Reinhard Klambauer

The aim of this work is to demonstrate and improve the use of Fiber Optical Current Sensors (FOCS) for high-frequency measurement of electrical currents at high-voltage levels in the field. A non-modulated Sagnac interferometer utilizing the Faraday effect is built and tested. Unlike modulated systems, the only limitation on signal measurement bandwidth imposed by the measuring technique in this arrangement is the propagation time of light. Functional tests were successfully carried out in the laboratory. Current events with a bandwidth of $\approx {100}\, {\text{kHz}}$ were recorded in the field. However, due to the non-common-path interferometer design and the broadband Super Luminescence Diode (SLD) light source, the system exhibits coherence limitations which affect fringe visibility if path length mismatches occur. The integration of a noise-modulated Distributed Feedback (DFB) laser was evaluated. To mitigate environmental drift and improve stability, spun fiber sensing heads were implemented and tested in extended field trials. These improvements demonstrate a feasible path towards robust high-frequency current monitoring using purely optical measurement principles.

This paper presents a novel wayside rail monitoring system for real-time detection and quantification of rail surface cracks with sub-millimeter precision. The core innovation lies in mounting piezoelectric transducers on the web of the rail—an unconventional and practical location that avoids interference with wheel passages while enabling continuous monitoring in real-world conditions. Moreover, to directly quantify crack depth, a customized signal processing pipeline is developed, employing surface acoustic waves (SAWs) and incorporating a parallel reference transducer pair mounted on an undamaged rail section for calibration. This auxiliary pair provides a real-time calibration baseline, improving measurement robustness and accuracy. The method is experimentally validated on rail samples and verified through metallographic analysis. This approach enables condition-based maintenance by improving detection accuracy and offers the potential to reduce operational costs and enhance railway safety.

This paper presents a measurement method for characterizing the frequency response of an optical microphone system using a purely optical approach. The use of optical methods allows to precisely determine the frequency response of the device from infra-sound up to 100 kHz in a single measurement, without the need of a reference microphone. The presented method relies on the inherently flat frequency characteristics of an optical cavity, allowing the assignment of any frequency-dependent behavior to secondary sources, such as the signal conditioning and data acquisition unit. The frequency characteristic was found to be strongly dependent on the settings of the internal amplifiers and high-pass filters, indicating the necessity of a calibration procedure if a flat frequency response is required.

Preserving the stable operation and proper functionality of the electric power grid is of utmost importance. Integral grid components such as power transformers are negatively affected by occurring disturbances. In particular, the time course and distribution on the different phases of direct currents within the transmission grid, among them geomagnetically induced currents, is of great interest. In this paper, we report on the development of a fiber optic current sensor exploiting the Faraday effect intended to observe these direct currents on all three phases of a high-voltage power grid. The proposed low-cost sensor is constructed with an adjustable phase retarder and a single-mode sensing fiber. A linear current relationship for direct currents down to 1A was observed. From the sensor signal, the presence of a direct current bias superimposed on an alternating current can be identified. Simulations based on a Jones formalism model provided application limits of the single-mode sensing fiber. Furthermore, we developed a calibration procedure to counteract temperature-induced variations of the sensor scale factor within the fiber-optic coil and achieve a maximum current error of 0.5% down to a rated current of 5A in a range from 15-65°C.

Developing measurement devices and methods to track increasingly stringent emission standards, including particle number, is crucial. This paper presents a novel analytical model to describe the signal response of an electrostatic particle sensor not only to particle mass concentration, but also to the particle number concentration of in-flowing particles. The uniqueness of this model lies in its ability to calculate the signal as a function of particle diameter, enabling the determination of particle number concentration from the signal. The model considers the effects of aerosol flow, electrode voltage and temperature, and can be used for the optimization of the sensor geometry parameters, length, width, and electrode gap. The model was designed to optimize the sensor’s geometry and signal retrieval as well as the optimization of the electric field between the electrodes. Comparative analysis was conducted between the proposed model and a model from the literature as well as experimental data from literature and experimental data collected in this paper.

Temperature is a crucial factor for the safe operation of lithium-ion batteries. During operation, the internal temperature rises above the external temperature due to poor inner thermal conductivity. Various sensors have been proposed to detect the internal temperature, including fiber Bragg grating sensors. However, to the authors’ knowledge, there is no detailed description of the encapsulation of the fiber Bragg grating sensor in the literature to shield it from strain. In this study, different encapsulation methods for strain compensation were compared to find the encapsulation material most compatible with the electrolyte. For this, we stored the proposed sensors with different encapsulation methods in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 3:7 with LiPF₆ (lithium hexafluorophosphate) electrolyte and applied temperature changes. After evaluating the sensor encapsulation methods in terms of handling, diameter, uncertainty, usability, and hysteresis behavior, the most suitable sensor encapsulation was found to be a fused silica capillary with polyimide coating.

This work presents an approach to monitoring the State-Of-Charge of Lithium-Ion battery cells via piezo disc-based ultrasonic Time-Of-Flight measurement by measuring the traveling time of a mechanical pulse through the cell between two surface-mounted sensors. The main advantage of this approach is the simplicity and the resulting low cost, which makes it suitable for future application in battery management systems. In detail, the excitation of the piezo actuator is done using a single semiconductor switch instead of a power amplifier, and the received signal is processed with an amplifier and Schmitttrigger combination to condition the signal for the microprocessor, which is part of a battery management system. Both the functionality and the limits of the design are evaluated with a high energy density Lithium-Ion pouch cell under different operational scenarios. Several parameters such as temperature, current rates, and excitation frequency are varied to prove the design concept. For validation purposes, an estimation function is generated and a real-world driving cycle applied. An estimation with an error of 1.29% of the Time-Of-Flight total value or 16.8%of the State-Of-Charge value under challenging conditions is achieved with the current setup.