Reflectivity and illuminating power compensation for optical fibre vibrometer

Abstract

In this paper, a simple and inexpensive optical fibre vibrometer with reflectivity and illuminating power compensation is presented. It consists of a light emitting diode, an optical fibre probe and two photodetectors. The bundling of the probe is divided into three parts: an illuminating fibre, the first-neighbour receiving fibres (group A) and the second-neighbour receiving fibres (group B). The ratio of mean values of the output signal from group A to that from group B is dependent on the mean distance between the probe and target surface, and is independent of the reflectivity of the target surface and illuminating power. By using this ratio, the mean distance between the probe and target surface is estimated. Then based on the calibration curve of group A or B, compensation of sensitivity is made. Because mean values of the photodetector outputs are used in ratio calculation, an increase in vibration frequency does not limit the application of this ratio technique. For this reason, this method is suitable for dynamic measurement. Results of experiments show that this optical fibre vibrometer is capable of compensating for target surface reflectivity, illuminating power and the mean distance between the probe and target surface.

A low-cost high-frequency plastic optical fiber vibrometer

“…Therefore a compensation technique is necessary for practical applications. In [9] a compensation method based on the usage of several fibers is described; our approach does not require additional fibers, as it will be outlined in the next paragraph.…”

Differential transmissive fiber‐optic distance sensor

“…More recently, developments in grand unified field theory and string theory do point out to the existence of magnetic monopoles in the universe, [3][4][5]. Even the size and mass of the elemental magnetic particle have already been predicted: radius % 10 230 m, mass % 10 211 kg (%1 MJ).…”

Modeling and Validation of Performance Limitations for the Optimal Design of Interferometric and Intensity-Modulated Fiber Optic Displacement Sensors

“…Aside from reductions in sensitivity and accuracy (which may or may not meet the demands of a particular sensing application), the primary drawback associated with intensitymodulated displacement sensors is that the reflected and measured power level at a single location is not robust to the previously mentioned environmental and hardware fluctuations, which may falsely indicate changes in DUT displacement. This undesirable characteristic has motivated the research of robust, differential intensity-modulated sensors that make use of power measurements at multiple locations, examples of which were reported in 1999 [24] and 2004 [25]. A general representation of a differential sensing architecture is shown in Figure 4, where receiving fibers have been arbitrarily assigned to one of two receiving groups.…”

“…By taking the ratio of two measured power levels, collected over an arbitrary spatial range, fluctuations in the transmission power level that occur prior to collection by receiving fibers are eliminated from the final sensor output. Various differential intensity-modulated sensor architectures have been proposed [24][25][26][27][28], and these sensor architectures have been shown to be robust even to significant changes in the DUT's reflection coefficient [25]. However, these proposed sensor architectures make use of just a few receiving fibers, failing to take full advantage of the light reflected off the DUT.…”