Search Results (135)

Tunneling modes in all-dielectric one-dimensional photonic crystals can be utilized for multi-channel filtering. However, these tunneling modes generally blue shift upon increasing the incident angle. When hyperbolic metamaterials are introduced into one-dimensional photonic crystals, the competition between the propagation phase shifts in the dielectric materials and hyperbolic metamaterials can result in different angle dependencies, including blue shift, abnormal zero shift, and abnormal red shift. When the reduction in the propagation phase in the dielectric layer exceeds the increment in the propagation phase in the hyperbolic metamaterial, the tunneling modes are blue-shifted; conversely, when the phase increment in the hyperbolic metamaterial exceeds the phase reduction in the dielectric layer, the tunneling modes are abnormally red-shifted. When the phase changes in the two materials are the same, the tunneling modes are angle independent. In this study, we investigated the multiple filtering effects of one-dimensional photonic structures composed of hyperbolic metamaterials. These composed structures exhibited multiple tunneling modes based on one-, two-, or three-angle dependencies and can be applied in novel optical devices with different angle-dependence requirements. Full article

Snow water equivalent (SWE) can be estimated using Differential SAR Interferometry (DInSAR), which captures changes in snow depth and density between two SAR acquisitions. However, challenges arise due to SAR signal penetration into the snowpack and the intrinsic limitations of DInSAR measurements. This study addresses these issues and explores the use of multi-band SAR data to derive SWE maps in alpine regions characterized by steep terrain, small spatial extent, and a potentially heterogeneous snowpack. We first conducted a performance analysis to assess SWE estimation precision and the maximum unambiguous SWE variation, considering incidence angle, wavelength, and coherence. Based on these results, we selected C-band Sentinel-1 and L-band SAOCOM data acquired over alpine areas and applied tailored DInSAR processing. Atmospheric artifacts were corrected using zenith total delay maps from the GACOS service. Additionally, sensitivity maps were generated for each interferometric pair to identify pixels suitable for reliable SWE estimation. A comparative analysis of the C- and L-band results revealed several critical issues, including significant atmospheric artifacts, phase decorrelation, and phase unwrapping errors, which impact SWE retrieval accuracy. A comparison between our Sentinel-1-based SWE estimations and independent measurements over an instrumented site shows results fairly in line with previous works exploiting C-band data, with an RSME in the order of a few tens of mm. Full article

To obtain a flat top shaped passband in a conventional thin-film-based optical bandpass filter (OBF), it needs a large number of constitutional layers of thin films, which makes the film deposition systems more complicated and accumulates errors in film growth. A flat top and polarization-independent optical bandpass filter structure is proposed based on experimentally verified polarization independency in the form of a prism-pair coupled planar optical waveguide (POW). The POW is composed of two waveguide stacks, which consists of nine planar thin-film layers. Theoretical simulations show that the flat band top spans about 5 nm with transmittance over 97.8%. The passband is designed to be centered at 632.8 nm, the He-Ne laser wavelength, and the FWHM (full width at half maximum) bandwidth is about 35 nm. Within 0.5° tuning for the incident angle of the light, the passband could be shifted within 50 nm, while its transmittance fluctuates only less than 1% and the passband shape distorts only slightly. This type of OBF is potentially applicable in various fields of optical and laser spectroscopies. Full article

In this work, we propose and analyze a thermally tunable metasurface based on indium antimonide (InSb), designed to operate in the terahertz (THz) frequency range. The metasurface exhibits dual functionalities: single-band perfect absorption and efficient polarization conversion, enabled by the temperature-dependent permittivity of InSb. At approximately 280 K, InSb transitions into a metallic state, enabling the metasurface to achieve near-unity absorptance (100%) at 0.408 THz under normal incidence, independent of polarization. Conversely, when InSb behaves as a dielectric at 200 K, the metasurface operates as an efficient polarization converter. By exploiting structural anisotropy, it achieves a polarization conversion ratio exceeding 85% over the frequency range from 0.56 to 0.93 THz, while maintaining stable performance for incident angles up to 45°. Parametric analyses show that the resonance frequency and absorption intensity can be effectively tuned by varying the InSb square size and the silica (SiO₂) layer thickness, achieving maximum absorptance at a SiO₂ thickness of 16 μm. The proposed tunable metasurface offers significant potential for applications in THz sensing, imaging, filtering, and wavefront engineering. 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

The design and operating regime of centrifugal fans operating with contaminated flows must consider the influence of different geometric parameters and flow dynamics design variables on fan wear. The influence of fan rotation speed and blade angle of attack on the erosion wear they may experience when moving fluids contaminated with solid particles is especially relevant. A method is proposed for performing experimental tests that emulate centrifugal fans using a slurry bucket installation, at tangential velocities of 2, 4, and 6 m/s and fluid incidence angles of 16, 22, and 28 degrees. An equation for cumulative wear is found, in which the independent variables incidence angle and linear velocity have a linear and quadratic influence, respectively. It can be specified that when the fan operates at revolutions between 814 and 815 rpm, for a tangential speed of 2 m/s and a flow rate of 20.16 m³/h, an accumulated wear of 1.3124 mg/g is recorded, caused by the impact of solid particles transported by the flow that could impact the surface of the blade when the angle is 22°24′. Full article

This study investigates wave-power extraction by an oscillating water column (OWC) device over a porous-to-rigid step bottom using linearized water-wave theory. The interaction between water waves and the OWC device is analyzed by solving the governing boundary-value problem with the eigenfunction expansion method (EEM) and the boundary element method (BEM). The study examines the effects of key parameters, including the porous effect parameter of the bottom, OWC chamber width, and barrier height, on the device’s efficiency. The results indicate that the porous effect parameter significantly influences OWC performance, affecting resonance characteristics and efficiency oscillations. A wider OWC chamber enhances oscillatory efficiency patterns, leading to multiple peaks of full and zero efficiency. The efficiency shifts towards lower wavenumbers with increasing step depth and barrier height but becomes independent of these parameters at higher wavenumbers. Additionally, incident angle plays a crucial role, decreasing efficiency at lower angles and exhibiting oscillatory behavior at higher angles. Furthermore, susceptance and conductance follow an oscillatory pattern concerning the gap between the porous bottom and the OWC chamber as well as chamber width. The porous effect parameter strongly modulates these oscillations. The findings provide new insights for enhancing OWC efficiency with complex bottom topography. Full article

Electromagnetically induced transparency based on bound states in the continuum (EIT-BIC) has emerged as a significant research focus in photonics due to its exceptionally high quality factor (Q-factor). This study investigates a periodic dielectric metasurface composed of silicon bar–square ring resonators, with a comparative analysis of both monolayer and bilayer configurations. Through systematic examination of transmission spectra, electric field distributions, and Q-factors, we have identified the existence of EIT-BIC and quasi-BIC phenomena in these structures. The experimental results demonstrate distinct characteristics between monolayer and bilayer systems. In the monolayer configuration, a single BIC is observed in the low-frequency region, with its quasi-BIC state generating an EIT window. In contrast, the bilayer structure exhibits dual BICs and dual EIT phenomena in the same spectral range, demonstrating enhanced spectral modulation capabilities. Notably, in the high-frequency region, both configurations maintain a single BIC, with the number remaining independent of structural layer count. The number and spectral positions of BICs can be effectively modulated through variations in incident angle and structural symmetry. In particular, the bilayer configuration demonstrates superior modulation characteristics under oblique incidence conditions, where the quasi-BIC linewidth broadens with increasing incident angle, forming a broader high-Q transparency window. This comparative study between monolayer and bilayer systems not only elucidates the influence of structural layers on BIC characteristics but also provides new insights for flexible spectral control. These findings hold significant implications for artificial linear modulation and play a crucial role in the design of future ultra-high-sensitivity sensors, particularly in optimizing performance through structural layer engineering. Full article

Objectives: The aim of this study was to investigate the incidence of vertebral refractures following percutaneous kyphoplasty (PKP) and to explore risk factors for augmented vertebral refractures, thereby assisting spinal surgeons in clinical practice. Methods: We analyzed the records of 495 patients with single-segment osteoporotic vertebral compression fractures (OVCFs) who were treated with single-entry PKP at our institution from March 2016 to August 2022. Univariate analysis, binary logistic regression, and ROC curve analysis were performed to determine potential risk factors, independent risk factors, and discrimination ability. Results: A total of 168 patients were included in the study, with a median follow-up duration of 7.00 months. In total, 143 patients did not experience vertebral refracture after surgery, while 25 patients did, including 22 augmented vertebral fractures and 3 adjacent vertebral compression refractures. The correction rate of the Cobb angle (p < 0.001; OR = 1.070) and postoperative anti-osteoporosis treatment (p = 0.002; OR = 0.021) were independently associated with augmented vertebral refracture. The ROC curves showed that these variables demonstrated satisfactory predictive values for augmented vertebral refracture. Conclusions: A high degree of restoration of the Cobb angle was the factor contributing to vertebral refracture after PKP. Conversely, postoperative anti-osteoporosis treatment was observed to be a protective factor against subsequent vertebral refracture. Full article

The automatic extraction of large-scale tie points (TPs) for Synthetic Aperture Radar (SAR) images is crucial for generating SAR Digital Orthophoto Maps (DOMs). This task involves matching SAR images under various conditions, such as different resolutions, incidence angles, and orbital directions, which is highly challenging. To address the feature extraction challenges of different SAR images, we propose a Gamma Modulated Phase Congruency (GMPC) model. This improved phase congruency model is defined by a Gamma Modulation Filter (GMF) and an adaptive noise model. Additionally, to reduce layover interference in SAR images, we introduce a GMPC-Harris feature point extraction method with layover perception. We also propose a matching method based on the SAR Modality Independent Neighborhood Fusion (SAR-MINF) descriptor, which fuses feature information from different neighborhoods. Furthermore, we present a graph-based overlap extraction algorithm and establish an automated workflow for large-scale TP extraction. Experiments show that the proposed SAR-MINF matching method increases the Correct Match Rate (CMR) by an average of 31.2% and the matching accuracy by an average of 57.8% compared with other prevalent SAR image matching algorithms. The proposed TP extraction algorithm can extract full-degree TPs with an accuracy of less than 0.5 pixels for more than 98% of 2-degree TPs and over 95% of multidegree TPs, meeting the requirements of DOM production. Full article

Currently, perfect absorption properties of metamaterials have attracted widespread interest in the area of solar energy. Ultra-broadband absorption, incidence angle insensitivity, and polarization independence are key performance indicators in the design of the absorbers. In this work, we proposed a metamaterial absorber based on the absorption mechanism with multiple resonances, including propagation surface plasmon resonance (PSPR), localized surface plasmon resonance (LSPR), electric dipole resonance (EDR), and magnetic dipole resonance (MDR). The absorber, consisting of composite nanocylinders and a microcavity, can perform solar energy full-spectrum absorption. The proposed absorber obtained high absorption (>95%) from 272 nm to 2742 nm at normal incidence. The weighted absorption rate of the absorber at air mass 1.5 direct in the wavelength range of 280 nm to 3000 nm exceeds 98.5%. The ultra-broadband perfect absorption can be ascribed to the interaction of those resonances. The photothermal conversion efficiency of the absorber reaches 85.3% at 375 K. By analyzing the influence of the structural parameters on the absorption efficiency, the absorber exhibits excellent fault tolerance. In addition, the designed absorber is insensitive to polarization and variation in ambient refractive index and has an absorption rate of more than 80% at the incident angle of 50°. Our proposed absorber has great application potential in solar energy collection, photothermal conversion, and other related areas. Full article

We developed and applied a new calibration method to make more accurate measurements with our multi-color ellipsometric mapping tool made from cheap parts. Ellipsometry is an optical technique that measures the relative change in the polarization state of the measurement beam induced by reflection from or transmission through a sample. During conventional ellipsometric measurement, the data collection is relatively slow and measures one spot at a time, so mapping needs a long time compared with our new optical mapping equipment made by an ordinary color LED monitor and a polarization-sensitive camera. The angle of incidence and the incident polarization state is varied point by point, so a special optical calibration method is needed. Three SiO₂ samples with different thicknesses were used for the point-by-point determination of the angle of incidence and rho (ρ) corrections. After the calibration, another SiO₂ sample was measured and analyzed using the calibrated corrections; further, this sample was independently measured using a conventional spectroscopic ellipsometer. The difference between the two measured thickness maps is less than 1 nm. Our optical mapping tool made from cheap parts is faster and covers wider area samples relative to conventional ellipsometers, and these correction enhancements further demonstrate its performance. Full article

This study presents a novel simultaneous double-exposure contact mirror-based method for fabricating holographic multi-notch filters with dual operational central wavelengths. The proposed method leverages coupled wave theory, the geometric relationships of K-vectors, and a reflection-type recording setup, incorporating additional reflecting mirrors to guide the recording beams. To validate the approach, a holographic notch filter was fabricated using photopolymer recording materials, resulting in operational wavelengths of 531.13 nm and 633.01 nm. The measured diffraction efficiencies at these wavelengths were η_s = 52.35% and η_p = 52.45% for 531.13 nm, and η_s = 67.30% and η_p = 67.40% for 633.01 nm. The component’s performance was analyzed using s- and p-polarized spectral transmission intensities at various reconstruction angles, revealing polarization-independent characteristics under normal incidence and polarization-dependent behavior under oblique incidence. The study also explored the relationships between recording parameters, such as incident angle, wavelength, emulsion expansion, and dispersion. The findings demonstrate that the first operational central wavelength is primarily influenced by the recording wavelength, while the second is primarily determined by the incident angle, covering a range from visible light to near-infrared. This method offers significant potential for cost-effective, mass-produced filters in optoelectronic applications. Full article

Background/Objective: Limited data exist regarding the long-term clinical outcomes and related factors after adult spinal deformity (ASD) surgery. This study aims to characterize patients who experienced poor clinical outcomes during long-term follow-up after ASD surgery. Methods: Patients who underwent ASD surgery with ≥5-vertebra fusion including the sacrum and ≥5-year follow-up were included. They were divided into two groups according to the Oswestry Disability Index (ODI) at the last follow-up: group P (poor outcome, ODI > 40) and group NP (non-poor outcome, ODI ≤ 40). Clinical variables, including patient factors, surgical factors, radiographic parameters, and mechanical complications (proximal junctional kyphosis [PJK] and rod fracture), were compared between the groups. Results: A total of 105 patients were evaluated, with a mean follow-up of 100.6 months. The mean age was 66.3 years, and 94 patients (89.5%) were women. There were 52 patients in group P and 53 patients in group NP. Univariate analysis showed that low T-score, postoperative correction relative to age-adjusted pelvic incidence-lumbar lordosis, T1 pelvic angle (TPA) at last follow-up, and PJK development were significant factors for poor clinical outcomes. Multivariate analysis identified PJK as the single independent risk factor (odds ratio [OR] = 3.957 for PJK development relative to no PJK, OR = 21.141 for revision surgery for PJK relative to no PJK). Conclusions: PJK development was the single independent factor affecting poor clinical outcomes in long-term follow-up. Therefore, PJK prevention appears crucial for achieving long-term success after ASD surgery. Full article

In this paper, we generated polarization-independent ring-Airy beams by designing metasurfaces that can realize modulations of both phase and amplitude. In numerical simulation, such metasurfaces are designed by placing subwavelength rectangular slits in Au film uniformly. Two orthogonal types of slits, with orientation angles of 45 and −45 degrees, are used to obtain the binary phase profile in the light transmitted from the metasurface under illumination with either right circular polarization (RCP) or left circular polarization (LCP). This satisfies the phase required for Airy beam generation. Meanwhile, the difference between the phase profile under RCP illumination and that under LCP illumination is right 2π, which can be regarded as the same. This makes the metasurface available to generate Airy beams regardless of incident polarization. We also analyzed the auto-focusing, self-healing, and frequency-response properties of the generated Airy beams with different parameters. This work opens up more opportunities for applications of Airy beams. Full article