bluuebunny/crossref_metadata_2025 huggingface dataset:
Bone ultrasound transducer
Authors: Okino Masahiro , Mizuno Katsunori , Suga Daisuke , Matsukawa Mami
Published: April 2012

Low-intensity pulsed ultrasound (LIPUS) is used on bone-healing. One expected healing mechanism of this technique is the contribution of piezoelectricity. Actually, the piezoelectricity in dry bone at low frequencies has been reported by many investigators. However, the ultrasonic investigation of the piezoelectricity in bone has still remained very few. We have then made original transducers with bovine cortical bone samples, which were fabricated into plates (diameter: 10 mm, thickness: 0.5~1.0 mm). Using a conventional ultrasonic pulse technique in MHz range, we confirmed the observation of ultrasonic wave by the transducer. Here, the bone transducer was set in water at the focal position of a PVDF transmitter, which was excited by a single sinusoidal pulse of 70 Vp-p in the MHz range. The maximum voltage of the received wave was about 200 μVp-p. It was almost 1/2000 of the homemade PVDF transducer, which was made by the same procedure. The observed wave amplitude changed due to the sound wave frequency and bone thickness. Considering the inhomogeneous bone microstructure and the thickness dependence of the bone transducer, the piezoelectricity of bone in the MHz range is discussed.
A quantitative imaging of bonding strength at the bonded solid-solid interface obtained by nonlinear test
Authors: Chen Jianjun
Published: April 2012

As well known, when a longitudinal wave propagates through an interface with micro-cracks and micro-defects between solids, the contact acoustic nonlinearity (CAN) will be generated dramatically and the nonlinear parameter can be used to contour the bonding state of the interface. However the contour can only show the relative state of bonding strength and can not be used to judge weather the multilayered composite materials in use is safe because the safe judgment is not by the relative state while by the absolute value of the bonding strength. Therefore characterization of quantitative bonding strength at the interface is very important for judging a multilayered material in safe use. In this paper, how to get the quantitative bonding strength from the CAN parameter is studied. After the vibration amplitude of incident focusing wave at the bonded interface was calculated, the standard bonding strength with complete bonding state was established by tension test and CAN parameter is calibrated, the quantitative imaging of the bonding strength is obtained by CAN microscope in experiments. From the imaging, the positions with weak bonding strength could be easily located, which can be used to decide whether the material could be employed continuously.
Nonlinear spring model for adhesive bonding interface
Authors: An Zhiwu , Wang Xiaomin , Deng Mingxi , Mao Jie , Li Mingxuan
Published: April 2012

The boundary conditions for an interface between two solids are analyzed to model second harmonic generation in a thin elastic adhesive layer. The approximate boundary condition models termed as “nonlinear spring models” are rigorously developed using an asymptotic expansion of the exact solutions in the limit of small ratio of interface layer thickness to wavelength. The applicability of such boundary conditions is analyzed by comparison with exact solutions for ultrasonic wave transmission. Numerical calculation indicate that as the acoustic nonlinearity increases, the model tends to be more accurate, meanwhile the second-harmonic amplitude increases in direct ratio. The present nonlinear spring models may provide a potential to evaluate the nonlinear mechanical behavior of bonding interface. Acknowledgment: This work is supported by the National Natural Science Foundation of China (Grant No.10834009)
A mutual radiation impendence measurement method for 2-element transducer array considering nonlinear interaction
Authors: Zhang Xuesen , Ji Peifeng , Yang Jun
Published: April 2012

Mutual radiation impedances represent the acoustical interaction between transducers in an underwater array, which are inherent in the distance between transducers and the geometry of the array. The influence of mutual radiation impedances, which are important to evaluate the performance of the underwater array, especially needs to be intensively studied on condition that the power of transducers is high enough because of nonlinear interaction. A method for determining mutual radiation impedances of transducers in a 2-element array is proposed in this paper, which applies to estimation of mutual radiation impedances for an underwater array with high radiation power. This method derives from V method in which the mutual radiation impedances are considered as the acousto-motive force generated on the surface of each transducer. By using nonlinear acoustic analysis, theoretical foundations of this method based on equivalent circuits are described. Detailed experimental procedures to implement the method are illustrated.
Performance of optimized sound field control techniques in simulated and real acoustic environments
Authors: Coleman Philip , Møller Martin , Olsen Martin , Olik Marek , Jackson Philip , Pedersen Jan Abildgaard
Published: April 2012

It is of interest to create regions of increased and reduced sound pressure ('sound zones') in an enclosure such that different audio programs can be simultaneously delivered over loudspeakers, thus allowing listeners sharing a space to receive independent audio without physical barriers or headphones. Where previous comparisons of sound zoning techniques exist, they have been conducted under favorable acoustic conditions, utilizing simulations based on theoretical transfer functions or anechoic measurements. Outside of these highly specified and controlled environments, real-world factors including reflections, measurement errors, matrix conditioning and practical filter design degrade the realizable performance. This study compares the performance of sound zoning techniques when applied to create two sound zones in simulated and real acoustic environments. In order to compare multiple methods in a common framework without unduly hindering performance, an optimization procedure for each method is first used to select the best loudspeaker positions in terms of robustness, efficiency and the acoustic contrast deliverable to both zones. The characteristics of each control technique are then studied, noting the contrast and the impact of acoustic conditions on performance.
On frequency characteristics of bone conduction actuators—subjective and objective measurements of inner canal type and head-of-mandible type actuators
Authors: Fukuda Yoshimi , Yae Yuki , Nakahara Fumihiro , Nakatani Hidenori , Kobayashi Koji , Chisaki Yoshifumi , Usagawa Tsuyoshi
Published: April 2012

Recently, bone conduction actuators which can reproduce the high frequency signal around 10 kHz are released in the market and those are used not only for speech but also music reproduction. However, the detail characteristics of bone conduction actuators, such as threshold, loudness vibration and frequency characteristics are not yet clear. Because there are difficulties to make clear the relationship between input signal and loudness of perceived sound even if acceleration of actuator is given. In this paper, threshold and loudness of stimuli are measured by means of psychoacoustical test for two types of bone conduction actuators; inner canal type and head-of-mandible type. Frequency characteristics of actuators are measured as acceleration. Comparison between subjective and objective measurements is performed in order to make clear the characteristics of measured bone conduction actuators.
The study on vibratory tactile sensor using piezoelectric bimorph resonator
Authors: Kudo Subaru
Published: April 2012

Piezoelectric vibratory tactile sensors are used for measuring the softness and hardness of an object. In this work, a new construction of vibratory tactile sensor was investigated using a piezoelectric bimorph resonator. The bimorph resonator was driven in one side by constant voltage and constant driving frequency. When the tip of a resonator was contacted with a test piece, the output voltage in the other side of resonator was changed by contact impedance. Then, the contact impedances were calculated with experimental characteristics of output voltage using the equivalent circuit of the bimorph resonator. It was experimentally clarified that the electrical contact capacitance gradually decreased as the load added to test piece increased. The amount of decrease for hard test piece was larger than those of the soft test pieces. Next, the Young's moduli of test pieces were calculated from the experimental results in this method. The calculated values were compared with actual material constants of test pieces. It was examined that the possibility for detecting the softness and hardness of an object by this method on bimorph resonator. These results in this study may be useful for designing on the piezoelectric tactile sensor.
Theoretical approach on SAW characteristics of layered structures for gas sensing
Authors: Xie Xiao , Wang Wen , Liu Minghua , He Shitang
Published: April 2012

Integrating the self-assemble sensing film with SAW devices has advantage for organic gas detection. It generally requires a thin metal layer like Au acting as a catalytic base for the sensing film formation. This leads to a double layer SAW device sensing area fabrication consisting of a metal layer deposited on the piezoelectric substrate. Therefore, the SAW characteristics will be affected when propagating through the sensing area. Various layer parameters such as stiffness constants and the thickness are needed for consideration. In this paper, the SAW phase velocities have been calculated theoretically for ST-X Quartz/Gold structure under different normalized thickness configurations.
Optimal design of surface wave emats for enhancing their ultrasonic signal strength
Authors: Kang Lei , Wang Shujuan , Li Zhichao , Zhai Guofu
Published: April 2012

The strength of the ultrasonic signal transmitted by electromagnetic acoustic transducers (EMATs) is very weak, which severely confines the further expansion of the application scope of EMATs. To solve this problem, the features of the transmission process of a surface wave EMAT are studied based on a 3-D model. Simulation reveals that performances of the transducer are significantly affected by its parameters. Aiming at enhancing the strength of the ultrasonic signal, this paper investigates the influence of EMAT parameters on the ultrasound field of the transducer and accomplishes the optimal design of the EMAT by utilizing orthogonal test method. Experiments indicate that after optimization, the received signal of the EMAT has increased by 162.3%, which suggests the ultrasonic signal of EMATs can be effectively enhanced by utilizing orthogonal test method based on the 3-D EMAT model. Acknoweledgement: Supported by “the Fundamental Research Funds for Central Universities” (Grant No. HIT. NSRIF. 2012008)
Numerical research on the flow characteristics of confined sonic and supersonic air-modulated speakers
Authors: Yun Zhao , Xinwu Zeng , Changchao Gong
Published: April 2012

Air-modulated speaker is one of the most famous high-intensity sources. Sound waves with SPL above 160 dB are generated by the modulation of sonic air flow through a time-varying valve. To overcome the source saturation at high chamber pressures, the performance and flow characteristics of a new design, in which the flow speed increases from sonic to supersonic by a converging and diverging nozzle, were investigated. Based on the analytical results from the widely used quasi-steady model, the source level improvement was verified for the same pneumatic power. The SPL increment of more than 5 dB is obtained at Mach number 2.75. The transient flow inside the source was simulated using a recent developed numerical model in which the compressible flow is governed by the Navier-Stokes equation and the valve movement is modeled by the dynamic mesh method. Compared with the ordinary sonic flow modulation, the source mechanism on the supersonic case has shown several distinct features: the effect of the flow-acoustic coupling could not be neglected; some complex phenomena such as shock wave formation and propagation arise in the transient flow inside the nozzle; the establishment of supersonic flow and the resulting improvement are related to the valve modulation frequency.
On the adjoint problem in duct acoustics and its solution by the time domain wave packet method
Authors: Hu Fang , Kocaogul Ibrahim , Li Xiaodong
Published: April 2012

The Time Domain Wave Packet (TDWP) method has the advantage of obtaining radiated sound by a given duct mode at all frequencies in one computation. It also makes possible the separation of the acoustic and shear flow instability waves. In this paper, the TDWP method will be applied to the adjoint duct acoustics problem. As a microphone records the sound radiated by all duct modes combined, the adjoint approach has the advantage of obtaining the relative mode strengths of all the propagating modes at all frequencies in one computation. The novelty of the paper is on the formulation of adjoint equations in time domain and the numerical solution using the TDWP method. The theoretical formulation of the duct adjoint problem and derivation of various reciprocal relations are presented. The adjoint equations are then solved numerically in reversed time by the TDWP method, in which a point source in the far field is enforced with a Broadband Acoustic Test Pulse time function. PML absorbing boundary conditions for the adjoint equations are also discussed. By an FFT, the relative strengths of all duct modes at all frequencies to the far field point are computed at once.
A robust acoustic feedback suppression algorithm based on spectral subtraction
Authors: Yang Feiran , Wu Ming , Ji Peifeng , Yang Jun
Published: April 2012

Acoustic feedback is caused by the coupling between the loudspeaker and the microphone. In this paper a new acoustic feedback suppression (AFS) method is proposed to address this problem. The cross-spectrum of the loudspeaker and the microphone signal and power spectrum of the loudspeaker signal are estimated by the recursive averaging of periodograms. Then, the magnitude spectrum of the acoustic feedback path is obtained by dividing the cross-spectrum by the power spectrum of the input signal. The spectrum of the acoustic feedback signal is calculated using the above magnitude spectrum. Moreover, the spectral modification technique originally proposed for speech enhancement is adopted to remove the acoustic feedback from the microphone signal. The proposed algorithm is less sensitive to the acoustic feedback path changes than the existing adaptive filter approach. Simulation results demonstrate the effectiveness and the robustness of the new method.
A novel decentralized velocity feedback strategy of plate vibrations using piezoelectric patch actuators
Authors: Cao Yin , Sun Hongling , Li Xiaodong , Tian Jing
Published: April 2012

Previous studies have shown that, similar feedback gains are required to minimize the kinetic energy of a plate and to maximize the absorbed energy by each force actuator in a wide-band excitation. The energy absorption of a force actuator is easy to measure, but it is hard to get the energy absorption by a moment actuator such as a piezoelectric patch actuator which needs the angular velocity at the mounting point of the actuator. In this paper, the energy absorption of piezoelectric patch actuators for decentralized velocity feedback control of plate vibrations is investigated numerically. A kind of virtual energy absorption of the piezoelectric patch actuator is proposed, which is the multiplication of the torque produced by the piezoelectric patch actuator and the velocity at the mounting point of the actuator. Numerical investigations are performed to explore the relationship of the virtual energy absorption by the piezoelectric patch actuators and the kinetic energy of the structure. The results show that maximizing the wide-band virtual energy absorption is nearly equivalent to minimizing the kinetic energy.
Tranquility analysis by soundwalks in Pisa's green areas
Authors: Licitra Gaetano , Chiari Claudia , Menichini Irene , Ascari Elena
Published: April 2012

Identification and analysis of main quiet areas in Pisa agglomeration has been carried out by the University of Pisa and Tuscany Environmental Protection Agency (ARPAT). According to suggestions given by the Environmental Noise Directive (END) 2002/49/CE, authors measured noise levels (using different indicators) and perceived tranquility of users at four different park/green areas in the city (Monumental site – Miracle square, Botanic Garden, Riverside park “Le Piagge”, City Park “Giardino Scotto”). In order to analyze tranquility, measurements and analysis on site has been carried out including noise levels acquisition, video recording, binaural audio acquisition and users surveys. At first some different methodologies has been tested and compared to identify most suitable measurement instruments and analysis procedures. The survey, based on similar studies carried out by G. Watts in UK, intended to identify most annoying sources and subjective users impression of the park. In the same sites, soundwalks have been recorded to allow a laboratory test to obtain a second evaluation of the park (video and binaural audio reproduction). First results highlighted the negative effects on objective and subjective evaluation of tranquility done by different type of transport ( trains, cars, aircraft) in Pisa's parks.
The Swedish soundscape-quality protocol
Authors: Axelsson Ãsten , Nilsson Mats E. , Berglund Birgitta
Published: April 2012

The Swedish Soundscape-Quality Protocol was developed to help non-experts (e.g., officials working for municipalities rather than soundscape researchers) to make informed, accurate measurements of soundscape quality. The Protocol has hitherto been used in England, France, Italy, Spain, Sweden, and The Netherlands; a Korean version is being developed. Based on field studies – soundwalks in urban residential areas, recreational areas, and parks – the present paper reports on the psychometric properties of the scales of the Protocol. Participants were residents, or visitors to the areas and their results support the reliability and validity of the scales in the Protocol. Because high acoustic quality has a greater effect in visually attractive than in visually poor areas, the Swedish Soundscape-Quality Protocol includes scales for cross-sensory tabulation. These are sound source identification – sounds from humans, nature and technology – attribute scales (e.g., eventful, exciting, pleasant, and calm), overall soundscape quality, and concomitant visual impressions. In brief, the Swedish Soundscape-Quality Protocol is an easy to use and practical tool for measuring soundscape quality. It has the potential to help operationalize how soundscapes can be measured in quiet areas to meet a future guideline value of the World Health Organization.
Laser ultrasonic inspection for water transport through membrane in a PEM fuel cell
Authors: Yin Ching-Chung , Wu Min-Hsiu , Liu Yu-Shyan
Published: April 2012

The performance of a proton exchange membrane fuel cell (PEMFC) was reported to be strongly influenced by water management. This work presents laser ultrasonic inspection for in-situ detection of water across the membrane electrode assembly (MEA). A laser induced grating or an alternative interdigitated piezoelectric fiber composite based acoustic wave transducer was placed on an extension of the flow field plate to launch fixed-wavelength plate waves propagating parallel to the flow channels. The acoustic waves passing through the flow channels underlain by the moist MEA were detected at the opposite end using knife-edge technique. The phase velocities of the acoustic guided waves do not change much between both moist and moist-free states. The insight of water transport could be gained through the excess attenuation of guided waves. The synthetic aperture focusing technique was utilized to establish clear B-mode images of water transport through the membrane.
Laser ultrasound technique for determine the guided waves propagation in layered medium with temperature gradients
Authors: Tseng Sheng-Po , Yang Che-Hua
Published: April 2012

This paper focuses on the modeling and measurements on the propagation behaviors of guided waves propagating along plate-like wave guides with temperature gradients along their thickness direction. A theoretical model based on a recursive asymptotic stiffness matrix method (RASM) with recursion computation algorism is used to provide numerical calculations for the dispersion relations. A laser ultrasound technique is used to measure the dispersion relations. For all the experiments, the measured dispersion curves show good agreement with the theoretical calculation, indicating the reliabilities in the measurement and modeling. This study is useful to thermometry in different temperature gradient environment in a non-contact and non-destructive ways. This paper demonstrates a procedure employing a LUT introduced the dispersion curves for the steel plate with different temperature distribution. In the spectra, the higher mode dispersion curve could be observed more significant phase velocity difference by LUT system. The phenomenon of temperature gradient is more sensitive for the higher mode. This method is proved to have better accuracy for plate-like structures with lower thermal conductivity. However, applications for structures with higher thermal conductivity will be also applicable while the measurement accuracy is further improved.
All-optical probing of laser-induced modulation of crack parameters by surface Rayleigh and surface skimming longitudinal bulk acoustic pulses
Authors: NI Chen-Yin , Chigarev Nikolay , Tournat Vincent , Delorme Nicolas , Shen Zhong-Hua , Gusev Vitalyi
Published: April 2012

All-optical monitoring of the nonlinear motion of surface-breaking cracks is reported. Crack closing is induced by quasi-continuous laser heating, while Rayleigh acoustic pulses and skimming longitudinal surface acoustic pulses are also generated and detected by lasers. By exploiting the strong dependence of the acoustic pulses reflection and transmission efficiency on the state – open or closed – of the contacts between crack faces, the parametric modulation of ultrasonic pulses is achieved. It is demonstrated that detection of the parametric modulation of the reflected and transmitted skimming longitudinal waves and Rayleigh waves mode converted by the crack from skimming longitudinal waves is a sensitive technique for the evaluation of crack modifications and local closure. It is observed that skimming longitudinal waves can be more sensitive to crack motion than Rayleigh waves, which are probing the crack motion without mode-conversion. In comparison with an all-optical frequency-domain technique, 1 the time-domain technique is potentially faster for the imaging applications. This research is supported by the grant ANR-10-BLAN-092302 and a post-doctoral fellowship from the Région des Pays de la Loire for Dr. C. Ni. Also, the support for travelling and participation to the conference from China Postdoctoral Science Foundation (No. 20110491409) is acknowledged. 1 S. Mezil, N. Chigarev, V. Tournat, V. Gusev, “All-optical probing of the nonlinear acoustic of a crack”, Opt. Lett. 36, 3449-3451 (2011).
Theoretical and experimental study of wedge wave mode transformation and energy attenuation
Authors: Jia Jing , Shen Zhonghua , Yuan Ling , Ni Xiaowu
Published: April 2012

Wedge Waves are guided acoustic waves propagating along the tip of wedge. In this paper, both theoretical and experimental work are done to research the wedge wave modes transformation and energy attenuation. Firstly, finite-element method (FEM) was used to simulate the laser induced wedge waves and different orders of wedge wave modes and the mode transformation process were clearly observed. Then pulsed laser excitation and optical deflection beam method for detection was built to investigate these characteristics experimentally. Plenty of wedge waves at different locations were recorded by scanning the excitation laser along the wedge tip, and different orders of wedge waves were observed. By fixing the distance between the excitation and detection position and scanning the samples along the direction normal to the wedge tip, the modes transformation process was obtained. Finally, theoretical solution by the method of potentials is used to explain the principle of mode transformation and energy attenuation. By integrating the power spectra of the acoustic waves, the energy distribution of these acoustic waves is calculated. Both theoretical and experimental results were found that the energy of acoustic waves decrease exponentially to a steady energy of Rayleigh wave within the main wavelength range.
High quality photoacoustic tomography in scattering biological tissue
Authors: Wu Dan , Tao Chao , Liu Xiaojun
Published: April 2012

Photoacoustic tomography is an emerging biomedical imaging method, which has a high image contrast and good spatial resolution in deep tissues. Because of these merits, PAT has broad applications in biomedical imaging. However, acoustic scattering is unavoidable in tissue with inhomogeneous acoustic properties. Acoustic scattering brings a challenge for the applications of PAT. A new PAT method is presented to obtain the photoacoustic images in scattering tissue. This method is based on the time-reversal invariance of acoustic wave propagation during the acoustic scattering process. Both numerical simulations and experiments are used to validate this method. The results show that the proposed method can provide better PAT images in scattering tissues than the traditional photoacoustic tomography. Therefore, this method could serve as an alternative for imaging inhomogeneous biological tissues with acoustic scattering.
Design of wavelet frequency-division based signal processing algorithm for an implantable middle ear hearing device
Authors: Tian Jiabin , Rao Zhushi , Ta Na
Published: April 2012

A signal processing algorithm was designed based on wavelet frequency division for an implantable middle ear hearing device(IMEHD) to make the piezoelectric actuator's vibration simulate normal middle ear transfer function. Firstly, the input digital signals were divided into seventeen bands based on Bark frequency scale using wavelet transform. Then, the assigned band gains were applied corresponding to middle ear transfer function. Finally, the algorithm was implemented and verified the performance through an experiment. The satisfactory agreements between the output of the piezoelectric stack and normal middle ear transfer function indicate that the designed algorithm is feasible. This work is supported by the National Natural Science Foundation of China (Grant No. 11072145 and No. 81170910) and the Science and Technology Commission of Shanghai Municipality Foundation (No. 08JC1404700). We are also thankful to Dr S. K. Yin, Department of Otolaryngology, Shanghai Sixth People's Hospital, China, for the facilities and encouragement given.
Study of ocean ambient noise characteristics based on vector signal processing of acoustic
Authors: Li Jialiang , Lin Jianheng , Yi Xuejuan
Published: April 2012

With the development of technology, vector sensors are more and more applied in underwater acoustics measurements. As one of the signal processing methods, vector signal processing method based on acoustic energy flow is gradually developed. Methods based on acoustic energy flow overcome some inherent shortcomings of traditional pressure signal processing methods and increase processing gain and DOA estimation accuracy. Methods based on acoustic energy flow have been verified to be practically useful by trials. The existing vector sensor frequency measurement model is modified in this paper. The anisotropy and other characteristics of ocean ambient noise are studied in the paper based on vector signal processing of acoustic energy flow, and the simulation results are reasonable.
Bispectrum and cross-bispectrum feature extraction based on vector hydrophone
Authors: Zhang Lanyue , Wang Yang , Yang Desen
Published: April 2012

A vector hydrophone co-locating and simultaneously measures pressure and particle, which obtains more entire information of acoustic field than pressure hydrophone, so that to render the more methods of signal processing. Bispectrum is a kind of high order spectrum analysis method, which impose a lot of information that two order statistics can't obtian. In this paper, the algorithms of bispectrum was researched based on vector hydrophone to obtain the feature of acoustic signals. Bispectrum of particle velocity and cross-bispectrum of pressure and particle velocity were analyzed. Different methods were used to compress the information measured of bispectrum and cross-bispectrum to get the signal feature quickly and effectively. The experiment was carried on based on theoretical research, and the bispectrum and cross-bispectrum were used to extract the features of radiation noise of two kinds of acoustic targets, and the pressure and vector features were obtiand. The researched results showed that Gaussian noise and no-correlated noise by bispectrum and cross-bispectrum could be compressed. The more information of sound field of targets was obtained by vector hydrophone and the distinguishing probability could be improved.
Fast prediction of underwater sound scattering based on Fourier diffraction theorem with modified born approximation
Authors: Zhang Peizhen , Wang Shuozhong , Wang Runtian , Chen Yunfei , Wang Luxian
Published: April 2012

It has been shown in a previous work that the directional pattern of underwater sound scattered from an object insonified by an incident plane wave can be efficiently predicted based on a reversal of diffraction tomography. The method uses the Fourier diffraction theorem with the first order Born approximation. In this paper, modification to the Born approximation is proposed by taking into account the difference in acoustic impedance between the object and water. The impedance difference was ignored in the original derivation of the Fourier diffraction theorem, leading to inaccuracy in the computation. In a two-dimensional case, the proposed modification causes a shift of a circle in the 2D Fourier transform domain, from which spectral samples are taken to give a more accurate generalized projection in the sound field. This leads to improved prediction of acoustic scattering. Extension to 3D is straightforward. The Fourier diffraction theorem with modified Born approximation is applied to produce far-field directional patterns of scattered sounds from several objects of different shapes. Comparison with the original method shows effectiveness of the proposed method. The work was supported by the Natural Science Foundation of China under the Grant No. 61071187.
Performance simulation and implementation of gold sequences in underwater acoustic CDMA
Authors: Tao Yi , Zou Zheguang , Xu Xiaomei
Published: April 2012

Underwater Acoustic Network (UAN) is becoming a hotter research area of underwater acoustic communication recently. Underwater acoustic channels are restricted by narrow bandwidth, long delay and high ambient noise, so Code Division Multiple Access (CDMA) appears to be a promising multiple access technique for UAN. However, due to low underwater data rate, only short pseudo-random sequences are available. Comparing to m sequences, Gold sequences with the same length show the same cross-correlation properties but enable networks to support more users. This paper examines the performance of short Gold sequence in underwater acoustic channel, to determine whether it is a good choice for UAN. Specifically, the paper makes contributions on the following fronts: (1) Based on a Rayleigh fading shallow water acoustic channel model, the performance of bit error rate (BER) of a 63-bit Gold-sequence up to 65 users CDMA is simulated and evaluated in MATLAB platform. (2) Underwater CDMA nodes using Gold-sequence Direct Sequence Spread Spectrum (DSSS) modulation is implemented with National Instruments' new embedded device (cRIO9076). An experiment at sea will be conducted at Xiamen Port to confirm the better performance of short Gold sequences in underwater CDMA.
Deployment analysis of underwater acoustic wireless sensor networks
Authors: Li Xia , Fang Shiliang
Published: April 2012

In this paper, underwater sensor nodes and gateway nodes deployment strategies for two-dimensional communication architecture in Underwater Acoustic Wireless Sensor Networks(UWSNs) are proposed. In the sensor nodes deployment strategy, underwater sensor nodes are deployed in two rows along the coastline, which is of complete coverage and connectivity, localization available and scalable. In the gateway deployment strategy, the gateway deployment is modelled as an optimization problem, by finding the locations of underwater gateway nodes required to achieve a given design objective, which can be minimal expected delay and minimal expected energy consumption. The OPNET network simulator is used to measure the performance of the strategies we studied. Acknowledgment of support: This work was supported by the key laboratory of underwater acoustic signal processing of ministry of education.
Robust wideband adaptive beamforming using waveguide invariant focusing method
Authors: Jiang Biao
Published: April 2012

The waveguide invariant describing the dispersive propagation in underwater environment can provide useful information for signal processing. In this paper, waveguide invariant focusing is exploited to preprocess the received horizontal array signal, such that the moving target is aligned in a single rank-one signal subspace over the bandwidth, results a reduction of the number of the snapshots necessary for the adaptive beamforming, and the diagonal loading is optimized using the robust Capon method to further improve the robustness. Numerical results show that the proposed method can improve the detection performance with limited observation time. Moreover, passive ranging is accomplished when the beamforming output achieves the maximum over a scanned target range limit.
Experimental study for short-range acoustic field fluctuations and time-space related characteristics in shallow
Authors: Ma ZhongCheng , Cao QingGang
Published: April 2012

Short-range sound propagation characteristic in shallow is an important basis for the underwater test parameters settings, and it is also an important basis for the data summarized and analysis. The interference of the interface reflection and the direct wave in water makes shallow water acoustic show complex time-space variability. By a series of experimental design, fluctuations and time-space characteristics variation in short-range sound field were analysis. Statistical characteristics of the sound field fluctuations and variability characteristics were obtained.
The effect on the propagation in shallow water with a mega-ripple
Authors: Cho Sungho , Kang Donhyug , Lee Young-Kuk , Choi Jee Woong
Published: April 2012

It is well known that acoustic propagation in shallow water is greatly influenced by an interaction of reflection, transmission, and scattering with the boundary condition. Especially, acoustic propagation of low frequency is depended on the structures of seabed and sub-botttom layer. In this study, acoustic propagations for low-frequency in shallow water were measured from field experiments under the condition of mega-ripple. The study area formed various mega-ripple caused by strong tidal current. Precisely bathymetry and sub-bottom structure were obtained from multi-beam and sparker system. In the experiments, acoustic source and receiver for propagation measurement were single bulb system and multiple self recording hydrophone system, respectively. From the measurement, we described characteristics of acoustic transmission for low frequency around the mega ripple regions. [Supported by KORDI (Korea Ocean Research & Development Institute)]
Research on waveform design of sinusoidal frequency-modulated to extract target phase feature
Authors: Yongqing Wu
Published: April 2012

The majority of active sonar systems to detect and classify a target based on the amplitude of the received echo strength or the induced Doppler shift. However, additional classification information is available from the phase shift introduced by some targets as a result of the acoustic boundary conditions. In this paper, waveform design of sinusoidal frequency-modulated (SFM) based on the use of sub-band correlators is presented for measuring the phase shifts associated with certain stationary and moving targets when insonified by broadband transmissions. With the aim of providing improved range resolution, it maintains the amplitude of the transmission constant to maximize energy efficiency and compatibility with existing nonlinear power amplifiers. And the influences on target echo phase measurement are analyzed from reverberation gain achievable with broadband, Doppler sensitive SFM transmissions in littoral waters. At last, field trial results are given for a mine-like classification sonar system and a forward-looking sonar system designed for operation near the sea surface.
Analysis of influence of line array beamforming on the target modulation feature
Authors: Luo Xinwei
Published: April 2012

In the line array sonar, the target signal was obtained after beamforming processing. The beamforming processing could improve the Signal to Noise Ratio (SNR) by using array signal's spatial processing gain. But the distortion would be brought in signal characteristics under non-ideal conditions during line array beamforming in practical application, which increased the difficulty of target characteristics extraction. As an important basis for target classification and recognition, the performance of modulation characteristics detection and extraction is affected by SNR, signal bandwidth, modulation depth and other factors. In this paper, the influence of the time delay error on target characteristics was analyzed based on the conventional beamforming of linear array. And then a method with the combination of theroy and simulation is proposed to analyze the influence of plane wave assumption, azimuth estimation error and disturbance of array shape on modulation characteristics.
Simulation of time reversed acoustic inversion in shallow water
Authors: Choi Bok Kyoung , Kim Byoung-Nam , Kim Bong-Chae , Jung Seom-Kyu , Kang Donhyug
Published: April 2012

For simulation to time reversed acoustic inversion in any enclosure system as shallow water, we must know the impulse response of the system. Throughout this process we can reproduce an original signal at focal point by convolution of time reversed inversion. To apply this TRA simulation to shallow water environment, after extracting the impulse response about simple condition as shallow water, we analyze the acoustic focusing by TRA inversion. In result, the spatial focusing and time signal patterns can be built by TRA simulation for shallow water condition. [Supported by KORDI (Korea Ocean Research & Development Institute)]
Time-reversal passive localization for underwater radiated noise source
Authors: An Liang , Chen Lijun , Fang Shiliang
Published: April 2012

Time reversal (TR) is a technique of passive acoustical sources localization using a time reversal mirror (TRM) and is especially useful in multi-path environments. TR is commonly used to localize noise sources in aero acoustics and in many cases pulsed waveforms are used. A TR passive localization method for long duration waveforms was presented in this paper. The TR is applied to actual radiated noise recorded by only one hydrophone to estimate the source distance and depth. Compared to a standard time reversal approach, the proposed technique is based on the virtual time reversal mirror which can match the acoustic channel automatically and leads to an adaptive spatial focusing and temporal compressing as the conventional TRM. The processing result of simulated data and experiment data show this method could mitigate the multi-path interference on passive localization.
Measurement of propeller-induced cavitation noise for ship identification
Authors: Widjiati Endang , Djatmiko Eko Budi , Wardhana Wisnu , Wirawan
Published: April 2012

Acoustic cavitation noise caused by propeller is used in many underwater applications as one of the ships noise signatures. This paper reports characterization process done by measuring the cavitation noise generated by a propeller in a cavitation tunnel. The cavitation tunnel used for the measurement is of the K16B type belonging to the Indonesian Hydrodynamic Laboratory, Surabaya, Indonesia. The experiment is done using a B-series four-blade bronze propeller (diameter 23cm) using a hydrophone placed in the tunnel at window section (60x90)cm2 of the measurement section (400x85x85)cm3. Some of the solutions to get accurate and reliable measurement results include calibration measurement and minimizing acoustic noise system and environment. Preliminary process has been done to analyse the characteristics of the measurement results in the time-frequency domain, with the objective being to detect when and which type of cavitation noise occurs in any kind of condition. Measurement outcomes in the form of acoustic data signals are obtained in different conditions by varying the water pressure, flow velocity and propeller speed rotation.
Underwater signals' characteristics of power spectrum based on data mining
Authors: Wang Qingfu , Du Shuanping , Ge Huiliang
Published: April 2012

Power spectrum was always utilized for underwater signal recognition. Distance based data mining was applied to feature extraction of power spectrum. The distances within and between classes were first calculated, then, the weight for each frequency bin was get according to its discrimination, finally, the weighted power spectrum was used to feature extraction and classification. All kinds of signals were generated with underwater acoustic propagation model through wave guide. Experiments and tests were conducted and performance of the method was verified.
Research on the reverberation measuring technique of underwater directional sound sources
Authors: Chi Lee , Dajing Shang , Lin Zhang
Published: April 2012

The radiated noise of underwater directional sound sources was generally measured in the corresponding ocean environmental condition. Influenced by the ocean environmental noise, the reflection of ocean bottom and ocean surface, it is very difficult to get the radiated sound power of underwater directional sound sources. Reverberation method used in the Architectural acoustics was taken in this paper for measuring the radiated sound power of underwater directional sound sources. It has been used in the radiated sound power measurement of underwater spherical sound sources, but never been used in underwater directional sound sources. The reverberant theoretical formula of directional sound sources was derived by introducing the directivity factor. The radiated sound power of directional sound sources such as dipole and the two same-phase sphere was measured. The measuring and analyzing results show that the reverberant radius of directional sound sources is related to directivity factor. With the directivity factor turns strong, the reverberant radius will become larger but the reverberant controlled area will become smaller, so the measurement range of spatial averaging will become small. The radiated sound power of directional sound sources such as dipole and two same-phase spheres can be measured by large-range of spatial averaging. The measurement techniques can apply to measure the radiated sound power of underwater complex sound sources.
45 years of spatial impression
Authors: Barron Mike
Published: April 2012

The story of spatial hearing has a certain circularity about it. To date, two separate spatial effects have been identified. The first effect is that created by a reverberant field in an enclosure, which is particularly obvious in a cathedral-type space. A second spatial effect was proposed 45 years ago linked to early lateral reflections. These two are now known as Listener Envelopment (LEV) and Source Broadening (or Apparent Source Width, ASW). Interesting research had been conducted into “Raumlichkeit” in Germany during the '60s. But following the revelations by Marshall, interest in the effects of early lateral reflections overshadowed interest in what is now called LEV. Sound level also contributes to the magnitude of these spatial effects. Measures have been proposed for both ASW and LEV, which include both reflection directional distribution and sound level. The paper will summarise the history of spatial impression and what implications it has for concert hall design. Historical reference: Applied Acoustics (2001) 62, 91-108 and 185-202.
The preference is driven by intimacy—which is furthermore provided by lateral reflections
Authors: Lokki Tapio , Kuusinen Antti , Pätynen Jukka , Tervo Sakari
Published: April 2012

Nine concert halls were measured with a calibrated loudspeaker orchestra which eliminates all variables except the acoustics of the halls. The loudspeaker orchestra was located on the stage and the microphone array at 12 m distance from it in the audience area. Subjective data including preference ratings of 17 assessors and subjective sensory profiles were collected with the individual vocabulary profiling process. The objective room acoustic parameters were also calculated. All data were analyzed in a common factorial space with the hierarchical multiple factor analysis and preference mapping. The results show that the preference of assessors is divided into two groups and the factors influencing the preference can be explained with sensory profiles. However, the most interesting result is that the overall preference is driven by the intimacy, i.e., how close to the listener the sound is perceived by the listener. None of the current objective parameters could explain the perceived intimacy. The presentation will explain that the perceived distance, thus intimacy, is mainly affected by the seat-dip effect and the number of early lateral reflections, in addition to overall loudness particularly at low frequencies.
Why the conventional RT is not applicable for testing the acoustical quality of unroofed theatres
Authors: Mo Fangshuo , Wang Jiqing
Published: April 2012

The rate of sound decay in an enclosed space has been used as the measure for assessing the reverbrance initiated by Sabine a century ago. Such evaluation is based on the energy consideration and can be tested by a monophonic receiving system. But, it is questionable for reverberance evaluation of unroofed spaces, such as, traditional Chinese courtyard theatres or Greek/Roman amphitheatres. It can be seen that even the decay rates of the enclosed and unroofed spaces are similar, but their reflectograms show significant difference due to the absence of reflections from top in the unroofed space. The spatial distributions of the reflections toward the listeners for both spaces are also very different. Series of subjective comparison tests of synthetic room impulse responses through stereo-system (pickup and playback) in our laboratory also showed that the reverberance in an unroofed space was quite different from the result through mono-system as in the conventional way following ISO 3382. However, subjective tests through mono-system for enclosed and unroofed spaces with similar decay rate do not show significant difference of reverbrance. Therefore, in an unroofed theatre, the factor of spatial information of the reflections should not be neglected for reverbrance criteria.