SE同轴测试装置中阶梯电容的研究与优化

在屏蔽材料的屏蔽效能(shielding effectiveness,SE)测试装置中,通过对锥形连接器内导体进行微小移位,优化固定同轴装置的支撑介质的内、外径比值,并在支撑介质中挖去一定厚度的环形沟道构成小电感等技术对阶梯电容进行补偿,减小由截面不连续引起的回波损耗,设计了频率范围为10 MHz至3 GHz的SE同轴测试装置.利用软件仿真验证了表面电阻为5Ω的屏蔽材料在该装置中测试有稳定的SE值,证明该装置不仅改善了基于ASTM D4935测试装置频率范围窄的不足,同时具备良好的阻抗匹配特性.     

同轴传输反射法测量高损耗材料微波介电常数

同轴传输反射方法可以用来测量高损耗材料的微波介电常数。该方法将环形样品嵌入同轴线内,通过测量样品两端的散射系数来确定材料的微波介电常数。文中介绍了测量原理及测量系统,测量了一种石蜡基混合样品的微波介电常数,并通过改进的Bruggeman数学模型,推算出其中陶瓷材料的介电常数。     

The influence of solder-filling on the ac losses of pulsed superconducting cables

AC losses of various kinds of pulsed conductors were measured. First we found that the ac losses of braid filled with Pb-Sn solder were much greater than those of the braid without filler. Since the braid consists of ‘three component strands’ with the mixed matrix of Cu and CuNi, the intra-strand coupling loss should be quite small. Therefore, we concluded that the large increase in ac losses due to solder-filling was caused by the inter-strand coupling through the outer copper sheath. To verify this, we measured the ac losses of two kinds of braids composed of Cu- and CuNi-sheathed strands, respectively. Both samples had the same size and characteristics except that one had copper sheath, while the other had cupro-nickel one. By replacing Cu sheath with CuNi, the ac losses were decreased to the level of those of the braid with Cu- sheathed strands.We also measured the ac losses of the compacted cables, one, filled with Ag-Sn solder and two, without solder. Again, solder filling caused an increase in the ac losses.When cables are not solder-filled, contact resistance among strands cuts the inter-strand coupling effectively.     

新生儿经皮黄疸检测仪的校准

针对经皮黄疸检测仪在使用过程中测量结果无法溯源的问题,通过分析经皮黄疸检测仪的检测原理,研究其测量结果与血清法测胆红素的相关性,提出可尝试采用标准溶液法、标准板法和胆红素浓度模拟法对经皮黄疸检测仪进行校准,并探讨了校准方法的可行性。     

Residual strength prediction of a complex structure using crack extension analyses

The residual strength of a flat panel (thickness 7.6 mm) with five stringers, machined from a monolithic block of Al2024-T351 material, which contained a crack that divided the central stringer, was to be predicted during a Round Robin organised by ASTM. The initial crack tips were right ahead of the stringers #2 and #4, respectively, so that crack branching along the skin and into the stringers occurred after initiation. The prediction has been achieved using finite element simulations including crack extension, for which a cohesive model was utilised. Conventional material properties, yield and ultimate strength as well as experimental results from M(T) specimens in terms of force, COD and Δa, were given. The residual strength prediction was performed in two-steps: First the crack extension parameters for the cohesive model, the cohesive strength, T₀, and the cohesive energy, Γ₀, were determined by numerical reproduction of the results of the M(T) specimen. With the optimised parameters, the five-stringer panel was modelled. These steps were conducted by two different finite element models: by a shell and a 3D finite element mesh. It turned out that it is possible to analyse the structure with both models. In the 3D case, the residual strength prediction was conservative and the deviation of the predicted from the experimental value was below 9%. The results of the shell simulation were even closer to the experiment (deviation approximately 3%), but the simulation was non-conservative.     

Residual strength prediction of a complex structure using crack extension analyses

The residual strength of a flat panel (thickness 7.6 mm) with five stringers, machined from a monolithic block of Al2024-T351 material, which contained a crack that divided the central stringer, was to be predicted during a Round Robin organised by ASTM. The initial crack tips were right ahead of the stringers #2 and #4, respectively, so that crack branching along the skin and into the stringers occurred after initiation. The prediction has been achieved using finite element simulations including crack extension, for which a cohesive model was utilised. Conventional material properties, yield and ultimate strength as well as experimental results from M(T) specimens in terms of force, COD and Δa, were given. The residual strength prediction was performed in two-steps: First the crack extension parameters for the cohesive model, the cohesive strength, T₀, and the cohesive energy, Γ₀, were determined by numerical reproduction of the results of the M(T) specimen. With the optimised parameters, the five-stringer panel was modelled. These steps were conducted by two different finite element models: by a shell and a 3D finite element mesh. It turned out that it is possible to analyse the structure with both models. In the 3D case, the residual strength prediction was conservative and the deviation of the predicted from the experimental value was below 9%. The results of the shell simulation were even closer to the experiment (deviation approximately 3%), but the simulation was non-conservative.     

磁性液位计(模拟法)检测方法

在分析实液法的基础上,提出一种新的针对磁性液位计的模拟法检测方法。介绍其检测过程,探讨了通过精确标记V形磁铁移动距离提高测量准确度的关键方法,并对其可行性与准确性进行实验验证。     

Multi-objective optimization of a triple layer piezoelectric bender with a flexible extension using genetic algorithm

This article presents an electromechanical analysis for a piezoelectric bimorph actuator with a flexible extension, which is used to increase the tip deflection. The performance measuring attributes of such an actuator are derived, and a genetic algorithm is used for multi-objective optimization. The analysis reveals that for a thick flexible extension, the length of the extension provides Pareto optimal solutions for multi-objective optimization. The analysis also shows that as the thickness of the flexible extension decreases, the Pareto optimal solutions converge to a single solution for multi-objective optimization. We have considered nonlinear deflection behavior of piezoelectric materials at high electric fields, and series and parallel electrical connections in the analysis.     

The special features of certifying open test sites for tests on technical equipment for electromagnetic compatibility

The particular features of estimating the attenuation of open test sites in electromagnetic compatibility tests are considered. It is shown by calculation that existing indirect methods of certification do not ensure reliable results. It is proposed to estimate the reflection coefficient of the screening plane, which defines the attenuation of the site. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 52–54, July, 2006.     

The Effect of Compressive Loading on the Ultrasonic Detectability of Kissing Bonds in Adhesive Joints

The effect of compressive loading on the ultrasonic detectability of kissing bonds in adhesive joints was studied. Two distinct types of kissing bond were considered. The first type was a dry contacting interface that represented a disbonded adhesive interface subsequently subjected to compressive loading. The second type were manufactured by contaminating the joint with a thin layer of various liquids. The interaction of normal incidence 10-MHz ultrasound with both these kissing bond types has been quantified. In particular the effect of compressive loading on their detectability was investigated. A quasistatic spring model has been used to predict the interaction of ultrasound with the solid-solid interfaces in the dry-contacting kissing bonds. The reasons for the discrepancy between the experiments and the model are discussed.