSIC algorithm is applied to 2-D vector-sensor vertical linear array to make full use of the sca-lar-vector quantity of the vector-sensors and the time-frequency information of the signals for two-dimensional DOA estimation.The validity of the algorithm is verified by simulation.

Simulation research on target localization algorithm using a guide source in low signal-to-noise (SNR) ratio

Abstract: In order to achieve the accurate location of the target localization algorithm using a guide source(GTL algo-rithm) in low signal-to-noise(SNR) ratio condition,a denoising processing method for the GTL algorithm based on the field average method is proposed.Some guide sources and objective sources with different SNRs are used for the GTL algorithm simulation,and the simulation results before-and-after denoising processing are analyzed.The analytic results show that the location efficiency of the GTL algorithm is improved by the denoising processing of using the field average method.

Design of underwater repeater based on orthogonal frequency division multiplexing

Abstract: In order to solve the problems of long-distance high-speed underwater acoustic data transmission,a good method is to transmit the data by using repeaters.In the paper,an underwater repeater system based on orthogonal frequency division multiplexing is designed.The structure of the repeater is very simple and it has the characteristic of low power.The repeater can overcome the problems due to multi-path propagation and limited bandwidth in underwater acoustic communication to achieve reliable high-speed transmitting communication.According to lake testing,the bit rate reaches 4.32kb/s for the bandwidth of 3kHz within 6000m with the bit error rate(BER) lower than 10-3.The experi-ments show that the repeater can reach high data rate with low BER.

Simplified finite element model for simulation of ultrasonic transducer

Abstract: A method of simplifying finite element model is proposed,which uses the fundamental physical theory of FEM(Finite Element Method) to simplify and analyze the fluid model in some engineering applications without the necessity of calculating precise acoustic parameters and beam characters of radiation sound field.By the ultrasonic transducer simulation with the method,a sample is developed and measured,and the result is substantially in accord with that of the simplified finite element model.Thereby it is proved to be feasible and effective for optimizing trans-ducer design.

Experimental study of sludge disintegration with dual-frequency ultrasound

Abstract: A 20 kHz and 25 kHz ultrasonic device has been developed and used to study the effect of dual-frequency ultrasound on sludge disintegration by changing COD,NH3-N,TP in filtrate.Effect factors including different frequency combination,different function mode,different power combination and different time combination of dual-frequency ultrasound have been discussed in detail.It has been indicated that dual-frequency ultrasound is more efficient to sludge disintegration.This study provide a basis for the application and the further study of sludge disintegration methods.

Simulative analysis of extracting weak target information from sonar outputs

Abstract: In many cases the outside-ship-platform becomes strongly jammed,which makes the ship's sonar hard to detect weak targets.Two methods for extracting weak target information from sonar outputs,the beamspace MVDR (b-MVDR) and the post-beamformer interference canceller (PIC),are analyzed through computer simulations.And simulation results show that the PIC has the improved resolution performance over the b-MVDR,but the PIC's capability to extract weak target decreases as the signal-to-interference ratio (SIR) increases.However the b-MVDR has better performance in all situations.

Analysis of some new applications of parametric sonar

Abstract: Recent applications of parametric array technology in shallow water detection sonar,dipping sonar,torpedo homing sonar and shallow water communication sonar is introduced briefly in this paper.A parametric sonar design according to the linear sonar whose working frequency is 30k Hz is analyzed.The primary frequency of the parametric sonar is 90 kHz and the difference frequency is the same as the working frequency of the linear sonar.It is shown that the parametric sonar has better performance than the linear sonar in reverberation limited environment.The encountered difficulties for parametric sonar in recent applications are also analyzed,and a relatively simple method to achieve broadband parametric array is suggested.

Structural characteristic and acoustic absorption behaviors of fiber assemblies

Abstract: Fiber assemblies are studied by using the standing wave tube method to explore the effect of several parameters on their acoustic absorption propertiesThe parameters include the average bulk density of assemblies,density and structure of fiber and the effect of air gapThe results show that with average bulk density increasing,the sound absorption coefficient is enhanced on whole testing frequency range,and the peak of the absorption spectra shifts towards lower frequencyHowever,it seems to have a critical bulk density,over which the absorption coefficient will not raiseThe variety of fibers does not influence the sound absorption obviouslyAnd changing the combination of fibers and air gap can increase the absorption capacity,especially in the low and medium frequency rangeFurthermore,the increasing fiber volume fraction will raise the number of fiber cut ends on an arbitrary cross section and reduce the pore radius and length of the free distance,meanwhile make the peak of sound absorption coefficient shift towards lower frequency

A method for extracting radiated noise modulation spectrum of underwater target

Abstract: The limitation of frequency overlap existing in multi-resolution wavelet decomposition is analyzed.And a narrowband FIR filter method directly to extract interested data is proposed.By using Morlet complex resolution wavelet transform and setting appropriate band and center frequency the envelope of modulated signal is extracted and then analyzed with frequency spectrum method,finally the screw propeller shaft frequency,which is the important value for object speed calculation,can be obtained.

NI-CompactRIO based underwater acoustic signal parameter estimation and implementation

Abstract: Three algorisms are commonly used for underwater acoustic signal parameter estimation: 1the method of measuring signal frequency requency with the ratio of maximum spectrum line to sub-major spectrum line;2the signal retransmission is to send the received signal with added feature information;3the matched filter is to carry out convo-lution of matching function and received signal to determine the receiving signalThe latest real-time embedded de-velopment platform NI-CompactRIO and the Labview development environment are selected to implement the above three algorithmsExperimental results prove the correctness of the algorithms,and verify the feasibility of NI-Com-pactRIO platform

A time measuring method in underwater acoustic pulse ranging

Abstract: The time measurement is the key technology in underwater acoustic ranging,which would directly influence the accuracy.A new method of time measurement is presented:Signal is re-built by cubic spline interpolation and the peak value of each carrier wave cycle is calculated out accurately,therefore signal envelope is collected effectively.Signal envelope is smoothed and positions of maximum gradient points are figured out.The performance is examined,which shows that the algorithm could achieve a high estimation precision.

Detection of torpedo radiated noise in strong interference background

Abstract: Broadband energy detection has been widely used to passive sonar.But its performance degrades dramatically under condition of the low SNR and strong interference.Since there are abundant line spectra in torpedo radiated noise,a combined detection algorithm of the torpedo radiated noise is put forward.After each beam output is processed by the narrowband processing and line spectrum extraction,the energy of line spectrum with specified frequency band is used as the weighted factor of broadband beam output in order to improve the detection ability of the targets containing line spectrum.This algorithm can effectively suppress the strong interference of targets without line spectrum and improve the detection ability of the low SNR targets.The processing results from simulation and sea trial data show the validity of the proposed algorithm.