Determining the Diameter of Reinforcing Bars Inside Concrete Structures Regardless of Magnetic Properties

In this work, using a series of numerical experiments, the dependence of the magnetic field strength of the response of the reinforcing bar to an external magnetizing field on the magnetic properties of the reinforcing bar was investigated. The possibility of determining with high accuracy the diameter of reinforcing bars, regardless of the magnetic properties of the material from which they are made, has been proven.

Some Thermomagnetic and Mechanical Properties of Amorphous Fe75Zr4Ti3Cu1B17 Ribbons

The microstructure, revealed by X-ray diffraction and transmission Mössbauer spectroscopy, magnetization versus temperature, external magnetizing field induction and mechanical hardness of the as-quenched Fe75Zr4Ti3Cu1B17 amorphous alloy with two refractory metals (Zr, Ti) have been measured. The X-ray diffraction is consistent with the Mössbauer spectra and is characteristic of a single-phase amorphous ferromagnet. The Curie point of the alloy is about 455 K, and the peak value of the isothermal magnetic entropy change, derived from the magnetization versus external magnetizing field induction curves, equals 1.7 J·kg−1·K−1. The refrigerant capacity of this alloy exhibits the linear dependence on the maximum magnetizing induction (Bm) and reaches a value of 110 J·kg−1 at Bm = 2 T. The average value of the instrumental hardness (HVIT) is about 14.5 GPa and is superior to other crystalline Fe-based metallic materials measured under the same conditions. HVIT does not change drastically, and the only statistically acceptable changes are visibly proving the single-phase character of the material.

Remarks on Selecting Length of Cylindrical Sample to Determine Magnetic Properties of its Material

When experimentally studying magnetic properties of the ferromagnetic materials, preferences are often given to a more convenient method involving the use of sufficiently long cylindrical samples with the L length and the D diameter placed in the solenoid field as an alternative to the method based on using classical samples of the toroidal shape (to exclude manifestations of the demagnetizing factor). Currently, required justification is practically missing for specific values of the relative L/D length, which would indicate such [L/D] values (for L/D ≥ [L/D]), at which magnetic properties of a sample (already long enough) correspond to magnetic properties of its material. While the existing recommendations such as [L/D] = 50 are postulated, let us note that relevant experimental studies of magnetic properties of the cylindrical samples with the L/D parameter targeted variation were not made. An attempt was made to fill this gap. For cylindrical steel samples with the different L/D values (from 1 to 50), families of the B magnetic induction and of the μ permeability field dependencies were obtained experimentally using the ballistic method. The sought [L/D] values were determined from the B and μ dependencies on the L/D by the junction abscissa of the ascending and self-similar branches. It was established that in the accepted field strength in the range of H = 0.94--54.2 kА/m magnetizing field, the [L/D] parameter is a variable substantially depending on H (and/or μ). It varies from [L/D] = 10--15 at H = 54.2 kA/m (μ = 30) to [L/D] = 50--60 at H = 4.7 kA/m (μ = 270). And at H < 4.7 kA/m, [L/D] > 50--60, i.e., more than is commonly believed. Thus, it was stated that the data on magnetic properties obtained when using even long samples (L/D = 50) and declared as data on the magnetic properties of the corresponding material, are only close to those with H < 4.7 kA/m. Phenomenological expressions were obtained for the [L/D] determination: exponential with the H argument and logarithmic with the μ argument

Giant Stress-Impedance Effect in CoFeNiMoBSi Alloy in Variation of Applied Magnetic Field

The article presents the stress impedance investigation of CoFeNiMoBSi alloy in variation of the applied magnetic field. In order to carry out the study, a specialized stand was developed that allows for loading the sample with stresses and simultaneous action of the DC (direct current) magnetizing field. The tests were carried out for as-cast and Joule annealed samples. The significant influence of the magnetizing field acting on the sample on the stress-impedance results was demonstrated and the dependence of the maximum impedance change in the stress-impedance effect was determined, depending on the field acting. The obtained results are important due to the potential use of the stress-impedance effect for the construction of stress sensors.

Восстановление топографии поверхностных дефектов ферромагнетиков при нормальном намагничивающем поле

A technique for reconstructing the topography of defects in ferromagnetic materials in a normal magnetizing field is considered. It is shown that with such a magnetization, the surface of a soft magnetic ferromagnetic material is an equipotential surface. An approximation is proposed that makes it possible to obtain its topography from the results of measuring the three components of the magnetic field at a small distance from the defect. The reconstruction accuracy was estimated from the results of calculating the field from the defect by the finite element method and reconstructing the topography of the defect using the proposed approximation.

Difference between Brownian and Néel relaxation mechanisms in a magnetizing field

Measurements of the dynamic susceptibility of a magnetic fluid based on cobalt ferrite particles stabilized in water by a double surfactant layer have been carried out. Cobalt ferrite, in comparison with magnetite, has a significantly higher energy of magnetic anisotropy. Therefore, for particles of cobalt ferrite, the Brownian mechanism of relaxation of magnetic moments is characteristic. The Debye (with a finite relaxation time) contribution to the dynamic susceptibility and the high-frequency (dispersionless) contribution are distinguished by constructing Cole-Cole diagrams. It was found that with an increase in the magnetizing field, the Debye contribution to the dynamic susceptibility decreases, while the high-frequency one (having a zero relaxation time) remains unchanged. The indicated property of the dynamic susceptibility of a fluid with a Brownian relaxation mechanism is radically different from the properties of the susceptibility of a fluid with Néel particles. Previously, measurements were made of the susceptibility of a fluid based on magnetite particles stabilized with oleic acid in kerosene. The magnetite particles have significantly lower anisotropy energy and are characterized by the predominance of the Néel relaxation mechanism. Turning on the magnetizing field caused a decrease in both the Debye part of the susceptibility and the high-frequency part of the susceptibility of magnetite particles.

A peculiarity of the magnetization of a ferromagnet by an alternating field

It has been experimentally established that the demagnetizing field of the magnetic poles formed at the ends of an open ferromagnetic cylinder decreases with increasing frequency of the magnetizing field due to a decrease in their size under the influence of the surface effect. For this reason, as the frequency of the magnetizing external field increases, the internal field in a ferromagnetic cylinder near the surface approaches it in amplitude. In addition, it has been found that the field on the surface of a ferromagnetic rod magnetized by an alternating field significantly exceeds the latter in strength with increasing frequency of this field.

Was the moon magnetized by impact plasmas?

The crusts of the Moon, Mercury, and many meteorite parent bodies are magnetized. Although the magnetizing field is commonly attributed to that of an ancient core dynamo, a longstanding hypothesized alternative is amplification of the interplanetary magnetic field and induced crustal field by plasmas generated by meteoroid impacts. Here, we use magnetohydrodynamic and impact simulations and analytic relationships to demonstrate that although impact plasmas can transiently enhance the field inside the Moon, the resulting fields are at least three orders of magnitude too weak to explain lunar crustal magnetic anomalies. This leaves a core dynamo as the only plausible source of most magnetization on the Moon.

Strain Dependence of Hysteretic Giant Magnetoimpedance Effect in Co-Based Amorphous Ribbon

The significant strain dependence of the hysteretic Giant Magnetoimpedance (GMI) effect in a Co67Fe3Cr3B12Si15 amorphous alloy in a low magnetizing field is presented. A simplistic test stand capable of continuous measurements of GMI characteristics under the influence of strain is detailed. Based on the results, a stress-impedance (SI) sensor is proposed, with a gauge factor similar to semiconductor strain gauges but more robust. An effective method of minimizing external magnetic field influence on the SI effect is given.