The ideal of controlling the vibrations of a structure by using variable stiffness members has been around for over fifteen years. Two types of mechanical springs, Type I and II, have been devised with control laws to reduce the dynamic response of structures due to disturbances. By comparing the mechanical springs and their control laws to the novel real-time piezoceramic shunt switching techniques, it is clear that piezoceramic actuators can act similar to Type I and II mechanical springs. In this paper, piezoceramic actuators are used with three different shunt circuits (capacitance ladder, switching ground circuit, and switching resistor/inductor circuit) and are compared to their mechanical spring counterparts. A new type of spring, Type III, is introduced along with a new semi-active multi-modal control scheme for piezoceramic actuators. The new multi-modal control technique is used on a simple six degree of freedom numerical example.

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