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New blue phosphorescence from trifluorosulfonyl-substituted iridium complexes
摘要： For color-pure phosphorescence organic light emitting diodes (PHOLEDs), we synthesized the trifluoromethyl sulfonyl substituted ligand and two new blue Iridium complexes with perfluoro-sulfonyl group (SOCF3pic and SOCF3mpic). The both iridium complexes showed similar photophysical and thermal properties while the HOMO energy leves of two Iridium complexes slightly differnet to be -5.84 eV for SOCF3pic and -5.74 eV for SOCF3mpic, respectively. The device with the SOCF3mpic dopant exhibited higher device efficiencies of 7.17 cd/A and 3.7 % compared to that with the SOCF3pic dopant (4.03 cd/A and 2.78 %). Two-dimensional GIXD images of scattered X-ray intensity from surface to full depth for SOCF3pic-doped and SOCF3mpic-doped TCTA:4PTPS films were characterized for preferential orientation along the out-of-plane direction.
关键词： preferential orientation along the out-of-plane direction,blue phosphorescence,iridium complex,grazing incidence wide-angle X-ray diffraction,organic light emitting diodes
更新于2025-09-23 15:23:52
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Dual-Linear Polarized Phased Array with 9:1 Bandwidth and 60° Scanning off Broadside
摘要： We present for the first time a novel dual-linear polarized tightly coupled dipole array (TCDA) with integrated balun operating across a 9:1 bandwidth, from 2GHz to 18GHz. This dual-linear polarized array employs a tightly coupled dipole topology and scans down to 60° from boresight. The overall geometry consists of cross-located tightly coupled dipoles integrated with a folded Marchand balun that serves as an impedance transformer to achieve a wideband feeding network. Notably, the traditional dielectric superstrate is replaced with double layers of frequency selective surfaces (FSS) to enable scanning down to 60° in both E-, H-, and diagonal (D-) planes across the entire band. The design achieves VSWR<3 across 2 to 18GHz at broadside. This dual-polarized array is also demonstrated to have a good polarization isolation of -20dB for most of the band. The array’s total height is less than 12mm (λlow/10). The design is validated through fabrication and testing of an 11×11 prototype. Measurements of this prototype are presented and are in good agreement with simulations.
关键词： tightly coupled dipole array,low profile array,ultra-wideband,wide-angle scanning
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - Auckland (2018.8.5-2018.8.8)] 2018 IEEE Asia-Pacific Conference on Antennas and Propagation (APCAP) - A Broadband and Wide-angle Band-stop Frequency Selective Surface (FSS) Based on Dual-layered Fractal Square Loops
摘要： In this work, a broadband and wide-angle band-stop FSS based on dual-layered periodic arrays of fractal square loops was proposed and demonstrated. Equivalent circuit model and full-wave electromagnetic simulation were used to analyze this FSS. The sample of designed FSS with optimized structure parameters for center working frequency about 13GHz was fabricated and measured. The experimental results agree well with the simulated ones. Both of them indicated that the FSS has broad stop bands for both TE and TM polarization under incident angles from 0° to 60°. Specifically, the stop bands under incident angle 60° are over 7.35GHz and 5.91GHz for TE and TM polarization, respectively.
关键词： wide-angle,fractal Square Loop,broadband,band-stop frequency selective surface,dual-layered
更新于2025-09-23 15:22:29
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Magnetoelectric uniaxial metamaterials as wide-angle polarization-insensitive matching layers
摘要： Antire?ection or impedance matching is a topic that has been extensively researched by the optical and microwave communities over the past century and until today. However, due to the diverging wave impedances of TE (s) and TM (p) polarizations with increasing incident angle, it is impossible to achieve perfect matching simultaneously for both polarizations at varying incidence angles with a single conventional isotropic matching layer. To achieve polarization-insensitive matching at an arbitrary incident angle, we propose a magnetoelectric uniaxial metamaterial layer (MEUML) that is inspired by the perfectly matched layer (PML) concept in computational electromagnetics. Similar to the PML, the MEUML requires speci?c uniaxial permittivity and permeability tensors. However, to simultaneously control both the transversal and longitudinal material parameters is not an easy task. To date, a true PML has not been realized with metamaterials. In this paper, we employ a simple and yet special metamaterial unit cell to achieve such control and synthesize a physical MEUML. The unit cell comprises two parallel metallic rings separated by a holey substrate. The transversal electric and magnetic dipole moments, and the longitudinal capacitive and diamagnetic coupling between the rings are judiciously controlled to achieve the required permittivity and permeability tensors. To aid the MEUML synthesis, we also introduce a technique that can extract the material parameter tensors at any incident angle. We ?rst demonstrate this concept by achieving polarization-insensitive matching of a high-index substrate at 45? with a single subwavelength-thick MEUML. We further adapt the concept to the microwave regime by developing a MEUML-based radome. Exceptional matching performance was obtained both in the simulations and measurements. The re?ectance remains below 5% from normal incidence (0?) to near grazing angle (85?) for both polarizations and over a wide bandwidth. With this unprecedented control of the material parameter tensors, the MEUML concept not only can be applied to impedance matching, but also can be utilized in many exotic applications that require extreme control of the material properties.
关键词： wide-angle,impedance matching,polarization-insensitive,radome,magnetoelectric uniaxial metamaterials
更新于2025-09-23 15:21:21
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DIAMAGNETO-DIELECTRIC ANISOTROPIC WIDE ANGLE IMPEDANCE MATCHING LAYERS FOR ACTIVE PHASED ARRAYS
摘要： In this paper, we present the full process of designing anisotropic metamaterial (MM) wide angle impedance matching (WAIM) layers. These layers are used to reduce the scan losses that occur in active phased arrays for large scanning angles. Numerical results are provided to show the improvement in performances that such layers can ensure. The proposed anisotropic MM-WAIM layers achieve an improvement of about 1 dB of more radiated power at θ = 70? from broadside, in a 13% of fractional bandwidth on the azimuthal plane φ = 90?. Weaker improvements are obtained in the other azimuthal planes, however keeping the active re?ection coe?cient below ?9 dB for all azimuthal planes up to θ = 60? and up to θ = 70? o?-axis for planes φ = 45?, 90? in the whole operational band.
关键词： scan losses,wide angle impedance matching,anisotropic metamaterial,active phased arrays,impedance matching
更新于2025-09-23 15:21:21
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Combined Wide-Angle Scanning by a Two-Dimensional Dipole Array
摘要： An analytical solution of an impedance synthesis problem for a two-dimensional dipole antenna array is obtained. The array consists of thin impedance electric dipoles whose centers are located at nodes of a planar rectangular grid with double periodicity. Radiation patterns of each dipole in the array does not differ from that of an isolated dipole. A new method for wide-angle scanning of the array radiation pattern, combining the simultaneous variation of phases of the excitation currents in the dipoles and of their surface impedances is proposed.
关键词： thin impedance dipole,flat two-dimensional antenna array,wide-angle scanning,radiation pattern,wave zone,impedance synthesis method
更新于2025-09-23 15:21:21
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Multiband ultrathin polarization-insensitive terahertz perfect absorbers with complementary metamaterial and resonator based on high-order electric and magnetic resonances
摘要： Terahertz perfect metamaterial absorbers (PMA) based on higher-order resonances have exhibited important applications in detecting, sensing and imaging. However, most of them suffer from polarization and incident-angle dependence due to their asymmetrical structure. Here we numerically investigate a kind of ultrathin triple-band PMA with polarization stability and wide angle of incidence. Numerical results reveal that three resonance peaks with nearly 100% absorptivity are obtained at 1.605 THz, 4.425 THz and 4.946 THz under different polarization angles. It is interestingly found that the absorptance of two higher-order resonances is inversely increased when the size of the middle dielectric spacer is smaller. The three resonance peaks in transverse electric (TE) and transverse magnetic (TM) modes nearly maintain fixed for oblique incidence up to 60°. Importantly, another four-band and dual-band perfect absorptions are easily achieved by complementary method without doing iterative numerical simulation. The complementary metamaterial based absorber (CMA) reaches more than 98% absorptance at four resonance frequencies. The metamaterial absorber based on complementary resonator (CRMA) also obtains two absorption peaks at 2.65 THz and 5.84 THz.
关键词： complementary resonator,polarization,wide angle,complementary metamaterial,Perfect metamaterial absorbers
更新于2025-09-23 15:21:01
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The Phase Behavior in the Active Layer of Small Molecule Organic Photovoltaics: The State Diagram of p-DTS(FBTTh <sub/>2</sub> ) <sub/>2</sub> :PC <sub/>71</sub> BM
摘要： A comprehensive study was undertaken to obtain a more fundamental understanding of the phase behavior of the p-DTS(FBTTh2)2:PC71BM system, used in small molecule organic solar cells, with a strong focus on the amorphous phase and its influence on crystallinity. Three dedicated thermal protocols were used in combination with advanced thermal analysis, solid-state NMR, and wide angle X-ray diffraction. Rapid cooling, to avoid structure formation and gain insight in the amorphous phase, and slow cooling, to promote structure formation, were used as limiting cases to explain the intermediate behavior after device processing from solution. A complete state diagram was developed and the glass transition (Tg) - composition relationship was determined. In the case of slow cooling and the procedure used for device processing, the rapid crystallization of p-DTS(FBTTh2)2 leads to an enrichment of the amorphous phase in PC71BM, increasing its Tg and causing vitrification of the mixed amorphous phase before crystallization when the total amount of PC71BM exceeds 70 wt%. The common processing additive 1,8-diiodooctane (DIO) was found to lead to a lower p-DTS(FBTTh2)2 crystallinity and smaller average crystal size. More importantly, it acts as a strong plasticizer, lowering Tg significantly and thus reducing the morphological stability of the p-DTS(FBTTh2)2:PC71BM mixtures.
关键词： p-DTS(FBTTh2)2:PC71BM,glass transition temperature,wide angle X-ray diffraction,phase behavior,crystallinity,amorphous phase,small molecule organic photovoltaics,thermal analysis,solid-state NMR,1,8-diiodooctane (DIO)
更新于2025-09-23 15:19:57
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Broadband, wide-angle antireflection in GaAs through surface nano-structuring for solar cell applications
摘要： We demonstrate broadband and wide-angle antireflective surface nanostructuring in GaAs semiconductors using variable dose electron-beam lithography (EBL). Various designed structures are written with EBL on a positive EB-resist coated GaAs and developed followed by shallow inductively coupled plasma etching. An optimized nanostructured surface shows a reduced surface reflectivity down to less than 2.5% in the visible range of 450–700 nm and an average reflectance of less than 4% over a broad near-infrared wavelength range from 900–1400 nm. The results are obtained over a wide incidence angle of 33.3°. This study shows the potential for anti-reflective structures using a simpler reverse EBL process which can provide optical absorption or extraction efficiency enhancement in semiconductors relevant to improved performance in solar photovoltaics or light-emitting diodes.
关键词： GaAs,surface nano-structuring,broadband,solar cell applications,wide-angle,antireflection
更新于2025-09-23 15:19:57
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Wide-angle scanning circular polarization phased array based on polarization rotation technology
摘要： A wide-beam circular polarization (CP) antenna and a wide-angle scanning phased array based on novel polarization rotation reflective surface (PRRS) are proposed. The CP wide-beam pattern is obtained by the combination of the radiation wave from the patch antenna and the orthogonal reflected wave from the PRRS with a 90(cid:1) phase difference. The proposed CP wide-beam antenna obtains the patterns with the 3-dB beamwidth more than 136(cid:1) and the axial ratio (AR) beamwidth more than 132(cid:1) in the xoz-plane. Furthermore, an eight-element phased array based on the wide-beam CP antenna element is also developed. The measured results show that the main beam of the array can scan from ?65(cid:1) to 65(cid:1) with a gain fluctuation less than 3 dB and the ARs at every scanning angle less than 3 dB.
关键词： polarization rotation,phased array,wide-beam,circular polarization,wide-angle scanning
更新于2025-09-19 17:15:36