Multiband Response Research Articles

Strong and wide-angle nonreciprocal radiation in modified distributed Bragg reflector-Weyl semimetal heterostructure

An approach to obtain easy-to-fabricate and spectrally selective nonreciprocal thermal emitter (NTE) has been proposed. The presented hybrid structure is composed of Weyl semimetal (WSM) film sandwiched by Ge/BaF2/Ge tri-layer and metal substrate. It has been shown that structural parameters hold tolerance on the order of hundreds of nanometers, which are highly favorable for fabricating with low cost and high performance. Multiband responses of the device can be realized through controlling the thickness of last Ge layer, which boosts the flexibility of preparation and potential applications. The giant nonreciprocity can be maintained with broad polar and azimuthal angle ranges. By manipulating the structural parameters, a remarkable result of nonreciprocal radiation is realized under both the transverse electric (TE) and transverse magnetic (TM) wave incidence. By changing the azimuthal angle (ϕi) of incidence, the nonreciprocity (η) can be effectively manipulated. The simulated η spectra is symmetric along the azimuthal angle ϕi=90°, and η=0 when ϕi=90°. Our results provide a much simpler way to achieve the multi-channel nonreciprocity and could lead to the advancement of power scavenging and conversion devices.

Construction of Fe7S8 anchoring S-doped porous graphene with enhanced multi-band electromagnetic absorptions

At present, research bottleneck on electromagnetic absorption materials lied in achieving strong absorption with broadband and multi-band responses. In this paper, Fe7S8 anchoring S-doped porous graphene was synthesized for multi-band electromagnetic absorptions. Rhodanine played the role of ‘two birds in one stone’, converting Fe3O4 to Fe7S8 and constructing porous S-doped carbon. The hybrids exhibited multi-band electromagnetic absorptions at 10.52, 12.56 and 15.03 GHz, with effective bandwidth achieved up to 12.07 GHz. This paper showcases reference path for the design of multi-band electromagnetic absorption materials.

Measurement of the Excitation Spectrum of a Dipolar Gas in the Macrodroplet Regime.

The excitation spectrum of a cigar-shaped strongly dipolar quantum gas at the crossover from a Bose-Einstein condensate to a trapped macrodroplet is predicted to exhibit peculiar features-a strong upward shift of low momentum excitation energies together with a strong multiband response for high momenta. By performing Bragg spectroscopy over a wide range of momenta, we observe both key elements and also confirm the predicted stiffening of excitation modes when approaching the macrodroplet regime. Our measurements are in good agreement with numerical calculations taking into account finite size effects.

Design of Vertically Integrated Folded SISL Patch Bandpass Filters With Single and Multiband Responses

Design of Vertically Integrated Folded SISL Patch Bandpass Filters With Single and Multiband Responses

An optoelectronic Coupler based on graphene patterns and SU-8 photoresist

PurposeThe purpose of this research is to efficiently separate incident terahertz (THz) waves into distinct transmission and reflection channels by minimizing the absorption ratio. So, the optical systems operating within the THz frequency range can developed. To achieve a multi-band response, four different periodic arrays of graphene patterns are used. These arrays are strategically stacked on both sides of three SU-8 photoresists, serving as dielectric materials. Consequently, each layer exhibits a unique influence on the device's response, and by applying four external bias voltages, the behavior of the device can be precisely controlled and adjusted.Design/methodology/approachA novel optoelectronic device operating in the THz frequency range is introduced, using periodic arrays of graphene patterns and SU-8 photoresist dielectrics. The design of this device is based on meta-surface principles, using both the equivalent circuit model (ECM) and transmission line concept. The output of the device is a THz coupler implemented by analyzing the reflection and transmission channels. The structure is characterized using the ECM and validated through comprehensive full-wave simulations. By representing the electromagnetic phenomenon with passive circuit elements, enabling the calculation of absorption, reflection and transmission through the application of the theory of maximum power transfer.FindingsBased on simulation results and theoretical analysis, the proposed device exhibits sensitivity to gate biasing, enabling efficient reflection and transmission of THz waves. The device achieves reflection and transmission peaks exceeding across the five distinct THz bands 90%, and its behavior can be tuned by external gate biasing. Moreover, the device's sensitivity to variations in geometrical parameters and chemical potentials demonstrates its reliable performance. With its outstanding performance, this high-performance meta-surface emerges as an ideal candidate for fundamental building blocks in larger optical systems, including sensors and detectors, operating within the THz frequency band.Originality/valueThe proposed device covers a significant portion of the THz gap through the provision of five adjustable peaks for reflection and transmission channels. Additionally, the ECM and impedance matching concept offers a simplified and time-efficient approach to designing the meta-surface. Leveraging this approach, the proposed device is effectively represented using passive circuit elements such as inductors, capacitors and resistors, while its performance is validated through the utilization of the finite element method (FEM) as a full-wave simulation tool. This combination of circuit modeling and FEM simulation contributes to the robustness and accuracy of the device's performance evaluation.

A Highly Isolated Tapered Triangular Dual‐Polarized Multiband MIMO Antenna for WLAN, C, X and Ku Bands

This research work presents the design of a multiband dual‐polarized eight‐element MIMO antenna having dimensions (0.51 λ × 0.66 λ × 0.009 λ). The antenna is observed to be radiating between 1.7 GHz and 2.4 GHz, 4.1 GHz and 10 GHz and 10.6 GHz and 19.8 GHz, featuring 3 dB axial ratio bandwidth between 9.7 and 10 GHz, 12.1 and 13.1 GHz, 14.4 and 14.5 GHz and 17.9 and 18.9 GHz. In the proposed MIMO antenna, the triangular‐shaped monopole antenna is tapered at its two sides. The isolation between the various elements of the proposed antenna is observed to be in range of −20 dB–−70 dB for the concerned frequency range. On the basis of comparison with similar existing structures, the proposed antenna demonstrates superior performance in terms of total active reflection coefficient (TARC < −5 dB), diversity gain (DG around 10 dB), channel capacity loss (CCL < 0.3 bits/s/Hz), mean effective gain (MEG) and envelope correlation coefficient (ECC < 0.024). The proposed antenna provides wide bandwidth (15.8 GHz) and high value of peak gain (6 dB). The proposed geometry is novel as it exhibits both linear as well as circular polarization with multiband response and it provides the least ECC and maximum isolation. The experimental results are found to be in agreement with the simulated results, so the proposed antenna can be useful for WLAN, C‐band, X band and Ku band applications.

Multilayer MoS 2 Photodetector with Broad Spectral Range and Multiband Response

As a typical 2-dimensional material, molybdenum disulfide (MoS 2 ) has atomic thickness in longitudinal size, showing unique optical and electrical properties. MoS 2 has become a research hotspot in the field of photodetection. The properties of MoS 2 devices are highly dependent on their material characteristics, device structures, and fabrication techniques. Therefore, their photoresponse characteristics may be determined by multiple physical effects, which contribute to the development of MoS 2 -based broadband photodetectors. Here, we present an experimental study on the broadband MoS 2 photodetector ranging from 410 to 1,550 nm, obviously wider than that of conventionally reported MoS 2 photodetectors. Our results indicate that the performance of the MoS 2 device is dependent on the fabrication procedures. Under the optimal process, the maximum responsivity is 33.75 A W −1 and the corresponding specific detectivity is 6.1 × 10 11 cm Hz 1/2 W −1 at 480-nm illumination. Through a series of electrical and optoelectronic experimental analysis, the working mechanisms of multiband photoresponse of the MoS 2 device are clarified.

Ring Shape Microstrip Antenna Backed by Modified Ground Plane for Multiband Response in GSM and Radar Applications

Ring Shape Microstrip Antenna Backed by Modified Ground Plane for Multiband Response in GSM and Radar Applications

Quad Element MIMO Antenna for C, X, Ku, and Ka-Band Applications.

This article presents a quad-element MIMO antenna designed for multiband operation. The prototype of the design is fabricated and utilizes a vector network analyzer (VNA-AV3672D) to measure the S-parameters. The proposed antenna is capable of operating across three broad frequency bands: 3-15.5 GHz, encompassing the C band (4-8 GHz), X band (8-12.4 GHz), and a significant portion of the Ku band (12.4-15.5 GHz). Additionally, it covers two mm-wave bands, specifically 26.4-34.3 GHz and 36.1-48.9 GHz, which corresponds to 86% of the Ka-band (27-40 GHz). To enhance its performance, the design incorporates a partial ground plane and a top patch featuring a dual-sided reverse 3-stage stair and a straight stick symmetrically placed at the bottom. The introduction of a defected ground structure (DGS) on the ground plane serves to provide a wideband response. The DGS on the ground plane plays a crucial role in improving the electromagnetic interaction between the grounding surface and the top patch, contributing to the wideband characteristics of the antenna. The dimensions of the proposed MIMO antenna are 31.7 mm × 31.7 mm × 1.6 mm. Furthermore, the article delves into the assessment of various performance metrics related to antenna diversity, such as ECC, DG, TARC, MEG, CCL, and channel capacity, with corresponding values of 0.11, 8.87 dB, -6.6 dB, ±3 dB, 0.32 bits/sec/Hz, and 18.44 bits/sec/Hz, respectively. Additionally, the equivalent circuit analysis of the MIMO system is explored in the article. It's worth noting that the measured results exhibit a strong level of agreement with the simulated results, indicating the reliability of the proposed design. The MIMO antenna's ability to exhibit multiband response, good diversity performance, and consistent channel capacity across various frequency bands renders it highly suitable for integration into multi-band wireless devices. The developed MIMO system should be applicable on n77/n78/n79 5G NR (3.3-5 GHz); WLAN (4.9-5.725 GHz); Wi-Fi (5.15-5.85 GHz); LTE5537.5 (5.15-5.925 GHz); WiMAX (5.25-5.85 GHz); WLAN (5.725-5.875 GHz); long-distance radio telecommunication (4-8 GHz; C-band); satellite, radar, space communications and terrestrial broadband (8-12 GHz; X-band); and various satellite communications (27-40 GHz; Ka-band).

Design and Analysis of Fractal-Shaped High-Impedance Surface Unit Cell Characteristics

Fractal geometries consistently provide solutions to several electromagnetic design problems. In this paper, fractal geometries such as Hilbert and Moore curves are used to design efficient High-Impedance Surfaces. Modern communication devices have many sensors that are needed to communicate wirelessly. The critical component of wireless communications is antennas. Planar microstrip patch antennas are popular due to their low profile, compactness, and good radiation characteristics. The structural disadvantages of microstrip antennas are that they have surface waves that propagate over the ground plane. High-Impedance Surface (HIS) planes are a prominent solution to minimize and eliminate surface waves. The HIS structures behave as active LC filters that suppress surface waves at their resonance frequency. The resonance frequency of the structure is obtained by its LC equivalent or by analyzing the reflection phase characteristics. This work presents conventional HIS structures similar to mushroom HIS and fractal HIS such as Hilbert curve and Moore curve HIS. The HIS reflection phase characteristics are obtained by applying periodic boundary conditions with plane wave illumination. The results were obtained in terms of the reflection phase angle. The conventional mushroom structures show narrow band characteristics at given dimensions of 10 mm × 10 mm and 20 mm × 20 mm. These structures are helpful in the replacement of PEC ground planes for patch antennas under sub-6 GHz. The Hilbert and Moore fractals are also designed and have a multiband response that can be useful for L, S, and C band applications. Another design challenge of HIS is protrusions, which make design difficult. The work also presents the effect of having vias and the absence of vias on reflection phase characteristics. The response shows the least and no significant effect of vias under the x-band operation.

Design and analysis of split ring resonator engraved metamaterial broadband and high gain patch antenna for THz applications

We propose a new split ring resonator engraved metamaterial MIMO patch antenna design which applies in 6–11 THz frequency band. Four different THz antennas are investigated and their results are compared to find the optimized antenna design with superstrate. The four antenna designs evolved by adding superstrate layers and metamaterials in the form of complementary split ring resonators are investigated. They are THz patch antenna (TPA), THz complementary split ring resonator patch antenna (TCPA), THz patch antenna with complementary split ring resonator superstrate (TPACS), and THz complementary split ring resonator patch antenna with complementary split ring resonator superstrate (TCPACS). The results show that the complementary split ring resonator metamaterial added in the patch as well as in the superstrate affects the antenna gain and bandwidth while the addition of the superstrate affects the multiband and gain characteristics. All four designs are optimized and show the multiband response. The TCPACS design exhibits the highest bandwidth of 900 GHz 8.88%) and the highest gain of 9.19 dB. The TCPA design is having highest bandwidth of 530 GHz (5.3%) and the highest gain of 8.05 dB. The TPACS design is having highest bandwidth of 300 GHz (3%) and the highest gain of 7.47 dB. The TPA design is having highest bandwidth of 60 GHz (0.6%) and the highest gain of 6.42 dB. The proposed antenna design with multiband, broadband, high-gain and optically transparent characteristics can be used in Terahertz Wireless Area Networks, Terahertz Wi-Fi, 6 G, Internet of Things, Sensing and Imaging applications. Availability of data and materialsThe data supporting the findings in this work are available from the corresponding author with a reasonable request.

Multiband polarization insensitive metamaterial absorber for radar cross-section reduction

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands.

Analytical Design of Compact Multiband Bandpass Filters with Multiconductor Transmission Lines and Shunt Open Stubs

A compact topology for implementing compact multiband bandpass filters is presented in this paper. To achieve the desired frequency response, two identical short-circuited multiconductor transmission lines (MTLs) and properly connected shunt open stubs are interconnected. Using this configuration, it is possible to design multiband bandpass filters effortlessly. As both the MTLs and the stubs are distributed elements, spur-line band-stop filters are added to mitigate the first replica of the structure’s frequency response. To assess the behavior of the developed filter design procedure, a prototype consisting of a six fingers-MTL and two shunt open stubs has been designed, manufactured, and analyzed, showing excellent agreement between analytical and measured results, considering that no simulation or optimization process has been performed during the design process, just for result verification. Furthermore, it is possible to establish a design criterion that allows the fast and reliable synthesis of multiband responses by varying just a small number of geometrical parameters of the MTLs and the corresponding stubs.

Perovskite/GaAs-nanowire hybrid structure photodetectors with ultrafast multiband response enhancement by band engineering

We developed a hybrid structure photodetector combining one-dimensional (1D) inorganic GaAs nanowires and two-dimensional (2D) organic perovskite materials, which can achieve various performance enhancements using a relatively simple structure. Via the optical absorption enhancement of perovskite and the type-II energy band structure formed by the heterostructure, the responsivity and detectivity of the photodetector from ultraviolet (UV) to visible (Vis) wavelengths are significantly enhanced, reaching 75 A/W and 1.49×1011 Jones, respectively. The response time of the photodetector was significantly decreased by 3 orders, from 785 ms to 0.5 ms, and the dark current was further reduced to 237 fA. A photodetector was prepared with enhanced responsivity and ultrafast response time in the multiband region from the UV to Vis wavelength. To the best of our knowledge, this is the first time to combine inorganic III-V GaAs nanomaterials with organic perovskite materials, which verifies the effective combination of inorganic and organic materials in a mixed dimension. The excellent photoelectric performance of the perovskite/GaAs-nanowire hybrid structure photodetector makes it a potential candidate material for a wide range of photoelectric applications such as multiband photodetection.

Design and fabrication of rudimentary shaped and effective 1 × 2 printed MIMO antenna using low profile material for WLAN and satellite applications

AbstractThe presented article represents the rudimentary‐shaped effective 1 × 2 MIMO antenna structure. The five variation types in the ground region shape are analyzed. The structure's total dimensions are 40 × 36 × 1.6 mm3. For efficiently manufacturing, the low‐profile substrate FR4 is employed, and the reflectance response of a simulated and modelled design is compared. The placement of two T‐shaped slits in the ground area aids in achieving a wider bandwidth, multiband response, excellent Gain, and directivity. Overall, the PW:4 has a minimum reflectance coefficient of −34.54 dB, a broad bandwidth of 3.38 GHz, a peak gain of 13.02 dB, maximum narrow band isolation of 62 dB, and a maximum normalized directivity of 156°. The Envelop Correlation Coefficient, Channel Capacity Loss, Total Active Reflection Coefficient, and Diversity Gain for MIMO design are also examined. These findings indicate the provided design's behavior as per the standard requirements.

Bandgap-independent photoconductive detection in two-dimensional Sb2Te3

Broadening the spectral range of photodetectors is vital for photodetection. However, current photoelectric detectors are selective to wavelength, which depends on bandgap, and thermal detectors respond slowly at room temperature. It is challenging to achieve photoconductivity independent of the semiconductor bandgap, which is needed to broaden the spectral range of photodetectors. Here, we use 2D semiconductor Sb2Te3 to develop a photodetector with metal-semiconductor-metal structure for multiband response, covering visible, infrared, terahertz and millimeter wavelengths at room temperature. This is achieved by the synergy of the photoconductivity of photo-excited electron-hole pairs above the bandgap, and an electromagnetic-induced well effect below the bandgap. The photodetector achieves a responsivity of 0.6 A W−1 at 1550 nm, 515 A W−1 at 0.340 THz with a bias of 0.2 V, respectively. The response time is 900 ns, which is short compared to the reported detectors based on 2D materials. In addition, it also exhibits a high polarization extinction ratio of 90. These results suggest that our strategy achieves a photoconductivity independent of the semiconductor bandgap to broaden the spectral range of photodetectors, and could be a strong candidate for multiband photodetection systems.

Design of 3-D Integrated SIW Multiband Bandpass Filter With Split-Type Extended Doublet Topology

A new class of 3-D integrated multiband bandpass filters (BPFs) based on substrate integrated waveguide (SIW) technology is presented in this work, for the first time. Split-type dual-extended doublet (SDED) coupling topologies are developed to propose these BPFs with a desired multiband response by the LEGO-style assembly of planar SIW resonant-mode blocks. These design schemes offer attractive and promising advantages with regard to compact size, low cost, flexible and expandable topology, as well as integration of high-density integrated circuits. For demonstration, dual- and triple-band BPFs are designed, fabricated, and measured. The measurement results are in good agreement with the simulation ones. Results indicate that the proposals can provide not only nice selective multiband signal transmission in such flexibly extensible topologies with new spatial schemes but also increase space utilization and reduce footprint.

Excitation of higher order modes in terahertz antenna using graphene strip

A terahertz (THz) antenna is implemented with a technique of achieving the multiband response by exciting the higher order modes without changing the antenna structure. A patterned triangular shaped THz microstrip patch radiator is designed and numerically analyzed for providing the dual-band response with TM10 and TM20 modes. A graphene strip is applied in the antenna structure which can act as a controller or tuner responsible for the generation and mitigation of resonant modes. The insertion of graphene strip can generate the higher order resonances of TM11 and TM21 mode and antenna response can be attained with dual, triple or four operating passbands by varying the chemical potential of the applied graphene strip. The antenna operation is verified with the electrical equivalent circuit model. Moreover, conical or bi-conical radiation beam can be obtained from the antenna corresponding to the nature of the excited resonant mode.

FSS bandwidth design using miniaturized elements for angular stability in transmission

Frequency-selective surfaces (FSSs) are commonly employed at microwave frequencies in electromagnetic filtering applications. This paper reports the use of cascaded dual miniaturized elements for radio secure environments where miniaturized elements have been used creating a reduced unit cell (<0.1 wavelengths), and exceptional angular stability. Thin, flexible and optically transparent FSS samples were fabricated by laser engraving elements into a conductive aluminium layer, with a supporting Mylar substrate (relative permittivity 2.7), and thickness of 65 μm. The linearly polarized transmission response was investigated numerically by exploring the scattering parameters and the surface currents at resonance. Miniaturized elements in both single and cascaded FSS structures, have been explored to create both broadband and multiband responses across the L and S frequency bands. The theoretical and experimental results were in good agreement for the fabricated dual element dual layer translated band-stop FSS, displaying a resonant frequency reduction of 70% compared to a square loop with the same dimensions, along with significantly broad operation bandwidths of 118% and 104% for simulated and measured, respectively. These improvements were due to the selection of the individual elements in the array, their geometric arrangement, and the introduction of additional layers with lateral offsets.

Multiband acoustic topological metamaterials with valley-switchable higher-order corner states

Topological insulators have become a hot research area in the field of acoustics in recent years, particularly the recently-appearing higher-order topological insulators (HOTIs) that support low-dimensional corner states. However, most HOTIs reported are implemented in tetragonal lattices, and only support single-frequency operation, which enables the higher-order states to be fixed at specific corners and at specific frequencies, lacking the multiband response and flexibility of switching. Herein, the experimental realization of flexibly valley-switchable topological corner states in multiple frequency bands with acoustic metamaterials in the triangular lattice are reported in a 2D system. The designed topological metamaterials, whose second-order topology is characterized by nontrivial bulk polarization, exhibit diverse topological valley-switchability in different bandgaps, as verified by simulation and experiments. Furthermore, an arbitrary structure containing complex patterns with various crossing angles is designed and experimentally implemented, where selected corners can be switched on or off by valley switching, and the switching modes are distinct in different bandgaps. The reported valley topological metamaterials enrich the fundamental understanding of the interaction between multiband higher-order topology and valley degrees of freedom, which inspire potential applications for multiband communication devices and integrated acoustics and photonics.