Search Results (379)

Metamaterial absorbers in terahertz (THz) based bands have garnered significant attention for their potential applications in military stealth, terahertz imaging, and other fields. Nevertheless, the limited bandwidth, low absorption rate, and heavy weight greatly reduce the further development and wide application of terahertz absorbers. To solve these problems, we propose a polystyrene (PS)-based ultra-broadband metamaterial absorber integrated with a polyethylene terephthalate (PET) double-sided adhesive layer and a patterned indium tin oxide (ITO) film through the simulation method, which operates in the THz band. The electromagnetic wave absorption properties and underlying physical absorption mechanisms of the proposed metamaterial absorbers are comprehensively modeled and rigorously numerically simulated. The research demonstrates the metamaterial absorber can achieve absorption performance of over 90% for fully polarized incident waves in the ultra-wideband range of 1.2–10 THz, especially achieving perfect absorption characteristics of over 99.9% near 1.8–1.9 THz and 5.8–6.2 THz. The proposed absorber has a lightweight physical property of 0.7 kg/m² and polarization-insensitive characteristic, and it achieves a broad-angle that allows a range of incidence angles up to 60°. The simulation research results of this article provide theoretical support for the design of terahertz absorbers with ultra-wideband absorption characteristics. Full article

Ubiquitous digital array radar (UDAR) extends the integration time of moving targets by deploying a wide transmitting beam and multiple narrow receiving beams to cover the entire observed airspace. By exchanging time for energy, it effectively improves the detection ability for weak targets. Nevertheless, target motion introduces severe across-range unit (ARU), across-Doppler unit (ADU), and across-beam unit (ABU) effects, dispersing target energy across the range–Doppler-beam space. This paper proposes a beam domain angle rotation compensation and keystone-matched filtering (BARC-KTMF) algorithm to address the “three-crossing” challenge. This algorithm first corrects ABU by rotating beam–domain coordinates to align scattered energy into the final beam unit, reshaping the signal distribution pattern. Then, the KTMF method is utilized to focus target energy in the time-frequency domain. Furthermore, a special spatial windowing technique is developed to improve computational efficiency through parallel block processing. Simulation results show that the proposed approach achieves an excellent signal-to-noise ratio (SNR) gain over the typical single-beam and multi-beam long-time coherent integration (LTCI) methods under low SNR conditions. Additionally, the presented algorithm also has the capability of coarse estimation for the target incident angle. This work extends the LTCI technique to the beam domain, offering a robust framework for high-speed weak target detection. Full article

The proliferation of electromagnetic wave applications has accentuated electromagnetic pollution concerns, highlighting the critical importance of electromagnetic wave absorbers (EMA). This study proposes innovative I-Wrapped Package Lattice electromagnetic wave absorbers (IWP–EMA) based on the triply periodic minimal surface (TPMS) lattice structure. Through a rational design of porous gradient structures, broadband wave absorption was achieved while maintaining lightweight characteristics and mechanical robustness. The optimized three-dimensional configuration features a 20 mm thick gradient structure with a progressive relative density transition from 10% to 30%. Under normal incidence conditions, this gradient IWP–EMA basically achieves broadband absorption with a reflection loss below −10 dB across the 2–40 GHz frequency band, with absorption peaks below −19 dB, demonstrating good impedance-matching characteristics. Additionally, due to the complex interactions of electromagnetic waves within the structure, the proposed IWP–EMA achieves a wide-angle absorption range of 70° under Transverse Electric (TE) polarization and 70° under Transverse Magnetic (TM) polarization. The synergistic integration of the TPMS design and additive manufacturing technology employed in this study significantly expands the design space and application potential of electromagnetic absorption structures. Full article

Multibeam echosounder systems (MBESs) are widely used in unmanned surface vehicle swarms (USVs) to perform various marine bathymetry surveys because of their excellent performance. To address the challenges of systematic error superposition and edge beam error propagation in multibeam bathymetry surveying, this study proposes a novel error adjustment method integrating crossover error density clustering and beam incident angle (BIA) compensation. Firstly, a bathymetry error detection model was developed based on adaptive Density-Based Spatial Clustering of Applications with Noise (DBSCAN). By optimizing the neighborhood radius and minimum sample threshold through analyzing sliding-window curvature, the method achieved the automatic identification of outliers, reducing crossover discrepancies from ±150 m to ±50 m in the deep sea at a depth of approximately 5000 m. Secondly, an asymmetric quadratic surface correction model was established by incorporating the BIA as a key parameter. A dynamic weight matrix ω = 1/(1 + 0.5θ²) was introduced to suppress edge beam errors, combined with Tikhonov regularization to resolve ill-posed matrix issues. Experimental validation in the Western Pacific demonstrated that the RMSE of crossover points decreased by about 30.4% and the MAE was reduced by 57.3%. The proposed method effectively corrects residual systematic errors while maintaining topographic authenticity, providing a reference for improving the quality of multibeam bathymetric data obtained via USVs and enhancing measurement efficiency. Full article

This paper proposes a broadband and high-efficiency anomalous reflection device based on a dielectric catenary metasurface, addressing the bottleneck problems of low efficiency and narrow bandwidth in traditional discrete metasurfaces. By designing a silicon-based equal-strength catenary structure, the efficient control of circularly polarized light beams within a wide angular range in the infrared band has been achieved. Simulation results show that the designed metasurface exhibits excellent beam steering performance when the deflection angle reaches 65°. Furthermore, to characterize the diffraction efficiency of the metasurface within a large angular range, the results indicate that under oblique incidence (0–60°), the diffraction efficiency of the ±1st order exceeds 80%, and the undesired higher-order diffractions are significantly suppressed. This ultrahigh working efficiency is attributed to the nearly perfect polarization conversion and continuous phase profile of the dielectric catenary structure. By combining catenary optics with the low-loss properties of the dielectric material, this design provides a new solution for the design of efficient, broadband, and wide-angle planar optical devices. Full article

Galactic cosmic rays (GCRs), composed of protons and atomic nuclei, are accelerated in sources such as supernova remnants and pulsar wind nebulae, reaching energies up to the PeV range. As they propagate through the interstellar medium, their interactions with dense regions like molecular clouds produce secondary particles, including gamma-rays and neutrinos. In this study, we use the Geant4 Monte Carlo toolkit to simulate secondary particle production from GCR interactions within the Perseus molecular cloud, a nearby star-forming region. Our model incorporates realistic cloud composition, a wide range of incidence angles, and both hadronic and electromagnetic processes across a broad energy spectrum. The results highlight molecular clouds as significant sites of multi-messenger emissions and contribute to understanding the propagation of GCRs and the origin of diffuse gamma-ray and neutrino backgrounds in the Galaxy. Full article

Electromagnetic absorbers combining ultrathin profiles with robust absorptivity across wide incidence angles are essential for applications such as stealth applications, wireless communications, and quantum computing. Traditional designs, including Salisbury screens, typically require thicknesses of at least a quarter-wavelength ($\lambda /4$), restricting their use in compact systems. While metamaterial absorbers (MMAs) offer reduced thicknesses, their absorptivity generally decreases under oblique incidence conditions. Here, we introduce an adjoint optimization-based inverse design method that merges the ultrathin advantage of MMAs with the angle-insensitive characteristics of Salisbury screens. By leveraging the computational efficiency of the adjoint method, we systematically optimize absorber structures as thin as $\lambda /20$. The optimized structures achieve absorption exceeding 90% at the target frequency (7.5 GHz) and demonstrate robust performance under oblique incidence, maintaining over 90% absorption up to 50°, approximately 80% at 60°, and around 70% at 70°. Comparative analysis against particle swarm optimization further highlights the superior efficiency of the adjoint method, reducing the computational effort by approximately 98%. This inverse design framework thus provides substantial improvements in both the performance and computational cost, offering a promising solution for advanced electromagnetic absorber design. Full article

We theoretically investigated two types of nonlinear optical effects of photonic band edges (PBEs) in photonic crystals containing hyperbolic metamaterial (HMM) based on the intensity-dependent phase-variation compensation, where the HMM is composed of alternating the noble metal Ag with large-nonlinear-coefficient and dielectric material. Considering nonlinear conditions, the local field strength variation in nonlinear materials with the increase in the incident angle will lead to the movement of the PBE, resulting in two anomalous optical nonlinear effects. When the PBE is angle-independent under the linear condition, the PCs have angle-sensitive optical bistability and the critical threshold intensity always increases. However, if the PBE is designed to have angle dependence under linear conditions, the optical bistability in the PC can be angle-independent, and the critical threshold intensity is angle-independent over a wide range. This research provides important reference values for manufacturing direction-selectable devices that utilize different kinds of nonlinear optical effects. Full article

With the increasing energy consumption of buildings, transparent heat mirror films have been widely used in building windows to enhance energy efficiency owing to their excellent spectrally selective properties. Previous studies have typically focused on spectral selectivity in the visible and near-infrared bands, as well as single-parameter optimization of film materials or thickness, without fully exploring the performance potential of the films. To address the limitations of traditional design methods, this paper proposes a deep reinforcement learning-based approach that employs an adaptive strategy network to optimize the thin-film material system and layer thickness parameters simultaneously. Through inverse design, a Ta₂O₅/Ag/Ta₂O₅/Ag/Ta₂O₅ (42 nm/22 nm/79 nm/22 nm/40 nm) thin-film structure with broadband spectral selectivity was obtained. The film exhibited an average reflectance of 75.5% in the ultraviolet band and 93.2% in the near-infrared band while maintaining an average visible transmittance of 87.0% and a mid- to far-infrared emissivity as low as 1.7%. Additionally, the film maintained excellent optical performance over a wide range of incident angles, making it suitable for use in complex lighting environments. Building energy simulations indicate that the film achieves a maximum energy-saving rate of 17.93% under the hot climatic conditions of Changsha and 16.81% in Guangzhou, demonstrating that the designed transparent heat mirror film provides a viable approach to reducing building energy consumption and holds significant potential for practical applications. Full article

SPR biosensors operate on the principle of evanescent wave propagation at metal–dielectric interfaces in total internal reflection conditions, with consequent photonic energy attenuation. This plasmonic excitation occurs in specific conditions of incident light wavelength, angle, and the dielectric refractive index. This principle has been the basis for SPR-based biosensor setups wherein mass/concentration-induced changes in the refractive indices of dielectric media reflect as plasmonic resonance condition changes quantitatively reported as arbitrary response units. SPR biosensors operating on this conceptual framework have been designed to study biomolecular interactions with real-time readout and in label-free setups, providing key kinetic characterization that has been valuable in various applications. SPR biosensors often feature antibodies as target affinity probes. Notably, the operational challenges encountered with antibodies have led to the development of aptamers—oligonucleotide biomolecules rationally designed to adopt tertiary structures, enabling high affinity and specific binding to a wide range of targets. Aptamers have been extensively adopted in SPR biosensor setups with promising clinical and industrial prospects. In this paper, we explore the growing literature on SPR setups featuring aptamers, specifically providing expert commentary on the current state and future implications of these SPR aptasensors for drug discovery as well as disease diagnosis and monitoring. Full article

This paper presents a rectifying metasurface (RMS) that enables wide-angle, polarization-insensitive wireless energy harvesting in the Wi-Fi frequency range. The RMS consists of a metasurface integrated with rectifying diodes, a low-pass filter (LPF), and a resistive load. In the structural design, the RMS incorporates four Schottky diodes placed on the bottom structure and connected to the top structure through four metallized vias. This configuration facilitates impedance matching between the metasurface and the diodes, omitting the need for conventional rectifier circuits or external matching networks and removing the impact of soldering variations. A 3 × 3 RMS prototype was manufactured and subjected to experimental validation. The measurements confirm that the RMS achieves a peak RF-to-DC conversion efficiency of 68.3% at 5.8 GHz with a 12.5 dBm input power, while maintaining stable performance across a wide range of incident angles and polarization states. Full article

Conventional metalenses struggle with chromatic aberration and narrow field of view (FOV), making it challenging to meet the dispersion requirements for large apertures and compensate off-axis aberrations for wide FOV. Here, we demonstrate a hybrid metalens module consisting of five refractive plastic lenses and a polarization-insensitive metalens to achieve broadband achromatic imaging within 400–700 nm and a wide FOV up to 100°. The system exhibits negligible variation in focal length (~1.2%) across the visible range (460–656 nm) and consistently achieves modulation transfer function (MTF) values > 0.2 at 167 lp/mm across all wavelengths and incident angles. We also demonstrate integrated lens modules that capture high-quality images from distances ranging between 0.5 and 4 m without post-processing, showcasing its potential for compact, wide-angle optical systems. Full article

A novel single-layer multi-coupling 3D frequency-selective surface featuring high selectivity and a 3D dual-band frequency-selective surface (3D-DBFSS) is presented in this paper. By incorporating three different coupling gaps within each unit cell, the design achieves two distinct passbands with wide bandwidths and steep transition edges. For the first passband, the −3 dB bandwidth ranges from the lower cutoff frequency of 9.9 GHz to the upper cutoff frequency of 15.2 GHz, yielding a bandwidth (BWL3dB) of 5.3 GHz. For the second passband, the −3 dB bandwidth extends from 22 GHz to 26 GHz, providing a bandwidth (BWU3dB) of 4 GHz. The structure exhibits eight transmission poles and four transmission zeros within a single layer, enhancing its selectivity. The simulation results indicate that the dual passbands are centered at 12 GHz and 24 GHz, respectively, with bandwidths sufficient for practical applications. The proposed frequency-selective surface demonstrates a low insertion loss of just 0.8 dB, which is significantly lower compared to most reported dual-band FSS designs. Furthermore, the thickness of the 3D-DBFSS is only one-third of the wavelength in free space, making it considerably thinner than other 3D-FSS structures operating in the same frequency range. The proposed design also ensures stable performance over a wide range of incident angles, which is crucial for practical deployment. Additionally, the overall size of the unit cell of the frequency-selective surface is 4 × 4 × 10.8 m³. The structure is easy to fabricate, which contributes to its potential for cost-effective mass production. Overall, the 3D-DBFSS offers high frequency selectivity, effective bandpass performance, and strong suppression in the stopband region. Full article

Recent advancements in photonics have intensified the performance requirements for optical systems and present significant challenges for optical coating technologies. Conventional interference coating systems often prove to be insufficient, especially in applications requiring large angles of light incidence or a wide wavelength range. Nanostructures, which consist of an air material mixture, offer promising alternatives. In this work, silica nanostructures are manufactured by the AR-plas2 method, in which first an organic layer is evaporated onto a substrate. This organic layer forms self-organizing nanostructures by a plasma etching step, which are subsequently coated with silica. Finally, the organic residues are removed by additional plasma etching and heat treatment steps, which results in hollow silica structures. The work examines the optical and functional properties of these structures designed for 355 nm to demonstrate their use as anti-reflective coatings for advanced optical systems. Full article

Highly (0002)-oriented Al_1−xSc_xN thin films with different Sc doping concentrations (x = 0, 0.2, 0.25, 0.3, and 0.43) were prepared via a magnetron sputtering system. The effects of Sc doping on the crystal structure and electrical property of the as-prepared thin films were investigated experimentally. The results of synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) demonstrated that the Sc³⁺ substitution for Al³⁺ induced asymmetric lattice distortion: the a-axis exhibited monotonic expansion (reaching 3.46 Å at x = 0.43) due to the larger atomic radius of Sc (~0.87 Å), while the c-axis attained a maximum value of 5.14 Å at x = 0.2 and subsequently contracted as the bond angle reduction became dominant. The dielectric constant increased to 34.67 (225% enhancement) at x = 0.43, attributed to the enhanced polarization of Sc-N bonds and interfacial charge accumulation effects. Simultaneously, the dielectric loss increased from 0.15% (x = 0) to 6.7% (x = 0.43). Leakage current studies revealed that high Sc doping (x = 0.43) elevated the leakage current density to 10⁻⁶ A/cm² under an electric field of 0.2 MV/cm, accompanied by a transition from Ohmic conduction to space-charge-limited current (SCLC) at a low electric field strength (<0.072 MV/cm). Full article