关于室内混响声能衰减规律的探讨

从"吸声系数"的定义出发,对室内混响声能衰减规律进行探讨,通过室内混响时间与平均吸声系数计算公式的推导,说明室内声能的衰减规律是按"一个平均自由程时间"衰减的。     

Linear dipole response in a reverberation chamber

A new spatial correlation function is derived for the axial electric field and is compared with the previously known spatial correlation function for the total electric field. The new correlation function is used to determine the average power received by a linear dipole antenna in a reverberation chamber. The result for the average received power agrees with the previous result for an arbitrary impedance-matched antenna derived by the angular spectrum method     

混响室的声学设计

混响室是声学专业的实验室用房,它在测量声波无规入射时材料的吸声系数和测量噪声源的声功率级中得到了广泛应用。结合混响室建设的工程实例,介绍了混响室设计中有关体积、体形、吸声、隔声和声扩散等方面的技术问题。测量表明,建成完工后的混响室在声学方面的各项指标均满足或优于国家标准的要求。     

Delay spread and coherence bandwidth in reverberation chamber

The reverberation chamber becomes an attractive tool for simulating a multipath environment. Starting from the definition of the delay spread and of the coherence bandwidth, analytical expressions in terms of the Q-factov of the room are determined and compared with those of the power density decay factor and of the mode bandwidth, allowing a better insight into the chamber characterisation.     

Influence of diffraction coefficient and corner shape on rayprediction of power and delay spread in urban microcells

For a low base-station (BS) antenna located on one street, signals propagate into crossing and parallel streets by reflection and diffraction at corners of buildings. Therefore, in order to accurately predict the received signals, it is necessary to properly model the diffraction coefficient at the building edge and to accurately represent the shape and the electrical properties of the building near the corner. This paper compares ray-tracing predictions to measurements of received power and root mean square (rms) delay spread and shows the need for a diffraction coefficient having larger values than suggested by the commonly used heuristic diffraction coefficient. A new heuristic diffraction coefficient is proposed that has higher diffracted field strength in the deep shadow region and in the region between the two shadow boundaries. The proposed diffraction coefficient shows better agreement with measurements of both received power and delay spread compared to the commonly used heuristic diffraction coefficient. The influence of building shape near the corner and its electrical properties on the ray-tracing predictions are also presented. The shape is shown to have an important role in accurately predicting both received power and delay spread     

无规入射散射系数测量的研究

无规入射散射系数是在扩散声场中界面散射声能与总反射声能之间的比值,它是采用计算机模拟来对室内声场进行预测的重要参量。国际标准化组织(ISO)即将公布其对无规入射散射系数的定义及其在混响场中的测量方法。关于这一方法的有效实施以及准确地获得实验数据,显得尤为重要。根据测量的基本原理建立了完整的无规入射散射系数测量系统,并给出典型散射试件的测量结果,分析了测量中的一些技术问题。     

三角阵列电极的太赫兹光电导天线结构设计

光电导天线具有室温操作、紧凑设计和宽带辐射等优点,但辐射功率低限制了其广泛应用,其中低光吸收率是辐射功率低的主要原因之一。传统的天线电极无尖端结构,边缘电场弱,导致了低的光吸收率。为了提高光电导天线的辐射功率,设计了一种三角阵列天线电极结构,该电极结构由5个三角形尖端排列组成。使用时域有限差分(FDTD)方法研究了800 nm飞秒激光照射下电极的电场增强和衬底对光的吸收。此结构增加了激光入射到衬底的面积,并且减小了光载流子传输距离,在无电场情况下光的吸收率达到30.57%,相对于传统天线提高了161%。三角阵列电极结构为传统电极结构设计提供了新思路,有望与纳米结构结合进一步提高辐射功率。     

Spatial coherence properties of planar antennas

Lateral spatial coherence of an antenna is modeled by random phase front tilts. An effective source coherence length is introduced, and a generalized Fresnel coefficient which takes into account the coherence of the source is abstracted. Generalized reciprocity relationships for beamwidth and source coherence as well as for observed coherence and source power distribution valid in the near and far field are developed     

Aperture excitation of electrically large, lossy cavities

We present a theory based on power balance for aperture excitation of electrically large, lossy cavities. The theory yields expressions for shielding effectiveness, cavity Q, and cavity time constant. In shielding effectiveness calculations, the incident field can be either a single plane wave or a uniformly random field to model reverberation chamber or random field illumination. The Q theory includes wall loss, absorption by lossy objects within the cavity, aperture leakage, and power received by antennas within the cavity. Extensive measurements of shielding effectiveness, cavity Q, and cavity time constant were made on a rectangular cavity, and good agreement with theory was obtained for frequencies from 1 to 18 GHz     

Investigation of Reverberation Chamber Measurements Through High-Power Goodness-of-Fit Tests

This paper aims to improve the analysis of distribution functions of a rectangular component of the electric field (E_R) and the power received in an overmoded reverberation chamber. All data and analysis were achieved in the Institute of Electronics and Telecommunications of Rennes (IETR) mode-stirred chamber. For the power received on a large antenna, tests are consistent with the exponential probability density function assumption. However, high-power goodness-of-fit tests modify the determination of the lowest frequency from which the ideal underlying theoretical distributions can be associated with measurements. For the electric field in an overmoded regime, a Weibull distribution is proposed to model E_R measurements, instead of the Rayleigh distribution hypothesis, which is rejected by statistical tests. Furthermore, Weibull distribution provides better agreement with standard deviation of samples. An additional experiment with a monopole-like antenna illustrates that the exponential distribution is rejected when the monopole is small with respect to the wavelength, but is accepted when the antenna length is roughly over lambda/4. Experimental results are provided by a large number of goodness-of-fit tests. The paper highlights that the use of adapted critical values is necessary for testing a distribution function whose parameters are estimated.     

Optimal Characteristics of an Arbitrary Receive Antenna

Several fundamental questions about the operation of receiving antennas are addressed, such as “Why does a receiving antenna scatter an incident field?” and “Under what conditions does a receive antenna capture all of the available incident power?” A new method is described by which the received power can be maximized for an arbitrary receiving antenna. The technique is first illustrated for two-dimensional infinite receiving arrays of electric and/or magnetic dipole elements, which result in simple plane waves for the scattered (re-radiated) fields. Optimal results (for maximum received power) are derived for several cases, and it is established that half the available incident power may be received by an array of electric (or magnetic) elements in free space, and that all available incident power may be received by an array that combines electric and magnetic elements, or one that incorporates a ground plane. Next, an arbitrary finite three-dimensional antenna enclosed by a mathematical spherical surface is treated using spherical vector wave functions. It is shown that half the available incident power can be received by such an antenna consisting of either TM or TE only elements, while all available incident power can be received when both TM and TE elements are used. It is also shown that the absorption efficiency for any optimal arbitrary antenna is 50%.      

漫射界面矩形扁平空间的混响时间计算

所谓矩形扁平空间就是指高度远小于宽度和长度的长方体空间,也可以称作二维空间。虽然高度比较小,但是其相对于声波波长来说仍然比较大。这样的空间内的声场一般不是完全的扩散声场或者自由声场,传统的处理声场的理论,例如赛宾公式,并不能很好地处理这种情况。对于完全漫射界面,一种可行的处理方法是采用辐射度算法。将计算机图形学中的辐射度算法加以改进,提出改进的声学辐射度算法,并且用这一算法计算一个矩形扁平空间的混响时间(RT)和早期衰减时间(EDT)。此外还分析了声源位置、接收点位置、界面吸声和空气吸声的影响。     

UAT analysis ofE-plane near and far-field patterns of electromagnetic horn antennas

The uniform asymptotic theory (UAT) of diffraction has been applied to arrive at expressions valid for both the near as well as far-field patterns of antenna with edges, namely an electromagnetic horn. It is found that the theoretically computed results agree very well with experiment. The agreement is found to be better than that reported by earlier authors in the far sidelobe and backlobe regions. The same theory is valid for near field as well with the pertinent values of radial distance where the uniform theory of diffraction (UTD) requires a slope diffraction correction.     

Receiving Properties of the Small Annular-Slot Antenna

An analytical formula for the effective height of an annularslot antenna is determined using the reciprocity theorem. This result generalizes the previously available single-frequency steady-state result and yields an equivalent circuit valid for computing the transient response of the small annular-slot antenna. the theory has application in calibrating near-zone field strength instrumentation and in determining the response of an unsheathed coaxial cable connector mounted flush with the skin of a missile to intense plane-wave electromagnetic field pulses.     

卫星定位有源天线性能测试接口转换装置

在卫星有源接收天线测试过程中,受天线自身所带放大器增益的限制,其输出的信号功率无法达到后端测试设备最低输入灵敏度的要求,致使天线的某些性能测试工作无法进行。针对有源天线测试过程中遇到的接口不匹配和接收信号场强不匹配问题,提出了在被测有源天线与后端测试设备之间增加一个接口转换装置。该装置由SMA接头、低噪声放大器、直流电源隔离电路和防浪涌冲击电路构成。仿真表明,该接口转换装置能有效地完成在微波暗室里进行的卫星有源接收天线性能测试。     

超低频天线最优波束成形设计研究

针对现有超低频天线发射端单一化缺陷和通信距离受限瓶颈,为实现超低频电磁发信系统的小型化和远距离传输,该文对旋转式永磁体机械天线的超低频电磁发信技术进行了理论创新和工程实践。探究多输入单输出 (MISO)场景下超低频多机械天线电磁辐射理论,建立了基于三相感应电机的多机械天线阵列的空间磁场分布模型。仿真结果表明：利用三相感应电机组成的2元机械天线阵列可使磁感应强度在近场提高3 dB。该文还提出了多天线超低频近场最优波束成型技术。仿真结果表明：当天线之间的初始相位相等时径向接收磁场分量场强最大。设计高精度同步技术并搭建原理样机进行测试,实验结果表明：发送端采用2元天线组阵,信号功率提高6 dBm,传输距离可达50 m。     

镜像对称结构对多馈源混响室场性能的影响

为解决混响室大体积与场性能高要求之间的矛盾,提出了一种基于镜像原理的多馈源混响室的设计思想,从原理上分析了镜像多馈源混响室的可行性和有效性,并通过仿真计算研究了镜像双馈源混响室的场性能.结果表明,在输入功率一定时,两个单混响室系统组合成镜像双馈源混响室后,在工作区域的场均匀性能不下降的基础上,不但可用于电磁兼容测试的工作区域体积大幅度增大,而且测试区域的电场强度也得到了提高.同时,对镜像多馈源混响室进行了进一步的扩展分析,得出了组成镜像多馈源混响室的单混响室系统数量的理论表达式.     

Theoretical investigation of the field conditions in a vibrating reverberation chamber with an unstirred component

In this paper, we examine the use of a vibrating reverberation chamber in which an equipment under test (EUT) is directly illuminated by a source antenna. A three-dimensional theoretical model, based on a simplified ray tracing method has been applied on a reverberation chamber whose dimensions were varied. The field distribution together with the field homogeneity was investigated, introducing the Rice distribution due to the presence of the line-of-sight component between the antenna and the EUT.     

Analysis of DSRC Service Over-Reach inside an Arched Tunnel

In this paper, the prediction of received power in the out-of-zone of a dedicated short range communications (DSRC) system operating inside a typical arched highway tunnel is discussed. By conducting wideband directional channel sounding inside the tunnel, the gain, angle-of-arrival and delay of each propagation path are estimated by means of a multidimensional maximum likelihood estimation algorithm from the measured data. Using these estimated parameters and by employing simulations of application antennas according to the DSRC standard, the received power in the out-of-zone is predicted for 2 roadside unit (RSU) antenna positions. The dominant scatterers causing the over-reach of radiated power to the out-of- zone were identified and attributed to the ground and sidewalk. These scatterers can affect the received power level in the out- of-zone by as much as 10 dB. It can therefore be concluded that suppressing ground and sidewalk scatterings in the vicinity of RSU by installing composite pavement materials are needed to increase the electromagnetic absorption in order to guarantee DSRC services.     

邦达泡沫板的吸声特性及应用

通过对邦达吸声板混响室吸声系数的测量,分析了材料穿孔、不同空腔深度、安装方式对吸声特性的影响及其应用。并与目前常用的强吸声材料吸声特性进行了比较。