空间声的研究与应用——历史、发展与现状

空间声的目的是通过电声的手段重放声音空间信息,给聆听者再现特定的空间听觉感知。它在文化生活、通信、多媒体和虚拟现实等方面以及航空、航天等领域都有重要的应用。国内对空间声的研究起步于1958年,五十多年来进行了大量的基础研究工作,是和国际上的发展前沿相接轨的。本文在回顾空间声的基本原理与分类、国际上空间声发展历史的基础上,侧重评述了国内空间声研究和应用的历史、发展与现状,并展望了今后的发展前景。     

Velocity measurement for moving surfaces using spatial filtering method based on area image sensor

The idea of using spatial filtering method to measure velocity of vehicles for an inertial navigation system is put forward. Corresponding optical system, including a 532 nm solid-state laser as active illumination, is established. A 17.92 mm × 14.34 mm area charge coupled device (CCD) is employed both as detector and as spatial filter. The spatial filtering characteristics are theoretically analyzed using a power spectral density function. The spatial filtering operation of CCD is performed fully by software. Therefore, the parameters of the spatial filter, such as the size and the number of spatial period, are changeable. In addition, the CCD is arranged as two differential spatial filters without any other additional elements. Experiments are carried out to examine the feasibility of CCD as two differential spatial filters and the influence of the number of spatial period on the signal frequency. The results indicate that the more number of spatial period the more accurate measurements can be obtained, and show that the relation between signal frequency and velocity has good linearity. So this velocimeter is suitable to provide velocity information for a vehicle self-contained inertial navigation system.     

All-optical analog-to-digital conversion system with a spatial coding method using designed filter

We propose and demonstrate an all-optical analog-to-digital conversion system with a spatial coding method using a designed filter. To make available codes more flexible, the design technique for a computer-generated hologram is introduced to our spatial coding scheme. By designing the spatial coding filter appropriately, this coding scheme enables us to output various digital signals as spatial patterns. By combining this coding method with the optical quantization method using soliton self-frequency shifting in a fiber, the proposed system converts analog sampled signals into arbitrary digital signals. Preliminary experimental results show that 3-bit Gray codes are successfully output as spatial patterns using the designed spatial coding filter.     

The effect of a layer of varying density on spatial correlation of sea-bottom backscattering signal

The research is about the effect of a layer of varying density of sea-bottom sediments on spatial correlation of sea-bottom backscattering.The relationship between scattering cross section and spatial correlation is that backscattering cross section decreases quickly and the spatial correlation becomes stronger as the incident angle increases.Therefore,the densitydepth profile is introduced into sea-bottom high-frequency backscattering echo model,which is used to simulate sea-bottom backscattering and calculate the function of spatial correlation.The influence of the density gradient on spatial correlation of sea-bottom backscattering is investigated by analyzing the relations between vertical gradient of density and the scattering cross section.As can be seen from the simulation results,the impact of the density gradient on the spatial correlation is found more significant.While the density gradient increases,the scattering cross-section and the radius of the spatial correlation broaden,the spatial correlation becomes stronger.At the same time,the scattering cross-section decreases more quickly as the incident angle increases.     

基于液晶空间光调制器的空间滤波实验

空间滤波实验可以实现对输入物体的频谱分析及图像的边缘增强、噪声消除等各种图像处理。液晶空间光调制器可以作为衍射波面变换器件来使用。在空间滤波实验系统的滤波面上放置了液晶空间光调制器,并用CCD数码相机进行输出图像的观察和记录,分别给出了低通滤波、高通滤波、方向滤波等的仿真实验结果。该实验实现了输入数字物体的实时改变,并能够实时观察采用不同空间滤波器对输出像的影响。     

Comparative analysis and quantitative evaluation of the field of view and the viewing zone of single-shot phase-shifting digital holography using space-division multiplexing

We comparatively analyzed and quantitatively evaluated the field of view and the viewing zone of single-shot phaseshifting digital holography that uses space-division multiplexing, for the first time. We formulated the sampling intervals in the techniques in which the phase of the reference wave is spatially divided into two and four steps, and numerically simulated the areas. It was clarified that each area of the spatial two-step phase-shifting technique was twice as wide as that of the spatial four-step phase-shifting technique. We also experimentally investigated the areas. The ghost appeared for the spatial four-step technique when the object was between the boundary of the field of view of the spatial two-step technique and that of the spatial four-step technique, but did not appear for the spatial two-step technique.     

遥感影像信息量与空间分辨率的关系研究

目前,关于影像信息量的研究大多是注重信息量的计算模型,很少涉及空间分辨率与信息量之间的定量关系。为了对不同空间分辨率的遥感影像进行定量化评定,以信息论和模糊数学为理论基础,信息熵为测度,通过计算不同空间分辨率水平的全色影像和多光谱影像的信息量,对信息量与空间分辨率的关系进行直接量化模拟。结果表明,影像信息量随着空间分辨率的降低呈指数降低,空间分辨率在原影像基础上每增加一倍,影像信息量相应增加3~5倍。     

Display method with compensation of the spatial frequency response of a liquid crystal spatial light modulator for holographic femtosecond laser processing

Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing.     

On the spatial resolution of the IR remote sensing systems

According to the close relation between spatial resolution and radiant resolution and utilizing the experimental equation of MRTD, it is proved that there is a selectable optimum value of IFOV for particular spatial frequency or spatial frequency region which is interesting. The convolution process of line scanner is also analyzed, it is concluded that the spatial resolution can greatly exceed the limit of IFOV as long as the contrast is large enough, especially for linear or spot targets. Thus, the relative phenomena of the satellite image can be explained effectively. It is indicated that the spatial resolution can further be improved, if the processing of solving convolution operation is carried out in the digitized image processing.     

含分压电阻的光折变屏蔽光伏空间灰孤子

为了研究外加偏压光伏光折变晶体中的空间灰孤子,建立了含分压电阻的光折变屏蔽光伏空间灰孤子的演化方程,给出了灰孤子解.采用数值模拟的方法,求解灰孤子的数值表达式,得到了不同参量取值下的灰孤子包络.数值结果表明：当分压电阻、晶体的外加电场和光伏场取不同值时,可以分别得到有无分压电阻的屏蔽灰孤子|开路的光伏灰孤子,有、无分压电阻的闭路光伏灰孤子|有、无分压电阻的屏蔽光伏灰孤子.     

空间频率域的张量ABCD定律

运用张量分析方法把轴对称系统中的空间频率域的柯林斯公式推广到一般的非轴对称光学系统,并推导了在空间频率域中适用于非轴对称光学系统的张量ABCD定律。空间频率域中的柯林斯公式和张量ABCD定律直接给出了像散光束的空间傅里叶频谱的传输规律。它们在处理与空间频谱有关的问题,如空间滤波,成像系统的传递函数,复杂像散高斯光束在自由空间的传输等问题时更为简便。     

Eulerian spatial and temporal autocorrelations: assessment of Taylor's hypothesis and a model

We present measurements of Eulerian longitudinal velocity autocorrelations in homogeneous, isotropic, high-intensity (～9%) free-stream turbulence behind an active grid. Spatial correlations are measured using particle image velocimetry as well as with two-point hot-wire anemometry (HWA), while temporal correlations are measured using HWA. The temporal correlations are transformed into spatial correlations by using Taylor's ‘frozen’ hypothesis with both the mean as well as instantaneous velocities. A model relating Eulerian spatial and temporal autocorrelations is also used for this purpose. The differences from the measured spatial correlation resulting from the use of Taylor's hypothesis on the temporal correlation is quantified; even at this moderately high level of turbulent intensity, the result from the use of the instantaneous velocity as convection velocity is practically indistinguishable from that obtained using the mean velocity. Use of the model produces a good agreement between the estimates of the spatial correlation function. A relation between Eulerian spatial and temporal integral scales is also derived.     

Spatial Warped Gaussian Processes: Estimation and Efficient Field Reconstruction

A class of models for non-Gaussian spatial random fields is explored for spatial field reconstruction in environmental and sensor network monitoring. The family of models explored utilises a class of transformation functions known as Tukey g-and-h transformations to create a family of warped spatial Gaussian process models which can support various desirable features such as flexible marginal distributions, which can be skewed, leptokurtic and/or heavy-tailed. The resulting model is widely applicable in a range of spatial field reconstruction applications. To utilise the model in applications in practice, it is important to carefully characterise the statistical properties of the Tukey g-and-h random fields. In this work, we study both the properties of the resulting warped Gaussian processes as well as using the characterising statistical properties of the warped processes to obtain flexible spatial field reconstructions. In this regard we derive five different estimators for various important quantities often considered in spatial field reconstruction problems. These include the multi-point Minimum Mean Squared Error (MMSE) estimators, the multi-point Maximum A-Posteriori (MAP) estimators, an efficient class of multi-point linear estimators based on the Spatial-Best Linear Unbiased (S-BLUE) estimators, and two multi-point threshold exceedance based estimators, namely the Spatial Regional and Level Exceedance estimators. Simulation results and real data examples show the benefits of using the Tukey g-and-h transformation as opposed to standard Gaussian spatial random fields in a real data application for environmental monitoring.     

含分压电阻的光折变屏蔽光伏空间灰孤子(英文)

为了研究外加偏压光伏光折变晶体中的空间灰孤子,建立了含分压电阻的光折变屏蔽光伏空间灰孤子的演化方程,给出了灰孤子解.采用数值模拟的方法,求解灰孤子的数值表达式,得到了不同参量取值下的灰孤子包络.数值结果表明:当分压电阻、晶体的外加电场和光伏场取不同值时,可以分别得到有无分压电阻的屏蔽灰孤子;开路的光伏灰孤子,有、无分压电阻的闭路光伏灰孤子;有、无分压电阻的屏蔽光伏灰孤子.     

Study of modulation instability in a temporally incoherent photorefractive ring resonator below the threshold with incoherent light

Modulation instability (MI) and evolution of pattern formation inside a passive non-linear photorefractive ring resonator having cavity-length longer than the coherence length of the light circulating in the resonating cavity has been theoretically analyzed. Dynamics of the system below the threshold conditions have also been analyzed, numerically using linear perturbation theory for the Kerr-type non-linearity. The process of modulation instability in a temporally incoherent cavity below the cavity threshold and the influence of various parameters such as the cavity-length, intensity feedback of the perturbed wave field, amplitude of the incoming beam and spatial frequency on the gain factor and the spatial spectral density have also been studied. For the perturbed wave field, it has been found that the growth rate of MI increases with increase in the intensity feedback as well as the spatial frequency. It has also been found that increasing the intensity feedback of the perturbed wave field, for a given value of the spatial frequency, the spatial spectral density of the perturbation at the output of the non-linear medium increases with the shifting peak positions to the higher spatial frequency side.     

空间频率对透射式全息图衍射率的影响

为研究干涉条纹空间频率与透射式全息图衍射率的关系,在相同条件下,拍摄以平面波、发散的和会聚的球面波分别作参考光、物光的透射式全息图,通过实验测量其衍射效率,同时计算了干涉条纹的空间频率。然后以会聚的球面波为物光,平面波为参考光,分别改变入射角和球面波会聚点到记录面的距离制作另外4块透射式全息图,并计算了它们的空间频率,测量了其衍射效率。结果表明：在相同条件下制作透射式全息图时,衍射效率只由空间频率决定,与使用何种参考光和物光无关,空间频率仅随参考光和物光的夹角变化而变化。     

Modification of Spatial Coherence by Means of Low-Order Zernike-Mode Adaptive Optics

Spatial coherence of the field modified by low-order adaptive optics is analyzed to establish a theoretical basis for the recent idea of using adaptive optics as a spatial coherence modifier. In this context low-order adaptive optics has the ability to correct some of the low-order aberrations specified by Zernike polynomials. The initial field to be modified is assumed to be a spatially partially coherent one resulting from phase disturbance. It is demonstrated, as in the previous study, that low-order adaptive optics serves to enhance the spatial coherence of the resultant field and that the effect of the enhancement becomes stronger as the spatial coherence of the initially partially coherent field increases. Potential applications of low-order adaptive optics as a spatial coherence modifier are briefly discussed.     

Sensing characteristics of electrostatic inductive sensor for flow parameters measurement of pneumatically conveyed particles

The spatial sensitivity, spatial filtering effect, temporal frequency response characteristics and bandwidth are important parameters influencing the accuracy and response speed of a ring-shaped electrostatic inductive sensor. In this paper, the charge induced on the ring-shaped sensor with different geometric sizes from a single particle having a unity charge was modeled mathematically. And from the numerical solution obtained using the finite element analysis software ANSYS, the spatial sensitivity of the sensor was derived. The effect of the geometric size of the sensor on the spatial sensitivity was also investigated, and its spatial filtering fundamental theory and spatial filtering effect were also analyzed quantitatively. The temporal frequency response characteristics of the sensor were also derived. The experimental results on a gravity-fed conveyor were presented. The theoretical and experimental results obtained demonstrate that the ring-shaped sensor acts as a low-pass filter in the spatial frequency domain and its spatial frequency characteristics are closely related to the radial position of the charged particle and the axial length of the electrode. The measurement system, including the probe and signal conditioning circuit, acts as a band-pass filter, and the radial position, the axial length of the electrode, particle velocity and particle size have important effects on the temporal frequency characteristics of the measurement system.     

Effect of spatial patterns on population size

We investigate the role of the spatial pattern and temporal dynamics on the population properties of a diffusive Gause–Lotka–Volterra system. The average total population size is insensitive to the temporal dynamics, whereas a significant decrease of the population size can be found as the spatial diffusion effect is increased, implying that the spatial pattern plays an important role. At large diffusion coefficients, a saturation of the spatial pattern variation is observed, which can be understood by a spatial scaling analysis of the system. The existence of multiple attractors can also indicate that spatial patterns play a more important role than temporal dynamics in dominating the population size.     

诱导空间非相干束匀滑技术的近区特性及改善技术

诱导空间非相干技术是面向激光驱动惯性约束核聚变的一种具有自身独特优势的束匀滑方法.然而直接使用诱导空间非相干方法将引起强烈的近区强度空间调制,这将威胁装置的运行安全,并严重限制装置的最大输出能力.这也是该方法应用于聚变级高功率激光装置的主要技术障碍之一.本文介绍了一种通过双透镜滤波系统对诱导空间非相干束匀滑技术导致的近区空间强度调制进行匀滑的技术.利用该技术可以在保留诱导空间非相干束匀滑方法的先天优势(更好的远区匀滑特性)的前提下,获得均匀、稳定的近区强度分布,从而避免高功率激光系统在使用诱导空间非相干束匀滑技术时,因为近区强度不均匀、不稳定导致的器件损伤及输出能力受限.在理论建模和数值分析的基础上,以近区调制度、软化因子和透过率为主要评价指标,对比分析了方形、圆形、高斯型等3种滤波孔在不同尺寸下的近区输出效果,最终给出了一种典型的优化结果:16×16诱导空间非相干分割数、0.8倍衍射极限宽度、方形小孔.此时近区强度分布均匀,同时保证了较好的远区匀滑效果和高的能量利用率.在此基础上,针对装置的实际应用情况,进一步分析了准直误差对近区强度分布的影响,结果表明准直误差小于0.1倍衍射极限便不会影响输出的近区质量.对诱导空间非相干束匀滑方法所得焦斑的模拟分析表明,滤波系统的加入能进一步改善焦斑的低频不均匀性.