Figure 2: Schematic diagram illustrating frequency inversion by the dynamic magnonic crystal.
From: All-linear time reversal by a dynamic artificial crystal
The diagonal lines (green and red) represent the spin-wave dispersion curve. Incident signal waves have positive wave vectors (green section) and those reflected by the DMC have negative wave vectors (red section). These two groups of waves are counter propagating. Black dots mark the reference frequency fa lying in the centre of the bandgap and corresponding to the Bragg wave vectors ±ka=±π/a. The green open circle and square illustrate two spectral components of an incident signal waveform. The spatially periodic magnetic modulation of the waveguide's magnetic bias field brought about by the application of the current pulse to the DMC meander structure couples these components to corresponding components of a reflected waveform (red open circle and square). The difference between the wave vectors of the signal and reflected waves is fixed by the lattice constant a of the DMC so that the k-spectrum of the reflected waveform is uniformly shifted to the left by Δk=2π/a=2ka (lower panel). This uniform shift in k-space results in spectral inversion in the frequency domain (right panel). The reference frequency fa (black dots) is not shifted and provides the axis of inversion.
