Magnetic Field for Radiating and Receiving Loops Placed on Parallel Planes

In the calibration of radio receivers and field-intensity meters, a radiating loop and a receiving loop under test are mainly located either in a coaxial or coplane to each other. A formula to obtain the average magnetic-field strength incident on a receiving loop is derived for the case where the radiating and receiving loop antennas have a certain deviation on a parallel plane from the coaxial or coplanar alignment of the loops. In order to expand the uniform region of the magnetic field around the test point, the distribution of the magnetic field is investigated by using this formula for some alignments where the four (or less) radiating loops and a receiving loop lie on parallel planes to each other. It is obvious that the uniform regions are improved by factors of about 10 or 16 by increasing a radiating loop to two or four loops, respectively.     

A method for generating a standard magnetic field in a circularwaveguide

In order to minimize the effect of electromagnetic interference and the surrounding conductive materials in the calibration of small loop antennas used above HF frequencies, a novel method for generating a standard magnetic field in a circular waveguide is proposed. A method for obtaining the average magnetic-field strength incident on a receiving loop by placing the radiating and receiving circular loop antennas within a circular waveguide operated below the cutoff frequency region is described. The differences between the theoretical and experimental values of the field strength are within 0.1 dB between 10 and 150 MHz for the radiating and receiving loops with radii of 1.0 cm and within 0.15 dB between 10 and 110 MHz for radiating and receiving loops with a radii of 1.5 cm     

General formulas for calculating magnetic field at a receiving loopplaced at an arbitrary position from a radiating loop in a shielded room

The standard magnetic field radiated by a small loop antenna is used for sensitivity testing of radio receivers. To avoid interference from external sources, the test is often carried out in a shielded room. A formula to obtain the intensity of the magnetic field at the receiving loop, when a small radiating loop antenna and the receiving loop antenna are placed at random locations in a shielded room, is derived. The convergence of the formula is analyzed. Using the formula, an equation is derived which expresses the shielded room error or the effect of the room on the standard magnetic field. The correlations between the calculated values of the error and the measured results are reported     

Half-Integer Flux Quantization in a Superconducting Loop with a Ferromagnetic π-Junction

Superconducting loops containing a π-junction are predicted to show a spontaneous magnetic moment in zero external magnetic field. In order to confirm this longstanding prediction experimentally, we performed magnetization measurements on individual mesoscopic superconducting niobium loops with a ferromagnetic (PdNi) π-junction. The loops are prepared on top of the active area of a micro Hall-sensor based on high mobility GaAs/AlGaAs heterostructures. We observe switching of the loop between different magnetization states at very low-magnetic fields, which is asymmetric for positive and negative sweep direction. This is evidence for a spontaneous current induced by the intrinsic phase shift of the π-junction. In addition, the presence of the spontaneous current at zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in a half integer flux quantization in the loop at low temperatures. This work is dedicated to H. von L?hneysen on the occasion of his 60th birthday.     

Analysis of Minor Hysteresis Loops of Cold Rolled Low Carbon Steel

Minor hysteresis loops of cold rolled low carbon steel have been analyzed in connection with the rolling reduction. We found several simple relations between parameters of minor loops and obtained minor-loop properties that are independent of magnetic field amplitude and magnetic field. The properties increase with increasing rolling reduction and are in proportion to coercive force of the major loop. The present analysis method using minor loops can be applied to quantitative nondestructive evaluation of dislocation density in ferromagnetic materials     

Description of the process of magnetization of hollow cylindrical rods from soft magnetic materials in a homogeneous quasi-static magnetic field of a solenoid. Hysteresis loop

On the basis of the arctangential approximation of the magnetic hysteresis loop of the material and the expression for the central demagnetization coefficient of hollow cylindrical rods from soft magnetic materials, a method for calculating the hysteresis loops of these rods in a homogeneous quasi-static field of a solenoid is proposed. Calculation and comparison to experimental data of the basic parameters of the magnetic loops hysteresis of hollow cylindrical rods with a different value of the demagnetization coefficient have been made. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 181–188, November–December, 2007.     

Calibration of circular loop antennas

The calibration of a measuring loop antenna means assigning an antenna factor K for each frequency in the entire measurement band. Such a loop antenna factor can be found either by calculating the impedances of the loop, or by using a well-defined standard magnetic field of a transmitting antenna. For both methods, it is necessary to obtain an accurate relation between the magnetic field and the geometrical dimensions of the loops. Generally, a manufactured loop has a complex geometric shape with complex electrical behavior so that its impedances cannot be accurately determined. The standard magnetic field method must then be used for traceability of the calibration. The necessary expressions, taking into account the dimensions of the loops with finite conductor radii including the current distribution along the loop, are given. Greene's equations are accurately calculated with mathematics software on a personal computer for the near-zone as standard average magnetic field. With the procedure presented here, the calibration is reduced to an accurate measurement of attenuation     

Influence of a transverse magnetic field on the current distribution in parallel superconducting wires

In a system of parallel superconducting wires, which are connected at their ends, any two conductors form a closed superconducting loop, in which, according to the law of induction, no variation of the enclosed magnetic flux can occur. If a transverse magnetic field is applied to the system, the closed superconducting loops oppose the penetration of this field. As a consequence currents are induced in the conductors, whose magnetic field generates a certain current distribution, resulting from the geometrical arrangement of the conductors.The theoretical treatment depends upon whether the conductors are in the mixed or in the Meissner state. The current distribution was investigated in planar wire arrangements as well as in systems with wires positioned on a circle.     

Effect of various pulse wave forms for pulse-type magnetic flux pump

The excitation current of magnetic pole windings in magnetic flux pump needs to be generated by a control system. In this paper, the control system of pulse-type high temperature superconducting magnetic flux pump is discussed in detail. The control system consists of a control circuit and a drive circuit. A direct current power supply is the unique power supply of the drive circuit. The control circuit is powered by a computer through a USB interface of the computer. The control circuit receives commands from the computer and controls the drive circuit to generate different pulse waves. Each pulse wave generates a unique pulse-type traveling magnetic field and will pump magnetic flux into the superconducting loop. Experiments have been performed to examine the pumping effect of different pulse waves on both MgB₂ and Bi-2223 superconducting loops using the proposed control system, and the best pulse wave has been found. The experimental results show that the magnetic flux pump can compensate current decay up to 32.5 A for MgB₂ loop and 129 A for Bi-2223 loop. It indicates that the control system of the pulse-type magnetic flux pump is effective and feasible.     

几何因素对铁磁性纳米线阵列磁滞回线的影响

讨论了铁磁性纳米线磁滞回线的特点及其影响因素，使用蒙特卡洛方法模拟了在周期性边界条件下的磁性纳米线阵列的磁滞回线，研究了纳米线的几何因素对铁磁性纳米线阵列磁滞回线的影响．研究发现，纳米线的直径不均匀程度越大，纳米线阵列磁滞回线的剩余磁化强度越小，饱和磁化强度越大，矫顽力则基本上不受影响；在一定条件下，纳米线长度的增加，则会使纳米线阵列磁滞回线的剩余磁化强度、矫顽力和饱和场强均有所增大，而纳米线长度的不均匀程度则对纳米线阵列的磁滞回线没有明显的影响。     

Dipole Approximation for Electrically Small Loop Antennas

Measurement Techniques - An elementary magnetic emitter is considered as an approximation for the variable magnetic field of an electrically small radiating loop antenna. The frequency limits for...     

Tailoring of Magnetic Properties of Magnetostatically-Coupled Glass-Covered Magnetic Microwires

We report on tailoring of magnetic properties of Fe- and Co-rich microwires through magnetostatic coupling among them. We studied hysteresis loops of the arrays containing different number of the Co₆₇Fe_3.9Ni_1.5B_11.5Si_14.5M_0.6 and Fe₇₄B₁₃Si₁₁C₂ amorphous microwires. Fe₇₄B₁₃Si₁₁C₂ microwires have rectangular hysteresis loop, while Co₆₇Fe_3.9Ni_1.5B1_1.5Si_14.5M_0.6 with vanishing magnetostriction constant posses inclined hysteresis loop with low coercivity. The presence of neighboring microwire (Fe either Co-based) significantly modifies hysteresis loop of whole microwire array. In a microwire array containing Fe-based microwires, we observed splitting of the initially rectangular hysteresis loop with a number of Barkhausen jumps correlated with number of Fe-rich microwires. In Co?CCo arrays, we observed a change of inclination of overall hysteresis loop, and consequently magnetic anisotropy field under influence of the additional of Co-based microwire. In the case of mixed arrays containing Fe and Co-rich microwires, we were able to obtain irregular hysteresis loops with unusual shape. In this case, considerable increase of harmonics has been observed. Magnetic field amplitude and frequency affect the behavior of all studied arrays. Increasing the amplitude the shape of hysteresis loop of microwire array containing Fe-based microwires transforms from multi-step to single above certain magnetic field amplitude. In the array with Co-based microwires, we observe a change of coercivity. Observed dependences have been attributed by us to the magnetostatic interaction between the microwires with different magnetic domain structure. Together with the conventional method, such as thermal treatment, designing of arrays containing different types of microwires can serve for tailoring of their magnetic properties.     

The shearing of perpendicular loop with columnar structure

The experimental results on the hysteresis loops of magnetic films with perpendicular anisotropy show that the loop is sheared. The shearing of the loops depends strongly on the thickness of the film. This phenomenon was never successfully explained with the particulate model. We use a simple three dimensional particulate model with an effective demagnetizing field to calculate the slope of the perpendicular loops. The calculated results are compared with the experimental results for the CoCr sputtered films. By considering different separation distance of the columns, good agreement is obtained between the calculations and the experimental data for the shearing of the loop.     

A method for calculating hysteresis loops of interacting single-domain particle systems in a nonmagnetic binder

A method is given for calculating the minor and full hysteresis loops of a system of uniaxial single-domain particles with a common direction of easiest magnetization. A probabilistic approach is used in formulating the problem by means of two differential equations which are solved for the simple case of an infinite particle chain. The method is based on a model in which each particle is characterized by a rectangular hysteresis loop with a specific saturation field Hs, and the loops are influenced by the (homogeneous) external magnetic fieldHas well by the magnetization-dependent interaction of the particles among themselves.     

Effects of Biaxial Crystal Field on the Magnetic Properties on?a?Spin-1?Ising?System

Within the effective field theory (EFT) with a probability distribution technique that accounts for the self spin correlation functions, the magnetic properties such as the hysteresis loops, susceptibility and magnetization of a spin-1 Ising system with effects of a biaxial crystal field are studied. The effects of the biaxial crystal field on the magnetic properties are discussed and numerical calculations are performed and analyzed for the cases of the honeycomb lattice. A number of interesting phenomena such as the shape of the hysteresis loops and the susceptibility have been found.     

Hysteresis properties of sintered Sm Co5permanent magnets

The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions.     

Nonlinearity of Faraday loops

Faraday loops traced with an extinction method and magnetization hysteresis loops were compared. When a material consists of a magnetic multidomain, the detected apparent Faraday rotation is not proportional to the net magnetization. In addition to this nonlinearity, light diffraction by domains results in loop deformation. The loop traced with a larger part of diffracted light has more nonlinearity than when it is traced using only the zeroth-order diffracted beam. An extreme case for the nonlinearity of Faraday loop tracing appears when the image of the domains of the material is formed on the photodetector. The nonlinearity increases for a material with a larger Faraday effect while the differential fixed analyzer method gives a loop without nonlinearity. It has been shown that the extinction method for identifying polarization is not helpful for examining the magnetization hysteresis instead of evaluating the magnetization loop itself     

Absolute Measurements for Small Loop Antennas for RF Magnetic Field Standards

A method to determine accurately the strength of magnetic fields produced by a transmitting small loop antenna for the RF field standards is presented. The field strength can be determined by the magnetic dipole moment of the loop. A loop antenna factor is introduced to express the magnetic dipole moment of a transmitting small loop antenna in terms of the incident power to the antenna input port. The emergent power from the output port of a receiving small loop antenna can also be expressed in terms of the magnetic field to be detected and of the loop antenna factor. The insertion loss method (or the three antenna method) is applied to measuring the loop antenna factor. Small loop antennas with diameters 10 cm were designed, and loop antenna factors were measured by the insertion loss method over frequencies up to 30 MHz with a systematic error of 0.08 dB.     

VHF Loop Antenna Loss Measurements

The product of the loss ratios of two very small loop antennas, oriented such that their axes coincide, is given approximately by L1L2 = A(1.5)-2(1 + k2d2)-2(kd)6 where L1 and L2 are the dissipative power loss ratios of the loops, d is the spacing between the loops, and k = 2?/wavelength. A is the insertion loss measured between the ports of the two loops including their matching networks. The loops are assumed to be impedance-matched to the generator and to the load, respectively. A relationship is developed which takes into account the effects of the receiving loop current on the transmitting loop mesh. This makes possible measurements with more closely spaced loops than otherwise, without incurring intolerable errors. The minimum useful spacing depends on the loss ratios, being greater for more efficient antennas. For small antennas with practical loss ratios, the measurements can be made on the laboratory bench or in production test without special antenna test facilities. A more nearly exact field expression due to F. M. Greene is utilized for loops of appreciable size.     

Selection of circulatory loops for patrol vehicles operating in a network

Many applications exist in which a vehicle or set of vehicles have the responsibility of patrolling and providing coverage over a wide area or network for the purpose of responding quickly to service requests generated randomly at demand points in the network. One of the decisions in the operation of such patrol vehicles is that of determining the home location or circulatory loop for free or idle vehicles. A vehicle is said to be idle if it is not responding or attending to a service request. Such home location can be a point, a set of points in a network, a circulatory loop, or a set of circulatory loops in the network. The actual number of home locations is system, fleet size, and analyst dependent. Whether a point or loop strategy is implemented, the specification of the home locations or loops is usually done with the objective of improving the response time of idle vehicles to service requests originating from demand stations. In cases where circulatory loop strategy is adopted, the problem is one of determining the best overall circulatory loop or loops that would improve the overall system response time. In a typical conventional or generalized network, several loops may exist. Unless a systematic procedure is developed, non-optimal loops could be selected. In this paper, methodologies for determining the best circulatory loops for patrol vehicles for a given problem scenario in both unidirectional and bidirectional networks are presented. The problem is modelled as a mathematical programming problem. Example problems are given to illustrate the application of the approach. The criterion for optimization is the minimization of the maximum system response time.