Broadband Transmission Research Articles

Broadband Absorptive Frequency-Selective Rasorber Based on Multilayer Resistive Sheets Using Multilayer Resonator

In this article, the frequency-selective rasorber (FSR) built on multilayer resistive sheets, which achieves a broad absorption band, was proposed. First, the detailed analysis of the absorption and transmission performance for FSR with the single-layer/multilayer resistive sheets based on the equivalent circuit model (ECM) was demonstrated, which proved that the FSR with the multilayer resistive sheets can obtain a broader absorption band. Second, the multilayer resonator (MR) of a smaller size and higher design freedom compared with single-layer resonator was proposed. Then, the FSR on the basis of multilayer resistive sheets using MR was designed. It consists of the three-layered metallic structures and separated by an air spacer. For the top and middle layers, the lumped-resistor-loaded metallic dipole with the MR inserted into the center was applied to generate a wide absorption band and transparent window, respectively. For the bottom layer, the square-slot frequency-selective surface was optimized to match the transmission band of the resistive sheet. Simulated and measured results show that the broad absorption band and transmission band with low insertion loss have been realized, and the proposed FSR yields the widest relative bandwidth <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert \le -10$ </tex-math></inline-formula> dB of 145.2%.

Phase-Gradient Metagratings via Mode Conversion

Phase-gradient metagratings have exhibited unconventional abilities to manipulate electromagnetic waves owing to functionality inherited from metasurface and different physics. In this paper, by integrating homogeneous dielectric materials with gradient thickness into periodical metallic slits, a passive phased metagrating based on mode conversion is designed in which each unit provides nearly perfect broadband transmission. To validate the effectiveness of our scheme, anomalous scattering and planar metalenses with excellent efficiency in a finite band are designed theoretically and proved numerically. Good performance makes the implementation of other metasurface functions possible, providing a platform for functions from holography to caustic engineering. More interestingly, the high fluidity of this structure promises potential application in other physical fields, such as acoustics and water waves.

Extraordinary broadband impedance matching in highly dispersive media - the white light cavity approach.

Suppressing reflections from material boundaries has always been an objective, common to many disciplines, where wave phenomena play a role. While impedance difference between materials necessarily leads to a wave reflection, introducing matching elements can almost completely suppress this phenomenon. However, many impedance matching approaches are based on resonant conditions, which come at a price of narrow bandwidth operation. Although various impedance matching architectures have been developed in the past, many of them fail to produce a broadband and flat (ripple-free) transmission, particularly in the presence of strong chromatic dispersion. Here we propose and demonstrate an approach for designing an optimal matching stack capable of providing a flat broadband transmission even in the presence of significant group velocity dispersion. As an experimental example for the method verification, we used a strong modal dispersion in a rectangular waveguide, operating close to a mode cut-off. The waveguide core consists of alternating polymer sections with a variable filling factor, realized using additive manufacturing. As a result, a broadband matching in the range of 7-8GHz was demonstrated and proved to significantly outperform the standard binomial transformer solution. The proposed method can find use across different disciplines, including optics, acoustics and wireless communications, where undesired reflections can significantly degrade system's performances.

The Transit Timing and Atmosphere of Hot Jupiter HAT-P-37b

Abstract We perform transit timing variation (TTV) and transmission spectroscopy analyses of the planet HAT-P-37b, which is a hot Jupiter orbiting a G-type star. Nine new transit light curves are obtained and analyzed together with 21 published light curves from the literature. The updated physical parameters of HAT-P-37b are presented. The TTV analyses show a possibility that the system has an additional planet that induced the TTVs amplitude signal of 1.74 ± 0.17 minutes. If the body is located near the 1:2 mean-motion resonance orbit, the sinusoidal TTV signal could be caused by the gravitational interaction of a sub-Earth-mass planet with mass of 0.06 M ⊕. From the analysis of an upper-mass limit for the second planet, a Saturn-mass planet with orbital period less than 6 days is excluded. The broadband transmission spectra of HAT-P-37b favors a cloudy atmospheric model with an outlier spectrum in the B filter.

Efficient ULF Transmission Utilizing Stacked Magnetic Pendulum Array

A novel stacked magnetic pendulum array (MPA) is proposed as an antenna for efficient transmission in ultralow frequencies (ULF). The MPA structure consists of an array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m\times n}$ </tex-math></inline-formula> magnets stacked in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> rows (m magnets of the same magnetization per row) and a solenoid that encompasses the array. The magnetic flux generated by the solenoid couples to the magnets through a mechanical motion and creates a strong time variant magnetic field at the resonance frequency of the array. The proposed MPA is developed utilizing bearings with extremely small damping which hold the magnets, enable efficient oscillation, and guarantees a high-quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor). A comprehensive analysis to study the performance of the MPA and a conventional solenoid will be provided and accordingly, characteristics of an arbitrary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m\times n}$ </tex-math></inline-formula> array in terms of field strength, resonance frequency, transmission efficiency and inductance are studied. Furthermore, a figure of merit (FOM) is introduced as the ratio of efficiency to the maximum linear dimension of the antenna. The experimental results for a fabricated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5 \times 11$ </tex-math></inline-formula> array show a resonance frequency of 715 Hz and a Q-factor of 94 while the maximum linear dimension of the antenna is just 9 cm. Moreover, measurement results show 24.9 dB improvement in the transmission efficiency of the MPA compared to the efficiency of a single solenoid of the same dimensions. The MPA has the FOM of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.26\times 1}{0}^{{4}}$ </tex-math></inline-formula> which is noticeably higher than that of proposed antennas in the literature. To demonstrate broadband transmission with the MPA, a binary frequency shift keying (BFSK) signal is transmitted through the use of direct antenna modulation (DAM) at a rate of 18 bps.

Frequency Selective Rasorber with Broadband Transmission Window Using Characteristic Modes Analysis

Frequency Selective Rasorber with Broadband Transmission Window Using Characteristic Modes Analysis

Transmission polarization converter based on V-shaped metasurface in terahertz region

Metasurfaces have attracted extensive attention due to their powerful functions, especially the manipulation of the polarization state of electromagnetic wave in many different areas, which have aroused a lot of research interest. In this work, a broadband transmission polarization converter based on V-shaped element array in terahertz band is designed and analyzed, which consists of grating-V-shaped metasurface-grating. The top layer and bottom layer form a pair of crossed gratings, and the middle layer is a V-shaped metasurface, and the layers are separated by polyimide. The structure parameters of the polarization converter are optimized by CST microwave studio, changes of which can result in narrow band or low transmission. Cross-polarization transmission rate and polarization conversion rate can reach more than 80% and 99%, respectively, in a frequency range from 0.35 THz to 1.11 THz. By studying the electric field distribution in the substrate under the V-shaped metasurface , it is found that the real part of the cross-polarization electric field between adjacent V-shaped metasurfaces presents similar values in a frequency range from 0.35 THz to 1.11 THz, resulting in high cross-polarization transmission. However, the real part of the cross-polarization electric field between adjacent V-shaped metasurfaces presents opposite values, resulting in low cross-polarization transmission at 1.40 THz. At the same time, the responses of the single layer structure of the V-shaped array and the bi-layer structure of the grating placed behind the V-shaped array to vertically incident x-polarized terahertz waves are investigated respectively, and the results show that the single-layer V-shaped array can convert part of linearly polarized incident light into cross-polarization light, however, in the bi-layer structure, Fabry-Perot cavity is formed between the V-shaped array and the grating, and the cross polarization transmission increases. This indicates that the V-shaped array provides the capability of polarization conversion, and the existence of the grating makes the F-P cavity inside the structure create the conditions for the back and forth reflection of terahertz waves. The combined action of the V-shaped metasurface and orthogonal grating results in a high polarization conversion rate.

Quantum interference effect in plasmonic transmission in the presence of quantum emitters

In this paper, we show how to enhance the transmission of the surface plasmon field using several interacting two-level quantum emitters placed in a plasmonic environment. Our model relies on quantum interference effect and, therefore, can be treated as a plasmonic analog of the electromagnetic induced transparency, usually referred to in the context of driven atomic systems. Moreover, our model with multiple interacting quantum emitters, similar to Ising spin chain, can be used for broadband transmission of the surface plasmon field.

Retrieving the transmission spectrum of HD 209458b using CHOCOLATE: a new chromatic Doppler tomography technique

Multiband photometric transit observations or low-resolution spectroscopy (spectro-photometry) are normally used to retrieve the broadband transmission spectra of transiting exoplanets in order to assess the chemical composition of their atmospheres. In this paper we present an alternative approach for recovering the broadband transmission spectra using chromatic Doppler tomography based on physical modeling through the SOAP tool: CHOCOLATE (CHrOmatiC line prOfiLe tomogrAphy TEchnique). To validate the method and examine its performance, we use observational data recently obtained with the ESPRESSO instrument to retrieve the transmission spectra of the archetypal hot Jupiter HD 209458b. Our findings indicate that the recovered transmission spectrum is in good agreement with the results presented in previous studies, which used different methodologies to extract the spectrum, achieving similar precision. We explored several atmospheric models and inferred from spectral retrieval that a model containing H2O and NH3 is the preferred scenario. The CHOCOLATE methodology is particularly interesting for future studies of exoplanets around young and active stars or moderate to fast rotating stars, considering SOAP’s ability to model stellar active regions and the fact that the rotational broadening of spectral lines favors its application. Furthermore, CHOCOLATE will allow the broad transmission spectrum of a planet to be retrieved using high-S/N, high-resolution spectroscopy with the next generation of extremely large telescopes, where low-resolution spectroscopy will not always be accessible.

Survey on security issues of routing and anomaly detection for space information networks

Space information networks is network systems that can receive, transmit, and process spatial information lively. It uses satellites, stratosphere airships, Unmanned Aerial Vehicles, and other platforms as the carrier. It supports high-dynamic, real-time broadband transmission of earth observations and ultra-long-distance, long-delay reliable transmission of deep space exploration. The deeper the network integration, the higher the system’s security concerns and the more likely SINs will be controlled and destroyed in terms of cybersecurity. How to integrate new IT technologies such as artificial intelligence, digital twins, and blockchain to diverse application scenarios of SINs while maintaining SIN cybersecurity will be a long-term critical technical issue. This study is a review of the security issues for space information networks. First, this paper examines space information networks’ security issues and figures out the relationship between the main security threats, services, and mechanisms. Then, this article selects secure routing and anomaly detection from many security technologies to conduct a detailed overview from two perspectives of traditional methods and artificial intelligence. Subsequently, this paper investigates anomaly detection schemes for spatial information networks and proposes a deep learning-based anomaly detection scheme. Finally, we suggest the potential research directions and opening problems of space information network security. Overall, this paper aims to give readers an overview of the newly emerging technologies in space information networks’ security issues and provide inspiration for future exploration.

Broadband and Intense Sound Transmission Loss by a Coupled-Resonance Acoustic Metamaterial

The advent of acoustic metamaterials opened up a new frontier in the control of sound transmission. A key limitation, however, is that an acoustic metamaterial based on a single local resonator in the unit cell produces a restricted narrow-band attenuation peak; and when multiple local resonators are used the emerging attenuation peaks -- while numerous -- are each still narrow and separated by pass bands. Here, we present a new acoustic metamaterial concept that yields a sound transmission loss through two antiresonances -- in a single band gap -- that are fully coupled and hence provide a broadband attenuation range; this is in addition to delivering an isolation intensity that exceeds 90 decibels for both peaks. The underlying coupled resonance mechanism is realized in the form of a single-panel, single-material pillared plate structure with internal contiguous holes$-$a practical configuration that lends itself to design adjustments and optimization for a frequency range of interest, down to sub-kilohertz, and to mass fabrication.

Dual‐polarized frequency selective rasorber with broadband absorption and transmission

In this letter, a polarization-insensitive frequency selective rasorber (FSR) is proposed, which can achieve wide absorption band and wide transmission band at low frequency and high frequency, respectively. It consists of two layers and an air spacer in the middle. The top layer is a resistive sheet, which is realized by an improved Jerusalem metal strip loaded with lumped resistors, while a square ring slot-type bandpass FSS on the bottom is designed to match the passband of the resistive sheet. The working principle of the FSR is analyzed by the method of equivalent circuit. In order to verify our design, a sample prototype has been fabricated and measured, it can be seen from the measurement results that an insertion loss of about 0.12 dB is obtained at 21.6 GHz under normal incidence, the 1 dB transmission relative bandwidth and the relative bandwidth for 10 dB absorption reaches more than 80% and 24%, respectively. The FSR exhibits the characteristics of insensitivity to polarization with excellent angle stability. The simulation results and the measured results are relatively consistent, whether it is normal incidence or oblique incidence. The proposed FSR has the potential to be used in the applications of stealth performances improved of low-observable platforms in the future.

Gradient-index metasurface multilayer for quasioptical coupling of infrared detectors

Periodic surface grating structures made of machinable infrared-transparent dielectrics can offer broadband reflection and transmission in THz waves. We present geometrically varying periodic metasurface made by micromachining and integrated above a gradient-index dielectric multilayer to achieve a near-perfect longpass filter. We utilized techniques in two-dimensional and three-dimensional rigorous, coupled-wave analysis for understanding quasioptical electromagnetic wave coupling within photonic gratings. The low-index pyramidal metasurface shape factors show at-period interference to allow near-perfect transmission. A purely infrared dielectric and polymeric low-index material is compared to seek trade-offs in infrared absorption. We also establish relationships between minimum deposited layer thickness and longpass filter performance. This micromachined metamaterial focal plane filter-on-chip can perform combined antireflection and Bragg band-pass filtering at the near- to far-infrared wavelengths. Its capability can be used for infrared/THz focal plane thermal imaging for space-based applications, understanding the Earth’s surface and atmosphere, and observing cryogenic features of far bodies and exoplanets.

Simultaneous representation and separation for multiple interference allied with approximation message passing in vehicular communications

Reliable communication is a competitive task for broadband vehicular communications due to the fact that multiform interference has been introduced to the existing broadband transmission, which promotes the development of cognitive vehicular communication systems. To facilitate the improvement of the anti-jamming performance for the coexistence of diverse interference and signals in wireless heterogeneous networks, separating and eliminating various interference to cognitive communication systems is of importance. This paper formulated a novel sparse learning method-based cognitive transformation framework of interference separation for precise interference recovery, which can be efficiently resolved by iteratively learning the prior probability distribution of the sparse interference support. To further enhance the separation accuracy and iterative convergence, the principal component analysis and Bayesian perspective in orthogonal base learning were exploited to singly recover the multiple interference and communication signals. Moreover, through different sparsity states of spectrum analysis, the proposed novel interference separation algorithm was applied to simultaneous separation based on state evolving of approximation message passing, which iteratively learned the belief propagation posteriors and shrank by iterative shrinkage threshold. Simulation results demonstrate that the proposed methods were effective in separating and recovering sparse diversities of interference to communication systems, thereby significantly outperformed the state-of-the-art methods.

Experimental evidence of enhanced broadband transmission in disordered systems with mirror symmetry

We demonstrate in microwave measurements the broadband enhancement of transmission through an opaque barrier due to mirror symmetry. This enhancement relies on constructive interference between mirror scattering paths resulting from strong internal reflections at the left and right interfaces of a multichannel cavity. We observe a strong sensitivity of the conductance to a shift of the barrier from the center of the cavity. Remarkably, the impact of mirror symmetry can be further increased by tuning the degree of disorder within the cavity. We report an additional enhancement of the conductance found by symmetrically placing randomly located scatterers. Our results illuminate the impact of symmetry and disorder correlation on transmission through complex systems.

All-Fiber Gas Cavity Based on Anti-Resonant Hollow-Core Fibers Fabricated by Splicing with End Caps

In recent years, fiber gas lasers have obtained a rapid development, however, efficient and stable pump coupling is a key limitation for their applications in the future. Here, we report an all-fiber gas cavity based on anti-resonant hollow-core fibers which have the beneficial properties of adjustable broad transmission bands and potential low transmission attenuation, especially in the mid-infrared. This kind of all-fiber gas cavity is fabricated by directly splicing with end caps at both ends for the first time. The high-power laser transmission characteristics were studied, and the experimental results show that the all-fiber gas cavities have a very stable performance. The maximum input laser power at 1080 nm is about 260 W, and the output power is 203 W, giving a total transmission efficiency of 78.1%. This work opens a new opportunity for the development of high-power all-fiber structured fiber gas lasers.

Planar narrow bandpass filter based on Si resonant metasurface

Optically resonant dielectric metasurfaces offer unique capability to fully control the wavefront, polarization, intensity, or spectral content of light based on the excitation and interference of different electric and magnetic Mie multipolar resonances. Recent advances of the wide accessibility in nanofabrication and nanotechnologies have led to a surge in the research field of high-quality functional optical metasurfaces, which can potentially replace or even outperform conventional optical components with ultra-thin features. Replacing conventional optical filtering components with metasurface technology offers remarkable advantages, including lower integration cost, ultra-thin compact configuration, easy combination with multiple functions, and less restriction on materials. Here, we propose and experimentally demonstrate a planar narrow bandpass filter based on the optical dielectric metasurface composed of Si nanoresonators in arrays. A broadband transmission spectral valley (around 200 nm) has been realized by combining electric and magnetic dipole resonances adjacent to each other. Meanwhile, we obtain a narrow-band transmission peak by exciting a high-quality leaky mode, which is formed by partially breaking a bound state in the continuum generated by the collective longitudinal magnetic dipole resonances in the metasurface. Owing to the in-plane inversion symmetry of our nanostructure, the radiation of this antisymmetric mode is inhibited at far field, manifesting itself a sharp Fano-shape peak in the spectrum. Our proposed metasurface-based filter shows a stable performance for oblique light incidence with small angles (within 10°). Our work implies many potential applications of nanoscale photonics devices, such as displays, spectroscopy, etc.

Data-aided channel equalization scheme for FAST radio over fiber transmission system.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) located in Guizhou, China, is a very sensitive single dish telescope. Due to the large size of the telescope, optical fiber is used for the transmission of the 3-km astronomical signal from the telescope to the signal processing center. The optical fibers are suspended in the air above the telescope reflector, very easy to slide when the telescope feed cabin moves, resulting in phase drifts for the transmission signal. This phase drift has a negative impact on the observation mode of very long baseline interferometry, and can be compensated by the frequency transfer system in the FAST. In this manuscript, we propose a new phase drift compensation scheme, which is denoted as data-aided channel equalization scheme. The proposed scheme is based on a hypothesis of linear phase relationship between different wavelengths in the same optical fiber, and uses the channel response information of the data-aided channel to conduct signal recovery for the astronomical signal channel. Not only the phase drift, but also the frequency-dependent distortion of the broadband transmission link can be compensated. The proposed scheme has simple transmission structure, and the function part is well modularized, so that the Astronomer users can easily turn it on or off. In the proof-of-concept experiments, the estimation deviation can be significantly reduced by estimated channel responses averaging over training sequence repetitions, showing very high accuracy of the astronomical signal channel estimation.

Low-Temperature Oxide/Metal/Oxide Multilayer Films as Highly Transparent Conductive Electrodes for Optoelectronic Devices

Transparent conductors are essential for optoelectronic devices and flexible electronic devices. Oxide/metal/oxide (OMO) multilayer films with outstanding photoelectric performance have become a promising alternative for traditional transparent conductive oxides (TCOs). Most of the oxide films in OMO are deposited by magnetron sputtering or thermal evaporation processes, while the strong ion bombardment or high temperatures would deteriorate the device performance. For example, to fabricate a semitransparent solar cell, a top OMO will need to be deposited on the top of the semiconductor layer. Great care needs to be taken to reduce the damage to the semiconductor material to reduce the possible trapping of photogenerated charges. Recently, Mg and Ga codoped ZnO (MGZO) has been developed because of its wider spectral transmittance and less damage to the underlying functional layers in optoelectronics. However, the conductivity of MGZO remains limited. To produce low sheet resistance, the layer thickness needs to be several hundred nanometers. Here, we present high-quality MGZO films that are deposited by the reactive plasma deposition (RPD) technique with a soft growth process at room temperature (without intentional heating), providing broadband transmission and ultrathin pure Ag films prepared by magnetron sputtering at room temperature. Compared with the single MGZO, MGZO/Ag/MGZO multilayers effectively improve thin-film conductivity while maintaining high transmittances. The transfer matrix method (TMM) is used to determine the optimum thickness of each layer in OMO, and there is an excellent agreement between the simulation and experimental results. An MGZO/Ag/MGZO (40/9.5/45 nm) transparent electrode on a glass substrate presents an average transmittance of 87% (including glass) over a spectral range of 400–800 nm (relative transmittance, 94.7%), and sheet resistance (10 Ω sq–1). A semitransparent perovskite solar cell with an OMO top electrode exhibits a photoelectric conversion efficiency of about 11%. This work provides an insight to grow high-quality OMO films combining the RPD-TCO technique of high-rate deposition and low ion bombardment with ultrathin Ag films at room temperature, which pushes OMO forward to practical applications in more diverse optoelectronic devices.

A Dual‐Polarized Frequency Selective Rasorber With Wide Transmission Band

AbstractIn this paper, a novel and simple dual‐polarized frequency‐selective rasorber (FSR) which has a wide absorption band including a wide transmission band was presented. Detailed equivalent circuit was derived to accurately predict the frequency responses of the structure. Based on reasonable equivalent analysis of a traditional metal grid structure, a modified structure with improved performance was proposed. The structure consists of a lossy frequency‐selective surface (FSS) constructed with metal rings connected by center loaded strips as the top layer, and a broadband transmission FSS at the bottom, while the two layers are separated by air. To validate our proposal, a prototype was fabricated and measured. The measured results are in good agreements with simulations under normal incidence, which indicates a broad absorption bandwidth of 80% that from 3.40 to 8.16 GHz; in the meantime, a wide transmission band with an insertion loss of less than −1.25 dB is ranging from 9.03 to 12.01 GHz. It should be pointed out that, the reflection from the whole structure in the operation band can be kept below −10 dB from 4.15 to 11.87 GHz.