Acoustic buffeting by infrasound in a low vibration facility

Abstract

Measurement instruments and fabrication tools with spatial resolution on the atomic scale require facilities that mitigate the impact of vibration sources in the environment. One approach to protection from vibration in a building's foundation is to place the instrument on a massive inertia block, supported on pneumatic isolators. This opens the questions of whether or not a massive floating block is susceptible to acoustic forces, and how to mitigate the effects of any such acoustic buffeting. Here this is investigated with quantitative measurements of vibrations and sound pressure, together with finite element modeling. It is shown that a particular concern, even in a facility with multiple acoustic enclosures, is the excitation of the lowest fundamental acoustic modes of the room by infrasound in the low tens of Hz range, and the efficient coupling of the fundamental room modes to a large inertia block centered in the room. Published by AIP Publishing. [http://dx

Development of a scanning tunneling microscope for variable temperature electron spin resonance

“…Given that the lowest fundamental acoustic mode is at 11.16 Hz in the 5.69 m × 7.68 m × 6.28 m size room, the feature appearing at around 12 Hz in the noise spectrum [Fig. 1(c), QNS block] is presumably the result of acoustic stimulation of the concrete block motion 24 . The noise level we attained in the overall fre-quency range relevant to STM performance is comparable to or even better than noise levels measured in the world's leading precision laboratories [Fig.…”

Design and characterization of a low-vibration laboratory with cylindrical inertia block geometry

“…A more controlled solution employs one or more layers of massive inertia block(s), supported by pneumatic isolators or active dampers that act as soft springs to achieve a low rolloff frequency for vertical movement. [12][13][14][15][16][17][18][19][20][21] However, either separate base slabs or floating blocks may have flexural modes of their own that lie within the frequency range of typical building excitations. 12,15,22 Several researchers have noted that the relatively small mass of these blocks, compared to the larger building foundation, can increase their susceptibility to building vibrations, thus inadvertently magnifying noise transmission to the STM in some cases.…”