Microwave-induced electromigration in multicomponent metallic alloys
The crystallization of amorphous FeCoCuZrAlSiB alloy ribbons during microwave heating was investigated in situ using time-resolved X-ray powder diffraction. The formation of the nanocrystalline α-(Fe,Co)(SiAl) phase during the primary crystallization stage is followed by the crystallization of the residual glassy matrix. Scanning electron microscopy analysis after microwave exposure reveals the formation of nanosized hillocks evenly distributed over the ribbon surfaces. Local chemical composition analysis by energy-dispersive spectroscopy shows that the surface clusters are enriched in Cu and Al. The occurrence of this typical electromigration effect imposes a strong restriction on the dura…
A new empirical method for extracting unloaded resonant frequencies from microwave resonant cavities
Equivalent circuits traditionally used to model resonators and coupling networks in the vicinity of a resonance provide values of unloaded resonant frequencies which usually do not agree with experimental results. A new empirical method for the extraction of influence of coupling networks on resonant cavities is presented. The characterization of coupling structures is performed directly from measurements without the need of obtaining the electromagnetic fields inside the cavity, which is very interesting from a practical point of view. Results are validated with simulations and experimental measurements. The accuracy of some cavity applications, such as dielectric characterization techniqu…
Frequency Deviation Due to a Sample Insertion Hole in a Cylindrical Cavity by Circuital Analysis
One of the most widely used techniques for dielectric material characterization is the partially filled circular cavity. The exact analysis of this structure is well known in the bibliography. But in practice when the measured material is introduced through a circular pipe below its cut off frequency a problem arises. Traditionally the tube effect is neglected, but then some errors appear, whose magnitude depends on the material properties and the cavity and tube dimensions. In some cases, the errors introduced are noticeable and the tube effect should not be neglected. Some authors have tried to evaluate in a simple way this effect, but their equations are valid only in a restricted range …
Noninvasive monitoring of polymer curing reactions by dielectrometry
A microwave sensor system for the noninvasive monitoring of the curing process of a thermoset material placed inside a metallic mold is described. The microwave sensor is designed as an open-ended coaxial resonator with a curved surface adapted to the mold inner shape. The analysis of the microwave resonator comprises a recently developed method for deembedding the effect of coupling network in overcoupled resonators, so the range of permitted measurements encompass both low and high dielectric losses of polymeric materials. Results show that noninvasive, continuous monitoring of the microwave dielectric properties of the thermoset material can be performed in real time, allowing one to che…
In situ synchrotron radiation monitoring of phase transitions during microwave heating of Al–Cu–Fe alloys
The effect of rapid microwave heating has so far been evaluated mainly by comparing the state of materials before and after microwave exposure. Yet, further progress critically depends on the ability to follow the evolution of materials during ultrafast heating in real time. We describe the first in situ time-resolved monitoring of solid-state phase transitions during microwave heating of metallic powders using wide-angle synchrotron radiation diffraction. Single-phase Al–Cu–Fe quasicrystal powders were obtained by microwave heating of nanocrystalline alloy precursors at 650 °C in <20 s.
Application of the ADR method for the evaluation of the scattering matrix of an open ended coaxial
The use of ADR method for locating poles near the real axis is proposed when the scattering matrix for an open ended coaxial is analysed radiating over a multilayer structure ended in a perfect electrical wall. So a better and faster integral evaluation is made once the subintegral function behaviour is known.