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Bioengineering Aids to Reproductive Medicine
Published in Sujoy K. Guba, Bioengineering in Reproductive Medicine, 2020
A single optical fiber consists of a central core cylinder of a transparent material usually glass, but could be plastics, having a refractive index σ1 covered with a closely fitting concentric hollow tube known as the “cladding”, also made of glass or plastic but having a different refractive index σ2 (Figure 3.23). The refractive index of the core material is higher than that of the cladding. Recalling elementary high school physics that when a light ray traveling in a medium of high refractive index strikes an interface with a material of lower refractive index, the ray can take three possible paths. If the angle of incidence (the angle between the direction of the ray and the normal to the interface) is low the light ray will escape into the low refractive index material. If the angle of incidence is high, the ray will be subject to ‘total internal reflection’ and will traverse back into the high refractive index material. At a critical angle of incidence (the angle equal to inverse sine of the ratio of the refractive index of the core medium to that of the cladding medium), the ray will neither escape nor travel back into the original material but will travel along a path just bordering the interface. Optical fibers function with the high angle of incidence as in the diagram (Figure 3.23) where at the point a the angle i being greater than the critical angle the ray is reflected back into the core. Similar reflections occur at B and C and so on till the ray emerges from the other end of the fiber.
Interface Pressure Distribution Visualization
Published in J G Webster, Prevention of Pressure Sores, 2019
Figure 10.6 shows the principle of operation of the ischiobarograph. Light from the fluorescent lamps enters at angles, which causes total internal reflection between glass–air surfaces. For total internal reflection to occur, the light ray must be traveling from a medium with high refractive index to one with a low refractive index, and hit the surface at an angle greater than the critical angle for the materials concerned.
Optics and refractive errors
Published in Mostafa Khalil, Omar Kouli, The Duke Elder Exam of Ophthalmology, 2019
Nemat Ahmed, Omar Kouli, Mostafa Khalil, Obaid Kousha
Total internal reflection occurs when the angle of incidence is greater than the critical angle; the light will not pass through the medium, that is, it is completely reflected. Optical instruments such as prisms and gonioscopy rely on this principle of total internal reflection.
Single-molecule measurements in microwells for clinical applications
Published in Critical Reviews in Clinical Laboratory Sciences, 2020
Connie Wu, Adam M. Maley, David R. Walt
Multiple techniques have been used to fabricate microwell arrays of various materials and sizes. The first examples of microwell arrays were prepared using optical fiber bundles (Figure 3) [44,45]. Each optical fiber bundle consists of a pure silica core surrounded by a cladding of silica doped with germanium dioxide. Due to the decreased refractive index of the cladding, light entering each fiber at an incident angle greater than the critical angle undergoes total internal reflection and is transmitted along the fiber length. Upon exposure of one end of the fiber bundle to an acid bath, microwells are created via differential etching rates of the core and cladding materials. A highly packed array of microwells with uniform depth, controlled by acid exposure time, can thereby be generated at the distal end of the fiber bundle and imaged via an excitation light source at the proximal end. In the first demonstrations of single enzyme and protein measurements in microwell arrays, femtoliter-sized wells with diameters of 3–7 µm were typically generated using bundles of 50,000 fibers [41,46,47].
Applications of mid-infrared spectroscopy in the clinical laboratory setting
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
Sander De Bruyne, Marijn M. Speeckaert, Joris R. Delanghe
ATR-FTIR is able to overcome these potential problems. ATR-FTIR operates on the principles of total internal reflection. A radiation beam entering a crystal will undergo total internal reflection when the angle of incidence is greater than the critical angle, which is function of the refractive indices of the two surfaces. The beam loses energy when a material that selectively absorbs radiation is in contact with the internal reflecting element (IRE) [7,53,56]. One limitation of this approach is the fact that samples have to be in close contact with the IRE, which is sometimes difficult in the case of solid samples. Because of the small light penetration depth, the ATR technique is ideal for highly absorbing samples, surfaces and thin-film measurements [56]. The major benefits of ATR-FTIR, in contrast to transmission and transflection experiments, are its sample thickness independent measurements, the ability to probe highly IR absorbing materials without the need for complex sample preparations and the improved spatial resolution [57]. Furthermore, expensive IR transparent substrates are not needed [7].
Mathematical and computational modeling for the determination of optical parameters of breast cancer cell
Published in Electromagnetic Biology and Medicine, 2021
Shadeeb Hossain, Shamera Hossain
The transmittance and reflectance coefficient is pursuant to critical angle of tissue sample. This incident angle is the optimum threshold beyond which the electromagnetic wave undergoes total internal reflection when it strikes the tissue surface. Simultaneously, this optical parameter also describes the evanescent wave propagation and shifting dynamics in wave velocity through tissue. Therefore, critical angle is a disinterested non-invasive parameter, for malignant tissue diagnosis.