High Broadband Research Articles

Broadband Negative Reflection of Underwater Acoustic Waves from a Simple Metagrating: Modeling and Experiment

Metagratings are periodic arrays of subwavelength scatterers, or atoms, engineered to refract or reflect waves toward anomalous directions with unit efficiency. Here, we design and build a metagrating to control the reflection direction of waterborne ultrasound waves impinging on a rigid or free surface. The grating and its atoms are designed to cancel the specular reflection and to redirect acoustic power toward a negative-reflection direction, through the first-negative-order Floquet mode. Despite a simple design, based on C-shaped brass particles acting as Helmholtz resonators, the grating is efficient ($>90\mathrm{%}$) over a relatively broad range of frequencies (74--103 kHz) for a broad range of incidence angles (${14}^{\ensuremath{\circ}}$--${54}^{\ensuremath{\circ}}$). This good performance is obtained by tuning the distance between the atoms and the reflective surface. A multiple-scattering analytical model is presented to explain the phenomenon and a finite-element model is developed to further investigate the performance of the proposed design. Predictions from the model are confirmed experimentally in a water tank. The simplicity, reconfigurability, and scalability of the design, as well as its high efficiency, broadband behavior, and robustness to the incidence angle are all features that make the grating potentially useful for various applications in underwater acoustics, such as telemetry, communication, or noise mitigation.

Nonvolatile reconfigurable broadband photodiodes based on BP/α-In2Se3 ferroelectric p–n junctions

Imagers with pre-processing functions, such as image recognition and classification, contrast enhancement, and noise reduction, play a critical role in the neuromorphic visual system. Optoelectronic plasticity is a prerequisite to achieve these functions. In this study, we demonstrate a nonvolatile reconfigurable broadband photodetector based on a ferroelectric heterostructure composed of BP (black phosphorus)/α-In2Se3. The plasticity of the device comes from the ferroelectric polarization of α-In2Se3 that can tune the built-in potential of the p–n junction. As a result, the rectification ratio and responsivity increase almost one order when changing the gate voltage pulse from +16 V to −16 V. Due to the introduction of BP, the device has a wide spectral response covering 473–1550 nm. In addition, our devices show excellent performance in terms of a high responsivity of up to 4.73 × 104 A/W, a large specific detectivity of ∼2.09 × 1012 Jones, a high external quantum efficiency of 9.21 × 106%, and a notable photo-on-off ratio of 4.82 × 103. Due to its high performance, reconfigurability, and broadband response, our device shows considerable potential in neuromorphic visual systems even in the infrared region.

Experimental Study of Irradiation of Thin Oxide and Mo/Si Multilayers by High Brightness Broadband VUV/UV Radiation and Their Degradation

This study discusses the main features of the irradiation of prospective multilayer coatings by VUV/UV radiation from compressed plasma flows. Such radiation is characterized by a broadband spectrum and high brightness fluxes. Oxide and Mo/Si bilayers were used as the basis of the reflective multilayers for the visible and UV ranges. A gas-dynamic response from the irradiated surfaces was studied with schlieren photography. The properties of original and irradiated multilayers were described with ultra violet visible infrared spectroscopy (UV-Vis-IR), X-ray diffraction (XRD), X-ray reflectometry, scanning electron microscopy (SEM) and other techniques. Data on the degradation of optical properties and surface morphology were obtained.

Aperture coupled CPW feed for high gain and broadband circularly polarized slot loaded square patch metasurface antenna

AbstractA single layer planar antenna is designed for high gain and broadband circular polarization. The metasurface antenna consists of 3 × 3 arrays of 45° rotated slot‐loaded square patches on one side of the substrate. The stub loaded CPW fed aperture is designed on another side of the substrate to excite the metasurface antenna. Moreover, the size of square patches in the middle row is increased to achieve broadband bandwidth in −10 dB reflection coefficient and 3 dB axial ratio. Furthermore, the size of slots in the middle patches is increased to further enhance the bandwidth of −10 dB reflection coefficient and 3 dB axial ratio. The designed antenna has attained an impedance bandwidth of 30% (4.56–6.21 GHz) with an axial ratio bandwidth of 8.6%(5.23–5.7 GHz). Moreover, the peak value of antenna gain is 10.21 dBi which is incredibly very large in single layer planar antennas. The measured and simulated results are almost close to each other.

WS2/Bi2O2Se van der Waals Heterostructure with Straddling Band Configuration for High Performances and Broadband Photodetector

Abstract2D bismuth oxyselenide (Bi2O2Se) nanosheets have received increasing attention in the field of electronics and optoelectronics due to their high‐mobility, moderate energy bandgap, and air‐stability. However, due to the intrinsic high mobility, the photodetectors based on 2D Bi2O2Se have an inevitable high dark current, leading to high power consumption and limiting its potential application in photodetection. Herein, a novel highly sensitive WS2/Bi2O2Se van der Walls (vdWs) heterostructure with straddling band configuration is assembled on fluorophlogopite substrate. Owing to the effective separation of photogenerated electron–hole pairs and the quantum tunneling effect, the responsivity and external quantum efficiency of the WS2/Bi2O2Se heterostructure are 628 mA W−1 and 147.6% under 532 nm illumination, respectively. The Iphoto/Idark ratio with more than two orders of magnitude can be obtained, and the rise time is ≈33 ms, while the fall time is 38 ms. Furthermore, the heterostructure achieves a broadband photodetection capability from visible to near infrared (532–1450 nm). The results suggest that the WS2/Bi2O2Se vdWs heterostructure possesses a promising potential application prospect in high performance and broadband photodetectors.

Flexible CuO-rGO/ PANI thermal absorber with high broadband photoresponse and salt resistance for efficient desalination of oil-contaminated seawater

Solar Steam Generation (SSG) is a promising and efficient technology to limit the global water scarcity issue. Nevertheless, it is challenging to utilize versatile photothermal absorbers with salt-resistance and anti-oil-fouling capability through a facile, scalable, and cost-effective fabrication technique. This work demonstrated the combination of cheap semiconductor material with a porous ionic polymer (PIP), emeraldine salt (ES) form of polyaniline (PANI), as salt-resistant and oil-repellent evaporator, which was synthesized through a facile and cost-effective one-step method. PANI enhanced the photoresponse of the CuO-rGO and its honeycomb-like structure increased the photothermal conversion due to the multi-scattering of the incident light. The CuO-rGO/PANI achieved an evaporation rate of 2.02 kg m−2 h−1 and a solar-to-steam efficiency of 94.2% under 1 sun illumination. Furthermore, the composite presented high in-water (138.5°) and in-air (135.2°) oil contact angles with simultaneously high-water affinity (<8°) which proved the hydrophilicity and oleophobicity of this membrane. CuO-rGO/PANI can work effectively in high-concentration brine with no activity loss, due to the “Donnan exclusion” effect generated from cationic quinonoid and benzenoid structure of ES-PANI against cations from saline solution, which exhibit superb durable evaporation performance over 10 cycles.

High Gain Broadband Power Amplifier Design Based on Integrated Diplexing Networks

This letter presents an enhanced gain broadband power amplifier (PA) design approach that is based on using an integrated diplexer with a phase compensation network to combine PAs of narrower bandwidths (BWs) over a wider overall bandwidth PA. The input and output matching networks of each amplifier are individually synthesized using a wideband matching network. The diplexer is designed using a lowpass/highpass topology approach. The separate amplifiers are integrated with the proposed diplexer, resulting in extended bandwidth and enhanced gain. For verification purposes, a broadband PA is designed and implemented over the frequency range of 2–4 GHz. Measurements demonstrate that the output power varies between 40.1 and 41.2 dBm with a drain efficiency (DE) of 61%–75%. The proposed design achieves a high small-signal gain of 12.5–15.3 dB. The reported saturated power gain is 10.1–11.2 dB.

An ultra-broadband flexible polarization-insensitive microwave metamaterial absorber

In this paper, an ultra-broadband flexible polarization-insensitive microwave metamaterial absorber is proposed, characterized, and fabricated. To achieve high broadband absorption, a two-layer periodic indium-tin-oxide (ITO) patches array printed on polyethylene terephthalate (PET) dielectric layers is used to generate high ohmic loss. The simulation results show that the proposed absorber can achieve greater than 90% absorption in the microwave band range of 19.68 to 94.7 GHz. The absorber is polarization-insensitive due to the symmetry of the structure with high absorption over a wide incidence angle of 60°. The mechanism of ultra-broadband absorption is discussed by the impedance matching theory, the surface current distribution, and the electric field distribution. In addition, the equivalent circuit model is utilized to analyze the effect of the structural parameters. Furthermore, the bow-frame method validates that the experimental measurements are consistent with the simulated spectra. With advantages of absorption of ultra-broadband, polarization-insensitivity, and flexibility, the proposed absorber facilitates its use in numerous potential applications for energy harvesting, imaging and sensing, stealth technology, modulating, and so on.

A high-efficient and ultra-strong interfacial solar evaporator based on carbon-fiber fabric for seawater and wastewater purification

Interfacial solar-driven water evaporation is an effective strategy to solve freshwater scarcity. Efficient interfacial evaporation comes from excellent photothermal material. Herein, we developed a multilayer carbon-fiber fabric (MCF) evaporator with excellent mechanical properties for efficient solar-driven water purification. The all‑carbon composition and multilayer honeycomb structure endows the MCF with a high broadband light absorption (97%), rapid water transport, and good thermal management. As a result, the MCF shows an impressive purification capacity for seawater and organic wastewater and a good inhibition for the volatilization of low-boiling-point organic components. Under 1 sun irradiation, the evaporation rate can reach 3.39 kg∙m−2∙h−1. The outstanding salt-rejecting property also enables perfect stability and reusability. Even 20 wt% brine has no impact on the evaporation process and energy efficiency. More importantly, the MCF can effectively resist mechanical destruction from the environment, maintain its structural integrity. The concept of MCF with a hierarchical structure and multiple attributes will stimulate more inspiration for the development of solar-energy desalination and sewage treatment.

Dynamically Selective and Simultaneous Detection of Spin and Orbital Angular Momenta of Light with Thermoresponsive Self-Assembled Chiral Superstructures

Featuring a self-assembled helical nanostructure and external stimuli-responsive chiral photonic band gap, cholesteric liquid crystals (CLCs) create more opportunities in harnessing multiple degrees of freedom of light, especially the spin and orbital angular momenta (SAM/OAM). Here, we propose and demonstrate an innovative method for a dynamically selective and simultaneous detection of SAM and OAM of light via two cascaded CLC superstructures with thermal controllability and opposite chirality. By independently regulating their temperatures, on-demand selective detection for the intended wavelength and spin eigenstate is achieved with high efficiency and broadband tunability. The information of the desired angular momenta is vividly identified by the reflected diffraction patterns from cascaded chiral superstructures, while the nondetected components are preserved in the transmitted light. This indicates an in situ and nondestructive manner and may facilitate advanced optical manipulation, imaging, and information (de)multiplexing. This work brings important insights into the design, construction, and application of self-assembled chiral nanostructures, promoting multiple and active functionalities in diverse intelligent devices.

Fast physical random bit generation using a millimeter-wave white noise source.

A broadband millimeter-wave (MMW) white noise signal generated by optical heterodyning of two Fabry-Perot laser diodes (FP-LDs) subject to optical feedback is demonstrated and employed for fast physical random bit generation with a simple least significant bits (LSBs) retaining method. Firstly, under suitable feedback conditions, two external-cavity feedback FP-LDs can be easily driven into chaotic states. In this process, the optical spectra of multi-longitudinal modes are significantly broadened. Then, two spectral broadening multi-longitudinal chaotic signals are mixed and converted into an MMW white noise signal through the heterodyne beating technique combined with a fast photodetector. With such an approach, a high dimensional broadband chaos with perfect characteristics of MMW white noise (3-dB bandwidth beyond 50 GHz without any time-delay signature) is experimentally achieved. Finally, taking the generated MMW white noise as the entropy source, 640 Gb/s physical random bit generation is realized by directly selecting 4-LSBs at 160 GS/s sampling rate after an 8-bit analog-digital-convertor.

Broadband low-frequency acoustic absorber based on metaporous composite

Broadband absorption of low-frequency sound waves via a deep subwavelength structure is of great and ongoing interest in research and engineering. Here, we numerically and experimentally present a design of a broadband low-frequency absorber based on an acoustic metaporous composite (AMC). The AMC absorber is constructed by embedding a single metamaterial resonator into a porous layer. The finite element simulations show that a high absorption (absorptance A > 0.8) can be achieved within a broad frequency range (from 290 Hz to 1074 Hz), while the thickness of AMC is 1/13 of the corresponding wavelength at 290 Hz. The broadband and high-efficiency performances of the absorber are attributed to the coupling between the two resonant absorptions and the trapped mode. The numerical simulations and experimental results are obtained to be in good agreement with each other. Moreover, the high broadband absorption can be maintained under random incident acoustic waves. The proposed absorber provides potential applications in low-frequency noise reduction especially when limited space is demanded.

A New Approach for Designing and Analysis of High Flat Gain Broadband Low Noise Amplifier Using Real Frequency Technique

This paper introduces a high flat gain broadband Low Noise Amplifier (LNA) design approach, which is based on using a new methodology of Real Frequency Technique (RFT). To get this done, the optimum matching network has been designed with second-order LC lumped elements to minimize the Noise Figure (NF) and maximize the Transducer Gain (GT) based on selecting the optimum (ZS, ZL) LNA terminations that have been used over a 2.1-4.2 GHz. The design has demonstrated a high stable gain in the range of 19.19 –18.73 dB with ± 0.2 dB gain flatness over the specified band. Moreover, the NF has been obtained at 0.68 – 0.82 dB and a stable operation throughout a broad bandwidth. Furthermore, the proposed method results have been compared with an analytical methodology which is based on computing equivalent input and output circuits for the transistor model using its scattering parameters. For the verification purpose, the performances of the synthesized amplifier are compared using MATLAB platform and ADS simulation software. The output results have a good agreement with the proposed method outcomes, which makes this method a new promising technique for the high flat gain broadband LNA design.

Isolated attosecond pulse generation from helium atom irradiated by a three-color laser pulse

Isolated attosecond pulses enables the studying and controlling of ultrafast electron processes in atoms and molecules. High-order harmonic generation (HHG) is the most promising way to generate such pulses, benefiting from the broad plateau structure of the typical HHG spectrum. We theoretically investigate high-order harmonic and attosecond pulse generation from helium atom in a three-color laser field, which is synthesized by 16 fs/1600 nm, 15 fs/1100 nm and 5 fs/800 nm pulse laser. Compared with harmonic spectrum generated by a two-color laser field synthesized by 16 fs/1600 nm and 15 fs/1100 nm, the harmonic spectrum generated from the synthesized three-color field exhibits high conversion efficiency and broadband supercontinuum characteristics. The continuous spectrum range covers from 230th to 690th harmonics, and the generation of 128 attosecond isolated short pulses with higher intensity is realized after Fourier transform. This result is attributable to the fact that the synthesized three-color electric field exhibits high-intensity and few-cycle mid-infrared femtosecond pulse laser characteristics, which can effectively control atomic ionization and recombination occurring within an effective optical period of the mid-infrared femtosecond pulse. This scheme solves the problems faced by the current femtosecond pulse laser technology, i.e. the few-cycle mid-infrared femtosecond pulse laser cannot have both carrier envelope phase stability and high power output.

Promotion of High Capacity Broadband to Rebuild and Recover From the Pandemic

Promotion of High Capacity Broadband to Rebuild and Recover From the Pandemic

Broadband Characterization of Thin Dielectrics Using Heterolayer and Monolayer MIM Capacitors

Characterization of the complex permittivity and loss tangent of a dielectric is essential for broadband and microwave applications. Non-resonant methods are applicable over a wide frequency range. However, they can get less accurate dielectric properties than resonant methods. To overcome this limitation, in this study, a new non-resonant method is proposed to extract properties of thin dielectric accurately by measuring the reflection coefficient of two metal-insulator-metal (MIM) capacitors. First, we designed the heterolayer and monolayer MIM capacitor structures that are needed for high accuracy and broadband characterization. Second, the characterization method was formulated by analyzing the two structures by equivalent circuit modeling and verified via a 3D full&#x2013;wave electromagnetic simulation. Finally, by setting <i>HfO₂</i> and <i>Al₂O₃</i> as target dielectrics, heterolayer and monolayer capacitors were fabricated, and their reflection coefficients were measured using a vector network analyzer in the range of 0.1&#x2013;67 GHz&#x2014;a broadband range scarcely considered in prior studies on non-resonant methods. The results of applying the measurement data to the proposed method indicate that a high-accuracy characterization of the complex permittivity and loss tangent of the high-k dielectrics, <i>HfO₂</i> and <i>Al₂O₃</i>, in the broadband frequency range is achieved.

Young’s Double Slit Method-Based Higher Order Mode Surface Plasmon Microwave Antenna Sensor: Modeling, Measurements, and Application

This paper proposes Young’s double slit method based high gain broadband higher order mode spoof surface plasmon leaky wave antenna sensor (SSPLWA) for dual beam and sensing applications. Following and mimicking the double slit principle in microwave frequencies, the proposed surface plasmon leaky wave antenna sensor operating on higher order modes has been successfully measured to obtain a wideband of more than 15GHz (88.5%) and generate two simultaneous radiating beams towards the endfire direction with a peak gain of 16.6 dBi. The proposed antenna sensor operates in a broad frequency range from 10GHz-25GHz and maintains a minimum gain of > 10 dBi in the whole operating band. The SSPLWA has been tested by designing two prototypes without and with additional horizontal conducting strips so as to improve the overall gain, reflection and efficiency. The prototype with horizontal strips has been further tested for sensing application i.e. aqueous glucose solutions and it is found that the proposed dual beam sensor is providing high sensitivity and very stable measurement results in terms of resonance frequency shifts or magnitude variations. The proposed antenna sensor has achieved a high peak efficiency of 95 percent and can be very useful for dual beam applications and wireless sensing measurements.

Design and implementation of half-space radiation high frequency broadband “spherical” transducer based on anti-sound baffle and circuit matching

In underwater acoustic communication engineering applications, it is sometimes necessary to place the communication transducers underwater. This usually requires the transducers to have the ability to radiate in half-space. At the same time, in order to reduce the transmission error rate, it is also necessary that the transducers have the ability to operate in a wide band. The spherical piezoelectric transducers have full space radiation, and high power and energy density. The design of spherical transducer by using anti-sound baffle and circuit tuning can meet the requirements of underwater communication transducers. In this work, we analyze the directivity of a spherical transducer by comparing the simulations and theoretical computations. In addition, the broadband performance of a spherical transducer is analyzed based on series inductance tuning. Finally, a half-space broadband spherical transducer prototype is manufactured and its performance is tested and verified by performing experiments. The experimental results show that the bandwidth of the spherical transducer can be increased by series inductance. Moreover, the results show that the distance from the center of the spherical transducer to the anti-sound baffle and the working frequency have a significant effect on the directivity of a spherical transducer. The test results of transducer prototype show that the directivity angle of the transducer is greater than 180°, and the operating bandwidth is around 18 kHz–54 kHz.

Photothermal properties of stable aggregates of gold nanorods

Aggregation of the nanoparticles is a natural phenomena due to various biological and physical parameters but these aggregates are highly unstable. If aggregates would have been stable then it might be useful for some biomedical applications. To study the optical properties and photothermal heat generation of stable aggregates of the metal nanoparticles, we present a forced synthesis of aggregates of small gold nanorods in a mixture of Dulbecco’s Modified Eagle’s medium (DMEM) and Bovine Serum Albumin (BSA). We synthesized hexadecyltrimethylammonium bromide (CTAB) coated gold nanorods and then prepared the stable aggregates to study the optical characteristics of these aggregates. Absorption spectra of aggregates show the redshift compared to the monodispersive gold nanorods and confirm that the shape and size of aggregate depend on the amount of BSA in DMEM as well as on the concentration of CTAB in the stock solution of the gold nanorods suspension. The higher concentration of the BSA in DMEM and lower concentration of CTAB of monodispersive gold nanorod suspension causes greater redshift. We tuned the well defined plasmonic absorption resonance peaks of the aggregates of gold nanorods up to the second biological therapeutic window. We studied the stability of the synthesized aggregates of gold nanorods for up to one week and found that the aggregates were stable for at least one week. A photothermal study of these aggregates was also carried out using high power broadband near-infrared light source. Aggregates were also photothermally stable which warrants their repeated use for such applications. The photothermal conversion efficiency of these stable gold nanorod aggregates were higher than its monodispersive form of the nanorods. The present study on the optical and photothermal properties of stable aggregates could be useful for biomedical therapeutic applications, sensing, deep tissue light penetration for imaging and other scientific applications to redshift the plasmonic absorption resonance peak and enhance the photothermal effect.

Broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer design study.

A broadband high-spatial-resolution high-spectral-resolution flexible imaging spectrometer (B-2HSR-FIS) is presented, which includes two microlens arrays (MLAs), multiple fiber bundles, a scanning Fabry-Perot interferometer (FPI), a reflection grating, a cylindrical lens, and an area-array detector. The first MLA is arranged in a circular arc to obtain a field angle between 8° and 60° in the horizontal plane. The second MLA is arranged in a straight line. Each fiber bundle containing seven optical fibers is coupled to a separate microlens of the first MLA, subdividing the field angle of each microlens into seven smaller field angles to improve spatial resolution. The combination of a scanning FPI and a reflection grating enables the B-2HSR-FIS to obtain both high spectral resolution and broadband spectral range in the ultraviolet to near-infrared spectral region. Compared with all existing imaging spectrometers, the B-2HSR-FIS is the first to simultaneously obtain high spatial resolution, high spectral resolution, broadband spectral range, and moderate field angle, to the best of our knowledge. The B-2HSR-FIS has great potential for vision intelligence (e.g., as an eye of a robot).