Equivalent circuit analysis of ‘U’-shaped split ring resonators

An equivalent circuit model of ‘U’-shaped split-ring resonators (SRR), the basic structure of SRR has been proposed and studied. The proposed model, other than traditional equivalent circuit model, has taken both the influence of geometrical parameters and dielectric substrate into account and investigated them in detail. Furthermore, the calculation formula of extra mutual inductance induced by periodic cells has been derived. The performance of the ‘U’-shaped SRR analyzed by the equivalent circuit model shows a good agreement with experimental measurements and numerical simulation in terahertz region. This work presents a novel method to predict the resonance frequency of complicated SPP accurately and paves an avenue for the future terahertz devices applications.     

Stable high absorption metamaterial for wide-angle incidence of terahertz wave

We propose a metamaterial based on metallic Jerusalem cross and cross-wire structures for realizing relatively stable high absorption with respect to the wide angle incidence of both polarized terahertz (THz) waves. Numerical simulations are carried out to verify the proposed absorber. For both transverse electric and transverse magnetic polarizations, absorptions around 0.93?THz reach nearly up to unity under normal incidence and maintain above 97% over a wide incidence angle range. The THz absorber can be easily micro-fabricated due to a thickness about 40 times smaller than operating wavelength. The proposed metamaterial is a promising candidate as absorbing element in THz thermal imager, due to its wide angle, stable high absorption and very thin thickness.     

Influence of prepared plasma on THz emission from the plasma induced by ultrashort lasers: a quasi-analytical investigation

The influence of prepared plasma induced by a prepulse on the THz emission generated by main two-color femtosecond lasers (fs-lasers) has been investigated numerically and analytically by using a photocurrent model. Results observed in a previous report, such as the suppression of THz emission from the main pulse due to the existence of a prepulse, were easily reproduced. Further calculation showed that such suppression originates from residual electrons of the prepared plasma affecting the main pulse. Moreover, an exact expression between the E-field of THz waves generated by the main pulse and the residual electron density of the prepared plasma has been obtained.     

三维超材料制造技术现状与趋势

三维超材料是具有三维空间特定排布的亚波长人工周期结构,具有自然材料不具备的超常规物理性能。本文以三维超材料的电磁调控技术为线索,简要论述了近年来三维超材料在基础研究和制造工艺方面的研究现状;梳理了目前三维超材料的制造方法,包含印刷电路板及组装的方法、机械加工方法、3D打印技术、微纳制造工艺;选取电磁隐身罩、透镜天线、吸波器、柔性超材料等代表性应用类别,简述了三维超材料器件的电磁调控方法与实现手段,所涉及的超材料种类包括左手超材料、渐变折射率超材料、智能超材料等。基于目前三维超材料研究领域待解决的问题,对今后三维超材料的发展趋势进行了探讨。

     

超级电容器电极材料及器件的柔性化与微型化

随着可穿戴式电子设备的快速发展,各类柔性储能器件也相继出现。柔性超级电容器因其稳定性高、体积小、电化学性能优越等特点受到研究人员的广泛关注。开发一种工艺简单、电化学性能和柔性良好的电极材料对制备性能优越的柔性超级电容器具有重要意义。材料的选取、电极的制备及器件的微型化将是未来的主要研究方向。本文主要综述了柔性超级电容器电极材料的分类、具体的制备方法以及器件的主要构型,并探讨了柔性超级电容器电极材料及器件的主要发展方向和研究重点。     

高Q值THz类EIT超材料及传感特性研究

设计了一种具有类电磁诱导透明(EIT)效应的高Q值太赫兹超材料。该结构单元由上下平行的双金属线及中间垂直的单金属线组成。分别对单金属线、双金属线及组合结构进行仿真,分析了组合结构中金属线的位置和尺寸对透射率及品质因数Q的影响。结果表明,随着单金属线的水平移动产生了类EIT效应,透射率和Q值随着偏移距离的增大而发生变化,通过调整结构和尺寸可以实现不同Q值。通过优化,当偏移距离为8 μm时,在0.73 THz附近得到一个3 dB带宽约为11.56 GHz的透明窗,相应的Q值为63.09,其透射率为0.50。最后,对谐振器的传感特性进行了测量,其折射率灵敏度为60.69 GHz/RIU,FOM值为5.25/RIU,具有优异的传感特性。     

基于超材料的无标记光学生物传感

超材料(metamaterials)因为能够在亚波长尺度范围内精细调控电磁波而受到人们广泛关注。超材料具有丰富的电磁模态,在表面支持高度局域场增强且对周围介电环境极其敏感,可应用于无标记光学生物传感领域。与传统光学生物传感器相比,超材料生物传感器具有小型化、集成化、高度灵敏、多功能可定制等突出优点。本文总结了近年来超材料生物传感器在可见光、近红外、中红外以及太赫兹波段的研究进展,包括折射率生物传感、表面增强拉曼散射、表面增强红外吸收和太赫兹生物传感等。     

Highly efficient terahertz pulse generation by optical rectification in stoichiometric and cryo-cooled congruent lithium niobate

We report, and review in detail, experiments resulting in a record 3.7% optical-to-terahertz (THz) conversion efficiency by optical rectification (OR) in cryogenically cooled congruent lithium niobate (cLN) using a near-optimal 680 fs pump pulse at 1030 nm. In addition, we report a record conversion efficiency of 1.7% at room temperature using stoichiometric lithium niobate (sLN) which results in 21.8 μJ of THz energy from a 1.2 mJ optical pulse. Electro-optical sampling measurements reveal the THz pulses to be single-cycle and centered at 0.45?THz. The experimentally measured efficiency, THz waveform, and THz spectrum are in good agreement with theoretical calculations. Finally, spatial beam profile measurements are also provided. To our knowledge, these results represent an order of magnitude improvement in efficiency of THz generation by OR in lithium niobate over previous results.     

Active control of terahertz multimode resonance transmission through subwavelength metal annular aperture arrays

Ultrafast optical properties of U-shaped annular aperture arrays (UAAAs) fabricated on a silicon substrate were investigated for varying photodoping levels of the silicon from the back to front interfaces of the sample. Experimental data demonstrate that the transmission modulation depth of the multimode resonance can be realized about 90% under optical power 60 mW, and the off switch of these resonance peaks transmission can be also simultaneously achieved within several picoseconds. Such plasmonic structure is able to be used for ultrafast optical modulators, active terahertz plasmonics, and ultrafast optical off switch.     

Semiconductor split-ring resonators for thermally tunable terahertz metamaterials

As the variation of temperature alters the intrinsic carrier density in a semiconductor, numerical simulations indicate that the consequent variation of the relative permittivity in the terahertz regime provides a way to realize thermally tunable split-ring resonators. Electromagnetic metasurfaces and metamaterials that are thermally tunable in the terahertz regime can thus be implemented.