Increasing Propagation Distance Research Articles

Propagation Characteristics of a Partially Coherent Gaussian Schell‐model Array Vortex Beam in the Joint Turbulence Effect of a Jet Engine and Atmosphere

AbstractThis work investigates the joint effects of jet engine exhaust‐induced turbulence and atmospheric turbulence on the propagation of a partially coherent Gaussian Schell‐model Array (GSMA) vortex beam. Using the two‐process propagation method, analytical formulae are derived for the cross‐spectral density, spectral density, degree of coherence, and beam width of the considered beam. The results show that the considered beam takes different shapes; when the spatial coherence is large, the spectral density of the GSMA vortex beam takes an elliptical shape, whereas when the spatial coherence is smaller, the spectral density remains a Gaussian shape. The evolution profile of the degree of coherence weakens gradually when the propagation distance, topological charge, and turbulence strength increase. Moreover, the profile of the degree of coherence takes the Gaussian profile when the propagation distance is longer or turbulence atmospheric is stronger. Furthermore, the results reveal that the corresponding beam spreads faster with a larger propagation distance, lower spatial coherence, and high‐strength turbulence. This study also concludes from the results that the beam is affected more when its propagation is near the jet engine exhaust, which means that this latter has a significant impact.

Experimental investigation of the evolution and energy transmission of a type-a internal solitary wave packet over a gentle slope

Laboratory experiments were conducted to investigate the evolution characteristics of a type-a ISW packet propagating over a gentle slope. The elevation type-a ISW packet was generated by the gravity collapse of stratified density fluid, and its transformation process over the gentle slope was measured by use of the multichannel conductivity-probe arrays. The energy transmission and loss of the ISW packets during its evolution over the gentle slope were further analyzed. The experimental results showed that the evolution and energy transmission of the type-a ISW packet over the gentle slope is closely related to the amplitude of the leading wave in the wave packet. The conversion of the wave packet type is caused by the variations in amplitudes of the leading and tailing waves in the type-a ISW packet due to the topography effect. The distance between the adjacent waves in a type-a ISW packet gradually increases with the increasing propagation distance on the slope, as well as its increase rate is also enlarged. The wave speeds of both the leading and tailing waves always decrease with the propagation distance. The energy loss of the whole ISW packet increases with both the incident wave amplitude and the propagation distance.

Second-order coherence and polarization characteristics of partially coherent radially polarized cosh-Gaussian vortex beams in a turbulent atmosphere

The second-order coherence and polarization characteristics of partially coherent radially polarized cosh-Gaussian vortex (PCRPChGV) beams in atmospheric turbulence are investigated based on the extended Huygens–Fresnel principle. The analytical propagation formulas of cross-spectral density matrix, average intensity and degree of polarization (DOP) for PCRPChGV beams in turbulence are derived. The influences of initial correlation length, cosh factor and turbulence intensity on average intensity, on-axis intensity and DOP of PCRPChGV beams are examined numerically. Results show that with increasing propagation distance, the PCRPChGV beam evolves from the initially separated double-lobe spot into overlapping double-lobe spot, and Gaussian spot. The corresponding intensities of the two Cartesian components of light field rotate markedly around the beam axis in a unique manner. Initial correlation length and cosh factor have an obvious influence on the position and size of normalized on-axis intensity peak, respectively. In addition, PCRPChGV beams in moderate turbulence have strong anti-turbulence ability.

Roadways fracture response under varying dominant blasting frequencies and lateral pressure coefficients

Dominant frequency of blasting waveform attenuates with increasing propagation distance, leading to diverse diffractive effects on a roadway located in different sublevels. To investigate the roadway fracture characteristics in response to varying blasting wave frequencies and geo-stresses. Numerical simulation and experiments were performed by using discrete element methods and acoustic emission (AE) techniques, respectively. Roadway response differences in terms of microcracks propagation regions were primarily investigated, to reveal the relationships between damage-prone regions and the lateral pressure coefficient and blast waveform frequencies. The results showed that the excavation damage zone (EDZ) and the types of microcracks developed are primarily influenced by the principal stress direction. Low-frequencies blast waves contribute significantly to the overall damage to the surrounding rock around the roadway, while high-frequencies blast waves mainly damage the sides of the facing blast. Under the coupling effect of principal stress and blast wave, microcracks are more prone to generate in regions coupling with high-stress concentration regions induced by principal stress and disturbed regions diffracted by blast waves. With the results from this study, the roadway support should consider the difference in damage-prone regions triggered by blasting waves with varying dominant frequencies under different lateral pressure coefficients.

Effect of Pipe Bends on the Low-Frequency Torsional Guided Wave Propagation

Wave motion in pipe bends is much more complicated than that in straight pipes, thereby changing considerably the propagation characteristics of guided waves in pipes with bends. Therefore, a better understanding of how guided waves propagate in pipe bends is essential for inspecting pipelines with bends. The interaction between a pipe bend and the most used non-dispersive torsional mode at low frequency in a small-bore pipe is studied in this paper. Experiments are conducted on a magnetostrictive system, and it is observed that T(0,1) bend reflections and mode conversions from T(0,1) to F(1,1) and F(2,1) occur in the pipe bend. The magnitude of the T(0,1) bend reflections increases with increasing propagation distance and excitation frequency. The amplitude of the mode-converted signals also increases with increasing propagation distance, but it decreases with increasing excitation frequency. Because of their longer bent path, the test signals for a pipe bend with a bending angle of 180X are much more complicated than those for one with a bending angle of 90X. Therefore, it is even more difficult to scan a bent pipe with a large bending angle. The present findings provide some insights into how guided waves behave in pipe bends, and they generalize the application of guided-wave inspection in pipelines.

Beam intensity and spectral coherence of Hermite-cosine-Gaussian rectangular multi-Gaussian correlated Schell-model beam in oceanic turbulence

The beam spreading and evolution behavior of a partially coherent, Hermite-cosine-Gaussian (HcosG) rectangular multi-Gaussian correlated Schell-model beam propagating in oceanic turbulence is studied. Analytical expressions for the cross-spectral density function, as well as the root mean square (rms) beam width and the spectral degree of coherence, are derived based on the extended Huygens-Fresnel principle. The HcosG rectangular multi-Gaussian correlated Schell-model beam exhibits a multi-lobe pattern at short propagation distances. The dependencies of the number, size, shape, and centroid of the lobes on displacement parameters, source size, order of field distribution, and displacement are investigated. As the propagation distance increases, the spectral coherence decreases, and the differences between the spectral coherence curves gradually diminish. Additionally, for HcosG rectangular multi-Gaussian correlated Schell-model beams, better propagation performance was found in oceanic turbulence with larger mean square temperature dissipation rate, smaller turbulent kinetic energy dissipation rate per unit mass of fluid, and larger relative strength of temperature and salinity fluctuation.

전파 거리에 따른 신호의 감쇠와 분산이 고려된 순시 주파수 추정 알고리즘 및 장거리 전파용 반사파 계측법 시뮬레이터 개발

Time-Frequency domain Reflectometry(TFDR) is used for the purpose of fault detection and evaluating the integrity in cables. TFDR can diagnose live wire in nondestructive. but, the incident signal cannot aviod attenuation and dispersion according to increasing propagation distance, propagation velocity changes with propagation distance. attenuation and dispersion in long distance lead to decresing falut detection performance of cable. therefore, Developing instantaneous frequency Estimation algorithm of signal and signal restoration algorithm in order to determine tendency of propagation velocity for propagation distance, we demonstrate the performance of algorithm by implementing TFDR simulator possible long length.

Study on the Difference of Wavefront Distortion on Beams Caused by Wavelength Differences in Weak Turbulence Region

In dual-wavelength free-space optical communication systems, the wavefront distortion differences caused by the wavelength difference of the signal and beacon lights cannot be completely corrected. In this study, according to the method of geometric optics, the relationship between the wavefront phases of the signal and beacon lights is analyzed by establishing a mathematical model of the cross-correlation ratio of the arrival-angle fluctuation and phase relationship of different Gaussian-beam wavelengths under weak turbulence near the surface. The numerical results show that after Gaussian beams of different wavelengths propagate through the same atmospheric channel, the cross-correlation number of the arrival-angle fluctuation decreases with an increase in the wavelength difference, waist radius, and turbulence intensity, and increases with an increase in propagation distance. The beam-wavefront phase difference increases with an increasing wavelength difference. Finally, a wavefront distortion correction experiment of a dual-wavelength adaptive optical system verified the correctness of the wavefront phase-difference relationship between the signal light and beacon light established in this study.

Electromagnetic Ultrasonic Shear-Horizontal Wave to Detect Corrosion Defect of Flat Steel for Grounding Device of Transmission Pole Tower

Detecting defects in grounded flat steel is essential for ensuring the safety and reliability of transmission tower grounding devices. However, traditional inspection methods, such as physical excavation and verification, are costly and time-consuming. This paper proposes a corrosion defect detection method for flat steel transmission tower grounding devices based on electromagnetic ultrasonic SH waves. In addition, using commercial software, a three-dimensional finite element simulation model of grounded flat steel with simulated pitting corrosion defects is constructed. The specified displacements applied to multiple surface sources mimic the horizontal shear vibrations generated by the electromagnetic ultrasonic transducer on the surface of the grounded flat steel during actual inspection. A simulation was used to investigate the propagation and attenuation characteristics of shear-horizontal ultrasonic SH0guided waves for simulated corrosion defects with various geometric configurations in grounded flat steel. The simulation investigated the propagation and attenuation characteristics of the SH0 wave in grounded flat steel and the detection of various defects for linear analysis of the results. The simulation results show that the attenuation of the electromagnetic ultrasonic guided wave is small, at only 0.0016 dB/mm, and the displacement amplitude of the echo signal decreases with the increase of the SH0 wave propagation distance. Increasing the depth and length of corrosion defects increases the echo signal amplitude. At the same time, the width of corrosion defects has little effect on the echo amplitude. Finally, a flat steel defect detection experiment was conducted, and the experimental results fit with the simulation to verify the accuracy of the simulation model. This detection method introduces a new idea for the on-site detection and quantitative identification of corrosion defects in grounded flat steel, which has significant reference value and can provide a more effective and economical method for ensuring the safety and dependability of transmission tower grounding devices.

Experimental study on the pressure characteristics of an underwater-detonation gas jet

Pressure evolution in the process of an underwater-detonation gas jet is experimentally researched in this study. The pressure-test experimental system is established to analyze the propagation laws of shock waves and the morphological changes of bubble pulsation. The results show that the peak pressure attenuation of the shock wave gradually slows down as the propagation distance increases. Owing to the blockage of water, a high-pressure zone is formed near the tube exit (HPZ-NE). The shock wave continues to propagate downstream after separating from the HPZ-NE, with a high-pressure zone behind the wave (HPZ-BW). The HPZ-NE has a longer duration (approximately 3.7 ms) and higher initial pressure than the HPZ-BW, and its position does not move with the shock wave. After propagation of the shock wave, the gas jet in the detonation tube continuously penetrates the water, leading to the formation of a bubble. The bubble develops in an approximate spherical shape during the first pulsation period, which is divided into four stages: rapid expansion, slow expansion, slow contraction, and rapid contraction. The expansion and contraction processes account for half of the pulsation duration, respectively. The inertia and the pressure difference alternately become the main factors of morphological changes. When the bubble contracts to the minimum volume, a new shock wave is formed by the centroid. The bubble experiences several pulsation periods in the subsequent development, accompanied by a process whereby the centroid gradually moves away from the tube exit.

An Angular Radial Extended Interaction Amplifier at the W Band

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam-wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (-2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the -2° EIA can be improved by nearly 30% compared to the 0° EIA, and the -2° EIA has a greatly improved beam-wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed.

High resolution propagation-based lung imaging at clinically relevant X-ray dose levels

Absorption-based clinical computed tomography (CT) is the current imaging method of choice in the diagnosis of lung diseases. Many pulmonary diseases are affecting microscopic structures of the lung, such as terminal bronchi, alveolar spaces, sublobular blood vessels or the pulmonary interstitial tissue. As spatial resolution in CT is limited by the clinically acceptable applied X-ray dose, a comprehensive diagnosis of conditions such as interstitial lung disease, idiopathic pulmonary fibrosis or the characterization of small pulmonary nodules is limited and may require additional validation by invasive lung biopsies. Propagation-based imaging (PBI) is a phase sensitive X-ray imaging technique capable of reaching high spatial resolutions at relatively low applied radiation dose levels. In this publication, we present technical refinements of PBI for the characterization of different artificial lung pathologies, mimicking clinically relevant patterns in ventilated fresh porcine lungs in a human-scale chest phantom. The combination of a very large propagation distance of 10.7 m and a photon counting detector with 100,upmu hbox {m} pixel size enabled high resolution PBI CT with significantly improved dose efficiency, measured by thermoluminescence detectors. Image quality was directly compared with state-of-the-art clinical CT. PBI with increased propagation distance was found to provide improved image quality at the same or even lower X-ray dose levels than clinical CT. By combining PBI with iodine k-edge subtraction imaging we further demonstrate that, the high quality of the calculated iodine concentration maps might be a potential tool for the analysis of lung perfusion in great detail. Our results indicate PBI to be of great value for accurate diagnosis of lung disease in patients as it allows to depict pathological lesions non-invasively at high resolution in 3D. This will especially benefit patients at high risk of complications from invasive lung biopsies such as in the setting of suspected idiopathic pulmonary fibrosis (IPF).

Generation of the Bessel Beam of Longitudinally Varied Polarization with Dielectric Metasurfaces

AbstractThe beam with longitudinally varied polarization provides a new dimension for polarization applications, such as material processing, longitudinal depth detection, optical communications, etc. A few different methods have so far been investigated, including spatial light modulators and diffractive optical elements. However, these methods have complex optical path, large volume, which are difficult to integrate. Here, a birefringent dielectric metasurface is demonstrated, which is capable of generating Bessel beam whose polarization state continuously rotates along the propagation direction. According to the design, when a linearly polarized light illuminates on the metasurface, the outgoing light becomes linearly polarized zero‐order Bessel beam, whose polarization angle changes as the propagation distance increases. Experimental measurements are successfully carried out. Such scheme may open new doors for potential applications in depth perception, microscopic detection, and so on.

Theoretical analysis of the optical rotational Doppler effect under atmospheric turbulence by mode decomposition

The optical rotational Doppler effect associated with orbital angular momentum provides a new means for rotational velocity detection. In this paper, we investigate the influence of atmospheric turbulence on the rotational Doppler effect. First, we deduce the generalized formula of the rotational Doppler shift in atmospheric turbulence by mode decomposition. It is found that the rotational Doppler signal frequency spectrum will be broadened, and the bandwidth is related to the turbulence intensity. In addition, as the propagation distance increases, the bandwidth also increases. And when m−2/3 and 2z ≤ 2 km, the rotational Doppler signal frequency spectrum width d and the spiral spectrum width d 0 satisfy the relationship d = 2d 0–1. Finally, we analyze the influence of mode crosstalk on the rotational Doppler effect, and the results show that it destroys the symmetrical distribution of the rotational Doppler spectrum about 2l⋅Ω/2π. This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may help us better analyze the influence of the complex atmospheric environment on the rotational Doppler frequency.

Flame Propagation Characteristics of Gas Explosions in Utility Tunnels Considering Spatial Obstacles

Because of their adverse impact on social infrastructure and economic property, gas explosions are among the most dangerous disasters that can befall utility tunnels. Flame propagation is the most intuitive manifestation during the explosion process. It can be significantly influenced by spatial obstacles. To analyze the propagation law of gas explosions in utility tunnels more realistically, an explosion model of the utility tunnel was established by considering actual spatial obstacles, including the pipeline support and reserved frame. The flame propagation characteristics, including the flame shape, temperature distribution, and propagation velocity, were analyzed systematically. Results demonstrate that spatial obstacles have a prominent influence on flame evolution laws. Flame propagation is disturbed but not completely blocked by spatial obstacles. Rather, irregular flame shapes and wrinkles of the flame front are easily developed. The explosion process is insufficient because of the existence of residual methane in the obstacle area. Flame propagation velocity is improved remarkably, whereas temperature distribution is affected slightly. In particular, the spread velocity increases with the increase of propagation distance. The maximum velocity of monitoring surfaces can be improved by 60% under conditions with obstacles.

Investigation of nonlinear propagation effects on sound from supersonic bullets

ISO standard 17201-4 is a calculation method for sound levels generated by supersonic bullets. The standard takes into account nonlinear propagation effects, including broadening of a sound pulse with increasing propagation distance. Two elements of the ISO method are investigated in this paper: i) the accuracy for various Mach numbers, and ii) the effect of noise barriers. For the first element, calculation results are compared with measurement results. In general the agreement is good, but large deviations occur at Mach numbers near unity. Calculation parameters were varied in order to find an explanation for the deviations. For the second element, propagation paths along the horizontal top edge and the vertical side edges of a barrier of finite length are considered. For the path over the top edge, a possible approach is developed to account for the expected reduction of nonlinear propagation effects in the shadow region behind a barrier. For the paths along the vertical side edges, a simulation model with a dense distribution of point sources is employed. The three propagation paths are explained in terms of pairwise cancellation of Fresnel zones. The results of the simulation model are compared with results of an engineering model.

Enhancing the Self-Healing Ability of a Partially Coherent Airy Beam via Fourier Processing: Numerical Investigation

Almost all of the beams under propagation are believed to suffer severe distortion when the source coherence deteriorates, due to the optical diffraction. This implies that low-coherence beams have poor self-healing ability, but were found to be robust against the turbulence, distortion, scattering, etc. In this letter, we first prove numerically that partially coherent Airy beams (PCABs), generated via Fourier processing, have better self-healing ability than that of conventional fully coherent Airy beams. Moreover, as the source coherence deteriorates and the propagation distance increases, the self-healing ability is found to increase. We believe that such PCABs may find Airy beam-related applications in adverse environments, such as particle trapping in biological tissues.

Reconfigurable metasurface for generating flexibly tunable focusing Vortex Beams

As the vortex wave propagation distance increases, its dispersion increases, so its focus needs to be enhanced when performing information transmission. However, in order to expand the detection range, the dispersion needs to be increased in the detection scenario. Thus, it is important to dynamically adjust the focus dispersion of the vortex beam. Therefore, here we propose a novel programmable metasurface design to realize the generation of vortex beams and tune their near-field focusing dispersion performance. By introducing two new parameters m, n into the vortex beam electric field strength equation to modulate the field strength distribution of the vortex beam generated by the programmable metasurface in the near field, we achieve the tunable focusing function of the vortex beam.

On trailing waves rather than lamb waves being generated by buried in-plane dipoles in thick plates

The potential for trailing waves (TWs) rather than Lamb waves to be observed in the out-of-plane displacement signals from acoustic emission (AE) sources in thick plates was examined. Finite element modeling (FEM) was done for buried in-plane dipole (IPD) sources in steel plates with thicknesses up to 125 mm and propagation distances from 250 mm to 1500 mm. The domain was large enough so that significant reflections were not observed during the primary signal arrivals. The run times extended to 1 ms. “Ring-type” sources were used so that axisymmetric modeling could be done. The rise time of the IPDs was typically 1 μs with a cosine-bell time dependence, and the two 1 N forces were spaced by 200 μm. The IPDs were located at several depths from very near the top surface of the plates to the midplane. The displacements as a function of time were obtained on both the top and bottom surfaces. The analysis primarily considered a bandpass of 80 kHz to 500 kHz. In addition, fast Fourier transform results and time/frequency analysis were used. The typical character of TWs consisted of a train of short wave-packets (each 10 to 25 microseconds). The significant-amplitude TW packets arrived after an arrival time corresponding to the Rayleigh wave velocity. The number of packets in the train increased with increasing propagation distance. The likelihood of the signals exhibiting TWs increased with increases in plate thickness, increases in the distance of the IPD below the surface of interest. The presence of the TWs complicates the determination of fixed velocity arrival times necessary for source location determination. Also, since TWs rather than Rayleigh waves appear for IPD depths at some distance below the surface used to sense AE signals, there are potential issues when the AE approach depends on a Rayleigh wave being present.

Effect of unloading behavior on stress wave transmission in a double-scale discontinuous rock mass

Stress wave propagation through double-scale discontinuous rock masses considering unloading behavior was investigated. The piecewise linear loading and unloading models of macrojoint were proposed, which were combined with a split three-characteristics mothed to investigate the stress wave transmission properties. The effects of the waveform, frequency, amplitude and propagation distance on the energy and amplitude transmission coefficients were discussed. The results of the present study were compared with the traditional study that considered single-scale discontinuities. The results show that the present study can effectively analyze the effect of the waveform, frequency, amplitude and propagation distance on the energy and amplitude transmission coefficients. The energy and amplitude transmission coefficients for rectangular wave are the largest, while those for triangular wave are the smallest. The energy and amplitude transmission coefficients decrease as frequency and propagation distance increase. The energy and amplitude transmission coefficients increase as the amplitude increase. The results also show that the effect of macrojoint unloading effect and microdefect on wave transmission can be considered comprehensively in the present study. The unloading effect of macrojoint causes the smaller energy transmission coefficient, while it does not affect the amplitude transmission coefficient. The microdefects cause smaller energy and amplitude transmission coefficients. Highlights The effect of unloading behavior on wave propagation in rock mass was studied. The piecewise linear loading and unloading models of macrojoint were proposed. Macrojoint and microdefect in rock mass were considered in a framework. Energy and amplitude transmission coefficients were studied in present study.