多功能磁弹性仪及其应用

介绍了应用巴克豪森磁噪声和磁声发射技术研制的多功能磁弹性仪的原理、结构、特性以及应用.     

利用自旋流提高热电发电性能

正日本东北大学金属材料研究所斋藤英治教授等人,发现可提高热电发电性能的新理论,即自旋热电效应。在磁性绝缘体钇铁柘榴石(YIG)上制出铂膜,作为试料,测量自旋热电效应(电动势),结果表明,YIG的声子和磁(量)子在相同波长和振动数传输时,由于共振效应出现电动势最大值,形成具有声子和磁(量)子两种特性的混合波。长寿命的声子输送自旋流的距离比磁(量)子长,可以提高热电效应,从而提高热电器件的     

蜂窝夹层复合材料的压缩损伤声发射特征

应用声发射技术对蜂窝夹层复合材料压缩损伤过程进行了试验研究。分析载荷与声发射信号关联图,依据其损伤过程和声发射特征,发现随着加载条件下载荷的增加,复合材料的损伤逐步增大。在加载初始阶段,仅有少量声发射信号,各种表征信号量小幅度增加;在加载中期,声发射信号增多,各种表征信号量不断增大;在加载后期,声发射信号有明显突增,各种表征信号量急剧增加。复合材料压缩损伤破坏与声发射的幅值、能量、撞击、上升时间、持续时间和计数等参量特征相关。根据各阶段特征参量滤波后所得信号分布与实际断裂位置相吻合。     

雷达吸波涂层材料的研究进展

讨论了电磁波的吸波机理,及其性能测量和计算方法,叙述了电阻型损耗、介电损耗、磁损耗型三种损耗机制的涂层材料及其电磁波吸收损耗机理,对不同种类的吸波材料在雷达波隐身方面的应用进行了全面的综述,介绍了这一研究方向的最新进展,并分析了每种材料的主要特点。重点讨论了铁氧体、碳纳米管、导电高聚物等吸波材料的微观结构、化学性质、电磁特性对吸波性能的影响。对于磁损耗材料来说,良好的磁性能是其不可忽视的优点,但其密度高,稳定性较差,影响了其性能发挥。针对其存在的缺点,通过掺杂改性、共混等方式可提升涂层材料的吸波性能。在碳系材料中,多壁碳纳米管的吸波性能较好,将磁损耗吸波材料与碳纳米管进行复合、包覆是目前吸波性能提高的主要手段。导电聚合物等新型吸波材料具有质量轻、导电性好的特点,单独使用时,阻抗匹配性差,通过对其掺杂改性或与磁损耗型材料复合,可增强其阻抗匹配性,提升吸波性能。最后,指出了雷达吸波材料未来的研究发展方向。     

磁控双靶共溅射磁致伸缩TbFe薄膜的研究

采用直流磁控双靶共溅射方法,在玻璃基片上制备了非晶态的TbFe磁致伸缩薄膜,研究了溅射功率、工作气压等工艺参数对薄膜成分的影响.研究结果表明:当溅射功率从20W增加到100W时,TbFe薄膜中Tb含量从35.77at%增加到44.54at%;工作气压从0.2 Pa增加到1.0 Pa时,11)Fe薄膜中Tb含量从38.02at%增加到44.1at%.重点研究了真空退火处理对TbFe薄膜磁性及磁致伸缩性能的影响.结果表明,真空退火处理有利于提高平行于膜面的饱和磁化强度和磁导率;350℃真空退火60 min,在外加磁场为5 kOe条件下,TbFe薄膜的磁致伸缩系数可达到351x10-6.     

磁/电介质复合材料结构型吸波体制备及吸波性能

利用熔融沉积成型技术快速制备了石墨烯/聚乳酸复合材料和四氧化三铁/聚乳酸复合材料,测试了其电磁参数,并基于传输线理论计算模拟分析了石墨烯含量对其吸波性能的影响,进而确定了透波层、吸收层、再次吸收层的匹配材料和厚度范围,制造了石墨烯/纳米四氧化三铁吸波体。磁/电介质多孔结构型吸波体的测试结果表明:在X和Ku波段内实现了-8 dB吸收,反射率小于-10 dB的频宽达6.7 GHz,最大吸收峰值在14.2 GHz时达到-33 dB。研究发现,通过改变吸收层材料组成及其结构可以获得更好的吸波性能,周期性的多孔结构的存在可以使更多的电磁波进入复合材料内部,同时增加了吸收界面数量;此外,石墨烯和纳米四氧化三铁的组合使介电损耗与磁损耗之间产生了有效的互补,也增加了吸波性能。     

磁声发射检测装置的研制与性能测试

针对磁声发射信号特征易受励磁强度和励磁频率影响的问题,设计一个具有变励磁幅度及测量磁滞回线功能的磁声发射检测装置,主要研究励磁器的尺寸及励磁线圈匝数对励磁能力的影响,并确定最佳激励磁轭尺寸和线圈匝数,最后对磁声发射检测装置的整体性能进行相关评价。通过研究发现,将8#磁轭绕线圈600匝时满足励磁器设计中磁通势较大的需求,此时磁声发射检测装置具有较好的励磁性能,具有实际且广阔的应用前景。     

感应式磁声无损检测技术

针对金属材料的感应式磁声无损检测技术,采用电磁超声换能器激发并接收磁声信号,用于重建被测试件内部的电导率分布,同时具有超声无损检测的高穿透力和电磁无损检测的高灵敏度的优势。在介绍感应式磁声成像技术原理的基础上,对感应式磁声无损检测技术的研究现状进行总结归纳。同时,由于在金属材料中电导率的各向异性是普遍存在的,且对检测结果有一定的影响,还探讨了应用感应式磁声无损检测技术对电导率各向异性的金属材料进行缺陷检测的可行性,并分析了其所面临的技术难点。     

基于模态理论降低声发射源定位误差的方法

以玻璃纤维复合材料为研究对象,对声发射波在玻璃钢中传播的频率变化规律进行了研究,发现距声发射源不同位置采集到的声发射波的主要频率范围并不相同;根据模态声发射理论中不同频率段声发射信号传播特性不同的结论,对声发射波经不同通频带滤波器滤波后到达各传感器的时间差的线性关系进行了比较分析,得出声发射波到达时间的精确提取方法,发现模态滤波定位误差明显低于传统时间提取定位误差。     

新型碳系吸波涂层材料研究进展

作为解决电磁污染问题与实现装备战场隐身的有效手段,吸波涂层材料具有广泛的应用前景。碳系材料因其广泛的来源、简单的制备工艺、低密度、高导电率等优点,在吸波涂层材料领域受到国内外研究人员的高度重视。对吸波涂层材料的损耗机制进行了叙述,介绍了电阻型损耗、电介质型损耗以及磁损耗三种损耗机制中电磁波的损耗和吸收原理。综述了碳纤维、碳纳米管、石墨烯等新型碳系材料的特性及其在吸波涂层材料领域的研究现状。对碳纤维进行活化处理或使用多孔碳纤维、螺旋碳纤维等代替普通碳纤维能够有效提高其吸波性能。碳纳米管具有多种结构,其中阵列状多壁碳纳米管吸波性能最佳,采用一些具备磁损耗的材料与碳纳米管进行共混、包覆或填充处理是目前的主要研究方向。石墨烯几乎没有磁损耗,单独使用时,阻抗匹配较差,影响其吸波性能的发挥,通常将石墨烯与磁损耗型材料复合,改善材料的阻抗匹配,提高吸波效果。最后,根据碳系吸波涂层材料的研究现状,对其未来的发展方向进行了展望。     

Forced motion of solitary domains and domain walls in the field of a nonlinear magnetization wave

For a ferromagnet with an easy-axis anisotropy, exact solutions to the Landau-Lifshitz equations have been obtained, which describe the interaction of a nonlinear wave of the precession of arbitrary amplitude with soliton-like objects such as breathers, solitary domains, and domain walls. Changes in the internal structure and physical parameters of solitons as a result of their interaction with a magnetization wave have been analyzed. It is shown that the solitary domains and domain walls move in the direction opposite to the magnetization wave. Conditions have been found under which the nonlinear wave of magnetization destroys solitons. It has been established that the destruction of breathers can be accompanied by the generation of magnetization self-oscillations.     

瑞利波反射理论探讨

在瑞利波理论基础上，假设表面波以柱面波形式传播，考虑到质点位移振幅随深度作指数衰减的规律和声场基本限于两个波长深度范围内的特点，处理端面（无限大界面）反向声压比较简单。处理有限裂面反向问题，考虑自裂面反射的声能以柱面波形式辐射，从而志出与信号幅度成 正比的总声压。给出了表面波反射的理论结果，并得到比较满意的实验验证。     

Measurement of the thickness of a cylindrical shell with a focused beam

The acoustic scattering from a cylindrical or spherical object immersed in water and insonified with plane wave has been theoretically and experimentally studied. The backscattering spectra show minima, which are related to the circumferential waves circumnavigating around the object. These waves are identical to the Lamb waves propagating in a plate. Two types of resonances are observed on ultrasonic spectra: the resonances related to the thickness and the resonances related to the stationary state that establish around the cylindrical shell from the circumferential waves. To eliminate the second type of resonances a focused beam is used to excite only the thickness resonances. The cylindrical shell thickness is calculated from these experimentally measured resonance frequencies.     

Degenerated internal nonlinear resonance interaction of the waves on the surface of an uncharged dielectric jet in a longitudinal electrostatic field

Using the asymptotic analytical procedure of the second order of smallness with respect to the ratio between the amplitude of a wave and the radius of a jet for the calculation of the wave motion of a finite amplitude on the surface of a cylindrical jet of an ideal incompressible dielectric liquid, it was found that the nonlinear corrections for the jet’s profile and the potential of the fields of the rates and electrostatic potentials inside and outside of the jet have a resonance character. In a degenerate resonance interaction between the wave, which determines the initial deformation and the waves that become excited owning to the nonlinearity of the hydrodynamic equations, the waves with different symmetry (with different azimuthal numbers) can participate.     

Ultrasonic characterization of residual stresses in steel rods using a laser line source and piezoelectric transducers

The surface residual stresses in steel rods made of the same material but with different heat treatments have been studied from Rayleigh wave velocity measurements using the laser ultrasonics technique and piezoelectric transducers. The Rayleigh wave velocities, both along the circumference and in the axis direction on the cylindrical surface of every rod, are measured and compared with one another in order to evaluate qualitatively the surface stress state for each rod. The experimental results clearly show that the Rayleigh wave velocities on the cylindrical surfaces of these rods are different, and the results obtained by laser ultrasound are in good agreement with those measured with piezoelectric transducers. From the measured velocities, different stress states have been identified for these rods according to the heat treatments they have undergone.     

Acoustic emission source location considering refraction in layered media with cylindrical surface

To solve the problem that the existing acoustic emission (AE) source location algorithms cannot always obtain accurate results for multilayer cylindrical media, a new acoustic emission source location method considering refraction was proposed. AE source coordinates were solved by the complex method. Pencil-lead-break experiments were used to verify this method. The absolute distance errors of location results are less than 3 mm, much less than those by the traditional method. The numerical experiments were used to further analyze factors that affect location accuracy. The results of numerical experiments show that the location accuracy of the proposed method is not affected by the ratio of wave velocities but affected by the measurement accuracy of wave velocity. These results show that new method can obtain accurate AE source location in the two-layered cylindrical surface media such as the triaxial compression test.     

圆管中SH周向导波的频散特性

研究了圆管中的SH周向导波的传播特性。采用柱坐标系,从纳维运动方程开始推导,得到了SH导波沿周向传播、轴向振动的频散方程。以内外半径之比分别为0.3,0.5和0.7为例,通过数值计算得到了硬铝材料圆筒的频散曲线。结果表明其高阶模式比低阶模式频散显著,故在实际检测中宜选用低阶的SH导波。     

Cylindrical Rayleigh surface waves on a layer-coated cylinder measured by PVDF transducer and defocusing measurement method

This paper develops a measurement method for accurately determining dispersion curves of Rayleigh-type surface waves propagating on layer-coated elastic cylinders. It utilizes PVDF acoustic transducers and a defocusing measurement system. To deal with the cylindrically curved surface, a new cross-correlation waveform processing approach is proposed and verified. Cylindrical Rayleigh wave velocities of layered cylindrical solid samples have been successfully measured over a frequency range from 3 to 20 MHz. The measured dispersion curves are in good agreement with their theoretical counterparts. It demonstrates the potential application for non-destructive evaluation of coating layers deposited on cylindrical solids.     

Dynamics of the evolution of a magnetization-reversal nucleus in orthorhombic antiferromagnets with a weak ferromagnetism

Dynamics of a two-dimensional nucleus of magnetization reversal in a magnetic field in an orthorhombic antiferromagnet with a weak ferromagnetism has been investigated analytically and numerically. It is shown that along the nucleus of the stable phase inside the metastable phase there can propagate both slow periodic and rapid periodic and solitary waves of magnetization. It is shown that the wave that describes the intergrowth of a domain of the reverse magnetization can have a velocity greater than the maximum velocity of the stationary motion of the domain wall, equal to the minimum phase velocity of spin waves.     

Bending and Deformation Waves on the Surface of a Volumetrically Charged Cylindrical Jet of Dielectric Liquid Moving in Material Medium

Analytical research into the stability of axially asymmetric capillary waves on the surface of a volumetrically charged cylindrical jet of an ideal incompressible dielectric liquid that moves in an ideal incompressible dielectric medium made it possible to specify the conditions for realization of instability of waves with azimuthal numbers 1 and 2, which corresponds to excitement of bending and deformation waves. It was found that realization of the Kelvin-Helmholtz instability occurs on the media interface because of a tangential jump of the field of velocities on the jet surface for the axially asymmetric waves. The linear dimensions of wave numbers' ranges of unstable waves and the sizes of increments of instability are defined by values of the charging Weber’s parameters. The variation of dielectric permeability of a jet and medium affects the characteristics of wave motions, including those in the range of instability realization.