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Articles by H. Golnabi
Total Records ( 16 ) for H. Golnabi
  A. Asadpour and H. Golnabi
  In this study the optical beam transfer and imaging in an optical fiber coupling is discussed. In coupling two fibers, some measurements from intensity perspective are performed and intensity profile is investigated. A theoretical model for the power transmission in fiber coupling is developed and theoretical function is compared with the experimental results. The amount of light delivered to the receiving fiber depends on the acceptance angle of the receiving fiber and the core cross sections of both fibers. Intensity profile function obtained theoretically agrees well with the measured results. The intensity variation as a function of the air gap variation is investigated in this article. The image of emerging beam of the source fiber is also investigated. Using captured images one can measure acceptance angle and core diameter of the fiber by using two images of the output beam at two axial distances. The results of this report can be used in optical communications, data links and image transferring in which single or coupled optical fibers have been used as signal carrier or waveguide.
  G. Behzadi and H. Golnabi
  In this study by using a capacitive cell probe the temperature variation of the electrical properties of the water liquids is investigated. Variation of the reactance capacitance parameter of liquids with temperature in the range of 17-60 °C is measured for the plain water and water mixtures. The temperature variations of the capacitance for the cool distilled and tap water samples are studied for the range of 17-29 °C obtained. Present results indicate an averaged variation of 4.69 μF/ °C for the distilled water and 3.24 μF/ °C for tap water in warm up process to a near room temperature. The cooling behaviors for the warm mineral, tap and salt water liquids are also investigated in this study. Average variations of 0.54 μF/ °C for the mineral water, 0.76 μF/ °C for the tap water and 1.44 μF/ °C for the dilute salt water are obtained for the high temperature range. In comparing the results for different liquids, dilute salt water shows a factor of 2.6 increase in measured capacitance in comparison with the mineral water when temperature drops from 60.0 to 35.0 °C. Hence the reported cell probe provides a relatively accurate method to determine the temperature dependence of reactive capacitance for the pure liquids and also liquids with a trace impurity.
  H. Golnabi
  This study presents an up to date progress of the national and international laser research and developments. The number of scientific publications and accepted patents are considered as a figure of merit and based on these numbers the growth pace for the period of 1990-2003 is investigated. The share of top nations in scientific publications and in particular laser publications in term of their Gross Domestic Product (GDP) is presented. Four countries including the USA, Japan, Germany and China have a laser publication contribution of 58.9% while the rest of the world including (189) countries contribute 41.1%. However, for the case of accepted patents, which are the more important factor, these four countries hold a share of 90.1% while the remaining nations have a small share of 9.9%. The USA leads all the nations in the number of scientific publications, citations and laser publications, however, in terms of accepted laser patents Japan shows a big lead and has the highest patent/paper ratio (0.46). For Iran the total publication is 231 items (0.06% share) for the period of 1990-2003.
  A. Haghighatzadeh , H. Golnabi and M. Shakouri
  Design and performance of a beam shaping device based on a simple flexible plastic fiber-bundle stripe and a prism duct is described in this study. Such a system offers practical means to modify and change the output beam shape and also provides quantitative information concerning the transmitted power. It is possible to measure transmitted power signal by using a precise photodetector and also analyze beam images taken by a digital camera. The photograph picture of the illuminating LED beam just at its output point shows a circular shape with a radius of about 4 mm and the fiber-bundle output beam is rectangular shape with a dimension of 22.5x2 mm. A regular duct is tested in this study and the optimum condition for the maximum power transmission and best image quality is reported in this study. The transmitted output power signals by the fiber bundle and prism duct are measured as a function of distance from each optical element. Using this system at the first beam shaping stage, the input circular beam with a diameter of about 10 mm is changed into a rectangular beam shape of 22x2 mm width and height by the fiber bundle. The power signal efficiency of about 64.86% is obtained for this stage. The rectangular beam is then changed into a square beam shape of 5 mm width at the second stage and the overall power signal efficiency of about 6.48% is obtained for this design.
  R. Jafari and H. Golnabi
  In this study simulation results for three double-fiber optical designs for the reflection measurements are reported. Modeling is perused for three cases namely Equal Fibers (EF), transmitter fiber shorter (TS) and receiver fiber shorter (RS) designs. By proper modeling and written programs the operations of such symmetric double-fiber probes are simulated and the role of different crucial parameters such as fiber-to-fiber distance (t), fiber core radius (r) and fiber Numerical Aperture (NA) are investigated. In the second study simulation results for the transmitter fiber shorter and receiver fiber shorter designs are investigated for different fiber length differences (w). Finally simulation results for the three different designs of equal fibers, transmitter shorter and receiver fiber shorter probes are compared and optimum conditions are described. All three arrangements simulated here offer valuable results for sensing operations such as reflection or displacement measurements. However, the RS probe geometry offers a better design with the less dead region in comparison with the EF and TS designs.
  A. Asadpour and H. Golnabi
  In this study the output beam profiles of the single mode and multimode optical fibers are investigated by the cross sectional imaging technique. Different experiments are performed for the single mode and multimode fibers and the captured images are compared. The relative near field intensity distribution and their relative changes with respect to the distance is examined and some fiber parameters are obtained. A similar pattern in the real-time image is observed for the two type fibers and major differences are discussed. Using this method it is possible to determine the numerical aperture of the illuminated fiber, which is about 0.22 for the tested fiber. The effect of coherency of the light source on image formation is also investigated and speckle pattern formation in the case of coherence laser light source is discussed.
  H. Golnabi and P. Azimi
  In this study, design and operation of a cylindrical capacitive sensor based on the dielectric and reactance capacitance changes of the gap medium is reported. The proposed system was used to determine the electrical properties of different water liquids as a result of the capacitance variations. For capacitance measurement, the cylindrical gap can be filled up by water liquids under study, the electrical characteristics of different water liquids, mixture of ethanol and water, mixture of methanol and water, mixture of petroleum and water and other liquid mixtures were studied. In this research a big difference about 16200 nF was noticed in the measured capacitance of the corresponding liquids. It must be pointed out that the measuring capacitance of the sensor is different from that of the liquid capacitance, but the liquid electrical characteristics can be compared relatively with each other. The experimental results are promising for water liquids and verify the successful operation of such device as a liquid sensor and is a useful method for checking the electrical quality of the water mixture that is required for different applications.
  G. Behzadi and H. Golnabi
  In this study by using a Cylindrical Capacitive Sensor (CCS), the Electrical Conductivity (EC), effects on the capacitance measurements of the water liquids was investigated. Theoretical values of the capacitance measurements of water liquids with the cylindrical length in the range 0.5-5 cm are calculated. Our obtained results indicate that measured capacitance value by CCS depends on the liquid capacitance and reactance capacitance. Liquid capacitance value of the distilled water for permittivity of 80 is about 33.5 pF and reactance capacitance value is about 0.290 μF, when the cylindrical length value is about 1.6 cm. The reactance capacitance for the mineral, tap and dilute salt water liquids are also investigated in this study. The reactance capacitance value of 22.80 μF for the mineral water, 37.50 μF for the tap water and 47.80 μF for the dilute salt water obtained when the cylindrical length value is about 1.6 cm. A comparison of our obtained result indicated the liquid capacitance value in the capacitance measurement is negligible. A comparison of the theoretical and experimental values shows that theoretical values are smaller than the experimentally measured values that due to the stray capacitances. The minimum error is about 3.3% for distilled water and maximum error is about 12.9% for salt water. Hence, the reported CCS provides a high sensitivity to determine the reactance capacitance value for the different water liquids with low EC.
  A. Khorramnazari and H. Golnabi
  Design and operation of a light reflection system for surface profiling is reported in this article. This system consists of a double-fiber optical probe and a mechanical scanning system. In this arrangement one fiber transmits the source light to the object surface and the second one transmits the light reflected off the surface to a photodetector. By scanning the double-fiber probe assembly in one direction the reflection properties of different plane surfaces are investigated. The reported system can be used to monitor the surface profile of target surfaces made from metallic and non-metallic materials. Obtained results show that the reported method can be utilized to obtain structural information from the object surface with different materials and coatings. The variation of the background light for about 160 m sec scanning time is from 4.35 mV to about 4.75 mV that shows a very good time stability of the detection system. Considering a typical signal value of 30 mV an average signal-to-noise ratio of approximately 7 is obtained for this experiment. The reproducibility error is approximately 0.82% for the full scale measurements which is a good figure of merit. The reported opto-mechanical system provides a simple method for the object shape study and determination of different surface structures through the optical reflection monitoring.
  E. Entezari and H. Golnabi
  Determination of the surface structure using the light reflection is an important issue. The aim is to study such surface reflections using an opto-mechanical system. The effects of the fiber arrangements in the operation of an opto-pair probe system for surface profiling are described. The opto-mechanical testing system consists of a double-fiber optical probe design and an electro-mechanical scanning system. Reflection signals for the plane and cylindrical surfaces made with different curvatures and materials are investigated with both probes and the results are compared. The reflection signal for the plane surface is independent of the double-fiber orientation in probe but for the curves surfaces the reflection signal depends on the fiber direction with respect to the axial symmetry of the object surface under study. The reported system provides a simple and accurate means for the object shape study by obtaining the reflection data from the horizontal and vertical arrangements. Even though it is possible to rotate the object by 90 degree to obtain such information but in practice for real big objects it is much easier to change the fiber arrangements instead of object rotation. The novelty of the reported system is the fact that provides a great potential to analyze the curved surfaces with a one-dimensional scanning arrangement.
  A. Mehrabani and H. Golnabi
  In this study operation of an optical design based on the intensity modulation for the refractive index change has been described. The reported instrument measures the transmitted output power depending up on the medium refractive index in the light path of a fiber-to-fiber design. A liquid cell is located between the fibers in the light path and power variations for different cold and hot water levels in the cell are measured. By using a reference humidity meter the calibration curve representing the relative humidity (%RH) as a function of the transmitted output power is obtained. For the hot water with the final temperature of T = 32.7°C the output power range of 255.0 -313.0 nW is measured for a relative humidity change of 32.76 -41.26%. A power variation of 58 nW is noted for the 8.5% RH variation which shows the high sensitivity for the reported sensor. For the light transmitted in dry air path the output power is 516.7 nW while for the water path such power is 784.6 nW. Thus, the reported device can check the presence of the water vapor, water, or any other transparent liquid in the gap between the two axially aligned fibers. Performance of the new system is satisfactory as a refractive index monitoring mean and for the water/water vapor sensing.
  G. Behzadi , L. Fekri and H. Golnabi
  In this study, operation of the contact Cylindrical Capacitive Sensor (CCS) for the reactance capacitance measurement of the water liquids by using the charge/discharge measurement module is investigated. The effect of geometric factor on the capacitance measurement of different liquid samples is also studied. The measured capacitances for the distilled, mineral, tap and salt water samples are reported by using two contact CCSs with the active length of 16 and 74 mm. The measured capacitances by small contact CCS for the salt water is 1.76 μF and by big contact CCS is 47.8 μF, which shows a big difference for different probes. In another study, the effects of the liquid conductance on the capacitance values are theoretically investigated. The obtained results for different water liquids show that by increasing the conductance of the sample liquids both the stream discharge current and the stored load charge on the cylindrical electrodes are decreased, accordingly.
  H. Golnabi and N. Aghighi
  A simple opto-mechanical system is introduced to monitor the fiber bending effects. Investigation of fiber rolling loss mechanisms in plastic optical fiber by intensity modulation of the transmitted light is reported. The transmitted light powers in the plastic fibers in bend-free and under bending deformation are measured and compared. By reducing the bending diameter (from 18 cm to 7.33 cm) the bending power loss is increased, accordingly. For the green LED for the force-free case the transmitted power is 7456.0 nW, while for bending diameter of 18 cm is 7349.8 nW, for bending diameter of 15 cm is 7291.4 nW, for bending diameter of 9.82 cm is 6687.6 nW and finally for the bending diameter of 7.33 cm is decreased to 5863.6 nW. For all the measurements the green LED shows the highest transmitted power while the red LED shows the lowest output power. Theoretically, the critical bending radius is computed as a function of the core index of refraction for a fixed value of the cladding index of refraction for different core radii. For the core radius of 430 μm the critical bending radius is about 12 cm, while for the core radius of 50 μm it is reduced to 1.8 cm. For a fixed refractive index of the cladding (1.43), the critical bending radius is decreased by increasing the core refractive index (1.44-1.52). The reported system provides a simple and accurate means for the bending loss investigation of fibers even for large-diameter bending cases.
  M. Siadat and H. Golnabi
  Operation of an optomechanical system for color reflection study is reported. The reported system consists of a double-fiber optical design and an electro-mechanical scanning system. In the double-fiber arrangement one fiber transmits the source light to the target surface and the second one sends the reflected light off the sample target to a photodetector. By scanning the double-fiber probe in one-direction reflection properties of different color liquid samples are investigated in this study. A cubic cell made of glass material is used as the liquid container and reflection signals are compared for different filled color liquids. The maximum reflection signals are: for the yellow color (19.78 mV), next red color (12.43 mV) and finally black color shows the minimum reflection signal of (8.77 mV) from the same sample cell and experimental conditions. It must be pointed out that the corrected signal for the empty cell is 16.0 mV. Obtained results showed that the reported system can be used effectively to recognize the liquid color in a transparent cell container.
  R. Jafari and H. Golnabi
  Design and operation of an opto-mechanical system for spectral analysis using a double fiber design for light delivery are reported in this study. A simple mechanical drive system is used, which is able to perform a fine course of angular motion for the scanning of the dispersive optical element. The presented system consists of a mechanical drive system, a dispersive element, a double fiber assembly and a photodetector. A source light, a digital multimeter and a PC are used to test the presented design. The first-order diffraction of the white light source is obtained by using a reflection diffraction grating in Littrow arrangement. By comparing the output reflection signals of the plane mirror and plane grating it is concluded that the output signal is related to the first-order diffraction rather than zero order, which corresponds to that of the plane mirror. In another test a holographic grating is used in place of the ruled grating and the first-order diffraction is resolved for this grating. The groove number for the ruled grating is 1370 g mm-1 where the first-order diffraction angle is about 20° while for the holographic grating with 1200 g mm-1 the first-order diffraction angle at similar wavelength is about 17.45°.
  P. Azimi and H. Golnabi
  In this study a more precise formulation of electrical capacitance for a cylindrical capacitive sensor is reported. By using different theoretical models such as Coulomb law, Gauss law and Laplace equation the electrical capacitance is calculated. Based on the given models the relation between the capacitance and the geometrical parameters (e.g., cylindrical length) is formulated and by using suitable software capacitance variation is computed and compared for different methods. In Coulomb method, the electrical potential is first solved numerically by using Mathematica and then the electrical capacitance is computed. It is found that the active capacitor length is crucial parameter in the calculations and therefore variation of this parameter is considered in our calculations. It is noted that the capacitance value is very sensitive to the length according to the method and it is deviated sharply for small length (about 20 cm) from the Gauss approximation. By comparing obtained results one recognizes that there is a pronounced error difference using approximated laws in short capacitor length range while for long length a negligible difference is noted between the tested models.
 
 
 
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