Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring r...Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator(HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8-18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8-18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8-18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band.展开更多
Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSE...Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSEM. The propagation of the electromagnetic fields from a controlled source in the marine environment was studied with virtual interface method combined with discrete complex image method. Transmitter of finite length current source is approximated by dipole (HED) . A three-layered model is accepted,with sea water as intermediate conductive layer under air and a relatively high resistive seabed as basement,possibly containing a hydrogen layer of higher resistivity. The electromagnetic fields in whole space thus computed show that: (1) the spatial distribution of field component depends on its type; (2) inline Ex component is more sensitive to reservoir layer than that in broadside; (3) The airwave affects marine electromagnetic (MEM) exploration when sea water is relatively shallow; in the case of deep water MEM exploration,the airwave influence could be neglected; and (4) an appropriate frequency should be selected in order to balance the signal strength and electromagnetic induction effect.展开更多
After compositing three representative ENSO indices,El Nio events have been divided into an eastern pattern(EP) and a central pattern(CP).By using EOF,correlation and composite analysis,the relationship and possible m...After compositing three representative ENSO indices,El Nio events have been divided into an eastern pattern(EP) and a central pattern(CP).By using EOF,correlation and composite analysis,the relationship and possible mechanisms between Indian Ocean Dipole(IOD) and two types of El Nio were investigated.IOD events,originating from Indo-Pacific scale air-sea interaction,are composed of two modes,which are associated with EP and CP El Ni o respectively.The IOD mode related to EP El Nio events(named as IOD1) is strongest at the depth of 50 to 150 m along the equatorial Indian Ocean.Besides,it shows a quasi-symmetric distribution,stronger in the south of the Equator.The IOD mode associated with CP El Nio(named as IOD2) has strongest signal in tropical southern Indian Ocean surface.In terms of mechanisms,before EP El Nio peaks,anomalous Walker circulation produces strong anomalous easterlies in equatorial Indian Ocean,resulting in upwelling in the east,decreasing sea temperature there;a couple of anomalous anticyclones(stronger in the south) form off the Equator where warm water accumulates,and thus the IOD1 occurs.When CP El Nio develops,anomalous Walker circulation is weaker and shifts its center to the west,therefore anomalous easterlies in equatorial Indian Ocean is less strong.Besides,the anticyclone south of Sumatra strengthens,and the southerlies east of it bring cold water from higher latitudes and northerlies west of it bring warm water from lower latitudes to the 15° to 25°S zone.Meanwhile,there exists strong divergence in the east and convergence in the west part of tropical southern Indian Ocean,making sea temperature fall and rise separately.Therefore,IOD2 lies farther south.展开更多
基金Project(2017YFA0204600)supported by the National Key Research and Development Program of ChinaProject(51802352)supported by the National Natural Science Foundation of ChinaProject(2019JJ50768)supported by the Natural Science Foundation of Hunan Province of China。
文摘Left-hand materials have drawn increasing attention from many disciplines and found widespread application, especially in microwave engineering. A sandwiched metamaterial consisting of multi-nested square-split-ring resonators on the top side and a set of wires on the back side is proposed. Scattering parameters are retrieved by high-frequency structure simulator(HFSS) software based on the finite element method. Effects of square-split-ring number on the left-hand characteristics containing negative values of permittivity, permeability, and refractive index have been intensively investigated. Simulated results show that obvious resonant left-hand characteristics could be observed within 8-18 GHz, and the resonant frequency counts are inclined to be in direct proportion to the square-split-ring number over 8-18 GHz. Besides, the proposed sandwiched metamaterial with three square-split-ring resonators and three wires presents the widest frequency band of left-hand characteristics in a range of 8-18 GHz. Further, electromagnetic field distributions demonstrated that the induced magnetic dipole dominates the resonant absorption. The multi-peak resonance characteristics of square-split-ring resonant structure are considered to be a promising candidate for selective-frequency absorption or modulation toward microwave frequency band.
基金Supperted by project of the National Science Foundation of China(No.40874050)
文摘Marine controlled source electromagnetic signal could be used in mineral resource exploration,reservoir appraisal and communicative technique in ocean. It's necessary to study the electromagnetic generated by MCSEM. The propagation of the electromagnetic fields from a controlled source in the marine environment was studied with virtual interface method combined with discrete complex image method. Transmitter of finite length current source is approximated by dipole (HED) . A three-layered model is accepted,with sea water as intermediate conductive layer under air and a relatively high resistive seabed as basement,possibly containing a hydrogen layer of higher resistivity. The electromagnetic fields in whole space thus computed show that: (1) the spatial distribution of field component depends on its type; (2) inline Ex component is more sensitive to reservoir layer than that in broadside; (3) The airwave affects marine electromagnetic (MEM) exploration when sea water is relatively shallow; in the case of deep water MEM exploration,the airwave influence could be neglected; and (4) an appropriate frequency should be selected in order to balance the signal strength and electromagnetic induction effect.
基金National Key Basic Research Program of China(973 Program,2012CB417403)
文摘After compositing three representative ENSO indices,El Nio events have been divided into an eastern pattern(EP) and a central pattern(CP).By using EOF,correlation and composite analysis,the relationship and possible mechanisms between Indian Ocean Dipole(IOD) and two types of El Nio were investigated.IOD events,originating from Indo-Pacific scale air-sea interaction,are composed of two modes,which are associated with EP and CP El Ni o respectively.The IOD mode related to EP El Nio events(named as IOD1) is strongest at the depth of 50 to 150 m along the equatorial Indian Ocean.Besides,it shows a quasi-symmetric distribution,stronger in the south of the Equator.The IOD mode associated with CP El Nio(named as IOD2) has strongest signal in tropical southern Indian Ocean surface.In terms of mechanisms,before EP El Nio peaks,anomalous Walker circulation produces strong anomalous easterlies in equatorial Indian Ocean,resulting in upwelling in the east,decreasing sea temperature there;a couple of anomalous anticyclones(stronger in the south) form off the Equator where warm water accumulates,and thus the IOD1 occurs.When CP El Nio develops,anomalous Walker circulation is weaker and shifts its center to the west,therefore anomalous easterlies in equatorial Indian Ocean is less strong.Besides,the anticyclone south of Sumatra strengthens,and the southerlies east of it bring cold water from higher latitudes and northerlies west of it bring warm water from lower latitudes to the 15° to 25°S zone.Meanwhile,there exists strong divergence in the east and convergence in the west part of tropical southern Indian Ocean,making sea temperature fall and rise separately.Therefore,IOD2 lies farther south.
