A lower bound for limiting time delay for closed-loop stability of an arbitrary SISO plant

This correspondence is concerned with the time delay margin for closed-loop stability of a single-input single-output plant with time delay uncertainty. Since no restriction is placed on the stabilizing controller, the limiting value of time delay depends on the plant transfer function only. The approach, using a modified form of classical Nevanlinna-Pick interpolation theory, provides a lower bound for the limiting time delay given the plant open-loop poles and zeros only