Boundary-value problems and the validity of the Post constraint in modern electromagnetism

When a (frequency-domain) boundary-value problem involving a homogeneous linear material is solved to assess the validity of the Post constraint, a conflict arises between the fundamental differential equations of electromagnetism in the chosen material and a naïve application of the usual boundary conditions. It is shown here that the conflict vanishes when the boundary conditions are properly derived from the fundamental equations, and the validity of the Post constraint in modern macroscopic electromagnetism is thereby reaffirmed.     

Scale invariance rule in electromagnetic scattering

The volume integral equation formalism is used to prove the scale invariance rule for an arbitrarily sized scatterer with an arbitrary shape, morphology, and orientation. The only assumptions are that the scatterer is made of optically isotropic linear materials and is embedded in a homogeneous, linear, isotropic, and nonabsorbing infinite medium.     

Application of an electrostatically actuated cantilevered carbon nanotube with an attached mass as a bio-mass sensor

In the present paper, another latent capability of SWCNT as a mass sensor is investigated. The relationship between the resonant frequency, dynamic pull-in voltage at the resonance frequency shift, and the attached mass is established by using the nonlocal Euler–Bernoulli beam theory. Using this relationship, a general closed-form nonlinear sensor-equation has been derived for the detection of the mass attached to the SWCNT. The aim of this study and present model is to show the sensitivity of the Cantilevered SWCNT to the values and positions of attached mass. Moreover, the results indicate that by increasing the value of attached mass and considering a single non-local scaling parameter (e₀), the values of dynamic pull-in voltage at the resonance frequency shift are decreased. Because of the small scaling parameter (e₀), the mass sensitivity of carbon nanotube increases, when the position of the attached mass is in the tip of a Cantilevered SWCNT length. The authority and the accuracy of these formulas are examined with other pull-in sensor equations in literatures. The results demonstrate that the new sensor equation can be applied for CNT-based mass sensors with rational accuracy.     

Preparation, magnetic and electromagnetic properties of polyaniline/strontium ferrite/multiwalled carbon nanotubes composite

Strontium ferrite particles were firstly prepared by sol-gel method and self-propagating synthesis, and then the polyaniline/strontium ferrite/multiwalled carbon nanotubes composites were synthesized through in situ polymerization approach. Structure, morphology and properties of the composite were characterized by various instruments. XRD analysis shows that the output of PANI increases with the increase of the content of MWCNTs, due to the large surface area of MWCNTs. Because of the coating of PANI, the outer diameter of MWCNTs increases from 10 nm to 20-40 nm. The electrical conductivity of the composites increases with the amount increase of MWCNTs and reaches 7.2196 S/cm in the presence of 2 g MWCNTs. The coercive force of the composites prepared with 2 g MWCNTs is 7457.17 Oe, which is much bigger than that of SrFe₁₂O₁₉ particles 6145.6 Oe, however, both the saturation magnetization and the remanent magnetization of the composite become much smaller than those of SrFe₁₂O₁₉ particles. The electromagnetic properties of the composite are excellent in the frequency range of 2-18 GHz, which mainly depend on the dielectric loss in the range of 2-9 GHz, and mainly on the magnetic loss in the range of 9-18 GHz.     

Electromagnetic wave absorption of polymeric nanocomposites based on ferrite with a spinel and hexagonal crystal structure

We have investigated composites designed for microwave absorption based on magnetic filler, composed of phases within the SrO-Fe₂O₃ system, embedded in a polyphenylene sulfide matrix with a concentration ratio of 80:20 by weight. The formation of the nanosized particles of SrFe₁₂O₁₉ and Fe₃O₄, as the principal magnetic phases was achieved via the co-precipitation of Sr²⁺/Fe³⁺ ions using different molar ratios. The various precursors obtained were calcined between 600 °C and 900 °C in air. The electromagnetic parameters of the composites were measured with a vector network analyzer at 400 MHz to 32 GHz. The results show that with a composite composed of a complex magnetic filler comprising the nanoparticles of two magnetically diverse phases, i.e., a spinel phase as the electromagnetic wave absorber in the lower GHz range and a hexagonal phase operating at a higher GHz range, above 32 GHz, a microwave absorber with an broad absorption range can be prepared.     

Doping effect of Y ions on the microstructural and electromagnetic properties of Mn-Zn ferrites

Mn-Zn ferrites doped with different contents of Y³⁺ ions were prepared by conventional two-step synthesis method. The microstructure and electromagnetic properties of the as-prepared Mn-Zn ferrites were investigated. It was found that all the samples consisted of ferrite phases of typical spinel cubic structure, and when Y³⁺ ion content was upto 1.5 mol%, yttriumirongarnet (Y₃Fe₅O₁₂) phase with garnet structure was detected. With increasing doping content of Y³⁺ ions, the lattice constant and grain size increased, and after an increase to its maximum value, the sample apparent and relative densities dropped down. Through the analysis of magnetic properties, it was revealed that the saturation magnetization, and both the real and imaginary parts of permeability of the as-prepared samples raised with increasing doping content of Y³⁺ ions but decreased with more Y³⁺ ions, while their coercivity showed an opposite change trend; and the Curie temperature increased monotonously. The measurement of dielectric properties indicated that the dielectric constant of the doped Mn-Zn ferrites presented a rise with increasing Y³⁺ ion content, and dropped down gradually when more Y³⁺ ions were doped, while the dielectric loss tangent would decrease with Y³⁺ content upto 1.5 mol%, but after that, it increased.     

Influence of Fe-doping on the microstructure and electromagnetic performance of manganese oxides

A simple wet chemical method was used to synthesize Fe-doped MnO₂ composites with iron amount ranging from 0 to 90 M percent. X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and vector network analyzer were employed to investigate the effect of iron doping on the microstructure and electromagnetic performance of the as-synthesized samples. Results indicate that relative small content of Fe-doping cannot change the α-MnO₂ structure but can promote the formation of hollow-structural morphology. The as-obtained products are transformed into a novel compound (Fe_0.67Mn_0.33)OOH with the increase of Fe-doping to 30 mol%. The possible formation mechanism was proposed in detail. Compared with the pure MnO₂, the Fe-doped samples exhibit decreased dielectric loss but increased magnetic loss with increasing the iron content below 20 mol% while relatively poor electromagnetic properties with the iron content above 30 mol%.     

647W灯泵浦大功率连续Nd:YAG激光器

 报道了一台灯泵浦大功率连续Nd:YAG激光器。对影响大功率固体激光器模块输出功率和光束质量的主要因素进行了理论分析，并提出提高激光器效率的措施：对聚光腔的形状、结构和材料以及冷却方式，泵浦灯的参数和材料，激光晶体的参数和镀膜进行优化设计，采用径向固定的谐振腔镜。该灯泵浦YAG晶体棒总体电光转换效率为4%，光束质量为22mm·mrad，输出功率647W。     

RIBLL束流诊断

描述了兰州放射性离子次级束流线(RIBLL)上研制并安装使用的放射性束流(RIB)诊断装置的种类、结构、性能及在AIBLL上的位置和功能.重点叙述了以光纤为基础的几种诊断元件,它们探测效率高、响应时间快、制作容易、性能稳定.给出了RIB¹⁷N等高图,说明诊断装置辅助MBLL得到RIB的水平.     

Human-to-metal electrostatic discharge current measurements – Notes on the ESD current waveform

The Electrostatic Discharge (ESD) phenomenon has been described through the IEC 61000-4-2. ESD current parameters' values, have been set in this Standard. The theoretical ESD current waveform defined in this standard, describing the conventional Contact discharge mode, needs to be re-evaluated on the basis of accurate experimental data. Even though the standard deals with commercial ESD generators, its goal is to simulate the natural phenomenon as good as possible. More and accurate data may contribute to the better simulation of the natural phenomenon. New values and better comprehension of the phenomenon demand new measurements based on high end measuring equipment. Such works and publications have been carried out the past years. Yet, the need to systematize and integrate this work remains. Larger and trust-worthy series of measurements need to be carried out and presented clearly.This paper deals with new ESD-current data, taken with broadband equipment. New and more detailed measurements like these, were never before taken at such a large number of individuals. The goal of this work is that the data acquired can serve as a basis for re-evaluating the conventional approach of the scientific community to the ESD event.In this paper, using a broadband measuring system, new parameters' values are measured and relations are presented, following standard statistical procedures. The results, which occur from measurements carried out on tenths of human individuals, are questioning the Standard in many points. A new way of approaching the standardization of the ESD current is proposed, as the excuse of the poor measuring equipment that sets barriers on the measuring accuracy, does not apply any more. The charging voltages of 500 V and 1000 V were also examined since such range of voltages are often met at ESD events and they are considered very harmful.