Working Bandwidth Research Articles

Metasurface Absorbers with Film-Coupled Au Nanoclusters to Achieve Broadband and Polarization-Independent Absorption of UV-Vis Light.

Metasurface absorbers (MAs) have attracted widespread interest in the recent study of subwavelength artificial optical metasurfaces, although most reported MAs suffer from the actualities of costly and time-consuming fabrications, narrow working bandwidth, polarization-dependent responses, etc., somewhat limiting their practical applications. Herein, we introduce a facile and low-cost method to fabricate MAs with excellent absorption performances via the self-assembly of synthesized Au nanoclusters (NCs) on a Au film spaced by a nanoscale-thick dielectric SiO2. Interestingly, the proposed MAs with well-designed Au film-coupled Au NCs (i.e., an appropriate surface coverage of Au NCs and the compatible thickness of the SiO2 spacer) exhibited a measured average absorbance above 90% within a broad UV-vis wavelength band (200-800 nm). In addition, owing to the MAs' topological symmetry, their UV-vis absorption behaviors presented polarization insensitivity with the incident light angles ranging from 20 to 50°. It has been demonstrated that the excited different surface plasmon resonance modes between Au NCs and the adjacent Au film were vital; in addition, the light-trapping effects from "V"-shaped structures of Au NCs were favorable for the designed MAs with enhanced light absorption. We believe that such MAs and the potential self-assembly fabrication strategy may facilitate scalable optical applications such as photothermalvoltaics, ultraviolet protection, optical storage, and sensing.

High-solid-content paste for stereolithography self-supporting printing of Luneburg lenses with a high degree of geometric-design freedom

Luneburg lenses prepared by alumina stereolithography, have the advantages of low dielectric loss, corrosion resistance, and flexible structure. However, the supporting structure limits the degree of geometric design freedom. This paper analyzes the effects of modifiers and dispersants on paste properties from the molecular structure, which is different from the traditional process that doesn’t analyze the influence of similar mechanisms and binding site competition while ignoring the correlation. Based on the dispersant’s better flexibility bringing more obvious change in viscosity, we first determine the amount of dispersant and then adapt the amount of modifier to obtain self-supporting pastes of 82 wt % and 24.9 Pa.swithout gradation. The gain and beam deflection angle of Luneburg lenses with high geometric complexity and working bandwidth of 38° formed by stereolithography self-supporting process is matched to the simulation results without manufacturing defects, which provides a theoretical basis for more flexible design and manufacture of Luneburg lenses.

Compact high-resolution spectrometer based on super-prism and local-super-collimation effects of photonic crystal.

We propose a design of the compact high-resolution photonic crystal (PhC) spectrometer with a wide working bandwidth based on both super-prism and local-super-collimation (LSC) effects. The optimizing methods, finding the ideal incident angle and oblique angle of PhC for a wider working bandwidth and ideal incident beam width and PhC size for a certain resolution requirement, are developed. Besides the theoretical work, for the first time, the experiment of such a PhC spectrometer is conducted in the microwave frequency range, and the beam-splitting effects for different frequencies in a wide working bandwidth agree very well with the theoretical predictions. According to the scalability, with the condition to control the deviations in the fabrication processes the design could be extended to optical frequency ranges, e.g., infrared, visible-light, and ultraviolet ranges. The spectrometer in optical frequencies can be implemented on silicon-on-insulator (SOI) chips as a thin-slab structure so that the operating bandwidth can be expanded further through the multi-layer design. Theoretically, the size of the ultra-high-resolution PhC spectrometer in optical frequency ranges based on our design could be two orders smaller than the traditional design.

A Design Method of Diffraction Structure Based on Metasurface for High-Resolution Spectroscopy.

In this paper, a design method of diffraction structure based on metasurface is proposed for light splitting and focusing simultaneously. In the method, firstly, the light field calculation model of the proposed structure is established based on Fresnel diffraction and the transmittance function is calculated. Then, the model structural parameter selection mechanism is determined, and the spectrum resolution equation of the structure is derived. Simulation results indicate that the proposed method can offer a broader working bandwidth and enhanced higher resolution compared to off-axis meta-lens. Moreover, this proposed method can be deployed in high-resolution, wide-band ultra-compact spectrometer systems potentially.

Wideband image-reject RF channelization based on soliton microcombs (invited paper)

Wideband radio frequency (RF) channelization is essential for the reception and detection of cross-band RF signals in various applications, including communications, radar, and spectrum sensing. However, digital channelizers are inefficient at performing RF channelization over a working bandwidth above 10 GHz. Meanwhile, current photonic RF channelizers face challenges in simultaneously considering a wideband, multi-channel, and a high crosstalk suppression ratio. In this work, we proposed and demonstrated a wideband image-reject RF channelization scheme based on integrated dual-soliton microcombs. The dual-soliton microcombs are used for RF spectral copies and heterodyne detection, respectively. Supported by image-reject mixers, the RF channelization is verified with an 8–37 GHz working bandwidth, a 1.2 GHz channel bandwidth, and 25 channels. The image suppression ratio is higher than 34 dB for single-tone signals and 20 dB for wideband signals. Our approach provides an innovative architecture of integrated photonic RF channelizers with high performance, which can benefit a wide range of RF applications by miniaturizing the systems.

Dual-Degree-of-Freedom Multiplexed Metasensor Based on Quasi-BICs for Boosting Broadband Trace Isomer Detection by THz Molecular Fingerprint

The metasurface is a powerful tool for trace analyte sensing in a label-free manner by amplifying their THz molecular fingerprint signals. However, current technologies are still facing the problems of high background noise and narrow working bandwidth. Here, we propose a broadband dielectric metasurface sensor based on guided mode resonances (GMRs) with a dual-degree-of-freedom configuration, which boosts the generation of multiplexed quasi-bound states in the continuum (quasi-BICs). Our design shows the extraordinary sensing performance on molecular fingerprint identification of two trace explosive isomers whose distinctive spectral characteristics span an ultrawide THz band. In comparison to the conventional sensing method, the metasensor demonstrates that the signal enhancement factors of over 19 dB in the entire frequency range from 0.9 THz to 1.6 THz, and is capable of precisely analyzing the sample composition ratios of the two mixed isomers. Our study explores the multiplexing mechanism of quasi-BICs based on the reconfigurable GMR metasurface and facilitates its application on high-sensitivity broadband THz molecular fingerprint retrieval, which is promising for nondestructive detection of trace-amount analytes.

Dual-functional synergetic energy harvesting and flow-induced vibration control of an electromagnetic-based square cylinder integrated with a flexible bimorph piezoelectric wake splitter plate

A dual-purpose FIV-based hydroelastic energy harvesting and cylinder response suppression strategy that functions based on the synergy of piezoelectric and electromagnetic transduction (EMT) mechanisms is proposed and numerically implemented. The hybrid harvester consists of a linearly sprung (1DOF) square cylinder fitted on the wake side with a thin flexural-mode cantilever bimorph piezoelectric (PVDF) splitter plate in real-time collaboration with a transversely hooked induction-based magnet-coil type transducer. The Reynolds averaged Navier–Stokes (RANS) equations with the shear stress transport (SST) k-ω turbulence closure model are selected for qualitative/quantitative prediction of hydrodynamic flow behavior in a relatively wide Reynolds numbers range. Numerical simulations show that increasing Reynolds number for the single-alone EMT-equipped cylinder in the low to intermediate range (2×103≤Re≤3×104) can noticeably improve the system hydrokinetic energy harvesting performance where a distinct coupled VIV/galloping effect is observed. Also, the hybrid piezoelectromagnetic harvester is capable of effectively suppressing the key response parameters and considerably increase the total system electrical output in an extended working bandwidth (3×104<Re≤4×105). In particular, in contrast to the conventional fixed-base cylinder configurations, maximum power extraction can be achieved over most span of the flexible piezoelectric splitter plate at Re=4×105 where the flapping oscillations of splitter plate synchronizes with the downstream alternating wake vortices.

A Parallel Folded Dipole Antenna With an Enhanced Bandwidth for 5G Millimeter-Wave Applications

In this communication, a planar folded dipole antenna array with wide operating bandwidth and compact size is proposed for 5G millimeter-wave (mmWave) applications. The basic antenna element is a pair of parallel folded dipoles (PFDs) connected at the terminals. Compared with a single half-wavelength dipole, the PFD can achieve a flatter impedance curve in the working frequency band, and it is easier to achieve broadband impedance matching with 50Ω feeding line. Moreover, a coupling slot feeding method is adopted to feed the proposed antenna element. The capacitance provided by the coupling slot can counteract the inductance caused by the PFD, thus improving the impedance matching at the low frequency band. Benefiting from the innovative design, the proposed antenna element can achieve an ultra-wide impedance bandwidth of 64% and a compact size of 0.26λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.28λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Furthermore, a wide scanning angle with ±50° over wide bandwidth is testified by a 1×8 array using active simulation. For verification, a 4×4 full corporate-fed array is designed based on the proposed element. The measured results prove that the proposed 4×4 array has a -10 dB impedance bandwidth of 65% covering 17 to 33.75 GHz and a peak gain of 17.5 dBi. The measured total efficiency is from 69% to 82% over the working frequency band. With the merits of compact size, wide working bandwidth, and wide beam scanning angle, the proposed antenna is a good candidate for mmWave wireless communications.

Plasmonic dual-band waveguide with independently controllable band-notched characteristics

Abstract In this present paper, an investigation is conducted on a dual-band waveguide with independently controllable band-notched characteristics. The proposed slot structure, featuring a loaded gap, facilitates the operation of the plasmonic waveguide at two distinct frequency bands. Moreover, the working bandwidth of the waveguide can be flexibly adjusted through the use of varactors loaded across the gap. Notably, the dual band can be adjusted independently and flexibly by regulating the varactors. The measurement results demonstrate that the plasmonic filtering waveguide possesses excellent frequency selectivity and compact physical size, particularly concerning its real-time controllable notched-band response with the varactor voltages.

Modeling and performance analysis of a curve-shaped based doubly clamped piezoelectric energy harvester (CD-PEH)

In this paper, a curve-shaped based doubly clamped piezoelectric energy harvester (CD-PEH) is explored for improving the energy harvesting performance. The harvester consists of a composed beam constructed with two arc-shaped structures and a flat beam, as well as two proof masses. A method based on chained beam constraint model theory (CBCM) is first applied to build the nonlinear restoring force model of the CD-PEH, the developed analytical model is validated by the finite element analysis (FEA). Then the electromechanically coupled model for the CD-PEH is built to investigate the effect of excitation amplitudes, geometric parameters and load resistance on the output characteristics. Due to the geometric nonlinearity caused by the arc-shaped configuration, the CD-PEH orderly exhibits quasi-linear, softening nonlinear and mixed hardening &amp; softening nonlinearity behavior with the increasing of excitation level, which could effectively extend the frequency bandwidth of the system. For the excitation of A = 8 m/s2, the effective working bandwidth of the CD-PEH is increased by 633% compared with the effective bandwidth in the case of A = 2 m/s2. Moreover, comparison experiments demonstrate that the output voltage and the effective bandwidth are increased by 225 and 450%, respectively, compared with the typical doubly-clamped piezoelectric energy harvester (T-PEH) under the same excitation amplitude. Overall, this study provides a new way and theoretical framework for the design of high-efficiency doubly clamped piezoelectric energy harvester.

Dual-channel snapshot imaging spectrometer with wide spectrum and high resolution.

The comprehensive analysis of dynamic targets brings about the demand for capturing spatial and spectral dimensions of visual information instantaneously, which leads to the emergence of snapshot spectral imaging technologies. While current snapshot systems face major challenges in the development of wide working band range as well as high resolution, our novel dual-channel snapshot imaging spectrometer (DSIS), to the best of our knowlledge, demonstrates the capability to achieve both wide spectrum and high resolution in a compact structure. By dint of the interaction between the working band range and field of view (FOV), reasonable limits on FOV are set to avoid spectral overlap. Further, we develop a dual-channel imaging method specifically for DSIS to separate the whole spectral range into two parts, alleviating the spectral overlap on each image surface, improving the tolerance of the system for a wider working band range, and breaking through structural constraints. In addition, an optimal FOV perpendicular to the dispersion direction is determined by the trade-off between FOV and astigmatism. DSIS enables the acquisition of 53×11 spatial elements with up to 250 spectral channels in a wide spectrum from 400 to 795nm. The theoretical study and optimal design of DSIS are further evaluated through the simulation experiments of spectral imaging.

A Wideband Tangential Electric Probe Based on Common Mode Absorbing

A new tangential electric field probe covering a wide frequency band (1.4 GHz to 7.0 GHz) based on common mode absorbing is presented in this article. The self-resonance of a traditional electric field probe incorporating reflective balun is firstly characterized based on the principle of transverse resonance, which is the major barrier for achieving wideband. In order to annihilate the self-resonance for a wider working band, an absorbing-type balun is therefore proposed and integrated into the tangential electric field probe. The common mode rejection ratio of the new probe is greatly elevated, compared with the conventional ones. A prototype of the probe is fabricated and measured for different electromagnetic interference problems. The results demonstrate excellent performances in terms of the sensitivity, suppression of unwanted fields coupling and the spatial resolution over the wide working band.

Acoustic metamaterial composed of zigzag channel and micro-perforated plate for enhanced low-frequency sound absorption

We propose the theoretical design and experimental authentication of an ultrathin sound absorber consisting of a perforated plate and a back cavity with zigzag channels for realizing high-efficiency and broadband absorption of low-frequency sound. The dependence of the absorption performance on the structural parameters is analyzed, which suggests the possibility of decreasing the peak frequency of resonance noise absorption with equal compactness of device. Based on this, we propose a hybrid design composed of multiple structures with different parameters to effectively expand the working bandwidth, and propose to further optimize the low-frequency absorption performance by adjusting the inclined partitions in the zigzag channel. The experimental results show that nearly 100% sound absorption is obtained at the resonance frequency (< 500 Hz) with an absorber 30 times thinner than the wavelength. We envision our designed sound absorber with deep-subwavelength size, broadband functionality, and easy fabrication to find wide applications in noise control engineering.

Highly Integrated Ka-Band Multi-Beam Network Design Based on a Low-Cost Multi-Layer Printed Circuit Board

A Ka-band low-profile and low-loss tile-type four-beam network based on high-density interconnection printed circuit board (PCB) technology is proposed, which integrates a power supply network, serial peripheral interface (SPI) control network, and four-beam radio frequency (RF) feeding network. In order to realize the fast optimal design, an integrated multi-beam network topology and fast optimization methods are established. The proposed feed networks can be integrated with antenna array structures directly, which not only realizes low-profile, light, and miniaturized design but also achieves efficient heat dissipation and low-loss interconnection. The designed multi-beam network has an amplitude balance better than ±0.5 dB and a phase balance better than ±6° in the Ka-band with a 4 GHz working bandwidth. A prototype was fabricated and measured, and good performance was observed.

Terahertz broadband tunable chiral metamirror based on VO2-metal hybrid structure.

Aiming at the problems of narrow working bandwidth, low efficiency, and complex structure of existing terahertz chiral absorption, we propose a chiral metamirror composed of C-shaped metal split ring and L-shaped vanadium dioxide (VO2). This chiral metamirror is composed of three layers of structure, a gold substrate at the bottom, the first polyethylene cyclic olefin copolymer (Topas) dielectric layer and VO2-metal hybrid structure as the top. Our theoretical results led us to show that this chiral metamirror has a circular dichroism (CD) value greater than 0.9 at 5.70 to 8.55 THz and has a maximum value of 0.942 at f = 7.18 THz. In addition, by adjusting the conductivity of VO2, the CD value can be continuously adjustable from 0 to 0.942, which means that the proposed chiral metamirror supports the free switching of the CD response between the on and off states, and the CD modulation depth exceeds 0.99 in the range of 3 to 10 THz. Moreover, we discuss the influence of structural parameters and the change of incident angle on the performance of the metamirror. Finally, we believe that the proposed chiral metamirror has important reference value in the terahertz range for constructing chiral light detectors, CD metamirrors, switchable chiral absorbers and spin-related systems. This work will provide a new idea for improving the terahertz chiral metamirror operating bandwidth and promote the development of terahertz broadband tunable chiral optical devices.

An ultra‐wideband MIMO system with multi‐loop mode for full‐screen smartphone applications

AbstractIn this letter, an ultra‐wideband (UWB) eight‐element multiple‐input multiple‐output (MIMO) antenna system with multi‐loop modes for fifth‐generation (5G) smartphones is presented. The antenna unit has a simple structure and is composed of an inverted U‐shaped feeding strip and an L‐shaped grounding radiation strip with a hollow out in the middle. Owing to the generation of two coupling loop modes, the working bandwidth of the proposed antenna unit covers 3.2−6.4 GHz. Besides, the simulated and measured results show that the isolation between any two antennas is better than 12.0 dB, and the total efficiency of each element is higher than 50%. Meanwhile, the measured radiation pattern, envelope correlation coefficients, channel capacity loss, mean effective gain, and diversity gain are also given in this letter. The above results demonstrate that the MIMO system has the advantages of simple structure, convenient manufacture, and superior performance.

Performance enhancement of the wavy cylinder-based piezoelectric wind energy harvester with different wave-shaped attachments

The vortex-induced vibration (VIV)-based piezoelectric wind energy harvester (PWEH) has a small working bandwidth and poor wind energy harvesting performance. In order to improve the output power of the PWEH and achieve sustainable power supply for microelectronic products, this study proposes a novel wavy cylinder-based PWEH with two wavy attachment rods attached to the surface of the wavy cylinder, the mathematical model of PWEH is developed. The flow-induced vibration (FIV) response mechanism and the energy harvesting characteristics of the wavy cylinder-based PWEH are numerically explored. The wavy cylinder with wavy-shaped attachments produces a three-dimensional shear layer that can increase the wavy cylinder’s aeroelastic instability range and realize the synergistic effects of VIV and galloping, which increases the wave cylinder’s vibrational amplitude and lowers the galloping critical wind speed. Compared with the typical VIV-PWEH, the novel wind energy harvester can work outside the VIV lock-in range, and its output power and voltage rise as wind speed does. The wavy attachment rods with triangular cross section have greater advantages than other rods, its output power is 6.13 mW at a wind speed of 5.7 m/s and load resistance of 100 KΩ, compared with the circular cylinder PWEH, the average power increases by approximately 166%. The study’s findings can theoretically promote the enhancement of PWEH’s energy harvesting efficiency.

Development of a Mode-Locked Fiber Laser Utilizing a Niobium Diselenide Saturable Absorber

The saturable absorber of niobium diselenide (NbSe2), with a wide working bandwidth and excellent nonlinear optical response, was prepared using liquid-phase exfoliation. Its saturation intensity and modulation depth were 5.35 MW/cm2 and 6.3%, respectively. Stable mode-locking with a center wavelength of 1558.7 nm of an erbium-doped fiber laser based on a NbSe2 saturable absorber was successfully achieved. The maximum average output power of the mode-locked laser was 6.93 mW, with a pulse width of 1.3 ps and a repetition rate of 25.31 MHz at a pump power of 550 mW. The results show that NbSe2 is a promising photoelectric modulation material owing to its excellent nonlinear optical properties.

Extended topological interface modes with tunable frequency in the piezoelectric phononic crystal

Acoustic metamaterials have provided a versatile platform to explore more degrees of freedom for tunable topological wave manipulation. Recently, extended topological interface modes (ETIMs) with heterostructure have been proposed to extend the spatial degree of freedom. However, the absence of frequency tunability still restricts the application of the wave transports of ETIMs. Here, we propose a one-dimensional piezoelectric topological phononic crystal (PTPC) with electrically tunable working frequency by introducing external capacitor circuit. With the bandgap frequency actively controlled by appropriately tuning the capacitances, we construct the heterostructured PTPCs possessing high-energy-capacity ETIMs with electrically tunable working frequency range and bandwidth. This work paves the way to wide engineering applications on acoustic sensing enhancement, nondestructive testing, energy harvesting, information processing, and reconfigurable topological wave transports.

Design of a Novel Superwideband Dual Port Antenna with Second-Order Hilbert Branches and a Modified T-Decoupling Structure

A novel super wideband (SWB) dual port antenna with second-order Hilbert branches and a modified T-decoupling structure is proposed. The overall size of the antenna is only 32 mm × 26 mm × 1 mm. The SWB antenna front comprises a “house” shaped radiating patch and a trapezoidal-shaped microstrip line. Two SWB antenna units are placed symmetrically on FR4 dielectric substrate to form the SWB-MIMO (multiple-in multiple-out) antenna. Two second-order Hilbert branches expand the wideband of the SWB-MIMO antenna. The antenna decoupling is mainly achieved by loading a fence-like “T” decoupling structure on the ground plane. The antenna is also miniaturized and isolated by adjusting the distance between the radiating patches of the units. The simulations and measurements show that the SWB-MIMO antenna operates in the frequency band of 1.98-30.8 GHz (175.84% relative bandwidth). The bandwidth dimensional ratio (BDR) (BDR is a measure of the compactness of the antenna, the higher the BDR, the better the compactness of the antenna, and the wider the working bandwidth of the antenna.) is 14653.33. The overall isolation is below −16.4 dB, and the important part (8.5–24.1 GHz) is below −20 dB. The envelope correlation coefficient (ECC) is less than 0.03, and the radiation characteristics are excellent.