Complex Sound Intensity Research Articles

Precision device for measuring the three dimensional spectral intensity

On the basis of processing algorithms developed by the same authors in a companion paper [“On the general connection between wave impedance and sound intensity”, 173rd Meeting of the Acoustical Society of America and the 8th Forum Acusticum, Boston MA, 25-29 June 2017] where the equation between the complex sound intensity and the specific acoustic impedance/admittance has been stated and numerically validated in general form, the block diagram of a possible device for precision measurement of 3D spectral intensity is proposed here. In order to test its functionality, some measurements have been carried out, inside a tube of 28x28 cm2 square section and 4 m long, which was terminated with panels of different materials. Measurements have been carried out at different positions along the tube's axis by means of a 3D pressure-velocity probe below and above the cutoff frequency of the tube so to include also the effects of transversal modes. Preliminary results of such measurements are reported and discussed briefly here.

On the general connection between wave impedance and sound intensity

This paper presents the generalization to non-monochromatic non-monodimensional fields of the equation linking the complex sound intensity to the wave impedance/admittance already introduced with a different form in [D. Stanzial and C. E. Graffigna “On the connection between wave impedance, sound intensity and kinetic energy in monochromatic fields,” accepted for publication on POMA, Dec. 23, 2016]. Computer simulations have been now carried out, both for wave impedance and admittance, in quasi-stationary bi-dimensional waves fields with different reflection coefficients and spectral compositions. It turns out that the equation is validated in all space points of the sound field for each spectral component. This allows primarily to calculate the active intensity vector field as the vector sum of all vector fields obtained as the spectral components of the active intensity and therefore to determine the reactive intensity magnitude by simply subtracting the modulus of the so obtained active intensity from scalar field of the apparent intensity. This grand result will allow to develop a precision device for measuring 3D sound intensity and its active and reactive spectral components.

On holographic reconstruction without reference: Application to machinery noise and comparison with multi-reference holography approach

This article presents the implementation and application, to two complex machines, of two holography methods called CIBNAH (Complex Intensity Based Near-field Acoustic Holography) and MRNAH (Multi Reference Near-field Acoustic Holography) based on residual spectra. The first is a newly developed method that uses complex sound intensity as its basis and hence bypasses the need for reference signals. Here, several approaches are presented to validate both methods and to investigate each method’s advantages and limitations.

Complex acoustic intensity with deep receiver in the direct-arrival zone in deep water and sound-ray-arrival-angle estimation

In the direct-arrival zone in deep water, the sound ray arrival angle is one of the most important properties of the sound field. However, it is complicated to estimate the arrival angle only by using the information about the sound pressure. Vector sensors have significant advantages in direction-of-arrival estimation, and the acoustic energy flux detection is one of the most important estimation methods. In this paper, the properties of complex acoustic intensity in the direct-arrival zone in deep water are analyzed, and the arrival angles of sound rays are estimated with the complex acoustic intensity extracted from the experimental data. Firstly, the expressions of horizontal particle velocity, vertical particle velocity and complex sound intensity are provided based on the ray theory. It is shown that the amplitudes of the horizontal and vertical particle velocities and the components of the complex sound intensity are closely related to the sound ray arrival angle. The larger the sound ray arrival angle, the greater the vertical particle velocity and the vertical component of the complex sound intensity are, but the weaker the horizontal particle velocity and the horizontal component of the complex sound intensity are. Secondly, for the direct-arrival zone of the sound field generated by a shallow source in deep water, the properties of the complex sound intensity with deep receiver are analyzed based on the sound ray arrival structure. The theoretical and simulation results show that the arrival angles of the sound rays can be estimated with the complex sound intensities of pulses received by a deep receiver. The mean arrival angles of the direct ray and the surface-reflected ray can be estimated with the complex sound intensities of the pulses of the direct-arrival wave and the surface-reflected wave. The mean arrival angles of the bottom-reflected ray and the surface-reflected-bottom-reflected ray can be estimated with the complex sound intensities of the pulses of the bottom-reflected wave and the surface-reflected-bottom-reflected wave. The angle obtained with the complex sound intensity of the total field comprised of all sound rays is approximately equal to the mean arrival angles of the direct ray and the surfaced-reflected ray. Thirdly, the validity of the arrival angle estimation with the complex sound intensity is verified by the experimental data. During a deep water experiment conducted in 2014, a vector sensor was placed at a depth of 3146 m to receive the experimental signals. Within the range of 17 km, the vector sensor received the direct ray from the sound source towed at about 140 m. By using the pulses of the direct-arrival wave and the surface-reflected wave received by the vector sensor, the mean arrival angles of the direct rays and the surface-reflected rays are estimated. It is shown that the estimated arrival angles are consistent with the theoretical results.

Arthroplastie totale d’épaule inversée par prothèse sans tige humérale TESS

The modal expansion method has been used to formulate expressions for real and imaginary parts of the complex sound intensity inside enclosures. Based on theoretical results, the computer program has been developed to simulate the acoustic intensity vector field inside the irregular room whose shape resembles the capital letter L. Calculation results have shown that a low-frequency distribution of the acoustic intensity is strongly influenced by the modal localization and the characteristic objects in the active intensity field are energy vortices and saddle points positioned irregularly inside the room. It was found that for small sound damping the vortex centers lie exactly on the lines corresponding to zeros of the eigenfunction for a dominant mode. An increase in a sound attenuation results in the change of vortex positions and can cause the formation of new vortices. Finally, an influence of the wall impedance on the quantitative relation between the acoustic and reactive intensities was studied and it was concluded that for very small sound damping the behavior of the sound intensity is basically only oscillatory.

The Application of Single Vector Sensor in Direction Tracing of Water-Entry Object

Water-entry signal was important to broadcast the water-entry object. The vector sensor could gain the pressure and particle velocity signal, so the azimuth angle of water-entry signal could be estimated by single vector sensor. The complex sound intensity method was applied in vector signal processing in azimuth estimation. The estimated deviation in different SNR was give out via simulating experiment. The method was used in the experiment on the lake and was proved to be effective.

Direction Estimation of Water-Entry Point with Single Vector Sensor

The water-entry point was the first information collecting point on detecting an object which was dropped into water from air. Single vector sensor could estimate the direction of the water-entry point with its sound field pressure and particle velocity signals. The complex sound intensity method was applied in vector signal processing. The simulating experiment and the practical experiment on the lake were all based on the estimation deviation of the theory on different SNR. By processing the devided signal in time domain with this theory, the water-entry object could be tracing timely.

Analytical and numerical study of acoustic intensity field in irregularly shaped room

The modal expansion method has been used to formulate expressions for real and imaginary parts of the complex sound intensity inside enclosures. Based on theoretical results, the computer program has been developed to simulate the acoustic intensity vector field inside the irregular room whose shape resembles the capital letter L. Calculation results have shown that a low-frequency distribution of the acoustic intensity is strongly influenced by the modal localization and the characteristic objects in the active intensity field are energy vortices and saddle points positioned irregularly inside the room. It was found that for small sound damping the vortex centers lie exactly on the lines corresponding to zeros of the eigenfunction for a dominant mode. An increase in a sound attenuation results in the change of vortex positions and can cause the formation of new vortices. Finally, an influence of the wall impedance on the quantitative relation between the acoustic and reactive intensities was studied and it was concluded that for very small sound damping the behavior of the sound intensity is basically only oscillatory.

Active average intensity based on single vector sensor

Code divided multiple access underwater communication based on single vector sensor is studied in this paper. The most common methods to estimate azimuth with self-directivity of single vector sensor are average sound intensity method and complex sound intensity method, however, for the same frequency band multi-users, theoretical limitation for these methods is only two users.Spread spectrum communication is featured with strong anti-multipath, anti-interference, secret-keeping and communication web composing ability. Active average intensity method, which measures azimuths of multi-users simultaneously with the excellent correlative characteristics of pseudo-random code in spread spectrum communication, is proposed in this paper. Simulation and experiment for same frequency band spread spectrum multi-user communication testify the feasibility and utility of active average sound intensity method. With the estimated azimuth, vector combination can be generated to adjust the directivity of vector sensor, achieve multi-user beam communication, inhibit multi-path interference, and enhance processing gain and lower error rate. Key words: underwater acoustic communication; CDMA; single vector sensor; active acoustic intensity average

Code divided multiple access underwater acoustic communication based on active acoustic intensity average

Code divided multiple access (CDMA) underwater communication based on single vector sensor is studied in this paper. The most common methods to estimate azimuth with self-directivity of single vector sensor are average sound intensity method and complex sound intensity method, however, for the same frequency band multi-users, these methods are limited to the measurement of azimuths only for two users at the same time theoretically. An active average intensity method, which measures the azimuths of multi-users simultaneously with the excellent correlative characteristics of pseudo-random code in spread spectrum communication, is proposed in this paper. With the estimated azimuth, vector combination can be generated to adjust the directivity of vector sensor, achieve multi-user beam communication, inhibit multi-path interference, and enhance processing gain and lower error rate. Simulation and experiment for same frequency band spread spectrum multi-user communication testify the feasibility and utility of active average sound intensity method.

Variational principle and energy integrals in a complex sound intensity field

The information about sound energy distribution and transfer is contained in a complex sound intensity field. The fundamental variables are the auto-spectrum and the phase of sound pressure. From the point of view of a differential, applying the mechanical laws, the differential equations expressing change of the variables are given. From the point of view of an energy integral, applying the variational method, a variational principle for the variables in a complex sound intensity field is established. The paper also discusses energy integrals and explains the meaning of the reactive sound intensity.

Sound field analyses by complex sound intensity

Sound field analyses by complex sound intensity