Thin film tape heads, analog and digital applications

Analog and digital applications of thin-film tape heads are discussed. Magnetoresistive tape heads are discussed. A thin-film tape head which is used in analog voice documentation recorders is described. A table that lists a number of relevant system and head parameters is given     

Pulse properties of large 50-50 NiFe tape cores

Over 400 cores of 1-mil 50-50 NiFe, each core containing 40 or more pounds of material, are used in a linear induction accelerator, which is a part of a controlled thermonuclear research experiment. Each core couples a constant voltage pulse of approximately 10kV lasting 350 ns to an electron beam whose current is in the hundreds of amperes range. To achieve reasonable operation of the accelerator it is essential that the drive power to the cores, both during the forward pulse and reset, be kept to a minimum. Since cores of this size and constant voltage drives of this magnitude are both rarities, potential manufacturers of these cores have been reluctant to guarantee the pulse performance. To overcome this reluctance a study program consisting of both a theoretical analysis and experimental tests was conducted. Specifically, the purpose of the study was to find answers to three key questions. 1) What is the minimum current required in an optimum core? 2) What are the major contributors to deviations from the minimum current? 3) What can be done to insure consistently good cores? Results of the study for cores made of both 1-mil and 1/2-mil tape are discussed; the major findings being that at these drive levels, eddy currents both within individual wraps and between wraps cause the dominant losses. Recently about 200 such cores were obtained. The measured pulse values are compared with the predicted values.     

Comparison of readout characteristics between magnetooptic transferheads and magnetic heads

The readout characteristics of a magnetooptic transfer (MOT) head were compared with those of a magnetic head. Magnetic recording/readout was done on a CrO₂ flexible disk by using a head with a track width of 5 μm. A Bi-substituted garnet film with a domain width of 1.2 μm and an He-Ne laser spot focused down to 3 μm were used as the MOT head. Readout waveforms from both heads were surprisingly similar. The maximum carrier-to-noise ratio obtained was 50 dB (bandwidth: 30 kHz) for both heads. Experimental data for off-track and crosstalk characteristics demonstrated that the MOT head was suitable for use as a high-track-density readout head. The potential advantages of multitrack readout using MOT heads are described     

Fabrication and electromagnetic characteristics of microwave absorbers containing carbon nanofibers and NiFe particles

The objective of this study is to develop microwave absorbers by using both dielectric and magnetic lossy materials. Carbon nanofibers (CNFs) were used as dielectric lossy materials and NiFe particles were used as magnetic lossy materials. Twelve kinds of composite specimens were fabricated and classified into dielectric, magnetic, and mixed types. Their complex permittivities and permeabilities in the range of 2–18 GHz were measured. Parametric studies to aid in the design of single-layered radar absorbing materials (RAMs) were performed. The mixed RAMs generally showed improved absorbing characteristics with thinner matching thicknesses. The present mixed RAM showed the 10 dB absorbing bandwidth of 4.0 GHz in the X-band (2.00 mm thickness) and 6.0 GHz in the Ku-band (1.49 mm thickness). The measured absorbing properties of selected specimens were in very good agreements with simulations.     

二端连续元件动力学特性的矩阵描述法

在元件坐标系下,分别推导了简谐激励下横向振动的欧拉—伯努利梁和纵向振动的杆的输入端状态向量及输出端状态向量与微分方程的解的关系。在状态向量正方向的定义相同时,给出了向前传递矩阵、向后传递矩阵、阻抗矩阵和导纳矩阵的解析公式,研究了四种矩阵的特性。结合欧拉梁和杆的相关公式,得到了一般二维梁的传递矩阵和广义阻抗矩阵的解析公式。数值算例表明：在激励频率较低时,本文方法与有限元法的结果基本相同。最后,讨论了动力学中的矩阵描述法（阻抗矩阵法、导纳矩阵法和传递矩阵法）与静力学中的矩阵描述法（位移法、力法和混合法）的对应关系。矩阵描述法有利于利用计算机编程计算动力学问题,文中推导的公式可用于连续系统的动力学分析,计算工作量不大且精度较高。     

Compressive deformation of CoZr and (Co,Ni)Zr intermetallic compounds with B2 structure

B2 type (Co,Ni)Zr compounds which were prepared by arc-melting were deformed in compression at temperatures from liquid nitrogen temperature to 973 K. Their flow stress was anomalously dependent on the testing temperature, decreasing with increasing temperature up to room temperature and then increasing with temperature up to about 673 K, followed by a decrease. The peak of the flow stress was higher for PE specimens than for PA ones which were machined perpendicular and parallel to the direction of grain growth of the ingot, respectively. It is considered that this behaviour of the flow stress is caused, not by the phase transition but by the motion of superlattice dislocations. The ductility of CoZr was lowered by cracking at grain boundaries at which secondary phases were observed. The substitution of nickel for cobalt suppressed the grain boundary cracking and (Co,Ni)Zr had a higher ductility than CoZr.     

Preparation and Properties of Amorphous NiFe/Cu/NiFe Thin Films

The amorphous of Permalloy on the copper subtract was studied using composite electroplating method. A portion of hydrogen brings the counteraction on the surface of cathode leading nickel-iron alloys to be anomalous in the process of co-depositing. The results of X-ray diffraction (XRD) show that the Ni-Fe alloys layer is amorphous. The Giant Magneto -Impedance (GMI) effect of Ni-Fe alloys was obtained under the optimal conditions, dependence on the soft magnetic property of Ni-Fe amorphous thin film. As a result, the ratios△ Z/Z of NiFe/Cu/NiFe amorphous thin film are 30% at 40 kHz which is in low frequency. Furthermore, the GMI value of NiFe/Cu/NiFe amorphous thin film with a sandwich structure is higher than that of single-layer ferromagnetic films of the same thickness.     

Performance of electromagnet and permanent magnet quadrupoles with iron poles

The largest field that can be obtained at the pole tip of an iron core quadrupole is limited by saturation in the iron and by its excitation by either the current density in the coil or the remanent field of the permanent magnet material. An analytical model is used to find the saturation limited performance of quadrupoles with either electromagnet or permanent magnet excitation. The results are presented in a form that can be used to evaluate proposed magnet designs but, more significantly, show that the strength of the excitation has less of an effect on the pole tip field than the size of the magnet needed to achieve it and that saturation has more of an effect on the achievable field strength than excitation strength does.     

Total magnetic fields and read characteristics of infinite length pole piece magnetic recording heads

Magnetic recording head fields generated by current distributions of zero total current flux are calculated considering the two topological possibilities for the current elements being either external to infinite permeability pole pieces or contained entirely within the pole pieces. The frequency response for each of these field configurations is determined by application of the fast Fourier transform.     

Interface Reaction of Ta/NiFe and NiFe/Ta and the Dead Layer

The structures of Ta/Ni_(81)Fe_(19) and Ni_(81)Fe_(19)/Ta are commonly used in magnetoresistance multilayers. It is found that the thickness of dead layer in Ta/Ni81Fe19/Ta was about 1.6±0.2 nm. X-ray photoelectron spectroscopy (XPS) was used to study the interfaces of Ta/Ni_(81)Fe_(19) and Ni_(81)Fe_(19)/Ta. The results show that there is a reaction at the two interfaces: 2Ta+Ni=NiTa_2, which caused the thinning of the effective NiFe layer. Furthermore, this reaction could also explain the phenomenon that the dead layer thickness of spin valves multilayers prepared by MBE is thinner than those prepared by magnetron sputtering.     

履带牵引式换带装置液压系统动态特性研究

履带牵引式换带装置是一种矿井带式输送机胶带更换装置,为了解其液压系统的动态特性,应用Automation Studio软件对换带装置液压系统进行建模与仿真。在换带装置拉带速度仿真分析中,获得了在30,35,40,45,50 mL/r排量下液压马达的输入流量、转速仿真曲线以及履带底盘的拉带速度。通过对换带装置夹带速度的仿真,说明其液压缸夹紧与松开的时间差异并分析其原因。防溜带机构夹带速度的仿真表明该机构可在0.2 s内夹紧胶带。工业性试验中通过PLC（programmable logic controller,可编程逻辑控制器）采集现场液压系统压力并和仿真压力对比分析。夹带恒压自适应调节保证了在胶带厚度变化的情况下系统压力仍然能保持稳定。自动锁带油缸压力迅速变化确保了胶带更换作业安全进行。结果表明该装置系统响应速度较快,性能稳定,为履带牵引式换带装置的动力和安全性能提供了保障。     

Ta/NiFe和NiFe/Ta界面反应和"死层"现象的研究

Ta/Ni81Fe19和Ni81Fe19/Ta被广泛应用于磁电阻多层膜结构中。我们发现 ,在Ta/Ni81Fe19/Ta薄膜结构中 ,磁性“死层”的厚度大约为 1 6± 0 2nm。用X射线光电子能谱和图谱拟合技术研究Ta/Ni81Fe19和Ni81Fe19/Ta的界面成分和化学状态发现 ,在两上界面处都发生了反应 :2Ta +Ni=NiTa2 ,因此NiFe的有效厚度减少。利用这个反应也可以合理解释用分子束外延制备的自旋阀多层膜比用磁控溅射制备的自旋阀多层膜的“死层”更薄的现象     

成型工艺对片式PTCR素坯及瓷片性能的影响

将注凝成型、注浆成型与轧膜成型应用于片式PTCR的制备,研究了不同成型工艺对片式 PTCR素坯及瓷片性能的影响。研究发现,用注凝成型和注浆成型工艺制备的素坯比用轧膜成型更加均匀, 其陶瓷颗粒与粘结剂分布规则。在3种成型工艺所得的瓷片中,注凝成型瓷片晶粒生长最均匀,注浆成型瓷片晶粒生长较均匀,而轧膜成型瓷片晶粒生长不均匀。注凝成型和注浆成型工艺所制备瓷片的 PTC性能稍优于轧膜成型。瓷片的耐电压性能与成型工艺有较大的依赖关系。     

Research on resistance characteristics of YBCO tape under short-time DC large current impact

Research of the resistance characteristics of YBCO tape under short-time DC large current impact is the foundation of the developing DC superconducting fault current limiter (SFCL) for voltage source converter-based high voltage direct current system (VSC-HVDC), which is one of the valid approaches to solve the problems of renewable energy integration. SFCL can limit DC short-circuit and enhance the interrupting capabilities of DC circuit breakers. In this paper, under short-time DC large current impacts, the resistance features of naked tape of YBCO tape are studied to find the resistance – temperature change rule and the maximum impact current. The influence of insulation for the resistance – temperature characteristics of YBCO tape is studied by comparison tests with naked tape and insulating tape in 77 K. The influence of operating temperature on the tape is also studied under subcooled liquid nitrogen condition. For the current impact security of YBCO tape, the critical current degradation and top temperature are analyzed and worked as judgment standards. The testing results is helpful for in developing SFCL in VSC-HVDC.     

An in-depth study of accidents involving collisions with utility poles

This paper summarizes the objectives, methodology, findings, and recommendations of a large-scale study of automobile crashes involving utility poles. In an 8-month survey of accidents, information on site characteristics and accident severity was obtained for a sample of 879 crashes. Randomly-selected samples of 795 sites and 627 vehicles provided control information. An accident-predictor model which identifies accident risk on the basis of site measurements has been derived. The model reveals a range of relative risks in the population of exposed poles of the order of 1000:1, and enables the identification of the relatively small proportion of poles which account for the majority of accidents. The model was used in conjunction with estimates of the costs of accidents to show that a number of remedial treatments are warranted. The hazardous effects of low tyre tread depths and improper tyre inflation pressures are also demonstrated.     

High density recording with perpendicular Co-Cr-Nb media and ring heads

Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI).     

Numerical analysis of ferrite recording heads with complex permeability

Numerical methods based on finite differences are applied to the analysis of ferrite recording heads in which the permeability is complex and flux leakage effects are significant. The methods described allow computation of head efficiency, inductance, loss angle, and phase shift. As a specific example, the analysis is performed for a reduced track width version of the Memorex 3650 head for a wide range of the real and imaginary parts of the permeability. Using published values for the frequency dependence of the complex permeability, the frequency dependence of the head performance is estimated. Some experimental data are presented and compared to the theoretical predictions.     

限流器用第二代超导带材的电阻和冲击特性实验研究

为了评估用于电阻型超导限流器的第二代超导带的电阻和大电流冲击特性,实验研究了两种不同厚度的超导带的常温电阻和在100 ms交流大电流冲击下的电流和温升的关系。结果表明,厚带比薄带的耐受冲击电流性能好,但是常温电阻较小。限流器设计时,需在冲击性能和经济性两者之间做出平衡。