Synthesis of carbon-coated cobalt ferrite core-shell structure composite:A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

Cobalt ferrite has problems such as poor impedance matching and high density,which results in unsatisfactory electromagnetic wave(EMW)absorption performance.In this study,the CoFe_(2)O_(4)@C core-shell structure composite was synthesized by a two-step hydrothermal method.X-ray diffraction,transmission electron microscopy,Fourier transform infrared spectroscopy,thermogravimetric analysis,and vector network analysis et al.were used to test the structure and EMW absorption properties of CoFe_(2)O_(4)@C composite.The results show that the reflection loss(RL)of the CoFe_(2)O_(4)@C composite reaches the maximum value of25.66 dB at 13.92 GHz,and the effective absorbing band(EAB)is 4.59 GHz(11.20-15.79 GHz)when the carbon mass content is 6.01%.The RL and EAB of CoFe_(2)O_(4)@C composite are increased by 219.55%and 4.59 GHz respectively,and the density is decreased by 20.78%compared with the cobalt ferrite.Such enhanced EMW absorption properties of CoFe_(2)O_(4)@C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite,moreover,the carbon coating layer adjusts the impedance matching of the composite,and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.

Impedance matching for repetitive high voltage all-solid-state Marx generator and excimer DBD UV sources

The purpose of impedance matching for a Marx generator and DBD lamp is to limit the output current of the Marx generator,provide a large discharge current at ignition,and obtain fast voltage rising/falling edges and large overshoot.In this paper,different impedance matching circuits（series inductor,parallel capacitor,and series inductor combined with parallel capacitor） are analyzed.It demonstrates that a series inductor could limit the Marx current.However,the discharge current is also limited.A parallel capacitor could provide a large discharge current,but the Marx current is also enlarged.A series inductor combined with a parallel capacitor takes full advantage of the inductor and capacitor,and avoids their shortcomings.Therefore,it is a good solution.Experimental results match the theoretical analysis well and show that both the series inductor and parallel capacitor improve the performance of the system.However,the series inductor combined with the parallel capacitor has the best performance.Compared with driving the DBD lamp with a Marx generator direcdy,an increase of 97.3%in radiant power and an increase of 59.3%in system efficiency are achieved using this matching circuit.

Simulation of High-Transmission Chiral Metamaterial with Impedance Matching to a Vacuum

For a previously simulated eight-broadband negative-refraction-index chiral metamaterial, we use S-parameter retrieval methods to determine the complex effective permittivity, permeability, and the impedance. We also calculate the figure of merit, which is defined as the ratio of the real and the imaginary refraction components, and compare it with those of fishnet metamaterials. The simulation results show that our chiral metamaterial exhibits high transmission and impedance matching to a vacuum. Also, we determine that the electric and magnetic dipoles of the surface plasmons play an important role in determining the nine resonance frequencies. Therefore, this investigation provides an experimental basis for developing metamaterial devices with multiple and broad resonance frequency bands.

An easily-prepared impedance matched Josephson parametric amplifier

An impedance matched parametric amplifier(IMPA)with Josephson junctions is fabricated and characterized.A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions.The upper plate of the capacitor is isolated with SiNx without grounding as well as the strips.Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision,which makes the fabrication process more reliable.The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained.This broadband amplifier operates close to the quantum limit.By adjusting the working point,a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.

Impedance Matching Algorithm for Selection of Suitable Explosives for Any Rock Mass-A Case Study

Proper selection of the explosive is an important part of blast design.The judicious selection of explosives is governed by economic considerations and site/field conditions.The mine management desires to select an explosive that will give the lowest cost per unit of rock broken,while assuring that fragmentation,fragment size distribution,muck pile profile,muck pile diggability,displacement of the rock,onset of movement,face movement,burden relief rate,ground vibration and noise remains within control limits.Factors which influence the selection of an explosive include explosive cost,charge diameter,cost of drilling,fragmentation difficulties and fragment size requirement with loose muck pile condition,water conditions,atmospheric temperature,propagating ground,storage considerations,sensitivity considerations,explosive atmospheres and nearness of communities from mine.All these concerns can be handled effectively by using the impedance matching technology where explosive impedance is matched with rock impedance for optimal blast performance with due concern to productivity,economics and environment.This paper discusses a case study in limestone mines where rock impedance was determined by carrying out surface refraction test and a patented algorithm was used to estimate the explosives’properties i.e.VOD(velocity of detonation)and density of explosives required.

Theoretical Analysis of Triple Liquid Stub Tuner Impedance Matching for ICRH on Tokamaks

The impedance matching is crucial for continuous wave operation of ion cyclotron resonance heating（ICRH） antennae with high power injection into plasmas.A sudden increase in the reflected radio frequency power due to an impedance mismatch of the ICRH system is an issue which must be solved for present-day and future fusion reactors.This paper presents a method for theoretical analysis of ICRH system impedance matching for a triple liquid stub tuner under plasma operational conditions.The relationship of the antenna input impedance with the plasma parameters and operating frequency is first obtained using a global solution.Then,the relations of the plasma parameters and operating frequency with the matching liquid heights are indirectly obtained through numerical simulation according to transmission line theory and matching conditions.The method provides an alternative theoretical method,rather than measurements,to study triple liquid stub tuner impedance matching for ICRH,which may be beneficial for the design of ICRH systems on tokamaks.

Enhanced electromagnetic wave absorption via optical fiber-like PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites with improved impedance matching

Ti_(3)C_(2)T_(x) nanosheets have attracted significant attention for their potential in electromagnetic wave absorption(EWA).However,their inherent self-stacking and exorbitant electrical conductivity inevitably lead to serious impedance mismatch,restricting their EWA application.Therefore,the optimization of impedance matching becomes crucial.In this work,we developed polymethyl methacrylate(PMMA)@Ti_(3)C_(2)T_(x)@SiO_(2) composites with a sandwich-like core–shell structure by coating SiO_(2) on PMMA@Ti_(3)C_(2)T_(x).The results demonstrate that the superiority of the SiO_(2) layer in combination with PMMA@Ti_(3)C_(2)T_(x),outperforming other relative graded distribution structures and meeting the requirements of EWA equipment.The resulting PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites achieved a minimum reflection loss of-58.08 dB with a thickness of 1.9 mm,and an effective absorption bandwidth of 2.88 GHz.Mechanism analysis revealed that the structural design of SiO_(2) layer not only optimized impedance matching,but also synergistically enhanced multiple loss mechanisms such as interfacial polarization and dipolar polarization.Therefore,this work provides valuable insights for the future preparation of high-performance electromagnetic wave absorbing Ti_(3)C_(2)T_(x)-based composites.

Rational design of hollow rice-grainedα-Fe_(2)O_(3)/carbon nanofibers with optimized impedance matching for electromagnetic wave absorption enhanced

Electromagnetic wave absorption materials are widely used in electronic equipment and military fields.However,high cost and complex preparation processes become a major obstacle in promoting popularization in the civil field.To solve the problems above,researchers have made great efforts to develop Fe-based carbon composites.However,most of the typical composites require a high filling ratio while achieving excellent properties.Therefore,in this study,carbon nanofibers(CNFs)combined with the hollow rice-grainedα-Fe_(2)O_(3)nanoparticles were prepared by the in-situ transformation method.The rational microstructure design provided a solution for reducing the filling ratio,optimizing impedance matching,and improving electromagnetic wave absorption performance.The strong reflection loss value(−38.1 dB)and broad effective absorption bandwidth(4.6 GHz)for Fe_(2)O_(3)/CNFs composites were achieved with a low filling ratio(20 wt.%),and the analysis of electromagnetic parameters validated that the microstructure of Fe_(2)O_(3)/CNFs plays a crucial role in the performance improvement.With the optimized impedance matching and simple preparation method,Fe_(2)O_(3)/CNFs have broad application prospects in electromagnetic wave absorption.

Optimizing impedance matching by a dual-carbon Co-regulation strategy of Co_(3)O_(4)@rGO/celery stalks derived carbon composites for excellent microwave absorption

Both macroscopic composition and microstructure should be considered for reasonable microwave ab-sorbent designing.In this study,Co_(3)O_(4)@reduced graphene oxide(rGO)/Celery stalks derived carbon(CDC)was prepared by loading Co_(3)O_(4) particles into rGO and biomass-derived carbon mixture through oxidation precipitation.By changing the mass ratio of rGO to CDC,the dielectric and impedance matching proper-ties of the composites can be easily regulated.The RL min value of Co_(3)O_(4)@rGO/CDC_(13) composite(weight ratio for rGO:CDC is 1:3)reaches-84.3 dB with a thickness of 4.6 mm,and the widest effective band-width can be obtained at 4.5 GHz with a matching thickness of 2.8 mm.The Co_(3)O_(4)@rGO/CDC_(13) compos-ite with multiple components(Co_(3)O_(4),CDC,rGO)and 3D net structure produces magnetic/dielectric loss combinations,interfacial polarization,and multiple reflections and scattering,and the CDC with half tube and half sheet structure is conducive to the optimization of impedance matching.The strategy of co-regulating dielectric properties of materials with double carbon provides a novel pathway for the prepa-ration of lightweight,low-cost,and high-performance absorbers.

Achieving ultra-broadband electromagnetic absorption of Ag regulated hollow Ag/CuO@CuS through balancing conduction loss and impedance matching

Excellent impedance matching and high conduction loss are important factors for the preparation of high-performance electromagnetic wave(EMW)absorbing materials,but these two properties are of-ten contradictory.In this work,three absorbers with unique hollow structures,H-Ag/CuO@CuS,H-O-Ag/CuO@CuS,and H-P-Ag/CuO@CuS,are designed and synthesized by adopting hollow CuO@CuS with double shell as carrier and silver nitrate as the structural regulator.The more voids coming from hol-low structures,window-opened structures,and stacked pores improve the impedance matching of these absorbers,and the introduction of elemental Ag effectively regulates the conduction loss.Therefore,a balance between impedance matching and conduction loss is achieved to improve the reflection loss(RL)value and broadens the absorbing band of the absorbers.In comparison to H-Ag/CuO@CuS and H-O-Ag/CuO@CuS(hollow structure with open window)in which elemental Ag is uniformly dispersed in the CuO layer,H-P-Ag/CuO@CuS exhibits more excellent EMW absorption performance due to more voids and an optimized conductive network arising from Ag/CuO pieces distributed between the hol-low Ag/CuO@CuS particles and Ag distributed in the CuS layer.When the thickness is 2.3 mm,H-P-Ag/CuO@CuS provides an ultra-wide electromagnetic absorption band of 8.56 GHz(9.44-18 GHz),in which the RL<-10 dB and the minimum reflection loss of-41 dB.

Impedance matching for the reduction of signal reflection in high speed multilevel three-dimensional integrated chips

In high speed three-dimensional integrated circuits （3D ICs）, through silicon via （TSV） insertion causes impedance discontinuities along the interconnect-TSV channel that results in signal reflection. As demonstrated for a two-plane interconnect structure connected by a TSV, we incorporate an appropriate capacitance at the junction to mitigate the signal reflection with gigascale frequencies. Based on 65 nm technology and S-parameter analysis, the decrease of signal reflection can be 189% at the tuned frequency of 5 GHz. Extending this method to the five-plane interconnect structure further, the reduction of signal reflection can achieve 400%. So we could broaden this method to any multilevel 3D interconnect structures. This method can also be applied to a circuit with tunable operating frequencies by digitally connecting the corresponding matching capacitance into the circuit through switches. There are remarkable improvements of the quality of the transmitting signals.

Spray granulation of Fe and C nanoparticles and their impedance match for microwave absorption

The microwave absorbents of Fe and C nanoparticles as magnetic loss and dielectric loss material respectively were composited with the polyvinyl alcohol （PVA） as binder by spray granulation method, The electromagnetic parameters of Fe and C composite particles were analyzed by vector network. The complex permittivity and magnetic permeability of Fe and C composite particles matched well with increasing C nanoparticle content, and then the microwave loss property was improved. A minimum reflection loss （RL） of -42.7 dB at 3.68 GHz for a composite with 4.6 mm in thickness can be obtained when the content ratio of the C nanoparticles, the modified Fe nanoparticles and the PVA is 21：49：30 （Sample 3）.

Low-loss Cd-substituted Mg ferrites with matching impedance for high-frequency-range antennas

The effects of Cd^(2+) ions on the microstructure,magnetic properties,and dielectric properties of Bi_(2)O_(3)-added MgFe_(2)O_(4) ferrites(Cd_(x)Mg_(1-x)Fe_(2)O_(4),x=0.00,0.15,0.30 and 0.45)are obtained by adopting the solid-state reaction method at a low temperature(910℃).The objective is to achieve matching impedances,low magnetic and dielectric losses(tanδμand tanδε,respectively),and a relatively large miniaturization factor to reduce antenna size.Experimental results indicate that the cations occupying the tetrahedral(A)and octahedral(B)ion sites are redistributed,resulting in an enhanced super-exchange interaction between the two sublattices.As a result,improved magnetization,including the increase in saturation magnetization(41.74 emu/g)and decrease in coercivity(63.75 Oe),is realized.The real part of permeability(μ')also increases with increasing concentration of Cd^(2+) ions.When x is 0.15,matching impedances with equivalent μ'and ε'values are obtained over a long frequency range(1–150MHz).Moreover,the formation of a dense microstructure guarantees that losses occur at low orders of magnitude(tanδμ≈10−2 and tanδε≈10−3).Accordingly,these properties afford wide application perspectives for the proposed compounds in the high-frequency region,i.e.,from high-frequency to very-high-frequency bands.

Interface Engineering of Titanium Nitride Nanotube Composites for Excellent Microwave Absorption at Elevated Temperature

Currently,the microwave absorbers usually suffer dreadful electromagnetic wave absorption(EMWA)performance damping at elevated temperature due to impedance mismatching induced by increased conduction loss.Consequently,the development of high-performance EMWA materials with good impedance matching and strong loss ability in wide temperature spectrum has emerged as a top priority.Herein,due to the high melting point,good electrical conductivity,excellent environmental stability,EM coupling effect,and abundant interfaces of titanium nitride(TiN)nanotubes,they were designed based on the controlling kinetic diffusion procedure and Ostwald ripening process.Benefiting from boosted heterogeneous interfaces between TiN nanotubes and polydimethylsiloxane(PDMS),enhanced polarization loss relaxations were created,which could not only improve the depletion efficiency of EMWA,but also contribute to the optimized impedance matching at elevated temperature.Therefore,the TiN nanotubes/PDMS composite showed excellent EMWA performances at varied temperature(298-573 K),while achieved an effective absorption bandwidth(EAB)value of 3.23 GHz and a minimum reflection loss(RLmin)value of−44.15 dB at 423 K.This study not only clarifies the relationship between dielectric loss capacity(conduction loss and polarization loss)and temperature,but also breaks new ground for EM absorbers in wide temperature spectrum based on interface engineering.

From VIB‑to VB‑Group Transition Metal Disulfides:Structure Engineering Modulation for Superior Electromagnetic Wave Absorption

The laminated transition metal disulfides(TMDs),which are well known as typical two-dimensional(2D)semiconductive materials,possess a unique layered structure,leading to their wide-spread applications in various fields,such as catalysis,energy storage,sensing,etc.In recent years,a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption(EMA)has been carried out.Therefore,it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application.In this review,recent advances in the development of electromagnetic wave(EMW)absorbers based on TMDs,ranging from the VIB group to the VB group are summarized.Their compositions,microstructures,electronic properties,and synthesis methods are presented in detail.Particularly,the modulation of structure engineering from the aspects of heterostructures,defects,morphologies and phases are systematically summarized,focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance.Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

Preparation of CIP@TiO_(2) composite with broadband electromagnetic wave absorption properties

Scholars aim for the improved impedance matching (Z) of materials while maintaining their excellent wave absorption properties. Based on the hydrolysis characteristics of isopropyl titanate, a simple preparation process for the coating of carbonyl iron powder(CIP) with TiO_(2) was designed. Given the TiO2coating, the Z of the CIP@TiO_(2) composite was adjusted well by decreasing the dielectric constant. Moreover, the interfacial polarization of CIP@TiO_(2) was enhanced. Ultimately, the electromagnetic-wave (EMW) absorption property of the CIP@TiO_(2)composite was improved substantially, the minimum reflection loss reached-46.07 dB, and the effective absorption bandwidth can reach 8 GHz at the composite thickness of 1.5 mm. Moreover, compared with CIP, the oxidation resistance of CIP@TiO_(2)showed remarkable improvement. The results revealed that the oxidation starting temperature of CIP@TiO_(2) as about 400℃,whereas the uncoated CIP had an oxidation starting temperature of approximately 250℃. Moreover, the largest oxidation rate temperature of CIP@TiO_(2) increased to around 550℃. This work opens up a novel strategy for the production of high-performance EMW absorbers via structural design.

Self-Adaptive Matching Method of Signal and Energy Transmission

Aimed at the rapid message setting of the passive systems, the efficiency of energy transmission and the characteristics of signal transmission in the message setting are analyzed, which is based on the methods of the circuit analysis and the electromagnetic induction technology. A self-adaptive impedance matching method of signal and energy transmission, which can set the message rapidly and effectively, is put forward. The electromagnetic induct setting system will reach the highest energy transmission efficiency when the equivalent resistance of the second loop is equal to the resistance of the first loop. The greater the ratio of the equivalent resistances is, the higher efficient the signal transmission has. Moreover, the validity of the method is verified by circuit design and tests.

Insight to the enhanced microwave absorption of porous N-doped carbon driven by ZIF-8:Competition between graphitization and porosity

Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents.Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently required.Herein,utilizing the low boiling point of Zn,porous N-doped carbon was fabricated by carbonization of ZIF-8(Zn)at different temperature,and the microwave absorption performance was investigated.The porous N-doped carbon inherits the high porosity of ZIF-8 precursor.By increasing the carbonization temperature,the contents of Zn and N elements are decreased;the graphitization degree is improved;however,the specific surface area and porosity are increased first and then decreased.When the carbonization temperature is 1000°C,the porous N-doped carbon behaves enhanced microwave absorption.With an ultrathin thickness of 1.29 mm,the ideal RL reaches-50.57 dB at 16.95 GHz and the effective absorption bandwidth is 4.17 GHz.The mechanism of boosted microwave absorption is ascribed to the competition of graphitization and porosity as well as N dopants,resulting in high dielectric loss capacity and good impedance matching.The porous structure can prolong the pathways and raise the contact opportunity between microwaves and porous carbon,causing multiple scattering,interface polarization,and improved impedance matching.Besides,the N dopants can induce electron polarization and defect polarization.These results give a new insight to construct lightweight carbon-based microwave absorbents by regulating the graphitization and porosity.

Hollow Gradient-Structured Iron-Anchored Carbon Nanospheres for Enhanced Electromagnetic Wave Absorption

In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process.As a result,Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell.The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability,which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment.In addition,this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber.The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials.This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.

In-situ grown Ni Co bimetal anchored on porous straw-derived biochar composites with boosted microwave absorption properties

With the gradually increasing protection awareness about electromagnetic pollution,the demand for absorbing materials with renewability and environmental friendliness has attracted widespread attention.In this work,composites consisting of straw-derived biochar combined with NiCo alloy were successfully fabricated through high-temperature carbonization and subsequent hydrothermal reaction.The electromagnetic parameters of the porous biocarbon/NiCo composites can be effectively modified by altering their NiCo content,and their improved absorbing performance can be attributed to the synergy effect of magnetic-dielectric characteristics.An exceptional reflection loss of-27.0 dB at 2.2 mm thickness and an effective absorption bandwidth of 4.4 GHz(11.7-16.1 GHz)were achieved.These results revealed that the porous biocarbon/NiCo composites could be used as a new generation absorbing material because of their low density,light weight,excellent conductivity,and strong absorption.