Resonance In Hexagonal Ferrites Research Articles

Modulation of MM-Waves by an Acoustically Controlled Monocrystalline Hexagonal Ferrite Resonator

Modulation of mm waves with RF signals can be accomplished using stable non-linear resonance effects in monocrystalline hexagonal ferrite resonators (HFR), characterized by high crystallographic anisotropy. Acoustic oscillations excited in a piezoelectric slab having a good contact with the HFR can be used to control the HFR ferromagnetic resonance frequency. The design ideas of a modulator based on an HFR-piezoelectric slab structure are considered. Some experimental and calculation results are presented.

Electromagnetic modelling of 3D periodic structure containing magnetized or polarized ellipsoids

AbstractCoupling matrix and coupling coefficient concepts are applied to the interaction of an incident plane wave with a regular array of small magnetized or polarized ellipsoids, placed in a homogeneous surrounding medium. In general case, the angle of incidence and polarization of the plane wave upon an array of ellipsoids can be arbitrary. In this model, it is assumed that all the ellipsoids are the same, and the direction of their magnetization is also the same. The direction of magnetization is arbitrary with respect to the direction of the propagation of the incident wave and to the boundary plane between the first medium, where the incident wave comes from, and the array material under study. Any magnetized or polarized ellipsoid is represented as a system of three orthogonal elementary magnetic radiators (EMR) and/or three orthogonal elementary electric radiators (EER). Mutual interactions of individual radiators in the array through the incident plane wave and corresponding scattered electromagnetic fields are taken into account. The electrodynamic characteristics — reflection from the surface of the semi-infinite array (in particular, containing uniaxial hexagonal ferrite resonators), transmission through the array, and absorption are analyzed.

Modulation of millimeter waves by acoustically controlled hexagonal ferrite resonator

To develop millimeter-wave modulators, high-anisotropy uniaxial monocrystalline hexagonal ferrite resonators (HFRs) can be used. One of the ways to modulate the hexagonal ferrite resonator's resonance frequency is to periodically vary the angle between the equilibrium magnetic moment and the external magnetization field. This angular control can be exercised by the mechanical (acoustic) oscillations excited in a piezoelectric slab having a good acoustic contact with the HFR. We consider a quasi-static mathematical model of the uniaxial HFR with the angular control of its resonance frequency. We analyze the amplitudes of harmonics of the modulated millimeter-wave signal, and we derive the optimal orientation of the ferrite crystallographic axis. We suggest some ideas regarding the design of a modulator on the basis of an HFR and a piezoelectric slab, and we present experimental results.

Physical and technical bases of using ferromagnetic resonance in hexagonal ferrites for electromagnetic compatibility problems

Frequency-selective measurement of microwave signal parameters based on application of gyromagnetic converters has proven advantageous for the research of microwave radiation over a wide spectrum (several octaves) in multisignal regime in microwave path and for the solution of a number of electromagnetic compatibility (EMC) problems. The measurement frequency band can be enlarged to millimeter-waves with application of monocrystal hexagonal ferrite resonators (HFR) having high internal magnetic fields. Millimeter-wave field interactions with the HFR having alternating resonance frequency are analyzed. This is useful for millimeter-wave signal modulation and demodulation. The analysis is based on the solution of magnetization vector motion equation of the uniaxial spherical HFR with time-varying bias magnetic field or angle of the HFR orientation (for modulation problem) and with amplitude-modulated microwave signal action (for demodulation problem). The novel principle of the HFR frequency-selective measuring system based on automodulation design is discussed.

Tunable microwave and millimeter-wave band-pass filters

The authors present an overview of tunable microwave and millimeter-wave bandpass filters realized in different technologies. Some general design principles are described. Recent progress in the performance of various tunable filters is reported. The authors survey magnetically tunable filters (ferrimagnetic resonance filters, magnetostatic-wave filters, evanescent waveguide filters, E-plane printed circuit filters), electronically tunable filters, and mechanically tunable filters. The typical performance parameters are summarized. This comparison shown that none of these devices can simultaneously satisfy all requirements for perfect tunable filters. For microwave systems where multioctave tuning is essential, a YIG filter is an obvious choice. In systems where the requirement of high power handling capability combined with low insertion loss, predominates, mechanically tunable filters and magnetically tunable E-plane filters are recommended. If the tuning speed is a crucial requirement, varactor-tuned filters or E-plane filters with ferrite toroids are devices of choice. For millimeter-wave design, the most promising structures are ferrimagnetic resonance filters utilizing hexagonal ferrite resonators or, up to 60 GHz, magnetically tunable E-plane printed circuit filters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of higher-order anisotropy constants on the ferromagnetic resonance in hexaferrites

In this paper the characteristics of the ferromagnetic resonance in hexagonal ferrites are investigated theoretically. It is shown that when the absolute magnitude of the anisotropy constants of second and higher order is comparable to or greater than that of the first-order constant, the angular dependences of the resonant field exhibit stationary directions which do not coincide with the symmetry axes of the crystal. As a result, additional maxima appear on the FMR curves of polycrystalline hexaferrites, which makes it more difficult to determine the anisotropy fields from experiments on polycrystals.

Ferromagnetic resonance in hexagonal ferrites with anisotropic g-factors

Ferromagnetic resonance measurements on the hexagonal ferrite MgY are compared to theoretical predictions of frequency of resonance and linewidth of the Smit-Suhl and Rado models. At fixed frequency, both models give good agreement, but neither model predicts the experimentally observed dependence on frequency or field of the g-tensor component g⊥.