取向吸波贴膜电磁性能研究

提高吸波材料的电磁性能,是新型电磁波吸收材料的重要研究内容。采用朗道-利夫希兹-吉尔伯特(LLG)方程、等效媒介理论和传输线理论,分别对随机取向和一致取向吸波贴膜的本征磁导率、等效磁导率和反射损耗进行了计算。计算结果表明当微波吸收剂一致取向时吸波材料的本征磁导率、等效磁导率和反射损耗均有显著提升。通过改变吸波贴膜内部吸收剂空间排布的方式,可以有效地提高吸波贴膜的电磁性能。针对流延法制备吸波贴膜的过程,对刮刀下流延浆料速度曲线和微波吸收剂取向之间的关系进行了分析,通过微波吸收剂的取向张量对吸波贴膜的取向程度进行了表征。通过改变流延过程中的物理参数,可以调控吸波贴膜的取向状态。     

基于粒子群算法的宽带电阻型FSS吸波材料优化设计

利用电阻型FSS 吸波材料结构,结合粒子群算法优化设计了一种宽频带低剖面的微波吸波材料。通过设计不同的自适应度函数,探讨了优化策略对吸波材料设计结果的影响。在综合平衡宽带和低剖面的条件下,设计出的吸波材料,其-10dB 带宽达到6. 25 ~25. 30GHz,而厚度仅为3.92mm。对设计结果进行了实验验证,结果证明了粒子群优化算法设计的有效性。所采用的计算流程可以全程自动进行优化处理。     

粒子群算法在三维微带阵列优化设计中的应用

采用粒子群算法与微波仿真软件CST联合仿真的方法,针对拓展吸波带宽或降低吸波材料厚度的不同要求,通过设计不同的适应度函数,实现了对三维微带线阵列吸波结构材料的优化设计。设计结果表明,经过优化设计,吸波材料的吸波带宽可以增加30%,或在吸波性基本不变的条件下材料厚度减少15%。调节适应度函数中的权重,还可以有针对性地拓展吸波材料的频率低频段或高频段。所采用的计算流程可以全程自动进行优化处理。     

多向定向铁纤维吸波材料的雷达反射特性研究

基于电磁场理论用传输矩阵方法数值计算具有金属基底多向定向铁纤维吸波材料的雷达反射特性.结果表明具有强各向异性的单定向铁纤维材料,通过多向定向铺层在铺层层数不是很小时(通常大于10层)该吸波材料表面的反射场近似各向同性特性;指出它的反射特性可用反射系数平行分量(R//)0表征;通过等效电磁参数的计算和实验验证了数值分析的正确性.     

基于有效介质理论的吸波材料性能分析

应用有效介质理论,计算了不同体积比下几种复合吸波剂以及吸波剂与透波体组成的吸波材料的有效电磁参数,并分析了其吸波性能。通过与实验数据的对比,表明这种方法可以很好地预测吸波材料的吸波性能。而且,它可以计算出吸波剂及透波体的最佳配比及材料厚度,这对于设计吸收频带宽、吸收效率高的吸波材料具有一定的参考价值。     

利用改进简化PSO优化设计多层吸波材料

现有的粒子群优化算法(PSO)在传统多层平板吸波材料的优化过程中收敛速度慢,寻优精度低。为了改善设计的收敛速度和寻优精度,利用改进简化粒子群优化方法(ISPSO)在传输线法计算模型基础上对多层吸波材料进行了优化设计。优化设计结果表明,在0.8～6GHz范围内,5层吸波材料的反射系数在-22.98 dB以下,得到的结果比现有文献好。     

DF31导弹各向异性材料涂覆RCS缩减优化设计

在目标表面合理涂覆各向异性吸波材料,能够有效缩减目标的雷达散射截面.文章以DF31导弹为例子,提出了一种适用于复杂几何外形的各向异性吸波材料涂覆目标雷达截面缩减的优化设计方法.该方法由通用几何建模方法、各向异性材料电磁散射高频计算方法、常用遗传算法三部分组成,以各向异性阻抗为优化参量.仿真结果表明,采用各向异性吸波材料涂覆能够显著降低目标的雷达散射截面.     

等效模型误差对蜂窝吸波结构设计结果的影响

使用等效模型可以大大简化蜂窝吸波结构的设计复杂度,但等效模型的误差会对设计的结果产生影响。基于单轴各向异性介质中的电波传播理论和粒子群优化算法,通过定义更符合实际的随频率变化的相对误差,对不同情况下Hashin鄄Shtrikman(HS)模型的误差对蜂窝吸波结构优化设计结果的影响进行研究。结果表明,HS 模型的误差会在一定程度上影响蜂窝吸波结构的优化结果,特别是当电磁波斜入射时,由于纵向传播常数受到横向等效模型误差的影响较大,而受到纵向等效模型的影响较小,所以优化结果也主要受到横向等效模型误差的影响。     

单层雷达吸波涂层电磁参量匹配解析式的推导及其应用

从电磁场理论出发,严格推导了单层雷达吸波涂层的等效表面阻抗公式,得出了单层雷达吸波涂层反射系数的计算公式,在此基础上推导了基底材料为金属体时单层雷达吸波涂层的两条设计原则,得出了电磁参量的匹配解析式,最后讨论了这两条设计原则的应用.     

材料参数测量误差对吸波材料优化设计结果的影响

根据吸波材料电磁反射系数的传输线理论进行优化设计是微波吸收材料研究的重点,微波吸收材料的吸波效果与其电磁参数(介电常数与磁导率)和材料厚度密切相关,电磁参数测量的准确性与微波吸收材料厚度制作的精确性,对微波吸收效果有很大的影响。通过理论计算分析,探讨了电磁参数测量误差对微波吸收材料优化设计结果的影响,并讨论了微波吸收体厚度制作误差对微波吸收材料吸波效果理论计算值对优化值偏离的影响。     

On the Theory of the Ferrite Resonance Isolator

The attenuation constants for both directions of propagation in a rectangular waveguide loaded with a small slab of ferrite are calculated by means of perturbation theory. The maximum attainable ratio of reverse to forward attenuation is found to be inversely proportional to the square of the bandwidth, with a constant of proportionality that is dependent on the shape of the ferrite slab and the proximity of cutoff. The figure of merit is largest for the case of a thin ferrite slab magnetized perpendicular to the plane of the slab. It is shown that a significant increase in the figure of merit can be obtained by proper use of the anisotropy of grain-oriented materials or single crystals.     

Inductively heated shape memory polymer for the magnetic actuation of medical devices

Presently, there is interest in making medical devices such as expandable stents and intravascular microactuators from shape memory polymer (SMP). One of the key challenges in realizing SMP medical devices is the implementation of a safe and effective method of thermally actuating various device geometries in vivo. A novel scheme of actuation by Curie-thermoregulated inductive heating is presented. Prototype medical devices made from SMP loaded with nickel zinc ferrite ferromagnetic particles were actuated in air by applying an alternating magnetic field to induce heating. Dynamic mechanical thermal analysis was performed on both the particle-loaded and neat SMP materials to assess the impact of the ferrite particles on the mechanical properties of the samples. Calorimetry was used to quantify the rate of heat generation as a function of particle size and volumetric loading of ferrite particles in the SMP. These tests demonstrated the feasibility of SMP actuation by inductive heating. Rapid and uniform heating was achieved in complex device geometries and particle loading up to 10% volume content did not interfere with the shape recovery of the SMP.     

叠层式片状电感器的设计

采用铁氧体材料和多层厚膜印刷技术，把铁氧体膜片和导电浆料相间印刷、叠合起来，经过热压、切割，烧制成一体化的闭磁路螺旋管状磁芯线圈，具有矩形微型、封闭磁路、独石结构的特点。     

圆波导铁氧体锁式变极化器的阻抗匹配研究

本文对铁氧体环加载圆波导锁式变极化器进行了阻抗匹配研究。从而提出了一种设计铁氧体环加载圆波导变极化器阻抗匹配的方法。推导出了/4阻抗匹配的计算公式,计算得到了阻抗变换器的尺寸,测试了实际样品的匹配性能,实测结果和理论计算吻合得很好。     

The Point-Matching Solution for Magnetically Tunable Cylindrical Cavities and Ferrite Planar Resonators

This paper presents an exact field theory treatment for a cylindrical cavity containing a full-height triangular ferrite post as well as for ferrite planar resonators of arbitrary shape. The knowledge of the resonant frequencies of the cavity is essential for the construction of circulators with a triangular ferrite post; those of the planar circuits are needed for the design of microwave integrated circuits. The treatment is general and depends neither on the location of the ferrite post inside the cavity nor on the geometry of the planar resonator. The solution of the wave equations in the ferrite material and in a possible surrounding air region is written as an infinite summation of cylindrical modes. In the case of the cavity, the individual modes are exactly matched along the internal cylindrical metallic boundary of the cavity. The fields at the ferrite-air interface in both cases are matched using the point-matching technique, which leads to a finite system of homogeneous, simultaneous equations for which the determinantal equation must be zero. An example of a cavity with a triangular ferrite post is studied and calculated, and measured results are compared. Furthermore, examples of application of the theory on triangular and quadratic planar resonators are described and compared with published experimental measurements.     

Waveguide Subsidiary Resonance Ferrite Limiters

This paper gives an analysis of E-plane waveguide ferrite limiters under subsidiary resonance conditions. Since Suhl's high-power damping term is power sensitive, it is necessary to evaluate it in every part of the ferrite structure before forming the dispersion relation. This is done in this paper by dividing the waveguide assembly in small elements transverse and parallel to the direction of propagation and calculating it in each region. The dispersion relation in each section along the direction of propagation is then formed in conjunction with the appropriate Suhl damping constant by establishing the transverse resonance condition. The total output power is obtained by forming the input/output relation for each section one at a time along the structure. The theory has been found useful in describing both the onset of limiting and the dynamic range of a ferrite limiter mounted on one of the narrow walls of the waveguide.     

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (?_r) and permeability (µ_r) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ?′, e″, µ′, µ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ?_r if the filling factor is less than 0.30 and ratio |?₁| (host)/ |?₂| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ?₂ and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model µ_r. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.     

介质加载对微波铁氧体器件性能的影响

本文应用耦合波理论对微波铁氧体器件的三种介质加载方式进行了计算,得出了一些定量的结果,这对我们深入理解微波铁氧体器件的介质加载机理具有一定的意义     

手征等离子体波导理论

本文给出了手征等离子体波导(由在柱形波导中填充手征等离子体材料构成)中横向场量与纵向场量之间的关系式,并给出了纵向场量的求解公式。作为示例,文中具体研究了平行板手征等离子体波导,得到了其中几个低次传播模式的色散特性曲线。     

Cover Picture: Tuning the Rate‐Dependent Stiffness of Materials by Exploiting Néel Relaxation of Magnetic Nanoparticles (Adv. Funct. Mater. 3/2008)

The effective stiffness of materials that are impregnated with magnetic nanoparticles can be modulated by magnetic fields if the nanoparticle Néel relaxation rates are slower than the characteristic deformation rates. A numerical analysis indicates that the deflection of magnetic dipoles against the applied magnetic field on deformation of the material provides the energy absorption necessary for the enhanced stiffness observed in drop ball impact tests. The penetration depth, fraction of the impact energy that is absorbed by the rotating dipoles, and the effective increase in stiffness are shown to depend uniquely on the ratio of the characteristic magnetic energy density relative to the elastic energy density, and on the shape of the impacting object.