LC共振型巨磁阻抗效应的研究

采用化学镀方法成功制备了自带电容构成LC共振回路的CoP/Insulator/BeCu复合结构丝.研究了这种新型复合结构丝产生LC共振型巨磁阻抗效应的特征,长度为lm=9.5cm的复合结构丝,当驱动电流频率为LC共振频率fr=29.0MHz时,LC共振型巨磁阻抗效应为487.5%,磁场灵敏度为0.46%/A·m-1,大于常规复合结构丝;远离此频率时的巨磁阻抗效应很小,巨磁阻抗效应表现出很好的频率选择特性.根据LC共振型复合结构丝的特征建立了等效电路模型,采用等效电路模型对这种复合结构丝进行了数值模拟,等效电路的数值计算与实验测量结果符合较好.从等效电路角度分析了LC共振型巨磁阻抗效应产生的机理,以及复合结构丝的长度对LC共振型巨磁阻抗效应的影响.     

LC共振型巨磁阻抗效应的研究

采用化学镀方法成功制备了自带电容构成LC共振回路的CoP/Insulator/BeCu复合结构丝. 研究了这种新型复合结构丝产生LC共振型巨磁阻抗效应的特征,长度为l_m=95 cm的复合结构丝,当驱动电流频率为LC共振频率f_r=290 MHz时,LC共振型巨磁阻抗效应为4875%,磁场灵敏度为046%/A·m^-1,大于常规复合结构丝;远离此频率时的巨 关键词： 复合结构丝 LC共振')" href="#">LC共振 等效电路模型 巨磁阻抗效应     

电沉积复合丝及其巨磁阻抗效应的研究

采用脉冲电沉积工艺在Cu丝上沉积Fe Ni合金镀层 ,成功地制备出巨磁阻抗效应 (GMI)复合丝材料 ,研究了复合丝的磁性能和巨磁阻抗效应 .复合丝外壳磁性镀层软磁性越好 ,巨磁阻抗效应越明显 ,制备的复合丝最高巨磁阻抗效应为 2 7.19% .研究了复合丝阻抗与巨磁阻抗比值GMI随外加磁场的变化 ,其变化曲线的形状受复合丝磁各向异性场的影响 .此外 ,还研究了复合丝巨磁阻抗效应与驱动交变电流频率的关系 ,复合丝Fe17Ni83 样品巨磁阻抗效应的临界频率为 30kHz(GMI为 9.95 % ) ,特征频率为 30 0kHz(GMI为 2 7.19% ) ,截止频率为 10MHz (GMI为 10 .36 % ) .如此低的临界频率和特征频率及较宽的频率段对于实际应用非常有利 .     

基于Nyquist图研究铁基非晶薄带巨磁阻抗效应的非线性

测量了铁基非晶薄带巨磁阻抗效应的阻抗实部和虚部并且计算出磁导率的实部和虚部,通过磁导率的非线性解释了巨磁阻抗效应的非线性原因,并且利用Nyquist图推出磁导率等效电路模型,指出磁导率等效电路模型中的LC共振频率是解决磁导率非线性的关键.研究结果表明:在激励电源横向磁化和外加磁场纵向磁化的过程中,非晶薄带磁导率的变化无规则,导致非晶薄带的巨磁阻抗效应呈现非线性变化.当激励频率在5 MHz、纵向磁场发生改变时,磁损耗角依然保持不变,磁导率与纵向磁场的非线性关系转化为磁导率模值与纵向磁场的关系,通过实验数据可以拟合出纵向磁场与磁导率的函数关系.     

复合结构丝中的电流密度分布和巨磁阻抗效应

提出了由中间为高电导率的非铁磁性金属丝外面包裹一层铁磁材料组成的复合结构丝的电流 密度分布和巨磁阻抗(GMI)效应模型，并对Cu/FeCoNi复合丝进行了数值模拟. 结果表明：在 相同的磁性材料几何尺寸和磁特性时，Cu/FeCoNi复合丝铁磁层内的电流随频率的升高比匀 质FeCoNi铁磁丝内的电流更趋于表面分布，而且开始出现趋肤效应时对应的频率明显降低. 当在比较低的频率下就可以观察到明显的MI变化时，复合结构丝中的电阻和电抗变化主要是 由趋肤效应引起，趋肤效应仍然是引起复合结构材料(包括多层薄膜结构) 关键词： 电流密度 巨磁阻抗效应 趋肤效应     

射频溅射功率对FeZrBCu软磁合金薄膜巨磁阻抗效应的影响

用射频溅射法制备了FeZrBCu软磁合金薄膜.研究了不同溅射功率对FeZrBCu薄膜软磁特性和巨磁阻抗效应的影响.用电子探针显微镜测量发现，当溅射功率为240W时，薄膜样品中Fe的原子含量为8732%，Cu的原子含量为29%.这种样品的矫顽力最小，为68A/m，饱和磁化强度约为111×105⁵A/m，软磁性能最佳，巨磁阻抗效应最大，溅态膜在 13MHz最大巨磁阻抗比纵向为17%，横向为11%.重点分析了阻抗的电阻、电感分量及横向有 效磁导率随频率的变化，得到在低频下主要是磁电感 关键词： 铁基合金 薄膜 巨磁阻抗效应     

介观结构对纳米晶软磁合金巨磁阻抗效应影响的理论分析

根据用原子力显微镜对Fe基纳米晶Fe_73.5Cu₁Nb₃Si_13.5B₉合金薄带的介观结构和巨磁阻抗效应的实验研究结果，提出了纳米晶软磁合金巨磁阻抗效应受其介观结构影响的理论模型.该模型成功地解释了低频对纳米晶软磁合金巨磁阻抗效应的影响，反映了现有“三明治”理论的主要特征，并弥补了它的不足；同时指出了纳米晶粒电导率σ、磁导率μ对合金巨磁阻抗效应有影响. 关键词： 铁基纳米晶合金 介观结构 巨磁阻抗效应 介观模型     

FeCuNbSiB单层膜和三明治膜的磁特性与巨磁阻抗效应

用射频溅射法制备了Fe_73.5Cu₁Nb₃Si_13.5B₉单层膜和 Cu或Ag作为中间层的三明治膜.溅态膜为非晶态结构.磁畴观察结果表明,单层膜在380℃退火后,呈现均匀磁化的纳米晶结构,该样品软磁特性最佳,其巨磁阻抗效应最大,在13MHz,最大磁阻抗比纵向为18％,横向为14％.溅态三明治膜具有较大的巨磁阻抗效应,在13MHz,Cu夹层三明治膜的最大磁阻抗比纵向为32％,横向为11％,Ag夹层三明治膜的最大磁阻抗比纵向为47％,横向为57％.Cu夹层三明治膜经250℃退火后,在低频下表现为巨磁电感效应,在100kHz,最大磁电感比为1733％. 关键词：     

FeCuCrVSiB多层膜巨磁阻抗效应的研究

研究了结构为 (FM/SiO₂)₃/Ag/(SiO₂/FM)₃ 多层膜的巨磁阻抗(GMI)效应（这里的F M≡FeCuCrVSiB）．多层膜采用射频溅射法沉积在单晶Si衬底上，沉积过程中，沿膜面长方 向施加约72kA/m的磁场，然后在不同的温度下对样品进行了退火处理．结果表明，该多层膜 样品即使在沉积态便具有相当好的软磁性能和GMI效应，在7MHz的频率下，最大纵向和横向 巨磁阻抗比分别为45%和44%．在230℃下经90min退火处理后的样品具有最佳的GMI效应，在85MHz的频率下，最大纵向和横向巨磁阻抗比分别达到251%和277%．与磁性层总厚度相同的FeCuCrVSiB/Ag/FeCuCrVSiB三层膜相比较，在这种多层结构中出现的GMI效应更强． 关键词： 多层膜 巨磁阻抗效应 趋肤效应 有效磁导率     

磁环中非晶丝的阻抗效应分析

依据Landau-Lifshitz阻尼项和Gilbert阻尼项的磁矩转动方程,提出统一形式的磁化率张量表达式.基于等效磁导率将非晶丝中各向异性的电磁场求解问题转化为等效的各向同性问题,进而分析了套在绝缘磁环或导电磁环中非晶丝的阻抗.采用基于有限元的数值方法仿真磁环中非晶丝的阻抗,仿真结果验证了理论分析结论.理论分析和仿真实验均表明,外磁体的附加阻抗将严重降低阻抗变化率,破坏巨磁阻抗特性.为此,提出采用回路形式降低附加阻抗的方法,并基于仿真实验验证了该方法的有效性. 关键词： 巨磁阻抗效应 非晶材料 Maxwell方程 有限元     

Evolution of magnetic permeability and magneto-impedance effect in composite wires with insulator layer

CuBe/Insulator/NiCoP composite wire was prepared by electroless deposition on an insulated CuBe core with a diameter of 90 μm. The conversion relationship between the magneto-impedance and effective magnetic permeability of the composite wire was derived from an energy conversion model. The evolution of the magnetic permeability and the giant magneto-impedance (GMI) effect were investigated. The results show that a distinct GMI effect can be obtained at relatively low frequency. The largest GMI ratio is 240% at 600 kHz, and the maximal field sensitivity is 34%/Oe.     

Cathode-sheath driven low-speed aerodynamic flow actuation using direct-current surface glow discharges

Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO₂ seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption.     

Magnetic properties of electroplated wires coated by ferrofluid

Low-frequency magnetic properties of ferromagnetic composite wires were studied with and without coating by ferrofluid. Non-magnetic CuBe wires of 0.1 mm diameter were electroplated with FeCoNi layer of 1 μm thickness. Magnetization curves were measured in the frequency range of 10 Hz–3 kHz. The composite CuBe/FeCoNi/ferrofluid material shows a hysteretic behaviour in a small field. The hysteresis loop of ferrofluid covered electroplated wire is not a simple sum of the ferrofluid “wire” plus non-covered wire signals. It indicates an interaction between magnetic wire and ferrofluid which can be revealed by low-frequency measurements. The combination “electroplated wire/ferrofluid” can be considered as a new type of composite magnetic material consisting of solid magnetic core coated by complementary liquid magnetic material. Low-frequency measurements in presence of ferrofluid can be a useful method to study magnetic properties of ferromagnets.     

Enhancement of gas phase heat transfer by acoustic field application

This study discusses a possibility for enhancement of heat transfer between solids and ambient gas by application of powerful acoustic fields. Experiments are carried out by using preheated Pt wires (length 0.1-0.15 m, diameter 50 and 100 micro m) positioned at the velocity antinode of a standing wave (frequency range 216-1031 Hz) or in the path of a travelling wave (frequency range 6.9-17.2 kHz). A number of experiments were conducted under conditions of gas flowing across the wire surface. Effects of sound frequency, sound strength, gas flow velocity and wire preheating temperature on the Nusselt number are examined with and without sound application. The gas phase heat transfer rate is enhanced with acoustic field strength. Higher temperatures result in a vigorous radiation from the wire surface and attenuate the effect of sound. The larger the gas flow velocity, the smaller is the effect of sound wave on heat transfer enhancement.     

Effect of the duty ratio on the indium tin oxide (ITO) film deposited by in-line pulsed DC magnetron sputtering method for resistive touch panel

The indium tin oxide (ITO) film was deposited on PET (polyethylene terephthalate) film using in-line pulsed DC magnetron sputtering system with different duty ratios. The reverse time and the frequency of pulsed DC power were changed to obtain the different duty ratios. From the electrical and optical properties such as the sheet resistance, resistivity, thickness and transmittance, the pulsed DC sputtered ITO/PET films were also superior to the DC sputtered ITO/PET films. The reverse time had little effect on the properties of the ITO/PET film and the frequency of pulsed DC power had an immerse effect on the properties of the ITO/PET films. The optimal ITO/PET film was obtained when the frequency was 200 kHz, the reverse time was 1 μs, and the duty ratio was about 80%.     

Wide-band magnetoelectric characterization of a ferrite-piezoelectric multilayer using a pulsed magnetic field

The use of a pulsed magnetic field for studies on frequency characteristics of the magnetoelectric (ME) effect in multilayer composite structures is described. The method is based on the excitation of a ferrite-lead zirconate titanate multilayer with short magnetic field pulses, followed by the measurement and Fourier analysis of the ME response signal. It is shown that the ME voltage coefficient α_E generally decreases as the frequency increases from 1 kHz to 1 MHz except (i) at some discrete frequencies where the coefficient increases by an order of magnitude due to electromechanical resonance in the structure and (ii) a local maximum at 2-4 kHz in α_E vs. frequency due to relaxation processes caused by the conductivity of individual layers.     

Cut-off frequency of magnetostrictive materials based on permeability spectra

The loss behavior and cut-off frequency of TbDyFe alloy and TbDyFe/epoxy composite have been investigated by measuring their permeability spectra. The loss factor of TbDyFe alloy increases exponentially as the frequency goes up, while it is almost unchanged for the TbDyFe/epoxy composite. The loss factor value for the TbDyFe composite is only 4.3% of that for the monolithic TbDyFe alloy at high frequency of 10 kHz under the peak magnetic induction of 10 mT. The cut-off frequency of TbDyFe/epoxy composite is 6800 kHz, 3 orders of magnitude larger than that of TbDyFe alloy. The cut-off frequency is found to be the ferromagnetic resonance frequency and can be calculated from Snoek's law.