広帯域動吸振器を使った走査型電子顕微鏡の騒音像ノイズの低減

概要

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This paper addresses Scanning Electron Microscope (SEM). In detail, the image noise caused by the acoustic noise disturbs observation for correct shape of the specimen. Thus, SEM be less influenced by the acoustic noise is expected. This paper approaches to this image noise problem from the damping of the vibration of the base plate. Firstly, the transmission path of the vibrations of the base plate excited by acoustic noise, and the mode shapes of the plate, are explained. Secondary, in order to restrict these vibrations, a tuned mass damper using viscoelastic materials is designed. Using the effect of the shape of the viscoelastic material, the natural frequency of the damper was tuned to lower frequency by dividing the width of the material without decreasing the area of the material. Moreover, the damping factor showed less value when the width of the material was wider than certain value. Thus, it is important to set the ratio of the width and thickness of the material smaller than certain value for keeping the damping factor stable and for wider frequency range of the vibration restriction. Finally, the tuned damper is assembled to SEM, and remarkable restriction of the acceleration on the base plate from 250Hz to 1.3kHz, and remarkable image noise reductions under the acoustic noise excitation on 315 and 400Hz band with third octave band filtered pink noise are shown.
公益社団法人精密工学会の論文
2008-02-05