The concept of highly sensitive fibre optic displacement sensor is presented. It is based on macrobending step index
polymer optical fibre with multiple overlapping surface-side imperfections. The theoretical principles of optical power
losses in such fibres due to multiple curvatures are based on a surface that serves as a model for an imperfect layer and
has the same optical properties. The sensing element was tested using two different types of roughness topologies and
their combination. The various angles of imperfections (90 and 45 degrees) placed on the fibre's core were evaluated.
We discuss some experimental results that confirm our prediction of considerable dependence of the output signal on the
changing imperfections caused by bending the fibre. It was found that sensitivity to bending of the angular imperfections
could be further increased by implementing multiple overlapping imperfections.
In this paper we report results for an intrinsic evanescent field sensor based on not-regular plastic optical fiber with
polymer film containing Malachite Green MG+([PhC(C6H4NMe2)3]+) as an absorption reagent, which coats the fiber's
imperfected area. A theoretical model was developed which shows that changes of light in such structure result from the
attenuation of light in the strait and bent imperfected fiber. In this model, the imperfected area with malachite green
polymer film is replaced by a uniform layer with a complex refractive index. The changes in color and absorption
characteristics of the polymer film depend on the acidic and basic environmental properties in the sensing area.
Additional increase of the evanescent field interaction can be achieved by decrease the bending radius of the fiber with
the coated imperfection area at the middle of the bent fiber. An imperfected plastic optical fiber with Malachite Green
coating has been presented for the detection of ammonia vapor. The initial results show that depending on the sensing
application demands, it is possible to design a high sensitive sensor with a relatively long response time, while when the
demands require fast response times the sensor with less sensitivity can be used. In addition, the sensors' sensitivity can
be calibrated in real-time by changing the bending radius.
The concept of highly sensitive fiber optic displacement sensors is presented. It is based on macrobending plastic fiber with structural imperfections on the outer side. The theoretical principles of optical power losses in such fibers due to multiple curvatures are based on a surface that serves as a model for an imperfect layer and has the same optical properties. The sensor was tested using two different types of roughness topologies. We discuss some experimental results that confirm our prediction of considerable dependence of the output numerical aperture (the output signal) on the changing imperfections caused by bending the fiber.
Simultaneous measurements of the low frequency fluctuations of arterial blood pressure, heart rate, tissue blood content and tissue blood volume pulse were performed on 20 healthy male subjects. Arterial blood pressure was measured on the index finger by Finapres, simultaneously with photoplethysmography (PPG), which was measured on the other index finger. The changes in the PPG amplitude (AM), baseline (BL), and BV (defined by BV equals Const. - BL), are related to the changes in the tissue blood volume pulse (for AM) and the total tissue blood volume, (for BL and BV). The low frequency fluctuations of BV and AM were directly correlated, those of AM preceding those of BV by 4 - 13 heart beats. The low frequency fluctuations of SBP and DBP were inversely correlated to those of AM and BV. For most of the subjects P, which is the cardiac cycle period, was directly correlated with AM and BV. The interrelationship between the low frequency fluctuations in tissue blood volume, arterial blood pressure and heart period, provide us with a better understanding of the autonomic nervous control of the peripheral circulation.
Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously due to the autonomic nervous system activity. In the current study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using transmission photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BV, defined by: BV equals Const.-BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BV and AM show positive correlation, which is expected since BV depends on the tissue blood volume and AM depends on the compliance of the blood vessels, both of which decrease during vasoconstriction, which is caused by higher activity of the sympathetic nervous system. The analysis of the PPG signal provides, therefore, a potential tool for study in the mechanism of the regulation of the microcirculation by the sympathetic nerves.
A sensor for measuring chest circumference by means of an optical fiber has been developed. The method is based on the measurement of light transmitted through a bent optical fiber, which is connected to an elastic band, wrapped around the chest, and whose radius of curvature changes due to the respiratory act. The amount of transmitted light is related to the radius of curvature of the fiber which depends on the chest circumference. The output of the respiratory sensor was checked qualitatively by changing the respiration depth. The changes in breathing effort were clearly demonstrated in the sensor output recording. The respiratory effort was also correlated with the heart rate, measured by photoplethysmography. Statistically significant correlation was found between the lungs' volume and the heart rate, but the correlation coefficient was not high. The magnitude of the breathing depth and the height of the corresponding respiratory changes of the heart cycle period were not correlated.
Besides heart rate and arterial blood pressure, several parameters of the cardiovascular system fluctuate spontaneously. In the current study, the fluctuations of tissue blood content and blood volume pulse were investigated using two parameters of the photoplethysmographic (PPG) signal: the parameter BV, defined by: BV=Const−BL where BL is the baseline of the PPG signal, and the amplitude (AM), which are related to the blood volume and to the systolic blood volume increase, respectively. The PPG measurements were performed on the fingertips of ten healthy male subjects for 5 to 10 min and the PPG signal was digitally analyzed. Both BV and AM show low frequency fluctuations, which, for 23 out of 26 examinations, were positively correlated, with a lag of BV relative to AM. In three examinations, however, the two parameters were inversely correlated. A lower correlation was found between each of these parameters and the PPG period, which is actually the cardiac period. The results show that several mechanisms are involved in the spontaneous periodic fluctuations in the vascoconstriction level, which are known to be mediated by the sympathetic nervous system. The digital PPG provides, therefore, a potential tool for evaluating the role of the sympathetic nerves in the regulation of the microcirculation.
A new type of intensity-modulated sensors based on a coated light guide is presented. These sensors operate preferentially in the regime of total internal reflection (TIR), rather than relying on violation of TIR as in conventional intensity-modulated sensors. Using a physical model of the new sensor structure, the output light intensity is computed as a function of the complex reflection and transmission coefficients at the substrate-film and film-ambient interfaces. Based on the theoretical results, an experimental setup has been constructed and evaluated for measurements on various liquids. The results confirm the predicted dependence of the output signal on the characteristics of the substrate-film-ambient system. Of particular importance is the novel feature that the output signal increases as the refractive index of the ambient medium increases, at certain incidence angles.
Several methods have been developed for the qualitative and quantitative measurement of breathing effort. The most useful kind of breathing pattern monitor includes devices for recording chest and abdomen dimension changes, such as impedance plethysmography and respiratory induction plethysmography. These devices can measure the tidal volume in relative terms, and even measure it in absolute terms after suitable calibration. In this study a novel method for measuring chest circumference based on an optical fiber is presented. The sensor is based on the measurement of light transmitted through a bent optical fiber, which is connected to an elastic band, wrapped around the chest, and whose radius of curvature changes due to the respiratory act. The amount of transmitted light is related to the radius of curvature of the fiber which depends on the chest circumference. The output of the respiratory sensor was checked qualitatively by changing the respiration rate and depth. The changes in breathing effort were clearly demonstrated in the sensor output recording. The respiratory effort was also correlated with the heart rate, measured by photoplethysmography. Statistically significant correlation was found between the lungs' volume and the heart rate, but the correlation coefficient was not high.
Several parameters of the cardiovascular system such as heart rate, arterial blood pressure and blood flow fluctuate spontaneously. These fluctuations are related to the autonomic nervous system activity. In particular the low frequency fluctuations are mediated by the sympathetic nervous system. In the cuttent study, the low frequency fluctuations of the tissue blood volume and the blood volume pulse in the fingertips of healthy subjects were investigated using photoplethysmography (PPG). The baseline of the PPG signal (BL) is inversely related to tissue blood volume so that the parameter BV, defined by: BV equals Const. minus BL is directly related to the blood volume. The amplitude (AM) is directly related to the systolic blood volume increase. For most of the examinations BV and AM show positive correlation but in some examinations the two parameters were inversely correlated. PPG measurements performed in near infrared radiation, showed better correlation between BV and AM than for red light PPG. The results show that several mechanisms are involved in the low frequency fluctuations in the tissue blood volume. The analysis of the PPG signal provides, therefore, a potential tool for studying the mechanism of the regulation of the microcirculation by the sympathetic nerves.
The variability in heart rate is related to the activity of the autonomic nervous system, which influences the heart rate either directly or via the peripheral circulation. In this study direct measurement of peripheral circulation parameters and their variability was obtained by means of photoplethysmography which provides assessment of the blood volume in the tissue and its increase during systole by measuring the light absorption in the tissue. Both blood volume and systolic blood volume increase showed oscillations in very low frequency, about 0.02 Hz and in relative high frequency, about 0.3 Hz, which is related to respiration. In comparison to the variability of the heart rate the high frequency oscillation has lower amplitude but the low frequency oscillation is much higher.
A photoplethysmography (PPG) device, which filters the dc signal without distorting the pulse shape, was developed. Measurements were performed on the finger, for hand at heart level, below and above it. The PPG signal was highest above heart level, and lowest below heart level. It seems that the compliance and the resistance of the blood vessels influence the PPG curve.
We present a new type of intensity-modulated sensor based on a coated lightguide. Using a physical model of the coated lightguide the output light intensity was computed as a function of the reflection and transmission complex coefficients at the substrate-film and film-ambient interface. Based on these theoretical results an experimental setup for measuring various parameters of a liquid was constructed. The results demonstrate the dependence of the output signals on the characteristics of the substrate-film-ambient system. In particular the output signal increases for some incidence angles as the refractive index of the ambient medium increases.
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