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A NOVEL DUAL-BAND METAMATERIAL ABSORBER AND ITS APPLICATION FOR MICROSTRIP ANTENNA
摘要： In this letter, a novel dual-band metamaterial absorber is presented and analyzed. The absorber is composed of four patches on the top of a thin grounded dielectric substrate which can absorb incident wave at two di?erent frequency bands e?ectively. Then the absorber is loaded on the dual-band microstrip antenna, whose working frequency bands are overlapped with that of the absorber, to reduce the in-band RCS (Radar Cross Section) of antenna. The prototype is simulated, manufactured and measured. Simulated results show that the absorption of the absorber is as high as 98.6% at 4.29 GHz and 99.8% at 6.49 GHz. As to the dual-band antenna loaded with the proposed absorber, its radiation performance is unchanged while the RCS has declined by 8.59 dB at 4.29 GHz and 9.9 dB at 6.49 GHz respectively. There is a good agreement between simulated and measured results, which veri?es that this absorber can be used for in-band RCS reduction of dual-band antenna so as to improve its in-band stealth performance.
关键词： RCS reduction,dual-band metamaterial absorber,microstrip antenna,stealth performance
更新于2025-09-09 09:28:46
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First-principles investigation of the electronic band structures and optical properties of quaternary <i>A</i> Ba <i>MQ</i> <sub/>4</sub> ( <i>A</i> = Rb, Cs; <i>M</i> = P, V; and <i>Q</i> = S) metal chalcogenides
摘要： In this paper, we study the optoelectronic properties of quaternary metal chalcogenide semiconductor ABaM Q4 (A = Rb, Cs; M = P, V; and Q = S) compounds using state-of-the-art density functional theory (DFT) with TB-mBJ approximation for the treatment of exchange-correlation energy. In particular, the electronic and optical properties of the relaxed geometries of these compounds are investigated. Our first-principles ab-initio calculations show that the CsBaPS4 and RbBaPS4 compounds have direct bandgaps whereas the CsBaVS4 compound exhibits indirect bandgap nature. Importantly, the theoretically calculated values of the bandgaps of the compounds are consistent with experiment. Furthermore, our analysis of the electronic charge densities of these compounds indicates that the above quaternary chalcogenides have mixed covalent and ionic bonding characters. The effective masses of these compounds are also calculated which provide very useful information about the band structure and transport characteristics of the investigated compounds. Similarly, high absorptivity in the visible and ultraviolet regions of the electromagnetic spectrum possibly predicts and indicates the importance of these materials for potential optoelectronic applications in this range.
关键词： energy band structure,electronic charge densities,optical conductivity,Chalcogenides,refractive index,dielectric constants,optical reflectivity
更新于2025-09-09 09:28:46
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A COMPACT QUAD-BAND BANDPASS FILTER USING MULTI-MODE STUB-LOADED RESONATOR
摘要： This paper presents a compact shorted stub-loaded quad-band bandpass ?lter. The proposed ?lter simultaneously operates at GSM (0.83–0.97 GHz), LTE2300 (2300–2400 MHz), WiMAX (3.3–3.7 GHz), and WLAN (5.725–5.825 GHz) bands. The ?lter has been designed using the technique of stub-loaded resonator (SLR). By changing the length of the center-loaded stub, the resonant frequency of the even-mode can be varied without a?ecting that of the odd-mode. This simpli?es the design and tuning of the quad-band ?lter. Eight transmission zeros (TZs) around the three passband make the pass bands highly isolated. In order to validate its practicability, a quad-band bandpass ?lter (BPF) has been designed, fabricated and measured. Good agreement between simulated and measured results is observed.
关键词： LTE,GSM,WLAN,stub-loaded resonator,WiMAX,quad-band bandpass filter
更新于2025-09-09 09:28:46
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A NEW EQUAL POWER QUADRATURE BRANCH LINE COUPLER FOR DUAL-BAND APPLICATIONS
摘要： We present a new equal power quadrature branch line coupler (BLC) for dual-band applications in this paper. A new topology of the dual-band quarter wavelength transmission lines (TL) with the derivation of design equations is also introduced. The proposed BLC is designed using Advanced Design System (ADS) and fabricated on Rogers 5870 at 0.9 GHz and 2.4 GHz center frequencies. The design approach for the proposed dual-band BLC is endorsed by the simulated and measured results. A comparative analysis of this BLC with the previous BLCs is also carried out.
关键词： Advanced Design System,quarter wavelength transmission lines,equal power quadrature branch line coupler,Rogers 5870,dual-band applications
更新于2025-09-09 09:28:46
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DESIGN OF COMPACT RECONFIGURABLE BROADBAND BAND-STOP FILTER BASED ON A LOW-PASS FILTER USING HALF CIRCLE DGS RESONATOR AND MULTI-LAYER TECHNIQUE
摘要： This paper describes the design of a two-pole low-pass and band-stop ?lters. The low-pass structure is designed at the cuto? frequency of 2 GHz for the L-Band applications. This architecture uses half circle defected ground structure HCDGS instead full circle DGS resonator. Both the HCDGS shapes are etched in the ground plane and coupled via a substrate with a compensated capacitor. The rejection bandwidth of the LPF covers a large wideband spectrum. Therefore, the band suppression reaches more than 3f c. The ?lter is simulated and fabricated. The measured results are in good agreement with the full-wave simulated ones, showing the merits of compact size and sharp roll-o?. The multi-layer technique has been used in order to realize a transformation from low-pass behaviours to band-stop characteristics, keeping the same passband features. The new extracted band-stop topology is simulated and optimized using an RO4003 substrate with relative permittivity of 3.38 and thickness of h = 0.813 mm. The structure has a wide stopband with over 20 dB rejection from 3.5 GHz to 8.5 GHz. Such ?lters can be used for L-band and military applications.
关键词： compact,reconfigurable,broadband band-stop filter,half circle DGS resonator,low-pass filter,multi-layer technique
更新于2025-09-09 09:28:46
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POLARIZATION-INSENSITIVE TRIPLE-BAND MICROWAVE METAMATERIAL ABSORBER BASED ON ROTATED SQUARE RINGS
摘要： An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal ?lm separated by only 1 mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88 GHz, 7.88 GHz, and 11.32 GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-re?ection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.
关键词： polarization-insensitive,microwave,metamaterial absorber,triple-band,rotated square rings
更新于2025-09-09 09:28:46
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Structural, morphological, optical and dielectric properties of M <sup>3+</sup> /PVA/PEG SPE Films (M = La, Y, Fe or Ir)
摘要： Low band gap polymer complexes are promising due to its flexibility, and exhibiting electronic and optical properties of inorganic semiconductors. The effect of PEG on the physical properties of PVA was evaluated. Then, blend (PVA: PEG = 50:50) doped with rare earth (La or Y) and transition metal (Fe or Ir) chlorides to obtain solid polymer electrolyte films. XRD shows that adding PEG to PVA results in a new peak, 2θ = 23o with increased intensity as PEG ratio increases. However, doping with La3+, Fe3+ or Ir3+ eliminate this peak and decrease the crystallinity. SEM exhibits significant changes in the morphology of films. FTIR confirms miscibility between PVA & PEG and the complexation of the salts. The optical band gap (Eg) of PVA ~ 5.37 eV, decreased slightly by blending with PEG. While it decreased significantly to 2.64 eV and 2.78 eV after doping with Fe3+ or Ir3+. There are a consistency between Eg values obtained by Tauc's model and that obtained from the optical dielectric loss. The dielectric constant and loss, in temperature range 303–405 K & frequency range 1.0 kHz ‐ 5.0 MHz, indicate one or two relaxation peak(s) depending on the film composition. Accordingly, conduction mechanism varied between correlated barrier hopping and large polaron tunneling. The DC conductivity was strongly depend on the dielectric loss. The transition metal salts appear to be more effective than the rare earth ones in increasing σac of films to higher values that candidates them in semiconductors industry.
关键词： conduction mechanism,low band gap polymers,activation energy,PVA/PEG blend,rare earth metal complexation,solid polymer electrolyte
更新于2025-09-09 09:28:46
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[Springer Series in Materials Science] Introduction to Isotopic Materials Science Volume 248 || Energy Band Structure
摘要： Optical probing and manipulation of electron quantum states in isotope-mixed compounds at the nanoscale are key to developing future nanophotonic devices, which are capable of ultrafast and low-power operation. Before beginning a general discussion on the application of isotopic materials science, it is helpful to have the knowledge of the electronic band structure used in materials. The modern view of solid-state physics is based on the presentation of elementary excitations having mass, quasi-impulse, and electrical charge. The base of such view of solid is ideal gas, which described the behavior of the system, e.g., noninteracting electrons. Such an approach to model of elementary excitations as a suitable model for the application of the quantum mechanics for the solution of solid-state physics task. In this chapter, some peculiarities of isotopic materials science will be considered by taking into account the dependence of the properties of elementary excitations on the isotope effect. It is illustrated when the dimensions of a solid are reduced to the size of the characteristic length of electrons in the isotope-mixed materials (de Broglie wavelength, localization length), new physical properties due to quantum effects become apparent. Our intention has been to physics of low-dimensional isotope-based compounds and quantum devices would built up to the treatment of those new electronic, transport and optical properties.
关键词： nanophotonic devices,isotope effect,electronic band structure,solid-state physics,quantum effects,isotope-mixed compounds,quantum mechanics
更新于2025-09-09 09:28:46
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Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 phosphors: electronic, crystal structures and photoluminescence properties
摘要： The union of chemical compositions substitution and spectral controlling is of importance for the discovery of new materials or the implementation of properties optimization. In this work, we employed an effective strategy to regulate crystal structures by chemical unit co-substitution. We applied this strategy to Eu3+-doped Sr2(Al1?xMgx)(Al1?xSi1+x)O7 (0 ≤ x ≤ 1) solid solution phosphor, which was successfully synthesized by high temperature solid state reaction. The crystal structure remained the same group, P-421m, with controlling chemical compositions. The excitation peaks shifted between 263 and 270 nm and emission peaks shifted between 612 and 614 nm with a decreasing Stocks shift in overall tendency. The shift trend was clarified by Crystal Field Theory. The energy band structure and density of states of Sr2Al2SiO7 and Sr2MgSi2O7 were calculated by Density Functional Theory using the generalized gradient approximation. The band gap was also analyzed by diffuse reflectance spectrum as a contrast. The morphology was characterized by field emission scanning electron microscopy. Furthermore, the photoluminescence color of phosphors could be tuned from yellow to orange.
关键词： crystal structure,chemical unit co-substitution,phosphors,photoluminescence,energy band structure
更新于2025-09-09 09:28:46
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Dual-Bandgap Effect of Photonic Crystals on TiO2 Photocatalytic Activity in Ultraviolet and Visible Light Regions
摘要： Photonic crystals (PCs) have promising characteristic to raise the light harvest of materials. PCs with one photonic band gap (PBG) were usually used to enhance the light harvest of materials. In this research work, we used PCs with dual PBGs to increase the light harvest. SiO2 PCs with dual PBGs were constructed through depositing a SiO2 PCs layer on another SiO2 PCs layer by vertical deposition method. Then the bi-layer structured SiO2 PCs were composited with nanocrystalline TiO2 film which was sensitized by CdS quantum dots (QDs) (Q-T), to produce photocatalyst for photodegradation of gaseous acetaldehyde. By adjusting the PBGs of the bi-layer SiO2 PCs, namely one PBG matching with the absorption edge of TiO2 and another PBG matching with the absorbing range of CdS QDs, the photocatalytic activity of the composite film under white light irradiation was increased to 2.11 times of that of the control photocatalyst (the Q-T film coated on a disordered porous SiO2 film). When Q-T film was coupled with a monolayer SiO2 PCs, which has single PBG centered at TiO2’s electronic band gap (EBG) of 380 nm, its photocatalytic activity was increased by 1.34 times. When coupled with a monolayer SiO2 PC with the PBG centering at the EBG of CdS QDs (465 nm), the photo-catalytic activity of the Q-T film was increased by 1.54 times. Because the SiO2 PCs with dual-PBGs can simultaneously enhance the light harvest in ultraviolet and visible light region, the Q-T film coupled with dual-PBGs SiO2 PCs showed the highest activity.
关键词： Photocatalyst,SiO2 Opal,Dual photonic band gaps,TiO2,Photonic crystals
更新于2025-09-09 09:28:46