To counteract building vibration, active isolation systems can achieve a very low remaining vibration level, especially for low frequency disturbances without the resonance behavior of a passive isolation system.

Today’s key technologies require the best suited environmental conditions, such as cleanroom laboratories. In particular, the production, manipulation, and testing of very small items is a major task in a variety of industrial applications. In the semiconductor industry, wafer inspection systems are used to scan the wafer structure with a resolution of several nanometers. In the field of biotechnology, cell manipulation has to be carried out with a precision on the scale of microns. Material scientists investigate the molecular structure of new materials by using scanning electron microscopes (SEM). All these applications are limited in their performance by the presence of mechanical vibrations.

Unfortunately, mechanical vibrations are a physical phenomenon which can never be eliminated. These vibrations are generated by natural sources, e.g., wind and seismic activities, and artificial sources, e.g., traffic and plants. They travel through different paths from the source to the location of the sensitive equipment.

The technical solution for this problem is vibration isolation. The sensitive device is connected to an isolated stage which has an elastic link to the structural environment. This setup creates a spring-mass-system with a typical low pass characteristic. For excitation frequencies above the eigenfrequency of the spring-mass system, the remaining vibration amplitude on the isolated stage is smaller than the excitation amplitude.

The principle of vibration isolation by using a spring-mass-system is well known and successfully applied to many different sensitive devices. Nevertheless, this passive isolation approach has a major drawback which will be discussed in the following sections.