通过磁光效应研究磁性液体在外场下的颗粒成链现象

在对磁性液体的磁光效应的理论分析与实验测量的基础上讨论了其在磁场下的各向异性现象.首先,通过电磁理论对成链的各向异性介质模型的介电张量形式进行了一般性的分析,然后,基于磁性液体的微观理论模型讨论了磁性液体在外加磁场下出现凝聚成链的行为.基于上面的结果,我们将实验可观测量——两种传输模式的折射率差和不同颗粒数的链(长度不同的链)的比例以及磁场强度建立联系.最后,在实验上探测了磁性液体薄膜的透射光偏振状态变化随外磁场的变化,并对测得的数据进行计算机拟合分析,验证了不同长度的链的数目之间的比例关系.     

磁性液体薄膜的折射率在外加磁场作用下的变化特性研究

用两块玻璃夹持一层几个μm厚的磁性液体薄膜.将这一磁性液体薄膜垂直放置于由亥姆霍兹线圈建立的均匀磁场中.在迈克尔孙干涉仪上用对比测量法测量在不同外加磁场强度作用下磁性液体薄膜的折射率.实验发现, 磁性液体薄膜的折射率随外加磁场强度的变化而变化.结合实验研究, 提出了外加磁场改变了磁性液体颗粒链的大小, 改变了磁性颗粒链的大小和入射光波波长的比值, 从而改变了磁性液体的折射率的设想.初步建立起了磁性液体薄膜的折射率和外加磁场强度之间的关联式.为磁场测量、光学阀门等新型磁光器件的开发提供了新的技术.     

超声波流量计测量流体声速的实验方法

为获取液体介质的声速值,设计了一种测定流体声速的实验方法,该方法利用时差式超声波流量计和标准流量校验设备同时对封闭管道中的液体进行流速测量,分别得到流速的测量值和真实值,从而计算出超声波流量计的仪表系数,并以此导出了一定条件下液体介质的声速值随仪表系数的变化关系式.利用该方法测量给出了0.17 MPa下四氧化二氮(N₂O₄)在7.6-19.4 ℃、偏二甲肼((CH₃)₂NNH₂)在6.5-25.2 ℃范围内的流体声速值,并为其他液体介质的声速测量提供了借鉴. 关键词： 超声波流量计 声速 仪表系数 温度     

煤油基Fe_3O_4磁性液体薄层的光学特性研究

为研究煤油基Fe3O4磁性液体在磁场作用下的双折射效应和二向色性特性,根据振荡磁偶极子模型进行了理论分析和模拟计算,并设计了用于测试磁性液体光学特性的实验平台,测量了不同体积密度下的光学特性.通过理论分析和模拟计算发现,不同方向偏振光的折射系数和消光系数随磁场的变化相反,平行偏振光的折射系数和消光系数随外加磁场的增大而...     

磁性液体表观密度随磁场变化测量仪的研制

利用自制的磁性液体研制出测量固、液两相胶体溶液磁性液体表现密度的测量装置并给出了测量方法和测量原理．该装置既能测量磁性液体中不同液层的表观密度，也能测量磁性液体中某点的表观密度随磁场变化的规律．     

对充液聚焦球内液体声参数研究

本文叙述了充液聚焦球内低声速液体的声速测量,测得了声速与温度、混合比的关系曲线。用Wood混合液声速公式和测量结果导出了低声速液体的声速与温度、混合比的经验公式,解释了测量声速曲线和公式声速曲线出现的差异,本文对充液聚焦球内低声速液体的设计提供了实验基础和理论依据。     

磁性液体磁表面张力测试及其液膜拉脱过程受力分析

使用拉脱法测量了磁性液体的磁表面张力,根据计算机实时采集电压随时间的变化数据得到U-t曲线,进而将液膜拉脱过程分为6个阶段,分别研究了每个阶段的电压变化原因.无外加磁场作用时2F号磁性液体存在一电压变化较平缓的阶段,而白油和1F磁性液体并未出现此现象,这主要是因为白油和1F磁性液体表面张力较大,2F号磁性液体的表面张力较小造成.有外加磁场作用时,磁性液体的磁表面张力增加,主要是由于外加磁场增强了磁性颗粒之间的相互作用.     

磁性液体磁悬浮原理演示实验研究

基于磁性液体的Bernoulli方程推导了磁性液体中非磁性物体所受的磁悬浮力,通过演示实验研究了2种磁性液体对不同密度非磁性物体的磁悬浮情况．磁性液体中非磁性物体所受的磁悬浮力受磁性液体的磁化率、磁场强度、磁场梯度的影响．相同条件下,随磁场强度和磁场梯度增强,M FP-1磁性液体分别在不同电流时将6种非磁性双锥体浮起,当电流达到3．00 A时,还出现了Rosensweig尖峰;MFP-2磁性液体的磁化率小于MFP-1磁性液体,仅浮起了聚氟乙烯、玻璃、铝双锥体．随着电流增大,中心磁场梯度较强,边缘磁场梯度较弱,出现非磁性双锥体向侧壁移动现象．     

一种新型的基于磁性液体的光纤Sagnac磁场传感器

提出一种使用磁性液体的新型光纤Sagnac磁场传感器.磁性液体具有磁致可变双折射效应和二向色性,在外加磁场作用下,液体中的磁性纳米粒子沿磁场方向结链规则排列,形成各向异性.将其制成液体薄膜,放入具有一段保偏光纤的Sagnac环中,使光纤Saganc干涉仪的正弦形状干涉光谱可随外磁场变化.光纤中传输光垂直经过磁性液体薄膜...     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

因为磁性液体的磁性微粒有着很强的相互作用,Langevin顺磁理论不能很好描述磁性液体的磁化强度随外磁场的变化.研究认为影响磁化的主要因素是磁性液体内微粒整体的结构化,其结构的形成储存了部分磁化功,直接或间接地影响了磁化.在此基础上提出“压缩”模型,修正了描述磁性液体常用的Langevin函数,得出了与实验较好符合的曲线.所提出的一个压缩后等效体积分数与外磁场强度的关系式,近似地描述了磁性液体在磁场中磁化的过程.由修正式得出了近似初始磁化率随体积分数变化关系.     

The measurements of anisotropy of ultrasound propagation and magnetic susceptibility in viscous ferrofluid

Results of experimental study of anisotropy of ultrasound propagation and anisotropy of magnetic susceptibility in a ferrofluid of considerable viscosity are reported. The dependence of the propagation velocity and absorption coefficient of ultrasonic wave on the angle between the direction of measurement and that of the magnetic field provides important information on the ferrofluid structure in a magnetic field. The results show that the ultrasonic absorption coefficient of a wave propagating in a viscous ferrofluid in a DC magnetic field depends mainly on the rotational degree of freedom. Measurements of the anisotropy of the magnetic susceptibility of a ferrofluid bring the information on the magnetic moment of the magnetic particles and their mean radius.     

The influence of magnetic field swept rate on the ultrasonic propagation velocity of magnetorheological fluids

Structure of magnetorheological (MR) fluids depends on the strength of the magnetic field applied and on the mode of its application. The ultrasonic wave propagation velocity changes under the effect of an external magnetic field as a result of formation of clusters arranged along the direction of the field in the MR fluids. Therefore, we propose a qualitative analysis of these clustering structures by measuring properties of ultrasonic propagation. Since the MR fluids are opaque, the non-contact inspection using this ultrasonic technique can be very useful. In this study, we measured ultrasonic propagation velocity in MR fluid influenced by an external magnetic field for different swept rate precisely. With increasing magnetic field intensity, the changes of the ultrasonic wave velocity are more pronounced. Sedimentation effect takes place in certain time for different swept rate due to magnetic particle size and it follows linear relationship in log scale. Significant differences of the ultrasonic wave velocity are established between the case when the field is swept at a constant rate and the case when it is stepped up.     

Frequency dependences of the velocity and absorption coefficient of sound waves in a magnetic fluid

On the basis of molecular-kinetic theory, frequency-dependent expressions are derived for the velocity and absorption coefficient of sound in a magnetic fluid with allowance for the contribution of structural relaxation in the presence of an external inhomogeneous magnetic field. The asymptotic behavior of the expressions is investigated for both low-and high-frequency limits. A numerical study is carried out by taking as an example a magnetic fluid consisting of kerosene with magnetic particles of Fe₃O₄ suspended in it. The results of the numerical study show that the calculated frequency dependences of the velocity and absorption coefficient of sound in a magnetic fluid are in good agreement with the static experimental data.     

Correlation in the velocity of a Brownian particle induced by frictional anisotropy and magnetic field

We study the motion of charged Brownian particles in an external magnetic field. It is found that a correlation appears between the components of particle velocity in the case of anisotropic friction, approaching asymptotically zero in the stationary limit. If magnetic field is smaller compared to the critical value, determined by frictional anisotropy, the relaxation of the correlation is non-oscillating in time. However, in a larger magnetic field this relaxation becomes oscillating. The phenomenon is related to the statistical dependence of the components of transformed random force caused by the simultaneous influence of magnetic field and anisotropic dissipation.     

快离子导体玻璃滞弹性弛豫的红外发散响应

本文依据Ngai(倪嘉陵)的低频激发、弛豫、耗散理论和非晶态快离子导体的特点,提出了非晶态快离子导体的滞弹性弛豫理论。认为快离子导体玻璃中的超声吸收主要来源于与玻璃网络呈微弱联系的快离子的热激活弛豫及伴之而来的低能激发的损耗。理论成功地描述了超声吸收的频率、温度依赖关系,解释了弛豫时间分布理论所不能解释的快离子导体玻璃的实验特征。     

Dynamic simulations of the dipolar driven demagnetization process of magnetic multi-core nanoparticles

In this work, we investigate dynamically the dipolar driven demagnetization process of magnetic multi-core particles by solving the Landau-Lifshitz equation for single-domain particles distributed on a three-dimensional sphere. We analyze the relaxation time in respect to different geometry and material parameters. Further we show that the demagnetization times differ from the behaviour of a single magnetic sphere in the case of low damping. To explain these dynamics nanoparticular systems of different dimensions are investigated. We show that deviations can be attributed to a confinement of the relaxation dynamics to a lower dimensional submanifold of the k-space.     

Ultrasonic investigation of magnetic nanoparticles suspension with PEG biocompatible coating

Water suspension of nanoparticles was studied by ultrasound spectroscopy. Nanoparticles have a core-shell structure with magnetic core Fe₃O₄ and surfactant shells. The surface of magnetic particles was coated with oleate sodium as the primary layer and polyethylene glycol as the secondary layer. The acoustic properties of suspensions, such as velocity and attenuation of ultrasonic waves, have been measured. From experimental data mechanical properties have been determined. Adiabatic compressibility of nanoparticles suspension decreased with increase of temperature. The changes of ultrasonic wave attenuation under the influence of the external magnetic field, show that magnetic liquids with high concentration of magnetic material (despite two surfactant shells) show tendency to aggregate.     

磁性液体的介电特性

在外加磁化场的作用下,磁性液体的介电特性表现出与一般物质所不同的新效应——磁电方向效应,即介电常数不但依赖于外加磁化场的大小,而且还依赖于外加磁化场与电场之间的相对方向。根据实验观察到的磁性液体中的磁性颗粒呈球形,在外加磁化场的作用下,磁性颗粒呈长链形分布的这一实验事实,我们用长链模型进行理论分析,合理地解释了磁电方向效应。理论与实验结果符合。 关键词：     

Accelerating vinegar aging by combination of ultrasonic and magnetic field assistance

Most fermented foods need a natural aging process to enrich desired flavours. This process is normally the bottleneck for cost-effective production. Therefore, it is desirable to accelerate the process and obtain products with the same flavour profile. Here, we used physical interventions (ultrasonic field, alternating magnetic field, or combination of both) to assist the aging process with naturally brewed vinegar as a case example. Flavour profiles of different physical-assisted aging process were compared with that of the naturally aged vinegar by using gas-chromatography mass-spectrometry (GC–MS) and electronic nose. Principal component analysis (PCA) and Pearson correlation analyses show that ultrasonic and alternating magnetic fields treatment could accelerate the aging process of vinegar. The highest accelerating aging effect was combination of ultrasonic and magnetic field followed by individual ultrasonic or magnetic field and natural process (combination of ultrasonic and magnetic field > ultrasonic or magnetic field individual > natural process). These results suggest that physical field intervention could potentially be used for acceleration of aging of fermented products without affecting flavour quality.     

Magnetoacoustic effect in non-degenerate semiconductors

The effect of ultrasonic waves propagating at an angle ? relative to the direction of a magnetic field in nondegenerate semiconductors such as n-type InSb has been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that both the absorption coefficient and the change in the sound velocity depend on the direction of the propagation of ultrasonic waves relative to the magnetic field.