The primary purpose of this study is to evaluate and better understand the isolation properties of semiactive suspensions. Specifically, this study will answer the question regarding why semiactive dampers are able to isolate at frequencies well below; those for passive dampers, even though they do not add any energy to the system. A single suspension model is used to derive and analytically evaluate the transmissibility properties of passive and semiactive dampers. The results show that for semiactive dampers, the frequency range of isolation and the transmissibility amplitude are functions of xi, the damping ratio. In contrast, the isolation frequency range for passive dampers is completely independent of xi. Furthermore, the results show that for sufficiently large xi, semiactive dampers are able to provide isolation at all frequencies. This feature is useful for many applications, particularly for sensitive machinery that cannot tolerate any overshoot in power-up or power-down, and yet must have good isolation during normal operation. Passive suspensions offer only one of the two aspects, whereas semiactive suspensions offer both.
