Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks ...Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.展开更多
Radio Frequency Interference (RFI) degrades the quality of focused Ultra-WideBand Syn- thetic Aperture Radar (UWB SAR) images. From both the theoretical analysis and real data valida- tion, it is concluded that target...Radio Frequency Interference (RFI) degrades the quality of focused Ultra-WideBand Syn- thetic Aperture Radar (UWB SAR) images. From both the theoretical analysis and real data valida- tion, it is concluded that target echo and RFI have different Region Of Support (ROS) in 2-D fast- time wavenumber and aperture wavenumber domain. Consequently, a novel adaptive filter is pro- posed according to the Wiener optimum criterion on the distinct ROS characteristics of target echo and RFI. Compared with the notch filter and the Least Mean Square (LMS) adaptive filter in previ- ous literatures, the proposed method is more computationally efficient with satisfactory suppression results. In terms of Signal-to-Interference Ratio Improvement (SIRI) and processing time, the per- formance of the proposed adaptive filter is verified with the field data collected with a UWB SAR system.展开更多
Vacuum-assisted spin-coating is an effective polymer filling technology for sidewall insulating of through-silicon-via(TSV).This paper investigated the flow mechanism of the vacuum-assisted polymer filling process bas...Vacuum-assisted spin-coating is an effective polymer filling technology for sidewall insulating of through-silicon-via(TSV).This paper investigated the flow mechanism of the vacuum-assisted polymer filling process based on experiments and numerical simulation,and studied the effect of vacuum pressure,viscosity of polymer and aspect-ratio of trench on the filling performance.A 2D axisymmetric model,consisting of polymer partially filled into the trench and void at the bottom of trench,was developed for the computational fluid dynamics(CFD)simulation.The simulation results indicate that the vacuum-assisted polymer filling process goes through four stages,including bubble formation,bubble burst,air elimination and polymer re-filling.Moreover,the simulation results suggest that the pressure significantly affects the bubble formation and the polymer re-filling procedure,and the polymer viscosity and the trench aspect-ratio influence the duration of air elimination.展开更多
Silkworm silk fiber is an attractive material owing to its remarkable mechanical characteristics,excellent optical properties,and good biocompatibility and biodegradability.However,nano-processing of the silk fiber is...Silkworm silk fiber is an attractive material owing to its remarkable mechanical characteristics,excellent optical properties,and good biocompatibility and biodegradability.However,nano-processing of the silk fiber is still a challenge limiting its applications in nanoengineering and related fields.Herein,we report localized near-field enhancement-assisted ablation with an ultrafast laser to break this bottleneck.Localized processing of silk fiber,including nano-holing,nano-grooving,and cutting could retain the key molecular structure building blocks and the pristine functionality of the silk fiber.An extremely narrow nanohole with a width of^64 nm was successfully achieved.The processed silk fiber can be used to transfer micro/nanoparticles and drugs,showing potential for biomedical engineering.The processing strategy developed in this study can also be extended to other materials,paving a new way for fabricating functional nanostructures with precisely controlled size and morphology.展开更多
The existing spatially variant apodizations(SVAs) either cannot depress the sidelobes effectively or reduce the energy of the mainlobe.To improve this,a modified SVA(MSVA) is put forward in this paper,which expands th...The existing spatially variant apodizations(SVAs) either cannot depress the sidelobes effectively or reduce the energy of the mainlobe.To improve this,a modified SVA(MSVA) is put forward in this paper,which expands the traditional filter from 3-taps to 5-taps and sets relevant parameters according to different sampling rates to get the excellent result that satisfies constrained optimization theory.A modified super-SVA is also presented,which compares the result after the iteration with the original signal and makes the one whose amplitude is smaller as the initial value of the next iteration.This method can eliminate the sidelobes produced by the intermediate operation,so that the following bandwidth extrapolation is more available.Super-MSVA is presented based on the modified SVA and modified super-SVA,which is suitable for any Nyquist sampling rate,can extrapolate the signal bandwidth many times through iteration with a commensurate improvement in resolution,as demonstrated by the result of the experiment.展开更多
文摘Aperture-dependent motion compensation is important for wide beam Synthetic Aperture Radar(SAR) data processing.This paper studies a wide beam motion compensation algorithm based on frequency division.It takes blocks along azimuth dimension in frequency domain and applies an-gle-variant motion compensation in time domain.With this frequency division based motion com-pensation approach,the effects of aperture-dependent residual phase errors are corrected precisely.The rationale and procedure of this algorithm are introduced in detail.Point targets and images of a P-band airborne SAR with motion errors are simulated to validate this algorithm.Compared with the wide beam motion compensation algorithms based on time division,the proposed algorithm has better performance,especially in terms of high-frequency motion errors.
文摘Radio Frequency Interference (RFI) degrades the quality of focused Ultra-WideBand Syn- thetic Aperture Radar (UWB SAR) images. From both the theoretical analysis and real data valida- tion, it is concluded that target echo and RFI have different Region Of Support (ROS) in 2-D fast- time wavenumber and aperture wavenumber domain. Consequently, a novel adaptive filter is pro- posed according to the Wiener optimum criterion on the distinct ROS characteristics of target echo and RFI. Compared with the notch filter and the Least Mean Square (LMS) adaptive filter in previ- ous literatures, the proposed method is more computationally efficient with satisfactory suppression results. In terms of Signal-to-Interference Ratio Improvement (SIRI) and processing time, the per- formance of the proposed adaptive filter is verified with the field data collected with a UWB SAR system.
文摘Vacuum-assisted spin-coating is an effective polymer filling technology for sidewall insulating of through-silicon-via(TSV).This paper investigated the flow mechanism of the vacuum-assisted polymer filling process based on experiments and numerical simulation,and studied the effect of vacuum pressure,viscosity of polymer and aspect-ratio of trench on the filling performance.A 2D axisymmetric model,consisting of polymer partially filled into the trench and void at the bottom of trench,was developed for the computational fluid dynamics(CFD)simulation.The simulation results indicate that the vacuum-assisted polymer filling process goes through four stages,including bubble formation,bubble burst,air elimination and polymer re-filling.Moreover,the simulation results suggest that the pressure significantly affects the bubble formation and the polymer re-filling procedure,and the polymer viscosity and the trench aspect-ratio influence the duration of air elimination.
基金the support from the National Key R&D Program of China(2017YFB1104300,2016YFA0200103 and 2018YFB1107200)the National Program for the Support of Top-notch Young Professionalsthe National Natural Science Foundation of China(51775303)。
文摘Silkworm silk fiber is an attractive material owing to its remarkable mechanical characteristics,excellent optical properties,and good biocompatibility and biodegradability.However,nano-processing of the silk fiber is still a challenge limiting its applications in nanoengineering and related fields.Herein,we report localized near-field enhancement-assisted ablation with an ultrafast laser to break this bottleneck.Localized processing of silk fiber,including nano-holing,nano-grooving,and cutting could retain the key molecular structure building blocks and the pristine functionality of the silk fiber.An extremely narrow nanohole with a width of^64 nm was successfully achieved.The processed silk fiber can be used to transfer micro/nanoparticles and drugs,showing potential for biomedical engineering.The processing strategy developed in this study can also be extended to other materials,paving a new way for fabricating functional nanostructures with precisely controlled size and morphology.
基金supported by the Knowledge Innovative Program of the Chinese Academy of Sciences (Grant No.053Z170138)
文摘The existing spatially variant apodizations(SVAs) either cannot depress the sidelobes effectively or reduce the energy of the mainlobe.To improve this,a modified SVA(MSVA) is put forward in this paper,which expands the traditional filter from 3-taps to 5-taps and sets relevant parameters according to different sampling rates to get the excellent result that satisfies constrained optimization theory.A modified super-SVA is also presented,which compares the result after the iteration with the original signal and makes the one whose amplitude is smaller as the initial value of the next iteration.This method can eliminate the sidelobes produced by the intermediate operation,so that the following bandwidth extrapolation is more available.Super-MSVA is presented based on the modified SVA and modified super-SVA,which is suitable for any Nyquist sampling rate,can extrapolate the signal bandwidth many times through iteration with a commensurate improvement in resolution,as demonstrated by the result of the experiment.
