Apparent nonlinear effect of the microscope on the laser Doppler vibrometer

Hartono Sumali; Matthew S. Allen

doi:10.1117/12.803165

17 June 2008 Apparent nonlinear effect of the microscope on the laser Doppler vibrometer

Hartono Sumali, Matthew S. Allen

Proceedings Volume 7098, Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications; 709817 (2008) https://doi.org/10.1117/12.803165
Event: Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 2008, Ancona, Italy

Abstract

One powerful method for measuring the motion of microelectromechanical systems (MEMS) relies on a Laser Doppler Vibrometer (LDV) focused through an optical microscope. Recent data taken under a very simple and common condition demonstrate that the velocity signal produced by the LDV with an optical microscope may be different from the velocity signal produced by the LDV without a microscope. This is especially important if one wishes to estimate acceleration by differentiating velocity. In this study, the time derivatives of LDV signals are compared against the signal from an accelerometer when the LDV is focused through an optical microscope and without the microscope system. The signal from the LDV without the microscope is almost identical to the accelerometer signal. In contrast, the signal from the LDV with the microscope exhibits a nonlinear relationship with the accelerometer signal. Both the LDV and the accelerometer were measuring a sinusoidal velocity generated by an electromechanical shaker. The Fourier transform of the acceleration from the LDV with the microscope shows a multitude of high harmonics of the excitation frequency, which have much higher amplitudes than the harmonics present in the accelerometer signal. Without the microscope, the LDV gives a much less distorted sinusoidal signal, even after time differentiation. The distortion of the signal from the LDV is periodic, with the same period as the sinusoidal drive signal. The largest distortion occurs near points of maximum negative acceleration, corresponding to the positive displacement peak of the sinusoidal oscillation. Because the measured oscillation is out of plane, pseudo-vibrations caused by speckle noise do not explain the distortion. Instead, the distortion appears to be caused by the optics of the microscope.

Citation Download Citation

Hartono Sumali and Matthew S. Allen "Apparent nonlinear effect of the microscope on the laser Doppler vibrometer", Proc. SPIE 7098, Eighth International Conference on Vibration Measurements by Laser Techniques: Advances and Applications, 709817 (17 June 2008); https://doi.org/10.1117/12.803165

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available