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Classification of flat bands according to the band-crossing singularity of Bloch wave functions
摘要： We show that ?at bands can be categorized into two distinct classes, that is, singular and nonsingular ?at bands, by exploiting the singular behavior of their Bloch wave functions in momentum space. In the case of a singular ?at band, its Bloch wave function possesses immovable discontinuities generated by the band-crossing with other bands, and thus the vector bundle associated with the ?at band cannot be de?ned. This singularity precludes the compact localized states from forming a complete set spanning the ?at band. Once the degeneracy at the band crossing point is lifted, the singular ?at band becomes dispersive and can acquire a ?nite Chern number in general, suggesting a new route for obtaining a nearly ?at Chern band. On the other hand, the Bloch wave function of a nonsingular ?at band has no singularity, and thus forms a vector bundle. A nonsingular ?at band can be completely isolated from other bands while preserving the perfect ?atness. All one-dimensional ?at bands belong to the nonsingular class. We show that a singular ?at band displays a novel bulk-boundary correspondence such that the presence of the robust boundary mode is guaranteed by the singularity of the Bloch wave function. Moreover, we develop a general scheme to construct a ?at band model Hamiltonian in which one can freely design its singular or nonsingular nature. Finally, we propose a general formula for the compact localized state spanning the ?at band, which can be easily implemented in numerics and offer a basis set useful in analyzing correlation effects in ?at bands.
关键词： Chern number,singular band touching,flat bands,nonsingular band touching,bulk-boundary correspondence,compact localized states,Bloch wave functions
更新于2025-09-23 15:23:52
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Planar UWB Monopole Antenna with Tri-Band Rejection Characteristics at 3.5/5.5/8 GHz
摘要： A triple band-notched ultrawide band (UWB) antenna is presented to avoid the interference of services working in the UWB band, such as WLAN, WiMAX and X-band satellite systems. The arc H-shaped slot on the radiating patch creates a low frequency notched band, while the other two band-notched bands are formed by cutting narrow slots on the ground plane. The presented antenna can operate on the ultrawide band efficiently and inhibit interference from three different kinds of narrow band communication systems. The simulation and measurement results show that the antenna has excellent band-notched function on the rejectband and almost omnidirectional radiation pattern on the passband.
关键词： planar monopole antenna,slots,triple band-notched,ultrawide band (UWB) antenna
更新于2025-09-23 15:23:52
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Narrow-Band Green-Emitting Sr <sub/>2</sub> MgAl <sub/>22</sub> O <sub/>36</sub> :Mn <sup>2+</sup> Phosphors with Superior Thermal Stability and Wide Color Gamut for Backlighting Display Applications
摘要： The narrow-band emitting phosphors have been extensively investigated in recent years, with the expectation that a wide color gamut of phosphor-converted backlighting device could be fabricated. Due to the weak electric–phonon interaction and low structural relaxation caused by the high rigid crystal structure and symmetric coordination environment, Sr2MgAl22O36:Mn2+ (SMAO:Mn2+) shows a narrow full-width at half-maximum of 26 nm, a high color purity of 81.5%, and a low thermal quenching (82% at 473 K of the initial intensity at 298 K). Using K2SiF6:Mn4+ as the red phosphor, SMAO:Mn2+ as the green one, and GaN-based chip as the blue component, the white light-emitting diode exhibits a National Television Standard Committee value of 127%. All the results demonstrate that the SMAO:Mn2+ phosphor has a promising application in the field of advanced wide-color-gamut backlight display, and the establishment of the relationships between the narrow-band emission and crystal structure can also be applied to design other novel narrow-band phosphors for backlighting technologies.
关键词： color gamut,inorganic phosphors,narrow-band emission,white light-emitting diodes,Sr2MgAl22O36:Mn2+,thermal stability,backlight displays
更新于2025-09-23 15:23:52
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A thin-layer dielectric and metamaterial unit-cell stack loaded miniaturized SRR-based antenna for triple narrow band 4G-LTE applications
摘要： This article presents the design of a miniaturized dual-band antenna for long-term evolution (LTE) application is presented. In the basic antenna design, split ring resonator was loaded in the radiating plane of the patch and frequency of resonance was further modified with the help of E-shaped stub. The antenna has been fabricated using FR-4 substrate and the measured dual bands at 2.11 and 2.665 GHz are found in a close match with the simulated data. By placing a thin dielectric resonator of permittivity εr = 10.2 and thickness of 1.27 mm, two closely spaced narrow bands are obtained at 2.217 and 2.28 GHz. A novel metamaterial unit-cell having near-zero refractive index is designed and mounted above the dielectric resonator. This stack configuration generates triple narrow frequency band in the LTE 2 GHz spectrum range. The overall size of the proposed antenna is 20 × 25 mm2.
关键词： triple band,split ring resonator,thin layer dielectric resonator,reflection coefficient,patch,unit-cell
更新于2025-09-23 15:23:52
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A dual-band efficient circularly polarized rectenna for RF energy harvesting systems
摘要： A multilayered circularly polarized (CP), dual-band, stacked slit-/slotted-patch antenna with compact size and with compact rectifier is offered for RF energy harvesting systems. The compact dual-band CP antenna size is able to achieve by stacking slotted-circular-patch (SCP) on the substrate above the tapered-slit-octagon patch (TSOP). Dual-band CP radiation is realized by stacking the SCP on the TSOP and the microstrip feedline with metallic-via to SCP. Eight-tapered-slit with length difference of 6.25% are embedded along the octagonal directions symmetrically on the TSOP from the patch's center and two unequal size circular slots are embedded in diagonal axis onto SCP to produce dual-orthogonal modes with almost equal magnitude for CP waves. The designed antenna is realized measured gain of greater than 5.2 dBic across the band (0.908-0.922 GHz) with maximum gain of 5.41 dBic at 0.918 GHz and gain of greater than 6.14 dBic across the band (2.35-2.50 GHz) with maximum gain of 7.94 dBic at 2.485 GHz. An overall antenna volume is 0.36λo × 0.36λo × 0.026λo (λo is free space wavelength at 0.9 GHz). A compact composite right-/left-handed (CRLH) based rectifier with dual-band at 0.9 and 2.45 GHz is designed, prototyped, and measured. The right-handed (RH) part of the CRLH transmission line (TL) is formed by a microstrip line. The left-handed (LH) part of the CRLH-TL is formed by lumped components. The measured RF-DC conversion efficiency is 43% at 0.9 GHz and 39% at 2.45 GHz with rectifier size of 0.18λo × 0.075λo × 0.0002λo at 0.9 GHz.
关键词： slotted-patch,stacked antenna,energy harvesting,rectenna,rectifier,circular polarization,dual-band
更新于2025-09-23 15:23:52
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Polarization independent quad-bandpass frequency selective surfaces with wide-band ratio
摘要： A single layer polarization independent quad-bandpass frequency selective surface (FSS) with wide-band ratio is demonstrated theoretically as well as experimentally. The proposed structure passes four frequency bands with wide band ratio. The proposed FSS design is implemented by incorporating alternate arrangement of four units which are rotated 90° clockwise to form a unit cell of metal over a FR4 substrate. The geometrical dimensions of proposed unit cell are optimized and arranged in such a way that the structure possesses the quad bandpass characteristic and aspect dimensions of one unit is 0.11λ × 0.11λ with respect to first resonant frequency. This FSS provides stable response for different angle of incidence in transverse electric (TE) mode and transverse magnetic (TM) mode. To validate the results proposed FSS array has been fabricated and measured in free space environment. The measured results are in good agreement with the simulated results. Excellent stability is also observed for different incident angle.
关键词： quad bandpass,polarization independent,frequency selective surface,band ratio
更新于2025-09-23 15:23:52
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Bandwidth enhancing method using tri-ring resonator metamaterial for small devices
摘要： Metamaterials are composite structures of the specific behavior for electromagnetic properties of permittivity, permeability, and refraction, which are not commonly found in regular materials. Metamaterial structure, which has negative value of permittivity and permeability that shows passband response in transmission line, where as if any of these two properties has opposite polarity then it shows stopband response. These behaviors of metamaterial are frequency dependent and have resonance for particular frequencies. At frequency resonance, the traditional metamaterials have narrow band response and to improve its frequency bandwidth, a method using tri-ring resonator is proposed with increasing number of order of resonator. The proposed metamaterial structure is simulated in full-wave simulator and MATLAB tool is used to analyze the properties of metamaterial structure from simulated S-parameter. Proposed technique gives flexibility to use the design for multiple application like, rejection filter for Bluetooth 2.4 GHz, Wi-Fi (2.4 and 5 GHz), WiMAX (2.5 and 3.4 GHz), and 5G (3.4-3.8 GHz).
关键词： SRR,band rejection,split ring resonator,metamaterial,broadband
更新于2025-09-23 15:23:52
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A dual-band circularly polarized microstrip patch antenna with a cross shaped slot for 0.92/2.45 GHz RFID applications
摘要： A double-band circularly polarized (CP) patch antenna is presented. It is a round patch antenna with a cross-shape slot. Furthermore, it radiates wide beam CP waves at two radio-frequency identification (RFID) bands: 920 MHz and 2.45 GHz. Slightly oblate round patch antennas generally radiate CP waves and have resonant frequencies at two or more harmonic bands. To radiate wide beam CP waves at two bands, a cross-shape slot was made on a round patch antenna in this study. As a result, the cross-shape slot has made it possible for a 920 MHz round patch antenna to simultaneously radiate wide beam CP waves at 2.45 GHz which is higher than a harmonic frequency.
关键词： circularly polarized,RFID,cross shaped slot,double-band,patch antenna
更新于2025-09-23 15:23:52
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Co-designed defected ground structure filter with UWB slot antenna
摘要： In this study, one kind of novel co-designed defected ground structure (DGS) filter with slot antenna is proposed to realize bandpass reflection coefficient and gain performance. This antenna consists of two parts: 1) a 50 Ω feeding line and 2) a modified stepped slot with additional narrow slot and defected ground structure. The extra narrow slot, which can effectively prolong the current path of low frequency and generate reflection zero, is introduced to improve the lower band-edge selectivity. DGS is used to improve the upper band-edge selectivity, which can produce transmission zeros in certain frequencies and provides excellent stopband characteristics. In addition, the modified stepped slot with DGS can produce additional resonance frequency, which is helpful to improve the in-band impedance characteristics and radiation efficiency of the antenna. Measured results show that not only the band-edge selectivity of the antenna is improved, but also the in-band impedance matching and radiation efficiency are improved. The experimental results show that the proposed design could be a good candidate for UWB applications.
关键词： UWB antenna,defected ground structures (DGS),band-edge selectivity
更新于2025-09-23 15:23:52
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Novel solid polymer electrolyte based on PMMA:CH3COOLi effect of salt concentration on optical and conductivity studies
摘要： Novel solid polymer electrolyte (SPE) films based on poly(methyl methacrylate) (PMMA) and lithium acetate (CH3COOLi) with different weight ratios of PMMA:CH3COOLi wt% (60:40, 70:30, 80:20 wt%) were prepared by solution casting technique. XRD analysis confirmed the amorphous nature of Li–PMMA SPE films. FTIR analysis revealed the structural changes in polymer by complexation with Li salt. From the optical absorbance studies, the value of lowest energy band gap was found to be 3.06 eV for the composition, PMMA:CH3COOLi (60:40 wt%). From AC impedance studies, the highest value of ionic conductivity 8.21 × 10?5 S/cm at 303 K for the SPE film PMMA:CH3COOLi (60:40 wt%) is observed compared to the reported literature. From the results of Li–PMMA SPE film with high ionic conductivity, it is a promising material for the application of solid-state battery.
关键词： Band gap,Ionic conductivity,Dielectric measurements,Li–PMMA SPE
更新于2025-09-23 15:23:52