Martin Jakobi

Rauheitsmessung an pharmazeutischen tabletten mittels angularer speckle-korrelation

Zusammenfassung Eine vollständige Charakterisierung von pharmazeutischen Tabletten besteht nicht nur in der Analyse der chemischen Zusammensetzung, sondern auch in der Untersuchung der Fertigung der inneren Struktur und der Oberflächenstruktur. Ziel dieser Arbeit ist es, die Oberflächenrauheit von Tabletten an Originalpräparaten und Generika mittels Angularer Speckle Korrelation (ASK) zu bestimmen. Die Ergebnisse zeigen unterschiedliche Rauheitswerte bei Tabletten mit gleichem Wirkstoff bei verschiedenen Trägerstoffen. Berührungslose Speckle-Rauheitsmessung könnte eingesetzt werden, um die Regelung des Produktionsprozesses zu verbessern, z. B. während die Tabletten aus Pulver gepresst werden.

Non-phase unwrapping interferometric approach for a real-time in-plane rotation measurement

This Letter proposes a novel interferometric approach for the in-plane rotation measurement. With a simple and compact measurement system, the rotation angle and its direction can be determined simultaneously in real time by applying the spatial carrier frequency. Besides, the phase unwrapping process is not required for the angular evaluation, which simplifies the data processing procedure. Theoretically, the relationship between the in-plane rotation and the phase change distribution has been deduced to demonstrate the possibility of this interferometric method. Practically, the preliminary experiments have been carried out to verify the feasibility of this approach and quantify the measurement accuracy.

Strain Measurement in Aluminium Alloy during the Solidification Process Using Embedded Fibre Bragg Gratings

In recent years, the observation of the behaviour of components during the production process and over their life cycle is of increasing importance. Structural health monitoring, for example of carbon composites, is state-of-the-art research. The usage of Fibre Bragg Gratings (FBGs) in this field is of major advantage. Another possible area of application is in foundries. The internal state of melts during the solidification process is of particular interest. By using embedded FBGs, temperature and stress can be monitored during the process. In this work, FBGs were embedded in aluminium alloys in order to observe the occurring strain. Two different FBG positions were chosen in the mould in order to compare its dependence. It was shown that FBGs can withstand the solidification process, although a compression in the range of one percent was measured, which is in agreement with the literature value. Furthermore, different lengths of the gratings were applied, and it was shown that shorter gratings result in more accurate measurements. The obtained results prove that FBGs are applicable as sensors for temperatures up to 740 °C.

Impact of angle ranges on thickness resolution in thin film reflectometry

Thin film reflectometry is a common way to monitor film thicknesses in numerous processes. Semiconductor and optics producing industries, e.g., require film thickness observation. Spectral reflectometry interrogation is one of several methods, which can be assessed by various algorithms depending on resolution and measuring range demands. Incident angle is a crucial parameter to these interrogation methods. Light, under different incident angles, produces different spectral reflectivity functions. These are integrated by a detector, in this case a spectrograph. Therefore, one needs to minimize the range of incident angles onto the measured object in order to increase the resolution of film thickness. Lateral resolution may also be a crucial parameter in some processes. Lateral resolution is a function of the range of incident angle, it increases with increasing angle range. These two crucial facts result in an estimate of measuring error introduced by the angle range under a given maximal lateral resolution. A measuring setup for a range of incident angle measurements is presented, as well as an example interrogation of a thin film under different incident angles.

Thin film interferometer using a light source with spectrally nonequidistantly distributed sampling points

Numerous processes, e.g. in semiconductor and optics producing industries require film thickness observation. These measuring systems depend on different working principles, e.g. spectral reflectometry or ellipsometry. The spectral reflectometry interrogation method can be evaluated by various algorithms depending on resolution and measuring range demanded. All methods require a broad spectral distribution of the light source in order to sample the signal sufficiently for parameter extraction. Spectral sampling is often realized using a spectroscope, which produces equidistant sampling points in frequency space. In contrast to conventional spectrally broad light sources, the one employed here emits several spectral lines, which are non-equidistantly distributed. It also introduces problems like variations of intensity in the output spectrum and narrow wavelength bands, in which the reflected spectrum can be investigated. Non-equidistant sampling points additionally imply problems in conventional analysis algorithms, e.g. a FFT anticipates equidistant sampling points. Narrow wavelength bands imply little information to interrogate at the same spectral resolution of the interrogator. Strong variations of intensity lead to high noise levels at wavelengths with low intensities. Therewith, accuracy, resolution and measuring range are limited. An interrogator based on a Hg-Ar light source, a fiber coupler and a commercial spectroscope is described in this work. Both, accuracy and measuring range, are investigated by simulation and are experimentally proven on a glass on silicon demonstrator. Introducing an advanced algorithm, uncertainties invoked by the sources spectral and intensity distribution are minimized and resolution as well as measuring range are increased.

Contouring of surfaces with discontinuities using ESPI

Electronic speckle pattern interferometry (ESPI) can provide accurate contour measurements in the micron range and short measurement times far below one second. Typical surfaces in industrial applications, however, often show discontinuities, like steps or holes. An unambiguous measurement of such surfaces is possible, if the synthetic wavelength is chosen larger than the largest surface step. A long synthetic wavelength, however, introduces a high noise level such that an unambiguous measurement combined with a high accuracy is not possible in any case. Our preferred solution for this problem is the combination of two or more synthetic wavelengths. In contrast to other publications (hierarchical, pixel-wise approach) our area-based approach uses only two synthetic wavelengths minimizing measurement time and device complexity. In this paper we present different methods for merging the phase images of the two synthetic wavelengths into one measurement result combining accuracy and unambiguousness.

Faseroptische Überwachung von mechanisch deformierten Kabelgeflechtsstrukturen mittels optischer Zeitbereichsreflektrometrie / Fiber-optic monitoring of mechanically deformed cable structures by means of optical time-domain reflectometry

Zusammenfassung In diesem Beitrag wird ein neuartiger Ansatz zur Schadensdetektion in Stromversorgungskabeln vorgestellt. Die Funktionalität des Messsystems kann bezüglich des durch Makrobiegungen induzierten Anstiegs des Dämpfungsbelags verifiziert werden. Durch den verwendeten Integrationsansatz sind Mantelschäden im Stromversorgungskabel detektierbar, wodurch langfristige Ausfallgründe frühzeitig erkannt werden. Über eine integrierte optische Faser und ein optisches Zeitbereichsreflektometer kann unabhängig von der elektrischen Energieübertragung im Kabel eine exakte und effiziente Schadenslokalisierung sichergestellt werden, was wiederum eine Zeit- und Kostenersparnis zur Folge hat. Abstract This article presents a novel type of damage detection system for power cables. The functionality of the measuring system can be verified with respect to macrobending-induced increase of attenuation. Due to the used integration approach, damage to the sheath at the power supply cable can be detected, whereby longterm failure causes can be detected at an early stage. By means of an integrated optical fiber and an optical time domain reflectometer, regardless of the electrical energy transmission in the cable, an exact and efficient damage localization can be provided, resuloting in time and costeffectiv procedure.

Online 3D Displacement Measurement Using Speckle Interferometer with a Single Illumination-Detection Path

Measurement systems for online nondestructive full-field three-dimensional (3D) displacement based on the single-shot and multiplexing techniques attract more and more interest, especially throughout the manufacturing industries. This paper proposes an accurate and easy-to-implement method based on an electronic speckle pattern interferometer (ESPI) with single illumination-detection path to realize the online nondestructive full-field 3D displacement measurement. The simple and compact optical system generates three different sensitivity vectors to enable the evaluation of the three orthogonal displacement components. By applying the spatial carrier phase-shifting technique, the desired information can be obtained in real time. The theoretical analysis and the measurement results have proven the feasibility of this ESPI system and quantified its relative measurement error.

Intensity distortions due to phase-only spatial light modulation: Characterization for applications in electronic speckle-pattern interferometry

Electronic speckle-pattern interferometry (ESPI) is a powerful tool for precise, full-field, and non-contact contouring of optically rough surfaces. Due to the interferometric principle, the sensitivity of ESPI is directly related to the involved wavelengths and is thereby a global parameter. Surfaces with a broad variation of phase gradients, as, for instance, a target with both smooth and comparatively steep areas, result in just partially resolvable fringe interferograms. In recent studies, spatial light modulators (SLMs) have been implemented to adapt the interferometric reference phase front to the measurement task and broaden or squeeze the fringe spacing locally in critical areas. This method is limited by diffraction effects, observable for all types of phase-only SLMs. We demonstrate a straight-forward model, describing the diffraction-based intensity distortions occurring in interferograms after wavefront adaptation. The aim is to characterize the intensity distortions by means of the proposed model and minimize their impact, especially with regard to phase-only spatial light modulation in ESPI. For validation, the modeled behavior of SLMs is compared to the experimental results, obtained for two different SLM designs. Finally, experiments are presented, which demonstrate a successful adaptation of the interferometric reference phase front in compliance with the boundary conditions determined by the model.

Damage detection in cable braidings using integrated fiber-optic reflectors

In cable industry, structural health monitoring is becoming more and more important. Of special relevance is the damage detection in cables which supply large excavation equipment like bucket wheel excavators in opencast mining. Here, damage localization is often still carried out manually. With a usual cable length of a few kilometers, this method is inefficient and can lead to unnecessary revenue losses caused by long repair and machine downtime. Because of their electromagnetic immunity, their functionality over long transmission distances, their resistance to difficult environmental conditions, and their comparatively easy integrability, fiberoptic sensors are particularly suitable for detecting damages in this application. Therefore, in this paper, a novel spatially resolving and inexpensive damage detection system based on fiberoptic reflectors is presented. With a physical vapor deposition method, an increased reflectance of the coated single mode fiber ends was achieved. Due to the special integration position of the sensors in the braiding structure of a cable, damage in the jacket area can be detected. Via measurements of the reflected signal intensities, the position of the damage can be resolved over long distances. Furthermore, the sensor arrangement engages only slightly in the manufacturing process of the cable braiding and the cable. The ability of the presented measurement system to perform damage detection independent of the regular power transmission of the cable offers an advantage over standard cable conductor based electrical damage detection techniques.