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In ultrasonic flaw detection, lateral cylindrical drilling is traditionally used to adjust and check equipment parameters. Other volumetric reflectors such as vertical drilling or spherical pores are rarely used. In this article, it is noted that volumetric reflectors of various types are convenient for use as a model of internal and surface defects of welds. Moreover, drillings of various orientations are easy to manufacture. For a long time, the limitations on using drilling for modeling in ultrasonic nondestructive testing were related to the noise caused by diffraction effects as elastic waves bypass cylindrical cavities. It is noted that these effects are currently well studied. They can be used to identify the type of defects and measure their size. The present paper describes the results of experiments on the observation of scattering of longitudinal and transverse waves with various polarization by cylinders and spheres and provides typical examples of the manifestation and use of these diffraction effects. The expediency of using not only drilling but also spherical pores is also noted. Experiments with scattering of ultrasonic waves by pores were performed on transparent glass samples for clarity. Comparative data are presented showing how diffraction effects manifest themselves on various volumetric cavities. In particular, it is noted that a focusing of signals that envelope spherical pores is observed. Limitations on the pulse duration of ultrasonic waves are noted in which diffraction signals can be used to increase information content in the detection of defects. It is recommended to expand the use of lateral drilling with a diameter of 2 mm in samples to adjust sensitivity during ultrasonic monitoring with an echometer. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) flume experiments are useful in investigating the performances of floating breakwaters (FBs), including hydrodynamic performances, motion responses, and mooring forces. Designing a reasonable gap between the flume wall and the FBs is a critical step in 2D flume tests. However, research on the effect of the gap on the accuracy of 2D FB experimental results is scarce. To address this issue, a numerical wave tank is developed using CFD to estimate the wave-FB interaction of a moored dual-cylindrical FB, and the results are compared to experimental data from a previously published work. There is good agreement between them, indicating that the numerical model is sufficiently accurate. The numerical model is then applied to explore the effect of gap diffraction on the performance of FBs in 2D experiments. It was discovered that the nondimensional gap length LGap/WPool should be smaller than 7.5% to ensure that the relative error of the transmission coefficient is smaller than 3%. The influence of the gap is also related to the entering wave properties, such as the wave height and period. [ABSTRACT FROM AUTHOR]

The measurements of the Total Solar Irradiance (TSI) is a primary means to investigate solar activity and key measurement for understanding global climate change. The aperture diffraction is an error factor for the Solar Irradiance Absolute Radiometer (SIAR) on the Fengyun-3F (FY-3F) satellite. The diffraction effect correction factors can currently only be obtained by simulation, and they are obtained based on a series of approximate conditions that do not allow the accuracy of the diffraction correction results to be assessed. In this paper, we establish the diffraction effect measurement equipment based on the dark imaging technology and the theory of diffraction by Fraunhofer. The total light image and the aperture diffraction images of different angles were obtained by the CCD camera. The images were corrected by linearity, background, and continuity. Then, the diffraction effect curve of diffraction angle can be obtained. Finally, the diffraction correction factor of SIAR/FY-3F can be obtained by the accumulation of multiple apertures and combining the weighted integration of the solar spectrum. The results illustrated that the value of the diffraction correction factor of the SIAR aperture system on the FY-3F satellite is 2.85 × 10 − 3 , and the uncertainty of diffraction effect experimental measurement is 4.62%, which reduces the measurement error of the diffraction effect on the total solar irradiance to 1.32 × 10 − 4 . This result provides a technical basis for high-precision TSI measurement. [ABSTRACT FROM AUTHOR]

The polarised Bidirectional Reflectance Distribution Function (pBRDF) model relates the properties of target materials to the polarisation information of the incident and reflected light. The Priest–Germer (P-G) model was the first strictly pBRDF model to be officially released; however, some shortcomings remain. In this study, we first analyse the assumption framework of the P-G model, analyse the assumption framework to determine the imperfections in the framework, supplement the boundary conditions of the model for diffraction and transmission effects, and propose and construct a polarised pBTDF model based on the existing P-G model and parameter inversion; the output results of the model are compared with the experimental data through simulation. The results show that the intensity relative error and Degree of Linear Polarisation relative error of the target can be reduced by more than 40%, using the improved model, proving its accuracy and precision. [ABSTRACT FROM AUTHOR]

The GNSS performance is significantly degraded in urban or natural canyons because of the signal interferences caused by buildings, trees and slopes. Besides the multipath and non-line-of-sight receptions, the diffraction effect frequently occurs in urban and natural canyons to cause large errors when the Global Navigation Satellite System (GNSS) signals transmitting path is close to the obstruction edge. We first analyzed the characteristics of diffraction errors and proposed an obstruction adaptive elevation masks (OAEMs) determination method to eliminate the diffractions in the data processing. It shows that the diffraction error has an approximately linear pattern and was largely dependent on the horizontal distance of the diffraction point to the phase center of the GNSS antenna and the diffraction elevation. It can be far beyond the theoretical limitation of multipath error and achieve several phase wavelengths, and could have various patterns in time series, such as trend, period and regular or unregular fluctuations, according to the features or distributions of obstruction edges. We proposed an OAEMs determination method by detecting diffractions in time series subsections and mapping and stacking them in a hemispherical map. The results show that it can eliminate the large diffraction errors to reduce the outliers and large fluctuations in the time series, and the positioning precision and reliability could be improved to a large extent. Especially in vertical directions, the precision can be improved by more than 40%. [ABSTRACT FROM AUTHOR]

Optical neural networks can effectively address hardware constraints and parallel computing efficiency issues inherent in electronic neural networks. However, the inability to implement convolutional neural networks at the all-optical level remains a hurdle. In this work, we propose an optical diffractive convolutional neural network (ODCNN) that is capable of performing image processing tasks in computer vision at the speed of light. We explore the application of the 4f system and the diffractive deep neural network (D 2 NN) in neural networks. ODCNN is then simulated by combining the 4f system as an optical convolutional layer and the diffractive networks. We also examine the potential impact of nonlinear optical materials on this network. Numerical simulation results show that the addition of convolutional layers and nonlinear functions improves the classification accuracy of the network. We believe that the proposed ODCNN model can be the basic architecture for building optical convolutional networks. [ABSTRACT FROM AUTHOR]

In driver assistance or self-driving systems, millimeter-wave radar is an indispensable sensing tool because of its applicability to all weather conditions or non-line-of-sight (NLOS) sensing.This study focuses on a human recognition issue in the NLOS scenario by applying the support vector machine (SVM)-based machine learning approach to a diffraction signal.We show that there is a significant difference in diffraction signals between man-made objects (e.g., metallic cylinder and human body) even without motion.Hence, by exploiting such difference, an SVM achieves a high recognition rate, even in deeply NLOS situations.The experimental investigation, using a 24-GHz millimeter-wave radar in an anechoic chamber demonstrates that a diffraction signal-based recognition accurately classifies the real human and human mimicking man-made object, even in the NLOS scenario shielded by the parking vehicle.

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This study investigates the diffraction effects of the IEC 63034 standard micro–baffle (SMB) on the frequency response (FR) measurements of microspeakers based on the extended Biot–Tolstoy–Medwin technique. Two different cases with and without the consideration of the backward diffractions of the SMB were investigated, which correspond to different practical measurement conditions of microspeaker drivers and closed-box microspeaker modules. The experimental results obtained were consistent with the theoretical analysis and numerical calculations. Normalized FR curves characterizing the SMB diffraction effects were presented, which can be used to compensate the FRs measured on the SMB to obtain the results measured on an ideal infinite baffle and eliminate the SMB diffraction effects. [ABSTRACT FROM AUTHOR]

Offshore structures are generally classified as small-scale structures or large-scale structures. Their wave forces are then estimated by Morison equation and diffraction/radiation theories, respectively. However, the classification criterion is not well quantified. In the present paper, a numerical wave flume is established to simulate the wave forces acting on a fixed and vertical surface-piercing circular cylinder under linear waves. By solving Navier–Stokes equation and Euler equation with free surface involved, respectively, the viscous force and inertia force are separated accurately. The variation of viscous force and inertia force with the cylinder diameter to wave length ratio is discussed in detail. The scale intervals for significant viscous and diffraction effects are given. The error caused by neglecting viscous and diffraction forces is quantitatively analyzed. Based on these analysis, the concept of medium-scale structure is proposed and the classification criteria for small-, medium- and large-scale structures are given. In the meantime, the estimation methods of wave forces for different scales of structures are suggested. A numerical wave flume is established to simulate the wave forces on a fixed and vertical surface-piercing circular cylinder under linear waves. By solving Navier–Stokes and Euler equations, respectively, the viscous and inertia forces are separated accurately. The dependence of these two force components on the cylinder diameter to wave length ratio is quantified. A new concept of medium-scale structure is proposed and the novel classification criteria for small-, medium- and large-scale structures are given. Correspondingly, the estimation methods of wave forces for different scales of structures are suggested [ABSTRACT FROM AUTHOR]

The aperture size of microlens is a key parameter of a plenoptic camera, which strongly influence the performance of the camera. Generally, the size of microlens aperture is submillimeter, which will introduce obvious diffraction effect with large $f$ -number. Besides, optical distortions of plenoptic camera also bring degradation effect in raw plenoptic image. In this letter, based on wave optics, a more accurate imaging model with diffraction effect and optical distortion for focused plenoptic camera is proposed. The modulation transfer function (MTF) evaluation suggests that the proposed model is more close to the real one when compared to the previous models. Additionally, the raw images under different microlens aperture sizes are synthesized. Finally, a relatively optimal size of microlens aperture is obtained according the results of depth estimation. [ABSTRACT FROM AUTHOR]

This study investigates the diffraction effects of the IEC 63034 standard micro–baffle (SMB) on the frequency response (FR) measurements of microspeakers based on the extended Biot–Tolstoy–Medwin technique. Two different cases with and without the consideration of the backward diffractions of the SMB were investigated, which correspond to different practical measurement conditions of microspeaker drivers and closed-box microspeaker modules. The experimental results obtained were consistent with the theoretical analysis and numerical calculations. Normalized FR curves characterizing the SMB diffraction effects were presented, which can be used to compensate the FRs measured on the SMB to obtain the results measured on an ideal infinite baffle and eliminate the SMB diffraction effects.

An estimation method for direction of arrival (DOA) of muzzle blast is proposed to solve the shell-induced deviation problem in target orientation estimation of a partially shaded microphone array em¬bedded in a small-aperture gunshot detection system. The adverse effect of non-line-of-sight (NLOS) propagation on the time difference of arrival ( TDOA) is analyzed, and a convex optimization algorithm with low-rank and geometric constraints is devised to correct TDOA matrix for simultaneously suppressing the influence from both diffraction propagation and random noise. The non-shaded microphone closest to the target is chosen as the reference microphone. The statistical mean and variance values of least squares DOA estimation error are obviously decreased. The experimental results obtained using a real embedded planar array system demonstrate that the proposed method provides superior muzzle blast DOA estimation performance compared with the conventional approach, by which the cumulative probability of estimation error meeting the requirement of practical products is improved from 0. 86 to 0. 94. [ABSTRACT FROM AUTHOR]

Abstract Operations involving the launch or recovery of a smaller vessel from a larger one are extremely dangerous in high sea states and, therefore, they are normally carried out in low to moderate sea states. However, this can be severely restrictive and in some situations, carrying out such operations in high sea states is unavoidable. Here we report on a detailed investigation of the interaction between two vessels of different size in order to characterise their hydrodynamic interaction under different conditions and to provide insight for operational purposes. Model experiments were conducted to investigate the hydrodynamic interaction between two vessels in close proximity in waves. Previous studies into this interaction have focused on two vessels with comparable size/displacement. This study focused on the interaction between vessels of very different sizes, a platform supply vessel and a lifeboat, at various separation distances between the two models and wave headings. It is found that the effect of the hydrodynamic interaction on the wave loads on the lifeboat model is substantial. The load responses show a strong non-linearity (high order harmonic components). In head waves, the effect of the hydrodynamic interaction on the wave loads is greater in the transverse modes (sway, roll and yaw) than in the longitudinal modes (surge, heave and pitch). The sheltering effects of the larger model on the lifeboat model were also evident from the experiments. The results of this investigation may be used to inform the planning of marine operations, such as the launch and recovery of a lifeboat or an Autonomous Underwater Vehicle (AUV) from a mothership and the transfer of equipment or personnel between vessels. The data will also provide a useful resource for validation of Computational Fluid Dynamics (CFD) codes and other numerical simulations, and can be used to better understand the limitations and potential widening of the operational weather windows and to ensure that operations are carried out safely. [ABSTRACT FROM AUTHOR]

Deterministic channel models, such as the three-dimensional (3D) ray launching method, can yield wireless channel parameters. In the non-line-of-sight (NLOS) propagation, the outdoor 3D ray launching method that considers diffraction effects is more accurate than the one that does not. While considering the diffraction effect, obtaining the diffraction point is challenging. This paper proposed a method for determining diffracted rays using the receiving sphere method in 3D ray launching. The diffraction point is determined using the shortest distance method between two straight lines, and the signal loss from the transmitting to receiving antennas is obtained. Furthermore, experiments on a millimeter wave in a microcell scenario were performed. The test results of the wireless channel parameters were compared with theoretical calculations. The results obtained via the 3D ray launching method that only considers the specular reflection and direct rays agree with the experimental results in the line-of-sight (LOS); furthermore, they generate larger errors compared with the experimental results in the NLOS. The results obtained via the 3D ray launching method that considers the direct ray, reflected rays, and diffracted rays agree with the experimental results both in the LOS and NLOS. Therefore, the 3D ray launching method that considers the diffraction effect can improve the prediction accuracy of the millimeter wave channel parameters in a microcell.

This paper experimentally investigates the performances of two bottom-hinged-flap wave energy converters (BHF-WECs) operating in tandem. Firstly, the inertia effects of a single BHF-WEC operating in isolation are theoretically and experimentally examined to show their negligibility in coastal-water applications with the non-dimensional wave number ∼  O(1) . Experiments of two in-tandem BHF-WECs with separation distance ( d ) varing from 0.5 λ to λ (incident wavelength) with increment of λ/16 are then conducted in a small wave basin. Hydraulic pumps are used as the power take-off and their forcing characteristics as an energy damper are determined using a rating platform. Time-series images of flapping motions of the BHF-WECs, recorded with high-speed cameras, are analyzed using a processing and analysis procedure based on the correlation algorithm to evaluate their capture factors (CF). The CF variations of the first BHF-WEC with d exhibit a sinusoidal wave form with wavelength of λ/2 . The combined CF of the two in-tandem BHF-WECs is always greater than 1.0, indicating that the wave energy outside the frontal area is drawn via diffraction. It reaches the maximum at around d  =  14λ/16 with λ/4 apart from the minimum at around d  =  9λ/16 owing to the underlying mechanism of the Bragg Reflection. [ABSTRACT FROM AUTHOR]

Accurate Q parameter is hard to be obtained, but there is great difference between Q measurements from different measurement methods in seismic physical modelling. The influence factors, stability and accuracy of different methods are analyzed through standard sample experiment and the seismic physical modelling. Based on this, we proposed an improved method for improving accuracy of pulse transmission method, in which the samples with similar acoustic properties to the test sample are selected as the reference samples. We assess the stability and accuracy of the pulse transmission, pulse transmission insertion, and reflection wave methods for obtaining the quality factor Q using standard and reference samples and seismic physical modeling. The results suggest that the Q-values obtained by the pulse transmission method are strongly affected by diffraction and the error is 50% or greater, whereas the relative error of the improved pulse transmission method is about 10%. By using a theoretical diffraction correction method and the improved measurement method, the differences among the Q-measuring methods can be limited to within 10%. [ABSTRACT FROM AUTHOR]

Sound transmission through a fluid-loaded finite perforated panel set in an infinite unperforated rigid baffle is considered. Using a fully coupled formulation in the 2-D wavenumber domain, the transmitted pressure due to an incident plane wave is obtained. The change in the panel resonances caused by the perforations is accounted for. The formulation also takes into account the self- and inter-modal coupling coefficients arising due to the fluid-loading effect. The derivation is almost entirely analytical with numerical computations done at the very end. Transmission loss (TL) curves are plotted for various cases and the physics is discussed. Along the way an uncoupled calculation is also done for the sake of comparison. The results are mainly for a light medium like air. For a light medium, in general, the perforate impedance is lower than the panel impedance. Thus, most of the transmission happens through the perforations. The panel velocity contribution is insignificant and hence the uncoupled calculation is adequate. In general, the absolute perforate impedance increases with increasing frequency. So does the TL. At low frequencies, because the resistive component of the hole impedance increases, the absolute perforate impedance rises. Thus, the TL curves rise at the lower frequencies. This effect is prominent for sub-millimeter hole radii, i.e., for micro-perforations. An important issue with the TL values for perforated panels is that they sometimes acquire negative values at low frequencies. This apparent anomaly is resolved by showing that at low frequencies there is an additional power component that flows from the baffle region onto the panel. Upon inclusion of this additional term, the TL values remain positive at all frequencies. [ABSTRACT FROM AUTHOR]

Based on the angular spectrum representation of the Maxwell equations and the method of stationary phase, this paper presents the far-field analytical expression of a pulsed hollow Gaussian beam with constant waist width diffracted by the circular aperture, and the result can be simplified for the case of the paraxial propagation of pulsed Gaussian beam in the free space. Based on the analytical result, the influences of truncation parameter on the transverse intensity distribution of the pulsed beam are analyzed. Comparisons of normalized temporal intensity between the pulsed Gaussian beam and the fourth order pulsed hollow Gaussian beam are presented. We find that the spatial mode can induce the temporal shape changing. [ABSTRACT FROM AUTHOR]

Abstract: Active touch localization based on a learning process of touch-disturbed broadband bending wave propagation in thin objects is used to transform any 3D surface into a multi-touch interface. Fast prototyping permits easy manufacturing of various 3D shapes that can be as quickly transformed into touch interfaces. The drawback is their weak mechanical stability with temperature. This paper details the temperature behavior differences between a sintered plastic such as polyamide polymer of type PA12 and raw injected Acrylonitrile-Butadiene-Styrene composite polymer (ABS), in particular how their physical parameters such as Young's modulus and Poisson's ratio are affected by temperature. Correlatively, longitudinal and transversal waves within injected and sintered plastics are investigated across a commercial temperature range of 10 °C to 70 °C. The internal grain structure in plastics obtained by laser sintering of powder makes these materials prone to stronger damping and clear non-linear temperature dependency of the shear wave velocity compared with injected plastics. [Copyright &y& Elsevier]

Abstract: In lithography using spatial light modulators, the irradiance is influenced by diffraction effects. The intensity distribution under diffraction effects due to binary reflections is investigated. Dynamic sub-pixelation, a method of dividing an image pixel reflected off a single micromirror into equal-sized sub-pixels on a translating substrate by the superposition of an array of image pixels, is proposed to enhance image resolution. The influence of dynamic sub-pixelation on exposure intensity distribution under diffraction effects is analyzed. The potential of utilizing dynamic sub-pixelation for suppressing diffraction effects and further enhancing image resolution while maintaining throughput is demonstrated through simulations and experiments. [Copyright &y& Elsevier]

Abstract: Diffraction effect of the injected beam in axisymmetrical structural CO2 laser is studied based on the injection-locking principle. The light intensity of the injected beam at the plane where the holophotes lie is derived according to the Huygens–Fresnel diffraction integral equation. And then the main parameters which influence the diffraction light intensity are given. The calculated results indicate that the first-order diffraction signal will play an important role in the phase-locking when the zero-order diffraction cannot reach the folded cavities. The numerical examples are given to confirm the correctness of the results, and the comparisons between the theoretical and the experimental results are illustrated. [Copyright &y& Elsevier]

Vanadium dioxide thin films were fabricated through annealing vanadium oxide thin films deposited by dual ion beam sputtering. X-ray diffraction (XRD), atom force microscopy (AFM), and Fourier transform infrared spectrum (FTIR) were employed to measure the crystalline structure, surface morphology, and infrared optical transmittance. The phase transition properties were characterized by transmittance. The results show that the annealed vanadium oxide thin film is composed of monoclinic VO, with preferred orientation of (011). The maximum of transmittance change is beyond 65% as the temperature increases from 20 to 80°C. The reversible changes in optical transmittance against temperature were observed. The change rate of transmittance at short wavelength is higher than that at long wavelength at the same temperature across semiconductor-metal phase transition. This phenomenon was discussed using diffraction effect. [ABSTRACT FROM AUTHOR]

Based on the potential flow theory, the mathematical formula of the wave action of the non-coaxial double-layer cylinder structure is derived, and the effect caused by the non-coaxial of the upper and lower single cylinders is analyzed. In this paper, the water area is divided into two regions, and their respective coordinate systems are established in each region to describe the velocity potential function. The velocity potential of the two regions is linked by the matched eigenfunction expansion method (MEEM) at the interface of the two regions. The cross-sectional radius function of the interface is expressed by Fourier series. After verifying the accuracy of the mathematical formula, the effect of asymmetric structure is analyzed. The results show that when the relative angle of the two axes is 0°, the wave force on the structure can be reduced to a greater extent if the two axes are as far away as possible. At the same time, the effect of this reduction weakens with the increase of the relative angle, and even increases the wave force when α = 90°. When the lower-lawyer cylinder radius is 0.6 times the upper-lawyer cylinder radius, the effect of wave force reduction caused by the non-coaxial is the largest. • The upper- and lower-layer of the structure are composed of larger and smaller cylinders, respectively. At the same time, the symmetry axes of the upper- and lower-layer cylinders do not coincide, resulting in the non-central symmetry of the double-layer cylinder structure. • Based on the potential flow theory, the mathematical formula of the wave action of the non-coaxial double-layer cylinder structure is derived. • The effect of the relative distance and relative angle between the upper- and lower-layer cylinders on the wave force of the structure are analyzed. • The effect of the upper-layer cylinder height and the lower-layer cylinder radius on the non-coaxial structure are analyzed. [ABSTRACT FROM AUTHOR]