EM behavior when the wavelength is much smaller than the object
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney in Basic Introduction to Bioelectromagnetics, 2018
Optical mirrors are usually made of conductive metal coatings (such as aluminum) on a substrate such as glass. The reflection of optical waves from conductive coatings follows the same boundary conditions as for lower-frequency microwaves (see Section 3.3.1). The reflectivity R depends upon the conductivity of the coating but is generally around 90% for aluminum and higher for silver and gold. As before, the angle of reflection is equal to the angle of incidence. This is known as specular reflection. It makes ray tracing of the paths of the reflected waves from mirrors easily visualized. For example, Figure 4.7 shows parallel incident rays reflected from both a flat mirror and a spherical mirror. Since the spherical mirror surface is curved inward (concave), specular reflection causes the parallel rays to focus to a point halfway between the center of curvature and the mirror surface. (This is true for rays near the axis; for rays farther toward the periphery, some spreading of the focus spot, known as aberration, occurs.) Thus, for a concave spherical mirror, the focal length f is equal to one-half the radius of curvature R0, or f = R0 /2.
Properties, limitations and artefacts of B-mode images
Peter R Hoskins, Kevin Martin, Abigail Thrush in Diagnostic Ultrasound, 2019
When reflection is from a large, smooth interface, i.e. an interface which is larger than the beam width, specular reflection occurs. That is, the reflected ultrasound propagates in one direction. When the angle of incidence is zero (normal incidence), the reflected echo from a large, smooth interface travels back along the same line as the incident beam to the transducer, where it is detected (Figure 5.18a). When the angle of incidence is not zero (Figure 5.18b), the beam is reflected to the opposite side of the normal at the angle of reflection. The angle of reflection is equal to the angle of incidence. Hence, when a beam is incident on a large, smooth interface at an angle of incidence of 10° or more, the reflected beam may miss the transducer so that no echo is received.
Bioengineering Aids to Reproductive Medicine
Sujoy K. Guba in 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.
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Refraction is defined as the change in direction of a transmitted light beam after it enters a second medium. Reflection is defined as the change in direction of a light beam at an interface that returns the light beam back to the original medium. The angle of incidence of the light beam on the surface and the material properties of the two media determine the intensity and direction of the refracted and reflected light beam. Another way to steer light is scattering: multiple changes in refractive index force the light beam to randomly change direction in a series of reflection events, resulting in diffuse light scattering. Lastly, a fundamentally different method to steer a light beam is diffraction. Diffraction is defined as the bending of light after encountering a small opening or obstacle. The light beam does not bend in one direction; instead, a diffraction pattern is generated by the interference of different wave fronts. Diffraction is predominant for apertures and obstacles with sizes in the range of the wavelength of the incident light.
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
Monochromatic coherent source of light on interaction with a tissue surface undergoes specular reflection due to sporadic index of refraction between tissue and air junction. The specular reflection is contingent on: (i) angle of incidence, (ii) intrinsic property of tissue. Breast tumors have a higher index of refraction (tentative magnitude of 1.39 to 1.41) than its healthier counterparts (Sarkar et al. 2011). Fresnel relation in Equation (1) allows quantifying the critical angle of tissue. A GUI developed with Matlab can be peripheral to peruse the distinction in optical property of diagnosed tissue sample from Equation (1).
Related Knowledge Centers
- Geometrical Optics
- Ray
- Sound
- X-Ray
- Total Internal Reflection
- Reflection
- Snell'S Law
- Milliradian
- Phase Angle
- Plane of Incidence