Lensless digital holographic imaging could support high resolution, large field of view and three-dimensional (3D) imaging, but improving the resolution and quality of the reconstruction is still challenging. In this review paper, the compressive holographic models based on diffraction propagation method arc introduced. Compressive sensing arc developed based on total variation regularization and two-step iterative shrinkage/thresholding algorithm. The physical mechanism of removing two-order noise and twin image is discussed. A filter layer is designed to improve the signal to noise ratio of 3D reconstruction. A block-wise algorithm based on effective anti-aliasing region is proposed, which can improve computational efficiency of compressive holography. A single-shot compressive holographic model based on two-angle illumination beam is proposed. It effectively improves the axial resolution of 3D imaging. High-resolution 3D reconstruction of multilayer masks and particle flow field arc demonstrated by using this algorithm.

Holographic imaging suffers from twin images and cross-talks between different layers of three-dimensional objects even at millimeter scale. Compressive sensing associated with holographic microscope achieves micron level depth-resolved imaging free from the mentioned noises above.

A resampling ring-mask method in spatial spectral domain (RRM-SSD) is proposed for speckle reduction in one-shot digital holography. Spatial spectrum of a hologram with speckle is divided into several subspectra using the resampling ring masks. Different subspectra are individually used to obtain the corresponding reconstructed amplitude images by the angular spectrum method. With the random distribution of the speckle, averaging these uncorrelated amplitude images would successfully enable speckle-reduced reconstruction. No specific operations for hologram recording or complex process for reconstruction are required in this method. Comparison with the previous rectangular mask method in spatial domain proves the advantage of the RRM-SSD method for both speckle reduction and high-resolution reconstruction. Experimental results show that the RRM-SSD method is efficient and simple for speckle reduction, which can be widely used in holographic imaging. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

Holographic reconstruction is troubled by the phase-conjugate wave front arising from Hermitian symmetry of the complex field. The so-called twin image obfuscates the reconstruction in solving the inverse problem. Here we quantitatively reveal how and how much the twin image affects the reconstruction and propose a compressive sensing (CS) approach to reconstruct a hologram completely free from the twin image. Using the canonical basis, the incoherence condition of CS is naturally satisfied by the Fourier transformation associated with wave propagation. With the propagation kernel function related to the distance, the object wave diffracts into a sharp pattern while the phase-conjugate wave diffracts into a diffuse pattern. An iterative algorithm using a total variation sparsity constraint could filter out the diffuse conjugated signal and overcome the inherent physical symmetry of holographic reconstruction. The feasibility is verified by simulation and experimental results, as well as a comparative study to an existing phase retrieval method.

We propose a novel single-pixel imaging system using encoded switchable phase-shifting sinusoid structured patterns. The simulation results demonstrate the feasibility and flexibility of our method. It has the inherent advantage in imaging around a corner.

The image reconstruction process in super-resolution structured illumination microscopy (SIM) is investigated. The structured pattern is generated by the interference of two Gaussian beams to encode undetectable spectra into detectable region of microscope. After parameters estimation of the structured pattern, the encoded spectra are computationally decoded and recombined in Fourier domain to equivalently increase the cut-off frequency of microscope, resulting in the extension of detectable spectra and a reconstructed image with about two-fold enhanced resolution. Three different methods to estimate the initial phase of structured pattern are compared, verifying the auto-correlation algorithm affords the fast, most precise and robust measurement. The artifacts sources and detailed reconstruction flowchart for both linear and nonlinear SIM are also presented.

利用连续光纤激光器对烧结NdFeB永磁体与SPCC钢实施了激光搭接点焊,分析了接头的显微组织特征.结果表明:熔核内部存在结晶裂纹和多种不同类型的气孔缺陷,NdFeB内部的熔核周围存在液化裂纹;熔核中的凝固组织主要为α-Fe和富Nd相;α-Fe主要为柱状树枝晶,局部位向相近的柱状树枝晶形成柱状晶区,不同柱状晶区的位向存在明显差别;富Nd相主要分布在熔核上表面的外围,少量分布在熔核内部、熔核缩颈处的外围及部分气孔内壁.对形成上述显微组织的机理进行了初步分析.

The metallurgical behavior of laser welds in NdFeB permanent magnets is investigated using laser spot welds made with N48H with the deep penetration mode weld or the heat conduction mode weld using a 2 kW continuous fiber laser.The joint microstructures show that the heat affected zones (HAZ) of both joints have cracks caused by melting of the grain boundary phase,with the fusion zones having Nd2Fe14B and α Fe,while the nuggets in both joints have ultrafine equiaxed grains of Nd2Fe14B.α-Fe eolumnar dendrites develop on the surfaces of the nuggets in the deep penetration mode weld but not in the heat conduction mode weld.A Nd-rich phase is found on the edge of the nugget surface for the deep penetration spot weld and in the middle of the nugget surface for the heat conduction spot weld.Different temperature fields and flow patterns are believed to be the main causes of the different microstructures for the different welding modes.

Long-term service of large hydropower stations confronts the problem of stainless steel blade erosion of hydraulic turbines.A method of vertical down welding is proposed for the automatic in-situ maintenance.Stable MIG short circuiting transfer is achieved through process parameters adjustment.Experiments demonstrate that the proposed method ensures appropriate penetration depth,high deposition efficiency and satisfactory weld appearance.The method provides fundamental basis for industrial application.

The design of a high-frequency switching mode charger (HFSMC) was optimized using a PSPICE simulation of the charging system including a valve regulated lead-acid (VRLA) battery pack and the HFSMC. A high-frequency battery charging circuit model was developed to describe the battery dynamics when charging with DC current having high-frequency ripples. An IGBT circuit model, a high-frequency pulsed transformer coupling model and a silicon fast recovery diode model were also developed. Simulations were compared to laboratory measurements to verify the battery and system models. Simulation of the working states of an Fe-based nanocrystalline magnetic core used in the transformer shows that the transformer design can be optimized by adjusting the core gap and by employing an RC network. Further simulations show that the components in the output unit of the charger main circuit can also be optimized. Simulations also show that the battery dynamics including the inductance should be considered for design optimization of the HFSMC.

Thin films of M-C (M = Cr, Mn, Fe) have been deposited on silicon substrates by magnetron sputtering. It was found that interdiffusion between carbide films and silicon substrates occurred for Mn-C/Si and Fe-C/Si samples. The hardness and elastic modulus of the Cr-C films were around 16 +/- 1 GPa and 210 +/- 21 GPa, respectively. Mn-C and Fe-C films were not so hard as Cr-C films. The resistivity of these films at room temperature was between 0.267 and 3.40 m Omega cm. The resistivity of Cr-C and Mn-C films changed a little with time at 673 K in air.

Welding distortion and residual stress in welding process were two important factors that affected the precision and property of welded products,and they were still important issues that needed to be solved in the industry production nowadays.At present,the main method used to predict welding distortion is three dimensional thermo-elastic-plastic FEA method.Due to the limit from calculating capability of computers,it's still impractical to predict the welding distortion of complicated structures.The inherent strain method was brought out by a Japanese researcher aiming to solve the distortion problem in complicated structures.This method neglects the welding history,and predicts distortion using an elastic finite element analysis by applying the inherent strains on the structure.In the present study,the inherent strains are firstly obtained for an flat butt joint of 5052 aluminum alloy through experiments and three dimensional thermo-elastic-plastic FEA.The distortion of the joint was then predicted using inherent strain method based on the obtained inherent strains,the feasibility of inherent strain method in predicting distortion of aluminum alloy structure was confirmed finally.Computational and experimental results showed that the inherent strain method could predict welding distortion with acceptable accuracy and greatly reduced running time when comparing to the thermo-elastic-plastic FEA method.

To apply the laser spot welding process in the joining of NdFeB permanent magnet and steel plate cold commercial(SPCC) steel, the effects of laser pulse power, pulse duration, and defocusing distance on weld features and strength were studied experimentally. The results show that there are both conduction welding and keyhole welding in the laser spot welding under our experimental conditions. Welding modes can be transformed by changing peak power or defocusing distance, but not altered by changing pulse duration. There are three fracture modes in shearing tests,i.e., exuviation, shear and crush fractures, with nugget dimensions and shearing load increasing in turn. To gain good joint strength, the pulse peak power and defocusing distance should be chosen appropriately to implement welding in keyhole mode, and moreover, pulse duration should not be too long.

GPS L2C 信号是GPS系统在L2频段上的新型民用信号,其主要由时分复用的CM码与CL码组成.CL码上没有导航电文的调制,所以可以进行更长时间的相干积分,适合于捕获微弱信号.但CL码码长较长,运用传统的捕获方法,难以直接捕获.提出一种基于分块折叠的捕获方法,利用折叠码与分块捕获技术,快速直接捕获CL码.与传统捕获算法相比,新算法能够实现捕获速度上的提高,且可根据需要优先考虑捕获速度或灵敏度.

The hybrid approaches of MoM and UTD is used to study the electromagnetic coupling between monopoles on the bounded conducting planes.The effect on the coupling of the size of the conducting planes and the slots is analyzed.And a novel method for reducing the coupling is presented.The calculation results show that proper size of each bounded conducting plane can make the coupling smaller,and lots of the half wavelength slots excavated on the bounded conducting planes can also reduce the coupling well,but the effect of the width and the space of the slots on the coupling is little.

Mechanical fastening or adhesive bonding methods are generally used to join a NdFeB permanent magnet to a steel component, while no research has been reported on the welding process to join magnet to steel. In this paper, laser spot welding was used to join a NdFeB permanent magnet to an SPCC (steel plate cold commercial) steel in an effort to achieve joining of magnet/steel dissimilar materials with high speed and quality, with the joint formation mechanism, hardness, strength, and fracture behavior analyzed. The results show that during the welding process, the two base metals quickly melt, mix and then solidify to form the weld that joins the two specimens together, but that the hardness in the joint is not uniform with the heat affected zone having lower hardness than the NdFeB base metal. Within the nugget, the region adjacent to the fusion line has the highest hardness while the middle part of the nugget has the lowest in the joint. The maximum fracture stress of the joint is about 75% the strength of the magnet. Hot cracks tend to occur at the interface between the nugget and the magnet base metal, whereat the cracks propagate and lead to joint failure during shear tests. The fracture is intergrannular which is a typical brittle fracture.

The paper studies the laser spot welding of SPCC steel and NdFeB permanent magnet. Results show that during welding process the two metals quickly melt, mix and then solidify to form a weld that joins two specimens together. The hardness in the joint is not uniform: the heat affected zone (HAZ) has a lower hardness than NdFeB base metal; within the nugget, the region adjacent to the fusion line has the highest hardness while the middle part of nugget has the lowest hardness in the joint. Hot cracks are apt to occur at the interface between nugget and magnet base metal, whereat the cracks propagate and lead to joint failure during shear tests. The fracture is intergrannular and is a typical brittle fracture. To increase the joint strength and prolong the service life of welded components, it is necessary to take some metallurgical and technological measures to improve the bonding quality between nugget and magnet base metal.

During the research and development of electronic products,the design which considers the compatibility of both the electronic and magnetic character is popular and it can affect the performance of the whole system.Shielding technique is very important for electromagnetic compatibility,and it can cut off the coupling route effectively.However,the inevitable slots degrade shielding effectiveness greatly.It is very difficult to analyze the coupling of complex slots.In this paper,a simple transmission line model was given to approximately represent a narrow slot with depth and spoilage.Since the analysis of the coupling with conductivity was more meaningful,the coupling with small conductivity was also presented in detail.

Laser-plasma arc hybrid welding is a promising technology which can be widely used in industry and it attracts attention of the researchers at home and abroad. Compared with the laser welding, laser-plasma arc hybrid welding can increase welding speed and tolerance towards poor joint fitup, reduce porosity as well as hot cracks and improve the appearance of weld. The technology can be applied to produce tailor welded blanks, lap joints of coated steels and thin sheet joints at high speed, and it can also be used for addition filler material in weld, surface alloying and even vertical welding. In order to widely apply this technology in industry, the researches on hybrid welding torch, mechanism about the appearance of weld and new application field about this technology should be strengthened in the future.

The interest in the development of lightweight transparent electromagnetic shields for RF range has been growing up in the recent years. Application of thin films is wide and attractive. A complete study of transparent mental is performed, from design to fabrication. Finally some recent experimental results are summarized and analyzed.