Magnetic behavior of Magneto-Rheological Foam under Uniaxial Compression Strain

This study reports the development of a Magneto-Rheological Foam, which consists in a porous matrix filled by ferromagnetic particles. The porous matrix of such a composite being easily deformable, large magnetic properties changes are expected. The measurements of the magnetic properties of such a Magneto-Rheological Foam submitted to a compressive strain are reported. Main aspect of the magnetic properties is the low field magnetic permeability as the function of the compression and filling factor. Then, larger field magnetization measurement allowed to investigate the saturation field as a function of the filling factor. Because of the large amount of pores in the material, the magnetic relative permeability, µr, is quite small (µr ~1). However, these materials can be easily deformed over a large range of strain providing important relative variation of the magnetic properties under mechanical solicitation. The composite magnetic permeability is increasing under compression for all the considered filling factors. A model is then developed to understand the variation of the permeability with the strain. Hence, from a simple concept consisting of taking advantage of high deformation of foams, the present study demonstrates the interest of such a highly compressible while cheap composite for obtaining a large magneto-rheological effect.

The intraoral permeability measurement as a screening for artifact formation by orthodontic products in MRI

Aim Metal dental products lack precautionary statements regarding MR compatibility due to an exemption in the labelling obligation. Hence, it is difficult for radiologists to decide whether to remove fixed metal objects in patients prior to MRI. A solution could be the direct determination of the magnetic permeability (µr) as a decisive material-related predictor of artifact formation and other interactions. Thus, the applicability of an industrially used measurement device as a screening instrument and the relevance of the manufacturer’s application restrictions in vitro and in vivo were tested. Methods Precision and trueness were tested using self-made test objects with different dimensions and different permeability. To clarify whether the measurement results are affected by the remanence (BR) induced in the objects, 28 brackets of different materials were exposed to a weak and a strong external magnetic field and the magnetic flux density before and after these exposures was compared. The clinical test was performed on a volunteer with an orthodontic appliance experimentally composed of brackets with different levels of magnetic permeability (µr). Validity and intra- and interrater reliability were calculated using two rater groups consisting of four dentists and four medical-technical radiology assistants (MTRA), respectively. Results With coefficients of variation below 0.14%, precision was excellent regardless of object surface and size. Trueness was high on objects with µr ≤ 1.002, and decreased with increasing µr, for which size-dependent correction factors were calculated. Intra- and interrater reliability and validity were excellent and independent of professional intraoral manipulation experience. Conclusions The permeability measurement allows for a valid and reliable determination of the magnetizability of intraoral metal objects. When used as a screening tool to detect nonartifact-causing objects, no correction factor needs to be calculated. For the first time, it offers radiologists a decision support for the selective removal of only the highly permeable components of the multiband apparatus.

Research of the process of thermal processing of milk in a cylindrical pasteurizer

Cylindrical coaxial heaters are increasingly used in agricultural production. However, their widespread use is restrained by the fact that it is still necessary to supplement the calculation methodology, which would make it possible to take into account its geometric dimensions, dielectric and magnetic permeability, surface effect and proximity effect, uneven distribution of electric and magnetic fields along the heater, and a number of other factors when choosing the parameters of the heater. Such a task is relevant in the design of electric heaters for the production needs of dairy farms, taking into account what the methodology presented below has been developed. This technique gave a positive effect in relation to the development of an experimental electric pasteurizer.

Towards a model of chain-by-chain magnetization of a granular medium: a variant of magnetic diagnostics of chains of spheres

In addition to information on the magnetic parameters of inhomogeneous magnetics, in particular, granular magnetics usually studied within the framework of the quasi-continuous medium model, it is of no less interest to obtain information from the standpoint of the model, when the object of study is the characteristic elements of an inhomogeneous magnetic. According to the well-proven model of selective magnetization of a granular medium, the elements that make up this medium are chains of granules – straight and sinuous, always manifesting themselves in the direction of its magnetization. They perform the function of conductor channels of the generated magnetic flux through the granular medium. As a result, it is a kind of branched «bundle» of conductor channels. For any of the chains of granules, for example, granules-balls of radius R, conceptually significant are the magnetic parameters of its conditional cores with radius r ≤ R, and these parameters, first of all, the magnetic permeability of quasi-continuous cores and magnetic induction in them, for different (in r) cores are variable, which requires appropriate magnetic diagnostics. To clarify the magnetic parameters of the conditional cores of a chain of granules-balls, as a physically self-sufficient element of a granular medium (i.e., in accordance with the model of chain-link magnetization of such a medium), it is practical to make measuring magnetic flux sensors in the core as circular sensors surrounding the contact point of granules-balls, however, not as traditional wire loops, but as circuits on thin printed circuit boards (with mounting holes) placed between adjacent balls. Based on the obtained data of the magnetic flux in cores of different radii r (r/R = 0.2–0.9) of a chain of spheres with a radius of R = 20 mm, the values of the magnetic induction B in them, as well as their magnetic permeability μ, were determined when the chain is magnetized in the solenoid by a field of strength from 4.8 to 54.5 kA/m. It is shown that with formal thickening of the cores, the values of B and μ decrease due to a decrease in the volume of the ferromagnet in the core, and for the limiting core (r/R → 1), i.e., for the chain as a whole, they correspond to the values of B and μ for a poly-ball backfill medium.

The Study of Magnetoimpedance Effect for Magnetoelectric Laminate Composites with Different Magnetostrictive Layers

The rectangular magnetoelectric (ME) composites of Metglas/PZT and Terfenol-D/PZT are prepared, and the effects of a magnetostrictive layer’s material characteristics on the magnetoimpedance of ME composite are discussed and experimentally investigated. The theoretical analyses show that the impedance is not only dependent on Young’s modulus and the magnetostrictive strain of magnetostrictive material but is also influenced by its relative permeability. Compared with Terfenol-D, Metglas possesses significantly higher magnetic permeability and larger magnetostrictive strain at quite low Hdc due to the small saturation field, resulting in the larger magnetoimpedance ratio. The experimental results demonstrate that the maximum magnetoimpedance ratios (i.e., ΔZ/Z) of Metglas/PZT composite are about 605.24% and 239.98% at the antiresonance and resonance, respectively. Specifically, the maximum ΔZ/Z of Metglas/PZT is 8.6 times as high as that of Terfenol-D/PZT at the antiresonance. Such results provide the fundamental guidance in the design and fabrication of novel multifunction devices based on the magnetoimpedance effect of ME composites.

Development of Low-Magnetic-Permeability Welds of 316L Stainless Steel

Austenitic stainless steel is often used as the construction material for particle accelerator vacuum chambers. It is also a strong candidate construction material for helium vessels of superconducting radiofrequency cavities of highenergy, high-power particle accelerators. One of the major limitations of austenitic stainless steels for their application in particle accelerators is the relatively higher magnetic permeability of its welds. The present paper describes an experimental study to obtain a low-magnetic-permeability gas tungsten arc weld of 316L stainless steel while using ER 316L stainless steel filler metal through controlled addition of nitrogen in the argon shielding gas. It was demonstrated that 316L stainless steel welds, made with the addition of 1.5% nitrogen in the argon shielding gas, were associated with magnetic permeability close to that of the base metal. The welds exhibited good strength and ductility in addition to qualifying the impact test requirement of the American Society of Mechanical Engineers Boiler & Pressure Vessel Code (BPVC) for operation at room temperature and liquid helium temperature (4 K). The technique is important for the fabrication of BPVC-compliant 316L stainless steel vacuum chambers and pressure vessels of particle accelerators, including helium vessels of superconducting radiofrequency cavities.