Wave Impedance Research Articles

The angular distribution of characteristic parameters in eccentric magnetically insulated transmission lines

In pulse power modules designed with linear transformer driver (LTD) and magnetically insulated inductive voltage adder (MIVA) technologies, the phenomenon of electrode eccentricity in long-distance magnetically insulated transmission lines (MITLs) cannot be overlooked due to its impact on pulse power transmission. The paper conducts a theoretical analysis of the distribution of electromagnetic fields, vacuum impedance, and characteristic parameters such as self-limited flow in eccentric MITLs with respect to the angular direction. Additionally, it constructs an eccentric MITL model to validate the theoretical findings.

Anti-ballistic properties of hybrid UHMWPE fiber-reinforced composite armour

The ballistic performance of three hybrid composite plates, including ultra-high molecular weight polyethylene (UHMWPE), UHMWPE/Aramid, and UHMWPE/CFRP with similar surface density, was studied in the paper. These plates were tested under the impact of 7.62×25 mm full metal jacket (FMJ) bullets, with the dynamic back deformation (BFD) captured using Digital Image Correlation (DIC) technology. The effects of material combinations and striking faces on the dynamic response were discussed. The deformation and penetration mechanisms were analyzed using optical microscopy and micro-CT tomography. The results indicated that the UHMWPE/CFRP plate exhibited the lowest BFD, followed by UHMWPE and the UHMWPE/Aramid plate. When UHMWPE severed as the striking face, the fibers underwent through-thickness compression, which transitioned to in-plane tension and led to an elongated fracture of yarns. Similarly, Aramid fibers also experienced tensile fractures under similar conditions. In contrast, carbon fibers had brittle shear fractures when CFRP was the striking face. Additionally, the “V-shaped” cone traveling hinge velocity was calculated using DIC results, and the effects of the plate bending stiffness and wave impedance on protective performance were discussed. The findings emphasize the importance of an optimal material configuration to mitigate the propagation of compressive waves in the thickness direction and enhance bending stiffness, which is crucial for improving protection within ballistic limits.

Singular Points of the Radiation Spectrum of Leaky Surface Magnon Polarons

Within the dissipation-free approach, for a magnetic layer separating two semi-bounded ideal fluids, it is shown that, at the point of the phonon radiation spectrum where leaky surface magnon polarons of the “dark” state are formed (of interference or symmetry-protected type) at the interface with an acoustically less dense medium, both the numerator and the denominator of the input wave impedance can independently become zero (at the very point of existence of a bound state in the continuum, they vanish simultaneously). The calculation was performed for a two-sublattice model of an antiferromagnet, which simultaneously takes into account magnetoelastic, inhomogeneous exchange, and hyperfine coupling. Conditions have been found under which the mechanisms of formation of bound states in the spectrum of phonon radiation of leaky magnon polarons involving quasi-electronic or quasi-nuclear magnons are fundamentally different: elastodynamic or elastostatic.

Effect of coarse aggregates on contact explosion resistance of concrete—A mesoscopic investigation

The intricate relationship between the mechanical properties of concrete and its internal microstructure underscores the importance of comprehending explosion performance and damage mechanisms at a mesoscopic level to effectively enhance blast resistance. This study employed three-dimensional (3D) mesoscale models to numerically investigate the dynamic behavior of concrete mixed with coarse aggregates under contact explosion. Rigorous validation of numerical models and simulation techniques was untaken through the contact explosion tests. The study explored mesoscopic damage mechanisms in heterogeneous concrete targets with randomly distributed coarse aggregates, drawing comparisons with a homogeneous concrete target. Critical mesoscopic parameters influencing the contact explosion resistance of concrete were thoroughly examined. Structural effects of coarse aggregates emerge as pivotal, shifting the damage mode from overall failure with spalling-dominated damage in homogeneous concrete to localized failure in mesoscopic concrete. The mesoscopic concrete experienced a distinct four-stage damage evolution—cratering, crack initiation, perforation, and dynamic fragmentation—diverging from homogeneous concrete with multi-layer spalling originating from the boundaries. The exponential attenuation of shock waves observed in homogeneous concrete was locally disrupted by coarse aggregates in mesoscopic concrete, attributed to wave impedance mismatch and aggregate extrusion effects. Mortar strength primarily contributed to concrete cracking, with minimal impact on damage modes. Failure modes were predominantly influenced by the content and particle size of coarse aggregates. Higher volumetric fractions significantly reduced concrete spalling, while increased coarse aggregate size exacerbated perforation failure. This comprehensive study advances our understanding of blast-resistant concrete design at a mesoscopic level, providing valuable insights for strategies aimed at enhancing structural resilience.

Shock Waves in Nonlinear Transmission Lines

In the first half of the article, interaction between the small amplitude travelling waves (“sound”) and the shock waves in the transmission line containing both nonlinear capacitors and nonlinear inductors is considered. Herein, the “sound” wave coefficient of reflection from (coefficient of transmission through) the shock wave is calculated. These coefficients are expressed in terms of the speeds of the “sound” waves relative to the shock and the wave impedances. In the second half of the article, the dissipation in the system is explicitly included into consideration, introducing Ohmic resistors shunting the inductors and also in series with the capacitors. This allows us to justify the conditions on the shocks, postulated in the first half of the article. This also allows us to describe the shocks as physical objects of finite width and study their profiles, same as the profiles of the waves closely connected with the shocks—the kinks. The profiles of the latter, and in some particular cases, the profiles of the former are obtained in terms of elementary functions.

Collaborative Seismic Impedance Inversion under Bayesian Parameter Estimation

Abstract At present, the industry mainly divides seismic inversion methods into deterministic inversion and deterministic inversion based on the methods and principles used in inversion. There are two types of geostatistical inversion. Deterministic inversion is the process of directly modifying the model quantity through optimization algorithms under given initial constraint conditions to obtain a definite solution; Geostatistical inversion uses random simulation methods to obtain inversion results through simulation and selection. The seismic data did not participate in the direct modification of the model, but rather served as a matching optimization constraint for the random model. Starting from the Bayesian formula, this article unifies deterministic inversion and geostatistical inversion within the Bayesian parameter estimation framework. From a theoretical framework, it analyzes the similarities and differences between deterministic inversion and geostatistical inversion, and proposes a method that combines deterministic inversion and geostatistical inversion - seismic wave impedance co inversion. Sequential Gaussian simulation and model constrained inversion are used as examples of the two major methods, The correctness of the research results and the feasibility and effectiveness of the proposed new inversion method and process have been verified through the application of the Marmousi theoretical model and actual data from Fudong, Fukang Depression, Xinjiang. It has been proven that the proposed method can improve the accuracy and precision of inversion. The inversion method and process used in this study obtained high-resolution and high-precision inversion results, which have good application prospects.

Overvoltage phenomenon initiated by breakdown during on-site withstand voltage tests of GIL and GIS: Mechanisms and consequences

An overvoltage was observed in the withstand voltage tests of GIL and GIS projects in China in recent years. The overvoltage may result in insulation damage and secondary breakdown where there is no defect. The analysis shows that the reason for the overvoltage is the wave impedance discontinuity between the pipeline and the overhead line. It results in the superposition of the reflected and refracted waves, and thus the overvoltage is generated. In fact, in addition to the structural change, the branches in the structure can also form wave impedance discontinuities. For example, unlike GIL, there are many branches in GIS that can also cause the overvoltage. The overvoltage is actually a universal phenomenon. The analyses based on an actual GIS structure show that in on-site withstand voltage tests, the overvoltage may exceed the peak value of the rated lighting impulse voltage, and even the insulation limits of GIS. These analyses are verified by simulation and experiment results. This universal phenomenon seriously endangers the safety of GIL and GIS during the withstand voltage test, because of the possible secondary breakdowns. The GIS will even become more vulnerable. Therefore, the on-site test structures or voltages should be revisited.© 2017 Elsevier Inc. All rights reserved.

Metal-organic framework-derived hierarchical Ag/Ti3C2Tx/Co/C nanocomposite for enhanced electromagnetic wave absorption

The microwave absorption (MA) performance of 2D Ti3C2Tx is significantly restricted due to its lack of magnetic loss capacity and mismatched electromagnetic impedance. The Ag/Ti3C2Tx/Co/C (ATCC) structure, based on a unique 2D layered Ti3C2Tx, has shown exceptional electromagnetic wave absorption (EWA) properties. The addition of a silver nanoparticles enhances the polarization effect and conductance loss of Ti3C2Tx. By incorporating ZIF-67 with varying Co content, nanocomposite heterostructures and interfaces are formed in Ag/Ti3C2Tx. Moreover, the carbon source of organic ligand and the 3D network structure of Ti3C2Tx provide additional electronic transition channels and improve conductive loss. This modification results in non-uniform interfaces between Ti3C2Tx and metal nanoparticles, leading to electron accumulation and the formation of a micro-capacitance structure that generates interface polarization. Eddy current loss and magnetic loss from metal nanoparticles further enhance EWA properties. This study envisions a novel strategy for developing efficient Ti3C2Tx-based microwave absorbers modified with metal nanoparticles.

Influence of Substrate Materials on the Performance of a Triple-Band Notched Frequency UWB Antenna

In this paper, the influence of different substrate materials on the performance of a triple-band notched frequency of ultra-wide band (UWB) antenna is presented. The antenna has a rectangular shape with dimension 31 by 24 mm and operates at UWB frequency band of 3.1GHz to 10.6GHz. The antenna was simulated using HFSS software. The effect of eight different substrate materials with different dielectric constant was examined on the antenna. Under each substrate, the performance of the antenna was investigated based on the antenna gain, directivity, radiation pattern, voltage standing wave ratio (VSWR), impedance bandwidth and S-parameter. Through thorough analysis, the results gave strong indication that UWB antenna performance is greatly affected by the type of dielectric substrate material chosen for design. The paper demonstrates the effect dielectric substrate material has on the antenna performance measurement like radiation pattern, gain, directivity and VSWR.

Purcell gain equalized zero-mode waveguide

We refresh the design of zero-mode waveguides (ZMWs) by introducing metamaterials that makes the zeroth order resonant mode existence. Of particular importance, the resulting electromagnetic field exhibits nearly constant distribution but not a trivial solution of Maxwell’s equation, showing great advantage to equalize the excitation rate of molecules throughout the waveguides. A closed form expression for the wave impedance is derived which is verified by the finite-difference time-domain simulations. Benefitted from the cavity Purcell effect which is lacking in existing ZMWs, fluorescence amplification and lifetime reduction are simultaneously enhanced. A practical design where the excitation volume reduced down to sub-zeptoliter and the fluorescence lifetime shortened to picosecond scale is illustrated. This result makes single molecule real time (SMRT) sensing of biochemical reactions at biophysically relevant concentrations (~ μM) possible, combining off-the-shelf ultrafast lasers.

A circularly polarized graphene based wideband 1 × 2 array antenna for terahertz spectrum applications

A graphene-based 1 × 2 array antenna with circular polarization for terahertz applications is prescribed in this article. Initially, a novel concept of a folded quarter wave impedance transformer is utilized in the design process of a single element for minimizing the overall antenna size. The opposite corners of the patches have been truncated and structural modifications are performed with the insertion of four flower-shaped slots along with an additional circular slot for achieving a much-improved reflection coefficient and better impedance bandwidth. It also shows a much wider 3 dB axial ratio bandwidth, confirming circular polarization due to the suggested modifications in its geometry. Then, an array antenna has been formed to provide better gain. The configured patches are fed by a magic-T power divider to attain the required impedance matching. The results of the CP antenna array have been analyzed using the HFSS and CST simulators. The propounded 1 × 2 array antenna shows circular polarization with a 3 dB AR bandwidth of 205 GHz (2.345–2.55 THz) and wide spectral coverage of 210 GHz (2.345 − 2.555 THz) along with a maximum gain of 8.65 dB and 99.8 % radiation efficiency with a total size of 53.5 × 102 × 1.56 μm3. It could be utilized for high-speed data transmission, material characterization, terahertz spectroscopy, terahertz imaging, etc. applications.

Microwave absorption properties of Co/C and Ni/C composite nanofibers prepared by electrospinning

Abstract Carbon nanofibers with Co, Ni nanoparticle were synthesized by a two-step process involving electrospinning and heat treatment. Their phase composition, microstructure, elemental composition and electromagnetic characteristics were characterized using x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and vector network analyzer (VNA). The microwave absorption performance of these carbon nanofibers was also studied. The results indicate that these composite nanofibers are intact and consist of amorphous carbon and face-centered cubic structured magnetic metals. The resultant metal nanoparticles are uniformly dispersed along carbon-based nanofibers which enhance the synergistic and interfacial effects between magnetic loss and dielectric loss. When the thicknesses of the absorbers are 1.5 mm, the absorption bandwidths (RL ≤ −10 dB) are approximately 4 GHz and 2.5 GHz for the Co/C, Ni/C composite nanofibers, respectively, which are obviously superior to pure carbon nanofibers. Co/C composite nanofibers exhibit a wider absorption band range and stronger microwave absorption intensity compared to Ni/C composite nanofibers, attributed to their excellent electromagnetic impedance matching and attenuation characteristics. This indicates that the Co/C composite nanofibers are promising candidates for novel microwave absorbing materials.

Dynamic Topology Optimization with Multiple Materials Based on Impedance Mismatching of Wave

Topology optimization with multiple materials studies were commonly adopted to address the issues of complex structures and dynamic loading cases. However, the perturbation excited from the transient load will be propagated and change the local stress level in the structure. Therefore, it is indispensable to consider impedance mismatching of waves at the interfaces of multi-materials layers in the optimization model. In this work, the wave impedance will be regarded as constraint conditions and assessment indicators in the optimization design. Firstly, a multi-material interpolation model using SIMP models is established based on the variable density method. Secondly, the optimization process is applied by combining using Newmark-[Formula: see text] method which is used to solve the dynamic response, an adjoint variable method for sensitivity study, and an optimization criterion method employed to update the design variables. Finally, the simulation examples are used to analyze the influence of impedance mismatching and volume fraction for multilayer dielectric on response. The results indicate that the position and content of the Polymethyl Methacrylate (PMMA) plays a key role in reducing vibration and buffering action.

Biomimetic design and impact simulation of Al2O3/Al composite armor based on armadillo shell

The advancement of lightweight protective armors holds critical importance for enhancing the maneuverability and combat capabilities of helicopters. Leveraging insights from bionics, it provides a new idea for high-performance armor design. In this study, a new type of composite armor was designed by referring to the structural characteristics of hard phase-protection, soft phase-buffering of unitization armadillo shell. Through the numerical study, the anti-ballistic performance of armor with varying thickness ratios of the dense ceramic layer to the interpenetrating layer is obtained, and the influence of different structures of armor on the anti-ballistic performance is analyzed. The results show that compared with the traditional laminated composite armor, the Al2O3/Al biomimetic composite armor not only improves the separation phenomenon caused by wave impedance mismatch, but also greatly improves the speed drop in resisting high-speed and penetrating bullets. When the thickness ratio is 2:1, the armor has higher ballistic protection performance.

From waste to resource: Transforming Kraft black liquor into sustainable porous carbon fillers for radome applications

The study addresses environmental and commercial challenges posed by weak black liquor (WBL) generated through the Kraft process in the paper industry. WBL, a toxic waste, annually reaches a staggering 1.3 billion tonnes globally. Currently, it is either incinerated for energy production or subjected to costly and complex chemical treatments to extract valuable compounds. Despite efforts to develop a scalable value-added material, the existing methods are inefficient in fully reusing WBL. Here, we report a simple chemical synthesis process that reuses 100 % of WBL without generating any waste materials; even salts recovered during the process might be reintegrated into the industry as chemical byproducts. Furthermore, given the simplicity and efficiency of the proposed synthesis methodology to transform WBL into a novel and sustainable porous carbon material, the carbon Kraft (CK). The process can also be scaled by using the right synthesis proportions and within a circular economy. CK exhibited desirable characteristics with a renewable content of 65 wt%, including a turbostratic graphitic-like structure (48.8 % graphitized), carbon content of 85 wt%, large specific surface area of 234.0 m2∙g−1, nanoporosity of 0.13 cm3∙g−1, and density of 1.92 g∙(cm3)-1. Moreover, CK showed electrical and thermal insulating characteristics, essential for use as fillers for elastomeric composite in electromagnetic transparent radome structures used to protect antennas and radars of unmanned aerial vehicles (UAV) from harsh environmental effects. Radomes were designed through the electromagnetic impedance match theory of half-wavelength calculations over specific frequencies of 1.3, 10, 15, 20, and 30 GHz. Results showed excellent transmission loss between −0.41 and −1.48 dB, representing 90.8 % and 70.5 % of transmittance, respectively.

Wave transmission in layered composite rock mass comprising parallel joints and different rock materials

This study investigates wave propagation of layered composite rock mass composed of multiple joints and assorted rock materials. Firstly, the effect of multiple-reflection between joints on wave transmission was explored by modifying the method of characteristics. Secondly, the superposition of direct and indirect transmission induced by multiple-reflection was analyzed. Waveform variations in wave transmission were compared across three different layered composite rock mass. Finally, the effects of wave parameters (frequency), joint parameters (stiffness and number), and rock parameters (wave impedance ratio) on both direct and indirect transmission induced by multiple-reflection were considered. The results indicate that the effect of indirect transmission induced by multiple-reflection on both particle velocity and stress transmission of waves cannot be ignored in many cases. The results further indicate that effect of indirect transmission induced by multiple-reflection on both particle velocity and stress transmission coefficients decreases with increasing incident wave frequency, while it increases with increasing joint numbers. The effect initially increases and subsequently decreases with increasing joint stiffness. Furthermore, the effect of indirect transmission induced by multiple-reflection on the particle velocity transmission coefficient increases while its effect on the stress transmission coefficient decreases with increasing wave impedance ratio.

Penetration resistance of honeycomb ceramic matrix composites with filler material

The major purpose of this study is to analyze the resistance of honeycomb ceramic matrix composites to penetration and to explore the effect of the performance characteristics of the filler materials on this capability. We used alumina ceramics, polyurea, quartz sand powder, and boron carbide powder to manufacture composite materials, and conducted impact tests and numerical simulations on them. The simulation results of Abaqus were found to be very consistent with the test results. The results demonstrate that the polyurea coating and filler materials may effectively improve the anti-penetration penetration performance of the composites, and different filler materials have varying energy absorption effects. Extended research on composites was carried out utilizing experimentally validated numerical models with filler materials comprising silicon carbide, aluminum nitride, and silicon nitride. After a comparative analysis of the simulation results of different composites, compared to quartz sand composites, the energy absorption efficiency of boron carbide composites increased by 12.03 %, silicon carbide composites increased by 14.63 %, aluminum nitride composites increased by 15.16 %, and silicon nitride composites increased by 18.29 %. Among the relevant materials in this study, there exists an optimal value of the stress wave impedance difference between the matrix material and the filler material. Honeycomb ceramic matrix composites with an ideal combination of stress wave impedance differences can considerably increase the anti-penetration efficiency of the composites.

Monitoring the parameters of printed strip lines in the microwave range of electromagnetic waves

The characteristic impedance of printed strip lines is determined by their design, cross-sectional geometry, relative permeability of the insulating base, and other factors that cannot be accurately estimated. The known methods for monitoring its frequency dependence using microwave measurements are not perfect and require further development. The proposed work proposes a method for experimental monitoring of the entire set of parameters of printed strip transmission lines: wave impedance, relative effective dielectric constant, as well as phase velocity and attenuation coeffi cient of a propagating electromagnetic wave. The characteristic impedance is determined by the s-parameters of the connection of coaxial strip junctions with a segment of an electrically long line. The wave parameters measured in the coaxial channel are transformed in the area of contact of the coaxial and strip lines, which makes it possible to obtain an analytical estimate of the wave impedance over the entire frequency range of the vector network analyzer or at least in its individual frequency windows. In the proposed method, the phase velocity, attenuation coeffi cient and relative effective dielectric constant are controlled by the differential-phase method based on the results of measuring the transmission coeffi cients of coaxial strip junction connections transformed to the contact areas by sections of electrically long and short printed stripline transmission lines. The performance of the proposed method for monitoring the parameters of printed strip lines is confi rmed by automated modeling, and its effectiveness is confi rmed by a full-scale experiment. The results obtained are useful to development engineers of integrated microwave technology and specialists in the field of monitoring object parameters in non-standard guide systems.

Using multi-scale interaction mechanisms in yolk-shell structured C/Co composite materials for electromagnetic wave absorption

Advanced chemical engineering for simultaneous modulation of nanomaterial morphology, defects, interfaces, and structure to enhance electromagnetic and microwave absorption (MA) performance. However, accurately distinguishing the MA contributions of different scale factors and tuning the optimal combined effects remains a formidable challenge. This study employs a synergistic approach combining template protection etching and vacuum annealing to construct a controlled system of micrometer-sized cavities and amorphous carbon matrices in metal-organic framework (MOF) derivatives. The results demonstrate that the spatial effects introduced by the hollow structure enhance dielectric loss but significantly weaken impedance matching. By increasing the proportion of amorphous carbon, the balance between electromagnetic loss and impedance matching can be effectively maintained. Importantly, in a suitable graphitization environment, the presence of oxygen vacancies in amorphous carbon can induce significant polarization to compensate for the reduced conductivity loss due to the absence of sp2 carbon. Through the synergistic effects of morphology and composition, the samples exhibit a broader absorption bandwidth (6.28 GHz) and stronger reflection loss (−61.64 dB) compared to the original MOF. In conclusion, this study aims to elucidate the multiscale impacts of macroscopic micro-nano structure and microscopic defect engineering, providing valuable insights for future research in this field.

Understanding energy transformation mechanism of rockbursts through experimental and theoretical methods

Understanding the energy transformation mechanism in rockbursts is essential for predicting and mitigating potentially catastrophic rock failures. In this study, Double Springs Release Tests (DSRTs) were proposed in a laboratory setting to investigate the energy transformation of rockbursts from inception to development. High-speed cameras and image processing algorithms were utilized to calculate different types of energy throughout the duration of the burst. Theoretical analyses, grounded in structural dynamics and stress wave equations, was conducted and cross-referenced with the experimental results. The study found that wave impedance ρE is a key indicator of burst intensity. The research demonstrated that the impact energy in DSRTs originates from both the impact medium and the surrounding medium, and explored how these two components contribute to the total impact energy of the impact medium.