Nakagami-m水声信道中HARQ的性能分析

水声信道的多径扩展严重、环境噪声高、带宽受限、传输时延大等特点,极大地制约了水声通信系统的可靠性和有效性。以水声信道为研究对象,从理论上分析了Nakagami-m信道衰落模型下基于HARQ的期望吞吐率,并就给定的调制编码方案,给出了链路吞吐率的仿真。仿真结果表明,随着m值的增大,链路的期望吞吐率增大;但是,当m>2时,相同信干噪比条件下链路的吞吐率比较接近。同时,水声信道中节点相对移动速度对链路吞吐率没有显著影响。     

基于多层石墨烯的声表面波放大器的研究

为了研究多层石墨烯对声表面波的放大作用,分析了外加电场下石墨烯载流子的可变电导率,研究了不同衬底下多层石墨烯声表面波放大器的放大性能.对比研究了 ZnO和CdS为衬底的石墨烯声表面波放大器,分别对其在不同载流子漂移速度下的放大倍数进行了研究.结果表明,以ZnO为衬底,载流子漂移速度大于且接近声表面波相速度时,放大性能是...     

低声阻抗0—3型PZT/PT/PVDF压电复合材料的研制

压电陶瓷材料的高声阻抗制约着其在水听器和超声成像方面的应用。为了对压电陶瓷材料的声阻抗和声速进行调节,本研究以聚偏氟乙烯(PVDF)及钛酸铅(PT)和锆钛酸铅(PZT)压电陶瓷粉体为原料,经过流延、热压等工艺制得了4种含有不同量PT及PZT的0—3型PZT/PT/PVDF压电复合材料。研究了所制压电复合材料的声学、压电和介电性能。结果表明:所制压电复合材料的声阻抗均小于140 MPa.s/m,最优压电应变常数d33达43 pC/N,相对介电常数为185～210,介质损耗约为2×10–2。     

基于射线模型的水声信道的仿真软件设计

利用声线理论对多途水声信道进行了建模仿真软件设计。采用求解声线跨度方程的方法，搜索本征声线，并求解其参数。仿真结果表明，该基于射线模型的软件对多途信道参数预测精度高，具有很强的工程应用价值。     

一种基于麦克风阵列的声源定位算法研究

麦克风阵列声源定位广泛应用于视音频会议系统及枪声定位系统等领域。提出了一种基于最小熵值（ME）的麦克风阵列声源定位新方法,其特点在于利用最小熵值方法对麦克风阵列进行时延估计,并与离散网格方法相结合,对声源进行空间搜索。实验结果表明,在同等混响或噪声条件下,该方法定位优于广义互相关-相位变换方法（GCC-PHAT）。     

用于光无线局域网的通信系统设计

主要针对在点对点的光无线通信系统基础上组建而成的光无线局域网,具体描述了应用于光无线局域网的光无线通信系统的组成和原理,主要包括通信系统的光源的选择、发射电路的设计、接收光电二极管的选择、接收电路的设计以及发射和接收天线的选择。这种设计具有可靠性、数据传输速率高、成本低、抗电磁干扰能力和抗衰弱能力强、带宽高、器件尺寸小等优点。     

Effective wave propagation along a rough thin-elastic beam

Two methods for computing the complex-valued effective wavenumber of a rough beam in the context of linear time-harmonic theory are presented. The roughness of the beam is modelled as a continuous random process of known characteristic length and root-mean-square amplitude for either the beam mass or the beam rigidity. The first method is based on a random sampling method, with the effective wave field calculated as the mean of a large ensemble of wave fields for individual realisations of the roughness. The individual wave fields are calculated using a step approximation, which is validated for a deterministic problem via comparison to results produced by an integral equation approach. The second method assumes a splitting of the length scale of the fluctuations and an observation scale, employing a multiple-scale approximation to derive analytical expressions for the effective attenuation rate and phase change. Numerical comparisons show agreement of the results of the random sampling method and the multiple-scale approximation for a wide range of parameters. It is shown that the effective wavenumbers only differ by a real constant between the cases of varying beam mass and rigidity.     

Load’s temporal characteristics for annulling forced vibrations of linear elastic plates

We consider trapezoidal load-time pulses with linearly increasing and affinely decreasing durations equal to integer multiples of the time period of the first bending mode of vibration of a linearly elastic structure. For arbitrary spatial distributions of loads applied to monolithic and laminated orthotropic plates, it is shown through numerical solutions that plates’ vibrations become miniscule after the load is removed. This phenomenon is independent of the dwell time (i.e., the time duration between the rising and the falling portions) during which the load is kept constant. The primary reason for this response is that for such time-dependent loads, nearly all of plate’s strain energy is concentrated in deformations corresponding to the fundamental bending mode of vibration. Thus plate’s deformations can be studied by taking the mode shape of the 1st bending mode as the basis function and reducing the problem to that of solving a single second-order ordinary differential equation. We have verified this postulate by comparing strain energies computed from the 3-dimensional deformations of different plate geometries and boundary conditions with those determined by using the single degree of freedom (DoF) model. Thus for trapezoidal time-dependent loads applied on plates, the 1 DoF model provides reasonably accurate results and saves considerable computational effort.     

Acoustic topology optimization of sound power using mapped acoustic radiation modes

An efficient approach for acoustic topology optimization to minimize the radiated sound power from a vibrating structure is described. The topology optimization is implemented by modifying the local stiffness at discrete locations on the surface of the structure. The radiated sound power level from the structure is directly chosen as the objective function to be minimized. A sensitivity analysis is then implemented to further optimize the layout of the locations of the modified local stiffness. To speed up the computational process, the radiated sound power is computed based on mapped acoustic radiation modes. To demonstrate the acoustic topology optimization using mapped acoustic radiation modes, the radiated sound power of a compressor housing is examined. Based on results from the numerical model, the local stiffness of a compressor housing was experimentally modified. Good agreement in sound power reduction obtained both numerically and experimentally was observed for the overall trend for the sound power levels as a function of one-third octave frequency bands.     

Robust Disturbance Attenuation with Stabilization for Uncertain Networked Control Systems

This paper investigates the problem of robust stabilization and attenuation for a class of uncertain networked control systems (NCSs) with random communication network-induced delays. Based on the Lyapunov–Razumikhin method, a controller is designed such that both robust stability and a prescribed disturbance attenuation performance for the closed-loop NCS are achieved, irrespective of the uncertainties and network-induced delays. The controller design technique is given in terms of the solvability of bilinear matrix inequalities. An iterative algorithm is proposed to change this non-convex problem into quasi-convex optimization problems, which can be solved effectively using available mathematical tools. The effectiveness of the proposed design methodology is verified by a numerical example.