Real-time monitoring of structural vibration using spectral-domain optical coherence tomography

Abstract

We report in this paper the development of a spectral-domain optical coherence vibration tomography (OCVT) using a broadband CCD-based spectrometer and a short-coherence white light source. We demonstrate that both the vibration amplitude and frequency can be quantified, in the frequency range 0–250 Hz, with an axial resolution of 1 μm. Furthermore, the inner structure (layer thickness) of a vibrating sample can also be quantified simultaneously. The developed OCVT is non-contact and noninvasive in nature, thus is ideal for real time and in situ monitoring of low-frequency micro-vibrations that have critical impacts on many high-precision manufacturing and engineering processes

Enhanced optical coherence vibration tomography for subnanoscale-displacement-resolution calibration of piezoelectric actuators

“…Therefore, the results of FFT of the measured spectral interferogram must be corrected and enhanced for higher precision. In our present work, the Hanning window was used in the FFT of a measured spectral interferogram, and then an energy centroid discrete spectrum correction method [20] was used to precisely determine the signal parameters, such as frequency, amplitude, etc., thereby enhancing the vibration amplitude measurement with a subnanoscale displacement resolution of better than 0.05 nm, which is much higher than those of our OCVT [11] and 2DOCVT [18] systems reported previously. The detailed theory of the energy centroid discrete spectrum correction method can be found in Ref [21].…”

“…Therefore, the vibration amplitude measured by the previously reported OCVT system [11] is not a perfect result. Generally, applying windowing functions to the measured spectral interferogram is a common method to minimize the effect of leakage.…”

“…For a vibrating sample, the spectral interferogram of the interferometer of an optical coherence tomography system can be expressed as [11] …”

“…where  is the wavelength of light in air, ) and the depth profile of the sample [11]. We previously reported an OCVT system by which the layer thickness of the vibrating structures can be characterized.…”

“…Targowski et al [10] used OCT to track deformations in paintings on canvas caused by periodic humidity changes. Recently, an optical coherence vibration tomography (OCVT) system was reported, by which structural vibration monitoring and inner structure characterization can be characterized simultaneously [11]. Both the vibration amplitude and frequency were demonstrated to be quantified with an axial resolution of 1 m; therefore, this system cannot be used for nanoscale dynamic characterization of PZT actuators.…”