The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range,posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth.However,e...The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range,posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth.However,existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern.In this work,rare-earth La^(3+)and non-magnetic Zr^(4+)ions are simultaneously incorporated into M-type barium ferrite(BaM)to intentionally manipulate the multi-magnetic resonance behavior.By leveraging the contrary impact of La^(3+)and Zr^(4+)ions on magnetocrystalline anisotropy field,the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated.The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe^(3+)and Fe^(2+)ions.Additionally,Mosbauer spectra analysis,first-principle calculations,and least square fitting collectively identify that additional La^(3+)doping leads to a profound rearrangement of Zr^(4+)occupation and thus makes the portion of polarization/conduction loss increase gradually.As a consequence,the La^(3+)-Zr^(4+)co-doped BaM achieves an ultra-broad bandwidth of 12.5+GHz covering from 27.5 to 40+GHz,which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz.展开更多
In this paper,an induced current learning method(ICLM)for microwave through wall imaging(TWI),named as TWI-ICLM,is proposed.In the inversion of induced current,the unknown object along with the enclosed walls are trea...In this paper,an induced current learning method(ICLM)for microwave through wall imaging(TWI),named as TWI-ICLM,is proposed.In the inversion of induced current,the unknown object along with the enclosed walls are treated as a combination of scatterers.Firstly,a non-iterative method called distorted-Born backpropagation(DB-BP)is utilized to generate the initial result.In the training stage,several convolutional neural networks(CNNs)are cascaded to improve the estimated induced current.In addition,a hybrid loss function consisting of the induced current error and the permittivity error is used to optimize the network parameters.Finally,the relative permittivity images are conducted analytically using the predicted current based on ICLM.Both the numerical and experimental TWI tests prove that,the proposed method can achieve better imaging accuracy compared to traditional distorted-Born iterative method(DBIM).展开更多
基金supported by the National Natural Science Foundation of China(Nos.:52271180,51802155,12304020)National Key R&D Program of China(No.:2021YFB3502500)+2 种基金Natural Science Foundation of Jiangsu Province(BK20230909)Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutionsthe Center for Microscopy and Analysis at Nanjing University of Aeronautics and Astronautics.
文摘The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range,posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth.However,existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern.In this work,rare-earth La^(3+)and non-magnetic Zr^(4+)ions are simultaneously incorporated into M-type barium ferrite(BaM)to intentionally manipulate the multi-magnetic resonance behavior.By leveraging the contrary impact of La^(3+)and Zr^(4+)ions on magnetocrystalline anisotropy field,the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated.The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe^(3+)and Fe^(2+)ions.Additionally,Mosbauer spectra analysis,first-principle calculations,and least square fitting collectively identify that additional La^(3+)doping leads to a profound rearrangement of Zr^(4+)occupation and thus makes the portion of polarization/conduction loss increase gradually.As a consequence,the La^(3+)-Zr^(4+)co-doped BaM achieves an ultra-broad bandwidth of 12.5+GHz covering from 27.5 to 40+GHz,which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz.
基金National Natural Science Foundation of China(No.62101288)。
文摘In this paper,an induced current learning method(ICLM)for microwave through wall imaging(TWI),named as TWI-ICLM,is proposed.In the inversion of induced current,the unknown object along with the enclosed walls are treated as a combination of scatterers.Firstly,a non-iterative method called distorted-Born backpropagation(DB-BP)is utilized to generate the initial result.In the training stage,several convolutional neural networks(CNNs)are cascaded to improve the estimated induced current.In addition,a hybrid loss function consisting of the induced current error and the permittivity error is used to optimize the network parameters.Finally,the relative permittivity images are conducted analytically using the predicted current based on ICLM.Both the numerical and experimental TWI tests prove that,the proposed method can achieve better imaging accuracy compared to traditional distorted-Born iterative method(DBIM).
