Magnetoelastic YIG Delay Lines with Linear Dispersion

Abstract

The internal magnetic field in YIG cones and pyramids has been calculated. With a ratio of the height to the base diameter between 0.7 and 1, constant slopes of the axial fields and hence linear dispersion curves for the magnetoelastic echoes are obtained. The useful frequency range is estimated in terms of the focusing condition for spin waves which requires H(off axis) > H(on axis). Experimentally a nearly linear dispersion curve was obtained with a cone of 4.5-mm height and equal base diameter over a frequency range from 1 to 2 GHz; the dispersion rate was 1.7 nsec/MHz. When the turning surface approaches the region in the crystal where the focusing condition is violated, the echoes are cut off. Measured cutoff lengths and demagnetizing fields agree well with calculations. Similar results have been obtained for pyramids and truncated cones.