Wave Impedance Research Articles

Optimization of electromagnetic absorption properties based on graphene, carbon nanotubes, and Fe3O4 multidimensional composites

AbstractExcellent electromagnetic wave loss and impedance matching are typical characteristics of superior‐performance electromagnetic wave (EMW) absorption materials. Changing the component ratios and multidimensional combinations of various absorbing materials is one of the best methods to improve absorption performance. This work used a convenient physical mixing approach to combine three wave‐absorbing materials with various dimensions to successfully prepare Graphene/carbon nanotubes/Fe3O4 (G/C/Fe3O4)/paraffin composites. One‐dimensional (1D) tube carbon nanotubes (CNTs) pierced two‐dimensional (2D) sheet graphene to form a strong three‐dimensional (3D) conductive network, enhancing interfacial polarization without introducing zero‐dimensional (0D) magnetic Nano‐Fe3O4. Nevertheless, because of their significant dielectric characteristics, the graphene/carbon nanotube (G/C) paraffin composites displayed low impedance matching and electromagnetic wave absorption properties. At a mass ratio of 1:1, the G/C/paraffin composites achieved an ideal reflection loss (RL) of −11.99 db and an impedance matching value of 0.59. Adding Fe3O4 improved the impedance matching and electromagnetic wave loss performance and promoted the formation of a non‐homogeneous interface, improving interfacial polarization and reflection. The G/C/Fe3O4/paraffin composite, with a mass ratio of 1:1:6 and a filler ratio of 20%, achieved an optimum reflection loss of −37.2 dB and an effective absorption bandwidth of 4.16 GHz. This work optimized and improved the performance of EMW materials practically and rapidly, providing a research method for the widespread application of superior‐performance electromagnetic wave absorption materials.Highlights The EMW absorption materials with various architectures. 1D CNTs pierced 2D sheet graphene to form a strong 3D conductive network. Adding Fe3O4 promoted the formation of a non‐homogeneous interface. Electromagnetic synergies and different structural combinations It achieved excellent impedance matching and electromagnetic loss performance.

Behavior and design of functionally graded concrete subject to triple impacts of the shaped charge, projectile penetration and explosion

The present issue is how to improve the concrete structure to resist multiple impacts of the tandem warhead. This study developed an approach to design a functionally graded concrete (FGC) structure with fiber-graded (FG) and centralized high-strength aggregates (CHSA) to address this issue. The enhancement of the FG and CHSA in the concrete structure was verified by static mechanical performance tests and dynamic compressive simulation. The behavior of the FGC structure subject to the tandem warhead was investigated by the experimental and numerical dynamic destructive tests, including three stages: shaped charge, projectile penetration and explosion. There are three types of targets, including ultra-high-performance concrete (UHPC), ceramic aggregate reinforced (CAR) FGC and steel aggregate reinforced (SAR) FGC. The results showed that the SAR-FGC had the best multiple-impact resistance in concrete structures. The blocking effect to impact waves was improved by increasing the wave impedance of the anti-penetration layer. Energy absorption was increased by 7 times through the combined action of functional structures to ameliorate damage distribution. The triple destruction depth of it was reduced by 36% compared to UHPC. According to the Forrestal empirical equation, a penetration depth model was proposed for the FGC with jet damage.

Regulating loading strain rates under shockless quasi-isentropic compression using a resin-based areal density gradient flyer

Areal density gradient flyers (ADGFs) have important applications in quasi-isentropic compression and high strain rate loading. The wave impedance gradient distribution of the reported ADGFs is single, and the effects of different wave impedance gradient distributions and spikes number density on the loading results are unknown. In this study, the resin-based ADGFs with different spike areal density distribution and spikes number density were designed and prepared using projection micro stereolithography technology (PμSL). The printing accuracy of ADGFs was evaluated using three-dimensional optical profiler, optical microscope, Scanning Electron Microscopy (SEM) and ultra depth of field microscope. The loading process of the ADGF on the target was studied by experiment and simulation. The simulation result was consistent with the experimental result. Augmenting the wave impedance distribution index (P) of spikes and spikes number density increases the loading strain rate. Due to the high printing accuracy of PμSL, the fine ADGF structures with large spikes number density can be prepared, thereby promoting the formation of quasi-isentropic compression plane waves. This work realizes the regulation of loading strain rate under shockless quasi-isentropic compression, which is significant for understanding the mechanical response of materials under high strain rate loads.

Multi-Scale Dispersion Engineering on Biomass-Derived Materials for Ultra-Wideband and Wide-Angle Microwave Absorption.

Efficient electromagnetic waves (EMWs) absorbing materials play a vital role in the electronic era. In traditional research on microwave absorbing (MA) materials, the synergistic modulation of material dispersion and structural dispersion of EMWs by incorporating multi-scale effects has frequently been overlooked, resulting in an untapped absorption potential. In this study, the material dispersion customization method based on biomass carbon is determined by quantitative analysis. The study carries out thermodynamic modulation of carbon skeleton, micro-nano porous engineering, and phosphorus atom donor doping in turn. The dielectric properties are improved step by step. In terms of structural dispersion design, inspired by the theory of antenna reciprocity, a Vivaldi antenna-like absorber is innovatively proposed. With the effective combination of material dispersion and structural dispersion engineering by 3D printing technology, the ultra-wideband absorption of 36.8GHz and the angular stability of close to 60 ° under dual polarization are successfully realized. The work breaks the deadlock of mutual constraints between wave impedance and attenuation rate through the dispersion modulation methods on multiple scales, unlocking the potential for designing next-generation broadband wide-angle absorbers.

Subwavelength dielectric waveguide for efficient travelling-wave magnetic resonance imaging

Magnetic resonance imaging (MRI) has diverse applications in physics, biology, and medicine. Uniform excitation of nuclei spins through circular-polarized transverse magnetic component of electromagnetic field is vital for obtaining unbiased tissue contrasts. However, achieving this in the electrically large human body poses a significant challenge, especially at ultra-high fields (UHF) with increased working frequencies (≥297 MHz). Canonical volume resonators struggle to meet this challenge, while radiative excitation methods like travelling-wave (TW) show promise but often suffer from inadequate excitation efficiency. Here, we introduce a new technique using a subwavelength dielectric waveguide insert that enhances both efficiency and homogeneity at 7 T. Through TE11-to-TM11 mode conversion, power focusing, wave impedance matching, and phase velocity matching, we achieved a 114% improvement in TW efficiency and mitigated the center-brightening effect. This fundamental advancement in TW MRI through effective wave manipulation could promote the electromagnetic design of UHF MRI systems.

Teaching acoustic and electromagnetic waves

Students have observational experience with waves by speaking and hearing, seeing, and feeling but their use of mathematics may be delayed until introductory physics at middle school, high school, and/or college. Students following a university physics or engineering bachelor’s degree are usually required to take a course on electromagnetic wave theory because of the foundational science and/or applications such as communications and observation. Regrettably, it is common that a mathematical description of various wave propagations may be acquired but without a thorough understanding of the underlying physics – especially in electromagnetics. Thus, we have tried to develop an introductory graduate level course that teaches electromagnetics and optic waves and its applications on the foundation of first understanding acoustics. This serves as a preparation for research or vocation. Topics include traveling waves, standing waves, wave impedance, radiation patterns, interference, interferometry, sonar and radar, imaging, waveguides in more. Examples of introducing the mathematics of solution first and then derivations of wave equation is presented. The goal is that mathematics should be a useful language to communicate physical information and that acoustic demonstrations should reinforce learning in multiple physical modalities.

Picking of weak signal in seismic exploration of non-coal solid mines based on phase-locked technology

The exploration and development of mineral resources are of crucial significance to national economy, people's livelihood and national security. Therefore, in order to extract the weak signal in seismic exploration of non-coal solid mines in shallow surface layer to achieve high-resolution exploration, the mathematical model and physical model of multiplier are established by referring to the frequency point acquisition technology in wireless radar communication, that is, phase-locked technology. The weak effective seismic signals of different frequency points are picked out from the collected 120 dB dynamic range spectrum, and the information of stratigraphic structure under high noise background is obtained more effectively by using mixing detection and two-phase demodulation technology in the harmonic component spectrum, thereby improving the high resolution and high precision of mineral exploration. The lock-in amplifier is added to the front stage of the seismograph to obtain the effective seismic wave reflected by the wave impedance interface required in the exploration task. Experimental results show that this method significantly improves the SNR and protects the weak effective signal from loss. It adds new technology and method to seismic signal acquisition and processing, and provides a new way to obtain high-quality seismic data in the field of mineral geophysical exploration, and will be widely used after being promoted in the fields of mineral exploration, geological disaster prediction, military geophysics, and archaeology.

Influence of surface wave impedance ratios on the dynamic response and damage characteristics of slopes based on shaking table tests

Weathered slopes are often severely damaged during earthquakes, posing challenges to the study of their dynamic response and damage characteristics. In this study, we conducted physical modelling tests using the wave impedance ratio to investigate the influence of weathering layers on slope dynamics through shaking table tests. Model A utilized unweathered rock as a reference, while models B, C, and D included different weathering layers distinguished by varying wave impedance ratios. By comparing the peak acceleration amplification factors (AAFs) of the four models, we found that the AAF increases with increasing wave impedance ratio on the slope surface. Slopes with wave impedance ratio layers exhibited strong dynamic responses above 2/3 of the slope height, with both wave impedance ratio layers and elevation effects playing crucial roles. Further analysis using the Hilbert–Huang transform revealed wider excitation frequency ranges at the top of models B, C, and D than at the top of model A, resulting in resonance effects and significant damage in the top regions of models with higher wave impedance ratios and lower damping ratios. Furthermore, different damage patterns were observed, with the homogeneous model exhibiting a vibration crack–slip mode, while slopes with wave impedance ratio layers experienced cracking, crushing, and debris slipping at the top. This study provides new insights into the dynamic response analysis and stability evaluation of weathered slopes in active tectonic zones.

Waveform Imaging Based on Linear Forward Representations for Scalar Wave Seismic Data

The current reverse-time migration, which is based on wave equations for imaging wavefields, employs an imaging formula derived from Claerbout’s imaging principle. This imaging formula is only valid for plane waves with small incident angles on the perfectly flat reflecting surface. However, the complexity of seismic wave propagation may lead to situations that do not meet this requirement. Therefore, this paper divides the subsurface into local scattering and reflecting bodies. It proposes linear forward representations for scattering and reflection data based on perturbations in the physical parameters and wave impedance, respectively. To further describe the effect on the reflecting body boundary, the local reflection coefficient is defined and the linear forward representation for the reflection data based on it is obtained. After that, the proposed linear forward representations are used as the forward equations for the linear inverse of the seismic data, and the seismic data waveform imaging method is developed based on linear inversion theory. At the same time, the specific waveform imaging calculation formulas for scalar wave scattering data and scalar wave reflection data are provided and validated via numerical experiments. Compared with the current reverse-time migration, waveform migration not only has the correct phase and higher resolution in theory but also does not increase the computational complexity. To some extent, it improves the deficiencies of the current structural imaging and provides a basis for subsurface lithological imaging.

Fine characterization of interbedding sand-mudstone based on waveform indication inversion

Abstract Owing to the increasing challenges associated with coal mine exploration and development, extremely precise surveys with high-resolution images are required to support production. Conventional inversion methods cannot provide sufficiently precise images of the complex lithologies in coal measure strata. Accordingly, this study performed research in Qiyuan mining area, Shanxi Province, China, and predicted the complex lithology on the basis of facies control using waveform indication inversion and waveform indication simulation. Horizontal changes in seismic waveforms were used to reflect lithologic assemblage characteristics for facies-controlled constraints, and the vertical mapping the connection between seismic waveform and logging curves was shown. Moreover, high-resolution inversions of wave impedance and natural gamma parameters were conducted. Combined with lithologic shielding and accurate time–depth conversion, the inversions enabled the precise characterization of the lithological assemblage distribution in the study area. Our results showed that waveform indication inversion could distinguish between coal seams and limestone, whereas waveform indication simulation based on natural gamma could effectively distinguish between sandstone and mudstone. Furthermore, the horizontal resolution was improved and the vertical resolution extended to a thickness of 2–3 m. In addition, the inversion results were highly consistent with drilling results, with an error <0.1 m. Therefore, waveform indication inversion and simulation could be applied to coal mines for safe and efficient production.

Seismic vulnerability signal analysis of low tower cable-stayed bridges method based on convolutional attention network

Abstract Due to the particularity and complexity of sedimentary environments, the wave impedance differences between different reflection interfaces in underground media may vary greatly. Therefore, an encoder–decoder neural network is proposed to enhance erroneous seismic weak reflection signals. The convolutional neural network (CNN) has the problem of difficulty in parallel computing, resulting in slow network training and computational efficiency. Considering that attention has an innate global self-attention mechanism, can compensate for long-term dependency deficiencies, and has the ability to perform parallel computing, which greatly compensates for the shortcomings of CNNs and recurrent neural networks, a seismic impedance inversion method based on convolutional attention networks is proposed. To improve the ability to extract noise, residual structure and convolutional attention module (CBAM) were introduced. The residual structure utilizes residual jump to weaken network degradation and reduce the difficulty of feature mapping. The CBAM uses a mixed attention weight of channel and space, which can enhance features with high correlation and suppress features with low correlation. In the decoder, in order to improve the dimension recovery ability of feature fusion, bilinear interpolation is selected for upsampling. The application results of the model and actual data indicate that this method can effectively enhance the weak reflection signals caused by the formation itself and improve the reservoir identification ability of seismic data.

An electromagnetic Hopkinson bar for low wave impedance material and complex stress paths loading tests

The split Hopkinson bar has been widely used for testing the dynamic mechanical properties of various materials. However, there are still difficulties in ensuring stress uniformity when testing some low wave impedance materials such as soft materials and brittle materials and difficulty in achieving true multi-axial and multi-directional synchronous loading experiments and other issues. To overcome these issues, this paper uses an electromagnetic Hopkinson bar for experimental research and introduces its principle and implementation process. Finite element analysis and experimental methods were used to verify the feasibility of the electromagnetic Hopkinson bar in addressing the relevant issues. The superiority of the new device was demonstrated by its capability in performing compression experiments on two typical low wave impedance materials: polymethacrylates (PMMA) and polyurethane (PU), and two-way tension experiments on 2024 aluminum alloy. The results indicate that the electromagnetic Hopkinson bar can effectively solve the problem of uniform stress in low wave impedance materials testing, and can achieve synchronous loading of complex stress paths.

Wave-absorbing performance of alumina thin-walled hollow particles under freezing condition

The reliability of the absorbing layer is crucial for realizing protective engineering’s protection function. However, the typical wave-absorbing material, sand, is unable to fulfill its intended wave-absorbing function in areas with seasonally frozen soil. This is because the internal pores of the material become filled with ice and the particles freeze. To address this issue, alumina thin-walled hollow particles were chosen as a new wave-absorbing material. These particles can introduce the gas phase into the absorbing layer which is essential for attenuating the stress waves and its wave-absorbing capacity under freezing conditions was investigated by the split Hopkinson bar (SHPB) test. According to the test data, the alumina thin-walled hollow particles are less dense than sand and have a lower wave impedance, allowing them to reflect more incident energy. Moreover, these particles have a better capacity for dissipating the absorbed energy, as compared to sand. Under freezing circumstances, the average transmittance coefficient of alumina thin-walled hollow particles is only 21.95% to 49.30% of ordinary sand. Additionally, the particle size positively correlates with the capacity for wave-absorption. The capacity of alumina thin-walled hollow particles to shatter and release the gas phase under impact stress significantly increases the compressibility of the absorbing layer under freezing conditions, which accounts for their enhanced wave-absorbing effectiveness. The stress-strain curve specifically manifests as a smoother curve and a longer stage of plastic energy dissipation. Other than that, the dynamic deformation modulus of the material and peak stress is lower, while the peak strain is larger. The findings of this study provide a low-cost, high-reliability solution to the problem of frost damage in the absorbing layer in regions with seasonal freezing.

A review on PZT in civil engineering

Civil engineering is not just about construction of buildings, towers, bridges etc. but also of their caring and maintenances. For this purpose all the constructed structures have to be monitored for their structural health in terms of damage detection, severity of damage etc., collectively called structural health monitoring (SHM) of structures in civil engineering. For SHM, electromagnetic impedance (EMI) technique is one of the best methods of NDTs being used in the field of civil engineering. EMI uses lead zirconate titnate (PZT) as its piezoelectric component for the purpose of measurement. PZT based devices are widely used in civil engineering. There is a huge demand for health monitoring now a days and to full fill those demands of health monitoring, PZT is one among the most reliable and cost efficient material. Piezoelectric sensor can be used to measure changes in acceleration, strain, pressure and to ensure the better safety measures. These PZT based sensors can be used for predicting the natural disasters like earthquake that helps to save the thousands of lives and can decrease property lose. The piezoelectric sensors can be used to monitor the civil structure which helps an engineer to analyses the characteristics of that structure. It is also used for collecting the data of force that is being exerted on the ground by the building, temperatures and pressure differences in environment etc. Damage detection is a technique that is used to monitor the civil structure, this can improve safety and ensure durability, and for concrete structures, damage detection plays an important role. For the purpose of SHM and damage detection PZT based sensors can be used. For civil engineering applications, PZT-cement based composites have been developed. The concrete and host structure such PZT-cement based composites shows better matching when compared to normal or other piezoelectric ceramics. In this review work we have discussed about SHM/Damage detection, Vibrational control, PZT embedded cement composites and PZT embedded in concrete.

High-Frequency Electromagnetic Behavior, Impedance Modeling, and Enhancement of Low-Permeability Powder Cores

High-Frequency Electromagnetic Behavior, Impedance Modeling, and Enhancement of Low-Permeability Powder Cores

Application of a quantum wave impedance approach for a set of delta-potentials in 1D

Application of a quantum wave impedance approach for a set of delta-potentials in 1D

Wave Impedance Equivalent Circuit Model for Square Loop Frequency Selective Surfaces

Wave Impedance Equivalent Circuit Model for Square Loop Frequency Selective Surfaces

Metasurfaces for Resonant Tunneling Diodes with Double Metal Waveguides

The paper proposes designs of distributed resonant tunneling diodes (RTDs) with a double metal waveguide (DMW), in the top electrode of which a periodic pattern (metasurface) is formed based on holes in a hexagonal array and a chain of slotted (split-ring) resonators. This solution will make it possible to control the phase velocity of the propagating wave and increase the wave impedance in order to reduce ohmic losses in the waveguide, as well as to create a generation mode in it. For the proposed designs of metasurfaces, electromagnetic modeling was carried out and the input impedances of the resonators were calculated.

Component modulation and integrated multidimensional heterostructures of bimetallic MOFs derived 0D Co3ZnC/Co encapsulated in 2D CNTs-grafted 3D N-doped porous carbon polyhedron for high-efficient microwave absorption

Component modulation and multidimensional structural design are effective strategies to regulate the electromagnetic parameters and impedance matching, resulting in high-efficient microwave absorption. Herein, multidimensional integrated Co3ZnC/Co@C heterostructures compounding of 0D Co and Co3ZnC NCs, 1D CNTs and 3D porous carbon polyhedrons were fabricated by pyrolysis of bimetallic MOFs. Co and Co3ZnC NCs are uniformly encapsulated in CNTs-grafted porous carbon polyhedrons, forming 0D-1D-3D integrated heterostructures. The Co3ZnC/Co@C composites show component-modulated electromagnetic parameters and microwave absorption properties, which can be simply regulated by adjusting the ratio of Co/Zn in the MOFs precursor. With a filling ratio of 30 wt%, the optimal Co3ZnC/Co@C heterostructures show a minimum reflection loss (RL) value of −66.78 dB at 7.43 GHz with a thickness of 4.5 mm, located at the C band. The maximum effective absorption bandwidth (RL≤−10 dB) is up to 4.8 GHz (12.9–17.7 GHz) at only 2.0 mm. The high-efficient microwave absorption performance is attributed to that the multidimensional integrated heterostructures can sufficiently maximize the synergistic effects of each component. The uniformly distributed 0D Co and Co3ZnC NCs can promote magnetic loss and interfacial polarization. 1D CNTs are beneficial to enhance the conductive loss. 3D porous carbon polyhedrons grafted with CNTs are favored to promote the scattering of microwaves and impedance matching. These findings suggest a new insight to achieve high-performance microwave absorption by modulating the component and integrating multidimensional structures.

Justification of the need to build underground substations and power lines

This work is aimed at finding the world experience in the creation of underground high-voltage substations, identifying their organisational features and solutions to ensure the most efficient operation modes. The positive and negative aspects of this approach are considered. The article identifies operational characteristics that can have a significant impact on substation operations, complicate the design process, and change the rules for selecting equipment for facilities. The experience of Western and Eastern colleagues in this area is analysed. Much attention is paid to the Xudong underground substation with a rated voltage of 220 kV in the Hubei power system, which is the first underground substation in central China. The same example reveals the peculiarities of organising an underground substation in urban areas. The article considers the peculiarities of organising underground substations near rivers, where groundwater complicates the design. Based on the examples considered, possible measures and changes in the design of typical substations to create new underground configurations are analysed. A comparison of the efficiency of phase convergence is made and the dependencies and conditions under which a significant change in the efficiency of electricity transmission on the territory of substations are established. The effect of using phase convergence on the bandwidth and wave impedance of conductors is determined. The positive impact of underground operating conditions on most elements of the system is established. The analysis of operating conditions and the use of efficient configurations allowed us to find potentially the most promising ways to implement underground substations. A reasonable range of measures to influence individual elements of the underground substation, based on the operating conditions, to ensure the most efficient configuration in terms of capacity and thermal conditions of the equipment is proposed.