Wave Impedance Research Articles

Topological features of Bloch impedance

The bulk-boundary correspondence (b-bc) principle states that the presence and number of evanescent bandgap modes at an interface between two periodic media depend on the topological invariants (Chern numbers in 2D or Zak phases in 1D) of propagating modes at completely different frequencies in all Bloch bands below that bandgap. The objective of this letter is to explain, on physical grounds, this connection between modes with completely different characteristics. We assume periodic lossless 1D structures and lattice cells with mirror symmetry; in this case the Zak phase is unambiguously defined. The letter presents a systematic study of the behavior of electromagnetic Bloch impedance, defined as the ratio of electrical and magnetic fields in a Bloch wave at the boundary of a lattice cell. The impedance-centric view confers transparent physical meaning on the bulk-boundary correspondence principle. Borrowing from the semiconductor terminology, we classify the bandgaps as p- and n-type at the Γ and X points, depending on whether the Bloch impedance has a pole (p) or a null (n) at the bottom of that gap. An interface mode exists only for pn-junctions per our definition. We expect these ideas to be extendable to problems in higher dimensions, with a variety of emerging applications.

Quantitative inversion of the elastic parameters outside the borehole based on exact Zoeppritz equations

The acoustic remote detecting method in the borehole has developed rapidly in the past few decades. It uses the reflected waves recorded by array receivers based on monopole or dipole sources in the fluid filled borehole to image geological structures outside the well. The result can provide guidance on the exploration and evaluation of oil and gas reservoirs and mineral resources. However, the present structure imaging results lack of the elastic information, which limit the quantitative evaluation of the resources. The AVO (amplitude variation with offset) inversion theory is introduced into the analysis of borehole waves. The interested interfaces (fractures or minor faults) with a generally larger wave impedance difference makes the widely used approximate equation in the surface exploration no longer applicable. Therefore, the exact Zoeppritz equations are used as the forward equations in the inversion. To reduce the nonlinearity of inversion, the initial model combining structure tensor and mode wave velocity analysis is constructed. The simultaneous inversion of the wave velocity and density of the reflector provides a theoretical basis for quantitatively evaluating the elastic parameters of the reservoir outside the borehole. [Work supported by the National Natural Science Foundation of China (42004117 and 42127807).]

Decay Law of Supercritical CO2 Phase Transition-Induced Shock Waves in Rocky Media

Supercritical CO2 phase change fracturing technology has been widely used in rock engineering, with the advantages of low disturbance and no pollution. However, the phase change shock wave inevitably affects the surrounding environment, and the influence range is still unclear. In this paper, we present a computational model for the symmetric generation, propagation, and attenuation of supercritical CO2 phase transition shock waves, with the center of the borehole as the origin, based on the C–J theory. The attenuation of the shock wave in the rock medium under the influence of the type of fracturing tube, the thickness of the shear sheet, and the rock performance parameters are further analyzed. The results show that the rock stress under the action of the phase change shock wave attenuates logarithmically with the propagation distance, which correlates with the magnitude of the incident rock stress at the borehole wall. The incident rock stress decreases with the increase in the initial density of CO2 in the fracturing tube, increases linearly with the thickness of the shear sheet, and correlates with the rock wave impedance.

Numerical Analysis of the Mitigation Performance of a Buried PT-WIB on Environmental Vibration.

Environmental vibration pollution has serious negative impacts on human health. Among the various contributors to environmental vibration pollution in urban areas, rail transit vibration stands out as a significant source. Consequently, addressing this issue and finding effective measures to attenuate rail transit vibration has become a significant area of concern. An infilled trench can be arranged periodically along the propagation paths of the waves in the soil to attenuate vibration waves in a specific frequency range. However, the periodic infilled trench seems to be unsatisfactory for providing wide band gaps at low and medium frequencies. To improve the isolation performance of wave barriers at low to medium frequencies, a buried PT-WIB consisting of a periodic infilled trench and a wave impedance block barrier has been proposed in this paper. A three-dimensional finite element model has been developed to evaluate the isolation performance of three wave barriers. The influence of the PT-WIB's parameters on isolation performance has been analyzed. The results indicate that the combined properties of the periodic structure and the wave impedance block barrier can effectively achieve a wide attenuation zone at low and medium frequencies, enhancing the isolation performance for mitigating environmental vibration pollution.

Pomegranate-like ATO/SiO2 microspheres for efficient microwave absorption in wide temperature spectrum

High-performance microwave-absorbing materials (MAMs) should meet both impedance matching and attenuation performance. Commonly, it is hard to maintain excellent microwave absorption (MA) performance at an elevated temperature because the reliance on impedance matching and dielectric loss about temperature mutually restricts. In this work, the pomegranate-like antimony-doped tin dioxide (ATO)/ silica dioxide (SiO2) spheres were fabricated via a simple spray drying process. When the spheres were used as functional units and dispersed in the matrix, the corresponding composites exhibit an outstanding anti-reflection effect on microwaves. Moreover, the unique pomegranate-like structure of the ATO/SiO2 spheres provides both the effective local eddy current and abundant heterogeneous interface, which therefore contribute harvest enhanced dielectric relaxation and improved absorption performance when compared with that of the corresponding ATO/SiO2 composition. As a result, the maximum reflection loss of the ATO/SiO2 spheres composites can reach –47.8 dB at 9.7 GHz with a thickness of 1.8 mm, while the reflection loss could reach –47.3 dB at 573 K and the effective absorption bandwidth is 2.4 GHz. This work reveals the importance of local eddy current loss in optimizing the electromagnetic wave (EMW) absorption performance and impedance matching, providing novel guidance on designing advanced high-temperature MAMs.

A gauge field theory of coherent matter waves

A gauge field treatment of a current oscillating at frequency ν of interacting neutral atoms leads to a set of matter-wave duals to Maxwell's equations for the electromagnetic field. In contrast to electromagnetics, the velocity of propagation has a lower limit rather than upper limit, and the wave impedance of otherwise free space is negative real-valued rather than 377 Ω. Quantization of the field leads to the matteron, the gauge boson dual to the photon. Unlike the photon, the matteron is bound to an atom and carries negative rather than positive energy, causing the source of the current to undergo cooling. Eigenstates of the combined matter and gauge field annihilation operator define the coherent state of the matter-wave field, which exhibits classical coherence in the limit of large excitation.

Ultra-wide bandwidth electromagnetic wave and enhanced microwave absorption of Cu0.5Ni0.5Fe1.9Mn0.1O4 @CaTiO3 @MWCNTs nanocomposite in X-band frequency

Broad bandwidth electromagnetic (EM) wave absorbers are persistently desired due to their massive applications in many fields. This paper reports the development of ultra-wide bandwidth microwaves, with the enhanced microwave absorption of thin-thickness absorbers. The design of RAMs requires a structure composed of magnetic-dielectric elements, meta-materials, and large impedance matching. This paper highlights the strategic approach to obtain the ultrawide, thin, and high impedance matching of the absorber. The Spinel-ferrite Cu0.5Ni0.5Fe1.9Mn0.1O4 (SF), Spinel ferrite doped calcium titanium oxide, Cu0.5Ni0.5Fe1.9Mn0.1O4@CTO (SF@CTO), and Spinel ferrite doped calcium‑copper titanate and multiwalled carbon nanotubes Cu0.5Ni0.5Fe1.9Mn0.1O4@CaTiO3@MWCNT (SF@CTO@MWCNT) nanocomposites absorbers were reported. The spinel ferrite and calcium copper titanite were synthesized via a co-precipitation method, and hydrothermally with the MWCNT by acid functionalization process. The effectiveness of microwave absorbing the samples was measured using a vector network analyzer with sample thicknesses of 1.0 mm, 2.0 mm, and 3.0 mm, in the frequency range of 8.0 to 12.0 GHz. The highest reflection loss (RL) of −33.3 dB at 9.6 GHz was anticipated using the complex permittivity and permeability characteristics. Interfacial electric polarisation, electromagnetic impedance matching, as well as the numerous scattering network structure of SF@CTO@MWCNT nanocomposites, are all credited with effective ultra-wide bandwidth microwave absorption. This report is important for paving future work in obtaining a desired thin and ultra-wide bandwidth absorber.

Real-time reading system for pointer meter based on YolactEdge

Despite the extensive deployment of digital instruments in modern times, their stability is challenging to maintain in adverse environmental conditions such as extreme temperatures, pressure, or powerful electromagnetic radiation. Analog meters, owing to their mechanical resilience and electromagnetic impedance, persistently find usage across nuclear power plants, petroleum, and chemical industries. However, under these harsh conditions, manual reading of the instruments may prove to be difficult and dangerous while failing to meet the requirements of real-time monitoring. In recent years, several machine vision-based meter reading systems have been proposed, however, achieving high accuracy through camera-based methods under varying angles and lighting conditions poses significant challenges. Cloud deployment may compromise plant privacy, while edge computing faces limitations in real-time meter reading due to limited computing power. To address these issues, we propose a real-time reading system based on the YolactEdge instance segmentation framework for single-point analog meters. Our system is more accurate than previous studies and is implemented and deployed on the Jetson Xavier NX edge computing device. Our performance evaluation shows that our model outperforms other baselines, with low reference values and relative errors of 0.0237% and 0.0300%, respectively, and an average inference speed of 10.26 FPS with INIT 8 linear acceleration on Nvidia Jetson NX.

Method of defining rock damage variable on the basis of wave impedance

AbstractA method of determining rock damage variable from wave impedance, which is suitable for the study of dynamics, is presented. The determined variable provides a more reasonable quantitative description of the degree of rock damage. First, the Taylor model of mesoscopic damage mechanics is used to derive the relationship between the velocity of longitudinal waves and the density of rock materials. Based on the measured data of rock samples with different lithology and the same lithology, the relationship between the longitudinal wave velocity and density of rock materials is studied. It is demonstrated that using the wave impedance to define the rock damage variable has advantages over using the P‐wave velocity. Second, the relationship between the wave impedance and degree of damage to the rock material is studied using an electron microscope and ultrasonic testing technology, and the microstructure of rock samples with a wave impedance gradient and time–frequency‐domain characteristics of the ultrasonic signals are compared and analyzed. It is found that it is feasible to determine the damage degree of the rock from the wave impedance. Finally, a method of defining rock damage variable with the wave impedance is further proposed and its rationality verified. The research results show that there is a good positive correlation between the longitudinal wave velocity and density of rock materials, and there is a strong correlation between the degree of rock damage and its wave impedance. The damage variable defined by wave impedance can better reflect the damage state and damage evolution process of rock.

Performances of fissured red sandstone after thermal treatment with constant-amplitude and low-cycle impacts

In the engineering practices, it is increasingly common to encounter fractured rocks perturbed by temperatures and frequent dynamic loads. In this paper, the dynamic behaviors and fracture characteristics of red sandstone considering temperatures (25 °C, 200 °C, 400 °C, 600 °C, and 800 °C) and fissure angles (0°, 30°, 60°, and 90°) were evaluated under constant-amplitude and low-cycle (CALC) impacts actuated by a modified split Hopkinson pressure bar (SHPB) system. Subsequently, fracture morphology and second-order statistics within the grey-level co-occurrence matrix (GLCM) were examined using scanning electron microscopy (SEM). Meanwhile, the deep analysis and discussion of the mechanical response were conducted through the synchronous thermal analyzer (STA) test, numerical simulations, one-dimensional stress wave theory, and material structure. The multiple regression models between response variables and interactive effects of independent variables were established using the response surface method (RSM). The results demonstrate the fatigue strength and life diminish as temperatures rise and increase with increasing fissure angles, while the strain rate exhibits an inverse behavior. Furthermore, the peak stress intensification and strain rate softening observed during CALC impact exhibit greater prominence at increased fissure angles. The failure is dominated by tensile damage with concise evolution paths and intergranular cracks as well as the compressor-crushed zone which may affect the failure mode after 400 °C. The second-order statistics of GLCM in SEM images exhibit a considerable dependence on the temperatures. Also, thermal damage dominated by thermal properties controls the material structure and wave impedance and eventually affects the incident wave intensity. The tensile wave reflected from the fissure surface is the inherent mechanism responsible for the angle effect exhibited by the fatigue strength and life. Ultimately, the peak stress intensification and strain rate softening during impact are determined by both the material structure and compaction governed by thermal damage and tensile wave.

Fault location in hybrid transmission lines on the basis of VMD energy entropy and SVM

Finding the head of a traveling wave is challenging because an overhead line-cable hybrid transmission line’s wave impedance is not constant. Because of this, it is difficult to measure the hybrid transmission line precisely. This leads to the proposal of a hybrid transmission line fault location algorithm, which combines VMD energy entropy for training support vector machines and traveling wave law graphs. The VMD energy entropy is first used to train SVM to identify the faulty section. The method of traveling waves with a single end is utilized to precisely fix the fault distance within the faulty segment when the type of traveling wave has been identified. The simulation results demonstrate that the method provides precise measurements and is effective for hybrid transmission lines with a range of fault distances and grounding resistances.

Confinement engineering to enhance broadband microwave absorption of hierarchically magnetic carbon tubular composite

The development of carbon materials remains challenging due to a single loss mechanism and an electromagnetic impedance mismatch. Confinement engineering has been shown to provide a chemical microenvironment for the formation of confined object materials in order to regulate the physical and chemical properties of nanomaterials. In this study, we choose lightweight one-dimensional biomass carbon microtubes as the base, for the first time cleverly using the transition metal nickel only on the inner surface of carbon microtubes with an ultra-small CNT array, and construct a composite with a hierarchically magnetic carbon tubular structure (HMCT-I) on the basis of the theoretical analysis of electromagnetic parameters. Thanks to enhanced magnetic loss and the synergy of multiple polarization losses, HMCT-I ultimately shows encouraging microwave-absorption performance, with an ultra-wide effective absorption bandwidth of 8.44 GHz and an ultra-low reflection loss of −77.7 dB. In addition, the reasonable design makes HMCT-I have superior environmental stability, broadening the way for developing practical broadband carbon-based composite absorbers. This work also provides theoretical guidance and innovative ideas for the design of broadband and efficient microwave absorbers.

Numerical modelling of blast mitigation of pre-fractal obstacles

The mechanics of downstream blast wave attenuation caused by interaction with obstacles arranged into a pre-fractal shape based on the Sierpinski carpet was numerically investigated using a high-fidelity CFD solver. The blast mitigation was qualitatively and quantitatively assessed for four pre-fractal iterations at three different scaled distances ( Z = 1.87, 2.24, 2.99 m/kg1/3). Mitigation was seen to occur in zones associated with the location of destructive wave interference patterns in the downstream region. Crucially, these zones were found to widen spatially with increasing pre-fractal iteration, and strong shock-shock interactions that result in load amplification, commonly encountered in downstream regions of a solitary block-like obstacle, were not observed for the more fractal-like obstacles. The mechanisms of attenuation are explored in terms of wave impedance. It is found that pre-fractals reduce wave transmission in the downstream, increase reflection of the blast wave, and enhance trapping within the confines of the pre-fractal obstacle, dramatically changing the directionality and hence the strength of the transmitted wave. Reductions in peak pressure of up to 60% and peak specific impulse of up to 40% were recorded for the highest iteration pre-fractal, that is, obstacles that most closely represent a true fractal, thereby highlighting the effectiveness of such shapes for protective structure design for improved blast mitigation.

Designing of an rGO-based heterostructure for highly efficient microwave absorption performance and flame retardancy

To meet the increasingly serious challenges of electromagnetic pollution and fire hazards, highly efficient electromagnetic absorbing materials with good flame retardancy have been accurately developed. A complex high-performance electromagnetic absorber was designed by doping graphene oxide heterostructures (including zero-dimensional nanoparticles and two-dimensional graphene) containing cobalt, nickel and iron oxyhydroxide through the coordination effect. When 20 wt% CNFO@rGO was incorporated into paraffin, the minimum reflection loss (RL) reached -51.6 dB at a thickness of 3.5 mm, showing a high electromagnetic absorption efficiency. It was concluded that the excellent impedance matching, the best dielectric loss and the higher magnetic loss caused by the heterostructure combined with the electromagnetic parameters, Cole-Cole semicircle, impedance matching (Z) and attenuation coefficient resulted in excellent electromagnetic wave absorption performance. Moreover, the peak heat release (PHRR) and heat release rate (HRC) decreased by 55.5% and 55.1%, respectively, when 10 wt% CNFO@rGO was incorporated into the epoxy resin (EP), indicating enormous potential for the enhancement of flame-retarding electromagnetic absorbing materials.

Study of switching overvoltages in electrical networks up to 1000 V

The aim was to study the effect of switching modes on the power of supply transformers in electrical networks up to 1000 V on the multiplicity of switching overvoltages, as well as to develop recommendations for their reduction. The study was carried out during switching of supply transformers in networks up to 1000 V. Vacuum contactors were used to study overvoltages arising during switching of supply transformers. Overvoltages were recorded using an RDN-1000 active divider and a Tektronix TDS2024B digital oscilloscope. The RC circuit capacitance was measured by a Mastech MY6243 digital LC-meter. To limit switching overvoltages, RC quenchers based on RC circuits were used, reducing not only the switching pulse amplitude, but also the rate of the switching pulse voltage rise. In addition, RC quenchers lack fading zones under high-frequency switching pulses. The capacitance of the primary winding of the transformers under study was measured. An increase in the transformer power was found to lead to a decrease in the multiplicity of switching overvoltages, when the transformer is disconnected from the mains. Under a 1.5-fold increase in the power of the transformer, its inductance and wave impedance decreases. As a result, when the same capacitance is connected to the transformer terminals, the wave resistance in more powerful transformers will be reduced to a larger extent (by 3 to 6 times), thus providing a more effective overvoltage limitation. The conducted experimental studies confirmed the effectiveness of RC circuits in limiting switching overvoltages.

Effects of projectile parameters on the momentum transfer and projectile melting during hypervelocity impact

The effects of projectile/target impedance matching and projectile shape on energy, momentum transfer and projectile melting during collisions are investigated by numerical simulation. By comparing the computation results with the experimental results, the correctness of the calculation and the statistical method of momentum transfer coefficient is verified. Different shapes of aluminum, copper and heavy tungsten alloy projectiles striking aluminum, basalt, and pumice target for impacts up to 10 km/s are simulated. The influence mechanism of the shape of the projectile and projectile/target density on the momentum transfer was obtained. With an increase in projectile density and length-diameter ratio, the energy transfer time between the projectile and targets is prolonged. The projectile decelerates slowly, resulting in a larger cratering depth. The energy consumed by the projectile in the excavation stage increased, resulting in lower mass-velocity of ejecta and momentum transfer coefficient. The numerical simulation results demonstrated that for different projectile/target combinations, the higher the wave impedance of the projectile, the higher the initial phase transition velocity and the smaller the mass of phase transition. The results can provide theoretical guidance for kinetic impactor design and material selection.

Phragmites-derived magnetic carbon fiber with hollow assembly architecture toward full-covered effective bandwidth at Ku band

Lightweight and efficient electromagnetic wave absorption (EMA) materials are in high demand, and magnetic carbon fiber composites show potential. However, impedance matching issues make achieving full coverage of the Ku band challenging, hindering improvements in effective absorption bandwidth. This study proposes innovative compositional and structural designs coupling magnetic carbon fibers to balance electromagnetic attenuation and impedance matching. We assemble 1D phragmites-derived hollow carbon fibers (PCF) with 3D CoFe2O4 (CFO) hollow nanoparticles to create a composite with two different dimensions and mechanisms of loss. CFO hollow nanoparticles uniformly distributed on the PCF conductively lose energy and enable multiple reflections. Furthermore, by designing the thermal decomposition temperature and magnetic components, high-frequency electromagnetic parameters can be controllably adjusted. Notably, PCF7-CFO exhibits excellent reflection loss of −57.8 dB at 14.8 GHz with a filling ratio of 20 wt% and matching thickness of 2.0 mm, with an effective absorption bandwidth reaching 5.9 GHz, almost covering the entire Ku band. The hollow-assembly structure balances impedance matching and high-frequency attenuation, achieving full-Ku-band coverage for developing efficient electromagnetic wave absorbers with biomass-derived carbon materials.

Dual-phase digital lock-in implementation based on Nyquist rate and sampling subtraction.

Lock-in amplifiers (LIA) are widely used in laboratory environments to detect low-amplitude signals buried in noise as well as real and imaginary parts of a complex quantity. They are based on the technique of synchronous detection, where the signal of interest is modulated into a desired frequency, sent to the medium or device to be analyzed, and captured by a detector. The detector scheme relies on the concept of phase-sensitive detection, generally resulting in two components: in-phase and quadrature. This article shows a very simple and low computational-cost way to implement a dual-phase LIA, using readily available microcontrollers, running a simple and fast algorithm. Three examples of signal detection are presented (sound wave signal, impedance meter, and weak signal recovery) to point out the flexibility and capabilities of the proposed methodology.

A Novel Folded Rectangular-Grating Slow Wave Structure for Dual-Beam Traveling Wave Tube

Increasing the input current is an important method to achieve the high-power output for the traveling wave tubes (TWTs) operating in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{W}$</tex-math> </inline-formula> -band and higher terahertz (THz) band. For the folded waveguide (FW) TWT, increasing the height of the straight waveguide section of slow wave structure (SWS) can realize a double tunnel to increase the input current, but its electromagnetic characteristics, such as the operating passband, interaction impedance, and ohmic loss, become worse. Thus, a novel SWS, called folded rectangular-grating (FRG), with two tunnels for more input current, was proposed. Its two beam tunnels, where the electromagnetic wave in the operating band is cutoff, are located on the upper and lower edges of the grating, respectively, which makes the FRG-SWS have a wider operating passband, higher interaction impedance, and lower ohmic loss by freely adjusting its grating height. More importantly, its structural complexity is the same as that of FW-SWS. First, the electromagnetic characteristics, including dispersion, interaction impedance, and ohmic loss, are analyzed. Then, the particle-in-cell (PIC) simulation was carried out to verify that the saturated power, gain, and electron efficiency of TWT using FRG-SWS have been significantly improved compared with the TWT using FW-SWS. In the end, the cold test of transmission characteristics for FRG-SWS was done, and the experimental results are basically in good agreement with the simulation ones when the conductivity is set as 2.25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\text{7}}$</tex-math> </inline-formula> S/m.

The March 1940 Superstorm: Geoelectromagnetic Hazards and Impacts on American Communication and Power Systems

AbstractAn analysis is made of geophysical records of the 24 March 1940, magnetic storm and related reports of interference on long‐line communication and power systems across the contiguous United States and, to a lesser extent, Canada. Most long‐line system interference occurred during local daytime, after the second of two storm sudden commencements and during the early part of the storm's main phase. The high degree of system interference experienced during this storm is inferred to have been due to unusually large‐amplitude and unusually rapid geomagnetic field variation, possibly driven by interacting interplanetary coronal‐mass ejections. Geomagnetic field variation, in turn, induced geoelectric fields in the electrically conducting solid Earth, establishing large potential differences (voltages) between grounding points at communication depots and transformer substations connected by long transmission lines. It is shown that March 1940 storm‐time communication‐ and power‐system interference was primarily experienced over regions of high electromagnetic surface impedance, mainly in the upper Midwest and eastern United States. Potential differences measured on several grounded long lines during the storm exceeded 1‐min resolution voltages that would have been induced by the March 1989 storm. In some places, voltages exceeded American electric‐power‐industry benchmarks. It is concluded that the March 1940 magnetic storm was unusually effective at inducing geoelectric fields. Although modern communication systems are now much less dependent on long electrically conducting transmission lines, modern electric‐power‐transmission systems are more dependent on such lines, and they, thus, might experience interference with the future occurrence of a storm as effective as that of March 1940.