Based on the research of modern electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell.The process of thixo-extrusion with SiCp/A356 composites was simulated by the f...Based on the research of modern electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell.The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed.The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation.The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.展开更多
We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the claddin...We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the cladding region. By increasing the size of the outermost-ring air holes in the cladding region,highly birefringent PCFs with low confinement loss can be successfully achieved. The design strategy is based on the fact that the modal birefringence of PCFs is dominated by the inner-ring air holes in PCF,which is verified by a full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that modal birefringence in the order of 10-3 and confinement loss less than 0.1 dB/km can be easily realized in the proposed PCF with only four rings of air holes in the cladding region. We expect that such fibers will be much easier to be fabvicated than those with more air holes in the cladding region.展开更多
In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part...In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part of an approximate infinite periodic structure is analyzed by periodic method of moment (PMM);the outer part is then analyzed by method of moments (MoM). For the finite periodic structures, the accuracy of the new method is much better than that of the pure PMM, and is almost the same as that of pure MoM. Because pure PMM uses the periodic boundary conditions, it takes much less memory resources and computation time. For hybrid PMM-MoM method, because the inner part is calculated by PMM, the calculation work concentrates on the outer part. Consequently, compared with the exact MoM, the new method saves much more memory resources and computation time, which provides a drastic reduction of unknowns.展开更多
The developments of the high speed analog to digital converters(ADC) and advanced digital signal processors(DSP) make the smart antenna with digital beamforming(DBF) a reality. In conventional M-elements array antenna...The developments of the high speed analog to digital converters(ADC) and advanced digital signal processors(DSP) make the smart antenna with digital beamforming(DBF) a reality. In conventional M-elements array antenna system,each element has its own receiving channel and ADCs. In this paper,a novel smart antenna receiver with digital beamforming is proposed. The essential idea is to realize the digital beamforming receiver based on bandpass sampling of multiple distinct intermediate frequency(IF) signals. The proposed system reduces receiver hardware from M IF channels and 2M ADCs to one IF channel and one ADC using a heterodyne radio frequency(RF) circuitry and a multiple bandpass sampling digital receiver. In this scheme,the sampling rate of the ADC is much higher than the summation of the M times of the signal bandwidth. The local oscillator produces different local frequency for each RF channel. The receiver architecture is presented in detail,and the simulation of bandpass sampling of multiple signals and digital down conversion to baseband is given. The principle analysis and simulation results indicate the effectiveness of the new proposed receiver.展开更多
In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly d...In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly described.Owing to the high efficiency,low profile,and light weight of the active array microsystems,the application prospects and advantages in the engineering of multi-functional airborne radar,spaceborne radar,and communication systems are analyzed.Moreover,according to the characteristics of the post-Moore era of integrated circuits,scientific and technological problems in the active array microsystems are presented,including multi-scale,multi-signal,and multi-physics field coupling.The challenges are also discussed,such as new architectures and algorithms,miniaturization of passive components,novel materials and processes,ultra-wideband technology,and new interdisciplinary technological applications.This paper is expected to inspire in-depth research on active array microsystems.展开更多
An integrated microwave photonic mixer based on silicon photonic platforms is proposed,which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector.The modulated optical signals from microwave ph...An integrated microwave photonic mixer based on silicon photonic platforms is proposed,which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector.The modulated optical signals from microwave photonic links can be directly demodulated and down-converted to intermediate frequency(IF)signals by the photonic mixer.The converted signal is obtained by conducting of-chip subtraction of the outputs from the balanced photodetector,and subsequent fltering of the high frequency items by an electrical low-pass flter.Benefting from balanced detection,the conversion gain of the IF signal is improved by 6 dB,and radio frequency leakage and common-mode noise are suppressed signifcantly.System-level simulations show that the frequency mixing system has a spurious-free dynamic range of 89 dB·Hz^(2/3),even with deteriorated linearity caused by the two cascaded modulators.The spur suppression ratio of the photonic mixer remains higher than 40 dB when the IF varies from 0.5 to 4 GHz.The electrical-electrical 3 dB bandwidth of frequency conversion is 11 GHz.The integrated frequency mixing approach is quite simple,requiring no extra optical flters or electrical 90°hybrid coupler,which makes the system more stable and with broader bandwidth so that it can meet the potential demand in practical applications.展开更多
Due to the advantages of low propagation loss,wide operation bandwidth,continuous delay tuning,fast tuning speed,and compact footprints,chirped Bragg grating waveguide has great application potential in wideband phase...Due to the advantages of low propagation loss,wide operation bandwidth,continuous delay tuning,fast tuning speed,and compact footprints,chirped Bragg grating waveguide has great application potential in wideband phased array beamforming systems.However,the disadvantage of large group delay error hinders their practical applications.The nonlinear group delay spectrum is one of the main factors causing large group delay errors.To solve this problem,waveguides with nonlinear gradient widths are adopted in this study to compensate for the nonlinear efect of the grating apodization on the mode efective index.As a result,a linear group delay spectrum is obtained in the experiment,and the group delay error is halved.展开更多
Active sonar can separate clutter,reverberation,and moving targets in the Doppler frequency shift domain using Doppler sensitive signals,but time and Doppler leakages of strong interference can inundate weak targets a...Active sonar can separate clutter,reverberation,and moving targets in the Doppler frequency shift domain using Doppler sensitive signals,but time and Doppler leakages of strong interference can inundate weak targets at low signal-to-interference ratios.Therefore,a small moving target interference suppression detection method based on an adaptive least mean square(LMS)algorithm and wide-band ambiguity function(WAF)is proposed.First,an adaptive notch filter based on LMS is used to suppress interference in the spatial Doppler frequency shift domain and then WAF used to detect targets in the fast-time Doppler frequency shift domain.Numerical simulation and pool experiments are performed and the results demonstrated that the proposed method effectively suppress strong interference and accurately estimate the target delay and Doppler shift.About 13 dB of interference suppression is observed in experiments.In addition,the system is able to tolerate interference fluctuations with normalized amplitude fluctuation variance less than 0.5 and improve the active detection capacity for small moving targets.展开更多
This paper presents a supervised polarimetric synthetic aperture radar(PolSAR)change detection method applied to specific land cover types.For each pixel of a PolSAR image,its target scattering vector can be modeled a...This paper presents a supervised polarimetric synthetic aperture radar(PolSAR)change detection method applied to specific land cover types.For each pixel of a PolSAR image,its target scattering vector can be modeled as having a complex multivariate normal distribution.Based on this assumption,the joint distribution of two corresponding vectors in a pair of PolSAR images is derived.Then,a generalized likelihood ratio test statistic for the equality of two likelihood functions of such joint distribution is considered and a maximum likelihood distance measure for specific land cover types is presented.Subsequently,the Kittler and Illingworth minimum error threshold segmenta-tion method is applied to extract the specific changed areas.Experiments on two repeat-pass Radarsat-2 fully polarimetric images of Suzhou,China,demonstrate that the proposed change detection method gives a good performance in determining the specific changed areas in PolSAR images,especially the areas that have changed to water.展开更多
The relative pose between inertial and visual sensors equipped in autonomous robots is calibrated in two steps. In the first step, the sensing system is moved along a line, the orientations in the relative pose are co...The relative pose between inertial and visual sensors equipped in autonomous robots is calibrated in two steps. In the first step, the sensing system is moved along a line, the orientations in the relative pose are computed from at least five corresponding points in the two images captured before and after the movement. In the second step, the translation parameters in the relative pose are obtained with at least two corresponding points in the two images captured before and after one step motion. Experiments are conducted to verify the effectiveness of the proposed method.展开更多
基金Project(2007AA03Z119) supported by the National High-tech Research and Development Program of ChinaProjects(2102029,2072012) supported by the Natural Science Foundation of Beijing,China
文摘Based on the research of modern electronic packaging materials, thixo-forming technology was used to fabricate electronic packaging shell.The process of thixo-extrusion with SiCp/A356 composites was simulated by the finite element software DEFORM-3D, then the flow velocity field, equivalent strain field and temperature field were analyzed.The electronic packaging shell was manufactured by extrusion according to the results from numerical simulation.The results show that thixo-forming technology can be used in producing electronic package shell with SiCp/A356 composites, and high volume fraction of SiCp with homogeneous distribution can be achieved, being in agreement with the requirements of electronic packaging materials.
基金This work hes been is supported in part by National Natural Science Foundation of China (No. 60507007)the Program for New Century Excellent Talents in University (NCET, Min Zhang 2007)
文摘We present a systematic scheme to achieve both high birefringence and low confinement loss in index-guiding photonic crystal fibers(PCFs) ,using a structurally-simple PCF with finite number of air holes in the cladding region. By increasing the size of the outermost-ring air holes in the cladding region,highly birefringent PCFs with low confinement loss can be successfully achieved. The design strategy is based on the fact that the modal birefringence of PCFs is dominated by the inner-ring air holes in PCF,which is verified by a full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that modal birefringence in the order of 10-3 and confinement loss less than 0.1 dB/km can be easily realized in the proposed PCF with only four rings of air holes in the cladding region. We expect that such fibers will be much easier to be fabvicated than those with more air holes in the cladding region.
文摘In this paper, a hybrid method (hybrid PMM-MoM method) is presented for the effective and accurate analysis of finite periodic structures. This method divides a finite periodic structure into two parts. The inner part of an approximate infinite periodic structure is analyzed by periodic method of moment (PMM);the outer part is then analyzed by method of moments (MoM). For the finite periodic structures, the accuracy of the new method is much better than that of the pure PMM, and is almost the same as that of pure MoM. Because pure PMM uses the periodic boundary conditions, it takes much less memory resources and computation time. For hybrid PMM-MoM method, because the inner part is calculated by PMM, the calculation work concentrates on the outer part. Consequently, compared with the exact MoM, the new method saves much more memory resources and computation time, which provides a drastic reduction of unknowns.
基金Supported by the Foundation of Aeronautics Science (No. 03F52042)
文摘The developments of the high speed analog to digital converters(ADC) and advanced digital signal processors(DSP) make the smart antenna with digital beamforming(DBF) a reality. In conventional M-elements array antenna system,each element has its own receiving channel and ADCs. In this paper,a novel smart antenna receiver with digital beamforming is proposed. The essential idea is to realize the digital beamforming receiver based on bandpass sampling of multiple distinct intermediate frequency(IF) signals. The proposed system reduces receiver hardware from M IF channels and 2M ADCs to one IF channel and one ADC using a heterodyne radio frequency(RF) circuitry and a multiple bandpass sampling digital receiver. In this scheme,the sampling rate of the ADC is much higher than the summation of the M times of the signal bandwidth. The local oscillator produces different local frequency for each RF channel. The receiver architecture is presented in detail,and the simulation of bandpass sampling of multiple signals and digital down conversion to baseband is given. The principle analysis and simulation results indicate the effectiveness of the new proposed receiver.
基金Project supported by the National Natural Science Foundation of China(No.92373115)the Natural Science Foundation of Anhui Province,China(No.2308085MF193)+2 种基金the Major Natural Science Project of Anhui Provincial Education Department,China(No.KJ2021ZD0003)the Key Research and Development Project of Anhui Province,China(No.2023n06020026)the Innovation and Entrepreneurship of Anhui Province,China(No.Z020118060)。
文摘In the post-Moore era,the development of active phased array antennas will inevitably trend towards active array microsystems.In this paper,the characteristics and composition of the active array antenna are briefly described.Owing to the high efficiency,low profile,and light weight of the active array microsystems,the application prospects and advantages in the engineering of multi-functional airborne radar,spaceborne radar,and communication systems are analyzed.Moreover,according to the characteristics of the post-Moore era of integrated circuits,scientific and technological problems in the active array microsystems are presented,including multi-scale,multi-signal,and multi-physics field coupling.The challenges are also discussed,such as new architectures and algorithms,miniaturization of passive components,novel materials and processes,ultra-wideband technology,and new interdisciplinary technological applications.This paper is expected to inspire in-depth research on active array microsystems.
基金supported by the Key Research and Development Program of Anhui Province(Nos.2022a05020027 and 202104a05020052)Open Project Program of Wuhan National Laboratory for Optoelectronics(No.2020WNL0KF005).
文摘An integrated microwave photonic mixer based on silicon photonic platforms is proposed,which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector.The modulated optical signals from microwave photonic links can be directly demodulated and down-converted to intermediate frequency(IF)signals by the photonic mixer.The converted signal is obtained by conducting of-chip subtraction of the outputs from the balanced photodetector,and subsequent fltering of the high frequency items by an electrical low-pass flter.Benefting from balanced detection,the conversion gain of the IF signal is improved by 6 dB,and radio frequency leakage and common-mode noise are suppressed signifcantly.System-level simulations show that the frequency mixing system has a spurious-free dynamic range of 89 dB·Hz^(2/3),even with deteriorated linearity caused by the two cascaded modulators.The spur suppression ratio of the photonic mixer remains higher than 40 dB when the IF varies from 0.5 to 4 GHz.The electrical-electrical 3 dB bandwidth of frequency conversion is 11 GHz.The integrated frequency mixing approach is quite simple,requiring no extra optical flters or electrical 90°hybrid coupler,which makes the system more stable and with broader bandwidth so that it can meet the potential demand in practical applications.
基金supported by the key research and development program of Anhui province(202104a05020052,2022a05020027)open project program of Wuhan national laboratory for optoelectronics(2020WNL0KF005).
文摘Due to the advantages of low propagation loss,wide operation bandwidth,continuous delay tuning,fast tuning speed,and compact footprints,chirped Bragg grating waveguide has great application potential in wideband phased array beamforming systems.However,the disadvantage of large group delay error hinders their practical applications.The nonlinear group delay spectrum is one of the main factors causing large group delay errors.To solve this problem,waveguides with nonlinear gradient widths are adopted in this study to compensate for the nonlinear efect of the grating apodization on the mode efective index.As a result,a linear group delay spectrum is obtained in the experiment,and the group delay error is halved.
基金supported by the National Natural Science Foundation of China(61871145)。
文摘Active sonar can separate clutter,reverberation,and moving targets in the Doppler frequency shift domain using Doppler sensitive signals,but time and Doppler leakages of strong interference can inundate weak targets at low signal-to-interference ratios.Therefore,a small moving target interference suppression detection method based on an adaptive least mean square(LMS)algorithm and wide-band ambiguity function(WAF)is proposed.First,an adaptive notch filter based on LMS is used to suppress interference in the spatial Doppler frequency shift domain and then WAF used to detect targets in the fast-time Doppler frequency shift domain.Numerical simulation and pool experiments are performed and the results demonstrated that the proposed method effectively suppress strong interference and accurately estimate the target delay and Doppler shift.About 13 dB of interference suppression is observed in experiments.In addition,the system is able to tolerate interference fluctuations with normalized amplitude fluctuation variance less than 0.5 and improve the active detection capacity for small moving targets.
基金This work was supported in part by the National High-Tech Research and Development Program of China under grant number[2011AA120404]in part by the National Natural Science Foundation of China under grant numbers[4133176]and[41371352].
文摘This paper presents a supervised polarimetric synthetic aperture radar(PolSAR)change detection method applied to specific land cover types.For each pixel of a PolSAR image,its target scattering vector can be modeled as having a complex multivariate normal distribution.Based on this assumption,the joint distribution of two corresponding vectors in a pair of PolSAR images is derived.Then,a generalized likelihood ratio test statistic for the equality of two likelihood functions of such joint distribution is considered and a maximum likelihood distance measure for specific land cover types is presented.Subsequently,the Kittler and Illingworth minimum error threshold segmenta-tion method is applied to extract the specific changed areas.Experiments on two repeat-pass Radarsat-2 fully polarimetric images of Suzhou,China,demonstrate that the proposed change detection method gives a good performance in determining the specific changed areas in PolSAR images,especially the areas that have changed to water.
基金supported by National Natural Science Foundation of China (Nos. 60805038 and 60725309)Beijing Natural Science Foundation (No. 4082032)
文摘The relative pose between inertial and visual sensors equipped in autonomous robots is calibrated in two steps. In the first step, the sensing system is moved along a line, the orientations in the relative pose are computed from at least five corresponding points in the two images captured before and after the movement. In the second step, the translation parameters in the relative pose are obtained with at least two corresponding points in the two images captured before and after one step motion. Experiments are conducted to verify the effectiveness of the proposed method.
