Low-loss Ni-Zn porous ferrite ceramics have been obtained (porosity close to 40%) after appropriate heat treatment and shaping of nanosized powders. The key point in this process is a moderate ...reaction sintering that promotes desired value of porosity. Measured complex permeabilities and permittivities in the 10 7 Hz -10 10 Hz frequency range are presented. The developed materials show almost constant refractive index value n close to 5 up to 900 MHz. The sum of the magnetic and dielectric losses shows moderate values up to a frequency value f, unusual for spinel ferrites: tanδ μ +tanδ ε <; 0.083 at f=600 MHz. Their efficiency for miniaturization and performances improvement of several new antennas for Digital Video Broadcasting Handheld (DVB-H) devices (frequency ranging: 470-862 MHz) are presented. High miniaturizations (about 40% to 60% when compared to not loaded antenna) are obtained. Low loss, wide bandwidth and good radiation efficiency are measured. Antennas performances are enhanced. A new antenna is also presented. Its dimensions are very small and it covers the entire DVB-H band. Suitability of Ni-Zn porous ferrites ceramics for antenna miniaturization for DVB-H applications is demonstrated.
3D printing of microwave absorbers gave rise to new shape optimization possibilities. However, new printable materials dedicated to this application have to be developed. In this study, an iron flake ...polymer composite was elaborated and characterized. Scanning Electron Microscopy observations demonstrated that iron flakes particles are naturally aligned along the flow direction in the nozzle without applied magnetic field during the 3D printing process. Magnetic anisotropy was demonstrated with both Vibrating Sample Magnetometer and microwave measurements. Indeed, at 5.4 GHz, a ratio of 1.67 between parallel and perpendicular susceptibility was observed. These measurements demonstrated a self-induced magnetic anisotropy that can be used to control the angular robustness of free-space microwave absorbers. Simulations show that an induced planar anisotropy allows improving a better stability of absorption at oblique incidence compared to an isotropic absorber.
This study provides a behavioural analysis of the particular demagnetizing effects displayed by disordered heterostructures close to a particular value (
C
p) of their magnetic load
C. The emphasis ...is put on the convergence of evidences, got from several independent ways (experimental, analytical and numerical), of a percolative phenomenon in random distributions of magnetic particles that rules the sharp variations of the inner and outer demagnetizing effects at concentrations close to
C
p. When
C<
C
p, magnetic gaps, which originate from the magnetic dilution, may cause a cut-off of the magnetic flux paths in the composite medium, leading to inner demagnetizing effects only. When
C>
C
p, the delocalization of the magnetic poles leads the outer demagnetizing factor of the sample to switch from zero to its maximum value. The analytical approach of this phenomenon is based on an effective medium theory. It leads to a description of the interactions between magnetic inclusions that show a deep similarity with the main notions the reciprocity principle calls for.
Nano crystalline Ni–Zn ferrites of composition Ni0.5Zn0.5Fe2O4have been prepared by a chemical co-precipitation method. The powdered samples were sintered at a temperature of 800°C and 900°C for ...three hours. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to study their structural and morphological changes. The enhanced magnetic properties were investigated by using a Vibrating Sample Magnetometer (VSM). The saturation magnetization was found to increase from 73.88 to 89.50emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1GHz. These results have been explained on the basis of various models and theories.
Experimental studies on the complex susceptibility of soft magnetic composite materials (magnetostrictive Ni-Zn and Ni-Zn-Co spinels) in their region of ferrimagnetic resonance (FMR) show that the ...FMR is an increasing function of the applied pressure. It is shown that powders could advantageously replace their sintered materials counterpart to measure without any ambiguity the natural ferrimagnetic resonance (NFMR) frequencies of bulk materials. It is also shown that such soft ferrite composites can be realized in order to shift FMR to higher values, and to obtain low magnetic losses up to 900 MHz. High frequencies applications can be envisaged.
IMPORTANCE: The optimal approach to the use of venoarterial extracorporeal membrane oxygenation (ECMO) during cardiogenic shock is uncertain. OBJECTIVE: To determine whether early use of moderate ...hypothermia (33-34 °C) compared with strict normothermia (36-37 °C) improves mortality in patients with cardiogenic shock receiving venoarterial ECMO. DESIGN, SETTING, AND PARTICIPANTS: Randomized clinical trial of patients (who were eligible if they had been endotracheally intubated and were receiving venoarterial ECMO for cardiogenic shock for <6 hours) conducted in the intensive care units at 20 French cardiac shock care centers between October 2016 and July 2019. Of 786 eligible patients, 374 were randomized. Final follow-up occurred in November 2019. INTERVENTIONS: Early moderate hypothermia (33-34 °C; n = 168) for 24 hours or strict normothermia (36-37 °C; n = 166). MAIN OUTCOMES AND MEASURES: The primary outcome was mortality at 30 days. There were 31 secondary outcomes including mortality at days 7, 60, and 180; a composite outcome of death, heart transplant, escalation to left ventricular assist device implantation, or stroke at days 30, 60, and 180; and days without requiring a ventilator or kidney replacement therapy at days 30, 60, and 180. Adverse events included rates of severe bleeding, sepsis, and number of units of packed red blood cells transfused during venoarterial ECMO. RESULTS: Among the 374 patients who were randomized, 334 completed the trial (mean age, 58 SD, 12 years; 24% women) and were included in the primary analysis. At 30 days, 71 patients (42%) in the moderate hypothermia group had died vs 84 patients (51%) in the normothermia group (adjusted odds ratio, 0.71 95% CI, 0.45 to 1.13, P = .15; risk difference, −8.3% 95% CI, −16.3% to −0.3%). For the composite outcome of death, heart transplant, escalation to left ventricular assist device implantation, or stroke at day 30, the adjusted odds ratio was 0.57 (95% CI, 0.36 to 0.90; P = .02) for the moderate hypothermia group compared with the normothermia group and the risk difference was −12.7% (95% CI, −22.3% to −3.2%). Of the 31 secondary outcomes, 30 were inconclusive. The incidence of moderate or severe bleeding was 41% in the moderate hypothermia group vs 42% in the normothermia group. The incidence of infections was 52% in both groups. The incidence of bacteremia was 20% in the moderate hypothermia group vs 30% in the normothermia group. CONCLUSIONS AND RELEVANCE: In this randomized clinical trial involving patients with refractory cardiogenic shock treated with venoarterial ECMO, early application of moderate hypothermia for 24 hours did not significantly increase survival compared with normothermia. However, because the 95% CI was wide and included a potentially important effect size, these findings should be considered inconclusive. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02754193
M-type hexagonal barium ferrites Ba(M x Ti x )Fe 12−2x O 19 (M=Co or Ti, x=0-0.5) are synthesized by chemical topotactical reaction. Both randomly oriented and self-polarized samples are prepared. ...Experimental values of the anisotropy fields, first and second anisotropy constants, and remanent magnetizations are extracted by combining hysteresis loops and microwave measurements. A salient result of this study is that, comparing with K1, K2 cannot be disregarded for these co-doped BaM hexaferrites, even at low doping levels. Results show that the compositions Ba(CoxTix)Fe12−2xO19 are more suitable for microwave applications that operate at frequencies between 30GHz and 40GHz.
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