HTS双饼线圈的加工工艺及实验研究

详细介绍了高温超导双饼线圈的加工工艺和流程,针对绕制时带材弯曲形变使临界电流退化的技术难点,重点阐述了其解决方法。在液氮温度、自场环境下对采用该加工工艺制作的YBCO双饼线圈及Bi2223/Ag双饼线圈进行低温实验,测试其V-I特性曲线。实验结果表明:该工艺制作的双饼线圈性能良好,工艺安全可靠,是合适的。同时,实验测量数据也为线圈在磁体中的进一步应用提供了可靠依据。     

Edge linking and image segmentation by combining optical and digital methods

We present a hybrid method for segmentation of intensity images, which combines an optical contouring technique and digital algorithms for linking edge points or image segmentation. In a first stage, the digital image to be processed is displayed in a twisted-nematic liquid-crystal display (LCD), which is placed between a polarizer–analyzer pair at 45 deg (instead of 90 deg as occurs in standard LCDs). It is not difficult to demonstrate that the proposed setup produces a resultant image with very pronounced dark contours at middle intensity. After the optical preprocessing, two different digital algorithms are applied: an edge linking algorithm (modified chain code) and a simple thresholding technique for image segmentation. The proposed procedure works well with monochromatic and color images. The method could be useful as a robust technique for segmentation of large images in real-time, which presents potential applications in medical and biological imaging.     

Self-similar propagation region in passive optical fibers based on low-order approximation

For the first time, we numerically demonstrate that similaritons in passive fibers can only propagate with parabolic profile without oscillations in a limited self-similar propagation region when low-order approximation is applied. Dispersion-decreasing fiber (DDF) and nonlinearity increasing fiber (NIF) are used here to generate self-similar pulse in different passive ways. Moreover, we put forward several self-similar features to judge effective similariton propagation and determine self-similar region by numerical simulations and waveform observation. Finally we compare in DDF and NIF the dependence of these regions on incident pulse and fiber parameters in order to obtain parabolic similariton more effectively and steadily. These results extend the low-order propagation properties in passive fibers and are beneficial for the generation of high-quality similariton pulse by parameter selection in experimental studies and practical applications.     

A bubble detection technique based on light intensity and Mie scattering theory for spinning solution

A novel bubble detection technique based on light intensity and Mie scattering theory for spinning solution is presented theoretically and experimentally. With the light intensity in every direction, the particle or bubble size distribution can be calculated with the Mie scattering theory. The light intensity distribution in every direction, corresponding to the light intensity received by every assumed annulus of the detector has been calculated theoretically. According to the light intensity distribution, the size distribution of bubbles can be deduced. A series of standardized polystyrene micro-sphere (with 7 μm diameter) solution has been used not only as sample for experiments and calibration, but also as the bubbles in the glycerin. Theoretical and experimental results show that the technique can be used for bubble detection, in order to improve the traditional bubble detection scheme, and to lower production costs.     

Experiment on the object-image distance parameter in the X-ray phase contrast imaging system

For the X-ray phase contrast imaging system, in addition to the hardware-related parameters, the object-image distance is an important parameter that affects the imaging results. Based on the Fresnel diffraction theory, the X-ray phase contrast formation mechanism is analyzed to find the theoretical relationship between the object-image distance parameter and the image contrast. Through the experimental simulation on a ball model, images with edge enhancement effect and image contrast data were obtained with regard to different object-image distance conditions. The analysis and experimental results show that, clear image information about the edges of the sample structures can be got if the object-image distance parameter is set suitably.     

Comparison of subwavelength focusing properties of diffraction and Fresnel zone plate plasmonic planar lenses

The subwavelength focusing properties of diffractive plasmonic planar lenses (DPLs) and Fresnel zone plate plasmonic planar lenses (FZPs) have been compared in this paper. To that end, we use the same lens material, incident wavelength, thickness and focal length for comparison. Both DPLs and FZPs consist of central circular slits surrounded by transparent and opaque zones and can get clear focusing performances. By using the rigorous electromagnetic numerical method, the fields in the focal region are analyzed in detail, and our results demonstrate that FZP can generate higher transmission efficiency, and higher peak field intensity at the focal plane. Focusing polarization properties of the lens illuminated by linearly polarized state, are calculated and analyzed also. The numerical results show that both the DPL and the FZP produce asymmetrical focal spot distributions with a low f-number. To the FZP, the full-width at half-maximum (FWHM) varies from 256 nm (along y-axis) to 516 nm(along x-axis) and to the DPL, the FWHM varies from 256 nm(along y-axis) to 580 nm(along x-axis), respectively. But for a high f-number, the asymmetrical performance of the focal spot will be reduced due to complicated electromagnetical field interferences and micro waveguide effect. Otherwise, the DPL can get a higher depolarization effect than the FZP does.     

One-dimensional integral imaging based on parallax barrier

One-dimensional integral imaging (1DII) which only has horizontal disparity is a practical solution of high resolution in the vertical direction, low-cost, easy-viewable three-dimensional (3D) display. A 1DII based on a parallax barrier is proposed in this paper. The 1DII consists of a parallax barrier and a display panel. The operation principle and parameter calculation of the 1DII are described in detail. Two prototypes of the proposed 1DII and conventional 1DII based on a lenticular lens array are developed. The proposed 1DII improves the quality of the 3D image and provides larger viewing angle than that based on a lenticular lens array, and it is simpler and has lower cost than that based on a lenticular lens array.     

Goos–Hänchen shifts of a light beam reflected from the interface of colloidal ferrofluids

Controllable Goos–Hänchen shift of a light beam reflected from the colloidal ferrofluids is investigated by using the stationary-phase method. It is found that the Goos–Hänchen shift can be easily controlled by the local H_e factor and the volume factor. Using this scheme, the peak value, the peak position and the width of the Goos–Hänchen shift can all be controlled by adjusting the external magnetic field for a fixed configuration, which also provides a possibility for obtaining larger negative Goos–Hänchen shift by changing the external controlling field. Our results have potential applications in optical devices.     

Study on an optical system with coherent laser array source and phase optimization in turbulent atmosphere

Model of an optical system with coherent laser array source and the piston phase optimized by the stochastic parallel gradient descent algorithm is established. With this model, theory of beam propagation through the optical system in turbulent atmosphere is analyzed, and the analytical formulas of the beam average intensity along the propagation path are derived. Strehl ratio of the received beam induced by intensity disorderly distribution and power efficiency of the received beam are introduced to evaluate performance of the optical system. Under the H-V 5/7 atmospheric turbulent model, performance of an optical system with determinate parameters was calculated, and the influences of the propagation distance and the laser wavelength were numerically analyzed, respectively.     

Effect of emitter layer doping concentration on the performance of silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si:H(15 nm)/a-Si:H(10 nm)/ epitaxial c-Si(47 μm)/epitaxial c-Si(3 μm) structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot-wire chemical vapour deposition. The effect of the doping concentration of emitter layer S_d (S_d=PH₃/(PH₃+SiH₄+H₂)) on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with S_d increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at S_d = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm², a fill factor of 63.3%, and a conversion efficiency of 7.9%.