Polymer-based aerogels are emerging as promising candidates for lightweight and high performance electromagnetic(EM)wave absorption materials.In this study,an ultralight and rigid poly(p-phenylene benzobisoxazole)nano...Polymer-based aerogels are emerging as promising candidates for lightweight and high performance electromagnetic(EM)wave absorption materials.In this study,an ultralight and rigid poly(p-phenylene benzobisoxazole)nanofiber(PNF)based composite aerogel with excellent EM wave absorption performance was fabricated with cobalt-nickel alloy(CoNi)nanoparticles and carbon nanotubes(CNTs)as magnetic and conductive fillers,respectively.A CNT/PNF composite aerogel was first prepared through a sol-gel and freeze-drying method,and then CoNi nanoparticles were introduced therein through hydrothermal reaction and thermal annealing to obtain the CoNi/CNT/PNF aerogel.CNTs and PNFs were interwoven and constructed a three-dimensional conductive/magnetic cage-like skeleton structure decorating with magnetic CoNi nanoparticles.The cage-like skeleton structure allowed the dissipation of EM waves through multiple mechanisms encompassing conduction loss,magnetic loss,multiple reflection,scattering,and absorption.When its thickness was 4 mm,the CoNi/CNT/PNF aerogel showed a minimal reflection loss of-44.7 dB(at 6.88 GHz),and its broad effective absorption bandwidth covered the entire X-band and Ku-band and most of the C-band(12.32 GHz,from 5.68 GHz to 18 GHz).In addition,the rigid aerogel exhibited an ultralow density(0.107 g/cm^(3)),excellent thermal insulation,and flame retardancy,demonstrating its potential application as a high-performance EM wave absorption material in the fields of aerospace and national defense.展开更多
Magnetic domain structure plays an important role in regulating the electromagnetic properties, which dominatesthe magnetic response behaviors. Herein, unique magnetic vortex domain is firstly obtained in the Ni nanopa...Magnetic domain structure plays an important role in regulating the electromagnetic properties, which dominatesthe magnetic response behaviors. Herein, unique magnetic vortex domain is firstly obtained in the Ni nanoparticles (NPs) reduced from the Ni-based metal-organic frameworks (MOFs) precursor. Due to both the highsymmetry spheres and boundary restriction of graphited carbon shell, confined magnetic vortex structure isgenerated in the nanoscale Ni core during the annealing process. Meanwhile, MOFs-derived Ni@C assemblypowders construct special magnetic flux distribution and electron migration routes. MOFs-derived Ni@C microspheres exhibit outstanding electromagnetic (EM) wave absorption performance. The minimum reflection lossvalue of Ni@C–V microspheres with vortex domain can reach 54.6 dB at only 2.5 mm thickness, and theefficient absorption bandwidth up to 5.0 GHz at only 2.0 mm. Significantly, configuration evolution of magneticvortex driven by the orientation and reversion of polarity core boosts EM wave energy dissipation. Magneticcoupling effect among neighboring Ni@C microspheres significantly enhances the magnetic reaction intensity.Graphitized carbon matrix and heterojunction Ni–C interfaces further offer the conduction loss and interfacialpolarization. As result, MOFs-derived Ni@C–V powders display unique magnetic vortex, electronic migrationnetwork, and high-performance EM wave energy dissipation.展开更多
In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering c...In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering cross-section and total cross-section are evaluated analytically in different approximate conditions, and the physical interpretations are discussed. When the wavelength of incident wave is much longer than the vortex radius （kia〈〈1）, it is found that the angle at which the scattering cross-section reaches its maxim depends significantly on the approximation of the parameters of the vortex used. It is also found that the total scattering cross-section has an affinitive relation with the parameters of the plasma, while it is irrelevant to the frequency of the incident wave in a wide range of parameters of the vortex. In a totally different range of parameters when incident wave is in the radar-frequency range （then kia 〈〈 1, the wavelength of incident wave is much shorter than the vortex radius）, the numerical procedure is conducted with computer in order to obtain the distribution and the total expression of the scattering crosssection. Then it is found that the total scattering cross-section in the low frequency range is much larger than that in high frequency range, so the scattering is more effective in the low frequency range than in high frequency range.展开更多
The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular mom...The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular momentum(OAM)modes in different non-line-of-sight situations are simulated.The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space.According to the research,the effects about spectrum spreads of higher OAM modes are more obvious.The error in detection is mainly affected by OAM spectrum spreading,which can be reduced by reasonably using different combinations of OAM modes in different practical situations.The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.展开更多
The attenuation of electromagnetic （EM） waves in unmagnetized plasma generated by an inductively coupled plasma （ICP） actuator has been investigated both theoretically and experimentally. A numerical study is cond...The attenuation of electromagnetic （EM） waves in unmagnetized plasma generated by an inductively coupled plasma （ICP） actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square fiat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.展开更多
The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabri...The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabricated with the assistance of EM waves for simultaneous splitting of the MoS_(2)flakes and dispersive growth of FeCo nanoparticles.The resultants in-return have been used for EM wave absorption with excellent performance,providing minimum reflection loss(RL_(min))of-40.7 dB and a broad effective absorption bandwidth(EAB)of 6.4 GHz at a thickness of 2.5 mm.Real-time compression has been introduced to reveal the evolution of EM parameters.The aerogels maintain satisfactory performance even under 50%compression due to the balance of impedance matching and attenuation.Despite the deterioration of impedance matching,the attenuation is significantly enhanced due to both strengthened conductive loss and magnetic loss.In addition,features such as lightweight,self-cleaning and refractory can be achieved for the aerogels for applications in complex environments.As such this work not only provides a versatile synthetic route assisted by EM wave energy,but also insights on the evolution of absorption performance under deformation together with the design strategy of multifunctional flexible wave absorbers.展开更多
In this paper, we investigate the problem of electromagnetic (EM) wave scattering by one and many small perfectly conducting bodies and present a numerical method for solving it. For the case of one body, the problem ...In this paper, we investigate the problem of electromagnetic (EM) wave scattering by one and many small perfectly conducting bodies and present a numerical method for solving it. For the case of one body, the problem is solved for a body of arbitrary shape, using the corresponding boundary integral equation. For the case of many bodies, the problem is solved asymptotically under the physical assumptions a d a is the characteristic size of the bodies, d is the minimal distance between neighboring bodies, λ = 2π/k is the wave length and k is the wave number. Numerical results for the cases of one and many small bodies are presented. Error analysis for the numerical method is also provided.展开更多
In this paper, we study electromagnetic (EM) wave scattering problem by many small impedance bodies. A numerical method for solving this problem is presented. The problem is solved under the physical assumptions ka??1...In this paper, we study electromagnetic (EM) wave scattering problem by many small impedance bodies. A numerical method for solving this problem is presented. The problem is solved under the physical assumptions ka??1, where a is the characteristic size of the bodies and k is the wave number. This problem is solved asymptotically and numerical experiments are provided to illustrate the idea of the method. Error estimate for the asymptotic solution is also discussed.展开更多
The high-speed advances in electromagnetic(EM)wave and laser detection technology have accelerated the innovation of absorbing materials toward specific multi-band compatibility.It is difficult to achieve dual absorpt...The high-speed advances in electromagnetic(EM)wave and laser detection technology have accelerated the innovation of absorbing materials toward specific multi-band compatibility.It is difficult to achieve dual absorption of EM waves and near-infrared lasers by absorbing materials in a single frequency band;the design of high-performance laser-EM wave multi-band compatible absorbing materials is imminent.Herein,ErBO_(3)@ATO(erbium borate/antimony-doped tin oxide)porous composite microspheres with an average size of 15-20μm are produced solvothermal method and self-assembly,which exhibit excellent laser-EM wave compatible absorption.The porous structure on the surface of ErBO_(3)microspheres provides heterogeneous nucleation sites for ATO particle deposition.The minimum reflectivity of the composite for1.06 and 1.54μm lasers is 9.59%and 4.79%,which is0.57%and 3.78%lower than those of pure ATO particles,respectively.The composites containing 70 wt%porous ErBO_(3)@ATO reveal the minimum reflection loss(RL)value of-31.6 dB,and an effective absorption band width reaches 2.08 GHz at 2.5 mm thickness.The mechanism of near-infrared laser and EM wave compatible absorption is the synergistic effect of the energy level transition of ErBO_(3)and the dielectric loss of ATO,coupled with the large surface area and porous structure of the micro spheres.Therefore,the designed porous ErBO_(3)@ATO composite microspheres can be an attractive choice for lasers and EM wave high-quality compatible absorption.展开更多
A theory of EM wave propagation through magnetic multilayers and superlattices is presented based on the propagation matrix of a magnetic film. By using the P matrix, the transmission and reflection coefficients of la...A theory of EM wave propagation through magnetic multilayers and superlattices is presented based on the propagation matrix of a magnetic film. By using the P matrix, the transmission and reflection coefficients of layered magnetic media, including: (l)semi-infinite magnetic surfaces, (2) magnetic multilayers, (3) semi-infinite magnetic superlattices are obtained. The numerical results show that the EM modes of a magnetic layer system is excited and manifested as the sharp dips in the S-polarized reflection and the dispersion curves of the magnetic polaritons can be measured by a method similar to the attenuated total reflection (ATR) technique.展开更多
A plasma-based stable,ultra-wideband electromagnetic（EM） wave absorber structure is studied in this paper for stealth applications.The stability is maintained by a multi-layer structure with several plasma layers an...A plasma-based stable,ultra-wideband electromagnetic（EM） wave absorber structure is studied in this paper for stealth applications.The stability is maintained by a multi-layer structure with several plasma layers and dielectric layers distributed alternately.The plasma in each plasma layer is designed to be uniform,whereas it has a discrete nonuniform distribution from the overall view of the structure.The nonuniform distribution of the plasma is the key to obtaining ultra-wideband wave absorption.A discrete Epstein distribution model is put forward to constrain the nonuniform electron density of the plasma layers,by which the wave absorption range is extended to the ultra-wideband.Then,the scattering matrix method（SMM） is employed to analyze the electromagnetic reflection and absorption of the absorber structure.In the simulation,the validation of the proposed structure and model in ultra-wideband EM wave absorption is first illustrated by comparing the nonuniform plasma model with the uniform case.Then,the influence of various parameters on the EM wave reflection of the plasma are simulated and analyzed in detail,verifying the EM wave absorption performance of the absorber.The proposed structure and model are expected to be superior in some realistic applications,such as supersonic aircraft.展开更多
The longitudinal wave term within Faraday’s law of electromagnetic induction (Faraday’s law) underwent recovery to ensure its suitability for theoretical derivation of the equation governing longitudinal electromagn...The longitudinal wave term within Faraday’s law of electromagnetic induction (Faraday’s law) underwent recovery to ensure its suitability for theoretical derivation of the equation governing longitudinal electromagnetic (LEM) waves. The revised Maxwell’s equations include the crucial parameters being the attenuation time constants of magnetic vortex potential and electric vortex potential generated by external electromagnetic field within the propagation medium. Specific expressions for them are obtained through theoretical analysis. Subsequently, a model for propagating magnetic P-wave generated by the superposition of a left-handed photo and a right-handed photon in a vacuum is formulated based on reevaluated total current law and revised Faraday’s law, covering wave equations, energy equation, as well as propagation mode involving mutual induction and conversion between scalar magnetic field and vortex electric field. Furthermore, through theoretical derivations centered around magnetic P-wave, evidence was presented regarding its ability to absorb huge free energy through the entangled interaction between zero-point vacuum energy field and the torsion field produced by the vortex electric field.展开更多
Multiple state-of-the-art techniques, such as multi-dimensional micro-imaging, fast multi-channel micro-spetrophoto-metry, and dynamic micro-imaging analysis, were used to dynamically investigate various effects of ce...Multiple state-of-the-art techniques, such as multi-dimensional micro-imaging, fast multi-channel micro-spetrophoto-metry, and dynamic micro-imaging analysis, were used to dynamically investigate various effects of cell under the 900MHzelectromagnetic radiation. Cell changes in shape, size under different power density electromagnetic waves radiation were presented in this paper. Experimental results indicated that the isolated human red blood cells (RBCs) do not have obviously real-time responses to the ultra-low density (15 μW/cm2, 31 μW/cm2) electromagnetic wave radiation when the radiation time is not more than 30 minutes;however, the cells do have significant reactions in shape, size to the electromagnetic waves radiation with power densities of 1 mW/cm2and 5 mW/cm2. The data reveals the possible influences and statistical relationships among living human cell functions, radiation amount and exposure time with high-frequency electromagnetic waves. The results of this study may be significant on protection of human being and other living organisms against possible radiation affections of the high-frequency electromagnetic waves.展开更多
An iterative physical optics（IPO） model is proposed to solve extra large scale electric electromagnetic（EM） scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the for...An iterative physical optics（IPO） model is proposed to solve extra large scale electric electromagnetic（EM） scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation（Fa FFA） in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle（LGA）.展开更多
In this work, the effect of metal loading on electromagnetic (EM) absorbing performance was investigated to obtain an excellent EM absorber through a simple process. Specifically, iron/cobalt/carbon nanocomposite fibe...In this work, the effect of metal loading on electromagnetic (EM) absorbing performance was investigated to obtain an excellent EM absorber through a simple process. Specifically, iron/cobalt/carbon nanocomposite fibers were prepared using electrospinning and the following heat-treatment method. With the increase of the metal filling ratio, the reflection loss (RL) of the composites shows a trend of increasing first and then decreasing. It can be concluded that the optimal metal content can provide good dielectric loss and magnetic loss, which is helpful in achieving excellent RL. When the filling ratio of the metal was 50 wt%, the sample showed a minimum RL value of −38.1 dB at a matching thickness of 2.5 mm with an effective bandwidth of 4.1 GHz. In addition, the radar cross section (RCS) reduction of composites was carried out using ANSYS Electronics Desktop 2018 (HFSS) to simulate the threat from a bistatic radar system in practical application. The results show that the sample can effectively broaden the detection angle. Hence, carbon fibers can improve the absorbing performance by loading an appropriate amount of metal, which provides a reference for the preparation process of absorbing materials.展开更多
In this paper,we combine the circular polarization technology and orbital angular momentum(OAM)into the array antenna design for the first time,achieve free switch of the different topological charges in the array by ...In this paper,we combine the circular polarization technology and orbital angular momentum(OAM)into the array antenna design for the first time,achieve free switch of the different topological charges in the array by using high-speed radio frequency(RF)switch technology.We arrange microstrip patch antenna elements equidistantly along the circumference to form eight elements multi-modal OAM vortex electromagnetic wave microstrip array antenna.It can generate elec-tromagnetic waves with dual characteristics of circular polarization and multi-modal vortex OAM(where OAM mode values are l=0,l=±1,l=±2,l=±3).Through simulation,we find mutual coupling between the radiating elements is small relatively,and increasing the number of array elements can not only improve the beam quality,but also generate electromagnetic waves with a higher order of OAM modes.Antenna model can meet the basic demands of ordinary array antenna,and also confirm the practicality of this circular polarized microstrip antenna array model.展开更多
基金the National Natural Science Foundation of China(52203100)Shaanxi Province Key Research and Development Plan Project(2024GX-YBXM-386)+3 种基金the Innovation Capability Support Program of Shaanxi(2024RS-CXTD-57)Natural Science Foundation of Chongqing,China(2023NSCQ-MSX2682)Undergraduate Innovation&Business Program of Northwestern Polytechnical University(S202310699322)the Analytical&Testing Center of Northwestern Polytechnical University for SEM tests performed in this work.
文摘Polymer-based aerogels are emerging as promising candidates for lightweight and high performance electromagnetic(EM)wave absorption materials.In this study,an ultralight and rigid poly(p-phenylene benzobisoxazole)nanofiber(PNF)based composite aerogel with excellent EM wave absorption performance was fabricated with cobalt-nickel alloy(CoNi)nanoparticles and carbon nanotubes(CNTs)as magnetic and conductive fillers,respectively.A CNT/PNF composite aerogel was first prepared through a sol-gel and freeze-drying method,and then CoNi nanoparticles were introduced therein through hydrothermal reaction and thermal annealing to obtain the CoNi/CNT/PNF aerogel.CNTs and PNFs were interwoven and constructed a three-dimensional conductive/magnetic cage-like skeleton structure decorating with magnetic CoNi nanoparticles.The cage-like skeleton structure allowed the dissipation of EM waves through multiple mechanisms encompassing conduction loss,magnetic loss,multiple reflection,scattering,and absorption.When its thickness was 4 mm,the CoNi/CNT/PNF aerogel showed a minimal reflection loss of-44.7 dB(at 6.88 GHz),and its broad effective absorption bandwidth covered the entire X-band and Ku-band and most of the C-band(12.32 GHz,from 5.68 GHz to 18 GHz).In addition,the rigid aerogel exhibited an ultralow density(0.107 g/cm^(3)),excellent thermal insulation,and flame retardancy,demonstrating its potential application as a high-performance EM wave absorption material in the fields of aerospace and national defense.
基金supported by the National Natural Science Foundation of China(52231007,51725101,11727807,52271167,22088101)the Ministry of Science and Technology of China(973 Project Nos.2021YFA1200600 and 2018YFA0209100)the Shanghai Excellent Academic Leaders Program(19XD1400400).
文摘Magnetic domain structure plays an important role in regulating the electromagnetic properties, which dominatesthe magnetic response behaviors. Herein, unique magnetic vortex domain is firstly obtained in the Ni nanoparticles (NPs) reduced from the Ni-based metal-organic frameworks (MOFs) precursor. Due to both the highsymmetry spheres and boundary restriction of graphited carbon shell, confined magnetic vortex structure isgenerated in the nanoscale Ni core during the annealing process. Meanwhile, MOFs-derived Ni@C assemblypowders construct special magnetic flux distribution and electron migration routes. MOFs-derived Ni@C microspheres exhibit outstanding electromagnetic (EM) wave absorption performance. The minimum reflection lossvalue of Ni@C–V microspheres with vortex domain can reach 54.6 dB at only 2.5 mm thickness, and theefficient absorption bandwidth up to 5.0 GHz at only 2.0 mm. Significantly, configuration evolution of magneticvortex driven by the orientation and reversion of polarity core boosts EM wave energy dissipation. Magneticcoupling effect among neighboring Ni@C microspheres significantly enhances the magnetic reaction intensity.Graphitized carbon matrix and heterojunction Ni–C interfaces further offer the conduction loss and interfacialpolarization. As result, MOFs-derived Ni@C–V powders display unique magnetic vortex, electronic migrationnetwork, and high-performance EM wave energy dissipation.
基金National Natural Science Foundation of China(Nos,10375063.40336052)
文摘In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering cross-section and total cross-section are evaluated analytically in different approximate conditions, and the physical interpretations are discussed. When the wavelength of incident wave is much longer than the vortex radius （kia〈〈1）, it is found that the angle at which the scattering cross-section reaches its maxim depends significantly on the approximation of the parameters of the vortex used. It is also found that the total scattering cross-section has an affinitive relation with the parameters of the plasma, while it is irrelevant to the frequency of the incident wave in a wide range of parameters of the vortex. In a totally different range of parameters when incident wave is in the radar-frequency range （then kia 〈〈 1, the wavelength of incident wave is much shorter than the vortex radius）, the numerical procedure is conducted with computer in order to obtain the distribution and the total expression of the scattering crosssection. Then it is found that the total scattering cross-section in the low frequency range is much larger than that in high frequency range, so the scattering is more effective in the low frequency range than in high frequency range.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11804073 and 61775050).
文摘The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed.The spectrum spreads of different orbital angular momentum(OAM)modes in different non-line-of-sight situations are simulated.The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space.According to the research,the effects about spectrum spreads of higher OAM modes are more obvious.The error in detection is mainly affected by OAM spectrum spreading,which can be reduced by reasonably using different combinations of OAM modes in different practical situations.The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.
基金supported by National Natural Science Foundation of China(Nos.51276197,11472306 and 11402301)
文摘The attenuation of electromagnetic （EM） waves in unmagnetized plasma generated by an inductively coupled plasma （ICP） actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square fiat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.
基金financially supported by the National Natural Science Foundation of China(No.52122106)the Key Research and Development Program of Zhejiang Province(Nos.2021C01033 and 2021C01193)。
文摘The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabricated with the assistance of EM waves for simultaneous splitting of the MoS_(2)flakes and dispersive growth of FeCo nanoparticles.The resultants in-return have been used for EM wave absorption with excellent performance,providing minimum reflection loss(RL_(min))of-40.7 dB and a broad effective absorption bandwidth(EAB)of 6.4 GHz at a thickness of 2.5 mm.Real-time compression has been introduced to reveal the evolution of EM parameters.The aerogels maintain satisfactory performance even under 50%compression due to the balance of impedance matching and attenuation.Despite the deterioration of impedance matching,the attenuation is significantly enhanced due to both strengthened conductive loss and magnetic loss.In addition,features such as lightweight,self-cleaning and refractory can be achieved for the aerogels for applications in complex environments.As such this work not only provides a versatile synthetic route assisted by EM wave energy,but also insights on the evolution of absorption performance under deformation together with the design strategy of multifunctional flexible wave absorbers.
文摘In this paper, we investigate the problem of electromagnetic (EM) wave scattering by one and many small perfectly conducting bodies and present a numerical method for solving it. For the case of one body, the problem is solved for a body of arbitrary shape, using the corresponding boundary integral equation. For the case of many bodies, the problem is solved asymptotically under the physical assumptions a d a is the characteristic size of the bodies, d is the minimal distance between neighboring bodies, λ = 2π/k is the wave length and k is the wave number. Numerical results for the cases of one and many small bodies are presented. Error analysis for the numerical method is also provided.
文摘In this paper, we study electromagnetic (EM) wave scattering problem by many small impedance bodies. A numerical method for solving this problem is presented. The problem is solved under the physical assumptions ka??1, where a is the characteristic size of the bodies and k is the wave number. This problem is solved asymptotically and numerical experiments are provided to illustrate the idea of the method. Error estimate for the asymptotic solution is also discussed.
基金financially supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)"Qinglan Project"Young and Middle-aged Academic Leaders Program of Jiangsu Province。
文摘The high-speed advances in electromagnetic(EM)wave and laser detection technology have accelerated the innovation of absorbing materials toward specific multi-band compatibility.It is difficult to achieve dual absorption of EM waves and near-infrared lasers by absorbing materials in a single frequency band;the design of high-performance laser-EM wave multi-band compatible absorbing materials is imminent.Herein,ErBO_(3)@ATO(erbium borate/antimony-doped tin oxide)porous composite microspheres with an average size of 15-20μm are produced solvothermal method and self-assembly,which exhibit excellent laser-EM wave compatible absorption.The porous structure on the surface of ErBO_(3)microspheres provides heterogeneous nucleation sites for ATO particle deposition.The minimum reflectivity of the composite for1.06 and 1.54μm lasers is 9.59%and 4.79%,which is0.57%and 3.78%lower than those of pure ATO particles,respectively.The composites containing 70 wt%porous ErBO_(3)@ATO reveal the minimum reflection loss(RL)value of-31.6 dB,and an effective absorption band width reaches 2.08 GHz at 2.5 mm thickness.The mechanism of near-infrared laser and EM wave compatible absorption is the synergistic effect of the energy level transition of ErBO_(3)and the dielectric loss of ATO,coupled with the large surface area and porous structure of the micro spheres.Therefore,the designed porous ErBO_(3)@ATO composite microspheres can be an attractive choice for lasers and EM wave high-quality compatible absorption.
基金Supported by the National Natural Science Foundation of China
文摘A theory of EM wave propagation through magnetic multilayers and superlattices is presented based on the propagation matrix of a magnetic film. By using the P matrix, the transmission and reflection coefficients of layered magnetic media, including: (l)semi-infinite magnetic surfaces, (2) magnetic multilayers, (3) semi-infinite magnetic superlattices are obtained. The numerical results show that the EM modes of a magnetic layer system is excited and manifested as the sharp dips in the S-polarized reflection and the dispersion curves of the magnetic polaritons can be measured by a method similar to the attenuated total reflection (ATR) technique.
基金supported in part by the National Basic Research Program of China (grant no.2014CB340205)in part by the Science and Technology on Space Physics Laboratory Fundsin part by the Fundamental Research Funds for the Central Universities (20101156180)
文摘A plasma-based stable,ultra-wideband electromagnetic（EM） wave absorber structure is studied in this paper for stealth applications.The stability is maintained by a multi-layer structure with several plasma layers and dielectric layers distributed alternately.The plasma in each plasma layer is designed to be uniform,whereas it has a discrete nonuniform distribution from the overall view of the structure.The nonuniform distribution of the plasma is the key to obtaining ultra-wideband wave absorption.A discrete Epstein distribution model is put forward to constrain the nonuniform electron density of the plasma layers,by which the wave absorption range is extended to the ultra-wideband.Then,the scattering matrix method（SMM） is employed to analyze the electromagnetic reflection and absorption of the absorber structure.In the simulation,the validation of the proposed structure and model in ultra-wideband EM wave absorption is first illustrated by comparing the nonuniform plasma model with the uniform case.Then,the influence of various parameters on the EM wave reflection of the plasma are simulated and analyzed in detail,verifying the EM wave absorption performance of the absorber.The proposed structure and model are expected to be superior in some realistic applications,such as supersonic aircraft.
文摘The longitudinal wave term within Faraday’s law of electromagnetic induction (Faraday’s law) underwent recovery to ensure its suitability for theoretical derivation of the equation governing longitudinal electromagnetic (LEM) waves. The revised Maxwell’s equations include the crucial parameters being the attenuation time constants of magnetic vortex potential and electric vortex potential generated by external electromagnetic field within the propagation medium. Specific expressions for them are obtained through theoretical analysis. Subsequently, a model for propagating magnetic P-wave generated by the superposition of a left-handed photo and a right-handed photon in a vacuum is formulated based on reevaluated total current law and revised Faraday’s law, covering wave equations, energy equation, as well as propagation mode involving mutual induction and conversion between scalar magnetic field and vortex electric field. Furthermore, through theoretical derivations centered around magnetic P-wave, evidence was presented regarding its ability to absorb huge free energy through the entangled interaction between zero-point vacuum energy field and the torsion field produced by the vortex electric field.
文摘Multiple state-of-the-art techniques, such as multi-dimensional micro-imaging, fast multi-channel micro-spetrophoto-metry, and dynamic micro-imaging analysis, were used to dynamically investigate various effects of cell under the 900MHzelectromagnetic radiation. Cell changes in shape, size under different power density electromagnetic waves radiation were presented in this paper. Experimental results indicated that the isolated human red blood cells (RBCs) do not have obviously real-time responses to the ultra-low density (15 μW/cm2, 31 μW/cm2) electromagnetic wave radiation when the radiation time is not more than 30 minutes;however, the cells do have significant reactions in shape, size to the electromagnetic waves radiation with power densities of 1 mW/cm2and 5 mW/cm2. The data reveals the possible influences and statistical relationships among living human cell functions, radiation amount and exposure time with high-frequency electromagnetic waves. The results of this study may be significant on protection of human being and other living organisms against possible radiation affections of the high-frequency electromagnetic waves.
基金supported by the National Natural Science Foundation of China(61372033)
文摘An iterative physical optics（IPO） model is proposed to solve extra large scale electric electromagnetic（EM） scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation（Fa FFA） in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle（LGA）.
基金support from the National Natural Science Foundation of China(No.:51971111)the Foundation of National Defense Science and Technology Key Laboratory(No.:6142908-KQ111501114).
文摘In this work, the effect of metal loading on electromagnetic (EM) absorbing performance was investigated to obtain an excellent EM absorber through a simple process. Specifically, iron/cobalt/carbon nanocomposite fibers were prepared using electrospinning and the following heat-treatment method. With the increase of the metal filling ratio, the reflection loss (RL) of the composites shows a trend of increasing first and then decreasing. It can be concluded that the optimal metal content can provide good dielectric loss and magnetic loss, which is helpful in achieving excellent RL. When the filling ratio of the metal was 50 wt%, the sample showed a minimum RL value of −38.1 dB at a matching thickness of 2.5 mm with an effective bandwidth of 4.1 GHz. In addition, the radar cross section (RCS) reduction of composites was carried out using ANSYS Electronics Desktop 2018 (HFSS) to simulate the threat from a bistatic radar system in practical application. The results show that the sample can effectively broaden the detection angle. Hence, carbon fibers can improve the absorbing performance by loading an appropriate amount of metal, which provides a reference for the preparation process of absorbing materials.
基金supported in part by the Nation Natural Science Foundation of China(No.61561039)the Nation Natural Science Foundation of Ningxia Province(No.NZ17041).
文摘In this paper,we combine the circular polarization technology and orbital angular momentum(OAM)into the array antenna design for the first time,achieve free switch of the different topological charges in the array by using high-speed radio frequency(RF)switch technology.We arrange microstrip patch antenna elements equidistantly along the circumference to form eight elements multi-modal OAM vortex electromagnetic wave microstrip array antenna.It can generate elec-tromagnetic waves with dual characteristics of circular polarization and multi-modal vortex OAM(where OAM mode values are l=0,l=±1,l=±2,l=±3).Through simulation,we find mutual coupling between the radiating elements is small relatively,and increasing the number of array elements can not only improve the beam quality,but also generate electromagnetic waves with a higher order of OAM modes.Antenna model can meet the basic demands of ordinary array antenna,and also confirm the practicality of this circular polarized microstrip antenna array model.
