Single Narrow Band Research Articles

Graphene and Vanadium Dioxide-Based Terahertz Absorber with Switchable Multifunctionality for Band Selection Applications.

This study proposes a multifunctional absorber in the terahertz (THz) regime based on vanadium dioxide (VO2) and graphene with either-or band selector applications, which can be realized by electrically and thermally controlling the Fermi energy level of graphene and vanadium dioxide, respectively. The broadband absorption can be achieved with absorptance exceeding 90%, when the VO2 film is in the metallic phase and the Fermi energy levels of the upper and lower graphene layers are simultaneously set to 0.6 and 0 eV, respectively. The double narrowband can be realized when the VO2 film is in the insulating phase and the Fermi energy levels in upper and lower graphene layers are set as 0 and 0.8 eV, respectively. By flexibly shifting between the broadband and the double narrowband, the proposed absorber can be used as an either-or band selector, corresponding optional bandwidth from 2.05 to 2.35 THz, and 3.25 to 3.6 THz. Furthermore, single narrowband absorption can be achieved by setting the conductivity of the VO2 film to appropriate values. The proposed absorber can be used in the THz regime in applications such as multifunctional devices, switches, cloaking objects, and band selectors.

Ultra-broadband triple-peak white light-emitting carbonized polymer dots materials based on Förster resonance energy transfer

Carbonized polymer dots (CPDs) with white-light-emitting property have greatly promising application in next generation of lighting and display technologies. However, most of the reported CPD materials exhibit single peak emission and narrow emission band, resulting in difficulty to obtain white-light emission. In this work, the ultra-broadband triple-peak emission (red, green, and blue) CD-based materials with high-efficiency white light-emitting property are realized for the first time by the Förster resonance energy transfer (FRET). Blue and green emissions are derived from the fluorescence and phosphorescence of donor CPDs, while the red light is derived from receptor by FRET. Remarkably, the fabricated CPD materials show bright pure white-light emission with high overall quantum yield (QY) of 36% and the full width at half maximum of 235 nm. Besides, afterglow colors of CPD-based materials can be tuned from green to red by adjusting the ratio of donor and acceptor. Based on the high-efficiency and wide-spectrum pure white light emission characteristics of CPD-based composites, white light emitting diodes were fabricated and they exhibit bright warm white light with CIE and CCT of (0.35, 0.31) and 4041 K.

Ultra-thin freestanding terahertz frequency selective surface on flexible cyclic olefin copolymer

Frequency selective surfaces (FSSs) are widely employed in spectrometers, selective absorbers, energy harvesting, and sensing devices. However, in the terahertz range, the performance of this ideal component is frequently constrained by the choice of material, which introduces a certain degree of attenuation, thereby diminishing the signal-to-noise ratio. Moreover, these FSS are often bulky and demonstrate a low extinction ratio, which limits their usage in wearables and miniaturised devices. In this work, a multi-band FSS composed of periodic microstructures on an ultrathin cyclic olefin copolymer sheet is proposed, analysed, fabricated, and evaluated using terahertz-time domain spectroscopy. The unit cell is composed of triple, evenly spaced, horizontal gold strips, linked around the middle by a fourth vertically oriented gold strip. By displacing the vertical strip, the asymmetric metasurface shows dual narrowband transmission at 1.04 THz and 1.67 THz. However, only a single narrowband transmission at 1.07 THz can be observed on a symmetric metasurface, with no displacement. The calculated Q factors are 4.52 and 16.63 at 1.04 THz and 1.67 THz, respectively, for the asymmetric metasurface. While for the symmetric metasurface, the calculated Q factor at 1.07 THz is 3.63. The proposed flexible metasurface can be tailored easily as single or dual narrowband frequency selective metasurface for channel filtering and broadband sources in emerging terahertz wireless systems.

Unmanned aerial vehicle defense based on jamming suppression

The number and scale of unmanned aerial vehicles (UAVs) are growing explosively, and the frequent occurrence of UAV intrusions poses a serious threat to national security and social stability. Therefore, it has become increasingly important to defend against UAVs and develop related defense technologies. In order to effectively defend against UAVs, it is necessary to interfere with their GPS/Beidou positioning and 2.4G communication technology, thus disrupting their positioning and communication and rendering them unable to function properly. This article designs and implements a continuous wave single tone narrowband interference, and tests its performance, achieving a power suppression effect that seriously interferes with GPS positioning and blocks communication.

Identification and Limit of Detection of Benzene, Chlorobenzene, Benzoic Acid, Phthalic Acid, and Mellitic Acid in Water Solutions Using Excitation, Emission, and Single-band Synchronous Fluorescence Spectroscopy

Introduction: This paper first introduces the use of computer-simulated single-band synchronous fluorescence (SF) obtained from experimental excitation and emission fluorescence spectra of a pure compound in solution. The simulation produces a single narrow band with a peak wavelength that identifies the compound. Methods: The method is used to show single peak identification of benzene, chlorobenzene, benzoic acid, phthalic acid, and mellitic acid in water solutions. Synchronous fluorescence spectroscopy (SFS) is a variant of fluorescence technique in which excitation and emission scans are simultaneously acquired and multiplied with a predetermined wavelength difference (Δλ) between the two. Commercial instruments have this option to get the SFS signals. Results: In response to the Δλ selected, the result will be an SFS signal producing a series of peaks that could be assigned to compounds. Instead of running the same experiment with different Δλ values to identify the compounds, our simulation program determines a specific Δλ value that generates a narrow SF band with a distinctive peak wavelength for identification purposes. Conclusion: Finally, binary mixtures of chlorobenzene with each compound in water are prepared. The SFS of the solution is acquired and compared with the SFS bands of the components for identification purposes. With the commercial lamp fluorimeter employed, the limits of detection are obtained at the ng/g concentration level with fluorescence emission. Possible limits of detection at lower concentrations are discussed using a laser source. The presence of these molecules in astrochemical studies is discussed.

Background noise model of spaceborne photon-counting lidars over oceans and aerosol optical depth retrieval from ICESat-2 noise data

The ICESat-2 (Ice, Cloud, and land Elevation Satellite-2) photon-counting lidar is a revolutionary active remote sensing device and is extremely sensitive to both laser signal and solar background induced noise photons. The weak laser signals, such as aerosol and water subsurface backscattered laser photons, may be buried in noise in the daytime. A noise model for spaceborne photon-counting lidars is of vital importance in understanding and evaluating the performance of a lidar system, as well as in data processing and applications. From the reciprocity perspective, the main noise source for photon-counting lidars is solar background radiation, which in turn is the signal source of ocean color sensors. In the absence of clouds, it is possible to estimate the aerosol information using background noise data of ICESat-2 if the background noise is accurately modeled. In this study, a background noise model of photon-counting lidars over oceans is proposed that carefully considers the contributions of gas molecules, aerosol, water surface, subsurface, and detector dark noise. As the background rate from clouds are much larger than the sum of other factors, in this study, we only consider the cloudless atmosphere by using a cloud screening process. By inputting the system and environmental parameters, the theoretical predictions of noise level in six study areas have an average MAPE of ∼5% compared with ICESat-2 measured noise data. The results also indicate that without clouds, the variation of aerosols dominates the variation of ICESat-2 total background noise in open ocean areas. Then, based on this noise model, a method to estimate aerosol optical depths (AODs) over oceans is proposed solely on the ICESat-2 product including background noise rate and environmental data. Validation against MODIS (Moderate Resolution Imaging Spectroradiometer) daily AODs indicates that the average MAPE is <20% and the average correlation coefficient is 0.95 in six study areas. This method may provide a new AOD retrieval way over oceans in the daytime, when it is difficult to directly calculate AODs using lidar backscattered signal under strong background noise. In addition, the background noise of the ICESat-2 photon-counting lidar in its six channels (or pixels) has the potential to be regarded as the signal of an “ocean color camera” with only a single narrow green band. Based on this consideration, future works may be conducted to combine ocean color remote sensing with ICESat-2 photon-counting lidar.

Estimating stellar population and emission-line properties in S-PLUS galaxies

ABSTRACT We present tests of a new method to simultaneously estimate stellar population and emission-line (EL) properties of galaxies out of the Southern Photometric Local Universe Survey (S-PLUS) photometry. The technique uses the AlStar code, updated with an empirical prior that greatly improves its ability to estimate ELs using only the survey’s 12 bands. The tests compare the output of (noise-perturbed) synthetic photometry of the Sloan Digital Sky Survey (SDSS) galaxies to properties derived from previous full spectral fitting and detailed EL analysis. For realistic signal-to-noise ratios, stellar population properties are recovered to better than 0.2 dex in masses, mean ages, metallicities, and ±0.2 mag for the extinction. More importantly, ELs are recovered remarkably well for a photometric survey. We obtain input − output dispersions of 0.05–0.2 dex for the equivalent widths of [O ii], [O iii], Hβ, Hα, [N ii], and [S ii], and even better for lines stronger than ∼5 Å. These excellent results are achieved by combining two empirical facts into a prior that restricts the EL space available for the fits. (1) Because, for the redshifts explored here, Hα and [N ii] fall in a single narrow band (J0660), their combined equivalent width is always well recovered, even when [N ii]/Hα is not. (2) We know from SDSS that $W_{\mathrm{H}\alpha +[\mathrm{N}\,\small {\rm II}] }$ correlates with [N ii]/Hα, which can be used to tell if a galaxy belongs to the left or right wings in the classical Baldwin–Phillips–Telervich (BPT) diagnostic diagram. Example applications to integrated light and spatially resolved data are also presented, including a comparison with independent results obtained with the Multi-Unit Spectroscopic Explorer (MUSE)-based integral field spectroscopy.

Magnetic fly ash@carbon microspheres for high-performance electromagnetic wave absorption

Magnetic fly ash (MFA) solid waste used as electromagnetic wave (EMW) absorbers has attracted considerable attention, due to its easy recovery, stable physicochemical property, and magnetic property. However, the single loss mechanism and narrow absorption frequency band of magnetic absorption materials, limit the improvement of absorption performance. In this study, MFA@carbon (MFA@C) microspheres with tunable microstructure are directly synthesized, by adjusting the heart treatment temperature of chemical vapor deposition process. The optimization of the absorption properties is realized, and the absorption mechanism of the MFA@C microspheres is analyzed and discussed. In addition, the optimal reaction temperature of the MFA@C microspheres is 700 °C. When the thickness is 2.9 mm, the reflection loss of the MFA@C microspheres is up to −49.6 dB, and the effective absorption bandwidth is 4.6 GHz. The results show that the excellent EMW absorption ability of the MFA@C microspheres is attributed to the synergistic absorption of carbon and MFA. The unique cluster structure of MFA@C microspheres enhances the multiple reflections and promotes the interfacial polarization.

Evaluation Method of Noise Electromagnetic Radiation Interference Effect

In order to evaluate the viability of frequency equipment in complex electromagnetic environment, the electromagnetic radiation effect evaluation model of random noise is established based on the analysis of the blocking effect mechanism of frequency equipment. Through MATLAB calculation, the corresponding relationship table between the ratio of the critical interference field strength effective value of single frequency continuous wave and sinusoidal amplitude modulation wave and the key parameters of the model is given, and the prediction method of noise electromagnetic interference of frequency equipment is proposed. Taking a Beidou navigation receiver as the test object, the accuracy of the noise electromagnetic radiation blocking effect model is verified by single frequency continuous wave, random noise and narrowband noise electromagnetic radiation blocking effect test, and the maximum error is only 1.51 dB, which indicates that the model and prediction method proposed in this article can accurately evaluate and predict the electromagnetic radiation interference of random noise.

Phased array imaging for damage localization using multi-narrowband Lamb waves

In the conventional phased array imaging methods based on only single narrowband Lamb waves, as the scattering behavior between Lamb waves and defects is closely related to the wavelength and the defect size, the information within only a single narrowband is limited. Besides, limited by the size of elements in phased arrays, the ratio of the element spacing to the wavelength may not be able to reach a small enough value, as a result, grating lobes in some directions and high sidelobes will inevitably appear. Aimed at utilizing Lamb wave information contained in multiple frequency bands so as to improve the image quality of Lamb wave phased array imaging, a multi-narrowband fusion method is proposed. The information of multi-narrowband Lamb waves with different carrier frequencies is fused using the geometric mean. Because the positions of grating lobes and the sidelobes are related to the carrier frequency once the sensor array is fixed, the mainlobe is retained and grating lobes as well as sidelobes can be suppressed after the fusion of multiple narrowband signals with different carrier frequencies. So imaging results with fewer artifacts are achieved compared with that generated using only single narrowband signals. The results of damage localization on an aluminum plate with two defects verify the effectiveness of the proposed method.

Prediction of surface crack growth life for AA7075-T6 under nonproportional loading

The growth direction and growth rate of fatigue cracks initiated from the surface of an aluminum alloy 7075-T6 plate were investigated under six sets of nonproportional loadings produced by combined axial-torsion loading. A digital image correlation method was simultaneously applied to measure the crack opening displacements around the crack tip during the fatigue tests. The effective stress intensity factor ranges were determined on the basis of the measured crack opening displacements and applied to arrange the crack growth rate. Results showed that fatigue crack tended to propagate orthogonally to the direction in which the resultant normal stress in the nonproportional loading cycle was maximized, suggesting that the maximum resultant normal stress dominates crack growth under nonproportional loadings. When the effective stress intensity factor range based on the maximum resultant normal stress was used to arrange the crack growth rates, all data collapsed into a single narrow scatter band. The growth lifetime until the surface crack penetrates the plate could be estimated within a relative error of about ± 20 % based on a modified Paris-type equation through numerical integration.

Interference suppression algorithm for wireless communication network based on joint estimation

When the wireless communication network is interfered, the communication effect will be affected. In order to improve the interference signal processing effect and the identification accuracy of the interference signal, a wireless communication network interference suppression algorithm based on joint estimation is proposed. Using the deep learning method to identify the interference signal, obtain the effective interference signal of wireless communication network, improve the accuracy of interference signal identification, and track and parameter modulation the identified signal; The node model of wireless communication network is established, and the joint estimation method is used to suppress the interference signal for the nodes in the model. The interference suppression of wireless communication network is realized through the state estimation of single tone interference and narrowband interference. The experimental results show that the proposed algorithm has a high accuracy of interference signal recognition, the highest value reaches 98%, and the wireless communication data packet loss rate is low, the highest value is only 0.37, which verifies its interference suppression effect.

An Ultra-Wideband Multilayer Absorber Using an Equivalent Circuit-Based Approach

An ultrawideband (UWB)absorber designed by equivalent circuit model (ECM) is presented in this article. The structural parameters of multilayer absorbers were calculated for full-wave simulation so as to verify the accuracy of this method. The simulation results illustrated that the ideal frequency response can be easily and quickly obtained by using ECM, such as single narrow absorption band, dual-band absorption peak, and ultrawide absorption band. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times20$ </tex-math></inline-formula> quadruple-layer absorber was fabricated and tested, which obtained 10 dB radar cross Section reduction (RCSR) from 2.1 to 37.5 GHz with bandwidth ratio (BWR) of 17.62:1. The overall dimension of the unit cell structure is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$280\times 280\times 14\,\,{\mathrm{ mm}}^{3}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.96\lambda _{\max } \times 1.96\lambda _{\max } \times 0.098\lambda _{\max } $ </tex-math></inline-formula> ), and the absorber exhibits stable response on conformal cylinders with central angles of 30° and 60°. Moreover, in order to reduce the influence of high-order modes above U-band, the space mapping (SM) technique was introduced to optimize the absorber’s parameters, which greatly expanded the high-frequency absorption bandwidth. A 10 dB RCSR was achieved from 3 to 94 GHz with BWR of 31.33:1.

Individually frequency and amplitude tunable metamaterial absorber with sensing functions based on strontium titanate and graphene

A terahertz metamaterial absorber with sensing function based on strontium titanate (STO) and graphene is designed. The optical characteristics of the designed structures are simulated and numerically calculated by the finite difference time domain (FDTD) and coupled mode theory (CMT) method. The results show that the temperature of STO is 300 K and Fermi level of graphene is 1.0 eV, the absorptance achieves 99.8 % and 92.7 % at 0.36 THz and 2.18 THz, respectively. When the temperature of the STO is set from 250 K to 400 K, the center frequency is moved from 0.32 THz and 1.96 THz to 0.43 THz and 2.54 THz. When the temperature is stable at 300 K, the dual narrow band absorption can be converted to single narrow band absorption by tuning the Fermi level from 1.0 eV to 0 eV. The physical mechanism of the dual narrow band absorptions and active tuning is analyzed by electric field distribution and impedance matching theory. The effect of polarization direction and incident angle on the absorber performance is also investigated. In addition, we also investigated the sensing characteristics of the absorber when the Fermi level of graphene is 0 eV, and the sensitivity and figure of meritis of the structure for detecting different refractive indices is 50 GHz/RIU and 0.33/RIU. The proposed structure provides new ideas for future multifunctional terahertz device design.

Quantitative temperature visualization with single harmonic-based magnetic particle imaging

Magnetic Particle Imaging (MPI) is a very promising imaging modality for disease theranostics. It allows quantitative visualization of magnetic nanoparticles (MNPs) by utilizing their non-linear response to an alternating magnetic field. In this study, we propose a new approach for the additional quantitative imaging of temperature with single harmonic-based narrowband MPI via measuring the phase lag of the 3rd harmonic of MNP response. Temperature dependent phase lag is measured and calibrated with both magnetic particle spectroscopy and MPI systems. Afterwards, phantom experiments are performed for quantitative temperature imaging with MPI. Experimental results demonstrate the feasibility of the proposed approach for temperature imaging with a systematic deviation of 0.9 °C and a standard deviation of 0.13 °C. We believe that the proposed approach will provide a novel tool for non-invasive and quantitative temperature imaging with applications to biomedicine.

Single harmonic-based narrowband magnetic particle imaging

Magnetic particle imaging (MPI) quantitatively visualizes in vivo superparamagnetic iron oxide nanoparticles (SPIONs), which has shown great promises in biomedicine. In this paper, we propose a single harmonic-based narrowband MPI approach via measuring a single harmonic—3f 0 harmonic—of the SPIONs induced in an excitation magnetic field with frequency f 0 = 5 kHz. The narrowband MPI scanner is built to scan the field-free-point, generated by a pair of permanent magnets, through an imaging field-of-view, and to measure the magnetic response of the SPIONs by a narrowband receive system. The narrowband MPI approach dramatically reduces the design efforts in the transmit system and noise matching in the receive system. Phantom experiments are performed with the custom-built narrowband MPI scanner to evaluate the spatial resolution and limit of detection (LOD). Experimental results indicate that the proposed single harmonic-based narrowband MPI approach allows a spatial resolution of 0.5 mm and an LOD of 27 μg (Fe) ml−1 (254 ng Fe weight) using Perimag® SPIONs, which can significantly be improved by using optimized SPIONs and by improving the detection circuitry. We believe that the proposed narrowband MPI approach minimizes the MPI hardware efforts but still allows for good performance in terms of spatial resolution and LOD.

Joint User Scheduling and Resource Allocation in Distributed MIMO Systems with Multi-Carriers

Compared with the traditional collocated multi-input multi-output system (C-MIMO), distributed MIMO (D-MIMO) systems have the advantage of higher throughput and coverage, making them strong candidates for next-generation communication architecture. As a practical implementation of a D-MIMO cooperative network, the multi-TRP (multiple transmission/reception point) system becomes a hotspot in the research of advanced 5G. Different from previous research on a cooperative D-MIMO network with single narrowband transmission, this paper proposes a joint optimization scheme to address the user scheduling problem along with carrier allocation to maximize the total spectral efficiency (SE) in the downlink of coherent multi-TRP systems with multi-carriers. We establish a joint optimization model of user scheduling and resource allocation to maximize the system spectral efficiency under the constraints of power consumption and the backhaul capacity limits at each RAU (remote antenna unit), as well as the QoS (quality of service) requirement at each user. Since the optimization model is both non-covex and non-smooth, a joint optimization algorithm is proposed to solve this non-convex combinatorial optimization problem. We first smooth the mixed-integer problem by employing penalty functions, and after decoupling the coupled variables by introducing auxiliary variables, the original problem is transformed into a series of tractable convex optimization problems by using successive convex approximation (SCA). Numerical results demonstrate that the proposed joint optimization algorithm for user scheduling and resource allocation can reliably converge and achieve a higher system SE than the general multi-TRP system without carrier allocation, and this advantage is more pronounced under a higher backhaul capacity or higher power consumption constraints.

Dual-band giant spin-selective full-dimensional manipulation of graphene-based chiral meta-mirrors for terahertz waves.

The ability to simultaneous achieve circular dichroism (CD) and wavefront manipulation is extremely important for many practical applications, especially for detecting and imaging. However, many of the previously observed weakness chiral features are limited to nanostructures with complex three-dimensional building configurations, single narrow-band response, and no active tunability, which are getting farther and away from the goal of integration and miniaturization. Here, a platform of bi-layer all-graphene meta-mirrors with spin-selective full-dimensional manipulation is proposed to simultaneously achieve giant dual-band CD response and wavefront shaping, based on the principle of the hybridization coupling. By simply controlling the structural variables of the meta-mirror and the characteristic parameters of graphene, that is, the combination of passive and active regulation, the proposed design can selectively manipulate the polarization, amplitude, phase, and working frequency of the incident circularly polarized wave near-independently. As a proof of concept, we used the meta-mirror to design two metasurface arrays with spin-selective properties for dynamic terahertz (THz) wavefront shaping and near-field digital imaging, both of which show a high-performance dynamic tunability. This method could provide additional options for the next-generation intelligent THz communication systems.

Broadband high-efficiency polymerized liquid crystal metasurfaces with spin-multiplexed functionalities in the visible

Traditional optical components are usually designed for a single functionality and narrow operation band, leading to the limited practical applications. To date, it is still quite challenging to efficiently achieve multifunctional performances within broadband operating bandwidth via a single planar optical element. Here, a broadband high-efficiency polarization-multiplexing method based on a geometric phase polymerized liquid crystal metasurface is proposed to yield the polarization-switchable functionalities in the visible. As proofs of the concept, two broadband high-efficiency polymerized liquid crystal metalenses are designed to obtain the spin-controlled behavior from diffraction-limited focusing to sub-diffraction focusing or focusing vortex beams. The experimental results within a broadband range indicate the stable and excellent optical performance of the planar liquid crystal metalenses. In addition, low-cost polymerized liquid crystal metasurfaces possess unique superiority in large-scale patterning due to the straightforward processing technique rather than the point-by-point nanopatterning method with high cost and low throughput. The high-efficiency liquid crystal metasurfaces also have unrivalled advantages benefiting from the characteristic with low waveguide absorption. The proposed strategy paves the way toward multifunctional and high-integrity optical systems, showing great potential in mobile devices, optical imaging, robotics, chiral materials, and optical interconnections.

An MXene based flexible patch antenna for pressure and level sensing applications

Flexible and wearable communication devices together with the sensing functionality are of great importance for next-generation flexible electronics towards the applications in IoT etc. However, metals still remain to be the dominant class of materials that satisfy the requirement for antenna fabrication. But metals do not exhibit excellent sensing capabilities when compared to functional nanomaterials. Hence there is a need to develop a functional nanomaterial-based antenna that serves the dual purpose of sensing and communication. This work demonstrates a flexible and low-cost patch antenna developed with a novel material MXene (Ti3C2Tx) coated cellulose paper on polyimide. The MXene based antenna is designed for a single narrowband frequency resonating at 5.8 GHz, which is having a fractional bandwidth of 1.72 % along with the gain of −6.14 dBi. To illustrate the real-time sensing performance of the MXene based antenna, the prototype is tested for pressure and level sensing under various temperature and stability conditions. The measured sensitivity for the pressure sensing is approximately 247 MHz/kPa. Successful demonstration of low-cost, scalable MXene based antenna sensor opens up new avenues of research in 2D materials-based antenna for potential applications in healthcare, security, etc.