Patrick Queffelec

Pressure Dependence of the Frequency Permeability Spectra of Soft Ferrite Composite Materials: A Method of Measuring the Natural Ferromagnetic Resonance Frequency

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.

Driven-Voltage Permeability Variation Measurements of Bilayered Magnetostrictive/Piezoelectric Materials &for Tunable Microwave Applications

The complex permeability variation measurements at microwave frequencies of a magnetostrictive/piezoelectric bilayer under different values of a dc electric field are reported. A 25% variation of the initial permeability is achieved under a 1.5times106 V/m static electric field

Broadband permeability measurement method for ferrites at any magnetization state: direct problem

A data processing program based on a full-wave electromagnetic (EM) analysis of a non-reciprocal transmission line partially filled with a ferrite sample is presented. A predictive permeability tensor model is introduced in the Maxwell equations to allow the program to work at any magnetization state. The dispersion diagram for the first significant modes inside the ferrite loaded region of the line is obtained. The presence of magnetostatic modes generated by magnetized ferrite inside the line is verified. Using a mode matching technique, the theoretical scattering parameters (S-parameters) of the non-reciprocal transmission line are calculated. The analysis is validated by the comparison between the calculated S-parameters with those obtained with a FEM based EM simulator and the measurements at limit cases.

Modeling non-saturated ferrite-based devices: Application to twin toroid ferrite phase shifters

This article describes a new set of tools developed to improve the conception and modeling of non-saturated ferrite-based devices such as twin toroid phase shifters. These new simulation tools benefit from a generalized permeability tensor model able to describe the permeability tensor of a ferrite sample whatever its magnetization state. This model is coupled to a homemade 3D multi-scale magnetostatic analysis program, which describes the evolution of the magnetization through the definition of a hysteresis loop in every mesh cell. These computed spectra are then integrated into 3D electromagnetic simulation software that retains the spatial variations of the ferrite properties by using freshly developed macro programming functions. This new approach allows the designers to accurately model complex ferrite devices such as twin toroid phase shifters. In particular, we demonstrated a good agreement between simulated and measured phase shifts as a function of applied current values with a predicted maximum ...