The existence of the sea surface is bound to affect the electromagnetic （EM） scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM t...The existence of the sea surface is bound to affect the electromagnetic （EM） scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories, the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves, a three dimensional geometric model is adopted together with Ufimtsev＇s theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.展开更多
In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed....In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.展开更多
An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and di...An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and distribution are still uncertain.We report a new 70-cm-wavelength radar image of the lunar south pole obtained by an Earth-based bistatic radar system consisting of the Sanya incoherent scatter radar(SYISR)and the five-hundred-meter aperture spherical radio telescope(FAST).The upper limit of water ice content(0 wt.%–6 wt.%)and its potential distribution are determined from a radar circular polarization ratio(CPR)map by considering the coherent backscatter opposition effect(CBOE)of water ice and ignoring the contribution of roughness to the CPR.This result is advantageous for future lunar exploration missions.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 61372004the Fundamental Research Funds for the Central Universitiesthe Foundation of Science and Technology on Electromagnetic Scattering Laboratory
文摘The existence of the sea surface is bound to affect the electromagnetic （EM） scattering from marine targets. When dealing with the composite scattering from targets over a sea surface by applying high-frequency EM theories, the total scattering field can be decomposed into three parts in low sea states, namely, the direct scattering from the sea surface, the direct scattering from targets and the coupling scattering between the sea surface and targets. With regard to high sea states, breaking waves make the direct scattering from the sea surface and the coupling scattering more complicated. To solve this issue, a scattering model is proposed to analyze the composite scattering from a ship over a rough sea surface under high sea states. To consider the effect of breaking waves, a three dimensional geometric model is adopted together with Ufimtsev＇s theory of edge waves for the scattering from a breaker. In addition, the coupling scattering between targets and breaking waves is taken into account by considering all possible scattering paths. The simulated results indicate that the influence of breaking waves on the scattering field from the sea surface and on the coupling field is non-negligible, and the numerical results also show the effectiveness of the proposed scattering model.
基金supported by the National Natural Science Foundation of China(11174060,11327405)the Ph.D.Programs Foundation of the Ministry of Education of China(20110071130004,20130071110020)+1 种基金the Science and Technology Support Program of Shanghai(13441901900)the Program for New Century Excellent Talents in University(NCET-10-0349)
文摘In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.
基金supported by the National Natural Science Foundation of China(42425403,62227901,and 42241151)the Project of Stable Support for Youth Team in Basic Research Field,CAS(YSBR-018)+2 种基金the Guizhou Provincial Science and Technology Projects(QKHFQ[2023]003 and QKHPTRC-ZDSYS[2023]003)the Meridian ProjectShuai Li for data support。
文摘An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and distribution are still uncertain.We report a new 70-cm-wavelength radar image of the lunar south pole obtained by an Earth-based bistatic radar system consisting of the Sanya incoherent scatter radar(SYISR)and the five-hundred-meter aperture spherical radio telescope(FAST).The upper limit of water ice content(0 wt.%–6 wt.%)and its potential distribution are determined from a radar circular polarization ratio(CPR)map by considering the coherent backscatter opposition effect(CBOE)of water ice and ignoring the contribution of roughness to the CPR.This result is advantageous for future lunar exploration missions.
