  The stability of a piezoelectric structure controlled by a digital vibration
absorber emulating a shunt circuit is investigated in this work. The formalism
of feedback control theory is used to demonstrate that systems with a low
electromechanical coupling are prone to delay-induced instabilities entailed by
the sampling procedure of the digital unit. An explicit relation is derived
between the effective electromechanical coupling factor and the maximum
sampling period guaranteeing a stable controlled system. Since this sampling
period may be impractically small, a simple modification procedure of the
emulated admittance of the shunt circuit is proposed in order to counteract the
effect of delays by anticipation. The theoretical developments are
experimentally validated on a clamped-free piezoelectric beam.
