The objective of this paper is to improve a semi-active control of structural vibrations, which is Synchronised Switch Damping on Inductor Maximum. The improvement is attained by adding a system to estimate the structure modal displacement. A model of smart structure shunted to resonant circuit is used and tested with Matlab (TM) environment and the performance of the new strategy based on Lenear Quadratic Guaussian and Neuro-Fuzzy observer are presented and compared with that one based on Proportional Integral Derivative observer. Results shows the new technique effectiveness when conventional one reaches its limits in the wide bande frequency case.