Metal–Organic Gel Leading to Customized Magnetic‑Coupling Engineering in Carbon Aerogels for Excellent Radar Stealth and Thermal Insulation Performances

Metal–organic gel(MOG)derived composites are promising multi-functional materials due to their alterable composition,identifiable chemical homogeneity,tunable shape,and porous structure.Herein,stable metal–organic hydrogels are prepared by regulating the complexation effect,solution polarity and curing speed.Meanwhile,collagen peptide is used to facilitate the fabrication of a porous aerogel with excellent physical properties as well as the homogeneous dispersion of magnetic particles during calcination.Subsequently,two kinds of heterometallic magnetic coupling systems are obtained through the application of Kirkendall effect.FeCo/nitrogen-doped carbon(NC)aerogel demonstrates an ultra-strong microwave absorption of−85 dB at an ultra-low loading of 5%.After reducing the time taken by atom shifting,a FeCo/Fe3O4/NC aerogel containing virus-shaped particles is obtained,which achieves an ultra-broad absorption of 7.44 GHz at an ultra-thin thickness of 1.59 mm due to the coupling effect offered by dual-soft-magnetic particles.Furthermore,both aerogels show excellent thermal insulation property,and their outstanding radar stealth performances in J-20 aircraft are confirmed by computer simulation technology.The formation mechanism of MOG is also discussed along with the thermal insulation and electromagnetic wave absorption mechanism of the aerogels,which will enable the development and application of novel and lightweight stealth coatings.

Nonlinear Control of Magnetically Coupled Rodless Cylinder Position Servo System

Magnetically coupled rodless cylinders are widely used in the coordinate positioning of mechanical arms,electro-static paintings,and other industrial applications.However,they exhibit strong nonlinear characteristics,which lead to low servo control accuracy.In this study,a mass-flow equation through the valve port was derived to improve the control performance,considering the characteristics of the dynamics and throttle-hole flow.Subsequently,a fric-tion model combining static,viscous,and Coulomb friction with a zero-velocity interval was proposed.In addition,energy and dynamic models were set for the experimental investigation of the magnetically coupled rodless cylin-der.A nonlinear mathematical model for the position of the magnetically coupled rodless cylinder was proposed.An incremental PID controller was designed for the magnetically coupled rodless cylinder to control this system,and the PID parameters were adjusted online using RBF neural network.The response results of the PID parameters based on the RBF neural network were compared with those of the traditional incremental PID control,which proved the superiority of the optimization control algorithm of the incremental PID parameters based on the RBF neural network servo control system.The experimental results of this model were compared with the simulation results.The average error between the established model and the actual system was 0.005175054(m),which was approximately 2.588%of the total travel length,demonstrating the accuracy of the theoretical model.

Mixed Electric and Magnetic Coupling Design Based on Coupling Matrix Extraction

This paper proposes a design and fine-tuning method for mixed electric and magnetic coupling filters.It derives the quantitative relationship between the coupling coefficients(electric and magnetic coupling,i.e.,EC and MC)and the linear coefficients of frequencydependent coupling for the first time.Different from the parameter extraction technique using the bandpass circuit model,the proposed approach explicitly relatesEC and MC to the coupling matrix model.This paper provides a general theoretic framework for computer-aided design and tuning of a mixed electric and magnetic coupling filter based on coupling matrices.An example of a 7th-order coaxial combline filter design is given in the paper,verifying the practical value of the approach.

Abnormality of Magnetic Behavior and Resistivity of La_(0.7-x)Dy_x Sr_(0.3)MnO_3 (0.00≤x≤0.30)System at Low Temperature

By measuring M-T curves, ρ-T curves and MR-T curves of the samples under different temperatures, the influence of Dy doping （0.00 ≤ x ≤0.30） on the magnetic and electric properties of La0.7-xDyxSr0.3MnO3 has been studied. The experimental results show that, with the increase of the Dy content, the system undergoes a transition from long range ferromagnetic order to the cluster-spin glass state and further to antiferromagnetic order. For the samples with x=0.20 and 0.30, their magnetic behaviors are abnormal at low temperature, and their resistivities at low temperature have a minimum value. These peculiar phenomena not only come from the lattice effect induced by doping, but also from extra magnetic coupling induced by doping.

Broadband energy harvesting via magnetic coupling between two movable magnets

Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester （PEH） is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.

π-π Stacking, Hydrogen Bonding and Magnetic Coupling Mechanism on a Mono-nuclear Cu^Ⅱ Complex

A new mono-nuclear CuII complex [Cu（DPP）（DP）Br]（ClO4）H2O （DPP = 2-（3,5- dimethyl-1H-pyrazol-1-yl）-1,10-phenanthroline, DP = 3,5-dimethyl-1H-pyrazole） has been syn- thesized with 2-（3,5-dimethyl-1H-pyrazol-1-yl）-1,10-phenanthroline and 3,5-dimethyl-1H-pyrazole as ligands, and its crystal structure was determined by X-ray crystallography. The crystal is of monoclinic system, space group P21/c with a = 13.765（2）, b = 17.044（3）, c = 10.9044（16）, β= 97.112（2）°, V = 2538.5（6）3, Z = 4, C22H24BrClCuN6O5, Mr = 631.37, Dc = 1.652 g/cm3, F（000） = 1276 and μ= 2.585 mm-1. In the crystal, DPP functions as a tridentate ligand and CuII ions assume a distorted square pyramidal geometry with Br atom lying on the apex, and at the same time, there is π-π stacking between adjacent complexes, which deals with two 1,10-phenanthroline plane rings. In addition to the π-π stacking, there are C-H···Br non-classic hydrogen bonds between adjacent complexes. The theoretical calculations reveal that the π-π stacking and C-H···Br non-classic hydrogen bond result in a weak anti-ferromagnetic interaction with 2J = -5.34 cm-1 and a weak ferromagnetic 2J = 5.92 cm-1, respectively. The magnetic coupling sign from the π-π stacking could be explained with McConnell I spin-polarization mechanism.

Decoupling technique of patch antenna arrays with shared substrate by suppressing near-field magnetic coupling using magnetic metamaterials

In this paper,we propose the decoupling technique of patch antenna array by suppressing near-field magnetic coupling（NFMC） using magnetic metamaterials.To this end,a highly-integrated magnetic metamaterials,the substrate-integrated split-ring resonator（SI-SRR）,is firstly proposed to achieve negative permeability at the antenna operating frequency.By integrating SI-SRR in between two closely spaced antennas,magnetic fields are blocked in the shared substrate due to negative permeability of SI-SRR,reducing NFMC between the two antennas.To verify the technique,a prototype was fabricated and measured.The measured results demonstrated that the isolation can be enhanced by more than 17 dB even when the gap between the two patch antennas is only about 0.067 A.Due to high integration,this technique provides an effective alternative to high-isolation antenna array.

Magnetic Coupling in La_(0.67)Ca_(0.33)MnO_3/La_(0.67)Sr_(0.33)CoO_3/La_(0.67)Ca_(0.33)MnO_3 Trilayer Films

The perovskite La_(0.67)Ca_(0.33)MnO_3/La_(0.67)Sr_(0.33)CoO_3/La_(0.67)Ca_(0.33)MnO_3 trilayers were fabricated by a facing-target sputtering technique and their magnetotransport properties were investigated. The magnetoresistance is dependent on spacer thickness and dramatically decreases when La_(0.67)Sr_(0.33)CoO_3 layer is thick enough because of its short-circuiting effect. Different from La_(0.67)Ca_(0.33)MnO_3 single layer, trilayer films with thin La_(0.67)Sr_(0.33)CoO_3 spacer have the enhanced metal-semiconductor transition temperature (T_(MS)) of La_(0.67)Ca_(0.33)MnO_3 layers. The magnetic coercivity H_C shows a nonmonotonic behavior with changing the spacer layer thickness at 230 K. The waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom La_(0.67)Ca_(0.33)MnO_3 layers across the spacer La_(0.67)Sr_(0.33)CoO_3 layer.

Development of a low-loss magnetic-coupling pickup for 166.6-MHz quarter-wave beta=1 superconducting cavities

166.6-MHz quarter-waveβ=1 superconducting cavities have been adopted for the High Energy Photon Source,a 6-GeV diffraction-limited synchrotron light source currently under construction.A large helium jacket was required to accommodate the enlarged cavity beam pipe for the heavy damping of higher-order modes;the original electric-probe pickup thus becomes inevitably long with unfavorable mechanical properties.Relocated to an existing high-pressure-rinsing port,a magnetic-loop pickup was designed,characterized by low radio-frequency and cryogenic losses and being multipacting-free and insensitive to manufacturing and assembly tolerances.The consequent removal of the original pickup port from the cavity largely simplified the helium jacket fabrication and may also reduce cavity contamination.This paper presents a comprehensive design of a low-loss magnetic-coupling pickup for quarter-waveβ=1 superconducting cavities.The design can also be applied to other non-elliptical structures.

Magnetic-Coupling Based Waveguide-to-Microstrip Transition

A novel millimeter-wave waveguide-to-microstrip transition based on magnetic-coupling is presented in this paper.The mode conversion of electromagnetic field is realized with the ring strip line of arbitrary shape in the E-plane of rectangular waveguide and the eccentric quasi-coaxial line,which is partially filled with media and consists of outer and inner rectangular conductors.The structure has the advantages of low loss,wide bandwidth,compact structure,and avoiding debug.From 27 GHz to 40 GHz,the experiment results show that the insertion loss is less than 1.2 dB and the return loss is better than 13.5 dB for the back-to-back transition with semicircle ring strip lines.

SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results.

Magnetic and electric characteristics and abnormality of low-temperature resistivity in La_(0.67–x)Er_xSr_(0.33)MnO_3(0.00≤x≤0.20) system

M-T curves, ρ-T curves, and MR-T curves of La0.67-xErxSr0.33MnO3(x=0.00, 0.10, 0.20) system were studied by experiments. The experiments showed that: with increasing the doping amount, the magnetic structure of the system transformed from long-range ferromagnetic ordering to spin-cluster glass state, and M-T curves bent up in the extremely low temperature range; the resistivity of the system increased with increasing doping amount and exhibited the minimum phenomenon of low-temperature resistivity. The variation of the magnetic and electric properties came from the extra magnetic coupling induced by the doping and from the Kondo effect induced by the lattice distortion and local magnetic moments which was similar to that induced by the scattering of magnetic impurities on electron spins. © 2009 The Chinese Society of Rare Earths.

Modeling and dynamics of double Hindmarsh-Rose neuron with memristor-based magnetic coupling and time delay

The firing of a neuron model is mainly affected by the following factors:the magnetic field,external forcing current,time delay,etc.In this paper,a new time-delayed electromagnetic field coupled dual Hindmarsh-Rose neuron network model is constructed.A magnetically controlled threshold memristor is improved to represent the self-connected and the coupled magnetic fields triggered by the dynamic change of neuronal membrane potential for the adjacent neurons.Numerical simulation confirms that the coupled magnetic field can activate resting neurons to generate rich firing patterns,such as spiking firings,bursting firings,and chaotic firings,and enable neurons to generate larger firing amplitudes.The study also found that the strength of magnetic coupling in the neural network also affects the number of peaks in the discharge of bursting firing.Based on the existing medical treatment background of mental illness,the effects of time lag in the coupling process against neuron firing are studied.The results confirm that the neurons can respond well to external stimuli and coupled magnetic field with appropriate time delay,and keep periodic firing under a wide range of external forcing current.

Electronic structures and magnetic couplings of B-, C-, and N-doped BeO

The electronic structures and magnetic properties of B-, C-, and N-doped BeO supercells are investigated by means of ab initio calculations using density functional theory. The magnetic exchange constants of C-doped BeO at different doping levels are also calculated. A phenomenological band structure model based on p–d exchange-like p–p level repulsion between the dopants is proposed to explain the magnetic ground states in B-, C-, and N-doped BeO systems. The evolution from the antiferromagnetic phase to the ferromagnetic phase of C-doped BeO supercell with C concentration decreasing can also be well explained using this model. The findings in this study provide a simple guide for the design of band structure for a magnetic sp-electron semiconductor.

π-π Stacking and Magnetic Coupling Mechanism on a Mono-nuclear Mn(Ⅱ) Complex

A new mono-nuclear Mn（Ⅱ） complex [Mn（MPT）2（NCS）（HOCH3）]ClO4（MPT = 2-methoxyl-1,10-phenanthroline） has been synthesized with 2-methoxyl-1,10-phenanthroline and thiocyanate anion as ligands,and its crystal structure was determined by X-ray crystallography.The crystal data：monoclinic system,space group P21/c with a = 12.8849（17）,b = 15.684（2）,c = 14.2703（19） ,β = 92.126（2）°,V = 2881.9（7） 3,Z = 4,C28H24ClMnN5O7S,Mr = 664.97,Dc = 1.533 g/cm3,F（000） = 1364 and μ = 0.679 mm-1.In the crystal,MPT functions as a bidentate ligand and Mn（Ⅱ） ion assumes a distorted octahedral geometry.In the crystal there are two types of π-π stacking interactions among the adjacent complexes,which involves 1,10-phenanthroline rings.The theoretical calculations reveal that the two types of π-π stacking resulted in a weak anti-ferromagnetic coupling with 2J =-14.68 cm-1 and a weak ferromagnetic coupling with 2J = 0.70 cm-1,respectively.The theoretical calculations also reveal that there are both spin polarization and spin delocalization in the two π-π stacking systems,and the magnetic coupling signs are unable to explain with McConnell I spin-polarization mechanism.

THE DOUBLE RESONANCES OF MAGNETISM AND SOLID COUPLING OF HYDROELECTRIC-GENERATOR STATOR SYSTEM

A double-shell model of hydroelectric-generator stator system was established. Applying the theory of mechano-electric analytical dynamics theory, the nonlinear vibration equation of magnetism and solid coupling of hydroelectric-generator stator system, under steadily balanced three-phases operating condition, was obtained. According to the method of multiple scales for nonlinear oscillations, the double resonances of magnetism and solid coupling of hydroelectric-generator stater system, were investigated. It is pointed out that the system has abundant dynamics phenomenon including the attendant jumps and coexistence of multiple stable motions.

Research on Magnetically Coupled Resonant Detection Method for Breakpoint of Four Mesh Grounding Grid

Magnetically coupled resonant technology is a novel method for solving the breakpoint locating of power grounding grid.But the method can only detect breakpoints of a single mesh grounding grid at present.In this paper,a magnetically coupled resonant detection method for four-hole grounding grid breakpoint is proposed.Firstly,the equivalent circuit model of the four mesh grounding grid with two types of breakpoints,namely edge branch and intermediate branch,is established.The input impedance and phase angle of the system are obtained by analyzing the equivalent capacitance and equivalent resistance in the model.Secondly,the magnetically coupled resonant physical process of grounding grid faults is solved via HFSS software.The magnetic field intensity and phase frequency characteristic curves of four mesh holes with different branches and positions of breakpoints and different corrosion degrees are studied,and an experimental system is built to verify the feasibility.The results show that under the condition of grounding grid buried depth of 0.5 m and input frequency of 1~15MHz,and there is an inverse relationship between equivalent capacitance and distortion frequency,the phase angle is positively correlated with the degree of corrosion of grounding grid,and the error of signal distortion frequency can be positioned at 5%.This paper provides some ideas for the application of magnetic coupling grounding grid detection technology.

Realizing optimized interfacial polarization and impedance matching with CNT-confined Co nanoparticles in hollow carbon microspheres for enhanced microwave absorption

The hollow porous structure with exceptional interfacial effect and customizable internal environment shows significant potential for application as electromagnetic shielding and absorption materials.However,designing hollow porous electromagnetic absorbers with both desirable impedance matching and high loss capability remains a challenge.Herein,3D hollow porous electromagnetic microspheres were constructed by assembling 0D Co magnetic nanoparticles,1D carbon nanotubes,and 2D carbon nanosheets.Due to the sufficient sites for Co^(2+)riveting,the high loading of magnetic carbon nanotubes(CoNC)and porous carbon spheres formed high-density interfaces,enhancing the interfacial polarization.Furthermore,high-density CoNC were grown in situ on the hollow porous carbon(HPC)microsphere,forming a highly dispersed 3D magnetic network that inhibited the aggregation of magnetic nanoparticles and enhanced magnetic coupling.Therefore,the asprepared CoNC/HPC microspheres exhibited excellent microwave absorption(MA)performance,with a minimum reflection loss of-33.2 dB and an effective bandwidth of 5.5 GHz at a thickness of only 1.8 mm.The interfacial polarization mechanism for enhanced MA performance was demonstrated by electron holography and density functional theory calculations.Magnetic holography and micromagnetic simulations also revealed magnetic confinement and coupling mechanism.This work provides a new approach for designing electromagnetic absorbers with optimized impedance matching and loss capability.

Online frequency and power regulation scheme of magnetic coupled resonant wireless power transfer

In order to address the issues that the magnetic coupled resonant wireless power transfer （MCR-WPT） system is sensitive to the resonant frequency and that transmission power is difficult to control with the non-resistive load in the MCR-WPT, a single-side regulation scheme for frequency and transmission power online is proposed, which is based on the inherent constraint relationships the among system parameters in the primary side. Thus, the communication between the primary side and the secondary side is avoided. First, the transfer models of resistance-capacitance load and resistance- inductance load are established, respectively. Next, the relationship between the input voltage phasor and the input current phasor is used to recognize the load property and value. Then, the coaxial rotation of the stepper motor and the rotating vacuum variable capacitor is conducted to unify resonant frequency both in the primary side and the secondary side. Finally, the regulations of both frequency and amplitude of input voltage are made to guarantee transmission power under a new resonant frequency point the same as the one when the only pure resistance part of load is accessed under the former resonant frequency point. Both simulation and experimental results indicate that the proposed regulation scheme can track remnant frequency and maintain transmission power constant.

MOF-Derived Ni1-xCox@Carbon with Tunable Nano-Microstructure as Lightweight and Highly Efficient Electromagnetic Wave Absorber

Intrinsic electric-magnetic property and special nano-micro architecture of functional materials have a significant effect on its electromagnetic wave energy conversion,especially in the microwave absorption(MA) field.Herein,porous Ni1-xCox@Carbon composites derived from metal-organic framework(MOF)were successfully synthesized via solvothermal reaction and subsequent annealing treatments.Benefiting from the coordination,carbonized bimetallic Ni-Co-MOF maintained its initial skeleton and transformed into magnetic-carbon composites with tunable nano-micro structure.During the thermal decomposition,generated magnetic particles/clusters acted as a catalyst to promote the carbon sp^2 arrangement,forming special core-shell architecture.Therefore,pure Ni@C microspheres displayed strong MA behaviors than other Ni1-xCox@Carbon composites.Surprisingly,magnetic-dielectric Ni@C composites possessed the strongest reflection loss value-59.5 dB and the effective absorption frequency covered as wide as 4.7 GHz.Meanwhile,the MA capacity also can be boosted by adjusting the absorber content from 25% to 40%.Magnetic-dielectric synergy effect of MOF-derived Ni1-xCox@Carbon microspheres was confirmed by the off-axis electron holography technology making a thorough inquiry in the MA mechanism.