A simple algorithm using an impulse response for a rectangular piston element is discussed. The impulse response of linear phased array is obtained hv stumming the impulse responses of rectangular piston elements with...A simple algorithm using an impulse response for a rectangular piston element is discussed. The impulse response of linear phased array is obtained hv stumming the impulse responses of rectangular piston elements with different delay times. The output response of the linear wide-band array is equal to the convolution of impulse response functions with wide-band pulse exeiting signal. Sound field distributions and impulse responses of three kinds of transducers are compared. The results can be used to optimize the parameters of the linear phased array transducers used in uhrasonie imaging in nondestructive testing （NDT）.展开更多
This paper proposes new interference estimation for power control in broadband wireless data networks. The proposed approach gives the filtered interference power in real-time removing undesired effects such as the fl...This paper proposes new interference estimation for power control in broadband wireless data networks. The proposed approach gives the filtered interference power in real-time removing undesired effects such as the fluctuation of interference power and the measurement noise due to receiver noise. The well-known Finite Impulse Response （FIR） structure filter is adopted for both the interference and the noise covarianee estimation. The proposed mechanism provides both the filtered interference power and the filtered number of active co-channel interferers, which shows good inherent properties. And the filtered interference power is not affected by the constant number of active co-channel interferes. It is also shown that the filtered number of active co-channel interference is separated from the filtered interference power. From discussions about the choice of design parameters such as window length and eovariance ratio, they can make the estimation performance of the proposed FIR filtering based mechanism as good as possible. Via extensive computer simulations, the performance of the proposed mechanism is shown to be superior to the existing Kalman filtering based mechanism.展开更多
Compared to a scalar pressure sensor, a vector sensor can provide a higher signal-to-noise ratio （SNR） signal and more detailed intbrmation on the sound field. Study on vector sensors and their applications have bec...Compared to a scalar pressure sensor, a vector sensor can provide a higher signal-to-noise ratio （SNR） signal and more detailed intbrmation on the sound field. Study on vector sensors and their applications have become a hot topic. Research on the representation of a vector field is highly relevant for extending the scope of vector sensor technology. This paper discusses the range-frequency distribution of the vector field due to a broadband acoustic source moving in a shallow-water waveguide as the self noise of a surface ship, and the vector extension of the waveguide impulse response measured over a limited frequency range using an active source of known waveform. From theory analysis and numerical simulation, the range-frequency representation of a vector field exhibits an interference structure qualitatively similar to that of the corresponding pressure field but, being quantitatively different, provides additional information on the waveguide, especially through the vertical component. For the range-frequency representation, physical quantities that can better exhibit the interference characteristics of the wavegaide are the products of pressure and particle velocity and of the pressure and pressure gradient. An image processing method to effectively detect and isolate the individual striations from an interference structure was reviewed briefly. The representation of the vector impulse response was discussed according to two different measurement systems, also known as particle velocity and pressure gradient. The vector impulse response representation can not only provide additional information from pressure only but even more than that of the range-frequency representation.展开更多
基金Sponsored by the Foundation of High Technology Research and Development Program of China (Grant No. 2001AA616170).
文摘A simple algorithm using an impulse response for a rectangular piston element is discussed. The impulse response of linear phased array is obtained hv stumming the impulse responses of rectangular piston elements with different delay times. The output response of the linear wide-band array is equal to the convolution of impulse response functions with wide-band pulse exeiting signal. Sound field distributions and impulse responses of three kinds of transducers are compared. The results can be used to optimize the parameters of the linear phased array transducers used in uhrasonie imaging in nondestructive testing （NDT）.
文摘This paper proposes new interference estimation for power control in broadband wireless data networks. The proposed approach gives the filtered interference power in real-time removing undesired effects such as the fluctuation of interference power and the measurement noise due to receiver noise. The well-known Finite Impulse Response （FIR） structure filter is adopted for both the interference and the noise covarianee estimation. The proposed mechanism provides both the filtered interference power and the filtered number of active co-channel interferers, which shows good inherent properties. And the filtered interference power is not affected by the constant number of active co-channel interferes. It is also shown that the filtered number of active co-channel interference is separated from the filtered interference power. From discussions about the choice of design parameters such as window length and eovariance ratio, they can make the estimation performance of the proposed FIR filtering based mechanism as good as possible. Via extensive computer simulations, the performance of the proposed mechanism is shown to be superior to the existing Kalman filtering based mechanism.
基金Supported by Office of Naval Research grant N00014-07-1-1069the National Nature Science Foundation of China grant 50979019the Belgian National Fund for Scientific Research (F.R.S. - FNRS)
文摘Compared to a scalar pressure sensor, a vector sensor can provide a higher signal-to-noise ratio （SNR） signal and more detailed intbrmation on the sound field. Study on vector sensors and their applications have become a hot topic. Research on the representation of a vector field is highly relevant for extending the scope of vector sensor technology. This paper discusses the range-frequency distribution of the vector field due to a broadband acoustic source moving in a shallow-water waveguide as the self noise of a surface ship, and the vector extension of the waveguide impulse response measured over a limited frequency range using an active source of known waveform. From theory analysis and numerical simulation, the range-frequency representation of a vector field exhibits an interference structure qualitatively similar to that of the corresponding pressure field but, being quantitatively different, provides additional information on the waveguide, especially through the vertical component. For the range-frequency representation, physical quantities that can better exhibit the interference characteristics of the wavegaide are the products of pressure and particle velocity and of the pressure and pressure gradient. An image processing method to effectively detect and isolate the individual striations from an interference structure was reviewed briefly. The representation of the vector impulse response was discussed according to two different measurement systems, also known as particle velocity and pressure gradient. The vector impulse response representation can not only provide additional information from pressure only but even more than that of the range-frequency representation.
