Reflection Bandwidth Research Articles

Double-Sided Metasurfaces for Dual-Band Mid-Wave and Long-Wave Infrared Reflectors

We present an innovative method for dual-band mid-wave infrared (MWIR) and long-wave infrared (LWIR) reflectors. By using double-sided metasurfaces, two high reflection bands can be generated with a single device. As individual guided-mode resonance (GMR) reflectors are combined with interlayer (or substrate) on the top and bottom sides, we achieved high reflection in the MWIR and LWIR bands simultaneously. Each GMR reflector was optimized as a germanium (Ge) grating structure on a potassium bromide (KBr) substrate. In our analysis, it was found that the transparency of the interlayer is critical to produce the dual-band reflection. The simulation results on the Ge/KBr/Ge double-sided metasurfaces demonstrated wideband reflection from ~3.3 to 4.8 μm and ~8.8 to 11 μm. Additionally, the device exhibited favorable angular tolerance. The work contributes to developing capability of metasurface technologies in various application fields.

Multifunctional Reconfigurable Vanadium Dioxide Integrated Metasurface for Reflection, Asymmetric Transmission and Cross‐Polarization Conversion in Terahertz Region

AbstractIntegrating reconfigurable and diverse functionalities into a single metasurface at terahertz (THz) frequencies is an emerging research topic that faces significant challenges. Here, a reconfigurable THz metasurface is proposed, offering diversified functionalities based on the phase transition of vanadium dioxide (). The proposed metasurface can switch from wideband reflection to wideband cross‐polarization conversion (CPC) and asymmetric transmission (AT) for linearly polarized waves. When is in its fully metallic state, the metasurface efficiently reflects normally incident waves ranging from 0.2 to 2.8 THz, with total reflection exceeding 0.8. When is in its insulating state, the metasurface achieves nearly perfect wideband cross‐polarization conversion with CPC efficiency above 0.99 from 0.46 to 2.67 THz, and excellent AT effect with efficiency over 0.9 from 0.65 to 2.29 THz for normal incidence of linearly polarized waves. Moreover, the high efficiency of CPC and AT effects is maintained over a wide range of incident angles. The proposed switchable metasurface with diverse functionalities is expected to enable cutting‐edge research and innovative applications in THz communication, sensing, and imaging.

Development model of a high-performance multiple input multiple output microstrip antenna based on a planar series array with 8×2 elements for 5G communication systems

MIMO (Multiple Input Multiple Output) makes a major contribution to 5G communication systems by increasing network capacity and spectrum efficiency. In 5G, MIMO enables the use of multiple antennas at base stations and user devices, allowing simultaneous sending and receiving of data over multiple paths. This significantly increases data throughput and connection reliability, especially in environments with high user density. In addition, MIMO technology supports the implementation of beamforming, which focuses signals on a specific direction, reduces interference, and improves signal coverage and quality, making it one of the keys to achieving faster and more responsive 5G performance. Therefore, antennas with wide bandwidth, high gain and MIMO performance are crucial for supporting 5G communication systems. This paper proposes a high-performance MIMO microstrip antenna based on a series planar array with 8×2 elements operating at a resonant frequency of 3.5 GHz for 5G communication systems. A spiral stub and a feed inset are proposed to control the reflection coefficient and bandwidth of the antenna while the series planar array is proposed to increase the gain. To support the MIMO communication system, the proposed antenna is separated into two different ports with a certain distance. From the measurement results, the proposed antenna has high performance indicated by a wide bandwidth of 680 MHz (3–3.68 GHz) and a high gain of 17.8 dB at a resonant frequency of 3.5 GHz. In addition, the proposed antenna has high mutual coupling and diversity indicated by ECC and DG of 0.001 and 9.99 dB, respectively. This work provides a solution to design a high-performance microstrip antenna and can be implemented as a receiving antenna for 5G communication systems

A novel miniaturized metamaterial inspired frequency reconfigurable antenna with switchable polarization for sub 6 GHz band

Abstract A metamaterial-inspired frequency reconfigurable antenna with switchable polarization realized for 2.4 GHz, 3.5 GHz, and 5.8 GHz frequencies, is reported in this work. Initially, a conventional rectangular patch is designed to resonate at 3.5 GHz. A regular square-shaped SRR (Split Ring Resonator) is a metamaterial-inspired structure that excites additional resonance at 5.8 GHz, without increasing the antenna form factor. Further, a parasitic patch is introduced to create one resonance at 2.4 GHz. Reconfigurability of frequency and polarization is achieved using MPP4203 series PIN diodes. The antenna is simulated using CST Microwave Studio Suite 2019. The designed antenna, characterized by reflection coefficient and bandwidth is analysed for three diode states. The devised antenna operates at 2.4 GHz, 3.5 GHz, and 5.8 GHz, with a maximum bandwidth of 346.2 MHz at the 5.8 GHz frequency band. The radiator outperformed other similar antennas reported in the literature in terms of antenna size, bandwidth, and frequency cum polarization reconfigurability.

One-Dimensional Photonic Crystals Comprising Two Different Types of Metamaterials for the Simple Detection of Fat Concentrations in Milk Samples.

In this study, we demonstrate the reflectance spectrum of one-dimensional photonic crystals comprising two different types of metamaterials. In this regard, the designed structure can act as a simple and efficient detector for fat concentrations in milk samples. Here, the hyperbolic and gyroidal metamaterials represent the two types of metamaterials that are stacked together to construct the candidate structure; meanwhile, the designed 1D PCs can be simply configured as [G(ED)m]S. Here, G refers to the gyroidal metamaterial layers in which Ag is designed in a gyroidal configuration form inside a hosting medium of TiO2. In contrast, (ED) defines a single unit cell of the hyperbolic metamaterials in which two layers of porous SiC (E) and Ag (D) are combined together. It is worth noting that our theoretical and simulation methodology is essentially based on the effective medium theory, characteristic matrix method, Drude model, Bruggeman's approximation, and Sellmeier formula. Accordingly, the numerical findings demonstrate the emergence of three resonant peaks at a specified wavelength between 0.8 μm and 3.5 μm. In this context, the first peak located at 1.025 μm represents the optimal one regarding the detection of fat concentrations in milk samples due to its low reflectivity and narrow full bandwidth. Accordingly, the candidate detector could provide a relatively high sensitivity of 3864 nm/RIU based on the optimal values of the different parameters. Finally, we believe that the proposed sensor may be more efficient compared to other counterparts in monitoring different concentrations of liquid, similar to fats in milk.

Five-pole wideband quasi-reflectionless interdigital BPF with second harmonic suppression

Abstract In this paper, a 5-pole quasi-reflectionless (QR) interdigital BPF with a wide range of non-reflecting signals is proposed, offering good impedance matching. Two absorptive T-shaped stubs are placed at the input and output ports of the interdigital BPF. The absorptive stubs are optimised to obtain the reflection as low as possible for a wide range. Additionally, we shift the adjacent resonators of the interdigital BPF up and down to improve overall performance. The design follows a specific procedure in order to investigate factors affecting the performance. Firstly, the convetional interdigtial bandpass filter is designed relying on the coupling matrix method. Next, we study the conversion of the stopband filter into an absorptive stub. The input impedance of the stub plays a vital role in determining the reflection bandwidth, so it is optimised as well. Meanwhile, the interdigital BPF and one abosrptive stub are combined, where the bandwidth of reflectionless becomes wider compared to the conventional interdigital BPF. Another absorptive stub is added into the other port of the BPF to make the proposed filter symmetric. Different orders of the interdigital PBF are analysed, where the fifth order has the best response. The proposed filter is fabricated and tested, and an FR4 substrate with a thickness of 1.5 mm and a dielectric constant of 4.5 is utilized. The simulation and measurement results agree well. The realised S11 is less than -10dB from 0.72GHz to 4.1GHz (i.e., -10dB reflectionless bandwidth 3.38GHz), while the realised S11 is less than -3dB from 0.42GHz to 6GHz (i.e., -3dB reflectionless bandwidth 5.58GHz). The S21 response is good for the transmission band. Finally, some slots are etched out from the gorund to reduce the influence of the second harmonic response.

Spectral behavior and expansion dynamics of Gd plasma generated by dual-pulse laser irradiation.

Laser-produced gadolinium plasma (Gd-LPP) emerges as a promising candidate for next-generation nanolithography light sources. In this study, a dual laser pulse scheme was implemented to achieve a narrow spectral peak. By varying the pre-main pulse delay and pre-pulse laser energy, optimal conditions of 40 ns delay and 50 mJ energy were identified to improve spectral purity. Radiation hydrodynamics simulations revealed that the improved spectral purity stems from a flatter density gradient at the ablation front and a lower average electron density in the EUV emission region. Additionally, reheating the pre-formed plasma with a short main pulse mitigated plasma squeezing, resulting in an even lower electron density and thus improved spectral purity. Our findings suggest that spectral narrowing in the dual-pulse scheme, essential for better matching with multilayer reflection bandwidths, can be optimized through precise control of pre-pulse energy, pre-main delay, and main-pulse duration.

Multilayer multiband hybrid fractal antenna for public safety and 5G Sub-6 GHz bands

In this work, a multiband hybrid fractal antenna is developed for public safety and 5G Sub-6 GHz bands. Proposed antenna design is designed, analyzed, and optimized using HFSS simulator. Radiating element of the proposed antenna consists of Hybrid Fractal shape which is designed using Koch and Hilbert curve fractal geometry. Hybrid Fractal Antenna (HFA) is designed on a Multilayer FR4 substrate which has an overall size of 0.22 × 0.47 × 0.044 ƛ3. Parametric analysis of the proposed design is done to get the optimum results. Proposed HFA resonates at 2.64 GHz (2.34–2.80 GHz), 3.87, 4.54, 5.02, 5.35 GHz (3.73–5.55 GHz), and 6.42 GHz (5.70–6.72 GHz) with a gain of 4.2, 0.9, 2.9, 3.3, 4.6, and 3.7 dBi respectively. The proposed HFA is useful for 5G bands such as: N7 band, N38 band, N40 band, N41 band, N47 band, N53 band, N79 band, N90 band and N93 band, and also useful for public safety band (4.9 GHz). Prototype of the proposed HFA is fabricated and tested in lab for the verification of simulated results. The results show good performance in terms of reflection coefficient, gain, and bandwidth. Measured results are in good agreement with the simulated results.

A wideband and low profile dual polarized antenna loaded with artificial magnetic conductor

In this paper, a wideband low profile dual-polarization antenna is proposed based on the in-phase reflection characteristic of artificial magnetic conductor (AMC). The AMC cells are designed as two concentric square metallic rings connected by a ‘*’ shaped metallic strip. Its in-phase reflection bandwidth is 2.12 GHz–3.31 GHz, and input-match bandwidth is 1.56 GHz–2.43 GHz. The relative bandwidth is 43.83% and 43.61%, respectively. In addition, the AMC cells are loaded on the reflector of the proposed dual polarized dipole antenna. The measured results show that the −10 dB reflection coefficient (|S 11|) bandwidth of the antenna is 1.55 GHz to 2.4 GHz (43%), and the height is only 0.136λ 0. Furthermore, the gain and front-to- back ratio of the antenna are increased by about 0.8 and 4 dB respectively due to the action of AMC.

Terahertz Meta-Mirror with Scalable Reflective Passband by Decoupling of Cascaded Metasurfaces

Electromagnetic metasurfaces have been playing exotic roles in the construction of ultracompact and versatile metadevices for wave–matter interactions. So far, multiple metasurfaces cascaded with intercouplings have been intensively investigated for extraordinary wavefront control and broadband spectral regulations. However, most cases face high structural complexity and little attention is paid to cascaded metasurfaces without interlayer couplings. In this paper, we demonstrate one type of terahertz Bragg mirror with ideally high reflectivity and ultra-broad bandwidth by simply resorting to decoupled metasurfaces. Cascaded metasurfaces with decoupled mode control prove practically straightforward for analytical design and easy to fabricate for engineering purpose in our scheme. Essentially, by flexibly tuning the decoupled metasurface mode, the middle Fabry–Perot mode that behaves like a defect mode inside the reflective passband can be eliminated for substantial band expanding. Fundamental analyses and rigorous calculations are performed to confirm the feasibility of our metasurface-based THz Bragg mirror with scalable bandgap. In comparison, our meta-mirror provides superior spectral performance of a larger bandgap and higher in-band reflectivity over that composed by ten layers of alternate dielectrics (Rogers 3003 and 3005). Finally, our analytical methodology and numerical results provide a promising way for the rapid design and fabrication of a Bragg mirror in the optical regime.

Plasma-grating-based laser pulse compressor.

To avoid damage in high-power laser systems, a chirped plasma-based grating is proposed for compressing laser pulses that have been previously stretched and amplified. This chirped grating is generated through the interaction of chirped pump laser pulses in a plasma slab. Particle-in-cell (PIC) simulations demonstrate that the grating exists for a duration sufficient to be utilized in the final chirped pulse amplification (CPA) stage. The generation of the grating is quite flexible, as several parameters can be adjusted, such as plasma density, chirp, length, and intensity of the pump laser. To begin, the structure of the grating is analyzed in terms of ponderomotive effects of the pump laser pulses. The primary application of the chirped plasma-based grating lies in compressing laser pulses to large amplitudes and short durations after they have been stretched and amplified beforehand. The compression factor is explored in connection with potential grating parameters. Reflectivity and effective bandwidth of chirped plasma gratings are parameters to be optimized. However, the grating spectral bandwidth can only be increased at the expense of reflectivity. The PIC results are made understandable through model calculations based on coupled mode equations.

Angular scattering measurements and modelling from building surfaces at sub‐THz frequencies between 92‐110 GHz

AbstractThis letter presents experimental angularly resolved measurements and a model framework for characterizing continuous wideband reflection coefficients at sub‐terahertz frequencies between 92 and 110 GHz. Surfaces that appear “smooth” but with internal features comparable to the wavelength have shown to cause frequency selective scattering. An nth‐degree polynomial regression model is employed to quantify non‐linear multi‐path scattering that cannot be described by a best‐fit line, with least‐squares regression applied to find the best‐fitting polynomial and hence the coefficients. The obtained coefficients are then validated against the delay domain statistics of the propagation channel, demonstrating the proposed model's good agreement with measurements and its efficiency in reproducing angle‐dependent reflection coefficients for use in ray‐tracing tools.

Wide spectral range guided-mode resonant grating designed for the wet etching process

We present wideband guided-mode resonant (GMR) gratings made of Si on a SiO2 substrate. Based on the base angle of the grating as the crystal orientation angle (54.74°) of Si, the design process of reflectors suitable for TM-polarized waves is demonstrated in the near-infrared (NIR) and mid-infrared (MIR) wavelengths. Benefiting from the mutual attraction and interaction of the two GMR modes, the bandwidth of reflectivity above 99% for the reflector under the NIR and MIR bands reaches 297 nm (from 1416 nm to 1713 nm) and 657 nm (from 3154 nm to 3811 nm), respectively. In addition, the effects of the incident light source state and the structural parameters on the performance of the reflector are analyzed in detail. The results show that the reflector will maintain good tolerance and stability during fabrication and use. This work will be compatible with the wet etching process in the microelectromechanical system, and the results can be extended to the design of broadband GMR reflectors in other wavelength bands.

Effect of different surface alignment layers and temperature changes on bandwidth of Bragg reflection in chiral nematic liquid crystal

In recent years, the practical properties of cholesteric liquid crystals (CLCs) have been widely studied due to their unique feature of selective Bragg reflection. In this study, we investigated the following aspects: (i) the effect of surface alignment using polyvinyl alcohol, polyamide, and polyimide as covering substrate, (ii) the impact of temperature changes on the reflection bandwidth and, consequently, variations in the cholesteric pitch. Furthermore, we extended Li’s four-parameter model to the cholesteric environment using Haller’s assumption and Vuk’s equations for nematic liquid crystals (NLCs) and Fergason’s theory for CLCs. The fit of the experimental data with this model demonstrated an excellent agreement. The experimental data revealed that the S5011 chiral dopant, with left-handedness, used in the NLC environment of the host, exhibits a significant helical twist power (HTP). This leads to the narrowing of the reflection band width with increasing temperature, without causing a noticeable change in the wavelength of the central reflection. This feature highlights the high potential of these types of chiral materials as thermally stable materials for creating selective-reflective optical filters that remain stable with temperature changes, particularly away from the cholesteric to isotropic transition point.

MMI waveguide reflector based on lithium niobate thin film

Based on the principle of multimode interference (MMI) imaging, an MMI waveguide reflector with high reflectivity, high bandwidth, and high process tolerance is designed using a lithium niobate thin film. The simulation results show that when the input light is transverse electric (TE) polarized, the maximum reflectivity of the designed MMI waveguide reflector is 96.5% at the working wavelength of 1.55 μm, and the bandwidth is 110 nm with more than 90% reflectivity. We also designed an experiment to measure its reflectivity. The experimental result of reflectivity is 85.24%. Compared with other proposed waveguide reflectors, it has the advantages of high reflectivity and large bandwidth. These results indicated that this optimized waveguide reflector design can be applied to integrated optical system based on lithium niobate thin film.

A Two-Port Dual-Band Dual-Circularly-Polarized Dielectric Resonator Antenna

A Two-Port Dual-Band Dual-Circularly-Polarized Dielectric Resonator Antenna

Near-infrared metamaterials for tunable wide-band perfect reflection

Achieving perfect reflection with minimal loss and high efficiency is possible through the utilization of all-dielectric metamaterials, capitalizing on Mie resonance in materials with high permittivity. In this study, we introduce a novel approach to create a tunable perfect reflector operating within the near-infrared spectrum. This reflector is constructed using an all-dielectric metamaterial consisting of a SiO2 substrate and a periodic array of Si cuboids. Through precise adjustments in size and period, we demonstrate the attainment of near-perfect reflection across the near-infrared band. Notably, the reflector exhibits a bandwidth of 350.5 nm and maintains an average reflection exceeding 99 % over the spectral range from 1444.5 nm to 1795.0 nm. By customizing the electric and magnetic resonances throughout the near-infrared spectrum, our design offers adaptability to fulfill specific reflection bandwidth requirements. The tunable perfect reflector shows great potential for applications in various fields, including filtering, sensing, and optical communication, offering enhanced performance and versatility.

Graphene-enhanced decagonal patch antenna for terahertz frequency operation in breast cancer detection

This paper presents a decagonal patch antenna loaded with graphene designed for terahertz (THz) frequency applications, with a specific emphasis on its potential for early breast cancer detection. The proposed antenna features a hybrid structure, integrating both copper and graphene materials. A decagonal graphene strip is intricately incorporated into the copper patch, yielding significant improvements in reflection coefficient, bandwidth, and gain. The antenna, with dimensions of 155µm×130µm×13µm, is designed on a polyimide substrate, characterized by a dielectric constant of 3.5 and a loss tangent of 0.0027. To ensure relevance in medical contexts, the design is optimized to operate within the frequency range of 2.1 to 5.7 THz, a critical spectrum for medical applications. Simulation results validate the effectiveness of the proposed antenna, demonstrating S11<−10dB within the frequency band of 2.1 to 5.7 THz (92.3% fractional bandwidth). The antenna exhibits an impressive bandwidth of 3.6 THz and a gain of 7.87 dBi at 4 THz. These findings establish the graphene-loaded decagonal patch antenna as a highly promising solution for breast cancer detection applications, showcasing its potential in the realm of medical diagnostics.

Doped nanofibers achieve tunable broadband in cholesteric phase liquid crystals

ABSTRACT In this study, polymer-stabilised cholesterol-based liquid crystal (PSLC) broadband reflective films were prepared by doping UV absorbers and chiral compounds in bilayer poly (methyl methacrylate) (PMMA) nanofiber films. Broadband reflection was achieved by diffusion of the UV absorber and chiral compounds in the bilayer nanofibers into the liquid crystal layer, which resulted in the formation of an inhomogeneous pitch distribution in the liquid crystal layer. To attain an optimal reflective effect, various factors such as polymer monomer concentration, concentration of chiral compounds in the spun film, diffusion temperature, diffusion time, and intensity of polymerised light were investigated. The effects of these factors on the reflective bandwidth were explored. The method significantly broadened the reflective bandwidth of the cholesteric phase liquid crystal layer, establishing the foundation for studying the combination of nanofiber films with cholesteric phase liquid crystals to form an adjustable pitch.

Analysis and Design of Microwave Absorbers Combining Surface Wave Attenuation and Reflection Bandwidth Properties

Analysis and Design of Microwave Absorbers Combining Surface Wave Attenuation and Reflection Bandwidth Properties