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David A. Krohn

Bio: David A. Krohn is an academic researcher. The author has contributed to research in topics: Optical fiber & Fiber optic sensor. The author has an hindex of 2, co-authored 6 publications receiving 262 citations.

Papers
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Patent
09 Oct 1990
TL;DR: In this article, a method of producing a hollow core optical fiber comprises the steps of depositing a thermal buffer layer on the interior wall of a silica tube, depositing germanium silicate cladding on said buffer layer, heating the composite structure so formed to its drawing temperature, and drawing the heated composite structure to form a hollow-core optical fiber.
Abstract: A method of producing a hollow core optical fiber comprises the steps of depositing a thermal buffer layer on the interior wall of a silica tube, depositing a film of germanium silicate cladding on said buffer layer, heating the composite structure so formed to its drawing temperature, and drawing the heated composite structure to form a hollow core optical fiber.

21 citations

Book ChapterDOI
07 Jan 2015
TL;DR: In this paper, the authors considered the case of light passing from a high index medium to a lower-index medium and showed that a certain portion of the incident ray is reflected at the interface, and no refraction takes place.
Abstract: Refraction occurs when light passes from one homogeneous isotropic medium to another; the light ray will be bent at the interface between the two media. The mathematical expression that describes the refraction phenomena is known as Snell's law, [Eq. (1.1)] where n0 = the index of refraction of the medium in which the light is initially travelling, n1 = the index of refraction of the second medium, φ0 = the angle between the incident ray and the normal to the interface, and φ1 = The angle between the refracted ray and the normal to the interface. Figure 1.1(a) shows the case of light passing from a high-index medium to a lower-index medium. Even though refraction is occurring, a certain portion of the incident ray is reflected. If the incident ray hits the boundary at ever increasing angles, a value of φ0 = φc will be reached, at which no refraction will occur. The angle φc is called the critical angle. The refracted ray of light propagates along the interface, not penetrating into the lower-index medium as shown in part Fig. 1.l(b). At that point, sin φc equals unity. For angles φ0 greater than φc, the ray is entirely reflected at the interface, and no refraction takes place [see Fig. 1.1(c)]. This phenomenon is known as total internal reflection (see Fig. 1.2). In Fig. 1.2, a ray of light incident upon the end of the fiber at an angle u will be refracted as it passes into the core. If the ray travels through the high index medium at an angle greater than φc, it will reflect off of the cylinder wall, will have multiple reflections, and will emerge at the other end of the optical fiber. For a circular fiber, considering only meridional rays (which will be discussed later in this chapter), the entrance and exit angles are equal.

2 citations

Book ChapterDOI
07 Jan 2015
TL;DR: In this paper, the optical fiber sensor is used to measure an external physical parameter by inducing changes in one or more of the optical properties of a light beam traveling inside and along an optical fiber.
Abstract: Optical fibers play an important role in many applications beyond communications, including sensing, control, and instrumentation. In these areas, optical fibers have made a significant impact and continue to be the subject of substantial research. In general, for these applications, fibers are made more sensitive and susceptible to the very external mechanisms that would render telecommunications fibers ineffective. In its simplest form, an optical fiber sensor is composed of a light source, an optical fiber, a sensing element, and a detector (see Fig. 2.1). The principle of operation of a fiber sensor is that the sensing element modulates some parameter of the optical system (intensity, wavelength, polarization, phase, etc.), which gives rise to a change in the characteristics of the optical signal received at the detector. Figure 2.2 depicts the various changes that can be introduced to the light traveling along the fiber. A fiber optic sensor (FOS) can affect one or more of the light-guiding characteristics of the transmitting fiber and correlate the particular parameter of interest (e.g., temperature, strain, pressure, chemical species, etc.) to these particular light changes. Hence, the fundamental principle is to measure an external physical parameter by inducing changes in one or more of the optical properties of a light beam traveling inside and along an optical fiber. The fiber is thus both the sensing element and transmission medium. Fiber optic sensors represent a technology base that can be applied to a multitude of sensing applications. The following are some characteristic advantages of fiber optics that make their use especially attractive for sensors: Nonelectrical Explosion proof Often do not require contact Remotable Small size and lightweight Allow access into normally inaccessible areas Potentially easy to install Immune to radio frequency interference (RFI) and electromagnetic interference (EMI) Solid-state reliability High accuracy Can be interfaced with data communication systems Secure data transmission Resistant to ionizing radiation Can facilitate distributed sensing

2 citations

Proceedings ArticleDOI
01 Jul 1991
TL;DR: In this article, three coatings on silica fibers were evaluated: acrylates, hard fluoropolymers, and polyimides, and the results showed that the polyimide fiber showed the highest static fatigue resistance.
Abstract: Optical fibers are required to withstand high stresses associated with bending. These bends often occur during exposure to high-moisture environments in medical applications. Various polymeric coatings were developed to provide fiber protection. Three coatings on silica fibers were evaluated: acrylates, hard fluoropolymers, and polyimides. The evaluation included dynamic strength and static fatigue. In general, all three coatings produced strong fibers, but the acrylate and hard fluoropolymer provided superior protection. Also a strength dependence on fiber size was demonstrated. The polyimide fiber showed the highest static fatigue resistance with hard fluoropolymers outperforming acrylates. However, the poor abrasion resistance and toughness of the polyimide coatings can degrade both the dynamic and the static fatigue properties of the fiber.

2 citations


Cited by
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Journal ArticleDOI
21 Feb 2019-Sensors
TL;DR: An overview of the currently available contact-based methods for measuring respiratory rate is provided, based upon the recording of respiratory airflow, sounds, air temperature, air humidity, air components, chest wall movements, and modulation of the cardiac activity.
Abstract: There is an ever-growing demand for measuring respiratory variables during a variety of applications, including monitoring in clinical and occupational settings, and during sporting activities and exercise. Special attention is devoted to the monitoring of respiratory rate because it is a vital sign, which responds to a variety of stressors. There are different methods for measuring respiratory rate, which can be classed as contact-based or contactless. The present paper provides an overview of the currently available contact-based methods for measuring respiratory rate. For these methods, the sensing element (or part of the instrument containing it) is attached to the subject’s body. Methods based upon the recording of respiratory airflow, sounds, air temperature, air humidity, air components, chest wall movements, and modulation of the cardiac activity are presented. Working principles, metrological characteristics, and applications in the respiratory monitoring field are presented to explore potential development and applicability for each method.

248 citations

Patent
26 May 2005
TL;DR: In this paper, a fiber optic tether disposed in coiled tubing for communicating information between downhole tools and sensors and surface equipment and methods of operating such equipment is described, which includes transmitting control signals from the surface equipment to the downhole equipment over the fiber-optic tether, or collecting information by measuring an optical property observed on the fiber optic property.
Abstract: Apparatus having a fiber optic tether disposed in coiled tubing for communicating information between downhole tools and sensors and surface equipment and methods of operating such equipment. Wellbore operations performed using the fiber optic enabled coiled tubing apparatus includes transmitting control signals from the surface equipment to the downhole equipment over the fiber optic tether, transmitting information gathered from at least one downhole sensor to the surface equipment over the fiber optic tether, or collecting information by measuring an optical property observed on the fiber optic tether. The downhole tools or sensors connected to the fiber optic tether may either include devices that manipulate or respond to optical signal directly or tools or sensors that operate according to conventional principles.

203 citations

Journal ArticleDOI
TL;DR: In this article, a review of the main classes of silica-based optical fibers are presented: radiation tolerant pure-silica core or fluorine doped optical fibers, germanosilicate optical fibers and radiation sensitive phosphosilicates and aluminosa-ilimideal optical fibers.

195 citations

Patent
10 Aug 2011
TL;DR: In this paper, a dissolvable bridge plug configured with components for maintaining anchoring and structural integrity for high pressure applications is presented, where the plug is configured such that these components may substantially dissolve to allow for ease of plug removal following such applications.
Abstract: A dissolvable bridge plug configured with components for maintaining anchoring and structural integrity for high pressure applications. Embodiments of the plug are configured such that these components may substantially dissolve to allow for ease of plug removal following such applications. In one embodiment the plug may effectively provide isolation in a cased well for applications generating over about 8,000 - 10,000 psi. At the same time, by employment of a dissolve period for the noted components, such a plug may be drilled-out in less than about 30 minutes, even where, disposed in a lateral leg of the well.

192 citations

Journal ArticleDOI
TL;DR: The current state-of-the-art of fiber optic sensing/monitoring technologies, including the basic principles of various optical fiber sensors, novel sensing and computational methodologies, and practical applications for railway infrastructure monitoring are reviewed.
Abstract: In recent years, railway infrastructures and systems have played a significant role as a highly efficient transportation mode to meet the growing demand in transporting both cargo and passengers. Application of these structures in extreme environmental situation under severe working and loading conditions, caused by the traffic growth, heavier axles and vehicles and increase in speed makes it extremely susceptible to degradation and failure. In the last two decades, a significant number of innovative sensing technologies based on fiber optic sensors (FOS) have been utilized for structural health monitoring (SHM) due to their inherent distinctive advantages, such as small size, light weight, immunity to electromagnetic interference (EMI) and corrosion, and embedding capability. Fiber optic-based monitoring systems use quasi-distributed and continuously distributed sensing techniques for real time measurement and long term assessment of structural properties. This allows for early stage damage detection and characterization, leading to timely remediation and prevention of catastrophic failures. In this scenario, FOS have been proved to be a powerful tool for meticulous assessment of railway systems including train and track behavior by enabling real-time data collection, inspection and detection of structural degradation. This article reviews the current state-of-the-art of fiber optic sensing/monitoring technologies, including the basic principles of various optical fiber sensors, novel sensing and computational methodologies, and practical applications for railway infrastructure monitoring. Additionally, application of these technologies to monitor temperature, stresses, displacements, strain measurements, train speed, mass and location, axle counting, wheel imperfections, rail settlements, wear and tear and health assessment of railway bridges and tunnels will be thoroughly discussed.

117 citations