凹面相控阵聚焦声场在液固界面上的反射和折射

开展了凹面线性相控阵列辐射声场在液固界面上的反射和折射特性研究,利用射线近似方法,得到了凹面相控阵聚焦声场在液固界面上反射和折射后的声场渐近解析表达式,对声波在液固曲面上的反射和折射声场进行了分析和讨论. 利用这个解析表达式,对凹面线性聚焦声场在液固平界面和液固圆柱界面情况下固体中折射纵波和折射横波的相控阵声场进行了分析和讨论,发现凹面线阵声场在液固圆柱界面下比液固平界面具有更好的聚焦效果. 关键词： 凹面阵列 超声相控阵 反射与折射     

折射是界面对光子的增透

本文利用光子的概念,在深入研究的基础上,提出了光在两介质界面上的折射是界面层对光子的增透作用这一观点,通过从微观上跟踪一个光子后,导出了“增透膜”的厚度和宏观的斯涅耳折射定律,得出了光子在界面的折射是两次折射的结论.     

用于相位突变界面的广义的反射定律和折射定律

考虑到位于两物质界面上的Metasurface对光线传播行为的影响, 从费马原理和边界条件连续两种角度出发, 推导了可用于相位突变界面的广义反射与折射定律. 该定律在界面对光波的相位改变量为零的情况下, 回归为通常的反射定律和折射定律. 利用广义的折射定律和反射定律讨论了介质折射率、界面上的相位梯度等因素对光传播行为的影响, 发现利用广义的折射定律和反射定律很容易实现反常反射和反常折射行为, 并给出了出现反常反射和反常折射的条件, 以此为基础可以实现对光波的随意控制. 依据广义的折射定律和反射定律分析了一维相位掩模板对光场传播行为的影响. 关键词： 超材料 相位突变界面 反射定律 折射定律     

光在高速运动界面上的反射和折射

依据闵可夫斯基运动介质电磁场理论，从物质方程和边界条件出发，导出了平行于入射面电场分量反、折射分配的Ｅｒ－Ｅｉ、Ｅｔ－Ｅｉ菲涅耳公式．用几何方法求得运动界面上法线方位角反、折射定律，进而导出光线的反、折射定律．基于光线速度满足洛伦兹变换，由光在静止界面上反、折射定律也可导出运动界面上光线的反、折射定律，最后给出了光线反、折射定律实例曲线，它们明显地依赖于界面速度．     

相位梯度界面对光传播规律的影响

在两种介质分界面上引入相位梯度形成相位梯度界面,这将使该界面的出射光和入射光之间产生相移.因此,与普通分界面不同,该界面对光的传播行为有着重大影响.为深入认识梯度相位界面的光学特性,本文研究了光在该类界面上的一般性传播规律.从费马原理出发,采用稳态相位法推导了基于相位梯度界面条件下的二维和三维广义反射和折射定律,该定律表明分界面也会成为影响光传播行为的重要因素,可以作为新的波前调制工具.利用广义反射和折射定律讨论了相位梯度对光传播行为的影响规律,得出了二维和三维情形下的临界条件(全反射和全透射条件),阐明了反射角不等于入射角、异常反射和折射、非平面反射和折射等一些新颖光学现象出现的原因;提出了以相位梯度界面为光学变换核心单元,依据广义反射和折射定律进行光学设计的思路,并以平面透镜和平面轴锥镜为例进行了详细说明与实验验证,实验结果和理论值符合较好,可为拓展广义定律在平面光学设计、自由曲面光学设计以及复杂光束控制中的应用提供参考.     

高频条件下运动边界的电磁场边界条件

在狭义相对论的基础上,对运动媒质界面的高频电磁特性进行了分析,给出了广义折射以及频率的特性关系. 关键词： 运动媒质界面 相对性 广义折射 频率     

凝聚炸药爆轰波在高声速材料界面上的折射现象分析

凝聚炸药爆轰在边界高声速材料约束下传播时,爆轰波会在约束材料界面上产生复杂的折射现象.本文针对凝聚炸药爆轰波在高声速材料界面上的折射现象展开理论和数值模拟分析.首先通过建立在爆轰ZND模型上的改进爆轰波极曲线理论给出爆轰波折射类型,然后发展一种求解爆轰反应流动方程的基于特征理论的二阶单元中心型Lagrange计算方法来数值模拟典型的爆轰波折射过程.从改进爆轰波极曲线理论和二阶Lagrange方法数值模拟给出的结果看出,凝聚炸药爆轰波在高声速材料界面上的折射类型有四种:反射冲击波的正规折射、带束缚前驱波的非正规折射、带双Mach反射的非正规折射、带λ波结构的非正规折射.     

液-液界面上折射声束位移的实验验证

对折射波束在液-液界面上的现象进行了数值和实验研究，结果表明：当声束从声阻抗大的介质入射到液-液界面上时，折射声束会存在反向位移现象。     

负折射率材料用于表面波传感的特性分析

利用严格电磁理论分析了负折射材料界面上激励表面波的相关特性,证明两种偏振入射都能在负折射材料与正折射材料界面上激发表面波,并推导出了相应表面波的传播波矢和激发条件.针对负折射材料在表面波传感方面的应用,对膜厚选择,偏振态,测量范围,线性度等性能参量进行了具体分析,与传统的金属表面等离子波传感器相比,使用负折射材料在灵敏度相当的情况下,能有效提高线性度,增大测量范围,提高信噪比.     

空间弯曲光束的折射特性

空间弯曲光束在光学捕获和光纤传感等领域具有重要的应用价值,在这些应用中,空间的介质环境起着重要作用。根据空间弯曲光束的激发原理提出了一种理论方法,应用折射定律反演空间弯曲光束的每一条几何射线,以描述空间弯曲光束在空气-介质界面的折射现象,同时以空间弯曲光束为例进行了有限元法模拟。所阐明的空间弯曲光束在空气-介质界面的折射机制为解释任意通过相位反演激发的空间弯曲光束的折射机制提供了一定的参考。     

平面波与线性粘弹海底的反射和折射

采用基于广义标准线性体Boltzmann叠加原理的固体流变模型来描述粘弹性海底底质结构,分析了沉积层和基岩的纵、横波速度频散和衰减的特点,计算了海水沉积层界面和沉积层基岩界面位移势反射和折射系数和能量反射和折射系数。结果表明,采取本模型的粘弹性海底的速度频散、衰减和已有文献的实验数据符合较好,能准确的描述海底底质的主要性质,反射和折射系数和声波的频率有关。      

Controlled experiments of the diffraction of sound by a curved surface

Controlled measurements of the sound field from a point source above a curved surface are described. The measurements were made in the frequency range between 0.3 and 10 kHz, in the case of a rigid boundary and a surface of finite impedance. Receiver positions include all of the area within, and above, the shadow zone and for various source heights. Particular attention is given to the region across the shadow boundary. The measurements are compared to diffraction theory expressed in terms of a residue series, or creeping wave solution. The calculation is extended by removing restrictive approximations and by carrying the computation to higher-order terms. A numerical algorithm allows the extension to the general case of a finite impedance. Above the shadow boundary, the sound field is calculated using geometrical theory that accounts for reflections from a curved surface. Deep within the shadow, theory and measurements agree to, typically, 0.5 dB. The same agreement is obtained between measurements and the geometrical theory well above the shadow boundary. In the vicinity of the shadow boundary, both theories agree to within 0.5 dB but differ from the measured results by 2 to 5 dB. Finally, the theory is compared to measurements obtained outdoors above a grass covered curved ground with no refraction and above flat ground with refraction.     

Amiet剪切层理论的角度折射验证研究

在开口射流风洞中进行气动噪声的定位测量试验时,射流边界的剪切层会对声传播产生折射影响。在处理过程中需要对传声器测量的信号进行剪切层修正,修正结果将直接影响到波束形成对气动噪声源定位的准确性。本文针对经典的Amiet剪切层修正理论,综合计算气动声学(Computational aeroacoustics,CAA)数值计算与试验测试,对该理论进行了验证,研究表明CAA计算与Amiet理论吻合,Amiet理论能够有效修正剪切层对声波的角度折射影响。     

Horizontal refraction of sound rays due to short-period internal waves in the ocean

The effect of a short-period internal wave measured in field conditions on the horizontal (side) refraction of sound rays is estimated. The angle of horizontal refraction, i.e., the angle between the direction of the signal arrival in the horizontal plane and the true direction to the sound source, is determined. The influence of various factors, such as the position of the receiving system in depth with respect to the layer of high sound velocity gradients, the rotation of the transmitter-receiver track with respect to the internal wave front, etc., on the horizontal refraction is estimated. Numerical calculations are carried out. Conclusions about the possible errors that arise in determining the azimuth direction to the sound source because of the effect of short-period internal waves are derived.     

非线性声学谐波方程的特解及其在边值问题中的应用

在流体或固体介质中,微扰法求解非线性声波的反射和折射问题时,谐波场通常满足非齐次波动方程。应用分离变量法及拉格朗日变动参数法求它的特解,出现了待定的分离常数,给这类非线性声学边值问题带来困难。本文结果表明,为不使定解问题出现佯僇,其独立的特解只有两类,一类是沿边界法线方向有积累效应的解,另一类则是沿平行边界面方向上有积累效应的解,由定解条件来决定究竟选用哪一类解。应用这个结果研究了平面边界的反射和折射谐波,该理论对非线性声学中的平面边值问题有普遍的应用意义。     

Shielding of Prof-Fan cabin noise by the fuselage boundary layer

Recent flight tests of a Prop-Fan (advanced technology turboprop) model mounted on a business aircraft revealed noise levels on the fuselage surface considerably lower than was expected from theoretical calculations and other test experience. In this paper the role of the fuselage boundary layer in shielding the surface from noise via classical refraction effects is examined. In order to study the physical phenomenon with minimum mathematical complexity, the boundary layer is modeled by concentrating its shear in an infinitesimally thin layer displaced an effective boundary layer thickness from a rigid wall. Incident energy is assumed to arrive in plane waves. For the Prop-Fan model at its design cruise Mach number of 0·8, the theory indicates a strong shielding effect. The shielding diminishes at lower flight Mach number and for larger sound wavelengths. At full scale, the shielding effects will be less than in model scale because the wavelength of the dominant noise is larger relative to the fuselage boundary layer thickness.     

Three-dimensional coupled-mode model and characteristics of low-frequency sound propagation in ocean waveguide with seamount topography

Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional (3D) coupled-mode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the 3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order Padé approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount.     

在Hell中超漏对第四声的折射

本文从平均压缩率和平均密度变化的观点计算了超漏颗粒对Hell中传播的第四声的折射。也从多重散射的方法,计算了由此引起的折射。分别得出了解析式。并进行了数值计算。结果表明,前者的影响不是主要的,而由多重散射导出的第四声声速变化所得的结果和实验吻合较好。 关键词：     

Low-frequency resonance of an oblate spheroidal cavity in a soft elastic medium

The horizontal ducting of sound by an oceanic temperature front over a sloping bottom is studied with an idealized wedge model consisting of a lateral interface across the slope. The water outside the frontal interface has higher temperature, hence faster sound speed, and it will produce inshore reflection/refraction of the sound. Combining the offshore refraction caused by the sloping bottom, propagating sound can be ducted along the front. An analytical solution to the sound pressure field in the idealized model is derived, and an example is presented to demonstrate and discuss the ducting effect.     

Oblique incidence properties of locally resonant sonic materials with resonance and Bragg scattering effects

A locally resonant sonic material (LRSM) is an elastic matrix containing a periodic arrangement of identical local resonators (LRs), which can reflect strongly near their natural frequencies, where the wavelength in the matrix is still much larger than the structural periodicity. Due to the periodic arrangement, an LRSM can also display a Bragg scattering effect, which is a characteristic of phononic crystals. A specific LRSM which possesses both local resonance and Bragg scattering effects is presented. Via the layered-multiple-scattering theory, the complex band structure and the transmittance of such LRSM are discussed in detail. Through the analysis of the refraction behavior at the boundary of the composite, we find that the transmittance performance of an LRSM for oblique incidence depends on the refraction of its boundary and the transmission behaviors of different wave modes inside the composite. As a result, it is better to use some low-speed materials (compared with the speed of waves in surrounding medium) as the LRSM matrix for designing sound blocking materials in underwater applications, since their acoustic properties are more robust to the incident angle. Finally, a gap-coupled LRSM with a broad sub-wavelength transmission gap is studied, whose acoustic performance is insensitive to the angle of incidence.