Estimation of thermal noise by a direct measurement of the mechanical conductance

We present a new method for estimating the thermal noise at off-resonant fr equencies in a mechanical system. Zn this method, the mechanical conductanc e is directly measured at anti-resonant frequencies, and then the fluctuati on-dissipation theorem is applied to the measured conductance in order to e valuate the thermal noise. To confirm the validity of this method, we demon strated a direct measurement of the mechanical conductance of a 2-mode osci llator at an anti-resonant frequency. The measured conductance was in good agreement with the value calculated by the normal-mode expansion. (C) 2000 Elsevier Science B.V. All rights reserved.