Broadband Response Research Articles

Design and numerical investigation of an ultra-wide bandwidth rolling magnet bistable electromagnetic harvester

To realize broadband energy harvesting at low-frequency excitation, this paper proposes a rolling magnet bistable electromagnetic harvester (RM-BEH) which utilizes the rolling motion of a magnetically levitated magnet. The dynamic model of the RM-BEH is established, based on which the output of the RM-BEH is predicted through electromagnetic induction combined with finite element analysis. By calculating the parameter region for monostable and bistable configurations, the broadband response characteristics of a bistable system with shallower potential wells are investigated. Results show that the RM-BEH could achieve interwell oscillation in the frequency range between 5.8 Hz and 22 Hz under sweep frequency excitation with a level of 0.5 g. Under constant frequency excitation, multiple vibrational patterns of the RM-BEH are presented and examined. To identify the multiple solutions, harmonic balance method results are presented, indicating that high-energy orbit oscillation can be achieved with appropriate initial conditions. Furthermore, the response of RM-BEH under Gaussian white noise and human motion excitations is considered and results indicate that the RM-BEH could travel across the potential wells easily to generate large output. In general, the broadband response characteristic under harmonic excitation and considerable output under human motion excitation demonstrate the excellent application foreground of the RM-BEH.

Electrically Driven Reprogrammable Vanadium Dioxide Metasurface Using Binary Control for Broadband Beam Steering.

Resonant optical phased arrays are a promising way to reach fully reconfigurable metasurfaces in the optical and near-infrared (NIR) regimes with low energy consumption, low footprint, and high reliability. Continuously tunable resonant structures suffer from inherent drawbacks such as low phase range, amplitude-phase correlation, or extreme sensitivity that makes precise control at the individual element level very challenging. We computationally investigate 1-bit (binary) control as a mechanism to bypass these issues. We consider a metasurface for beam steering using a nanoresonator antenna and explore the theoretical capabilities of such phased arrays. A thermally realistic structure based on vanadium dioxide sandwiched in a metal–insulator–metal structure is proposed and optimized using inverse design to enhance its performance at 1550 nm. Continuous beam steering over 90° range is successfully achieved using binary control, with excellent agreement with predictions based on the theoretical first-principles description of phased arrays. Furthermore, a broadband response from 1500 to 1700 nm is achieved. The robustness to the design manufacturing imperfections is also demonstrated. This simplified approach can be implemented to optimize tunable nanophotonic phased array metasurfaces based on other materials or phased shifting mechanisms for various functionalities.

Fundamental constraints on broadband passive acoustic treatments in unidimensional scattering problems

In a passive lossy acoustical system, sum rules derived from passivity explicitly relate the broadband response to the spatial dimension of the system, which provide important design criteria as well. In this work, the theory of Herglotz function is applied systematically to derive sum rules for unidimensional scattering problems relying on passive acoustic treatments which are generally made of rigid, motionless and subwavelength structures saturated by air. The rigid-boundary reflection, soft-boundary reflection and transmission problems are analysed. The derived sum rules are applied for guiding the designs of passive absorbers and mufflers: the required minimum space is directly predicted from the target (i.e. the desired absorption or transmission-loss spectra) without any specific design. Besides, it is possible to break this type of sum rules and fundamental constraints in particular cases. This property, if well used, could result in ultra-compact absorbers working at long wavelength up to infinity.

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.

Tunable Nanoplasmonic Photodetectors.

Visible and infrared photons can be detected with a broadband response via the internal photoeffect. By use of plasmonic nanostructures, i.e., nanoantennas, wavelength selectivity can be introduced to such detectors through geometry-dependent resonances. Also, additional functionality, like electronic responsivity switching and polarization detection, has been realized. However, previous devices consisted of large arrays of nanostructures to achieve detectable photocurrents. Here we show that this concept can be scaled down to a single antenna level, resulting in detector dimensions well below the resonance wavelength of the device. Our design consists of a single electrically connected plasmonic nanoantenna covered with a wide-bandgap semiconductor allowing broadband photodetection in the visible/near-infrared via injection of hot carriers. We demonstrate electrical switching of the color sensitivity as well as polarization detection. Our results hold promise for the realization of ultrasmall photodetectors with advanced functionality.

Reconfigurable multifunctional metasurfaces employing hybrid phase-change plasmonic architecture

Abstract We present a hybrid device platform for creating an electrically reconfigurable metasurface formed by the integration of plasmonic nanostructures with phase-change material germanium antimony telluride (GST). By changing the phase of GST from amorphous to crystalline through Joule heating, a large range of responses from the metasurface can be achieved. Furthermore, by using the intermediate phases of GST, the metasurface can interact with the incident light in both over-coupling and under-coupling regimes, leading to an inherently broadband response. Through a detailed investigation of the nature of the fundamental modes, we demonstrate that changing the crystalline phase of the GST at the pixel-level enables an effective control over the key properties (i.e., amplitude, phase, and polarization) of incident light. This leads to the realization of a broadband electrically tunable multifunctional metadevice enabling beam switching, focusing, steering, and polarization conversion. Such a hybrid structure offers a high-speed, broadband, and nonvolatile reconfigurable paradigm for electrically programmable optical devices such as switches, holograms, and polarimeters.

SnS Nanoflakes/Graphene Hybrid: Towards Broadband Spectral Response and Fast Photoresponse.

High responsivity has been recently achieved in a graphene-based hybrid photogating mechanism photodetector using two-dimensional (2D) semiconductor nanosheets or quantum dots (QDs) sensitizers. However, there is a major challenge of obtaining photodetectors of fast photoresponse time and broad spectral photoresponse at room temperature due to the high trap density generated at the interface of nanostructure/graphene or the large band gap of QDs. The van der Waals interfacial coupling in small bandgap 2D/graphene heterostructures has enabled broadband photodetection. However, most of the photocarriers in the hybrid structure originate from the photoconductive effect, and it is still a challenge to achieve fast photodetection. Here, we directly grow SnS nanoflakes on graphene by the physical vapor deposition (PVD) method, which can avoid contamination between SnS absorbing layer and graphene and also ensures the high quality and low trap density of SnS. The results demonstrate the extended broad-spectrum photoresponse of the photodetector over a wide spectral range from 375 nm to 1550 nm. The broadband photodetecting mechanisms based on a photogating effect induced by the transferring of photo-induced carrier and photo-hot carrier are discussed in detail. More interestingly, the device also exhibits a large photoresponsivity of 41.3 AW−1 and a fast response time of around 19 ms at 1550 nm. This study reveals strategies for broadband response and sensitive photodetectors with SnS nanoflakes/graphene.

Easy fabrication of performant and broadband response SnS/Si photodetector

Broad response band photodetectors from ultraviolet (UV) to infrared (IR) range have attracted much attention in environmental monitoring, telecommunications, and thermal imaging. In this study, a simple method is proposed to fabricate photodetectors based on graphene/stannous sul-fide/silicon (Graphene/SnS/Si) heterojunction. The device was obtained by depositing SnS film on the Si substrate using the thermal evaporation technique. The graphene film is used as a transparent electrode for charge collection efficiently, and SnS/Si ensures that the device generates a uniform photocurrent under the light. The fabricated photodetector has a broad response band from visible to the near-infrared regime, high response speed with a fast-rising time of 11.0 ms at the bias of −5 V under 980 nm, and excellent responsivity up to 1.17 AW-1, and the responsivity for 1550 nm is as large as 17.31 mAW−1. Simultaneously, the self-powered characteristic can be realized. The gra-phene/SnS/Si heterojunction has a wideband and fast response, which may be used in future in-frared and even mid-infrared photoelectric detection.

Hierarchical Nanosheet-Based NaBiS2 Flowers for High-Performance and Self-Powered Broadband Photodetectors

Alkali bismuth ternary sulfides have been increasingly studied in optoelectronic devices, owing to their unique properties. Here, sodium bismuth sulfide (NaBiS2) flowers are successfully fabricated for the first time via a facile hydrothermal method. The obtained NaBiS2 flowers with a mean diameter of approximately 6 μm, assembled from nanosheets (NSs), have a three-dimensional hierarchical structure. The NaBiS2 NSs, with a thickness of approximately 60–90 nm, are formed by many regularly crossed and interlaced ultrathin flakelets. The detection performance of the photodetector based on the NS-based NaBiS2 flowers is further investigated without an external power source. The obtained results suggest that the NaBiS2 flower photodetector achieves a broadband response ranging from ultraviolet (365 nm) to infrared (850 nm) at a zero bias voltage. The NaBiS2 flower photodetector exhibits excellent photodetection performance, including a fast response speed (rising time of ∼26.50 ms and decay time of ∼66.72 ms), high responsivity (∼10.36 mA/W), and specific detectivity (∼3.04 × 1010 Jones), as well as outstanding stability and reproducibility. Moreover, the possible detection mechanism of the NaBiS2 flower photodetector is also proposed.

Highly‐Bendable MoS2/SnS Flexible Photodetector with Broadband Infrared Response

AbstractFlexible electronics is one of the hotspots of interdisciplinary research and can promote disruptive technology for post‐Moore applications in the field of biomedical, electronic skin, wearable devices, etc. 2D materials have triggered great interest in flexible electronic devices since they have tunable bandgaps, excellent mechanical flexibility, good chemical stability, and outstanding optical properties. Their reducible atomic thickness greatly facilitates the design and construct for bending, crimping, and folding, whereas it comes at the expense of superior optoelectronic properties. Herein, a highly‐bendable flexible photodetector based on MoS2/SnS amorphous blended film is fabricated with a broadband response from 473 to 1550 nm. The responsivity at 808 nm is 1128 times larger than that of intrinsic MoS2 photodetector accompanied by a four‐fold acceleration in response time. It can bear a small bending radius as low as 3 mm for over 2000 bending–flatting cycles without a drastic performance decay. Moreover, it shows an ultrastrong stability in photoresponse exposed to air for 200 days. This work provides a promising candidate for high performance flexible photodetectors and opens up the prospect of 2D bulk blended materials in a facile all‐in‐one strategy for multifunctional flexible optoelectronics devices and systems.

Manipulating Nanowire Structures for an Enhanced Broad-Band Flexible Photothermoelectric Photodetector.

The photothermoelectric effect, directly converting light energy into electrical energy, shows promising prospects in self-powered broad-band optical detection, which can extend to various applications, such as sensing, optoelectronic communications, and wide-temperature-range measurements. However, the low photosensitivity, narrow-band response, and rapid performance degeneration under continuous illumination restrict its broad application. Herein, we propose a simple bottom-up strategy to manipulate nanowires (NWs) into a well-defined multilayer Te-Ag2Te-Ag NW film, resulting in a high-performance photothermoelectric photodetector with a broad-band responsivity (4.1 V/W), large detectivity (944 MHz1/2 W-1), and fast response speed (0.4-0.7 s from 365 to 1200 nm). In addition, the ultrathin structure endows this device with slow and weak transverse heat conduction, enabling a stable voltage without an obvious degeneration over 1500 s. The highly anisotropic arrangement of NWs gives this device a prominent polarization sensitivity. Prospectively, this hierarchically designed nanowire film provides a promising pathway toward engineering photodetectors with high performance.

Large‐Area Lasing in Nanoscale Complex Media: The Critical Role of Local Dielectric Environment

AbstractControlling how electromagnetic waves interact with complex media is critical for applications in imaging and focusing. Such lightwave interactions with complex media can lead to dramatic optical effects like lasing. While much work in random lasing focus on understanding how gain and scattering co‐operatively generate lasing, little work has focused on how to manipulate the lasing threshold without modifying the structural disorder. Here, a simple, mostly unexplored, strategy is demonstrated that employs atomic layer deposition (ALD) to tune the local near‐field environment while preserving the underpinning disorder—controlling lasing in a nanoscale complex medium on a large scale (&gt;cm2). The nanoscale complex medium is a quasi‐2D system of coupled zinc oxide nanospheres with overall thickness deep in the sub‐wavelength regime (≈λ/4). Near‐ultraviolet femtosecond spectroscopy probes the broadband response of the gain nanomaterial, details how ALD process fundamentally modifies the fast‐picosecond and slow‐nanosecond carrier dynamics, and informs on the relevant timescales critical for lasing. Full‐field electromagnetic simulations provide critical insights about how near‐field dielectric environment modifies the nanostructure's scattering cross‐section, which ultimately results in enhanced lasing. These results highlight a simple path to control how electromagnetic waves interact in a complex medium, a key step toward large‐scale implementation of complex lasers.

A procedure for 3D simulation of seismic wave propagation considering source‐path‐site effects: Theory, verification and application

AbstractThis paper aims at obtaining a semi‐analytical and semi‐numerical 3D model of source‐to‐site seismic wave propagation due to kinematic finite‐fault sources. To this end, a two‐step procedure integrating the frequency‐wavenumber (FK) approach with the spectral element method (SEM) is proposed based on the concept of domain reduction. First, the broadband responses of a stratified crust are accurately calculated by using a novel FK approach and are converted into effective seismic inputs around the region of interest. After that, the seismic wavefields at local and regional scales arising from complex geological and topographical conditions are finely simulated using the SEM, and a perfectly matched layer absorbing boundary condition is simultaneously applied to realize the absorption of outgoing waves. In this procedure, a hybrid source modelling scheme that combines the low‐wavenumber deterministic and high‐wavenumber stochastic components on the fault plane is introduced, effectively addressing the high‐frequency motion radiated from the source rupture process. Subsequently, the proposed FK‐SEM procedure is verified step‐by‐step using the point source and finite‐fault source models. To illustrate the feasibility of the procedure, 3D physics‐based numerical simulations (PBSs) of two seismic events, including a historical Sanhe‐Pinggu earthquake and a well‐recorded Yangbi earthquake, are performed. The case studies validate that the proposed FK‐SEM procedure allows a significant reduction in computational effort and a substantial improvement in modelling resolution and can be applied to the source‐to‐site broadband synthetics of earthquake scenarios with limited resources. In addition, this coupled geophysics‐engineering simulation meets the requirements of time‐history analysis for engineering structures, which facilitates the study of soil‐structure interactions and regional‐scale building damage assessment.

Optical Sensor for Monitoring Leakage Current and Weather Conditions in a 500-kV Transmission Line

The leakage current (LC) caused by the surface contamination of insulators, together with environmental variables, is one of the most basic online monitoring parameters for insulator status. However, the impact of weather conditions such as temperature, air humidity, and dew point on the LC has not been deeply studied until now. In this paper, based on meteorological data obtained online and LC obtained with an optical fiber sensor, installed in 500-kV insulator strings of a transmission line, the impact of weather conditions was studied. Results indicate that the LCs follow a specific pattern, according to weather conditions. The system has been continuously monitoring LC, humidity, temperature, and dew point uninterrupted for three years, sending the acquired data to a web page; therefore, it has been demonstrated to be robust, reliable, and repetitive. The sensor features the broadband response and acquisition capabilities of partial discharge pulses in high-voltage insulators, allowing the detection of high-frequency pulses. When comparing the LC measured in this work with those from other works, our measurements are substantially higher; this is due to the type of pollution found in this specific situation, which includes iron oxide powder, producing a conductive layer over the insulator surface that, unlike sea salt, does not depend on humidity to conduct an LC. One of the conclusions reached in this work is that partial discharge surges are caused when the local temperature reaches the dew point and not simply from the presence of high humidity, as stated in many works dealing with LCs. The monitored LC can be used as an indicative parameter of a possible flashover, enabling the proper planning of insulator predictive maintenance, either by jet-washing the surface or even changing the insulators when they are damaged.

All-angle broadband ENZ metamaterials

A novel type of metamaterial is presented to produce broadband near-zero effective permittivity to a defined polarized probing electromagnetic wave with varying angles of incidence. The metamaterial has a uniaxial unit cell structure made up of symmetric periodic multilayer superlattices with a rotational symmetry about the polarization of the probing electromagnetic wave. The unit cell is rigorously constructed based on the Bergman–Milton spectral representation of the effective permittivity, and its electrodynamic properties are theoretically verified by the eigenmode analysis, the band structure, the dispersion relation, and the isofrequency contours. The eigenmode analysis illustrates that the unit cell can be effectively regarded as a photonic crystal or a waveguide according to the incidence direction of the probing electromagnetic wave, and either of them is of the dynamic microstructure related to the frequency, which results in a broadband response. Meanwhile, the band structure, the dispersion relation, and the isofrequency contours show that the unit cell has the near-zero effective permittivity at all angles of incidence of the specified polarized probing electromagnetic wave. Finally, the reflection/transmission/absorption spectra to the prescribed polarization probing electromagnetic wave vividly reveal the all-angle broadband near-zero effective permittivity property of the metamaterial.

Broadband Chiral-Type Linear to Linear Reflecting Polarizer With Minimal Bandwidth Reduction at Higher Oblique Angles for Satellite Applications

This work presents a broadband linear–cross polarizer for K- and Ka-band applications. The design consists of a simple asymmetric width-based meander-line metasurface printed on a thin FR-4 grounded dielectric substrate. Normal incidence demonstrates 90% polarization conversion ratio (PCR) bandwidth (BW) of 20.64 GHz from 18.31 to 38.95 GHz with 72.1% fractional BW (FBW). Due to the destructive interference involved at greater oblique angles, reflective polarizers experience severe degradation of 90% PCR BW response. The proposed polarizer’s performance is obliquely stable up to 43° for transverse electric (TE) and 45° for transverse magnetic (TM) incidence with minimal 90% PCR BW reduction of only 13.95% (TE) and 15.25% (TM) compared with normal incidence. For the first time, transfer matrix method (TMM)-based equivalent surface impedance technique is modeled for oblique incidence analytically, closely resembling the full-wave analysis. The design is compact with a periodicity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \text{o}$ </tex-math></inline-formula> /5.98 and a thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda \text{o}$ </tex-math></inline-formula> /13.69. The surface current patterns at resonant frequencies illustrate the reason behind broadband behavior. Bistatic radar cross section (RCS) analysis of the proposed converter is studied with reference to PEC. To the best of the author’s knowledge, this structure demonstrates broadband response with wide angular stability with less than 90% PCR BW reduction at higher oblique angles reported so far.

Two-dimensional Materials based Printed Photodetectors

Two-dimensional (2D) materials offer several unique advantages for high-performance light detection including fast response, high responsivity, broadband response and relatively low noise levels. 2D materials integrated photodetectors often use chemical vapor deposition grown materials, which despite their good quality are relatively high cost and not easily scalable. 2D materials based inks, fabricated through liquid phase exfoliation of bulk crystals, are attractive alternatives due to their low cost, ease of processing and scalable production. Combined with these advantages, mature printing methods available for 2D inks allow large scale electronic device fabrication for a variety of high performance applications including energy storage, solar cells, photodetectors, etc. In this review, we summarize production of 2D materials based inks, their printing methods, and applications for high performance photodetection.

Ultra-wideband TE0,1-mode dielectric window assisted with ring- based meta-surface

A novel concentric ring-based meta-surface assisted dielectric window is considered in the present study for examining its broadband response. The tolerable return loss in the Ka-Q band is taken as 20 dB for calculation of the bandwidth. The proposed window supports a bandwidth of 20.30 GHz (54.06%) for the TE0,1 mode. While comparing with a plane disk window, the bandwidth is increased by 17.55 GHz and 46.55%. On the other hand, compared with previously designed meta-surface assisted dielectric windows with square cross-sectional pillars without and with cylindrical tips, the bandwidth is increased by 1.1 GHz and 190 MHz, respectively.

A Broadband SIW-Fed Rhombic Loop Antenna With Endfire Radiation for Millimeter-Wave Applications

A broadband endfire antenna with three rhombic loops is designed for millimeter-wave (MMW) applications in this letter. The broadband response is attributed to traveling waves along rhombic loops which are constructed by two sine-like strips in an 180° rotation symmetry printed on two opposites of a laminate, respectively. Then using U-notches and quasi-trapezoid grounds improves the gain on lower and higher bands, respectively. Also, a pair of quasi-half elliptical matching stubs is employed for impedance bandwidth (IBW) near the feed end of loops. Finally, the antenna is excited by a substrate integrated waveguide (SIW) realizing a planar and low profile of 0.16 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at 33 GHz). By these methods, the antenna prototype shows an IBW of 73.7% (21–45.5 GHz), a peak gain of 10.3 dBi, a 3 dB gain bandwidth of 61.2% (25–45.2 GHz) and radiation efficiencies of higher than 90% within the operating bandwidth.

Computational Approach on Acoustic and Flow Performances of a Combined Resistive and Reactive Muffler

Aim: The internal combustion engine (ICE) based vehicles must follow strict regulations regarding noise levels, especially in the racing competition. The noise level is typically gauged as per two different scenarios: stationary engine revolution and maximum achievable revolution. One cannot reach the required noise level by deploying just reactive or resistive muffler type separately. This research recommends a novel mix of reactive and resistive mufflers in a single package solution. For assessing the noise level, three different types of mufflers are devised and studied by means of a computational approach. The new exhaust design in this study becomes a novelty of the proposed article. In analyzing the acoustic capability of the muffler, up to now it has not been able to dampen in various frequency ranges. Method: In this paper, the author wants to perform a computational analysis of 3 muffler models that combine several methods of attenuation that are effective at different specific frequency ranges with different configurations in order to obtain a good combined attenuation capability in various frequency ranges. Muffler 1 uses simple reactive and dissipative techniques like standard mufflers, while muffler 2 combines the dissipative technique with a Helmholtz resonator acting as the reactive part. Muffler 3 has a multi-chamber system that uses a combination of several advanced techniques. The three mufflers are evaluated on the basis of their capacity to decrease noise level. This noise level is assessed by considering both transmission and insertion loss through mathematical calculations in the frequency range of 200 Hz to 6400 Hz with the help of pressure acoustic, frequency domain (ACPR) simulation. Apart from noise evaluation, this study also examines flow parameters to estimate the pressure drop for the proposed muffler. Result: Comsol simulation provided both insertion loss (IL) and transmission loss (TL) with different trends. Muffler 3 had broadband response compared to its counterparts. Verifiying the finite element simulation results, electroacoustic models of each muffler were simulated using Matlab Simulink to get frequency response. Both finite element and electroacoustic modeling results have a good agreement. Pressure distribution of each model was also evaluated in terms of isosurface total pressure. Conclusion: It is demonstrated that the proposed muffler having a multi-chamber setup provides the best performances showing both superior and consistent noise reduction throughout the 200-6400 Hz frequency range and good airflow that does not create backpressure due to noise suppression efforts.