An improved two-port magnetoelastic delay line

A new form of linearly dispersive microwave delay line is described, in which fine-wire transducers are mounted directly inside a magnetically saturated rod of yttrium iron garnet (YIG), through small diameter holes laser drilled in the rod. The delay line operates by utilizing the magnetoelastic interaction between spin waves and elastic waves with frequency dispersion controlled by a special nonlinear axial magnetic field profile synthesized by an appropriate pole piece geometry. Principal features include: physical separation between the input and output signals; longer delays than in the traditional 'single ended' delay line becuse the waves spend a longer time in the elastic domain; no acoustic reflections at the ends of the rod and good coupling between the antennas and the materials. Measurements made on the first designed YIG delay line of this type are reported. Results agree with theoretical predictions. It has been possible to delay a 10 ns pulse of 1200 ns over the range 3.2-3.4 GHz with an insertion loss of 31 dB.