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22.
介绍和分析了左手介质的构造原理和方法,通过对加载左手介质材料的贴片天线的研究,来说明左手介质天线的一些优异特性。仿真和实测结果表明,通过加载左手介质材料,普通贴片天线会产生新的特性,如工作频率的降低、天线增益的提高、方向性的增强等。而且,天线的物理尺寸能得到很大的减小,这就为高增益、高带宽的小型化贴片天线设计提供了新的方法和思路。 相似文献
23.
In this work, the permittivity of a tailored compound material was investigated consisting of a polyimide matrix in which hollow glass microspheres with a mean diameter of 30 μm are implemented as filler material. Choosing this approach the dielectric constant compared to that of the pure polyimide material is further decreased due to the enclosed air targeted to improve the high-frequency performance of patch antennas operated in the GHz range. Furthermore, the thickness of one single layer can be increased substantially from a maximum of about 10 μm for pure polyimide films to values above 80 μm by simply adding this type of filler material to the liquid polyimide precursor so that cavities in LTCC (low temperature co-fired ceramics) substrates can be filled more reliable. Two different variations of this compound material with filler to polymer ratios of 1:7.5 and 1:10 are realized. Basically, the film thickness depends on the spin coating speed and the microsphere content, respectively. The high initial surface roughness can be decreased to an average value of about 3 μm by applying additional layers of pure polyimide on top enabling thin film technology. The dielectric constant of the complete substrate comprising the LTCC and the compound material is measured using a ring resonator in microstrip configuration. From the resonances occurring in the transmission S-parameter |S21| spectrum between 1 and 10 GHz, the relative dielectric constant can be determined. Using 820 μm thick LTCC substrates the permittivity can be reduced from originally εr = 7.8-6.6. By applying numerical calculations, a reduced permittivity of the pure polymer film from εr = 3.3 to about 2.9 can be determined when adding the glass microspheres. 相似文献
24.
Silos are widely used in the food and chemical industries for the storage of granular materials. The calculation of their wall dimensions is complicated since the interaction between the stored material and that from which the silo is made is complex, a consequence of their very different mechanical behaviours. The loads exerted on the silo walls by stored materials must be taken into account in silo design, and the means for calculating them is contemplated in Eurocode EN 1991-4. The complexity of the phenomena that occur within silos often leads to the appearance of unexpected and asymmetrically distributed pressures. This is taken into account in the above Eurocode via the concept of the patch load, which is asymmetric and can be exerted at any point on the silo wall. A finite element model has been developed in order to check that the stress resultants derived from the patch load on steel silos with corrugated walls may be predicted by using the well-known expressions of shell theory. Then, a simplified analytical procedure has been developed for predicting the worst location of patch loads for all metal silos, but with special application to corrugated steel silos in Action Assessment Class 3. It has been found that significant differences may be found for most cases with the worst location for the patch load defined in Eurocode for welded silos in Action Assessment Class 2. On the other hand, the values obtained for the maximum meridional membrane stress resultant do not significantly differ, except for high slenderness values in intermediate slenderness silos. 相似文献
25.
如何求解声传递函数成为实现小尺度封闭空间可听化的关键技术。基于Helmholtz方程的有限元法能真实反映出声场内的波动现象,成为求解该问题的有效方法。基于SPR法对求解声传递函数的有限元法进行误差估计;在此基础上结合Helmholtz方程求解的误差理论,提出了求解该问题的自适应有限元法,使用该方法能预测出在各求解频率段内有限元网格的划分情况,从而能满足预先给定的误差要求;使用该方法求解了一个矩形封闭空间内的声传递函数。结果表明提出的方法是有效可行的。 相似文献
26.
Bolted patch repair of composite panels with a cutout 总被引:1,自引:0,他引:1
The present investigation concerns the analysis of bolted patch repairs of flat composite panels by using a complex potential–variational method. The validity of the current analysis predictions is established by comparison against experimental measurements and previous predictions. The experimental investigation used two patch repairs, with different bolt patterns, of a cutout in an aluminum skin under uniaxial loading. The previous predictions were made for a patch-repaired composite skin with 16 bolts under uniaxial loading. The same patch repair configuration is analyzed here under more complex loading conditions and with two bolts missing, leading to a non-symmetric bolt arrangement. Also, the influence of patch geometry and bolt pattern on the effectiveness of the repair is investigated by considering an elliptical cutout in the skin. 相似文献
27.
出生前氚水照射对仔鼠海马神经元电生理及神经行为的影响 总被引:3,自引:0,他引:3
妊娠13d的大鼠接受累积吸收剂量分别为0.000、0.044、0.088和0.264Gy的氚水照射,观察对新生大鼠体外培养海马神经元形态、细胞计数、最大Ca2+电流的影响,并通过Y迷宫刺激回避反射与条件反射试验的学习记忆行为进行综合评价。结果表明,出生前接受0.088Gy的氚水照射即可减少体外培养海马神经元的数目;随剂量的增加,Ca2+电流有下降趋势,剂量达0.264Gy时导致Ca2+电流显著降低;Y迷宫刺激回避反射与条件反射试验结果表明,剂量达0.088Gy时即可导致仔鼠学习记忆行为受损。 相似文献
28.
A. A. Shaalan 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(7):657-669
This paper presents the design of compact broadband H-slot and horizontal H-slot microstrip patch antenna with a single feed.
The antenna is also used for circular polarization application with a single narrowband frequency. The performance of single
feed notched and truncated corner circularly polarized microstrip antennas with the same substrate thickness for H-slot and
horizontal H-slot is studied. The simulated results such as return loss S11, axial ratio AR, radiation pattern (Eleft and Eright), and gain are presented in this paper for different shapes of patch antenna. 相似文献
29.
Cheng Huang Zeyu Zhao Wei Wang Xiangang Luo 《Journal of Infrared, Millimeter and Terahertz Waves》2009,30(7):700-708
In this letter, a kind of metamaterial superstrate based on rectangular metallic grids is presented to enhance the directivity
of patch antenna at two frequency bands for two orthogonal polarizations. According to the periodic boundary condition, the
influences of its important geometry parameters are investigated in detail by simulating its unit cell. It is found that the
transmission peak frequency is intimately related to the size of rectangular metallic grid. Then, a dual band dual polarization
patch antenna with metamaterial is studied and compared with conventional patch antenna. It is demonstrated that by introducing
the proposed metamaterial superstrate, the gain of the patch antenna is improved by 9.5 dB at 14.1 GHz for x polarization and 12 dB at 15.4 GHz for y polarization, respectively. 相似文献
30.
给出了结合人工神经网络进行双频RFID读写器天线的优化设计方法,该天线由一层双边开槽贴片,厚空气层及接地层的加载缝隙耦合实现双频工作.以天线电磁仿真结果作为人工神经网络模型的训练数据,以天线贴片的四个关键结构尺寸作为神经网络模型的输入参数,以天线回波损耗作为输出参数,实现天线的快速优化设计.所设计天线的性能指标为:在驻波比小于2.0时,低频段(900 MHz)的工作带宽约为70 MHz(870~940 MHz),高频段(2.4 GHz)的工作带宽约为300MHz(2.235~2.535 GHz);天线尺寸为179.3 mm×120 mm.神经网络模型和电磁仿真结果吻合良好. 相似文献