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Effective permittivity and permeability of one-dimensional dielectric photonic crystal within a band gap 总被引:1,自引:0,他引:1 下载免费PDF全文
We take a finite dielectric photonic crystal as a homogeneous slab and have extracted the effective parameters. Our systematic study shows that the effective permittivity or permeability of dielectric photonic crystal is negative within a band gap region. This means that the band gap might act as ε-negative materials (ENMs) with ε 〈 0 and μ 〉 0, or μ-negative materials (MNMs) with ε 〉 0 and μ 〈 0. Moreover the effective parameters sensitively rely on size, surface termination, symmetry, etc. The effective parameters can be used to design full transmission tunnelling modes and amplify evanescent wave. Several cases are studied and the results show that dielectric photonic band gap can indeed mimic a single negative material (ENM or MNM) under some restrictions. 相似文献
94.
We investigate the wave propagation through the tilted interface of one-dimensional photonic crystals. Negative refraction can be realized by excitation of the Bloch states in the extended Brillouin zone with suppressed reflection. Equi-frequency surface analysis shows that the positive refraction, negative refraction or birefringence in this configuration can be achieved under a proper incident angle, which is confirmed by finite-difference timedomain simulations. The results may be useful in applications in the new devices based on one-dimensional photonic or optical waveguide arrays. 相似文献
95.
针对开口房间内的变压器,在开口处布放若干扬声器和误差传声器构成虚拟声屏障,实验研究了虚拟声屏障对通过开口向外辐射的低频线谱噪声的控制效果。将15个次级源近似均匀分布在面积为2 m′ 2.7 m的开口面上,左右间距约58.5 cm、上下间距45-65 cm,15个误差传声器分别位于对应的次级源正前方1 m,系统采用自适应谐波降噪算法。结果表明:虚拟声屏障系统在误差点100 Hz、200 Hz和300 Hz的平均降噪量分别达到12.7 dB、19.9 dB和22.2 dB,虚拟声屏障对100 Hz、200 Hz、300 Hz线谱噪声的控制效果与单层封闭窗户相当,且内部合成参考信号,无需外接参考传声器。采用虚拟声屏障对开口房间内的变压器降噪的好处是实现室内外的自然通风,便于变压器的散热。 相似文献
96.
We investigate one-dimensional dielectric photonic crystal and optical Tamm modes formed by superposition of two band gaps and find that this kind of mode can be explained by the single negative materials tunnelling effect. A finite-size dielectric photonic band gap can mimic one kind of effective single negative material and this property sensitively depends on the frequency location in stop-band regions and surface termination and so on. The effective impedance match and effective phase match give the precise position of the optical Tamm mode. Complete transparency via tunnelling is achieved by two opaque media and demonstrates the validity of our approach. 相似文献
97.
Specimens of an oxide dispersion strengthened(ODS) ferritic steel(15 Cr-4 Al-0.6 Zr-0.1 Ti) are implanted with multiple-energy He ions at room temperature to create a damage plateau of 0.4 dpa for the average(corresponding to an He concentration of about 7000 appm) from the near surface to a depth about 1 um. The specimen is subsequently thermally annealed at 800°C for 1 h in a vacuum so that simple defects can be formed in the as-implanted state that has undergone significant recombination, meanwhile helium bubbles at nano-scale are formed. Hardness of the specimens are tested with the nano-indentation technique. A hardening by 25% is observed. Microstructures of the specimen after irradiation/annealing are investigated with transmission electron microscopy. Helium bubbles are generally located at dislocations and grain boundaries. Using the dispersed barrier strength model, the strength factor of helium bubbles in the ODS ferritic steel is estimated to be between0.1 and 0.26, which is close to that of helium bubbles in austenitic steels. 相似文献