高斯噪声和弱正弦信号驱动的时间差型磁通门传感器

提出了一种利用高斯噪声和弱正弦信号共同驱动的新型时间差型磁通门传感器.根据软磁材料双稳态特性及其Fokker-Planck方程推导了跃迁率的表达式.利用数值仿真的方法,研究了跃迁率和外磁场、激励磁场、噪声强度之间的关系.通过将周期变化的跃迁率信号转换为方波信号,建立了方波高低电平时间差与外磁场之间的关系,并推导了传感器灵敏度的表达式.研究表明,在一定的偏置磁场下,传感器灵敏度与激励磁场的幅值以及频率成反比,量程和激励磁场的幅值成正比.对所设计±10.7A/m量程的传感器样机进行了测试,传感器最小灵敏度为9.8696 ms/(A/m),可用于准静态微弱磁场的检测.     

Electrodeposition and characteristics of Ni80Fe20/Cu composite wires

Electrodeposited Ni₈₀Fe₂₀/Cu composite wire has significant advantages over amorphous wire as sensing element for weak magnetic field sensors, such as orthogonal fluxgate sensors, due to its non-ferromagnetic and conductive core structure. In this study, the key processing parameters are investigated, including electrodeposition current density, duty cycle, electrolyte solution, pH value, applied magnetic field, effect of seeded layers, and post annealing.     

Sensors based on bulk soft magnetic materials: Advances and challenges

Sensors with cores, yokes or field concentrators made of bulk magnetic material are more sensitive and stable than thin-film sensors. Non-linearity and temperature dependence of sensitivity is often suppressed by a feedback. The common problem of these sensors is remanence, cross-field sensitivity and temperature stability of offset. The long-time effort to miniaturize the fluxgates led only to a few practical designs. For flat sensors (either pcb or CMOS) the core etched from amorphous tape gives better properties then electrodeposited or sputtered core. We compare traditional miniature fluxgates using wire cores based on longitudinal fluxgate effect with sensors using transverse fluxgate effect and GMI effect. Well-designed field concentrators or yokes can improve the parameters of any magnetic sensor. The achievable stable amplification factor is 10–100. Having a means to demagnetize the field concentrator is desirable. Overview of magnetic sensors for mechanical quantities is also given with special focus on torque sensors.     

Coil-less fluxgate effect in (Co0.94Fe0.06)72.5Si12.5B15 amorphous wires

In this study, the coil-less fluxgate properties of the as-cast and annealed amorphous wires with the composition (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅ were investigated. As its name implies, a coil-less fluxgate is a new type of magnetic-field sensor without a coil. When the wire is periodically saturated in a magnetic field in the circumferential direction with a 30 kHz, 62 mA driving current under a 16.5π rad/m torsional strain, there is a linear variation in the second harmonic of the voltage from the wire ends as a function of the applied external DC magnetic field along the length of the wire.Current-stress annealing of each sample improved the sensitivity of the coil-less fluxgate sensor. This is the first time that it has been shown that a linear change in the output of the coil-less fluxgate sensor can be obtained using torsion annealed wire without the necessity of twisting the wire during measurement. We showed that the linear operating range of the sensor can be increased by increasing the demagnetization factor in the sensing direction, so that the coil-less fluxgate sensor can be miniaturised just by reducing the wire length.     

Analysis of Characteristics of the Sensing Elements for the Fiber-Based Evanescent Wave Spectroscopy in the Mid-IR

Characteristics of the sensing element of a fiber sensor for evanescent wave mid-IR spectroscopy have been studied within the electromagnetic theory of fiber waveguides by using the problem of determining the concentration of aqueous acetone solutions as an example. A multimode chalcogenide fiber was used as a sensing element. It has been shown that the selective excitation of the fiber modes may provide the possibility to increase the sensitivity of the fiber sensing element, decrease the minimum detectable concentration of a substance in a solution, and enhance the range of measured solution concentrations.     

Spin-wave excitation by direct current in obliquely magnetized nanostructures

The magnetization dynamics of magnetic nanostructures magnetized at an arbitrary out-of-plane angle is investigated with the spin-wave formalism. The magnetic excitations driven by a spin-polarized direct current are considered to be standing spin-wave modes appropriate for nanopillar structures. The spin waves grow exponentially above a certain critical value of the current density and their post-threshold nonlinear dynamics leads to magnetization oscillations in the microwave range. Due to demagnetizing fields, the current-driven excitation strongly depends on the direction of the applied external magnetic field. In order to calculate the microwave oscillation frequency we derive an equation of motion for the spin-wave amplitude as a function of the out-of-plane angle of the applied field. The results are compared with recent experimental data as well as with another theoretical approach.     

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.     

Spin orientation and excitation of magnetic nanocluster on metal surface

The spin orientation and excitation of the ferromagnetic nanocluster on the magnetic metal surface are studied numerically. We show that localized magnetic excitation modes are generated by the spin fluctuation of the cluster, when the ferromagnetic interaction J′ between the cluster and the metal surface is small and the spins in the cluster are oriented in the opposite direction with those of the metal surface by the external field. This magnetic structure is similar to the domain wall (DW) structure of a ferromagnetic wire, both sides of which connect with metal surfaces. As the interaction J′ increases, the sign of the thermal average of the spins in the cluster changes, i.e., the spin-flip takes place. In this time, the magnetic fluctuation of the cluster becomes large and the magnetic excitation energies, except for that of one excitation mode, overlap with the excitation spectrum of the spin wave. We also show that, by the overlap, sharp peaks and dips occur in the excitation spectrum of the spin wave.     

Environment-assisted precision measurement

We describe a method to enhance the sensitivity of precision measurements that takes advantage of the environment of a quantum sensor to amplify the response of the sensor to weak external perturbations. An individual qubit is used to sense the dynamics of surrounding ancillary qubits, which are in turn affected by the external field to be measured. The resulting sensitivity enhancement is determined by the number of ancillas that are coupled strongly to the sensor qubit; it does not depend on the exact values of the coupling strengths and is resilient to many forms of decoherence. The method achieves nearly Heisenberg-limited precision measurement, using a novel class of entangled states. We discuss specific applications to improve clock sensitivity using trapped ions and magnetic sensing based on electronic spins in diamond.     

用外磁场控制电流感应磁化翻转效应中的临界电流方法

应用基于磁动力学方程的宏观唯象模型,研究了弱外磁场下纳米尺度赝自旋阀结构的电流感应磁化翻转效应.在统一考虑铁磁/非磁界面的自旋相关散射以及铁磁层中的自旋积累和弛豫过程后,给出了赝自旋阀结构在弱外磁场下的磁化翻转条件和临界电流.对该效应的数值计算解释了弱外磁场下赝自旋阀结构的电阻-电流回线的偏移,并给出了用外磁场控制电流感应磁化翻转效应中的临界电流方法. 关键词： 电流感应磁化翻转 外磁场 临界电流 赝自旋阀     

Sensor design for development of tribo-electric tomography system with increased number of sensors

Electrodynamic sensor, which can also be called as tribo-electric sensor, senses the electrostatic charge carried by the particle. The tomography system using electrodynamic sensor is called as tribo-electric tomography system. Source of the signal induced on the electrodynamic sensor is brought by the object to be measured and no excitation circuit is necessary. This electrodynamic sensing is a passive sensing and the fast and light weighted tomography system is expected. On the other hand, most of tomography system, like capacitance tomography or resistance tomography, demands excitation circuit and is an active sensing. The number of measurements with the passive sensing is equal to the number of sensors and that of active sensing is the number of the combinations of two sensors. The passive sensing tomography system demands more sensors to be settled. We plan to improve in reconstructed images by increasing the number of the electrodynamic sensors in tribo-electric tomography system. We investigate the influence of surface area to signal intensity solving the electrical field in the sensing zone using finite element method.     

基于光纤微结构加工和敏感材料物理融合的光纤传感技术

将功能敏感材料与光纤在物理层面进行有机融合,充分发挥光纤传感器在结构集成、材料集成等方面的优势,将有望发展新型的光纤传感器件和系统.本文综述了飞秒激光光纤微加工技术分别在标准的单模光纤和光纤光栅上制备微结构,再结合敏感材料制备技术,实现在物理层面上光纤传感器材料和结构的集成和融合,探索实现新型高性能的光纤传感新技术.     

Linear intermode conversion of electromagnetic wave energy in a magnetically soft gyrotropic material

The excitation of axial radio-frequency (rf) magnetic induction by an axial rf current is observed in a conductor with circular magnetic anisotropy when a weak magnetizing field is applied. The conductor is an amorphous cobalt-based wire, which exhibits azimuthal magnetic anisotropy. It serves as the central conductor in a coaxial line. The axial rf magnetic induction produces an emf in an induction coil coaxial to the conductor. The induction coil is part of a matched receiving circuit. The power conversion coefficient is as high as tens of percent. The measurements demonstrate the high sensitivity of the conversion coefficient to an external field. The theory of ferromagnetic resonance faithfully describes the results of the observations. Zh. Tekh. Fiz. 69, 58–63 (March 1999)     

Possibility of increasing the efficiency of spin injection by current in magnetic junctions

The nonequilibrium spin polarization of electrons is calculated under the conditions of spin injection by current passing from one ferromagnetic film to another in a magnetic junction. It is shown that the nonequilibrium spin concentration may substantially increase with an appropriate choice of parameters of the films and operation conditions. This leads to a decrease in the threshold current density required for switching the magnetic junction by several orders of magnitude.     

基于激光直写的微流光学触摸传感阵列

设计并制作了一种基于激光直写技术的光学触摸传感器件。该器件采用光学微流结构实现对外加压力的连续比例测量。器件制作采用紫外激光直写技术配合高精度平移台实现,整体工艺过程在3min内完成。对所设计的传感器件的性能测试表明,光强信号随外力变化的曲线平滑,实测灵敏度为0.995mV/kPa。同时设计并制作了基于传感单元的阵列结构,不仅消除了光学累积误差,而且对集成化触摸传感的应用具有优势。     

基于声表面波的氢气传感器*

将钯基材料对氢气分子的特异选择性吸附能力与声表面波的快速响应特点相结合,可实现一种快速、高灵敏和低功耗的氢气检测与报警技术。传感器由双通道差分式振荡器与沉积在传感器件表面的声表面波传播路径上的钯基气敏薄膜组成。为提升传感器响应速度,该文探讨了采用钯镍合金薄膜与钯铜纳米线作为气敏材料的氢气传感器响应特性,通过对气敏材料制备方法及参数的优化,研制了两种沉积不同钯基气敏材料的氢气传感器件,并对其性能进行了评测。实验测试结果表明:钯铜纳米线气敏材料由于具有大体积表面积比和多孔结构,大幅提高了SAW氢气传感器响应速度,针对浓度为10%、4%以及0.5%的氢气响应时间可达～2s。     

Coupling-induced oscillations in nonhomogeneous, overdamped, bistable systems

Coupling-induced oscillations in a homogeneous network of overdamped bistable systems have been previously studied both theoretically and experimentally for a system of N (odd) elements, unidirectionally coupled in a ring topology. In this work, we extend the analysis of this system to include a network of nonhomogeneous elements with respect to the parameter that controls the topology of the potential function and the bistability of each element. In particular, we quantify the effects of the nonhomogeneity on the onset of oscillations and the response of the network to external (assumed to be constant and very small) perturbations, using our (recently developed) coupled core fluxgate magnetometer as a representative system. The potential applications of this work include signal detection and characterization for a large class of sensor systems.     

Spin injection-driven switching in a magnetic junction

We investigate a perpendicular electric current passing through a “ferromagnetic nanojunction”, that is through some layered nanosized structure of spin-valve type, containing two ferromagnetic metallic layers. Spacer may be used between the metallic layers to prevent the rotation of the moving spin phases. Such an arrangement is typical for spin valves: one of the metallic layers has strongly pinned magnetic lattice and the other one has free magnetic lattice and free mobile spins. Further the conditions are derived to provide a very high nonequilibrium spin injection level. It appears that the so-called spin resistances of the constitutive layers should be in definite relations to each other. These relations lead to the situation where the spin injection becomes dominant and significantly suppresses the “ordinary” spin-transfer torque. As a result, the threshold current becomes lowered down to 2-3 and even more orders of magnitude.     

Theoretical study of phonon spectra in ferromagnetic nanoparticles

Based on the spin-phonon model we analyze the influence of surface and size effects on the phonon properties of ferromagnetic nanoparticles. A Green's function technique in real space enables us to calculate the renormalized phonon energy and its damping depending on the temperature and the anharmonic spin-phonon interaction constants. With decreasing particle size the phonon energy can decrease or increase for different surface spin-phonon interaction constants, whereas the damping increases always. The influence of an external magnetic field is discussed, too. The theoretical results are in reasonable accordance to experimental data.