Experimental implementation of a low-frequency global sound equalization method based on free field propagation

An experimental implementation of a global sound equalization method in a rectangular room using active control is described in this paper. The main purpose of the work has been to provide experimental evidence that sound can be equalized in a continuous three-dimensional region, the listening zone, which occupies a considerable part of the complete volume of the room. The equalization method, based on the simulation of a progressive plane wave, was implemented in a room with inner dimensions of 2.70 m × 2.74 m × 2.40 m. With this method, the sound was reproduced by a matrix of 4 × 5 loudspeakers in one of the walls. After traveling through the room, the sound wave was absorbed on the opposite wall, which had a similar arrangement of loudspeakers, by means of active control. A set of 40 digital FIR filters was used to modify the original input signal before it was fed to the loudspeakers, one filter for each transducer. The optimal arrangement of the loudspeakers and the maximum frequency that can be equalized is analyzed theoretically in this paper. The presented experimental results show that sound equalization was possible from 10 Hz to approximately 425 Hz in the listening zone. A flat frequency response with deviations within ±5 decibels from the desired value was achieved. A higher demanding performance with deviations within ±1.5 decibels from a flat frequency response was attained in the interval between 20 Hz and 280 Hz. At the same time, the impulse response was quite well approximated to a delayed delta function in the listening zone. Examples of the spatial distribution of the sound field are also shown.     

An implicit high-order spectral difference approach for large eddy simulation

The filtered fluid dynamic equations are discretized in space by a high-order spectral difference (SD) method coupled with large eddy simulation (LES) approach. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model (WALE). We solve the unsteady equations by advancing in time using a second-order backward difference formulae (BDF2) scheme. The nonlinear algebraic system arising from the time discretization is solved with the nonlinear lower–upper symmetric Gauss–Seidel (LU-SGS) algorithm. In order to study the sensitivity of the method, first, the implicit solver is used to compute the two-dimensional (2D) laminar flow around a NACA0012 airfoil at Re = 5 × 10⁵ with zero angle of attack. Afterwards, the accuracy and the reliability of the solver are tested by solving the 2D “turbulent” flow around a square cylinder at Re = 10⁴ and Re =  2.2 × 10⁴. The results show a good agreement with the experimental data and the reference solutions.     

Investigations on order and width of RZ super Gaussian pulse in pre-, post- and symmetrical-dispersion compensated 10 Gb/s optical communication system using standard and dispersion compensating fibers

We show the effect of varied order and width of super Gaussian pulse at 10 Gb/s in dispersion compensated optical communication system. The optical communication system consists of standard single-mode fiber of 16 ps/nm/km of a certain length, whose dispersion is compensated using pre-, post- and symmetrical-dispersion compensation schemes with proportionate length dispersion compensating fiber of −80 ps/nm/km. Performance of these three compensation schemes is compared at 14 dBm values of Er-doped fiber amplifiers (EDFA) power at 1st, 2nd and 3rd order RZ super Gaussian optical pulse. The pulse width, full width at half maximum (FWHM) is also varied from 5 to 30 ps to highlight the optimum performance. The graphical results obtained show a relationship among the attributes pulse width, order of RZ super Gaussian optical pulse and dispersion compensation scheme implemented. It shows that to decrease BER and timing jitter in the system, smaller width and 3rd order super Gaussian pulse should be used. It is recommended that to decrease dependency of BER and timing jitter in the communication system on the pulse width i.e. FWHM, the symmetrical compensation scheme should be implemented.     

二维非均匀多孔介质中不可压两相驱替的有限分析算法

为提高油藏数值模拟算法的计算效率,在求解单向稳态渗流的有限分析算法基础上,构建二维非均匀多孔介质中不可压两相渗流的有限分析算法.算法中,网格界面上的平均渗透率不是简单地取为相邻网格渗透率的调和平均值,而是通过奇点邻域解析解积分求得.相比于传统的数值算法,有限分析算法随着网格的加密,能够很快地收敛(仅需将原始网格细分至2×2或3×3),并且其计算精度和收敛性不依赖于介质的非均匀强度,从而计算效率得到提高.     

1 × 3 Beam splitter based on self-collimation effect in two-dimensional photonic crystals

The analysis and simulation result of a 1 × 3 beam splitter in a two-dimensional square-lattice photonic crystal is presented in this paper, where the light is self-collimated as dictated by the self-collimation effect. The frequency and the direction of propagation of the self-collimated beam are obtained by the equal-frequency contours (EFCs) plot which is calculated by plane wave expansion method. Then a line defect is introduced by simultaneously varying the radii and the dielectric constant of the rods along the proper direction, the self-collimated beam propagation in such structure is simulated by the two-dimensional finite-difference time-domain (2D FDTD) method with perfectly matched layer absorbing boundary conditions. The simulation results show that the self-collimated beam can be split into three beams. With the same principle, a 1 × 7 beam splitter is realized by introducing different line defects along (X direction. Such devices can greatly enhance photonic crystals for usage in high-density optical integrated circuits.     

Analysis on generation schemes of Schrödinger cat-like states under experimental imperfections

An analysis and a comparison of two generation schemes of Schrödinger cat-like state including experimental imperfections are presented. Under practical conditions, a scheme using a squeezed vacuum and a photon subtraction will generate a cat-like state with its fidelity to the Schrödinger cat state F = 0.815 and value of its Wigner function at the origin of the phase space W(0,0) = −0.203, and then turned out to be more feasible than the scheme using squeezed single-photon state. The non-classicality of these cat-like states is governed only by non-classical photon number statistics. The criteria for ensuring W(0,0) < 0 are also presented in terms of imperfection parameter diagrams.     

Sound source imaging of low-flying airborne targets with an acoustic camera array

Two-dimensional images of sound source distribution from near-ground airborne sounds are created using an array of 32 microphones and time-domain beamforming. The signal processing is described and array configurations spanning a square area with a side length of 3.45 m, approximately five wavelengths for a 500 Hz sound, are examined. Simulations of a 32-element under-populated log₆ × log₆ spaced array are given for sound sources centered over the array at 250 Hz, 500 Hz, and 1000 Hz. Stochastically optimized array geometry with a simulated annealing algorithm is discussed and a 32-element array optimized for a 500 Hz source is given along with a simulated image for direct comparison with the log₆ spaced array. Images from field testing a 32-element under-populated log₆ × log₆ spaced array are provided for a small aircraft flyover. Results show that this type of acoustic camera generates accurate images of sound source location. Suggested uses include monitoring small aircraft flying too low to be detected by radar as well as monitoring ecological events, such as bird migration.     

The spectral order of accuracy: A new unified tool in the design methodology of excitation-adaptive wave equation FDTD schemes

We define a new concept, termed the spectral order of accuracy (SOoA), which is the spectral domain analogue of the familiar order of accuracy (OoA). The SOoA is pivotal in a refined version of a recently-introduced methodology for formulating excitation-adaptive wave equation FDTD (WE-FDTD) schemes, described below. This concept is the basis for a unified classification for both existing and new schemes. Both one- and two-dimensional cases are presented for boundless, source free, homogeneous, isotropic and lossless media. The 1-D and 2-D cases are developed in detail for the (3, 2M + 1) (temporal, spatial) and (3, 3) 2-D stencils, respectively. Stability analysis is built into the methodology in terms of either analytical conditions or “stability maps” defined herein. The methodology is seen as a generalization of many existing schemes that also provides a unified tool for a systematical design of WE-FDTD schemes subject to specific requirements in terms of the spectral content of the excitation. The computational efficiency for all schemes remains the same for a given stencil, since the core of the FDTD code is unchanged between schemes, the difference being only in the values of scheme coefficients.     

Analytical and numerical calculations of optimum design frequency for focused ultrasound therapy and acoustic radiation force

Focused ultrasound therapy relies on acoustic power absorption by tissue. The stronger the absorption the higher the temperature increase is. However, strong acoustic absorption also means faster attenuation and limited penetration depth. Hence, there is a trade-off between heat generation efficacy and penetration depth. In this paper, we formulated the acoustic power absorption as a function of frequency and attenuation coefficient, and defined two figures of merit to measure the power absorption: spatial peak of the acoustic power absorption density, and the acoustic power absorbed within the focal area. Then, we derived “rule of thumb” expressions for the optimum frequencies that maximized these figures of merit given the target depth and homogeneous tissue type. We also formulated a method to calculate the optimum frequency for inhomogeneous tissue given the tissue composition for situations where the tissue structure can be assumed to be made of parallel layers of homogeneous tissue. We checked the validity of the rules using linear acoustic field simulations. For a one-dimensional array of 4 cm acoustic aperture, and for a two-dimensional array of 4 × 4 cm² acoustic aperture, we found that the power absorbed within the focal area is maximized at 0.86 MHz, and 0.79 MHz, respectively, when the target depth is 4 cm in muscle tissue. The rules on the other hand predicted the optimum frequencies for acoustic power absorption as 0.9 MHz and 0.86 MHz, respectively for the 1D and 2D array case, which are within 6% and 9% of the field simulation results. Because radiation force generated by an acoustic wave in a lossy propagation medium is approximately proportional to the acoustic power absorption, these rules can be used to maximize acoustic radiation force generated in tissue as well.     

通用硬件脉冲序列发生器的研制

为了满足任意核磁共振脉冲序列的需要,提高脉冲序列发生器的性能和稳定性,本文提出了一种基于现场可编程逻辑器件（FPGA）和大容量高位宽静态存储器（SRAM）的硬件脉冲序列发生器,详细讨论了这种设计方案的特点,并通过一系列实验验证了其性能和可行性.     

Coherent beam combining of 137 W 2 × 2 fiber amplifier array

We demonstrate coherent beam combining of two-dimensional fiber amplifier arrays with a total of 137 W output power using stochastic parallel gradient descent (SPGD) algorithm. Compact all-fiber polarization-maintained single frequency fiber amplifier chains are developed and four fiber amplifiers are arranged to 2 × 2 laser array with a fill factor of 70% in the near-field. Active phase control is implemented by a digital signal processor (DSP) based SPGD controller. The fringe visibility of the coherent combined beam profile is as high as 81% when the system is closed-loop controlled despite perturbations of the environment.     

声脉冲法空间电荷测量系统的研究

气体中空间电荷的分布与电晕放电的机理紧密相关, 获取电晕放电过程中空间电荷分布对深入研究电晕放电起始、自持过程有着重要作用, 但是如何准确获得电晕放电过程中的空间电荷分布一直是国际上尚未解决的难题. 本文基于声脉冲法提出一种电场信号解耦算法, 推导了空间电荷在声场中被调制产生的电场信号与声脉冲信号和空间电荷密度之间的数值关系, 讨论了不同测量情况下声发射系统的设计要求; 搭建了一套可用于实时测量针板电极电晕放电空间电荷分布的非接触式测量系统, 该系统主要包括声脉冲发生模块、空间电荷模块及电场信号解耦算法模块. 运用该系统实现了声脉冲激发作用下电场信号的测量, 通过提出的电场信号解耦算法得到了空间电荷密度, 对其测量结果与电晕电流法测量结果进行比较, 验证了电场信号解耦算法的有效性. 该算法可以应用于空间电荷一维、二维和三维测量系统中.     

Experimental and numerical study on aeroacoustic sound of axial flow fan in room air conditioner

Fan is one of the main noise sources of the room air-conditioners. Axial flow fans are widely used in the outdoor unit of split type air-conditioners. The interaction between the fan and the heat exchanger should be taken into consideration. However, only a few researches have been carried out on predicting the aeroacoustic noise because of the difficulty in obtaining detailed information of the flow field. This paper is to understand the generation mechanism of sound and to develop a prediction method for the flow field and the acoustic pressure field of the outdoor unit. Acoustic measurement is performed in a semi-anechoic chamber. Effects of each components is analyzed. Based on commercial computational fluid dynamics (CFD) code, Fluent, Fukano’s model is used to predict the overall sound pressure level of broadband noise. The predicted sound pressure levels based on original Fukano’s model are 7.66 dB and 7.42 dB lower than measurement results at 780 rpm and 684 rpm, respectively. And the errors are about 13%. However, when wake width and relative velocity are both calculated by numerical simulations and the distance to blade trailing edge is taken into consideration, the difference of sound pressure level between measurement and prediction is less than 3.4 dB and errors less than 5.5% while the distance is less than 10 mm. Thus, the distance to blade trailing edge should also be an important parameter for Fukano’s model. In comparison with experimental results, it is clearly shown that the Fukano method based on numerical simulation can provide more accuracy than the original Fukano model and numerical results are in a reliable level.     

A resource-saving decoding scheme of the orthogonally concatenated codes for optical transport networks in FPGA

A decoding scheme of the orthogonally concatenated codes with low resource utilizations is proposed. In the optical transport networks (OTN), forward error-correction (FEC) techniques are used to reduce the errors which occur in transmissions. Two-orthogonal-concatenated (TOC) codes are widely used in FEC techniques for their powerful error-correction capabilities based on the iterative decoding procedure. However, the framing structure is complex so the decoding procedure is more difficult than the decoding of in–out concatenated codes. And the powerful error-correction capability relies on the multi-iterative decoding processing, thus how to effectively utilize the hardware resources is a very important problem. Especially when the decoding procedure is implemented in the field programmable gate array (FPGA) devices, effective optimizations are required for the limited resources. In this paper we present an iterative decoding scheme in FPGA with low resource utilizations. As an example, an actual engineering application under the G.975.1 recommendation is given to show the efficiency of the proposed design.     

Implementation and performance analysis of three dimensional (3D) space/wavelength/time single pulse per plane codes with direct detection

In this paper, we present space/wavelength/time single pulse per plane (SPP) codes with direct detection (SPPDD) and implemented it as two dimensional codes by using W²T scheme. We analyze these codes by varying the number of space channels (S) and keeping other two dimensions, wavelength (W) and time (T) constant and report that it gives better results when (W > S). It is found that the space channels S = 2 and S = 3 provide better BER rate than other space channels and also analyze these 3D codes by using different data modulation formats. It is found that OCDMA system with NRZ data modulation format performs better than RZ.     

LARED集成程序辐射输运模拟的性能优化

分析定位高置信度辐射传输数值模拟效率瓶颈,针对物理模型和数值离散格式的特点,优化求解算法和程序设计,改进激光聚变二维总体LARED集成程序,提高输运建模模拟黑腔靶实验模型的计算效率：在相同的并行计算条件下,辐射输运方程离散求解计算效率提高2倍以上,全过程整体模拟计算时间减半.     

Improved beamforming using curved sparse 2D arrays in ultrasound

In this work we have investigated the effect of curving phase-steered sparse periodic two-dimensional arrays in one direction, and relate this effect to the geometry of the arrays. We have shown that curving is equivalent to removing some of the element periodicity, thus adding some “randomness” to the layout. Compared to flat phase-steered periodically sparse two-dimensional arrays, curving offers an even greater suppression of grating lobes located at directions along the curvature. The class of arrays yielding improved performance due to this suppression of grating lobes has been characterized.The point spread functions of some previously proposed array layouts, shown to be promising for ultrasonic imaging, have been simulated. The arrays have been simulated with various number of elements as well as various focal points, with array and field parameters typical to those in volumetric cardiac imaging. On a 48 × 48 element grid with a transducer center frequency of 3 MHz and the target at 40 mm, reductions in the peak sidelobe level of up to 12 dB were recorded for some critical steering directions, without significant differences in the beamwidth. The integrated sidelobe ratio was also examined, showing an almost equivalent performance as the flat array. This study shows that, without adding any complexity to the system, the overall image quality of a volumetric imaging system can be improved significantly by curving the array in one direction.     

基于现场可编程门阵列技术的混沌数字通信系统——设计与实现

提出了基于IEEE-754标准和现场可编程门阵列(FPGA)技术的混沌数字通信系统的通用设计与硬件实现的一种新方法,实现了混沌加密体制与传统密码体制的结合.根据Euler算法,对连续混沌系统作离散化处理,通过FPGA硬件设计混沌离散系统,使其产生作为密钥的混沌数字序列,其中加密算法采用置乱扩展技术,并对算法进行了分析.设计驱动响应式同步保密通信系统,构建包含信号在内的闭环,实现发送端与接收端离散混沌系统的同步.以网格蔡氏混沌系统为例,对该保密通信系统进行了FPGA硬件实验,给出了技术实现过程、算法流程、硬 关键词： 网格多涡卷蔡氏电路 置乱扩展矩阵 现场可编程门阵列技术 混沌数字通信系统     

A High-Efficiency Spectral Method for Two-Dimensional Ocean Acoustic Propagation Calculations

The accuracy and efficiency of sound field calculations highly concern issues of hydroacoustics. Recently, one-dimensional spectral methods have shown high-precision characteristics when solving the sound field but can solve only simplified models of underwater acoustic propagation, thus their application range is small. Therefore, it is necessary to directly calculate the two-dimensional Helmholtz equation of ocean acoustic propagation. Here, we use the Chebyshev–Galerkin and Chebyshev collocation methods to solve the two-dimensional Helmholtz model equation. Then, the Chebyshev collocation method is used to model ocean acoustic propagation because, unlike the Galerkin method, the collocation method does not need stringent boundary conditions. Compared with the mature Kraken program, the Chebyshev collocation method exhibits a higher numerical accuracy. However, the shortcoming of the collocation method is that the computational efficiency cannot satisfy the requirements of real-time applications due to the large number of calculations. Then, we implemented the parallel code of the collocation method, which could effectively improve calculation effectiveness.     

Efficient multi-party quantum state sharing of an arbitrary two-qubit state

We present an efficient scheme for sharing an arbitrary two-qubit quantum state with n agents. In this scheme, the sender Alice first prepares an n + 2-particle GHZ state and introduces a Controlled-Not (CNOT) gate operation. Then, she utilizes the n + 2-particle entangled state as the quantum resource. After setting up the quantum channel, she performs one Bell-state measurement and another single-particle measurement, rather than two Bell-state measurements. In addition, except that the designated recover of the quantum secret just keeps two particles, almost all agents only hold one particle in their hands respectively, and thus they only need to perform a single-particle measurement on the respective particle with the basis X. Compared with other schemes based on entanglement swapping, our scheme needs less qubits as the quantum resources and exchanges less classical information, and thus obtains higher communication efficiency.