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Sensing with Polymer Fiber Bragg Gratings
Published in Ricardo Oliveira, Lúcia Bilro, Rogério Nogueira, Polymer Optical Fiber Bragg Gratings, 2019
Ricardo Oliveira, Lúcia Bilro, Rogério Nogueira
The capability to characterize the optical properties of fluids is crucial in several processes, namely salinity of water, fuel quality, biotechnology processes, etc. Standard devices such as the Abbe refractometer are frequently used to measure the refractive index. However, they have limitations regarding their weight and size. Fiber optic sensors are an alternative since they are compact in size and have the ability to be used in quasi-distributed or tip-based sensing applications. Over the last decades, several fiber optic technologies based on silica fibers have been proposed for the detection of refractive index. Examples of those technologies are tapered fibers, FBGs, LPGs, tilted fiber Bragg gratings (TFBGs), Mach-Zehnder interferometers (MZI), single-mode-multimode-single-mode (SMS) structures and also the use of surface plasmon resonance (SPR) excitation [123,124]. POFs present similar properties to those of silica fibers also offering other characteristics, such as flexibility, non-brittle nature, biocompatibility, etc. Furthermore, the possibility to use Bragg gratings in these fibers offers lower complexity on the signal detection, as well as enabling multiplexing, making them attractive to be explored in refractive index sensing.
Length Measurement
Published in Rajpal S. Sirohi, Introduction to OPTICAL METROLOGY, 2017
Abbe refractometer is the most commonly used instrument for the determination of refractive indices of liquids and solids. It consists of two prisms P1 and P2 of dense Flint glass (Figure 6.7). The surfaces 1, 3, and 4 are polished and surface 2 is matt. The prism P1 is hinged at H, so that it can be hinged away from P2 or removed altogether if desired. For determining the refractive index of a liquid, a drop of the latter is placed on surface 2, which is then closed up into contact with surface 3; the liquid is squeezed out into a thin film. The light from a suitable source, usually white, is directed toward the prism system. It strikes the matt surface 2, and is scattered into the liquid film and prism P2. Figure 6.7 shows the path for a ray, which is grazing in the liquid medium and is refracted at critical angle θc in the prism medium. This ray exits from the prism at an angle θ.
Refractive Index Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Most instruments use the critical angle (or Abbe) method. They thus have a prism of known refractive index with a face to which the sample is offered. The larger manufacturers offer three types of critical angle instrument: The portable handheld models, which require no power or battery and are customized and calibrated for Brix (sugar), urine, antifreeze, cutting oil, etc. Their refractive index precision is typically between 10−3 and 10−4, but their range is small owing to their particular application. The user looks into an eyepiece and reads a scale on which is superposed the dark–light boundary caused by transmission or reflection in the region of angle each side of the critical angle, often termed the critical edge. The price varies greatly between models and manufacturers, typically U.S. $400. Some manufacturers offer digital readout portable models, of similar weight (less than 1 kg) and precision, and battery powered. These cost about U.S. $2000.The laboratory (Abbe) refractometer, which has a refractive index precision of typically 10−4–10−5 and covers a wide range of refractive index, typically 1.3–1.75 in a low refractive index instrument and 1.4–1.85 in a high refractive index model. Such instruments are calibrated so that the temperature can be varied using an external liquid bath, and the wavelength can be varied using external light sources. Very roughly, their weight, cost, and precision are about 10 times that of the portable instruments in (1) earlier. They require the user to estimate the position of the critical edge on a graduated scale viewed through an eyepiece.The digital refractometer. Compared with those in (2) earlier, these have similar precision and general facilities, a cost typically a few times greater, but with the advantage of a digital or electronic readout of the data. The upper refractive index offered by several manufacturers appears to be restricted to about 1.6.The process refractometer is a version of those described in (3) earlier, but where the prism is mounted to contact a fluid in a reactor or a pipe and viewed via a fiber-optic cable. Thus, high pressures and temperatures can be accommodated. The prism is usually of sapphire to avoid wear of the optical face, and the precision generally tends to be somewhat lower than those described in (2) and (3) earlier.
Apparent molar volumes and relative viscosity of [C3C1PYR][Br]/[C2OHC1PYR][Br] + H2O
Published in Chemical Engineering Communications, 2021
Qingshan Liu, Fengze Yu, Shurong Hui, Hui Liu
An Abbe refractometer was used for refractive index measurements from 288.15 to 318.15 K. The values of the binary solutions were measured and recorded every 5 K with controlled temperature 0.05 K. The standard uncertainty was confirmed and less than 0.0002 for refractive index. The measurement values are shown in Table 3 for the binary solutions.