Magnetic losses versus sintering treatment in Mn-Zn ferrites

partially_open5sìpartially_openBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, FaustoBeatrice, Cinzia; Tsakaloudi, Vasiliki; Dobák, Samuel; Zaspalis, Vassilios; Fiorillo, Faust

The temperature dependence of magnetic losses in CoO-doped Mn-Zn ferrites

CoO-doping is known to stabilize the temperature dependence of initial permeability and magnetic losses in Mn-Zn ferrites, besides providing, with appropriate dopant contents, good soft magnetic response at and around room temperature. These effects, thought to derive from the mechanism of anisotropy compensation, are, however, poorly assessed from a quantitative viewpoint. In this work, we overcome such limitations by providing, besides extensive experimental investigation vs frequency (DC–1GHz), CoO content (0 ≤ CoO ≤ 6000 ppm), and temperature (−20 °C ≤ T ≤ 130 °C) of permeability and losses of sintered Mn-Zn ferrites, a comprehensive theoretical framework. This relies on the separate identification of domain wall motion and moment rotations and on a generalized approach to magnetic loss decomposition. The average effective anisotropy constant ⟨Keff⟩ is obtained and found to monotonically decrease with temperature, depending on the CoO content. The quasistatic energy loss Wh is then predicted to pass through a deep minimum for CoO = 3000–4000 ppm at and below the room temperature, while becoming weakly dependent on CoO under increas- ing T. The rotational loss Wrot(f) is calculated via the complex permeability, as obtained from the Landau-Lifshitz equation for distributed values of the local effective anisotropy field Hk,eff (i.e., ferromagnetic resonance frequency). Finally, the excess loss Wexc(f) is derived and found to comply with suitable analytical formulation. It is concluded that, by achieving, via the rotational permeability, value and behavior of the magnetic anisotropy constant, we can predict the ensuing properties of hysteresis, excess, and rotational losses

Alternating and Rotational Losses up to Magnetic Saturation in Non-Oriented Steel Sheets

partially_open5sìpartially_openAppino, Carlo; Khan, Mahmood; de la Barrière, Olivier; Ragusa, Carlo; Fiorillo, FaustoAppino, Carlo; Khan, Mahmood; de la Barrière, Olivier; Ragusa, Carlo; Fiorillo, Faust

Soft Magnets for Passive Attitude Stabilization of Small Satellites

The spinning and oscillatory motions of small orbiting satellites can be damped exploiting the magnetic energy dissipation occurring in onboard soft magnetic strips, cyclically excited by the oscillation of the earth field component along their axis. In this paper we investigate the role played by the intrinsic magnetic properties of the material, the aspect ratio of the strips, and their mutual arrangement in achieving maximum energy dissipation under typical spacecraft working conditions. Grain-oriented Fe-Si, mumetal, and Fe-based amorphous alloys, all endowed with near-rectangular hysteresis loops, are considered. Their energy loss behaviour is calculated when, either as single strip samples or arranged into an array of strips, they are subjected to a slowly oscillating magnetic field of defined peak value, emulating the action of the earth magnetic field on the travelling satellite. The strip size and array layout leading to maximum energy loss are predicted. Amorphous alloys, combining high saturation magnetization with flexible hysteresis loop properties, are shown to lead to the best damping behaviour under both oscillating and spinning satellite motions. In the latter case the Fe-Si strips appear to provide comparably high damping effects, while inferior behaviour is always predicted with mumetal samples

FEM and Von Mises analysis on prosthetic crowns structural elements: evaluation of different applied materials

The aim of this paper is to underline the mechanical properties of dental single crown prosthodontics materials in order to differentiate the possibility of using each material for typical clinical condition and masticatory load. Objective of the investigation is to highlight the stress distribution over different common dental crowns by using computer-aided design software and a three-dimensional virtual model. By using engineering systems of analyses like FEM and Von Mises investigations it has been highlighted the strength over simulated lower first premolar crowns made by chrome cobalt alloy, golden alloy, dental resin, and zirconia. The prosthodontics crown models have been created and put on simulated chewing stresses. The three-dimensional models were subjected to axial and oblique forces and both guaranteed expected results over simulated masticatory cycle. Dental resin presented the low value of fracture while high values have been recorded for the metal alloy and zirconia. Clinicians should choose the better prosthetic solution for the teeth they want to restore and replace. Both prosthetic dental crowns offer long-term success if applied following the manufacture guide limitations and suggestions

Magnetic loss, permeability, and anisotropy compensation in CoO-doped Mn-Zn ferrites

Mn-Zn ferrite samples prepared by conventional solid state reaction method and sintering at 1325 °C were Co-enriched by addition of CoO up to 6000 ppm and characterized versus frequency (DC – 1GHz), peak polarization (2 mT – 200 mT), and temperature (23 °C – 120 °C). The magnetic losses at room temperature are observed to pass through a deep minimum value around 4000 ppm CoO at all polarizations values. This trend is smoothed out either by approaching the MHz range or by increasing the temperature. Conversely, the initial permeability attains its maximum value around the same CoO content, while showing moderate monotonical decrease with increasing CoO at the typical working temperatures of 80 – 100 °C. The energy losses, measured by a combination of fluxmetric and transmission line methods, are affected by the eddy currents, on the conventional 5 mm thick ring samples, only beyond a few MHz. Their assessment relies on the separation of rotational and domain wall processes, which can be done by analysis of the complex permeability and its frequency behavior. This permits one, in particular, to calculate the magnetic anisotropy and its dependence on CoO content and temperature and bring to light its decomposition into the host lattice and Co2+ temperature dependent contributions. The temperature and doping dependence of initial permeability and magnetic losses can in this way be qualitatively justified, without invoking the passage through zero value of the effective anisotropy constant upon doping

Broadband magnetic losses of nanocrystalline ribbons and powder cores

partially_open7sìFinemet type alloys have been investigated from DC to 1 GHz at different induction levels upon different treatments: as amorphous precursors, as ribbons nanocrystallized with and without an applied saturating field, as consolidated powders. The lowest energy losses at all frequencies and maximum Snoek's product are exhibited by the transversally field-annealed ribbons. This is understood in terms of rotation-dominated magnetization process in the low-anisotropy material. Intergrain eddy currents are responsible for the fast increase of the losses with frequency and for early permeability relaxation of the powder cores. Evidence for resonant phenomena at high frequencies and for the ensuing inadequate role of the static magnetic constitutive equation of the material in solving the magnetization dynamics via the Maxwell's diffusion equation of the electromagnetic field is provided. It is demonstrated that, by taking the Landau–Lifshitz–Gilbert equation as a constitutive relation, the excellent frequency response of the transverse anisotropy ribbons can be described by analytical method.partially_openBeatrice, Cinzia; Dobák, Samuel; Ferrara, Enzo; Fiorillo, Fausto; Ragusa, Carlo; Füzer, Ján; Kollár, PeterBeatrice, Cinzia; Dobák, Samuel; Ferrara, Enzo; Fiorillo, Fausto; Ragusa, Carlo; Füzer, Ján; Kollár, Pete

Temperature and Frequency Dependence of Magnetic Losses in Fe-Co

We investigate the temperature dependence of the energy loss W(f) of 0.10 and 0.20 mm thick Fe-Co-V sheets (Vacoflux (R) and Vacodur (R)) in the range-50(degrees)C <= T <= 155(degrees)C. The measurements, performed from DC to f = 5 kHz on ring samples and Epstein strips, show that W(f) passes through a minimum value around room temperature at all tested polarization values (1.0 <= J(p) <= 1.9 T). The largest effect occurs under quasi-static regime and declines with frequency, depending on the sheet thickness and the ensuing role of the dynamic loss. The somewhat abnormal increase of the quasi-static loss W-hyst with temperature, which contrasts with a concurrent decrease of the magneto crystalline anisotropy constant, is interpreted in terms of temperature-dependent internal stresses and their change with T. The stresses are assumed to derive from the different thermal expansion coefficients of the ordered and disordered structural phases, a conclusion made plausible by the highly magnetostrictive properties of the material, dwelling in a low anisotropy environment. The AC properties are treated by adapting the loss decomposition to the inception and development of a non-uniform induction profile across the sheet thickness (skin effect) at high frequencies. The classical loss component is calculated via the numerical solution of the Maxwell's diffusion equation, where the magnetic constitutive equation of the material is identified with the normal magnetization curve. It turns out that the so-found W-class(f) and the resulting excess loss W-exc(f) are moderately dependent on temperature and W(f) eventually tends towards a slow monotonical decrease with Tat the highest frequencies

Gallstone Ileus: An Unusual Cause of Small Bowel Obstruction: A Case Report

Gallstone ileus represents a rare complication of chronic cholelithiasis and is considered a mechanical bowel obstruction caused by one or more gallstones becoming lodged in the gastrointestinal tract. The etiology of gallstone ileus is due to the transit of a calculum through a cholecystointestinal fistula. In all cases of acute abdomen, diagnostic suspicion and appropriate first surgical treatment are important for an adequate clinical progression due to its low incidence. On other hand, due to the high incidence of gallstones, such situations may arise in ordinary clinical practices, and clinicians should evaluate gallstone ileus as a possible cause of bowel obstruction. However, because of the poor general health of ileus patients, choosing an appropriate treatment is challenging, and clinicians must make a decision on which surgery to perform. We present a case of an elderly patient who presented to our emergency department with gallstone ileus that received a prompt diagnosis and urgent surgical resolution

The Role of Staging Laparoscopy for Gastric Cancer Patients: Current Evidence and Future Perspectives

A significant proportion of patients diagnosed with gastric cancer is discovered with peritoneal metastases at laparotomy. Despite the continuous improvement in the performance of radiological imaging, the preoperative recognition of such an advanced disease is still challenging during the diagnostic work-up, since the sensitivity of CT scans to peritoneal carcinomatosis is not always adequate. Staging laparoscopy offers the chance to significantly increase the rate of promptly diagnosed peritoneal metastases, thus reducing the number of unnecessary laparotomies and modifying the initial treatment strategy of gastric cancer. The aim of this review was to provide a comprehensive summary of the current literature regarding the role of staging laparoscopy in the management of gastric cancer. Indications, techniques, accuracy, advantages, and limitations of staging laparoscopy and peritoneal cytology were discussed. Furthermore, a focus on current evidence regarding the application of artificial intelligence and image-guided surgery in staging laparoscopy was included in order to provide a picture of the future perspectives of this technique and its integration with modern tools in the preoperative management of gastric cancer