[Background and purposes]In recent years,there has been growing attention in academia and industry on the development of high-performance electromagnetic wave(EMW)absorbing materials.However,creating lightweight broad...[Background and purposes]In recent years,there has been growing attention in academia and industry on the development of high-performance electromagnetic wave(EMW)absorbing materials.However,creating lightweight broadband absorbers remains a challenge in terms of practical applications.EMW absorbing materials primarily rely on the magnetic loss of magnetic materials and/or the dielectric loss of dielectric materials to convert EMW energy into thermal energy for dissipation.Among various magnetic materials,Fe_(3)O_(4) plays an irreplaceable role in EMW absorption due to its high saturation magnetization,low cost and compatible dielectric loss in the gigahertz frequency range.Nevertheless,the high density,large matching thickness and narrow absorption bandwidth of Fe_(3)O_(4) pose significant challenges for practical applications.In contrast,one-dimensional(1D)structures not only retain the characteristic properties of lightweight,chemical stability and high dielectric loss,but also exhibit anisotropic structures and large aspect ratios.Additionally,researchers have found that the minimum reflection loss(RL)of hollow carbon materials with mesopores is nearly four times that of non-porous hollow carbon materials and nine times that of dense carbon materials.According to Maxwell's EMW theory,composites consisting of Fe_(3)O_(4) and one-dimensional(1D)mesoporous carbon materials can leverage their respective advantages by optimizing the composition and structure of the composites to balance u,and Er,thereby enhancing EMW absorption performance.Additionally,numerous studies have demonstrated that composites composed of multi-component heterostructures significantly enhance the EAB.This enhancement is primarily ascribed to the numerous interface polarization losses generated by the additional heterostructure interfaces,which also improve the overall impedance matching of the composites.In this study,we leverage the advantages of magnetic/carbon composites,one-dimensional(1D)mesoporous carbon and multi-component heterostructures to prepare a composite of 1D mesoporous carbon-coated manganese oxide(Mn_(3)O_(4) and MnO,denoted as Mn_(x)O_(y))embedded with Fe_(3)0_(4) nanoparticles(Mn_(x)O_(y)/C@Fe_(3)O_(4)).This composite was synthesized and its formation mechanism and microstructure were analyzed in detail.At the same time,the influence of this Mn_(x)O_(y)/C@Fe_(3)O_(4) structure on EMW properties and absorbing performance was further discussed.[Methods]Firstly,MnO_(2) nanowires were synthesized by using a simple hydrothermal method.Then,the MnO_(2) nanowires served as templates for the synthesis of MnO_(2)/PDA@Fe^(3+)composites through the in-situ polymerization of dopamine and Fe^(3+)adsorption.Finally,1D mesoporous carbon-coated manganese oxide composite embedded with Fe_(3)O_(4) nanoparticles(Mn_(x)O_(y)/C@Fe_(3)O_(4))composites were obtained after heat treatment at 550℃ in N_(2).The crystal structure of the samples was analyzed using X-ray diffractometer with Cu Ka irradiation.Scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(TEM)were used to observe microstructure and morphology of the samples.Nitrogen sorption measurements were obtained at 77 K on a Quantachrome surface area and pore size analyzer to measure the specific surface area and pore size distribution.XPS analysis was performed on X-ray photoelectron spectrometer with monochromatic Al Ka radiation.Magnetization curves of the samples were recorded with a Quantum Design physical property measurement system(PPMS-9)at room temperature.The electromagnetic parameters of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composites were measured using an Agilent N5230C network analyzer in the frequency range of 2-18 GHz.For electromagentic testing,the Mn,Oy/C@Fe34 composites and paraffin wax were mixed at 50°C according to the mass ratio of 15 wt.%,20 wt.%and 25 wt.%,and pressed in a special mold to make coaxial rings(inner diameter=3.04 mm,outer diameter-7 mm),which were denoted as S-1,S-2 and S-3,respectively.[Results]SEM images illustrate the preparation process of iD mesoporous carbon-coated manganese oxide embedded with Fe3O4 nanoparticles composites(Mn_(x)O_(y)/C@Fe_(3)O_(4)).Most of the manganese oxide(Mn,Oy)was reduced to granular after heat treatment,while the outer carbon layer remains its 1D morphology and the carbon layer is interspersed with Fe_(3)O_(4) nanoparticles.The diffraction peaks of MnO_(2) nanowires align well with the body-centered tetragonal a-MnO2.For the Mn_(x)O_(y)/C@Fe_(3)O_(4) composites,the signals of α-MnO_(2) disappears,followed by the emergence of Mn_(3)O_(4) and three prominent diffraction peaks for the cubic MnO.In addition,four weak diffraction peaks correspond to the magnetite Fe_(3)O_(4),consistent with the HRTEM results.The corresponding nitrogen adsorption-desorption isotherm and pore size distribution curve are presented to further analyze the mesoporous structure of composite.The surface composition and element valence states of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composite were investigated by using XPS.The polarization relaxation processes were analyzed according to the Debye theory which describes the relationship between e'and e".Besides the polarization loss,the contribution of the conduction loss plays an important role for the overall dielectric loss.The magnetization curve of Mn_(x)O_(y)/C@Fe_(3)O_(4) exhibits typical ferromagnetic behavior.The permittivity parameter(Co),defined as Co=u"(u)^(-2)f^(-1) determine the contribution of eddy current effect to magnetic loss.The tand values are all larger than those of tand,for the three samples,indicating that the loss capacity of Mn_(x)O_(y)/C@Fe_(3)O_(4) composites is mainly derived from the dielectric loss.Although tand,is smaller,it plays an important role in improving the impedance matching of Mn_(x)O_(y)/C@Fe_(3)O_(4) composites.When the filler loading is 15 wt.%,the RL of sample S-1 is about-10.0 dB at the thickness of 1.5 mm with narrow EAB.As the filler loading increased to 20 wt.%,the RL of sample S-2 reached-62.0 dB at a thickness of 2.2 mm and the EAB was 6.4 GHz at a small thickness of 1.7 mm.When the filler loading is further increased to 25 wt.%,the microwave absorption performance of sample S3 decreased significantly with a little region of RL<-10.0 dB at the thickness of 5.0 mm.The values of[Zin/Zol of the three samples at thicknesses of 1.5-5.0 mm were calculated.Due to good impedance matching of S-2,the incident EMW can enter the material and then can be dissipated through dipole polarization loss,interface polarization loss,conduction loss,eddy current loss and natural ferromagnetic resonance loss.[Conclusions]1D Mn_(x)O_(y)/C@Fe_(3)O_(4) was synthesized via a process involving the coating of polydopamine,adsorption of Fe(ll)salts and heat treatment,using MnO_(2) nanowires as templates.The multi-component heterostructure of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composite(Mn_(3)O_(4),MnO,Fe_(3)O_(4),and C)enhances the interfacial interactions between the different phases,providing increased interface polarization loss under the action of an alternating electromagnetic field.The numerous defects and terminal groups in the mesoporous carbon provide abundant dipole polarization centers.Additionally,the presence of mesopores reduces the weight of the material while increasing the multiple scattering losses of the electromagnetic waves within the material.The ID carbon structure in the matrix forms a conductive network between adjacent fibers,facilitating electron migration and transition,thereby enhancing conductive loss.The incorporation of magnetic Fe_(3)O_(4) nanoparticles introduces eddy current loss and natural ferromagnetic resonance loss,thus increasing magnetic loss.Moreover,the synergistic effect between dielectric and magnetic losses improves the impedance matching of the material,leading to excellent EMW absorption performance.展开更多
In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the ...In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.展开更多
Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematicall...Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.展开更多
In this paper, the reactive splitter network and meta-surface are proposed to radiate the wide-beam isolated element pattern and suppress mutual coupling (MC) of the low-profile phased array with the triangular lattic...In this paper, the reactive splitter network and meta-surface are proposed to radiate the wide-beam isolated element pattern and suppress mutual coupling (MC) of the low-profile phased array with the triangular lattice, respectively. Thus, broadband wide-angle impedance matching (WAIM) is imple-mented to promote two-dimensional (2D) wide scanning. For the isolated element, to radiate the wide-beam patterns approximat-ing to the cosine form, two identical slots backed on one sub-strate integrated cavity are excited by the feeding network con-sisting of a reactive splitter and two striplines connected with splitter output paths. For adjacent elements staggered with each other, with the metasurface superstrate, the even-mode cou-pling voltages on the reactive splitter are cancelled out, yielding reduced MC. With the suppression of MC and the compensa-tion of isolated element patterns, WAIM is realized to achieve 2D wide-angle beam steering up to ± 65° in E-plane, ± 45° in H-plane and ± 60° in D-plane from 4.9 GHz to 5.85 GHz.展开更多
The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To th...The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To this end,this paper is based on the impedance matching method to test the ODD conditions of CL-20 type aluminium explosive particle velocity.Calculated the interfacial pressure of the shock wave in different media.Determined the characteristic parameters of the reaction zone of the detonation of CL-20 aluminized explosives.Calibrated the parameters of the JoneseWilkinseLee(JWL)+γ equation for the detonation products(DPs).Revealed the effect of different DPs equation of state(EOS)on the Hugoniot pressure of ODD.The results indicate that when the content of aluminum powder ranges from 0%to 30%,the duration of the ODD reaction zone and the width of the detonation reaction zone of the CL-20-based aluminized explosive are directly proportional to the content of aluminum powder.The width of the detonation reaction zone is increased by 1.97 times to 2.7 times compared to that of the reaction zone without the addition of aluminum powder.However,the energy release efficiency of the detonation reaction zone is inversely proportional to the content of aluminum powder.When the aluminum powder content was held constant,the incorporation of AP caused a 25%reduction in the energy release efficiency of the detonation reaction zone.Compared with existing ODD state equations,the JWL +γ equation is superior in calibrating overpressure Hugoniot data and the isentropic expansion in the C-J state.The deviation between calculated pressure results and experimental measurements is within 6%.展开更多
Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy(EIS), an integrated equivalent circuit model and impedance formula for soils were propo...Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy(EIS), an integrated equivalent circuit model and impedance formula for soils were proposed, which contain 6 meaningful resistance and reactance parameters. Considering the conductive properties of soils and dispersion effects, mathematical equations for impedance under various circuit models were deduced and studied. The mathematical expression presents two semicircles for theoretical EIS Nyquist spectrum, in which the center of one semicircle is degraded to simply the equivalent model. Based on the measured parameters of EIS Nyquist spectrum, meaningful soil parameters can easily be determined. Additionally, EIS was used to investigate the soil properties with different water contents along with the mathematical relationships and mechanism between the physical parameters and water content. Magnitude of the impedance decreases with the increase of testing frequency and water content for Bode graphs. The proposed model would help us to better understand the soil microstructure and properties and offer more reasonable explanations for EIS spectra.展开更多
Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little ...Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little literature is available on experimental validation of these calculation techniques.To address this,a programme of experimental tests on various earth electrodes has been carried out at the lower water reservoir of a hydro pumped-storage power station in North Wales.In this paper,the earthing test facility at Dinorwig power station is described including the details of the experimental set up.The results from experimental tests on a 5 mX5 m earth grid,immersed in water and energized under ac,dc and impulse,are presented.The values of measured earth resistance/impedance and water surface potential distributions are compared with those obtained from analytical calculations and detailed numerical computer simulations.展开更多
Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedan...Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedance function transfer method. Firstly, the sediment under rock-socketed pile was assumed to be fictitious soil pile with the same sectional area. The Rayleigh-Love rode model was used to simulate the rock-socketed pile and the fictitious soil pile with the consideration of the lateral inertial effect of large-diameter pile. The layered surrounding soils and bedrock were modeled by the plane strain model. Then, by virtue of the initial conditions and boundary conditions of the soil pile system, the analytical solution of the vertical dynamic impedance at the head of rock-socketed pile was derived for the arbitrary excitation acting on the pile head. Lastly, based on the presented analytical solution, the effect of sediment properties, bedrock property and lateral inertial effect on the vertical dynamic impedance at rock-socketed pile head were investigated in detail. It is shown that the sediment properties have significant effect on the vertical dynamic impedance at the rock-socketed pile head. The ability of soil-pile system to resist dynamic vertical deformation is weakened with the increase of sediment thickness, but amplified with the increase of shear wave velocity of sediment. The ability of soil pile system to resist dynamic vertical deformation is amplified with the bedrock property improving, but the ability of soil-pile system to resist vertical vibration is weakened with the improvement of bedrock property.展开更多
Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significa...Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significant temperature difference at the interface.An attempt is made to study the thermo-hydro-mechanical coupling dynamic response of bilayered saturated porous strata with thermal contact resistance and elastic wave impedance.The corresponding analytical solutions for the dynamic response of bilayered saturated porous strata under a harmonic thermal load are derived by the operator decomposition method,and their rationality is verified by comparing them with existing solutions.The influences of thermal contact resistance,thermal conductivity ratio,and porosity ratio on the dynamic response of bilayered saturated porous strata are systematically investigated.Outcomes disclose that with the increase of thermal contact resistance,the displacement,pore water pressure and stress decrease gradually,and the temperature jump at the interface between two saturated porous strata increases.展开更多
Robotic systems are expected to play an increasingly important role in future space activities. The robotic on-orbital service, whose key is the capturing technology, becomes a research hot spot in recent years. This ...Robotic systems are expected to play an increasingly important role in future space activities. The robotic on-orbital service, whose key is the capturing technology, becomes a research hot spot in recent years. This paper studies the dynamics modeling and impedance control of a multi-arm free-flying space robotic system capturing a non-cooperative target. Firstly, a control-oriented dynamics model is essential in control algorithm design and code realization. Unlike a numerical algorithm, an analytical approach is suggested. Using a general and a quasi-coordinate Lagrangian formulation, the kinematics and dynamics equations are derived.Then, an impedance control algorithm is developed which allows coordinated control of the multiple manipulators to capture a target.Through enforcing a reference impedance, end-effectors behave like a mass-damper-spring system fixed in inertial space in reaction to any contact force between the capture hands and the target. Meanwhile, the position and the attitude of the base are maintained stably by using gas jet thrusters to work against the manipulators' reaction. Finally, a simulation by using a space robot with two manipulators and a free-floating non-cooperative target is illustrated to verify the effectiveness of the proposed method.展开更多
A new impedance controller based on the dynamic surface control-backstepping technique to actualize the anticipant dynamic relationship between the motion of end-effector and the external torques was presented. Compar...A new impedance controller based on the dynamic surface control-backstepping technique to actualize the anticipant dynamic relationship between the motion of end-effector and the external torques was presented. Comparing with the traditional backstepping method that has ＂explosion of terms＂ problem, the new proposed control system is a combination of the dynamic surface control technique and the backstepping. The dynamic surface control （DSC） technique can resolve the ＂explosion of terms＂ problem that is caused by differential coefficient calculation in the model, and the problem can bring a complexity that will cause the backstepping method hardly to be applied to the practical application, especially to the multi-joint robot. Finally, the validity of the method was proved in the laboratory environment that was set up on the 5-DOF （degree of freedom） flexible joint robot. Tracking errors of DSC-backstepping impedance control that were 2.0 and 1.5 mm are better than those of backstepping impedance control which were 3.5 and 2.5 mm in directions X, Y in free space, respectively. And the anticipant Cartesian impedance behavior and compliant behavior were nchieved successfully as depicted theoretically.展开更多
To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chroma...To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.展开更多
In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments,an impedance-based adaptive reference trajectory generation scheme is used.Secondly,in order ...In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments,an impedance-based adaptive reference trajectory generation scheme is used.Secondly,in order to improve the robustness to environmental changes and reduce the contact force errors caused by trajectory tracking errors,the backstepping sliding mode controller is combined with the adaptive reference trajectory generator.Finally,a virtual damping control based on velocity and pressure feedback is proposed to solve the problem of contact force disappearance and stall caused by sudden environmental change.The simulation results show that the proposed scheme has higher contact force tracking accuracy when the environment is unchanged;the contact force error can always be guaranteed within an acceptable range when the environment is reasonably changed;when the environment suddenly changes,the drive unit can move slowly until the robot re-contacts the environment.展开更多
A grasping force control strategy is proposed in order to complete various free manipulations by using anthropomorphic prosthetic hand. The position-based impedance control and force-tracking impedance control are use...A grasping force control strategy is proposed in order to complete various free manipulations by using anthropomorphic prosthetic hand. The position-based impedance control and force-tracking impedance control are used in free and constraint spaces, respectively. The fuzzy observer is adopted in transition in order to switch control mode. Two control modes use one position-based impedance controller. In order to achieve grasping force track, reference force is added to the impedance controller in the constraint space. Trajectory tracking in free space and torque tracking in constrained space are realized, and reliability of mode switch and stability of system are achieved. An adaptive sliding mode friction compensation method is proposed. This method makes use of terminal sliding mode idea to design sliding mode function, which makes the tracking error converge to zero in finite time and avoids the problem of conventional sliding surface that tracking error cannot converge to zero. Based on the characteristic of the exponential form friction, the sliding mode control law including the estimation of friction parameter is obtained through terminal sliding mode idea, and the online parameter update laws are obtained based on Lyapunov stability theorem. The experiments on the HIT Prosthetic Hand IV are carried out to evaluate the grasping force control strategy, and the experiment results verify the effectiveness of this control strategy.展开更多
In this work,the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths and full-scale tower footings were reported.These e...In this work,the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths and full-scale tower footings were reported.These electrodes were installed at an outdoor test site having nonuniform soil,with equipment facilities for generating low-and high-magnitude impulse currents.The tests on the horizontal electrode were used to determine the effective length,the voltage and current distribution along the electrode length and the effect of the injection point along the electrode.The tests on the tower footings were used to determine impulse resistance and demonstrate its non-linear variation with current magnitude.Computer simulations of the test electrodes using the electromagnetic field method showed good agreement with the measured result.展开更多
An adaptive technique adopting quantum genetic algorithm （QGA） for antenna impedance tuning is presented. Three examples are given with different types of antenna impedance. The frequency range of the dual standards...An adaptive technique adopting quantum genetic algorithm （QGA） for antenna impedance tuning is presented. Three examples are given with different types of antenna impedance. The frequency range of the dual standards is from 1.7 to 2.2 GHz. Simulation results show that the proposed tuning technique can achieve good accuracy of impedance matching and load power. The reflection coefficient and VSWR obtained are also very close to their ideal values. Comparison of the proposed QGA tuning method with conventional genetic algorithm based tuning method is Moreover, the proposed method can be useful for software wireless bands. also given, which shows that the QGA tuning algorithm is much faster. defined radio systems using a single antenna for multiple mobile and展开更多
This paper introduces the research work on the extension of multilevel fast multipole algorithm （MLFMA） to 3D complex structures including coating object, thin dielectric sheet, composite dielectric and conductor, c...This paper introduces the research work on the extension of multilevel fast multipole algorithm （MLFMA） to 3D complex structures including coating object, thin dielectric sheet, composite dielectric and conductor, cavity. The impedance boundary condition is used for scattering from the object coated by thin lossy material. Instead of volume integral equation, surface integral equation is applied in case of thin dielectric sheet through resistive sheet boundary condition. To realize the fast computation of scattering from composite homogeneous dielectric and conductor, the surface integral equation based on equivalence principle is used. Compared with the traditional volume integral equation, the surface integral equation reduces greatly the number of unknowns. To computc conducting cavity with electrically large aperture, an electric field integral equation is applied. Some numerical results are given to demonstrate the validity and accuracy of the present methods.展开更多
基金National Natural Science Foundation of China (52371171, 52222106, 51971008, 52121001)Fund of National Key Laboratory of Scattering and Radiation (Beijing Institute of Environmental Features)。
文摘[Background and purposes]In recent years,there has been growing attention in academia and industry on the development of high-performance electromagnetic wave(EMW)absorbing materials.However,creating lightweight broadband absorbers remains a challenge in terms of practical applications.EMW absorbing materials primarily rely on the magnetic loss of magnetic materials and/or the dielectric loss of dielectric materials to convert EMW energy into thermal energy for dissipation.Among various magnetic materials,Fe_(3)O_(4) plays an irreplaceable role in EMW absorption due to its high saturation magnetization,low cost and compatible dielectric loss in the gigahertz frequency range.Nevertheless,the high density,large matching thickness and narrow absorption bandwidth of Fe_(3)O_(4) pose significant challenges for practical applications.In contrast,one-dimensional(1D)structures not only retain the characteristic properties of lightweight,chemical stability and high dielectric loss,but also exhibit anisotropic structures and large aspect ratios.Additionally,researchers have found that the minimum reflection loss(RL)of hollow carbon materials with mesopores is nearly four times that of non-porous hollow carbon materials and nine times that of dense carbon materials.According to Maxwell's EMW theory,composites consisting of Fe_(3)O_(4) and one-dimensional(1D)mesoporous carbon materials can leverage their respective advantages by optimizing the composition and structure of the composites to balance u,and Er,thereby enhancing EMW absorption performance.Additionally,numerous studies have demonstrated that composites composed of multi-component heterostructures significantly enhance the EAB.This enhancement is primarily ascribed to the numerous interface polarization losses generated by the additional heterostructure interfaces,which also improve the overall impedance matching of the composites.In this study,we leverage the advantages of magnetic/carbon composites,one-dimensional(1D)mesoporous carbon and multi-component heterostructures to prepare a composite of 1D mesoporous carbon-coated manganese oxide(Mn_(3)O_(4) and MnO,denoted as Mn_(x)O_(y))embedded with Fe_(3)0_(4) nanoparticles(Mn_(x)O_(y)/C@Fe_(3)O_(4)).This composite was synthesized and its formation mechanism and microstructure were analyzed in detail.At the same time,the influence of this Mn_(x)O_(y)/C@Fe_(3)O_(4) structure on EMW properties and absorbing performance was further discussed.[Methods]Firstly,MnO_(2) nanowires were synthesized by using a simple hydrothermal method.Then,the MnO_(2) nanowires served as templates for the synthesis of MnO_(2)/PDA@Fe^(3+)composites through the in-situ polymerization of dopamine and Fe^(3+)adsorption.Finally,1D mesoporous carbon-coated manganese oxide composite embedded with Fe_(3)O_(4) nanoparticles(Mn_(x)O_(y)/C@Fe_(3)O_(4))composites were obtained after heat treatment at 550℃ in N_(2).The crystal structure of the samples was analyzed using X-ray diffractometer with Cu Ka irradiation.Scanning electron microscopy(SEM)and high-resolution transmission electron microscopy(TEM)were used to observe microstructure and morphology of the samples.Nitrogen sorption measurements were obtained at 77 K on a Quantachrome surface area and pore size analyzer to measure the specific surface area and pore size distribution.XPS analysis was performed on X-ray photoelectron spectrometer with monochromatic Al Ka radiation.Magnetization curves of the samples were recorded with a Quantum Design physical property measurement system(PPMS-9)at room temperature.The electromagnetic parameters of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composites were measured using an Agilent N5230C network analyzer in the frequency range of 2-18 GHz.For electromagentic testing,the Mn,Oy/C@Fe34 composites and paraffin wax were mixed at 50°C according to the mass ratio of 15 wt.%,20 wt.%and 25 wt.%,and pressed in a special mold to make coaxial rings(inner diameter=3.04 mm,outer diameter-7 mm),which were denoted as S-1,S-2 and S-3,respectively.[Results]SEM images illustrate the preparation process of iD mesoporous carbon-coated manganese oxide embedded with Fe3O4 nanoparticles composites(Mn_(x)O_(y)/C@Fe_(3)O_(4)).Most of the manganese oxide(Mn,Oy)was reduced to granular after heat treatment,while the outer carbon layer remains its 1D morphology and the carbon layer is interspersed with Fe_(3)O_(4) nanoparticles.The diffraction peaks of MnO_(2) nanowires align well with the body-centered tetragonal a-MnO2.For the Mn_(x)O_(y)/C@Fe_(3)O_(4) composites,the signals of α-MnO_(2) disappears,followed by the emergence of Mn_(3)O_(4) and three prominent diffraction peaks for the cubic MnO.In addition,four weak diffraction peaks correspond to the magnetite Fe_(3)O_(4),consistent with the HRTEM results.The corresponding nitrogen adsorption-desorption isotherm and pore size distribution curve are presented to further analyze the mesoporous structure of composite.The surface composition and element valence states of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composite were investigated by using XPS.The polarization relaxation processes were analyzed according to the Debye theory which describes the relationship between e'and e".Besides the polarization loss,the contribution of the conduction loss plays an important role for the overall dielectric loss.The magnetization curve of Mn_(x)O_(y)/C@Fe_(3)O_(4) exhibits typical ferromagnetic behavior.The permittivity parameter(Co),defined as Co=u"(u)^(-2)f^(-1) determine the contribution of eddy current effect to magnetic loss.The tand values are all larger than those of tand,for the three samples,indicating that the loss capacity of Mn_(x)O_(y)/C@Fe_(3)O_(4) composites is mainly derived from the dielectric loss.Although tand,is smaller,it plays an important role in improving the impedance matching of Mn_(x)O_(y)/C@Fe_(3)O_(4) composites.When the filler loading is 15 wt.%,the RL of sample S-1 is about-10.0 dB at the thickness of 1.5 mm with narrow EAB.As the filler loading increased to 20 wt.%,the RL of sample S-2 reached-62.0 dB at a thickness of 2.2 mm and the EAB was 6.4 GHz at a small thickness of 1.7 mm.When the filler loading is further increased to 25 wt.%,the microwave absorption performance of sample S3 decreased significantly with a little region of RL<-10.0 dB at the thickness of 5.0 mm.The values of[Zin/Zol of the three samples at thicknesses of 1.5-5.0 mm were calculated.Due to good impedance matching of S-2,the incident EMW can enter the material and then can be dissipated through dipole polarization loss,interface polarization loss,conduction loss,eddy current loss and natural ferromagnetic resonance loss.[Conclusions]1D Mn_(x)O_(y)/C@Fe_(3)O_(4) was synthesized via a process involving the coating of polydopamine,adsorption of Fe(ll)salts and heat treatment,using MnO_(2) nanowires as templates.The multi-component heterostructure of the Mn_(x)O_(y)/C@Fe_(3)O_(4) composite(Mn_(3)O_(4),MnO,Fe_(3)O_(4),and C)enhances the interfacial interactions between the different phases,providing increased interface polarization loss under the action of an alternating electromagnetic field.The numerous defects and terminal groups in the mesoporous carbon provide abundant dipole polarization centers.Additionally,the presence of mesopores reduces the weight of the material while increasing the multiple scattering losses of the electromagnetic waves within the material.The ID carbon structure in the matrix forms a conductive network between adjacent fibers,facilitating electron migration and transition,thereby enhancing conductive loss.The incorporation of magnetic Fe_(3)O_(4) nanoparticles introduces eddy current loss and natural ferromagnetic resonance loss,thus increasing magnetic loss.Moreover,the synergistic effect between dielectric and magnetic losses improves the impedance matching of the material,leading to excellent EMW absorption performance.
基金Supported by the Beijing Municipal Science&Technology Commission(Z211100004421012),the Key Reaserch and Development Pro⁃gram of China(2022YFF0605902)。
文摘In this paper,a linear optimization method(LOM)for the design of terahertz circuits is presented,aimed at enhancing the simulation efficacy and reducing the time of the circuit design workflow.This method enables the rapid determination of optimal embedding impedance for diodes across a specific bandwidth to achieve maximum efficiency through harmonic balance simulations.By optimizing the linear matching circuit with the optimal embedding impedance,the method effectively segregates the simulation of the linear segments from the nonlinear segments in the frequency multiplier circuit,substantially improving the speed of simulations.The design of on-chip linear matching circuits adopts a modular circuit design strategy,incorporating fixed load resistors to simplify the matching challenge.Utilizing this approach,a 340 GHz frequency doubler was developed and measured.The results demonstrate that,across a bandwidth of 330 GHz to 342 GHz,the efficiency of the doubler remains above 10%,with an input power ranging from 98 mW to 141mW and an output power exceeding 13 mW.Notably,at an input power of 141 mW,a peak output power of 21.8 mW was achieved at 334 GHz,corresponding to an efficiency of 15.8%.
基金Projects(82171030,81870678)supported by the National Natural Science Foundation of China。
文摘Magnesium alloys as medical implant materials necessitate a lower and adjustable corrosion rate for clinical applications.The microstructure and corrosion behavior of AZ31Mn-xEr(x=0.1,0.5,1.2)alloys were systematically investigated using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS),combined with Tafel polarization and electrochemical impedance spectroscopy(EIS)analyses.The findings showed that the alloying element Er refined the grain structure during solidification by increasing the nucleation rate and forming a secondary phase of Al_(3)Er with Al.The Er and Mg in the matrix co-oxidize to form a dense MgO/Er_(2)O_(3)composite oxide,preventing the formation of loose magnesium hydroxide/basic magnesium carbonate.The trace alloying element Mn interacts with impurities Fe in the magnesium matrix to form an AlFeMn second phase,reducing micro-galvanic corrosion driving force.Electrochemical testing in a 3.5%NaCl solution demonstrated a marked reduction in corrosion rate from 10.46 mm/a(AZ 31 Mn alloy)to 0.44 mm/a(AZ31Mn-1.2Er alloy).This research offers a reference for searching for corrosion-resistant magnesium alloy and degradable medical magnesium alloy materials.
基金supported by Sichuan Science and Technology Programs(2022NSFSC0547,2022ZYD0109)the 2020 Open Foundation of Key Laboratory of Cognitive Radio and Information Processing,Ministry of Education(Guilin University of Electronic Technology)(CRKL200201).
文摘In this paper, the reactive splitter network and meta-surface are proposed to radiate the wide-beam isolated element pattern and suppress mutual coupling (MC) of the low-profile phased array with the triangular lattice, respectively. Thus, broadband wide-angle impedance matching (WAIM) is imple-mented to promote two-dimensional (2D) wide scanning. For the isolated element, to radiate the wide-beam patterns approximat-ing to the cosine form, two identical slots backed on one sub-strate integrated cavity are excited by the feeding network con-sisting of a reactive splitter and two striplines connected with splitter output paths. For adjacent elements staggered with each other, with the metasurface superstrate, the even-mode cou-pling voltages on the reactive splitter are cancelled out, yielding reduced MC. With the suppression of MC and the compensa-tion of isolated element patterns, WAIM is realized to achieve 2D wide-angle beam steering up to ± 65° in E-plane, ± 45° in H-plane and ± 60° in D-plane from 4.9 GHz to 5.85 GHz.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.11872120,12102050)Key Laboratory of Explosion Science and Technology(Grant No.QNKT22-01).
文摘The new CL-20(hexanitrohexaazaisowurtzitane)type aluminized explosives in the overdrive detonation(ODD)conditions of the core problem is how to accurately represent the state of the overdrive detonation products.To this end,this paper is based on the impedance matching method to test the ODD conditions of CL-20 type aluminium explosive particle velocity.Calculated the interfacial pressure of the shock wave in different media.Determined the characteristic parameters of the reaction zone of the detonation of CL-20 aluminized explosives.Calibrated the parameters of the JoneseWilkinseLee(JWL)+γ equation for the detonation products(DPs).Revealed the effect of different DPs equation of state(EOS)on the Hugoniot pressure of ODD.The results indicate that when the content of aluminum powder ranges from 0%to 30%,the duration of the ODD reaction zone and the width of the detonation reaction zone of the CL-20-based aluminized explosive are directly proportional to the content of aluminum powder.The width of the detonation reaction zone is increased by 1.97 times to 2.7 times compared to that of the reaction zone without the addition of aluminum powder.However,the energy release efficiency of the detonation reaction zone is inversely proportional to the content of aluminum powder.When the aluminum powder content was held constant,the incorporation of AP caused a 25%reduction in the energy release efficiency of the detonation reaction zone.Compared with existing ODD state equations,the JWL +γ equation is superior in calibrating overpressure Hugoniot data and the isentropic expansion in the C-J state.The deviation between calculated pressure results and experimental measurements is within 6%.
基金Projects(5120833351078253)supported by the National Natural Science Foundation of China+4 种基金Projects(2014011036-12014131019TYUT2014YQ017OIT2015)supported by the Natural Science Foundation of Shanxi ProvinceChina
文摘Based on three different kinds of conductive paths in microstructure of soil and theory of electrochemical impedance spectroscopy(EIS), an integrated equivalent circuit model and impedance formula for soils were proposed, which contain 6 meaningful resistance and reactance parameters. Considering the conductive properties of soils and dispersion effects, mathematical equations for impedance under various circuit models were deduced and studied. The mathematical expression presents two semicircles for theoretical EIS Nyquist spectrum, in which the center of one semicircle is degraded to simply the equivalent model. Based on the measured parameters of EIS Nyquist spectrum, meaningful soil parameters can easily be determined. Additionally, EIS was used to investigate the soil properties with different water contents along with the mathematical relationships and mechanism between the physical parameters and water content. Magnitude of the impedance decreases with the increase of testing frequency and water content for Bode graphs. The proposed model would help us to better understand the soil microstructure and properties and offer more reasonable explanations for EIS spectra.
文摘Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little literature is available on experimental validation of these calculation techniques.To address this,a programme of experimental tests on various earth electrodes has been carried out at the lower water reservoir of a hydro pumped-storage power station in North Wales.In this paper,the earthing test facility at Dinorwig power station is described including the details of the experimental set up.The results from experimental tests on a 5 mX5 m earth grid,immersed in water and energized under ac,dc and impulse,are presented.The values of measured earth resistance/impedance and water surface potential distributions are compared with those obtained from analytical calculations and detailed numerical computer simulations.
基金Projects(51109084/E09070151308234/E08061) supported by the National Natural Science Foundation of China+1 种基金Project(2013J05079) supported by the Natural Science Foundation of Fujian Province,ChinaProject(Z012002) supported by the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(Institute of Rock and Soil Mechanics,Chinese Academy of Sciences),China
文摘Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedance function transfer method. Firstly, the sediment under rock-socketed pile was assumed to be fictitious soil pile with the same sectional area. The Rayleigh-Love rode model was used to simulate the rock-socketed pile and the fictitious soil pile with the consideration of the lateral inertial effect of large-diameter pile. The layered surrounding soils and bedrock were modeled by the plane strain model. Then, by virtue of the initial conditions and boundary conditions of the soil pile system, the analytical solution of the vertical dynamic impedance at the head of rock-socketed pile was derived for the arbitrary excitation acting on the pile head. Lastly, based on the presented analytical solution, the effect of sediment properties, bedrock property and lateral inertial effect on the vertical dynamic impedance at rock-socketed pile head were investigated in detail. It is shown that the sediment properties have significant effect on the vertical dynamic impedance at the rock-socketed pile head. The ability of soil-pile system to resist dynamic vertical deformation is weakened with the increase of sediment thickness, but amplified with the increase of shear wave velocity of sediment. The ability of soil pile system to resist dynamic vertical deformation is amplified with the bedrock property improving, but the ability of soil-pile system to resist vertical vibration is weakened with the improvement of bedrock property.
基金Projects(52108347,52178371)supported by the National Natural Science Foundation of ChinaProject(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,China。
文摘Porous materials can be found in a variety of geophysical and engineering applications.The existence of thermal contact resistance at the interface between bilayered saturated porous strata would result in a significant temperature difference at the interface.An attempt is made to study the thermo-hydro-mechanical coupling dynamic response of bilayered saturated porous strata with thermal contact resistance and elastic wave impedance.The corresponding analytical solutions for the dynamic response of bilayered saturated porous strata under a harmonic thermal load are derived by the operator decomposition method,and their rationality is verified by comparing them with existing solutions.The influences of thermal contact resistance,thermal conductivity ratio,and porosity ratio on the dynamic response of bilayered saturated porous strata are systematically investigated.Outcomes disclose that with the increase of thermal contact resistance,the displacement,pore water pressure and stress decrease gradually,and the temperature jump at the interface between two saturated porous strata increases.
基金supported by the National Natural Science Foundation of China (61673009)。
文摘Robotic systems are expected to play an increasingly important role in future space activities. The robotic on-orbital service, whose key is the capturing technology, becomes a research hot spot in recent years. This paper studies the dynamics modeling and impedance control of a multi-arm free-flying space robotic system capturing a non-cooperative target. Firstly, a control-oriented dynamics model is essential in control algorithm design and code realization. Unlike a numerical algorithm, an analytical approach is suggested. Using a general and a quasi-coordinate Lagrangian formulation, the kinematics and dynamics equations are derived.Then, an impedance control algorithm is developed which allows coordinated control of the multiple manipulators to capture a target.Through enforcing a reference impedance, end-effectors behave like a mass-damper-spring system fixed in inertial space in reaction to any contact force between the capture hands and the target. Meanwhile, the position and the attitude of the base are maintained stably by using gas jet thrusters to work against the manipulators' reaction. Finally, a simulation by using a space robot with two manipulators and a free-floating non-cooperative target is illustrated to verify the effectiveness of the proposed method.
基金Project(2006AA04Z228) supported by the National High-Tech Research and Development Program of ChinaProject(PCSIRT) supported by Program for Changjiang Scholars and Innovative Research Team in University
文摘A new impedance controller based on the dynamic surface control-backstepping technique to actualize the anticipant dynamic relationship between the motion of end-effector and the external torques was presented. Comparing with the traditional backstepping method that has ＂explosion of terms＂ problem, the new proposed control system is a combination of the dynamic surface control technique and the backstepping. The dynamic surface control （DSC） technique can resolve the ＂explosion of terms＂ problem that is caused by differential coefficient calculation in the model, and the problem can bring a complexity that will cause the backstepping method hardly to be applied to the practical application, especially to the multi-joint robot. Finally, the validity of the method was proved in the laboratory environment that was set up on the 5-DOF （degree of freedom） flexible joint robot. Tracking errors of DSC-backstepping impedance control that were 2.0 and 1.5 mm are better than those of backstepping impedance control which were 3.5 and 2.5 mm in directions X, Y in free space, respectively. And the anticipant Cartesian impedance behavior and compliant behavior were nchieved successfully as depicted theoretically.
基金Projects(U1534207,11790283,51878583)supported by the National Natural Science Foundation of China。
文摘To understand the effect of steam curing temperature on the hydrate and microstructure of hardened cement paste,several measuring methods including X-ray diffraction(XRD),atomic absorption spectroscopy(ASS),ion chromatography,conductivity meter,alternating-current impedance spectroscopy and nuclear magnetic resonance(NMR)are employed to investigate the hydration characteristics,pore solution composition and conductivity,resistivity and pore structure during the steam curing process.Experimental results show that steam curing promotes the hydration process,greatly raises the resistivity,and decreases the porosity of specimen at early age.Compared with being treated at 45℃,higher temperature leads to a fast decomposition of ettringite at initial stage of the constant temperature treatment period,which improves the relative content and ionic activity of the conductive ions in pore solution.Furthermore,the number of pores larger than 200 nm increases significantly,which reduces the resistivity of the hardened cement paste.Cement paste treated at 45℃ has a more stable and denser microstructure with less damages.
基金Projects(51975376,51505289)supported by the National Natural Science Foundation of ChinaProject(19ZR1435400)supported by the Natural Science Foundation of Shanghai,China。
文摘In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments,an impedance-based adaptive reference trajectory generation scheme is used.Secondly,in order to improve the robustness to environmental changes and reduce the contact force errors caused by trajectory tracking errors,the backstepping sliding mode controller is combined with the adaptive reference trajectory generator.Finally,a virtual damping control based on velocity and pressure feedback is proposed to solve the problem of contact force disappearance and stall caused by sudden environmental change.The simulation results show that the proposed scheme has higher contact force tracking accuracy when the environment is unchanged;the contact force error can always be guaranteed within an acceptable range when the environment is reasonably changed;when the environment suddenly changes,the drive unit can move slowly until the robot re-contacts the environment.
基金Project(2009AA043803) supported by the National High Technology Research and Development Program of China Project (SKLRS200901B) supported by Self-Planned Task of State Key Laboratory of Robotics and System (Harbin Institute of Technology),ChinaProject (NCET-09-0056) supported by Program for New Century Excellent Talents in Universities of China
文摘A grasping force control strategy is proposed in order to complete various free manipulations by using anthropomorphic prosthetic hand. The position-based impedance control and force-tracking impedance control are used in free and constraint spaces, respectively. The fuzzy observer is adopted in transition in order to switch control mode. Two control modes use one position-based impedance controller. In order to achieve grasping force track, reference force is added to the impedance controller in the constraint space. Trajectory tracking in free space and torque tracking in constrained space are realized, and reliability of mode switch and stability of system are achieved. An adaptive sliding mode friction compensation method is proposed. This method makes use of terminal sliding mode idea to design sliding mode function, which makes the tracking error converge to zero in finite time and avoids the problem of conventional sliding surface that tracking error cannot converge to zero. Based on the characteristic of the exponential form friction, the sliding mode control law including the estimation of friction parameter is obtained through terminal sliding mode idea, and the online parameter update laws are obtained based on Lyapunov stability theorem. The experiments on the HIT Prosthetic Hand IV are carried out to evaluate the grasping force control strategy, and the experiment results verify the effectiveness of this control strategy.
文摘In this work,the results of an experimental study of the impulse characteristic of practical ground electrodes consisting of horizontal conductors of various lengths and full-scale tower footings were reported.These electrodes were installed at an outdoor test site having nonuniform soil,with equipment facilities for generating low-and high-magnitude impulse currents.The tests on the horizontal electrode were used to determine the effective length,the voltage and current distribution along the electrode length and the effect of the injection point along the electrode.The tests on the tower footings were used to determine impulse resistance and demonstrate its non-linear variation with current magnitude.Computer simulations of the test electrodes using the electromagnetic field method showed good agreement with the measured result.
基金Projects(61102039, 51107034) supported by the National Natural Science Foundation of ChinaProject(2011FJ3080) supported by the Planned Science and Technology Project of Hunan Province ChinaProject supported by Fundamental Research Funds for the Central Universities, China
文摘An adaptive technique adopting quantum genetic algorithm （QGA） for antenna impedance tuning is presented. Three examples are given with different types of antenna impedance. The frequency range of the dual standards is from 1.7 to 2.2 GHz. Simulation results show that the proposed tuning technique can achieve good accuracy of impedance matching and load power. The reflection coefficient and VSWR obtained are also very close to their ideal values. Comparison of the proposed QGA tuning method with conventional genetic algorithm based tuning method is Moreover, the proposed method can be useful for software wireless bands. also given, which shows that the QGA tuning algorithm is much faster. defined radio systems using a single antenna for multiple mobile and
基金the National Natural Science Foundation of China (60431010, 60601008)New Century 0Excellent Talent Support Plan of China (NCET-05-0805)+3 种基金the International Joint Research Project(607048)in part by the "973" Programs(61360, 2008CB317110)Research Founding (9110A03010708DZ0235)Young Doctor Discipline Platform of UESTC
文摘This paper introduces the research work on the extension of multilevel fast multipole algorithm （MLFMA） to 3D complex structures including coating object, thin dielectric sheet, composite dielectric and conductor, cavity. The impedance boundary condition is used for scattering from the object coated by thin lossy material. Instead of volume integral equation, surface integral equation is applied in case of thin dielectric sheet through resistive sheet boundary condition. To realize the fast computation of scattering from composite homogeneous dielectric and conductor, the surface integral equation based on equivalence principle is used. Compared with the traditional volume integral equation, the surface integral equation reduces greatly the number of unknowns. To computc conducting cavity with electrically large aperture, an electric field integral equation is applied. Some numerical results are given to demonstrate the validity and accuracy of the present methods.
