Papers by Keyword: Reverberation

Abstract: The paper assesses the possibility of using the reverberation phenomenon to control the imperfections and the stress-strain state of solid dielectric materials by the method of mechanoelectrical transformations. The main advantage of reverberation is the repeated intersections of the excitation zones of inhomogeneities by acoustic waves, that is displayed in response parameters. The reverberation makes it possible to accumulate distortions of wave fronts. A comparative analysis of the responses from the sample under condition of uniaxial compression under different loads was performed. Differential analysis for the deterministic time component of the response in the interval (0–0.3) ms, and a statistical analysis of the differences for the pseudo-random component in the interval (0.8–1.8) ms were performed. For the statistical analysis, the distribution of the pulse flow is selected. The response was calculated according to the mathematical model under the conditions of a change in the speed of sound, which simulates a change in the sample inhomogeneity under load. The calculation showed a qualitative similarity with changes in responses in a real experiment. According to the obtained results, it was concluded that it is possible to use the deterministic and pseudo-random components of the responses in the reverberation condition to control the change in defectiveness and the degree of heterogeneity under the action of the mechanical load on the sample.

Abstract: The theory of full dimension and reduced dimension STAP was introduced. Based on the physical mechanism of reverberation formation, the suppression of moving sonar reverberation and the possibility of improvement of detection performance were analyzed and discussed, and the solutions of several key steps were given. The analysis shows that reverberation suppression using STAP is more difficult than clutter suppression of AEW, but its implementation is possible. The results of simulation show that the STAP method can achieve better detection performance than conventional method. The STAP method can utilize the space-time characteristic of moving sonar reverberation sufficiently, and so is a promising new method of reverberation suppression.

Abstract: For solving the problem which the performance of detection was reduced in the low signal to noise ratio (SNR) using Wigner-Ville Hough transform (WHT), the method of XWVD adaptive mean Ridgelet transform filtering (XWVD-M-FRIT) was proposed. In this method, due to the power distribution of signal is different from noise or reverberation in time-frequency domain, so designed adaptive axial mean filter, then using Ridgelet transform filtering to restrain noise or reverberation. At last, it is to detect the signal using Hough transform. The results of real and simulation experiments showed, compared with WHT, in the low SNR the new method is feasible to restrain noise or reverberation in time-frequency domain for improving the performance of signal detection. furthermore, the performance of varying implement of adaptive mean and Ridgelet transform filtering were compared.

Abstract: Target detection in the presence of strong seabed reverberation is a hot research topic nowadays. This kind of target detection method is similar to signal detection with known shape and unknown parameters under non-WGN or coherent signal detection in reverberation. When a LFM signal is choose as transmitted signal, target echo has excellent time-frequency focusing property on a certain rotating angle and reverberation could lose its original linear modulation property. LFM signal can be transformed to a sine signal with some rank FrFT. Since FrFT is a linear transform, interference including reverberation and noise will keep former statistic characteristics. So LFM signal detection is thus equivalent to detection of sine signals in absence of colored noise. The reverberation will be easily erased and target echo will be preserved. Based on the analysis above all, a sub-optimum detector based on reverberation-whiten in FrFT field is advanced. The validity of these conclusions is validated by computer simulations. A satisfying result is achieved.

Abstract: Absorption coefficient is an important parameter of the absorption function of the absorption material. Traditional measurement methods of absorption coefficient are standing wave tube and reverberation which have some shortcomings. In this paper, phase of the sound pressure measured by two equal distance microphones placed in the front of the absorption material is delayed in order to attain the absorption coefficient. At the last, an experiment for one absorption material is carried out, the experiment results compare with the results of the other methods above mentioned that denotes that the theory is correct and practicable. Key words: absorption material standing wave reverberation time delaying

Abstract: Against defects of lacking consideration of air absorption characteristics to the high frequency signal in Schroeder reverberation model, and the more complex structure in Moorer reverberation model, use equiripple Chebyshev approximation criterion to design 4 FIR comb filter with low-pass characteristics and make the FIR filters in parallel, to get a pure parallel reverberation model. This reverberation model considers the absorption characteristics of air to the high-frequency signal, and has a more simple structure.

Abstract: In order to use the STAP in reverberation suppression, and compare the performances of STAP for underwater LFM with CW, the method of STAP used for LFM was proposed. Firstly, the principle of STAP for CW was analyzed, according to the underwater echo of CW. Then, the space-time steering vector of LFM is deduced by analysing the underwater echo of LFM. Fianlly, the performances of STAP for LFM and CW were compared by simulations. The results show that the proposed method of STAP for underwater LFM with narrower modulation bandwidth can achieve a better performance in target detection and estimate, and the processing gain of STAP for CW is higher than that of LFM form 1.6dB to 5.5dB with the modulation bandwidth from 100Hz to 600Hz.

Abstract: If the number and the location of each cell in the array is determined, the space array processing gain is constant in designing the uniform line array in isotropic acoustic field. However, the spatial distribution of reverberation field will affect against the array gain, when the arrays are in anisotropic reverberation field. Reverberation is the unique interference of active sonar, and the energy distribution of space in reverberation field is anisotropic and random. Therefore, the arrays gain problem can be get in researching on the correlation between arrays in the reverberant field. In this paper, the calculation method is simple and useful which is calculated line array gain using the correlation coefficient in the reverberant field.

Abstract: The purpose of this paper is to detect the echo under reverberation background by using adaptive interference cancellation. And in this paper, experimental data was treated. Reference signal is separately one single beam or symmetrical double beams in the processing of adaptive reverberation cancel. As the results shown, it is clear that the reverberation is made a great degree of inhibition after adaptive reverberation cancellation treatment. And when symmetrical double beams are as the reference signals, the effect is obviously better than one single beam.

Abstract: Absorption coefficient is an important parameter of the absorption function of the absorption material. Traditional measurement methods of absorption coefficient are standing wave tube and reverberation which have some shortcomings. In this paper, phase of the sound pressure measured by two equal distance microphones placed in the front of the absorption material is delayed in order to attain the absorption coefficient. At the last, an experiment for one absorption material is carried out, the experiment results compare with the results of the other methods above mentioned that denotes that the theory is correct and practicable.