Creating a Reference Plane Ultrasonic Wave in a Fluid Using a Plane Piezoelectric Transducer with a Large Wave Dimension

Acoustical Physics - The article discusses the possibility of using a plane piezoelectric transducer with a large wave dimension as the source of a reference plane ultrasonic wave, which can be...     

Acoustic Radiation of a Water-Filled Piezoelectric Cylinder near a Rigid Plane

The combined finite-element-boundary-element method is used to solve the problem on the radiation of a water-filled piezoceramic cylinder positioned near an infinite plane. For the case of a perfectly rigid plane, the frequency characteristics of the transmitting response of the piezoelectric cylinder are obtained along with the frequency characteristics of the acoustic power, the directional characteristics, and the velocity and pressure distributions over the radiating cylindrical surfaces. It is found that, when the distance between the plane and the piezoelectric cylinder is small relative to the wavelength, the frequency characteristics of the cylinder and the velocity and pressure distributions noticeably differ from those obtained for a piezoelectric cylinder in an infinite space. The effect of the antisymmetric mode, which appears at small wave distances between the cylinder and the plane, on the characteristics of a water-filled piezoelectric cylinder is considered.     

Acousto-Optic Diffraction in an Ultrasonic Field of a Width-Profiled Transducer

Acoustical Physics - Acousto-optical diffraction in an ultrasonic field of a slow acoustic mode in paratellurite excited by a hexagonal-shaped piezoelectric transducer has been simulated in a...     

Peculiarities of Forming a Multiband Transmission Function Based on Multifrequency Acousto-Optic Diffraction

An analytical solution for the transmission function of noncoherent wideband radiation is obtained under acousto-optic (AO) filtering using a discrete set of monochromatic AO waves with a small spectral overlap. We studied characteristics of the AO transformation of a continuous spectrum of noncoherent radiation into a given set of discrete narrow bands of spectral transmission by excitation of a discrete set of sound frequencies. We carried out the analysis of transmission functions of individual channels taking into account a partial overlap of their spectra and possible intermodulation distortions. It is shown that a stationary value of the root-mean-square light power is found at the electronic output due to the photoelectric transformation and detecting diffracted light. Based on this, a necessary stationary, multiband, and nearly equidistant transmission function of a device can be formed by using a relevant spectrum of acoustic excitation. Peculiarities of this way of forming the multiband transmission function are revealed: the limitation of diffraction efficiency for an individual channel, the possibility of decoupling side lobes of adjacent channels, etc. A multiband acousto-optic filter (MAOF) was simulated that was based on a paratellurite monocrystal (TeO₂), which was previously used for experimental optical encoding. The theoretical and experimental results are in gratifying agreement.     

Radiation in the Far Zone of an Elementary Emitter Located on the Boundary of a Plane Layered Structure

Optics and Spectroscopy - A rigorous theory of determining radiation in the far zone of an elementary dipole that is located either on the boundary of a plane-layered structure or inside it is...     

Acousto-Optic Control of the Energy Profile of Laser Radiation

An acousto-optic shaper is developed for transformation of the Gaussian beam profile into almost rectangular profile. As distinct from lens devices, an acousto-optic device allows modification of the shape of the output beam in a fixed optical configuration using changes in radio control with relatively short response times of about 10 μs. The method is based on multibeam high-efficiency Bragg diffraction when the diffraction orders are overlapped with respect to angle. It is shown that the beam profile can be transformed into rectangular and more complicated profiles with an efficiency of no less than 80%. The experiments are performed using the TeO₂ crystal.     

Numerical and experimental study of Near-Field Acoustic Radiation Modes of a baffled spherical cap

In this paper, the Acoustic Radiation Modes (ARMs) of spherical structures are studied using the Pressure-Velocity (PV) method. This method yields the active and reactive modes, which refer to the radiated and non-radiated sound power components respectively, without restrictions on the observation distance. The accuracy of the method is verified through the analysis of Near Field ARMs (NFARMs) of a sphere in spherical coordinates compared to the analytical solution. Differences are analyzed between the NFARMs and the Far Field ARMs (FFARMs) of a baffled spherical cap, as well as between the active and reactive parts of the sound power radiated when varying the frequency and the observation distance to the source. It was found that the radiation efficiency of the active ARMs is independent of the observation distance, while that of reactive ARMs decreases sharply when retreating from the source. Experiments were performed using the acoustic reciprocity principle to measure the NFARMs and FFARMs of a 3D-printed spherical cap radiating in a hemi-anechoic room. Experimental results provided a reliable validation of the numerical results.     

Radiation of a Cascade near a Plane Interface and in a Planar Layer

In order to detect cosmic rays and ultrahigh-energy neutrinos, a number of experiments based on the detection of radio radiation of cascades initiated by these particles in dense media such as ground ice massifs or lunar regolith have been developed. In most of the experiments, radio radiation is detected at the emission to the atmosphere or cosmic space rather than in a dense medium. Consequently, it is necessary to calculate the radiation of a cascade taking into account an interface between two media. This problem is usually solved numerically by the Monte Carlo method. A simple analytical expression for a radiation field in the wave zone of the less dense medium has been obtained for the case of development of the cascade in the dense medium and the crossing of the interface between two media by radiation. The effect of the third, additional medium on the radiation field of the cascade has also been considered.     

黑腔端置靶辐照不均匀性分析

提供一种解析方法来研究激光加热黑腔所产生的平面辐射场的不均匀度与平面靶大小和位置的关系 ,解析结果与数值模拟结果进行了比较 ,两者的曲线形状基本一致 ,辐照不均匀度最小值的位置也是一致的。     

数字全息波前重建中的像平面滤波技术研究

基于数字全息图的频谱平面滤波及像平面滤波技术,最近出现两种可变放大率的物光波前重建方法.为适应数字全息精细检测的要求,对两种滤波方法进行了研究,导出让局部重建图像布满重建平面的表达式.研究结果表明,像平面滤波技术优于频谱平面滤波技术,基于像平面滤波技术的重建方法能够按照需要的放大率高质量地重建局部物光场.给出彩色数字全...     

Multi-Band Absorption Properties and Near-Field Enhancement in Mid-Infrared Based on the Interference Theory

We numerically study the multi-band absorption properties and near-field enhancement inside the microcavity based on the interference theory. The compact single unit cell consists of a gold square patch placed on the top of a metallic ground plane, separated by a dielectric layer. At the normal incidence of electromagnetic radiation, four bands of a maximum absorption of 98% are accomplished by appropriate sizes of the square patch. Furthermore, we demonstrate that the four bands, which are corresponding to the fundamental mode and higher modes of the standing wave, can be readily tuned in the mid-infrared region and associated with the near-field enhancement in the cuboid mierocavity. Since chemical and biological fingerprints of the common functional groups can be found in the mid-infrared region, we may readily tune the multi-bands of interest in the mid-infrared range and identify the molecular stretches of groups. Moreover, the proposed structure is insensitive to the polarization of the incident wave due to the complete rotational symmetry （C4 symmetry）. The unique properties of the optical metamaterial indicate that this approach is a promising strategy for surface-enhanced infrared absorption spectroscopy and for the tracking of characteristic molecular vibrational modes     

The Effect of a Silicon Substrate on the Directivity Pattern of Scattered Radiation of a Gold Nanospheroid and on Near-Field Polarization

We studied the radiation-directivity pattern and the near-field polarization of a spheroidal metallic nanoparticle located over a silicon substrate by interaction with a linearly and circularly polarized field. It is shown that the directivity pattern of the spheroidal particle near the silicon substrate becomes strongly asymmetric and forward scattering is predominant compared with the symmetric diagram of a particle in free space. The change of the near-field polarization of the nanoparticle in presence of the substrate is studied for different wavelengths in the vicinity of the plasmonic resonance. The near-field polarization is described using the generalized Stokes parameters, which allow pictorial visualization of results.     

像面滤波技术在无透镜傅里叶变换数字全息中的应用

无透镜傅里叶变换数字全息波前重建主要采用全息图的一次快速傅里叶变换方法,重建图像不能充分占有重建平面.本文基于像平面滤波技术,提出对物体局部区域光波场进行放大重建并让重建图像布满重建平面的方法,给出具有精细结构物体的数字全息波前重建实例.此外,将数字全息光波场重建视为具有方形出射光瞳的光学系统的相干光成像过程,导出了物体放大图像的分辨率与光学系统相关参量的关系,并通过实验给予证明.     

像面滤波技术在无透镜傅里叶变换数字全息中的应用

无透镜傅里叶变换数字全息波前重建主要采用全息图的一次快速傅里叶变换方法,重建图像不能充分占有重建平面.本文基于像平面滤波技术,提出对物体局部区域光波场进行放大重建并让重建图像布满重建平面的方法,给出具有精细结构物体的数字全息波前重建实例.此外,将数字全息光波场重建视为具有方形出射光瞳的光学系统的相干光成像过程,导出了物体放大图像的分辨率与光学系统相关参量的关系,并通过实验给予证明.     

六方氮化硼薄膜对石墨烯-碳化硅结构近场热辐射的增强

六方氮化硼(hBN)具有跟石墨烯类似的层状结构和晶格参数,研究发现hBN薄膜具有良好的热传导、电绝缘、光学和力学等性能.本文从理论上研究了 hBN薄膜对石墨烯-碳化硅(G/S)结构的近场热辐射的影响.研究发现在红外频段,hBN薄膜在低频率区和高频率区会增强G/S结构的近场热辐射,经计算在G/S结构中加入厚度为10 nm...     

Effect of Ionosphere on the Excitation of Electromagnetic Field at Extremely Low and Lower Frequencies in the Near-Field Zone

Excitation of electromagnetic fields at extremely low and lower frequencies in the near-field zone of the Earth–ionosphere waveguide is considered. Variations in the field amplitude in the lower part of the extremely low frequency (ELF) range and lower frequencies are experimentally determined under different geophysical conditions in the absence of variations in the ultralow frequency (ULF) range. The effects related to such variations are analyzed with the aid of theoretical calculations that show significant effect of ionosphere in the near-field zone at relatively low terrestrial conduction.     

微小孔近场衍射的能量传输

用标量衍射理论研究了圆孔近场衍射中的能量传输,计算了透系数及轴线上衍射场的能流密度,在微小孔衍射的情况下,讨论了矢量衍射理论对能量传输问题标量处理的修正。     

单模辐射场与N个原子相互作用理论

用玻色算符的三维型哈密顿量描述单模辐射场与Ｎ个两能级原子的相互作用。在原子系统处于低能态。光子数很大的初始条件下，得到了作用系统的动力学变化规律。