Real-time monitoring of vibration fringe patterns by optical reconstruction of digital holograms: mode beating detection.
ABSTRACT A new technique capable of monitoring two-dimensional vibration fringe patterns in real-time is presented. It is based on optical reconstructing of time-averaged digital holograms. Recording of the holograms is realized in a quasi-Fourier off-axis setup whilst reconstructing in an extended Fourier transform setup capable of spatial filtering of the hologram reconstructions. The effectiveness of the proposed device, tested on a silicon wafer, was verified by performing operations such as monitoring of vibration modes, adjusting the hologram recording parameters, or searching for resonant frequencies. Additionally, mode beating between two distant vibration frequencies is observed and reported. The proposed technique is suitable for various scientific and industrial applications.
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ABSTRACT: Recording of digital holograms of a weak signal [0.44 counts per second (cps)] hidden below the detector’s noise (21 cps) is investigated by employing the high dynamic range of a photon-counting detector. Recording conditions are discussed in terms of the most important holographic measures, namely, the fringe visibility (or contrast) and signal-to-noise ratio (SNR), and in relation to the main holographic parameters. Theoretically evaluated curves are tested by recording holograms for a wide range of the parameter values. We found that (i) the optimum set of holographic parameters can be determined for a harsh signal conditions, (ii) increasing the visibility does not necessarily improve the more important SNR, and (iii) in cases of nearly constant visibility, the SNR clearly reveals differences in the quality of holographic recordings.Optics Letters 09/2014; 39(17). · 3.39 Impact Factor
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ABSTRACT: The aim of this study was to (i) obtain the force-related interferometric patterns of loaded dental implant-abutment assemblies differing in diameter and brand using digital holographic interferometry (DHI) and (ii) determine the influence of implant diameter on the extent of load-induced implant deformation by quantifying and comparing the obtained interferometric data. Experiments included five implant brands (Ankylos, Astra Tech, blueSKY, MIS and Straumann), each represented by a narrow and a wide diameter implant connected to a corresponding abutment. A quasi-Fourier setup with a 25mW helium-neon laser was used for interferometric measurements in the cervical 5mm of the implants. Holograms were recorded in two conditions per measurement: a 10N preloaded and a measuring-force loaded assembly, resulting with an interferogram. This procedure was repeated throughout the whole process of incremental axial loading, from 20N to 120N. Each measurement series was repeated three times for each assembly, with complete dismantling of the implant-loading device in between. Additional software analyses calculated deformation data. Deformations were presented as mean values±standard deviations. Statistical analysis was performed using linear mixed effects modeling in R's lme4 package. Implants exhibited linear deformation patterns. The wide diameter group had lower mean deformation values than the narrow diameter group. The diameter significantly affected the deformation throughout loading sessions. This study gained in vitro implant performance data, compared the deformations in implant bodies and numerically stated the biomechanical benefits of wider diameter implants.Dental materials: official publication of the Academy of Dental Materials 01/2014; · 2.88 Impact Factor
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ABSTRACT: A new optical method of vibration mode analysis using time-average fringe is presented in this paper. A sequence of the deformed and partly blurred sinusoidal fringe images on the surface of a vibrating membrane are grabbed by a low sampling rate commercial CCD camera. By Fourier transform, filtering, inverse Fourier transform, the vibration mode is obtained from the fundamental component of the Fourier spectrum. The theoretical analysis of this approach is given. Computer simulations and experiments have proved to verify its validity. Under different excited vibration frequencies, the vibration modes of a vibrating surface can be qualitatively analyzed. In the experiment, when the excited vibration frequency changes continuously, the changing process of the vibration modes of membrane is observed clearly. Experimental results show that this approach as the features of rapid speed, high accuracy, and simple experimental set-up.Proceedings of SPIE - The International Society for Optical Engineering 12/2009; · 0.20 Impact Factor