The relative permeability of iron,nickel and permalloy in high frequency electromagnetic fields

The relative magnetic permeability of iron, nickel and permalloy was measured over the range of wave-lengths from 70 to 200 meters by the heterodyne balance method and by the resonance method. Nothing suggestive of the anomalous dispersion of the magnetic permeability reported in this region by Wwedensky and Theodortschik was found when certain precautions were observed in carrying out the measurements. When these precautions were neglected irregular breaks resulted in the curves of permeability as a function of wavelength which varied in position with the conditions of the circuit.The high frequency resistance of iron, nickel and permalloy wires was measured over the range of approximately fifty thousand kilocycles from two to three meter wave-lengths. What appeared to be anomalous variations at certain frequencies were found not to exist when the proper precautions were observed in making the measurements.     

电涡流传感器线圈充磁介质对抑制温漂及测量性能的影响

对充满磁介质的电涡流传感器进行了较为深入的理论研究，讨论了磁介质对抑制线圈阻抗温度漂移及测试性能产生的影响。研究结果对电涡流传感器线圈中是否加磁介质有较好的参考价值。     

Magnetic losses in remanent state ferrites

Magnetic loss in remanent state ferrites¹ has generally been described through the artifice of a magnetic loss tangent (tanδ_m = μ^″?μ′). This characterization is not directly relatable to intrinsic material parameters. The results presented in this paper indicate that magnetic loss in the remanent state can be related to intrinsic material parameters by describing the ferrite mathematically by a complex “average” permeability tensor. The “average” permeability includes the effects of magnetocrystalline anistropy, remanent magnetization, linewidth and an average demagnetizing field appropriate to the distribution of magnetic domains. Experimental examples are given showing that excellent agreement is obtained between theoretically predicted and measured losses.     

Standing waves in thin plates tensioned by in-plane loads subject to high frequency excitation

The problem investigated is that of the response of thin plates subjected to pure tone or wide band frequency excitation. A point load is applied perpendicular to the plates. In the case of isotropic or orthotropic plates excited at high frequencies ring shaped standing wave patterns are observed. No classical explanation exists covering this phenomenon. The present analysis indicates that there are two waves radiating from the excitation point with the same frequency, but at different speeds. One wave, a bending wave, is separated from the other one, a membrane wave.     

Damper circuits and rotor leakage in the transient performance of saturated synchronous machines

The sudden development of short-circuit currents, and of recovery voltages at interruption of currents, depends on the effects of stator and rotor leakages as well as of saturation in the generating synchronous machines.The non-linear problem of the interaction of these features with the performance of the main windings and auxiliary damper circuits is solved analytically.This leads to a simple graphical representation which is numerically determined by the well-known magnetic and electric characteristics of machine and network and by two time constants of very different magnitudes which are derived from the ordinary data of the machines. Hence the variation with time, of short-circuit currents and of recovery voltages, can easily and rigorously be computed for every given example.The deviations of actual damper circuits from the ideal form and the effects of eddy currents in solid steel parts of the rotor are discussed so far that numerical results can be derived readily.A new transient test for synchronous machines is suggested by which rotor and stator leakage voltages can be measured separately, avoiding the uncertainties of the usual steady state leakage tests.     

What is the magnetic permeability of iron?

This paper is a review of the changes brought about in the magnetic properties of “iron” during the period 1870 to 1928 and shows the absurdity of using “iron” as a standard for comparison. The latest (1928) value for the initial permeability (μ₀) of “iron” is given as 1150, its maximum permeability (μ_max) as 61,000, and its hysteresis loss (W_h) as 300 ergs per cubic centimeter per cycle for B = 10,000 gausses. The corresponding values prior to 1900 were: μ₀ = 250 μ_max = 2600, W_h = 3,000.     

The magnetic deflection experiments of Curtiss and of Mott-Smith

We have carried out a geometrical analysis which applies to that type of cosmic ray deflection experiment in which an extended region of magnetic field lies between the lower two of three or more Geiger-Mueller counters arranged in line for counting coincident discharges. It is apparent that charged particles of sufficiently low energy will be deviated away from the last counter and that the counting rate will therefore be reduced by application of the field. This paper presents a method for computing what proportion of electrons of a given energy will be eliminated by application of the field. The method is extended to include a constant loss of energy per unit path length as the particle traverses an iron core. The results of the experiments of Curtiss and of Mott-Smith are interpreted in the light of these calculations. Curtiss' result could be explained if all rays were electrons of 4 × 10⁸ volts energy. One may conclude from his observation that if all the radiation consists of positive or negative electrons, the fraction between 2 × 10⁷ volts and 1.5 × 10⁸ volts is less than 30 per cent. of the total above 2 × 10⁷, and that the fraction between 2 × 10⁷ and 10⁹ is greater than 30 per cent. A comparison of Curtiss' and Mott-Smith's experiments yields no reason for doubting the correctness of using the magnetic induction B when computing the deflection within iron. Nor does it necessarily sustain this procedure. An experiment by W. F. G. Swann and the writer is at present under way for the purpose of securing, if possible, more conclusive evidence on this point.     

The use of alternating currents for submarine marine cable transmission

This paper contains the results of experiments performed by members of the Signal Corps Research Laboratory, Bureau of Standards, in an attempt to develop a method or methods of signal transmission over submarine cables which would permit of a more effective use of existing cable systems.In the method proposed and developed, signals are transmitted by means of alternating currents simultaneously with the normal battery of direct-current operation of the cable. Currents of several different frequencies may be used, reserving a given frequency for each message, and by tuning or equivalent methods at the receiving end these messages may be separated, so that the simultaneous transmission of a number of messages is redered possible.Accurate determination of the fundamental physical properties of a particular cable for different frequencies has been accompalished, and the results are given herewith. From these physical properties accurate calculations for any length of cable can be made, so that the design of proper apparatus becomes purely a laboratory problem.Actual trial of the proposed alternating-current method was made covering distances up to approximately 700 kilometres, with results which were in all cases completely satisfactory, indicating that the method is an entirely feasible one, and one which will render cables of this length, and undoubtedly of several times this length, much more useful.     

Effects of a magnetic field on the free convective flow through a porous medium bounded by an infinite vertical porous plate with constant heat flux

This paper investigates the effects of a magnetic field on the free convective flow of a viscous, incompressible, dissipative fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite vertical and porous plate. The plate is subjected to a normal suction velocity and the heat flux at the plate is constant. The magnetic field is of uniform strength and is applied perpendicular to the plate. An analytical solution to the problem is obtained. The influence of the magnetic parameter (M) and permeability parameter (K) is discussed for the case of air (P = 0.71) when the plate is subjected to a constant suction velocity and is being cooled by free convection currents.     

Ultrafast microfluidics using surface acoustic waves

We demonstrate that surface acoustic waves (SAWs), nanometer amplitude Rayleigh waves driven at megahertz order frequencies propagating on the surface of a piezoelectric substrate, offer a powerful method for driving a host of extremely fast microfluidic actuation and micro∕bioparticle manipulation schemes. We show that sessile drops can be translated rapidly on planar substrates or fluid can be pumped through microchannels at 1–10 cm∕s velocities, which are typically one to two orders quicker than that afforded by current microfluidic technologies. Through symmetry-breaking, azimuthal recirculation can be induced within the drop to drive strong inertial microcentrifugation for micromixing and particle concentration or separation. Similar micromixing strategies can be induced in the same microchannel in which fluid is pumped with the SAW by merely changing the SAW frequency to rapidly switch the uniform through-flow into a chaotic oscillatory flow by exploiting superpositioning of the irradiated sound waves from the sidewalls of the microchannel. If the flow is sufficiently quiescent, the nodes of the transverse standing wave that arises across the microchannel also allow for particle aggregation, and hence, sorting on nodal lines. In addition, the SAW also facilitates other microfluidic capabilities. For example, capillary waves excited at the free surface of a sessile drop by the SAW underneath it can be exploited for micro∕nanoparticle collection and sorting at nodal points or lines at low powers. At higher powers, the large accelerations off the substrate surface as the SAW propagates across drives rapid destabilization of the drop free surface giving rise to inertial liquid jets that persist over 1–2 cm in length or atomization of the entire drop to produce 1–10 μm monodispersed aerosol droplets, which can be exploited for ink-jet printing, mass spectrometry interfacing, or pulmonary drug delivery. The atomization of polymer∕protein solutions can also be used for the rapid synthesis of 150–200 nm polymer∕protein particles or biodegradable polymeric shells in which proteins, peptides, and other therapeutic molecules are encapsulated within for controlled release drug delivery. The atomization of thin films behind a translating drop containing polymer solutions also gives rise to long-range spatial ordering of regular polymer spots whose size and spacing are dependent on the SAW frequency, thus offering a simple and powerful method for polymer patterning without requiring surface treatment or physical∕chemical templating.     

Behavior of dielectrics under alternating stress

The presence of maxima in the power factor-frequency and power factor-temperature curves of dielectrics has been explained by the Maxwell inhomogeneity theory and the Debye theory of polar molecular orientation. In order to ascertain the true cause of these maxima, a study has been made of the power factor of an essentially non-polar material with and without polar materials in dilute solution over extended ranges of frequency, 65 to 7.2 × 10⁶ c.p.s., and temperature, 2.9° C. to 90° C.The non-polar solvent is a mixture of paraffins having a pour point at 55° C. Small power factor maxima, 0.0003 in value, shifting over the audio frequency range with temperature variation, are observed for this solvent alone. Adding 3 per cent. phenol gives rise to molecular orientation maxima restricted largely to frequencies above 10⁷ c.p.s. At the lower temperatures, these maxima are greatly broadened, so that there is apparently a small contribution at power frequencies. Adding 10 per cent. stearic acid gives similar results. The failure of these maxima to shift to lower frequencies at the lower temperatures is due to the failure of the inner viscosity to increase very much in the solid state. The variation of the inner viscosity is calculated from the reciprocals of the short time conductivities since the degree of ionic dissociation is found to be essentially independent of temperature. The viscosity may be regarded as a function of particle size and varies within the medium. Where power factor maxima shift with essentially undiminished magnitude over a wide frequency range at ordinary temperatures, such as those observed here in the solvent above, it is believed that the cause is the orientation of associated or polymerized polar aggregates of such size as to be affected by the larger viscosity changes approaching the macroscopic.In the solid and amorphous states, the limited motion of ions leads to an ionic polarization as indicated by absorption curves of relatively large time constants and by high power factors in the low frequency range. The addition of organic acids greatly increases these effects and also increases the final conductivity. The true short time conductivity is largely caused by almost completely dissociated inorganic material.     

固体中冲击波及其一维一阶非线性演化方程数值模拟

定义固体中的冲击波为冲击波阵面及其后状态物理量发生急剧变化的狭窄区域。利用前人讨论结果进一步探讨了 4种边界输入形式下的冲击波形成距离计算式。分别采用具有二阶精度的显式MacCormack差分格式和MacCormackTVD格式对黏弹性、热弹性以及非均匀性非线性固体介质中一维一阶非线性演化方程进行数值模拟研究,探讨了这些复杂介质中冲击波的形成及演化的基本性质,并较成功地避免了非物理解的产生     

Using laser Doppler vibrometry to measure capillary surface waves on fluid-fluid interfaces

Capillary wave phenomena are challenging to study, especially for microfluidics where the wavelengths are short, the frequencies are high, and the frequency distribution is rarely confined to a narrow range, let alone a single frequency. Those that have been studying Faraday capillary waves generated by vertical oscillation have chosen to work at larger scales and at low frequencies as a solution to this problem, trading simplicity in measurement for issues with gravity, boundary conditions, and the fidelity of the subharmonic capillary wave motion. Laser Doppler vibrometry using a Mach–Zehnder interferometer is an attractive alternative: The interface’s motion can be characterized at frequencies up to 40 MHz and displacements of as little as a few tens of picometers.     

Ferrimagnetic mPEG-b-PHEP copolymer micelles loaded with iron oxide nanocubes and emodin for enhanced magnetic hyperthermia–chemotherapy

As a non-invasive therapeutic method without penetration-depth limitation, magnetic hyperthermia therapy (MHT) under alternating magnetic field (AMF) is a clinically promising thermal therapy. However, the poor heating conversion efficiency and lack of stimulus–response obstruct the clinical application of magnetofluid-mediated MHT. Here, we develop a ferrimagnetic polyethylene glycol-poly(2-hexoxy-2-oxo-1,3,2-dioxaphospholane) (mPEG-b-PHEP) copolymer micelle loaded with hydrophobic iron oxide nanocubes and emodin (denoted as EMM). Besides an enhanced magnetic resonance (MR) contrast ability (r₂ = 271 mM⁻¹ s⁻¹) due to the high magnetization, the specific absorption rate (2518 W/g at 35 kA/m) and intrinsic loss power (6.5 nHm²/kg) of EMM are dozens of times higher than the clinically available iron oxide nanoagents (Feridex and Resovist), indicating the high heating conversion efficiency. Furthermore, this composite micelle with a flowable core exhibits a rapid response to magnetic hyperthermia, leading to an AMF-activated supersensitive drug release. With the high magnetic response, thermal sensitivity and magnetic targeting, this supersensitive ferrimagnetic nanocomposite realizes an above 70% tumor cell killing effect at an extremely low dosage (10 μg Fe/mL), and the tumors on mice are completely eliminated after the combined MHT–chemotherapy.     

Magnetophoretic manipulation in microsystem using carbonyl iron-polydimethylsiloxane microstructures

This paper reports the use of a recent composite material, noted hereafter i-PDMS, made of carbonyl iron microparticles mixed in a PolyDiMethylSiloxane (PDMS) matrix, for magnetophoretic functions such as capture and separation of magnetic species. We demonstrated that this composite which combine the advantages of both components, can locally generate high gradients of magnetic field when placed between two permanent magnets. After evaluating the magnetic susceptibility of the material as a function of the doping ratio, we investigated the molding resolution offered by i-PDMS to obtain microstructures of various sizes and shapes. Then, we implemented 500 μm i-PDMS microstructures in a microfluidic channel and studied the influence of flow rate on the deviation and trapping of superparamagnetic beads flowing at the neighborhood of the composite material. We characterized the attraction of the magnetic composite by measuring the distance from the i-PDMS microstructure, at which the beads are either deviated or captured. Finally, we demonstrated the interest of i-PDMS to perform magnetophoretic functions in microsystems for biological applications by performing capture of magnetically labeled cells.     

Biodegradable magnesium alloy with eddy thermal effect for effective and accurate magnetic hyperthermia ablation of tumors

Magnetic hyperthermia therapy (MHT) is able to ablate tumors using an alternating magnetic field (AMF) to heat up magnetocaloric agents (e.g. magnetic nanoparticles) administered into the tumors. For clinical applications, there is still a demand to find new magnetocaloric agents with strong AMF-induced heating performance and excellent biocompatibility. As a kind of biocompatible and biodegradable material, magnesium (Mg) and its alloys have been extensively used in the clinic as an implant metal. Herein, we discovered that the eddy thermal effect of the magnesium alloy (MgA) could be employed for MHT to effectively ablate tumors. Under low-field-intensity AMFs, MgA rods could be rapidly heated, resulting in a temperature increase in nearby tissues. Such AMF-induced eddy thermal heating of MgA could not only be used to kill tumor cells in vitro, but also be employed for effective and accurate ablation of tumors in vivo. In addition to killing tumors in mice, we further demonstrated that VX₂ tumors of much larger sizes growing in rabbits after implantation of MgA rods could also be eliminated after exposure to an AMF, illustrating the ability of MgA-based MHT to kill large-sized tumors. Moreover, the implanted MgA rods showed excellent biocompatibility and ∼20% of their mass was degraded within three months. Our work thus discovered for the first time that non-magnetic biodegradable MgA, an extensively used implant metal in clinic, could be used for effective magnetic thermal ablation of tumors under a low-field-intensity AMF. Such a strategy could be readily translated into clinical use.     

Relationship between free iron and glycated hemoglobin in uncontrolled type 2 diabetes patients associated with complications

Free iron in serum has been found in several disease conditions including diabetes. In the present work, we studied the relationship between free iron, fasting blood glucose (FBG) and glycated haemoglobin (HbA_1c). Study was carried out on 50 type 2 diabetes cases under poor glycemic control associated with complications, 53 type 2 diabetes cases under good glycemic control and 40 healthy controls. We estimated free iron, both ferrous (Fe⁺²) and ferric (Fe⁺³) form, protein thiols, lipid hydroperoxides, FBG, HbA1c and serum ferritin levels in serum. There was a significant increase in free iron in Fe⁺³ state (p <0.01), HbA_1c (p<0.01), serum ferritin (p<0.01), lipid hydroperoxides (p<0.01) and significant decrease in protein thiols (<0.01) in diabetes cases under poor glycemic control compared to diabetes cases under good glycemic control and healthy controls. Free iron correlated positively with HbA_1c (p<0.01). Poor glycemic control and increase in glycation of haemoglobin is contributing to the increase in free iron pool which is known to increase oxidant generation.     

On the existence and the magnitude of electronic charges

In order to quantize Dirac's classical point electron¹ we supplement Einstein's classical equation (E/c)² ? p² = b2 with a reciprocal classical equation (CΔt)² ? (Δr)² = a² where b = mc and a is Dirac's signal radius. Δt is the time saved by a light signal in various states of motion of the electron, and a/c is the rest time saved. Our former efforts² of obtaining an integral equation for the probability amplitude have been rectified by Born.³ There is no solution of the integral equation, however, unless advanced and retarded phases are introduced simultaneously, along with Dirac's advanced and retarded potentials. We have obtained a transcendental equation for the eigen-value μ = αγ where α is the Sommerfeld fine-structure constant, and γ is the numerical factor in Dirac's signal radius a = γe²/mc². The smallest eigen-value is μ = 0.0299.That is, ab = hγ = h/210.     

Computational design optimization for microfluidic magnetophoresis

Current macro- and microfluidic approaches for the isolation of mammalian cells are limited in both efficiency and purity. In order to design a robust platform for the enumeration of a target cell population, high collection efficiencies are required. Additionally, the ability to isolate pure populations with minimal biological perturbation and efficient off-chip recovery will enable subcellular analyses of these cells for applications in personalized medicine. Here, a rational design approach for a simple and efficient device that isolates target cell populations via magnetic tagging is presented. In this work, two magnetophoretic microfluidic device designs are described, with optimized dimensions and operating conditions determined from a force balance equation that considers two dominant and opposing driving forces exerted on a magnetic-particle-tagged cell, namely, magnetic and viscous drag. Quantitative design criteria for an electromagnetic field displacement-based approach are presented, wherein target cells labeled with commercial magnetic microparticles flowing in a central sample stream are shifted laterally into a collection stream. Furthermore, the final device design is constrained to fit on standard rectangular glass coverslip (60 (L)×24 (W)×0.15 (H) mm³) to accommodate small sample volume and point-of-care design considerations. The anticipated performance of the device is examined via a parametric analysis of several key variables within the model. It is observed that minimal currents (<500 mA) are required to generate magnetic fields sufficient to separate cells from the sample streams flowing at rate as high as 7 ml∕h, comparable to the performance of current state-of-the-art magnet-activated cell sorting systems currently used in clinical settings. Experimental validation of the presented model illustrates that a device designed according to the derived rational optimization can effectively isolate (∼100%) a magnetic-particle-tagged cell population from a homogeneous suspension even in a low abundance. Overall, this design analysis provides a rational basis to select the operating conditions, including chamber and wire geometry, flow rates, and applied currents, for a magnetic-microfluidic cell separation device.     

Dynamic double layer effects on ac-induced dipoles of dielectric nanocolloids

Normal and tangential surface ionic currents around low-permittivity nanocolloids with surface charges are shown to produce three different conductive mechanisms for ac-induced dipoles, all involving dynamic space charge accumulation at the double layer∕bulk interface with a conductivity jump. However, the distinct capacitor dimensions and diffusive contributions produce three disparate crossover frequencies at which the induced dipole reverses direction relative to the bulk field. A highly conducting collapsed diffuse layer, with bulk ion mobility, renders the particle conductive and produces an ionic strength independent crossover frequency for weak electrolytes. A precipitous drop in crossover frequency occurs at high ionic strengths when charging occurs only at the poles through field focusing around the insulated colloid. A peculiar maximum in crossover frequency exists between these two asymptotes for colloids smaller than a critical size when normal charging of the diffuse layer occurs over the entire surface. The crossover frequency data for latex nanocolloids of various sizes in different electrolytes of wide ranging ionic strengths are collapsed by explicit theoretical predictions without empirical parameters.