Antonio Carlos da Cunha Migliano

CERAMIC PROCESSING ROUTE AND CHARACTERIZATION OF A NI-ZN FERRITE FOR APPLICATION IN A PULSED-CURRENT MONITOR

Pulsed-current sensors require transducers constituted of magnetic materials with high magnetic permeability in a frequency range compatible with the period and the frequency of the current pulse. The use of ferrites in this application has the advantage of low cost and low losses in high frequencies. The aim of this work is to present a procedure for selection of the ceramic processing route of Ni-Zn ferrite for application in a pulsed-current sensor. The ferrite samples were prepared under different processing parameters and characterized in terms of microstructure, chemical analysis, complex magnetic permeability, and magnetic hysteresis. The chosen processing route included high energy milling of the pre-sintered powder, its disaggregation before sample forming, and sintering of the samples

EVALUATION OF A Ni-Zn FERRITE FOR USE IN TEMPERATURE SENSORS

This work investigates the variation of the real part of the complex magnetic permeability of a Ni-Zn ferrite for application to temperature sensors. Ferrite samples were fabricated by means of the conventional ceramic method. Zinc, nickel and iron oxides were used as raw materials. The samples were sintered at 1200, 1300, and 1400 - C. The complex magnetic permeability of the samples was measured at temperatures ranging from i40 - C to +50 - C. The complex magnetic permeability of the samples was analyzed in the 100kHz{100MHz frequency range, and the temperature sensitivity of the magnetic permeability (@ 0 =@T) was analyzed at 100kHz. The magnetic permeability variation of the ferrite permits to use it as a temperature transducer with a maximum temperature sensitivity of about i119 - C i1 . The highest magnitudes of temperature sensitivity occurred between +30 - C and +50 - C. Therefore, the ferrite could be sensitive enough to allow temperature measurements at the human body temperature level. The results indicate that the

Finite element analysis of impedance of an electron beam current monitor

A current pulse monitor was designed and built to allow a nonintercepting measurement of the intensity and shape of an AC or pulsed current. To perform the impedance analysis of the device design, the magnetodynamic model coupled with the circuit equations was applied using the sinusoidal permanent finite-element method. The device impedance measurements are presented and compared with those obtained from the computer code simulations.

Microstructure and Complex Magnetic Permeability of Ni0.3Zn0.7Fe2O4 Ferrite

Ni-Zn ferrites are magnetic ceramics that are widely used in electric and electronic components. Among Ni1-xZnxFe2O4 ferrites, Ni0.3Zn0.7Fe2O4 is known to be the one of highest magnetic permeability in lower frequencies. This work is divided into two parts: the first part deals with the influence of sintering temperature and forming conditions on the microstructure of Ni0.3Zn0.7Fe2O4 ferrite. The second part deals with the influence of sintering temperature and environmental variations of temperature on the complex magnetic permeability of such ferrite. The ferrite studied in this work was fabricated by means of the conventional ceramic method. Complex magnetic permeability between 100 kHz – 100 MHz is discussed in relation to sintering temperature. The influence of environmental variations in temperature (-40 oC to +50 oC) on the complex magnetic permeability of the ferrite sintered at 1300 oC is discussed.

Polymer optical fibers for Terahertz: Low loss propagation and high evanescent field

In this paper, there are three different polymer optical fibers in THz range were investigated: a microwire, a tube and a porous fiber. The effective index of fundamental mode and the power fraction distribution in the material, the air cladding and within the air holes regions were detailed studied when the geometrical parameters were changed. The results show that all the structures have large power fraction being transmitted in air, around 60%, where absorption losses are greatly reduced, improving their application as evanescent field sensors.

Refractive index sensor based on terahertz multimode interference fiber device

A fiber-optic refractive index sensor based on terahertz multimode interference in a singlemode-multimode-singlemode fiber structure (SMS) is numerically demonstrated for the first time in the literature. The shift of spectral transmission is investigated as function of external refractive index. Moreover, the coupling efficiency between optical modes at singlemode and multimode sections are determined. The proposed sensor reaches average sensitivity of ~5 GHz/RIU (refractive index unit) over a refractive index range of 1.4-1.5.

Optical and Dielectric Properties of Manganese Cobalt Ferrite at Terahertz Frequencies

We present here the optical constants of Manganese Cobalt ferrites from 0.2 to 0.9 THz. Ferrites may find applications in THz communication systems, but there is a lack of information about them at THz frequencies.

Accuracy of GRL calibration considering time domain gating for the calculation of permittivity parameter in free space technique

An experimental method for increasing the accuracy of GRL calibration is presented. This paper shows how to make correct time gating, achieving better results of GRL calibrations for calculating permittivity parameters in free space technique.

Passive cancellation analysis of cylinder using Finite Difference Time Domain method

Radar Cross Section (RCS) is a technique to identify objects through electromagnetic scattering of an incident wave. Consequently, there are techniques to reduce RCS such as passive cancelation method. This technique was applied to a metallic cylinder where a dielectric load can be identified through a gap in the middle of cylinder. In this paper we present comparisons between experimental results and simulation using Finite Difference Time Domain (FDTD) method. RCS results in the frequency domain were analyzed from 0.8 to 2 GHz using three different sizes of gap and two different materials as load. The frequency where RCS reduction occurs experimentally is close to simulated ones. Experimental results showed a disturbance due to mechanical misalignment that was analyzed. Tridimensional RCS simulations at 1 GHz for PVC and Teflon loads are presented as well.

Effects of the axial magnetic field component on the electron trajectory in the wiggler section

A section of a wiggler with SmCo/sub 5/ magnets was designed to be utilized in an infrared free-electron laser (IRFEL). The choice of low-cost small magnets resulted in a small gap in the wiggler (/spl les/10.0 mm). This gap size accentuated the edge effects, thus making the profile of the magnetic field more susceptible to distortion. The solution of the magnetic field component was obtained from finite-element computer codes and measurements of the magnetic field distribution in the inner region of the wiggler were performed. Effects of the axial magnetic field component on the electron beam trajectories were studied using a single-particle model neglecting collective effects.