Wave Transmission Characteristics Research Articles

Model for Restoring Obstructed Beam Transmission in Atmospheric Turbulence Based on BP Neural Network

Atmospheric turbulence and obstacles can distort rays during transmission, resulting in significant wavefront distortion and loss of optical field information. This paper employs the phase screen method to simulate the transmission characteristics of a Gaussian plane wave in turbulent conditions, establishing an obstacle grid at the receiver to represent beam obstruction. A dataset of unobstructed transmissions is used to train a Backpropagation Neural Network, constructing neurons and connection weights. By scanning optical field data systematically, the model compensates for the obstructed portions of the optical field distribution. The results are compared to unobstructed transmissions, focusing on image similarity, and demonstrate the entire process from compensation to distortion correction. Simulation results indicate that the Backpropagation Neural Network effectively compensates for optical field information loss, showcasing strong performance within a certain time scale.

Research on the mechanism of electromechanical coupling response of pulse power multilayer ceramic capacitors under high impact and high voltage discharge composite environment

Pulse power multilayer ceramic capacitors (pulse power-MLCC) are commonly used in complex composite environments with high overload and high voltage due to their large size and capacitance. In order to study the electromechanical coupling response characteristics of pulse power-MLCC in high-impact and high-voltage composite environments, a split Hopkinson pressure bar (SHPB) testing system was used to simulate high impact. The mechanical and electrical parameters of pulse power-MLCC were collected under high-impact and voltage environments, and the capacitance changes at different impact velocities were obtained. The stress wave transmission characteristics of pulse power-MLCC were studied by combining numerical simulation and theoretical analysis, and the structural deformation of ceramic dielectric under impact stress was analyzed. The relationship between the capacitance and DC bias of the capacitor was analyzed. A capacitance calculation model for pulse power-MLCC in an electromechanical coupling environment was established, revealing the electromechanical coupling mechanism of pulse power-MLCC.

Measurement Method of Stress in High-Voltage Cable Accessories Based on Ultrasonic Longitudinal Wave Attenuation.

High-voltage cables are the main arteries of urban power supply. Cable accessories are connecting components between different sections of cables or between cables and other electrical equipment. The stress in the cold shrink tube of cable accessories is a key parameter to ensure the stable operation of the power system. This paper attempts to explore a method for measuring the stress in the cold shrink tube of high-voltage cable accessories based on ultrasonic longitudinal wave attenuation. Firstly, a pulse ultrasonic longitudinal wave testing system based on FPGA is designed, where the ultrasonic sensor operates in a single-transmit, single-receive mode with a frequency of 3 MHz, a repetition frequency of 50 Hz, and a data acquisition and transmission frequency of 40 MHz. Then, through experiments and theoretical calculations, the transmission and attenuation characteristics of ultrasonic longitudinal waves in multi-layer elastic media are studied, revealing an exponential relationship between ultrasonic wave attenuation and the thickness of the cold shrink tube. Finally, by establishing a theoretical model of the radial stress of the cold shrink tube, using the thickness of the cold shrink tube as an intermediate variable, an effective measurement of the stress of the cold shrink tube was achieved.

Reflection and transmission characteristic waves on the periodic rough interface of fluid-porous medium

Abstract Nondestructive testing (NDT) is a major method in practical applications such as material exploration and safety assessment. The interaction of ultrasonic waves with roughness material is crucial in NDT, thus the related ultrasonic diffraction theory at the rough interface is widely investigated and analyzed, especially for the periodic elastic medium interface. However, the actual surface is usually porous due to the long-term moisture infiltration. In this paper, the reflection and transmission characteristics of ultrasonic waves on the fluid-porous medium periodic rough surfaces are studied in details.

Mass-spring model for elastic wave propagation in multilayered van der Waals metamaterials

Multilayered van der Waals (vdW) materials have attracted increasing interest because of the manipulability of their superior optical, electrical, thermal, and mechanical properties. A mass-spring model (MSM) for elastic wave propagation in multilayered vdW metamaterials is reported in this paper. Molecular dynamics (MD) simulations are adopted to simulate the propagation of elastic waves in multilayered vdW metamaterials. The results show that the graphene/MoS2 metamaterials have an elastic wave bandgap in the terahertz range. The MSM for the multilayered vdW metamaterials is proposed, and the numerical simulation results show that this model can well describe the dispersion and transmission characteristics of the multilayered vdW metamaterials. The MSM can predict elastic wave transmission characteristics in multilayered vdW metamaterials stacked with different two-dimensional (2D) materials. The results presented in this paper offer theoretical help for the vibration reduction of multilayered vdW semiconductors.

Comprehensive analysis of band gap modulation of hexagonal fan blade and optimized ligament structure in the low-frequency range

This paper proposed a meta material model with low-frequency wide band gap and band gap tunability, optimized its structure as a multibranch chain structure, and analyzed the band gap relationship of above two models based on Brag's theorem and finite element method. Among them, the fan base structure has a band gap of 65.92 % within 20,000 Hz, and the band gap is optimized to low-frequency after the structure is optimized, and the band gap reaches 75.94 % within 10,000 Hz. The effects of the ligament width and the thickness of the center parcel layer on the band gap distribution of the structure are also discussed, and the wave transmission characteristics in the structure are explored by group and phase velocities to verify the acoustic performance of the structure. The results show that the smaller the ligament thickness is, the lower the first band gap opening frequency of the structure is; when the thickness of the central wrapping layer is increased, the structure develops the band gap at the center frequency of 3000 Hz to a lower frequency and generates an ultra-wide band gap at the center frequency of 6000 Hz. These findings can provide a new idea for low-frequency vibration isolation and noise reduction.

Terahertz wave propagation characteristics in SMM-based three-dimensional plasma fluid

During the return to the atmosphere of a hypersonic vehicle in adjacent space, a plasma sheath forms on the surface of the vehicle, which blocks normal electromagnetic communications. The ‘blackout’ phenomenon caused by plasma sheaths has received much attention. This paper focuses on the American RAM-C vehicle as the research object, and utilizes the fluid simulation software USim to numerically simulate the pressure, temperature, and electron density under different flight conditions, and based on the simulation results, selects the appropriate electron density and plasma collision frequency, introduces the terahertz (THz) wave, and adopts the scattering matrix method (SMM) to study the propagation characteristics of the vertically incident non-uniform magnetized plasma with the terahertz wave. Among other things, the transmission characteristics of terahertz waves in the plasma are affected by the flight altitude and flight angle of attack of the vehicle. The conclusions indicate that the transmissivity of terahertz wave transmission in plasma increases, and the reflectivity and absorptance decrease with increasing flight altitude and flight angle of attack. Under the condition of controlling other flight parameters unchanged, the plasma frequency and collision frequency decrease with the increase of flight altitude. The larger the flight angle of attack is, the larger the plasma frequency and collision frequency are. The electron density on the wall surface of the vehicle was also tested, and it was found that the lowest electron density was found at the tail end of the leeward surface. This study can provide some theoretical references for mitigating the ‘blackout’ phenomenon of re-entry vehicles.

A numerical study on machine-learning-based ultrasound tomography of bubbly two-phase flows

Ultrasound tomography (UT) of bubbly two-phase flows using machine learning (ML) was investigated by performing two-dimensional ultrasound numerical simulations using a finite element method simulator. Studies on UT for two-phase flow measurements have been conducted only for some bubbles. However, in an actual bubbly flow, numerous bubbles are complexly distributed in the cross-section of the flow channel. This limitation of previous studies originates from the transmission characteristics of ultrasound waves through a medium. The transmission characteristics of ultrasound waves differ from those of other probe signals, such as radiation, electrical, and optical signals. This study evaluated the feasibility of combining UT with ML for predicting dense bubble distributions with up to 20 bubbles (cross-sectional average void fraction of approximately 0.29). We investigated the effects of the temporal length of the received waveform and the number of sensors to optimize the system on the prediction performance of the bubble distribution. The simultaneous driving of the installed sensors was simulated to reduce the measurement time for the entire cross-section and verify the method’s applicability. Thus, it was confirmed that UT using ML has sufficient prediction performance, even for a complex bubble distribution with many bubbles, and that the cross-sectional average void fraction can be predicted with high accuracy.

Experimental investigation on the hydrodynamic performance of an inverted trapezoidal breakwater

ABSTRACT The wave transmission, reflection, and dissipation characteristics of conventional (trapezoidal (TBs)) and non-conventional (inverted trapezoidal (ITBs) and rectangular (RB)) breakwaters with the same volume and porosity are evaluated under different submergence ratios, wave heights, and wave periods in regular and random waves. The experimental investigation revealed that the ITB shape is the most efficient cross section for reducing wave transmission coefficient (Kt) when the breakwater is submerged or the still water level (SWL) is at the crest of the breakwater, whereas the conventional TB is the least efficient. Compared to the conventional TB, the ITB reduced Kt by 10%–20% under submerged conditions and by 20%–30% when the SWL is at the breakwater crest. Kt < 0.2 is obtained for a relative water depth d/Lp > 0.2, which is suitable for most wave damping applications in the field when the ITB crest is at the SWL or when the crest emerges.

Non-destructive testing of reinforced concrete structures using sub-terahertz reflected waves

Terahertz (THz) and sub-terahertz (sub-THz) waves are unexplored waves between the infrared and microwave ranges. This range features unique characteristics of both light resolution and electromagnetic wave transmission. Sub-THz waves are part of attractive new diagnostic methods for inner objects because they are safer than normal non-destructive inspection methods involving high energy, such as X-rays. In this study, a novel non-contact and non-destructive inspection method for reinforced concrete (RC) structures using sub-THz reflection imaging is proposed to inspect the deterioration of inaccessible damaged RC structures. The results of this study confirmed that the proposed sub-THz imaging method can detect cracks and voids in concrete, as well as in metals inside or behind the concrete, based on differences in reflectance. In addition, the camera-based measurement system makes real-time on-site field measurements possible.

SO-FDTD simulation on the transmission characteristics of terahertz waves in inhomogeneous magnetized dusty plasma

SO-FDTD simulation on the transmission characteristics of terahertz waves in inhomogeneous magnetized dusty plasma

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Frequency-selective coherent propagating spin waves induced by localized perpendicular magnetic anisotropy nanofilm stack

Magnonics has long been hailed as a promising technology poised to overcome the heat dissipation challenges in traditional electronic devices. With the escalating integration level of magnon devices, the demand arises for lower external field excitation conditions, coupled with enhanced coherence and frequency-selective excitation characteristics. In this proposal, we suggest introducing a localized perpendicular magnetic anisotropy nanofilm stack into the spin-wave transmission channel to finely regulate the propagation characteristics of spin waves. This adjustment can be achieved by altering the width and period of the stack in both horizontal and vertical dimensions. Additionally, the optimal transmission characteristics of spin waves are achieved at low frequencies (1–1.67 GHz) and in the presence of small magnetic fields (0–20 mT). Frequency-selective spin waves with triggering stability can effectively prevent signal folding resulting from changes in microwave power within the range of −30 to 0 dBm. At 1.08 GHz, the group velocity of frequency-selective spin waves can be increased by up to 2.86 times. This innovative method of regulating spin waves presents a potential alternative pathway for the development of future magnonic circuits.

Utilizing Wavelet Transforms for Analysis of Transmission Characteristics of Water-Hammer Vibration Waves in Pipelines Installed in Soil, Water, or Air Environments

Utilizing Wavelet Transforms for Analysis of Transmission Characteristics of Water-Hammer Vibration Waves in Pipelines Installed in Soil, Water, or Air Environments

The effects of joint spacing on transmission characteristics of stress waves through layered composite rock masses

AbstractThe effects of joint spacing on the transmission characteristics of stress waves through layered composite rock masses were investigated. First, a model of layered composite rock masses containing multiple parallel joints with different media in front of and behind the joints was introduced to study multiple reflections between joints. Second, wave transmission through layered composite rock masses was investigated and compared with wave transmission through traditional layered homogeneous rock masses. Finally, the effects of joint spacing and wave impedance ratio on particle velocity transmission coefficient were discussed. The results indicate that for wave propagation through rock masses with the same joint spacing, the onset time and amplitude of the transmitted wave in layered composite rock masses are smaller than those in layered homogeneous rock masses. For wave transmission through rock masses with the same nondimensional joint spacing, the onset time of the transmitted wave in the layered composite rock masses is similar to that in the layered homogeneous rock masses, while the amplitude of the transmitted wave in the layered composite rock masses is smaller than that in the layered homogeneous rock masses. In addition, the particle velocity transmission coefficient first increases and then decreases to be constant as the joint spacing increases, while it continues to increase as the wave impedance ratio increases for wave transmission through both layered composite rock masses and layered homogeneous rock masses.

Study on wave propagation in the modulation structure with gradually changing impedance according to specific waveform based on magneto-rheological fluid

This work proposes a novel hierarchical modulation structure with gradually-changed impedance built by magneto-rheological (MR) fluid and investigates its wave propagation characteristics theoretically and experimentally. Based on the impedance tunable property of the MR fluid, applying multiple magnetic fields to MR fluid realizes the modulation of this proposed structure, and regulating its magnetic field distribution law can effectively change the impedance variation forms in the structure. Establish the elastic wave propagation model of this modulated structure, and analyze the variation trends of its elastic wave propagation characteristics with different impedance distribution patterns, taking the vibration level difference as an indicator. Subsequently, conduct experimental testing for the transmissibility of elastic waves. The results show that the elastic wave transmission characteristics of the proposed modulation structure mainly depend on its impedance variation rate and the frequency of external excitation. On a broader band of the frequency range (20–300 Hz) studied in this paper, the gradual impedance distribution of MR fluid enhances the transmission loss of elastic waves compared to a uniform distribution of its impedance. Moreover, in the lower frequency range (40–125 Hz), the layered modulation structure with a non-monotonic variation of impedance following a wave-like waveform presents more significant attenuation on elastic waves than the structure whose impedance varies monotonously in a gradient waveform. This work contributes to expanding the design thoughts of the structure with gradually changing impedance and providing new ideas and means for the control of elastic waves.

Study on transmission and reflection characteristics of plane S1 wave at the interface between saturated frozen soil and elastic solid bedrock

Based on the propagation theory of elastic waves in frozen poroelastic media and elastic media, a theoretical model of saturated frozen soil and elastic solid bedrock is established. The saturated frozen soil is lying on an elastic solid bedrock and is modeled as a porous material containing a three-phase medium that contains two solids (soil skeleton and ice particles) and a compressible viscous fluid. Based on the Helmholtz vector decomposition and the boundary conditions on the interface, the theoretical expressions of the amplitude ratio and displacement of the plane S1 wave incident from the saturated frozen soil to the elastic solid bedrock interface are obtained. The effects of incidence angle, frequency, cementation parameters, saturation, and contact parameters on amplitude ratio and displacement were investigated. The results indicate that only S wave and horizontal displacement exist when the incident angle [Formula: see text] = 0°. As cementation parameters, saturation, porosity, and contact parameters increase, the critical angle appears earlier. Each wave has different degrees of pulses when reaching the critical angle, among which the transmitted P wave and the reflected S2 wave are the most significant. At higher saturation, it is observed that the amplitude ratio of the reflected S2 wave decreases significantly. The horizontal and vertical displacements increase significantly with increasing frequency.

3D Computational Fluid Dynamic Investigation on Wave Transmission behind Low-Crested Submerged Geo-Bag Breakwater

Wave transmission characteristics behind low-crested submerged breakwaters involve complex-hydrodynamic interaction of water waves on the structures. To properly comprehend the induced-nonlinear wave transformation, the problem necessitates a trustworthy prediction using a computational fluid dynamic (CFD) technique. The goal of this study is to develop a three-dimensional (3-D) computational model of the hydrodynamic performance of a narrow crest behind a submerged breakwater in order to gain a thorough understanding of the wave transmission coefficient, K_t. The simulation took into account a number of wave parameters such as wave steepness (H_i⁄L), relative submergence depth (H_i⁄h), and crest width (c_w⁄L) of the structure. A numerical wave flume model is included, which is based on the full Navier-Stokes solver and includes a shallow water model to account for nonlinearity in the incident wave field. In addition, laboratory measurements were also conducted using a geo-bag dike model as the main breakwater structure. The result shows that the reduction in transmission coefficient correlates highly with the wave steepness and the relative submergence and crest parameters. This can be attributed to most breaking waves over the submerged breakwater. The steeper the incident wave, the greater the reduction in the transmitted wave. And, the greater the principal dimensions of the breakwater, the greater the drop in transmission coefficient. For validation, the CFD results corroborate satisfactorily with measurements

Analysis of electromagnetic waves reflected by re-entry plasma sheath based on CSO-FDTD

A transmission model of terahertz waves in the plasma sheath is established based on a cascaded finite time domain difference method and analyzed the transmission characteristics of electromagnetic waves under the action of an external magnetic field and collision frequency. The flow field around the hypersonic aircraft is simulated and the characteristics of the flow field as the altitude changes of the aircraft are analyzed based on the flow field distribution of the RAM-C (Rapid Attenuation Measurement) vehicle. The results show the transmission characteristics of terahertz waves in plasma that will be affected by flight height, plasma parameters, external magnetic field, and collision frequency. In addition, under the action of an external magnetic field and the different collision frequency, the transmission characteristics of the left-handed terahertz wave will be improved. The application of the magnetic field will introduce an absorption peak in the right-handed terahertz wave, and it will move to the high frequency direction with the increase of the magnetic induction intensity.

Analysis of transmission and reflection characteristics of linear plane waves in pantographic lattices

Analysis of transmission and reflection characteristics of linear plane waves in pantographic lattices