远红外辐射黑瓷板研制及其性能研究

以提钒尾渣为主要原料制造的黑瓷远红外辐射板,具有宽泛的烧结温度、突出的着色作用和优良的成瓷性能,第四周期过渡金属氧化物的含量大于80%,辐射率高达0.95,经过2 000 h、650℃加速老化试验,辐射率无变化,黑瓷板表面层不会脱落。通过扫描电镜对素坯板和黑瓷板的断口形貌和显微组织进行观察发现,素坯板主要由钛铁矿、板钛铁矿和拉长石等矿物组成,颗粒间呈机械混合状态,黑瓷板由晶粒、玻璃体和气孔组成,原料中大部分金属氧化物转移到晶粒中富集,形成堇青石、锂辉石、锆英石等矿物,被玻璃体紧密包围,热冲击性优良,化学稳定性好,无毒无害无放射性,是一种成本低、寿命长、效率高的远红外辐射体。     

The geometric-optics theory of a plane chiral-metamaterial lens

The focusing properties of a double-layer plate (plane lens) made of isotropic chiral electromagnetic media with negative permittivity and permeability are considered.     

Full-wave analysis of circular microstrip resonators inmultilayered media containing uniaxial anisotropic dielectrics,magnetized ferrites, and chiral materials

In this paper, Galerkin's method in the Hankel transform domain is applied to the determination of the resonant frequencies, quality factors, and radiation patterns of circular microstrip patch resonators. The metallic patches are assumed to be embedded in a multilayered substrate, which may contain uniaxial anisotropic dielectrics, magnetized ferrites, and/or chiral materials. The numerical results obtained show that important errors can be made in the computation of the resonant frequencies of the resonators when substrate dielectric anisotropy, substrate magnetic anisotropy and/or substrate chirality are ignored. Also, it is shown that the resonant frequencies of circular microstrip resonators on magnetized ferrites can be tuned over a wide frequency range by varying the applied bias magnetic field. Finally, the computed results show that the resonance and radiation properties of a circular microstrip patch on a chiral material is very similar to those of a circular patch of the same size printed on a nonchiral material of lower permittivity     

Performance Study of a Double-Pass Thermoelectric Solar Air Collector with Flat-Plate Reflectors

In this paper the results of the influence of flat-plate reflectors made of aluminum foil on the performance of a double-pass thermoelectric (TE) solar air collector are presented. The proposed TE solar collector with reflectors was composed of transparent glass, an air gap, an absorber plate, TE modules, a rectangular fin heat sink, and two flat-plate reflectors. The flat-plate reflectors were placed on two sides of the TE solar collector (east and west directions). The TE solar collector was installed on a one-axis sun-tracking system to obtain high solar radiation. Direct and reflected incident solar radiation heats up the absorber plate so that a temperature difference is created across the TE modules to generate a direct current. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the absorber plate. Ambient air flows through the heat sink located in the lower channel to gain heat. The heated air then flows to the upper channel, where it receives additional heating from the absorber plate. Improvements to the thermal energy and electrical power outputs of the system can be achieved by the use of the double-pass collector system with reflectors and TE technology. It was found that the optimum position of the reflectors is 60°, which gave significantly higher thermal energy and electrical power outputs compared with the TE solar collector without reflectors.     

Radiation and scattering from thin wires in chiral media

The effect of chirality on thin wire antennas and scatterers in unbounded chiral material is examined through the application of fundamental principles and the examination of several canonical examples. In particular, the interplay between normalized chirality and wire length is investigated to classify radiation and scattering patterns. Chirality induces rapid decay in the currents on such wires, resulting in mountain-peak-shaped current distributions characteristic of wire antennas and bow-tie-shaped distributions characteristic of wire scatterers of sufficient length. These current distributions, in turn, cause radiation and scattering patterns which exhibit a chirality-dependent forbidden zone for both antennas and scatterers. In this zone, the fields are greatly reduced. These distinctive results lead naturally to the classification of wire scattering and radiation into subchiral, chiral, and superchiral regimes. All results are understood from the underlying physical principles of electromagnetic chirality, and are related to values of a dimensionless parameter involving normalized chirality and normalized wire length     

Backfire radiation from a monofilar helix with a small ground plane

Numerical analysis of a helical antenna is made in the presence of a finite-grid ground plane. It is found that the transition from forward-fire radiation to backfire radiation occurs as the ground-plane diameter is reduced to the order of the helix diameter. The investigation of the backfire helix with a small ground plane shows that a circularly polarized wave is radiated over a frequency range of more than 1 to 1.3. An application of the backfire helix to primary feed for a paraboloidal reflector is also described, in which the far-field pattern is evaluated by the physical-optics approximation     

FDTD analysis and measurement of aperture antennas based on thetriplate transmission-line structure

First, two aperture antennas designated as P-type and C-type antennas are analyzed using the finite-difference time-domain (FDTD) method. Each antenna is made of a triplate transmission line (TTL). A square aperture is cut out of the top plate of the TTL for both antennas to allow radiation. The bottom of the TTL is a planar plate for the P-type antenna and a plate with a hollow cavity for the C-type antenna. The power flow is expressed using Poynting vectors. It is revealed that parallel-plate mode power in the TTL is lower in the C-type antenna, compared with that in the P-type antenna. Second, an array antenna composed of two C-type elements is analyzed. The Poynting vector distribution in the aperture is found to remain almost unchanged when the element spacing is varied. The input impedance of the array antenna converges at an element spacing of approximately 0.9 wavelength. The theoretical radiation patterns are in good agreement with measured data     

基于薄板理论的密排结构CMUT发射声场研究

由微机电系统(MEMS)工艺制作的电容式微机械超声换能器(CMUT),其具有宽频带,易与电子电路集成制作等优势,在医学成像领域具有广阔的应用前景。为了研究一种密排结构CMUT超声换能器的发射声场特征,该文提出了一种简单的物理域相互作用分析方法。基于薄板的振动理论,由CMUT单元的声学辐射原理及特性计算得到CMUT阵元辐射声场的解析解。通过振膜振动分布实验验证了采用薄板振动理论一阶振型方程的正确性。通过仿真和实验研究了CMUT发射单元在不同排布方式和条件下的声场分布、声轴声压和指向性,为CMUT的设计和性能分析提供了理论依据。     

Radiation of an aperture antenna covered by a spherical-shellchiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE₁₁ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically     

梯形接地板结构超宽带天线设计

在圆形单极天线的基础上进行改进设计了一款梯形接地板结构的超宽带单极天线。根据接地板电流的分布强弱,削去矩形接地板两端对电流影响较小的三角形形状部分,构成梯形接地板。经过仿真优化实验结果表明,该天线电压驻波比VSWR2的阻抗带宽为3.1~17 GHz,工作频段内具有全向辐射特性,且天线只有20 mm×22 mm×1.6 mm,结构简单,适合超宽带无线通信系统的要求。     

一种新型小型化微带天线的分析与设计

针对传统微带天线低频端尺寸较大的缺点,设计了一种新型微带天线结构,即通过采用在传统微带天线贴片下方挖出凹槽,将辐射板放入凹槽中的办法,设计了一副小型化微带天线。与普通微带天线相比,新型天线谐振频率降低了870MHz,阻抗带宽从原来的170MHz增至560MHz,且天线在整个工作频段内具有良好辐射特性,从而验证了该设计方案的正确性。     

单层和双层手征介质柱域的并矢格林函数理论及其应用

本文应用散射叠加法,分别导出了单层和双层手征介质圆柱区域中的并矢格林函数。由此分析了位于手征介质圆柱和手征介质圆柱罩中心轴线上点偶极天线的辐射特性。结果表明,通过改变手征介质圆柱的尺寸和手征介质圆柱罩的厚度,可以任意调节辐射场的极化特性。另外,本文给出的并矢格林函数公式还可用于分析柱形手征微带天线的辐射特性。     

A double-element broad-band liquid crystal tunable filter-factorsaffecting contrast ratio

A double-element broad-band liquid crystal tunable filter consisting of a high-order quartz wave plate in series with a very-low-order electrooptically tunable liquid crystal phase plate and placed between crossed polarizers is described. A possible application for such a device is protection against intrusive laser radiation. The advantage of this double-element filter over a single-element low-order LC filter is that it increases the wavelength resolution of the device, which, when operated in the protect mode, allows continued sensing of the scene. Experimental and theoretical studies were made of the contrast ratios obtainable with such a filter     

A THz Spectroscopy System Based on Coherent Radiation from Ultrashort Electron Bunches

A spectroscopy system will be discussed for coherent THz transition radiation emitted from short electron bunches, which are generated from a system consisting of an RF gun with a thermionic cathode, an alpha-magnet as a magnetic bunch compressor, and a linear accelerator for post-acceleration. The THz radiation is generated as backward transition radiation when electron bunches pass through an aluminum foil. The emitted THz transition radiation, which is coherent at wavelengths equal to and longer than the electron bunch length, is coupled to a Michelson interferometer. The performance of the spectroscopy system employing a Michelson interferometer is discussed. The radiation power spectra under different conditions are presented. As an example, the optical constant of a silicon wafer can be obtained using the dispersive Fourier transform spectroscopy (DFTS) technique.     

Radiation of elementary sources in a chiral medium

The classical problem of radiation of elementary sources is generalized to the case of a chiral medium. The electromagnetic fields of right- and left-hand polarized waves are expressed in terms of vector potentials, and formulas for the components of the fields radiated by a vertical electric dipole in a chiral medium are obtained.     

双层手征介质板中电偶极天线的辐射特性

本文首先给出了电流源激励下双层手征介质中的并矢格林函数表达式。应用鞍点积分法,导出了有金属板衬底的双层手征介质中电偶极天线的辐射场表达式。分析了有、无空气隙时手征导纳对电偶极天线的方向图,＝0方向的最大场强和谐振频率的影响程度。结果表明,通过改变手征导纳参数,可以有效地调节电偶极天线的辐射特性。     

任意分层手征介质球域中并矢格林函数理论和应用

本文首先应用散射迭加法，给出了含源任意分层手征介质球域中的并矢格林函数，以手征介质球壳为例，分析了位于球中心处点偶极天线的辐射特性，以及归一化辐射阻抗随球壳厚度的变化规律，在平板近似条件下，研究了手征导纳对手征介质球壳传输特性的影响，并且讨论了手征介质球壳内、外表面与空气之间阻抗匹配时，点偶极天线远区辐射场的极化特性。结果表明，通过改变球壳的归一化厚度，可以调节辐射场的极化状态。     

Aperture Coupled Rectangular Dielectric Resonator Antenna Array Fed by Dielectric Image Guide

This paper presents the design of a rectangular dielectric resonator antenna array coupled to narrow slot apertures that are fed by dielectric image guide (DIG). The DIG is excited by an X-band rectangular waveguide through a waveguide transition, and DIG tapering is used to match between the waveguide and the DIG. Reflection cancelling slots are added near the original slots to improve impedance matching. Since the slots radiate in both directions, a reflecting conducting plate is inserted above the DIG to decrease the back radiation of the antenna. The antenna is fabricated and the measured results are compared to the simulated results.      

多孔橡胶板声辐射效率数值研究分析

多孔橡胶板具有优良的隔声吸声性能,是减振和降噪的首选材料,而声辐射效率是描述其声辐射能力的一个重要参数。为了深入分析多孔橡胶板的声辐射性能,建立了可以表征多孔橡胶板特性的描述性模型,采用混合FE-SEA方法对尺寸为500 mm×500 mm×30 mm的多孔橡胶板声辐射效率进行了数值计算分析,研究了多孔橡胶板结构参数(开孔率、孔径宏观参数)和材料特性(杨氏模量、橡胶密度)对声辐射效率的影响规律。结果表明,不同参数在不同频段对声辐射效率的影响特性不同,对不同工况下多孔橡胶板参数优化具有一定理论指导意义。     

Shape-Memory Photonic Thermoplastics from Cellulose Nanocrystals

Responsive materials prepared using shape-memory photonic crystals have potential applications in rewritable photonic devices, security features, and optical coatings. By embedding chiral nematic cellulose nanocrystals (CNCs) in a polyacrylate matrix, a shape-memory photonic crystal thermoplastic (CNC-SMP) allows reversible capture of different colored states is reported. In this system, the temperature is used to program the shape-memory response, while pressure is used to compress the helical pitch of the CNC chiral nematic organization. By increasing the force applied ( ≈ 140–230 N), the structural color can be tuned from red to blue. Then, on-demand, the CNC-SMP can recover to its original state by heating it above the glass transition temperature. This cycle can be performed over 15 times without any loss of the shape-memory behavior or mechanical degradation of the sample. In addition, multicolor readouts can be programmed into the chiral nematic CNC-SMP by using a patterned substrate to press the sample, while the glass transition temperature of the CNC-SMP can be tuned over a 90  ° C range by altering the monomer composition used to prepare the polyacrylate matrix.