Reflection Characteristics Research Articles

Unmanned-Aerial-Vehicle-Based Multispectral Monitoring of Nitrogen Content in Canopy Leaves of Processed Tomatoes

Nitrogen serves as a critical nutrient influencing the yield and quality of processed tomatoes; however, traditional methods for assessing its levels are both labor-intensive and costly. This study aimed to explore an efficient monitoring approach by analyzing the relationship between leaf nitrogen content (LNC) and canopy spectral reflectance characteristics throughout the growth stages of processed tomatoes at the Laolong River Tomato Base in Changji City, Xinjiang. The experimental design incorporated nine treatments, each with three replicates. LNC data were obtained using a dedicated leaf nitrogen content analyzer, while drones were utilized to capture multispectral images for the extraction of vegetation indices. Through Pearson correlation analysis, the optimal spectral variables were identified, and the relationships between LNC and spectral variables were established using models based on backpropagation (BP), multiple linear regression (MLR), and random forests (RFs). The findings revealed that the manually measured LNC data exhibited two peak values, which occurred during the onset of flowering and fruit setting stages, displaying a bimodal pattern. Among the twelve selected vegetation indices, ten demonstrated spectral sensitivity, passing the highly significant 0.01 threshold, with the Normalized Difference Chlorophyll Index (NDCI) showing the highest correlation during the full bloom stage. The combination of the NDCI and RF model achieved a prediction accuracy exceeding 0.8 during the full bloom stage; similarly, models incorporating multiple vegetation indices, such as RF, MLR, and BP, also reached prediction accuracies exceeding 0.8. Consequently, during the seedling establishment and initial flowering stages (vegetation coverage of <60%), the RF model with multiple vegetation indices was suitable for monitoring LNC; during the full bloom stage (vegetation coverage of 60–80%), both the RF model with the NDCI and the MLR model with multiple indices proved effective; and during the fruit setting and maturation stages (vegetation coverage of >80%), the BP model was more appropriate. This research provides a scientific basis for the cultivation management of processed tomatoes and the optimization of nitrogen fertilization within precision agriculture. It advances the application of precision agriculture technologies, contributing to improved agricultural efficiency and resource utilization.

Research on the Weakening Process at the Interface of Bonded-Layer Composite Structures Using Ultrasonic Longitudinal Waves

The interface weakening process of bonded-layer composite structures is calculated, simulated, and experimentally investigated using ultrasonic longitudinal waves. Firstly, the reflection coefficients of echoes are calculated theoretically. Subsequently, a time-domain simulation model of bonded-layer composite structures is established. The propagation law of ultrasonic waves in bonded-layer composite structures is obtained. The relationship between different bonding interface states and the ultrasonic reflection characteristics are investigated through ultrasonic experiments on bonded composite structures. The theoretical calculation, simulation, and experimental results are as follows: when the bonding strength of the bonding layer changes from weak to strong, the amplitude of the first echo gradually decreases, the amplitude of the second echo progressively increases, and the amplitude of the third echo is basically unchanged; when the bonding strength of the upper interface changes from weak to strong, the amplitudes of the first and the second echoes are same as in the previous variation whereas the amplitude of the third echo slightly increases; when the bonding strength of the lower interface changes from weak to strong, the amplitudes of the first and the third echoes remain essentially unchanged, but the amplitude of the second echo progressively increases in the experiment compared with the theoretical calculation and simulation. In addition, the time of the first echo remains broadly unchanged, and the times of the second and the third echoes gradually decrease under all conditions.

Weighted multichannel singular spectrum analysis for diffraction amplitude preservation

Diffractions generated by the wavefield response of small-scale discontinuous geological bodies carry a wealth of information regarding complex geological structures, which can be used for high-resolution imaging. However, the weak amplitudes of diffractions make them vulnerable to strong reflections. Thus, separating diffractions from strong reflections is crucial in the high-resolution imaging of underground structures. The low-rank (LR) characteristics of seismic wavefields enable LR methods to be used for diffraction extraction. However, traditional low-rank algorithms tend to disrupt the dynamic characteristics of diffraction during the separation process, which is detrimental to the subsequent high-precision imaging of diffractions. To address these shortcomings of traditional methods, we propose a weighted multichannel singular spectrum analysis (MSSA) algorithm designed to preserve the dynamic characteristics of diffractions. This algorithm fully considers the distribution characteristics of diffractions and reflections energies within the singular spectrum and redefines the singular values using a weighted approach, ultimately achieving amplitude-preserving separation of diffracted waves. Through a combined qualitative and quantitative analysis of synthetic and field examples, we demonstrate the effectiveness of this method in separating diffractions and suppressing reflections with robustness and high stability. Compared with the traditional MSSA method, the proposed approach can provide better high-precision imaging results for small-scale geological structures.

Reflectance and Thermal Micrometeorological Characteristics of an Urban Green Space in the Mediterranean During July’s 2023 Heatwave

Reflectance and Thermal Micrometeorological Characteristics of an Urban Green Space in the Mediterranean During July’s 2023 Heatwave

Beam steering of Fabry Pérot antenna by using hybrid metasurfaces

This paper presents a new approach for designing a superstrate for the Fabry Pérot antenna, to achieve beam steering over the full azimuthal plane. The superstrate of the proposed antenna consists of a linearly graded metasurface (LgMS) and a constant phase partially reflecting surface (PRS). The hybrid metasurfaces offer gradual changes in the magnitude and phase of the reflection and transmission coefficient characteristics, which causes tilting of the main lobe direction.Further, the mechanical rotation of the superstrate structure in the azimuthal plane causes the main lobe direction to steer in the same plane. The proposed antenna operates from 4.33 GHz to 5.1 GHz with a maximum directivity of about 11 dBi and offers beam steering over complete azimuthal plane for frequencies below 4.8 GHz. The proposed structure can be used as a beam steering antenna for applications like air traffic control, satellite communication, shipboard communication, etc.

First-in-human trial of atrial fibrillation ablation using real time tissue optical assessment to predict pulsed field lesion durability.

Loss of bipolar electrograms immediately after pulsed field ablation (PFA) makes lesion durability assessment challenging. The aim of this trial (NCT06700226) was to evaluate a novel ablation system that can optically predict lesion durability by detecting structural changes in the tissue during ablation. Patients with paroxysmal atrial fibrillation underwent pulmonary vein isolation (PVI) using PFA (AblaView®, MedLumics). Using polarization sensitive optical coherence reflectometry (PS-OCR), reflective characteristics of myocardial tissue and visualization of real-time contrast between healthy tissue and ablated tissue using a drop in tissue birefringence (BiR) was assessed. Wide antral PVI was performed using single point irrigated PFA (unipolar, 1800V, 3 trains, 21sec). Remapping was performed at 3 months. Primary efficacy outcome was the ability of PS-OCR to predict lesion durability at 3-month remapping. Serious adverse events were recorded. Ten patients were included. In total, 38/40 PVs could be isolated with the system. The mean drop of BiR was 17.3±11.5%. Dragging across the ablation lines showed a persistent drop in BiR. During the remap procedures (9/10 patients), 15 PVs (41.7%) were found to be electrically reconnected. The mean loss of BiR during the index ablation for durable lesions was 20.9%, while only 10.1% BiR loss was observed during the index ablation for reconnected areas (p<0.001). None of the points with ≥17% loss of birefringence was found to be reconnected. This first in human study supports the use of real-time drop in tissue BiR for lesion assessment during PFA delivery and its procedural safety.

Investigation of the October effect in very low-frequency (VLF) signals

Abstract. Subionospheric very low-frequency (VLF) radio signals are reflected by free electrons in the ionospheric D-region at about 60–90 km altitude and can propagate over long distances, which makes them useful for monitoring the state of the D-region or perturbations due to solar flares. At the D-region height, the ionosphere is mainly ionized by solar Lyman-α radiation. The reflection characteristics of VLF signals depend on the state and dynamics of the D-region, which is highly influenced by Lyman-α radiation. Although the amplitude of the received terrestrial VLF signal changes as a function of solar zenith angle over the course of the year, the VLF amplitude shows a distinctive sharp decrease around October, which is hence called the “October effect”. This study investigates the occurrence of the October effect and its dependencies on latitude and longitude. We developed a method to detect the occurrence of the October effect in the long-term VLF data and derive key parameters characterizing (start and end date, intensity) the sudden decrease in the signal amplitude. This investigation using a network of VLF stations distributed over low-, middle-, and high-latitude regions shows that the occurrence of the October effect has a clear latitudinal dependency, occurring earlier in high-latitude regions than at midlatitudes. No low-latitude signature is found.

Ultrasonic measurement of axial preload in anchor rods

This paper reports on ultrasonic measurement of the axial preload of anchor rods loaded by a pulling machine. The axial preload of ultrasonic measurement was as high as 90 kN, limited by manual operation and the anchor protection structure. Ultrasonic response characterisation, high accuracy and effective ultrasonic measurement of axial preload in anchor rods are reported here and are fully demonstrated. By bonding lead zirconate titanate (PZT) piezoelectric ceramic sensors and self-designed ultrasonic probes on the anchor rods, A-scan ultrasonic signals were successfully measured and originated from the bottom of the hollow anchor rod. The temporal A-scan signal featured a pure and broad frequency spectrum that peaked at around 16 MHz, but no original frequency signal component of the sensors was found. This phenomenon is attributed to the reflective characteristics of the thread-like structure of the hollow anchor rod, potentially inducing a non-linear ultrasound effect, independent of the test instrumentation and coupling agent. When the loading tension of the calibrated pulling machine is lower than 30 kN, the axial preload of the anchor rods obtained from the ultrasonic measurement has an error as high as ±16%. By comparison, the error is less than ±5% for the tension increasing from 60 kN to 90 kN. The experimental results indicate that the proposed ultrasonic measurement method is a simple, accurate and effective way to obtain the axial preload of anchor rods.

Accurate inversion of chlorophyll content based on PROSPECT-LSROGF-BAS-BP method

Accurate measurement of chlorophyll content in plant leaves is crucial for evaluating plant health. Leaf radiation transfer models are commonly used to estimate chlorophyll content from remote sensing data. However, current methods often show limited accuracy in certain scenarios. This study addresses these challenges by developing a more precise method for chlorophyll content retrieval. First, the PROSPECT model, which does not fully account for optical reflection on leaf surfaces, results in lower spectral simulation accuracy. To overcome this limitation, a surface geometric feature factor (σ) is introduced, leading to the PROSPECT-LSROGF model. This enhanced model incorporates the optical reflection characteristics of the leaf surface, expands the range of light source incident angles, and more accurately describes radiative transfer within the leaf. As a result, the PROSPECT-LSROGF model shows superior spectral simulation accuracy to the traditional PROSPECT and PIOSL models. Next, to improve the retrieval accuracy of traditional BP neural networks for chlorophyll content, the Beetle Antennae Search (BAS) algorithm is used to optimize the weights and thresholds of the BP neural network, forming the BAS-BP model. By combining the PROSPECT-LSROGF model with the BAS-BP network, the PROSPECT-LSROGF-BAS-BP model is developed for accurate chlorophyll content retrieval. The performance of this model is compared with that of the gradient boosting machine retrieval and the PROSPECT-BAS-BP model. Validation is conducted using the LOPEX93, CABO, and ANGERS datasets. The PROSPECT-LSROGF-BAS-BP model achieves root mean square errors (RMSEs) of 4.186, 4.258, and 3.894 g/cm2, with determination coefficients (R2) of 0.876, 0.862, and 0.903, respectively—outperforming the other methods in terms of accuracy. These results demonstrate that the proposed method significantly improves the model’s ability to accurately estimate chlorophyll content from spectral data.

Design and application of novel stripline for IC‐EMC characteristic measurement

AbstractThe International Electrotechnical Commission (IEC) has introduced the IEC 61967‐8 stripline measurement method for the measurement of radiated emissions in integrated circuits (ICs). This method stipulates that the stripline's voltage standing wave ratio (VSWR) must be less than 1.25 within the frequency range of 150 kHz to 3 GHz. The established IEC 61967‐8 stripline measurement method can accurately identify the location of EMI in an IC and hence mitigation measure can be effectively implemented. In this work, the IC stripline design is adapted for ICs with various functions and applications with the aid of Ansys HFSS 3D full‐wave simulations and actual measurements to study the impedance and reflection characteristics of IC striplines on test boards. A novel IC stripline structure design process is proposed to enhance the VSWR performance of IC striplines. Subsequently, a novel IC stripline has been fabricated and tested using the IEC 61967‐8 stripline measurement method. The designed novel IC stripline demonstrated compliance with IEC 61987‐8 specification and the measurement results showed consistency with the simulation results. The works can benefit the promotion of high frequency circuit design and the development of testing process and in turn, enabled the improvement of the reliability and performance of the designed products.

Seismic response characteristics of deep carbonate reservoirs with complex structures in the southwestern Tarim Basin

Abstract Seismic data in the Yubei region has a relatively low signal-to-noise ratio, with multiple interbed multiples developed in the Ordovician strata, significantly affecting the accurate imaging of complex structures and reservoirs, leading to considerable uncertainty in structural interpretation and reservoir prediction. This paper first determines the styles of complex structural belts influenced by interbed multiples through wave equation forward modeling. The parallel-layered reflection at the top of complex structures is due to the alteration of effective strata reflection caused by strong interbed multiples at the top. Second, integrating data from drilling, logging, and geological aspects in the region, seismic wavefield characteristic forward modeling analyses for different types of reservoir are conducted. The results show that factors such as the scale and spatial development position of fractured-vuggy reservoirs have significant impacts on seismic reflection characteristics, strong reflective interfaces may mask the reflection characteristics of the top reservoir, the development of fractured-vuggy reservoirs at different positions can weaken or enhance the reflection of strata interfaces; locally intensive development of fractures in the Ordovician manifests as weak bead anomalies, while large-scale fracture reservoirs exhibit chaotic reflections, and karst caves are characterized by distinct moderately strong bead or tabular amplitude anomalies. By comparing with actual seismic data, the correctness of the complex structural interpretation model is effectively verified, and seismic wavefield characteristics of various types of Ordovician reservoir are summarized, providing a certain basis for understanding the interpretation of complex structures and the reflection characteristics of fractured-vuggy reservoirs in the region.

Numerical Simulation of Hydrodynamic Performance of an Offshore Oscillating Water Column Wave Energy Converter Device

Wave energy, as a renewable energy source, plays a significant role in sustainable energy development. This study focuses on a dual-chamber offshore oscillating water column (OWC) wave energy device and performs numerical simulations to analyze the influence of chamber geometry on hydrodynamic characteristics and wave energy conversion efficiency. Unlike existing studies primarily focused on single-chamber configurations, the hydrodynamic characteristics of dual-chamber OWCs are relatively underexplored, especially regarding the impact of critical design parameters on performance. In this study, STAR-CCM+ V2302 software (Version 2410, Siemens Digital Industrial Software, Plano, TX, USA) is utilized to systematically evaluate the effects of key design parameters (including turbine configuration, mid-wall draught depth, and wall angles) on the hydrodynamic performance, wave energy capture efficiency, and wave reflection and loading characteristics of the device. The findings aim to provide a reference framework for the optimal design of dual-chamber OWC systems. The results show that the dual-chamber, dual-turbine (2C2T) configuration offers a 31.32% improvement in efficiency compared to the single-chamber, single-turbine (1C1T) configuration at low wave frequencies. In terms of reducing wave reflection and transmission, the 2C2T configuration outperforms the dual-chamber, single-turbine configuration. When the wall angle increases from 0° to 40°, the total efficiency increases by 166.37%, and the horizontal load decreases by 20.05%. Additionally, optimizing the mid-wall draught depth results in a 9.6% improvement in efficiency and a reduction of vertical load by 11.69%.

Study on spectral characterization of non-uniform PT symmetry Bragg gratings with duty-cycle modulation

Abstract It is a great challenge to improve the detection efficiency of optical structures. In order to increase the reflection effect of Bragg grating, a non-uniform PT-symmetric Bragg grating structure based on duty cycle modulation is proposed. The grating exhibits PT symmetry by quantum doping technology and is optimized by analyzing the structural parameters which have great influence on the grating. Two methods of Odd-function Duty-cycle Modulation (ODC) and Even-function Duty-cycle Modulation (EDC) are proposed to obtain the non-uniform grating structure under duty cycle modulation. The results show that the reflectivity of the grating is obviously enhanced under odd-function duty cycle modulation. Our method improves the reflection characteristics of the Bragg grating to a great extent, and is conducive to designing more efficient reflectivity detection devices.

Fano resonance and exceptional point enhanced sensing in a grating coupled heterostructure

Fano resonance line shape performs ultrasensitive sensing characteristics as its ultrahigh quality factor. Here, we theoretically investigate the sensitivity and figure of merit (FOM) of a novel, to our knowledge, multilayered heterostructure as a sensor. The heterostructure is non-Hermitian and composed of one layer of gold grating, multilayer polyethylene, and polymethyl methacrylate. The rigorous coupled wave analysis method (RCWA) is used to investigate the reflection characteristics of the structure. Interference between the “dark mode,” excited by the grating, and the “bright mode,” excited by the central layers, produces Fano resonance in the forward reflection spectra. Adjustment on the structure parameters can reduce the valley value of the Fano peak to zero, giving rise to scattering exceptional points (EPs). At the wavelength of the EP, the ambient temperature and mechanical stress fluctuations will lift the reflection, available for sensing signal. The sensitivity is higher than that of the structure without Fano peaks and EPs. Moreover, we use the spectral shift for refractive index sensing with a FOM exceeding 200RIU−1.

Reflective and quasi-reflectionless multiband bandpass filters using multi-resonant acoustic-wave lumped-element resonators

Abstract Surface acoustic wave (SAW) resonator-based compact multi-band bandpass filters (BPFs) with quasi-elliptic transfer functions (TF) and reconfigurable reflective or quasi-reflectionless characteristics are reported. They utilize bandpass-type multi-resonant acoustic wave lumped resonator (AWLR) stages, shaped by multiple in-parallel cascaded distinct SAW resonators and one lumped-element (LE) inductor. By incorporating resistively-terminated bandstop-type AWLR stages at the Radio Frequency (RF) input/output, their power reflection response can be tailored to be quasi-reflectionless. The multi-band BPF can be expanded to TF with: i) a high number of passbands by increasing the number of the acoustic wave resonators (AWRs) in the AWLR stages, and ii) higher selectivity by cascading bandpass-type AWLRs stages using impedance inverters, and iii) symmetric quasi-reflectionless characteristics. For N in-series cascaded stages, each comprising K distinct AWRs, K passbands with enhanced fractional bandwidth (FBW) can be created, with overall TF having N•(K) poles and N•(K+1) transmission zeros (TZs). The operating principles of the multi-band BPF concept are provided through detailed design examples. The concept is demonstrated through detailed design examples, with three multi-band BPF prototypes manufactured and characterized, exhibiting dual-/triple-band centered between 1029.8 and 1039.9 MHz, FBWs&gt; 0.4kt2, and effective Q-factors&gt; 5,000. The quasi-reflectionless prototype showed a maximum reflection of -11.5 dB.

Multichannel Wavelet Kernel Network for High Dimensional Inverse Modeling of Microwave Filters

This paper proposes a multichannel wavelet kernel network (MWKN) modeling technique with a two-stage training technique for high-dimensional inverse modeling of microwave filters. The real and imaginary parts of the transmission and reflection characteristics are used as the model inputs, while the geometric parameters of the filter are designated as the outputs. Since the electrical signal in microwave inverse modeling encompasses multiple frequency components and complex information arising from the subtle dimensional changes in the metal pattern, the wavelet transform is introduced by leveraging its powerful multi-scale and approximate detail features to form the discrete wavelet convolution layer in the proposed MWKN. To adapt to the learning of approximate detailed features at different scales, the learnable parameters of this layer and the weights of the backbone network are adjusted in stages through a two-stage training strategy based on particle swarm optimization (PSO), which jointly promotes the rapid convergence of the model. Three numerical examples demonstrate the effectiveness and robustness of the proposed MWKN model. Compared with the traditional design method using electromagnetic (EM) simulation, this approach significantly and substantially reduces the repeated calculation time and is capable of predicting the geometry that meets the design specifications within 0.42 s.

Spectral SPR effect in thin films of high-conductive metals and features of SPR-biosensors implementation in chromatic mode

In this paper, we have evaluated the application of various types of highly conductive metals for implementing the effect of spectral surface plasmon resonance (SPR) within a visible spectrum range to achieve more efficient and productive registration of biomolecules in a liquid medium using tricolor RGB cameras. Thin films of gold, silver, copper, and aluminum, as well as a bimetallic coating of silver with a gold superlayer on a glass substrate, are considered. Detailed calculations of the spectral characteristics of reflection at SPR excitation in the Kretschmann geometry are performed, particularly when a thin dielectric film is formed on the metal surface that imitates a layer of biomolecules. For each of the specified metals, the width of the region of implementation of the full-fledged SPR effect in the visible range of the spectrum is determined, and the sensitivity of the optical response to the influence of an external dielectric layer is assessed.

Nonlinear optical response and bistability of intersubband polariton in a planar microcavity: Role of dynamic Coulomb coupling

We theoretically investigate the steady-state bistable intersubband polariton response of quantum-well (QW) structures embedded into planar semiconductor microcavity to intense plane wave incident radiation. A rigorous semiclassical approach employs the transfer matrix formalism and the sheet model, which includes the dynamic depolarization effect. Results of comprehensive numerical simulations on reflectance characteristics of the structures with strong coupling between the ground cavity mode of the electromagnetic field and intersubband excitations in QWs are presented. The mechanism of the polariton-based optical bistability (OB) is revealed. Both the mirror-based optical bistability (MOB) and the intrinsic optical bistability (IOB) are investigated, with the focus on the MOB. Polariton-based bistabilities driven by cyclically changing intensity of the incident radiation, frequency of the incident radiation, and the angle of incidence are considered. It is found that the presence of the dynamic depolarization effect brings novel features to the OB reflectance characteristics of the structures. Effect of accumulation of the MOB cooperativity parameter is revealed. The concept of effective QW is proposed to describe a tremendously enhanced MOB response of multiple identical QWs particularly located in the cavity. A remarkable possibility of MOB in systems of multiple particularly located QWs with big values of dephasing rate is demonstrated. It is shown that the transition from bistability to multiple bistability and to multistability for two QWs can be controlled by slight manipulation of the angle of incidence. A possibility is found for an outstanding width of the hysteresis of the angular-domain OB, being about one degree.

Time-lapse amplitude variation with offset difference inversion based on the reformulated Biot-Squirt model

Time-lapse AVO (Amplitude variation with offset) inversion is a significant technique for the estimation of dynamic reservoir changes. The main theoretical foundation is Zoeppritz equations in single-phase media. At present, there are studies on the inversion method of using Biot's theory. Although it has some improvements in accuracy compared with the method of using Zoeppritz equations, the squirt-flow mechanism is not considered. Furthermore, the precision of difference data equations still needs to be improved in difference inversion. In view of the above problems, the reformulated BISQ (Biot-Squirt) model is introduced into the inversion, and the iterative optimization is used to increase the precision of difference data equations continually in this paper. First, we derive the difference data equations about the reservoir-parameter changes. The reformulated BISQ model is applied, and can describe the characteristics of P-wave reflection accurately and expediently. Secondly, the objective function about the reservoir-parameter changes is constructed. The Bayesian theory and the model smoothing constraint are used, and are helpful to obtain accurate and stable solutions. Thirdly, we derive the equation for estimating the reservoir-parameter changes, and the inversion is iterative for the continuous improvement of accuracy. The difference inversion method is applied, and is helpful to enhance the data repeatability and reduce the calculation amount. Finally, synthetic and real data are applied for the inversion and testing to prove the effectiveness and feasibility of the method.

A two-stage 6D pose estimation method for industrial textureless parts based on multi-feature fusion

Abstract 6D pose estimation is an essential supporting technology for many industrial applications such as robotic vision, human-robot collaboration and augmented reality. However, in industrial environments, due to the textureless, reflective, and occluded characteristics of industrial parts, the accuracy and adaptability to the application environment of pose estimation are limited. To solve this issue, a two-stage 6D pose estimation method for industrial parts is proposed, which uses a multi-feature fusion strategy. In the first stage, the semantic keypoints are selected to train a PVN3D-based RGBD fusion pose estimation network to predict the initial pose. In the second stage, we propose a pose iterative optimization method based on the fusion of appearance and geometric features. Experiments on the MP6D industrial dataset demonstrate that the proposed method exhibits the comparative methods. Our approach offers a novel idea for accurate and robust pose estimation of industrial parts.