Distributed active vibration absorbers

Another space related topic is the reduction of noise impacts on pay-loads through active noise control using technologies such as an acoustic foam with embedded PVDF material, distributed active vibration absorbers (DAVA) made from acoustic foam hnked to a metallic plate and in a latest version even added by a very small electrodjmamic shaker that allows to cover lower frequencies [103]. This sandwich of acoustic foam, PVDF and electrodynamic shakers is then used as an active coating on the fairings of space vehicles. 

O Regan, S.D. Burkewitz, B. Fuller, C.R. Lane, S. and Johnson, M. Payload noise suppression using distributed active vibration absorbers. Proc. SPIE Vol. 4698 (2002) pp. 150-159... 

Adaptronic solutions like active mounts, adaptive vibration absorbers, or distributed in-plane actuators can optimize these structural djmamic and vibroacoustic characteristics [149]. Typical target functions are the active control of introduction and transfer of disturbances and/or damping of elastic modes. Basically, three different conceptual approaches can be considered ... 

In laser measurements on hydrogen halides, the system under investigation is itself all, or part, of the active laser medium. Similar experiments have not yet been made on other molecules. However, in related experiments on CO, in the author s laboratory [242,432] and elsewhere [433], a CO cw laser has been used to probe the vibrational distributions in a reaction system outside the optical cavity that may act as an amplifier or absorber of lines from the laser. Time-resolved observations can be made for as long as one chooses after the reaction is initiated. If tunable infrared lasers become readily available this technique is likely to be applied more widely. 

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