On the Possibility of using Vertical Receiving Arrays for Underwater Acoustic Communication on the Arctic Shelf

Acoustical Physics - Numerical simulation is applied to analyze the possibilities of using vertical receiving arrays covering the entire waveguide for underwater acoustic communication on the...     

An Arctic-Type Shallow-Water Acoustic Waveguide as an Information Transmission Channel for Underwater Communications

Acoustical Physics - Model experiments are used to obtain the transfer functions of an Arctic-type shallow-water acoustic waveguide in the spring–summer period, including in the presence of...     

双网组合下的水声通信网络节点的设计与实现

针对水下通信平台之间通信网络在可靠性、快捷性等方面的不足,提出将水下成熟的通信网络与自组织网络相结合,在特定的区域部署通信网络节点系统对信息进行转发,从而提升了水下通信网络的稳定性与灵活性;研究并设计了水下通信网络节点的系统架构、硬件系统、软件系统;在户外水域相隔10 m的距离分别放置通信节点系统到水下3m的位置,在Matlab7.0平台上完成对对水下通信网络节点信号进行测试,在PC机上应用串口调试助手软件按照初始化的参数:8位数据位、1位停止位、无奇偶校验码、波特率115 200 b/s,测试结果表明:文章系统采样准确,误差低,满足实际需要。     

Use of Linear Receiving Arrays for Observing Horizontal Refraction of Low-Frequency Sound in Shallow Water with a Strongly Inhomogeneous Waterlike Bottom

Acoustical Physics - Numerical simulation is applied to study the features of a low-frequency (55 and 137 Hz) acoustic field and its recording by linear horizontal and vertical arrays in a...     

Generation of NOON States in Waveguide Arrays

A method to generate NOON states with three photons by injecting photons in an array of three waveguides is presented. Conditional measurements project the wave function in a given (desired) state. In passing, it is shown how the array of three waveguides, that effectively reproduces the interaction of three fields, may be reduced to the interaction of two fields.     

时变信道下的被动时间反转扩频水声通信

本文研究了时变信道条件下采用被动时间反转的直接序列扩频水声通信方案。多通道被动时间反转可通过对信道多径进行时间、空间聚焦实现信道匹配,但低信噪比、时变特性造成的信道特性失配对被动时间反转处理的性能造成严重影响。在垂直阵接收的基础上,本文采用码片级信道估计获取水声信道特性并进行周期性更新,并采用已判决码元产生的扩频码片作为信道估计训练序列,结合应用稀疏信道估计算法抑制零值抽头上的估计噪声,从而可有效改善时变、低信噪比条件下的被动时间反转处理的时、空多径聚焦效果,提高扩频通信性能。通过湖试实验比较了采用稀疏信道估计、传统信道估计算法的时反扩频接收机,以及经典直扩接收机的通信性能,实验结果表明：本文方案可在低信噪比获得较好的性能,并有效抑制时变信道对时反扩频通信性能的影响。     

基于改进卡尔曼滤波的水声通信盲自适应多用户检测算法

针对水声通信网络中遇到的多用户检测中目标用户的多址干扰等检测问题,提出了基于改进Kalman算法的盲自适应多用户检测算法,解决了多用户检测中的多址干扰对水声通信信道用户变动时的干扰抑制问题。仿真分析分别针对同步多用户、异步多用户通信过程,对比了传统Kalman算法及改进的Kalman算法的性能差异,通过仿真对比表明,改进后的Kalman检算法不需要训练序列即可以实现同步和异步通信状态下的多水声目标用户的盲自适应检测,改进后的算法目标检测的信干比比传统算法最大可提高6dB。新算法对于水下多用户检测、区分,准确、稳定的实现基于CDMA协议的快速水声通信具有重要意义。     

Spatial Divergence of Multimode Acoustic Beams Formed by a Vertical Array in a Refracting Oceanic Waveguide

We consider the patterns manifested during the formation of the spatial intensity distribution of an acoustic field excited by a vertical array in a deep-water oceanic waveguide with an underwater sound channel open to the surface and an acoustically transparent bottom. The study focuses on the dependence of the spatial divergence of multimode beams on the angle of compensation of an array emitting a tone signal. It is established that if the size of the array aperture significantly exceeds the optimal size, then at a certain angle of compensation appreciably differing from zero, a multimode beam forms with minimal diffraction divergence even in the absence of bending points and smooth extrema of the dependence of the length of the ray cycle on the ray parameter.     

Characteristics of an Electric Dipole in a Plane Waveguide with an Inhomogeneous Filling in the Long-Line Approximation

Within the framework of the long-line approximation, we obtain the expressions for the current distribution, input impedance, and admittance of a nonsymmetric thin electric dipole whose ends are connected to perfectly conducting walls of a plane waveguide filled by an inhomogeneous dielectric. The use of this approximation allows one to qualitatively interpret the results of rigorous solution of the problem of the effect of the medium inhomogeneity on the radiation characteristics of the antenna.     

三维海洋波导中散射目标快速声学远场成像

研究用声传播远场分布信息成像海洋波导环境中三维散射目标的反问题,提出一种指示器样本成像方法,在不需要预先知道散射目标的任何声学和几何特性的情况下,可以快速得到其位置、形状等几何信息的一个理想的像.数值试验表明,该方法对成像海洋波导中三维散射目标是有效的,即使在有限孔径测量方式和具有噪声测量数据时,也能够得到散射目标的一个理想成像,表明海洋波导边界的多重反射效应对成像效果具有一定的正面影响.     

Lifshitz Tails for Acoustic Waves in Random Quantum Waveguide

In this study, we consider acoustic operators in a random quantum waveguide. Precisely we deal with an elliptic operator in the divergence form on a random strip. We prove that the integrated density of states of the relevant operator exhibits Lifshitz behavior at the bottom of the spectrum. This result could be used to prove localization of acoustic waves at the bottom of the spectrum. 2000 Mathematics Subject Classification: 81Q10, 35P05, 37A30, 47F05     

Dispersion Characteristics of Waveguide Arrays in Optical Spectrum Analyzers

Formulas for calculating the spectral characteristics of waveguide arrays, which are incorporated into waveguide spectrum analyzers based on planar waveguides, channel waveguides, and fiber optical waveguides, are derived taking into account the contribution of both the waveguide dispersion and the material dispersion to the dispersion factor. These formulas are used to study the dependence of the dispersion factor on the waveguide-system parameters for specific models of waveguide arrays. It is shown that consideration of contributions of the waveguide dispersion and material dispersion can affect profoundly the spectral characteristics of waveguide arrays.     

An Acoustic Metamaterial Lens for Acoustic Point-to-Point Communication in Air

Acoustical Physics - Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML)...     

Propagation of ULF Radiation from an Artificial Ionospheric Source in a 3D Inhomogeneous MHD Waveguide

Radiophysics and Quantum Electronics - We analyze the propagation of electromagnetic waves of the ultralow-frequency (ULF) range emitted by an artificial ionospheric source arising in the...     

Full-Wave Analyses for Vertical Interconnections of Shielded Coplanar Waveguide

Three dimensional (3D) interconnection plays important role in modern millimeter wave integrated circuit (MMIC). In this paper, vertical interconnections of shielded coplanar waveguides, which appear typically in multichip module MMICs, are analyzed through the full-wave finite-difference time-domain (FDTD) method.     

Direction Finding of a Source in an Acoustic Waveguide and the Angular Resolution Limit

Acoustical Physics - A reduced-rank adaptive algorithm is constructed, which makes it possible to find sound sources directions using a horizontal array operating in a waveguide with inaccurately...     

Bionic Covert Underwater Acoustic Communication Based on Time–Frequency Contour of Bottlenose Dolphin Whistle

In order to meet the requirements of communication security and concealment, as well as to protect marine life, bionic covert communication has become a hot research topic for underwater acoustic communication (UAC). In this paper, we propose a bionic covert UAC (BC-UAC) method based on the time–frequency contour (TFC) of the bottlenose dolphin whistle, which can overcome the safety problem of traditional low signal–noise ratio (SNR) covert communication and make the detected communication signal be excluded as marine biological noise. In the proposed BC-UAC method, the TFC of the bottlenose dolphin whistle is segmented to improve the transmission rate. Two BC-UAC schemes based on the segmented TFC of the whistle, the BC-UAC scheme using the whistle signal with time-delay (BC-UAC-TD) and the BC-UAC scheme using the whistle signal with frequency-shift (BC-UAC-FS), are addressed. The original whistle signal is used as a synchronization signal. Moreover, the virtual time reversal mirror (VTRM) technique is adopted to equalize the channel for mitigating the multipath effect. The performance of the proposed BC-UAC method, in terms of the Pearson correlation coefficient (PCC) and bit error rate (BER), is evaluated under simulated and measured underwater channels. Numerical results show that the proposed BC-UAC method performs well on covertness and reliability. Furthermore, the covertness of the bionic modulated signal in BC-UAC-TD is better than that of BC-UAC-FS, although the reliability of BC-UAC-FS is better than that of BC-UAC-TD.     

Numerical and Asymptotic Solution of the Problem of Oscillations of an Inhomogeneous Waveguide with an Annular Crack of Finite Width

Acoustical Physics - The problem of waves in an inhomogeneous cylindrical waveguide with an annular crack is considered. A system of integral equations with hypersingular kernels is obtained for...     

Acoustic insulation capacity of Vertical Greenery Systems for buildings

Vertical Greenery Systems (VGS) are promising contemporary Green Infrastructure which contribute to the provision of several ecosystem services both at building and urban scales. Among others, the building acoustic insulation and the urban noise reduction could be considered. Traditionally vegetation has been used to acoustically insulate urban areas, especially from the traffic noise. Now, with the introduction of vegetation in buildings, through the VGS, it is necessary to provide experimental data on its operation as acoustic insulation tool in the built environment. In this study the acoustic insulation capacity of two VGS was conducted through in situ measurements according to the UNE-EN ISO 140-5 standard. From the results, it was observed that a thin layer of vegetation (20–30 cm) was able to provide an increase in the sound insulation of 1 dB for traffic noise (in both cases, Green Wall and Green Facade), and an insulation increase between 2 dB (Green Wall) and 3 dB (Green Facade) for a pink noise. In addition to the vegetation contribution to sound insulation, the influence of other factors such as the mass factor (thickness, density and composition of the substrate layer) and type of modular unit of cultivation, the impenetrability (sealing joints between modules) and structural insulation (support structure) must be taken into account for further studies.