Judith Spiegel

Permittivity Model for Ferromagnetic Nanowired Substrates

This letter presents the influence of ferromagnetic nanowires on permittivity and losses on a so-filled membrane. For this purpose a theoretical permittivity model has been developed by considering geometrical parameters of the substrate such as the porosity of the membrane and the height of the nanowires. It has been validated by microstrip line measurements on a composite substrate filled with cobalt nanowires. The ferromagnetic nanowires enhance the permittivity, but give no further contribution to the losses beyond the ferromagnetic resonance. This is confirmed by measurements on a similar topology including non ferromagnetic copper nanowires.

Differential phase shift in nonreciprocal microstrip lines on magnetic nanowired substrates

Nonreciprocal microstrip lines based on magnetic nanowired substrates were fabricated for the characterization of microwave differential phase shifts. We provide a fully integrated solution for the nonreciprocal edge guided mode, which is achieved by asymmetrically loading the width of the microstrip with nanowires of different heights. An analytical model explaining the microwave nonreciprocal propagation, which takes into account the substrate permittivity and the microstrip memductance, is validated with the experiment.

Microwave Properties of Ferromagnetic Nanowires and Applications to Tunable Devices

Microwave devices as circulators or tunable filters demand nowadays small size and broad bandwidth. Ferromagnetic nanowired membranes are ideal candidates for this purpose. This paper focuses on the dielectric properties of such substrates, as influenced by the ferromagnetic nature of nanowires and their filling factor. Two particular cases are considered: a membrane filled up to its top with nanowires, forming a one-layer substrate, and a membrane filled up to a certain percentage of its height with nanowires, forming a two-layer substrate. The models proposed in this paper for each case take the inductive and gyromagnetic effects in the wires into account. They predict for the one-layer case a magnetodielectric behavior which is tunable by applying an external magnetic field. The effect is no longer visible for the two-layer topology corresponding to microwave circuit applications.

Isolator concept based on ferromagnetic nanowired substrates

Microwave devices demand nowadays small sizes and broad bandwidth. Ferromagnetic nanowired membranes are ideal candidates for this purpose. Planar, tunable and nonreciprocal devices can be designed with them. Therefore we propose an isolator concept based on such a material. Its principle is based on a nonreciprocal microstrip line.

Ferromagnetic material with negative permeability for tunable left-handed devices

Microwave devices as filters or couplers demand nowadays small sizes and broad bandwidth. Because of their unusual characteristics, left-handed materials are an ideal candidate for this demand. This paper proposes a new concept for left- handed materials based on ferromagnetic nanowired substrates, which provides at the same time a planar and tunable solution. The concept is based on an accurate model for the permeability of the nanowired substrate.