Tuning limitations of the voltage-controlled planar microwave ferrite resonator

A microwave ferrite microstrip resonator with 15% tunability has been approached by application of mechanical strain alone. The frequency tuning arises from alignment control of the unpolarized pattern of magnetic domains by application of uniaxial stress. A variable stress can be produced by a variable voltage applied to a piezoelectric actuator, without a current-controlled magnetizing circuit. For guidance to performance design, the conditions required for stress-tuning of randomly oriented grains with cubic anisotropy constant K1 are analyzed. To account for magnetoelastic effects, the polycrystalline magnetostriction constant λ is the weighted average over the principal cubic symmetry axes. The analyses produce three results: (1) a relation for the tuning range that reflects a dependence on stress σ instead of magnetic field H, with the key materials parameter becoming λ/K1; (2) the stress dominating condition in the ferrite is σλ/K1 > 2/3 for the magnetic vectors along the axis of σ; and (3) for vol...