Design and operation of a fiber optic sensor for liquid level detection

Design and construction of an optical fiber sensor for liquid level detection are reported. This sensor operates based on light intensity modulation, and such modulation results from alteration of total internal reflection into partial reflection at the interface. The modulated intensity has been measured by using a pair of fibers, one transmitting source light, another acting as receiving fiber, and a glass prism providing the total and partial reflections. During the level measurements, when a liquid in a vessel touches the 45° faces of the 45-90-45° prism, the total internal reflection is disturbed, and the reflected light is modulated. The performance of this sensor is tested with different source lights including a light emitting diode (LED), a diode laser, and a He–Ne laser. Extinction ratio has been measured for different liquids, and compared. This ratio for water using LED source is about 0.03, for diode laser is 0.006 and for He–Ne laser is 0.003. Although this device was tested as a liquid level sensor, but the distinct results obtained for samples with different index of refractions demonstrate that the reported sensor can also be used as a liquid refractometer.     

A true fiber optic refractometer

The best instrument to measure the refractive index of liquids is the Abbe refractometer which can only provide accuracies of the order of 10⁻⁵ at visible wavelengths and 10⁻⁴ in the near infrared. Here we present a technique by which the exact wavelength positions in the near infrared frequency comb of a tilted grating inscribed in the core of an optical fiber can be used to measure the absolute value of the refractive index of a liquid in which the fiber is inserted, with an accuracy of ±5×10⁻⁵. This is in contrast to typical fiber optic‐based “refractometry” where only refractive index variations can be measured accurately, hence the appellation of “true” fiber optic refractometer here. In addition to the increased accuracy, the fiber refractometer proposed here offers the additional advantages associated with in situ measurements. The performance of this refractometer is demonstrated by measurements in water from room temperature down to near freezing at wavelengths in the 1550 nm window.

     

应用光纤液滴传感器进行液体测试

光纤液滴传感器是利用测试液滴的形成过程与液体成份之间的关系而制成的一种液体测试传感器。主要利用光纤来监测液滴的增长过程,得到随液滴下降过程的光强变化情况,从中获得反映液体的物理、化学性质的“液滴指纹图”。通过对指纹图进行分析对比得到液体的特性参数,实现对各种液体的鉴别。     

LFI法测量半透明油的折射率

LFI方法曾被用来测量大直径光纤的折射率.用一半盛油一半为空气的毛细管代替光纤,并用聚焦的条形光束照射毛细管,空气与油的干涉条纹同时产生.根据空气的条纹可以确定参数b,根据一组已知折射率的标准样品可确定另一参数c,同时可以建立标准液体最外条纹的偏折角与折射率的标准曲线.对于未知折射率的样品,一旦测量出其最外条纹的偏折角,从标准曲线上就可以读出其折射率.实测了一组半透明油的折射率,其结果与阿贝折射仪测量结果接近.     

Properties of a gold-deposited surface plasmon resonance-based glass rod sensor with various light-emitting diodes and its application to a refractometer

The performance of a simple sensor system prepared using gold (Au)-deposited glass rods of 1 to 4 mm in diameter with a deposition length of 100 mm based on surface plasmon resonance (SPR) is presented. The sensor properties of the Au-deposited glass rods of 2 mm in diameter with deposition lengths of 10 to 100 mm are also presented. The sensor system consists of a light-emitting diode (LED) as the light source and a photodiode (PD) as the detector. The response curves and sensor properties of the Au-deposited glass rod with a Au film thickness of 45 nm obtained by using three LEDs with yellowish green (563 nm), red (660 nm), and infrared (940 nm) emissions were investigated. The results were compared with those of a corresponding Au-deposited optical fiber sensor with a core diameter of 0.2 mm. Though the sensitivity, response, and detection limit of the Au-deposited glass rod sensor are lower than those of the optical fiber sensor, the fabrication and handling of the Au-deposited glass rod sensor are easier because of the robustness. Since the dielectric constant of Au changes with the light wavelength, the sensor properties of both the Au-deposited glass rod sensor and the optical fiber sensor depend strongly on the wavelength of the incident light and can be controlled by changing the LED emission wavelength. This sensor system is a new SPR-based refractometer with easy construction and operation. Ethanol concentrations in various spirits were measured with this SPR-based refractometer and the results agreed well with those measured with an Abbe refractometer.     

High resolution optical refractometer for dispersion measurement in UV-NIR range

A high resolution optical refractometer for dispersion measurement in the UV-NIR range is described. Using this refractometer, refractive index of a range of liquid samples, such as aqueous solutions of sugars, salts and alcohols, was measured as a function of wavelength in the range from 300 nm to 920 nm with accuracy better than 10 ^{- 5}. So accurate results can be used for improvement of resolution of OCT measurements conducted in biological samples.     

Gliding for Gold: The Physics of Winter Sports,by Mark Denny

A comparison of the basic properties of the superfluid phases of liquid ³He with those of electrons in Type I superconductors and of bosons in liquid ⁴He reveals their similarity and differences. This is followed by some examples of the liquid crystal and magnetic properties of superfluid ³He and an account of the relationships between the tensor order parameter and the collective modes of the superfluid phases. The article ends with some comments on our present understanding of quantum liquids.     

Preparation and characterization of a large mode area liquid-filled photonic crystal fiber: transition from isolated to coupled spatial modes

We describe in detail the manufacturing procedures for selectively closing holes in photonics crystal fibers and their infiltration with different liquids. We apply our method to create a large mode area liquid-filled photonic crystal fiber which consists of 19 liquid strands. By changing the mixing ratio between toluene and ethanol and by varying the temperature, we show continuous tuning from isolated to coupled behavior of the spatial mode profile. This demonstrates the versatility of selectively closed liquid-filled photonic crystal fibers for future photonic devices. Filling with nonlinear liquids, gases, metals, liquid crystals, low melting compound glasses, or quantum dots is possible, and spatial as well as temporal engineering of linear and nonlinear optical properties will become feasible, which should allow the observation of spatiotemporal solitons.     

The influence of repellent coatings on surface free energy of glass plate and cotton fabric

The aim of this research was to determine the influence of chemical finishes on the surface properties of glass plate, considered as a model homogeneous smooth surface and cotton fabric as a non-ideal heterogeneous rough surface. Microscopic slides and 100% cotton fabric in plain weave were coated with fluorocarbon polymers (FCP), paraffin waxes with zirconium salts (PWZ), methylolmelamine derivatives (MMD), polysiloxanes with side alkyldimethylammonium groups (PSAAC) and aminofunctional polysiloxanes (AFPS). From the goniometer contact angle measurements of different liquids, the surface free energy of the coated glass plates was calculated according to approaches by Owens-Wendt-Kaelble, Wu, van Oss-Chaudhury-Good, and Li-Neumann-Kwok. The results showed that all the coatings decreased the surface free energy of the substrate, which was also influenced by the liquid combination and the theoretical approach used. In spite of the fact that the liquid contact angles were much higher on the coated fabric samples than on glass plates and resulted in the lower values of work of adhesion, a very good correlation between the coatings deposited on both substrates was obtained. The presence of repellent coatings FCP, PWZ and MMD converted the solid surface from polar to highly apolar by masking the functional groups of glass and cellulose. PSAAC and AFPS coatings did not decrease the solid surface free energy to such an extent as the former three coatings due to their monopolar character.     

Determination of refractive indices of liquids by Fresnel diffraction

We demonstrate an easy, reliable, applicable, and sensitive method to measure refractive index of liquids by using Fresnel diffraction. In this method a cylindrical glass rod, in general, or an optical fiber in special case, is immersed into a liquid. Physical parameters of the rod, like radius and refractive index, should be well known. Then, the normalized intensity distribution on the Fresnel diffraction pattern of a plane wave diffracted from the immersed fiber is measured. Thereafter, refractive index of the liquid is evolved by the least-square method. This method applied to determine the refractive index of four liquids; pure water, 2-propanol (isopropanol), acetone and methanol. Index of refraction of each one has been acquired for four visible wavelengths. A theoretical approach and experimental results is presented.     

A proposed new experimental setup for determination of refractive indices of liquids by mode line measurements

A new experimental method is proposed for measuring the refractive indices of liquids based on mode line measurements. The experimental setup consists of a dielectric substrate in which a rectangular hollow is formed containing the concerned liquid. This is covered by a trapezium-shaped prism. The liquid, confined between both basin walls and the prism, forms a wavegude. Thus, the refractive index of the liquid can be determined by measuring the propagating modes in the structure. Using this technique, the refractive indices of liquids can be measured to an accuracy of the order of 1×10^-4.     

Characterization of thermal transport across single-point contact between micro-wires

A contact transient electrothermal technique (CTET) is developed to characterize the thermal transport between one-dimensional conductive and nonconductive microscale wires that are in point contact. This technique is a significant advance from the transient electrothermal method that is used to characterize the thermophysical properties of individual one-dimensional micro-wires. A steady-state analytical solution and a transient numerical solution are used to independently determine the value for the thermal contact resistance between the wires at the contact point. The CTET technique is applied to measurement of the thermal contact resistance between crossed Pt wires (25.4 μm diameter) and the thermal contact resistance between a glass fiber (8.9 μm diameter) in contact with a Pt wire (25.4 μm diameter). For Pt wire contact, the thermal contact resistance increases from 8.94×10⁴ to 7.05×10⁵ K/W when the heating current changes from 20 to 50 mA. For the Pt/glass fiber contact, the thermal contact resistance is much larger (2.83×10⁶ K/W), mainly due to the smaller area at the contact point.     

Non-destructive collimation technique for measuring glass constants using a Ronchi grating shearing interferometer

A non-destructive liquid immersion collimation technique in combination with a Ronchi grating shearing interferometer has been used for determining the constants of a transparent glass material, especially when it is in the form of a lens. Due to its simplicity and the fact that it will work equally well at any wavelength, the technique is superior to existing methods for determining the various glass constants (refractive index, Abbe number or v-value, partial dispersion factor etc).The shearing fringes appearing inside a Ronchi-gram are adequate to locate the exact position of the point source which has been treated as the target in the present communication. The fringe-free space in the overlapping region between the two laterally displaced spherical wavefronts indicates the sharply focused position of the target which corresponds to zero defocusing. In this way the target displacements with different liquids are determined.     

Glass/Crystal Interfaces in Liquid-Phase Sintered Materials

This paper presents a review of our studies of interfaces in liquid-phase sintered materials. Recent studies of three different types of interface are discussed, namely, (i) the interface between the free surface of the crystal and the glass, (ii) the interface between the intergranular glass and the crystal and (iii) the interface between the crystallized glass and the substrate crystal. Model systems with relatively well known thermodynamic and crystallographic properties have been chosen. The relationship between the three types of interface is discussed. The dewetting of silicate liquids on free surfaces provides an opportunity to study directly the interface between the free surface and glass. Observations on polycrystalline samples and bicrystals give new understanding of the interplay between intergranular glass layers and the adjoining crystalline grains. Crystallization of the glass on single-crystal substrates directly gives information about the crystallized-glass/crystal interface.     

Inherent Structure Approach to the Study of Glass-Forming Liquids

The inherent structure approach, wherein thermodynamic and structural changes in glass-forming liquids are analyzed in terms of local potential energy minima that the liquid samples, has recently been applied extensively to the study of thermodynamic aspects of glass-forming liquids. The evaluation of the configurational entropy, which arises from the multiplicity of local energy minima, plays a central role in such analyses. Results are presented here concerning the calculation of configurational entropy based on computer simulations of a model liquid; and the application of the inherent structure formalism to the study of the glass transition locus, and the fragility of glass-forming liquids.     

A new technology for studying multicomponent liquids using a quartz crystal resonator: Theory and applications

A new technique for analyzing multicomponent liquids is suggested. It is based on recording “electronic autographs” of liquids and thereby allows one to identify and certify them. In this technique, information comes from the dynamics of the complex process of self-organization in drying drops, this dynamics being dependent on the composition and structure of the liquid. Detecting the self-organization dynamics as acoustomechanical impedance, one can reveal quantitative distinctions between liquids and thereby test their quality by comparing with a reference.     

邻苯二甲酸二甲酯系材料的液态簧振动力学谱测量

用液态簧振动力学谱方法对邻苯二甲酸二甲酯、邻苯二甲酸二乙酯、邻苯二甲酸二丁酯和邻苯二甲酸二辛酯的系列样品进行了测量. 在升温过程中所测温区范围内，结果表明邻苯二甲酸二甲酯样品相继发生了动力学玻璃化转变、过冷液态的结晶、晶体—液态相变和挥发过程，而在邻苯二甲酸二乙酯、邻苯二甲酸二丁酯和邻苯二甲酸二辛酯样品中仅仅发生了动力学玻璃化转变和挥发过程. 上述实验结果与分析表明，液态簧振动力学谱方法是研究拥有液态过程的可靠和有效的方法，并且能够提供物质变化的丰富信息.     

In situ characterization of liquid network structures at high pressure and temperature using X-ray absorption spectroscopy coupled with the Paris-Edinburgh press

ABSTRACT

We review recent progress in studying structural properties of liquids using X-ray absorption spectroscopy coupled with the Paris-Edinburgh press at third-generation synchrotron facilities. This experimental method allows for detecting subtle changes in atomic arrangements of melts over a wide pressure–temperature range. It has been also employed to monitor variations of the local coordination environment of diluted species contained in glasses, liquids and crystalline phases as a function of the pressure and temperature. Such information is of great importance for gaining deeper insights into the physico-chemical properties of liquids at extreme condition, including the understanding of such phenomena as liquid–liquid phase transitions, viscosity drops and various transport properties of geological melts. Here, we describe the experimental approach and discuss its potential in structural characterization on selected scientific highlights. Finally, the current ongoing instrumental developments and future scientific opportunities are discussed.     

Optical multi-sensor for simultaneous measurement of absorbance,turbidity, and fluorescence of a liquid

We have built a novel optical multi-sensor apparatus (MSA) for the measurement of light absorption, scattering and fluorescence either separately or simultaneous from a liquid. From the measured data it is possible to calculate different optical properties of liquid samples, such as absorbance and turbidity. The MSA is a portable device which is an advantage considering different field applications. The MSA was tested in laboratory conditions using well-known reference liquids. Data obtained with the MSA were compared with data obtained with a commercial spectrophotometer, fluorometer and a nephelometer, respectively. Relatively good correlations between the data of MSA and the three commercial devices were found. It is proposed that MSA is a potential device for monitoring changes of process liquids and liquid products in industry.     

Ge20Sb15Se65硫系玻璃光子晶体光纤的中红外色散特性

硫系玻璃与石英玻璃相比具有高折射率(2.0~3.5)、低声子能量 (<350 cm^-1)、优良的中远红外透过性能(可至25 μm)等特性.本文制备了一种在中红外具有优良透过特性的无As环保型Ge₂₀Sb₁₅Se₆₅硫系玻璃材料,以此为基质材料设计了一种三层空气孔结构光子晶体光纤,利用多极法对光纤的中红外色散特性进行了数值模拟,系统研究了结构参量孔径d、孔间距Λ 以及d/Λ 对其色散特性的影响.分析表明:通过改变包层空气孔直径d或空气孔间距Λ,可灵活的调节光子晶体光纤的零色散波长向短波或长波方向移动.通过优化结构参量发现,当Λ=3 μm,d/Λ=0.35 附近变化时,可获得3~5 μm色散平坦,且色散值小于5 ps·nm^-1·km^-1的光子晶体光纤.