Extremely low-vibration experiments with resolutions nanometer range supported on air tables may also require a low-noise environment

Abstract

The paper reports key results from an extensive diagnostic study examining a room's vibration and acoustic noise environments and their correlation to measurement noise. Vibrations of unknown origin were contaminating research being performed on highly vibration-sensitive apparatus in the basement of a recently completed engineering building. The research involved extensive single‐molecule microscopy requiring resolutions down to 1 nm carried out on an optical table supported on pneumatic legs. Researchers reported that the experimental noise was reported to be of random amplitude less than 40 nm. The problem did not appear to correlate with obvious building or personnel activities. The design vibration and noise criteria for the new space had been VC-E and NC-40, respectively. At the time of the study, the ambient floor vibrations were several classes better; however, the acoustic environment was slightly worse. FRF correlation was calculated between combinations of the tabletop and floor vibrations and airborne sound. The best correlation was between tabletop vibration and airborne sound. The supply air was a significant part of the problem, but the ceiling offered very little attenuation from above. Some of the sound was being generated above the ceiling by HVAC components other than the supply air.