Excitation of Magnetoelastic Waves in YIG Delay Lines

Abstract

The excitation mechanism based on the propagation of magnetoelastic waves in axially magnetized single-crystal samples of yttrium iron garnet (YIG), of nonellipsoidal geometry, is proposed for microwave delay lines. A qualitative theory is advanced that excitation takes place by electromagnetic energy being coupled to a spin wave through magnetostatic modes, driven at the minimum value of internal dc magnetic field. The theoretical model decomposes the guided wave propagation in a ferrimagnetic slab, between metal plates, into pairs of plane waves, which essentially propagate in an inhomogeneous and anisotropic medium. This theory is supported by experiments in which a YIG rod was precisely translated along the dc field axis, with respect to the coupling antenna. These experiments demonstrate that minimum insertion loss requires that a large transverse rf magnetic field exist at the end face of the rod, that loss increases monotonically when the coupler is moved away from the end face, and that no minimum of the insertion loss occurs when a large transverse field exists in the vicinity of the theoretical turning point.