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Shape-sensing optical fibers have become increasingly important in applications requiring flexible navigation, spatial awareness, and deformation monitoring. Fiber Bragg Grating (FBG) sensors inscribed in multi-core optical fibers have been democratized over the years and nowadays offer a compact and robust platform for shape reconstruction. In this work, we propose a novel, computationally efficient method for determining the 3D tip position of a bent multi-core FBG-based optical fiber using a second-order polynomial approximation of the fiber’s shape. The method begins with a calibration procedure, where polynomial coefficients are fitted for known bend configurations and subsequently modeled as a function of curvature using exponential decay functions. This allows for real-time estimation of the fiber tip position from curvature measurements alone, with no need for iterative numerical solutions or high processing power. The method was validated using miniaturized test structures and achieved sub-millimeter accuracy (<0.1 mm) over a 4.5 mm displacement range. Its simplicity and accuracy make it suitable for embedded or edge-computing applications in confined navigation, structural inspection, and medical robotics.

Minimally Invasive Surgery is often limited by the lack of tactile feedback. Indeed, surgeons have traditionally relied heavily on tactile feedback to estimate tissue stiffness - a critical factor in both diagnostics and treatment. With this in mind we present in this paper a flexible sensor foil, based on polymer optical waveguide. This sensor has been applied for real-time contact force measurement, material stiffness differentiation and surface texture reconstruction. Interrogated by a commercially available optoelectronic device, the sensor foil offers precise and reproducible feedback of contact forces up to 5 N, with a minimal detectable limit of 0.1 N. It also demonstrates distinct optical attenuation responses when indenting silicone samples of varying stiffnesses under controlled displacement. When integrated onto a 3D-printed module resembling an endoscopic camera and manipulated by a robotic arm, the sensor successfully generated spatial stiffness mapsof a phantom. Moreover, by sliding over structures with varying surface textures, the sensor foil was able to reconstruct surface profiles based on the light attenuation responses. The results demonstrate that the presented sensor foil possesses great potential for surgical applications by providing additional haptic information to surgeons.

In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated into microchannel structures and characterized by various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was postprocessed by using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of −47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: the refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg-grating-based waveguide sensor demonstrates high potential for applications based on the lab-on-a-chip concept.

This research investigates the use of a fiber optic sensor for detecting hydrogen gas during a thermal runaway of lithium-ion batteries (LIBs). Timely detection of thermal runaway in LIBs, particularly in storage and logistics, is crucial for effective safety management and preventing the escalation of incidents to adjacent cells. The sensors employed in this study utilize fiber Bragg grating (FBG) technology. The FBG sensors are coated with palladium nanoparticles, enabling the detection of hydrogen concentrations up to 5%. In abuse tests, the sensors successfully identified hydrogen emissions. Cross-sensitivity effects were observed during a secondary test and were thoroughly investigated. These interferences were found to be primarily caused by carbon monoxide (CO), a common byproduct of battery venting. While the presence of CO can interfere with hydrogen detection, both signals remain independently valuable as indicators of cell malfunction. This dual-response behavior enhances the robustness of fault detection under real-world battery failure scenarios.

A novel endoscopic palpation tool (EPT), designed for tactile and stiffness sensing using fiber Bragg gratings (FBGs) was evaluated in a surgical environment for intraoperative safety and effectiveness. The EPT consisted of four FBGs arranged in a cross pattern and embedded within an elastic, hollow, silicone hemispherical dome designed to deform upon contact with soft tissue. The EPT was employed to scan both in vivo and ex vivo tissue samples. Monitoring of porcine vital signs during minimally invasive and open surgical procedures showed no significant changes during use of the EPT. Perioperative blood tests including inflammatory markers and liver and renal function studies were unremarkable. Histopathological analyses of tissues involved (liver, spleen, bowel, and abdominal wall) showed no evidence of inflammation, necrosis, or tissue damage, confirming the device’s biocompatibility. To the best of our knowledge, this is the first study reporting in vivo stiffness measurements using an FBG-based EPT. The probe successfully distinguished between soft and hard tissue regions’ relative stiffness. Furthermore, successive measurements on liver samples demonstrated the device’s ability to generate stiffness maps, enabling clear visualization of spatial variation in tissue stiffness.

Fiber optic shape sensing is an innovative technology that has enabled remarkable advances in various navigation and tracking applications. Although the state-of-the-art fiber optic shape sensing mechanisms can provide sub-millimeter spatial resolution for off-axis strain measurement and reconstruct the sensor’s shape with high tip accuracy, their overall cost is very high. The major challenge in more cost-effective fiber sensor alternatives for providing accurate shape measurement is the limited sensing resolution in detecting shape deformations. Here, we present a data-driven technique to overcome this limitation by removing strain measurement, curvature estimation, and shape reconstruction steps. We designed an end-to-end convolutional neural network that is trained to directly predict the sensor’s shape based on its spectrum. Our fiber sensor is based on easy-to-fabricate eccentric fiber Bragg gratings and can be interrogated with a simple and cost-effective readout unit in the spectral domain. We demonstrate that our deep-learning model benefits from undesired bending-induced effects ( e.g ., cladding mode coupling and polarization), which contain high-resolution shape deformation information. These findings are the preliminary steps toward a low-cost yet accurate fiber shape sensing solution for detecting complex multi-bend deformations. High-resolution fiber shape sensors face limited application due to high costs. Manavi et al. proposed a solution employing deep learning for shape prediction directly from the fiber sensor’s spectrum. This approach eliminates the need for expensive measurements and complex post-processing, providing a cost-effective yet accurate method for detecting complex multi-bend deformations.

In this scientific publication, a new sensor approach for status monitoring, such as state of charge and state of health, of lithium ion batteries by using special Bragg gratings inscribed into standard optical glass fibers is presented. In addition to well-known core gratings, embedded into the anode of 5 Ah lithium ion pouch cells as a strain monitoring unit, the manufacturing of a surface cladding waveguide Bragg grating sensor incorporated into the cell’s separator, that is sensitive to changes of the refractive index of the surrounding medium, is demonstrated. On the basis of the experiments carried out, characteristics of the cell behavior during standard cyclization and recognizable marks in subsequent post-mortem analyses of the cell components are shown. No negative influence on the cell performance due to the integrated sensors have been observed; however, the results show a clear correlation between fading cell capacity and changes of the interior optical signals. Additionally, with the novel photonic sensor, variations in the electrolyte characteristics are determinable as the refractive index of the solution changes at different molar compositions. Furthermore, with the manufactured battery cells, abuse tests by overcharging were conducted, and it was thereby demonstrated how internal battery sensors can derive additional information beyond conventional battery management systems to feasibly prevent catastrophic cell failures. The result of the research work is an early stage photonic sensor that combines chemical, mechanical and thermal information from inside the cell for an enhanced battery status analysis.

Electricity is an indispensable building block for sustainable development. As national and international electrification measures in rural areas of Tanzania are progressing slowly, a solar-powered mini-grid system with second-life battery storage was commissioned on an island in Lake Victoria in 2019 to support local development. This article evaluates the socio-economic impacts associated with electrification through this system. On average, 42.31 kWh of electricity could be provided per day. The daily demand of the main infrastructure (hospital and school) was 18.75 kWh on average. The remaining capacity thus offers enough potential to supply private households and possible economic activities. In order to evaluate the impact of electrification, a qualitative survey was conducted on site 12 months after commissioning, with 7% of the people living there being interviewed. Language barriers as well as intercultural hurdles made the survey difficult and required an adaptation of the on-site implementation. The focus of the survey was on the areas of health, education and economics. The study revealed that the availability of electricity has enormous potential to improve people's living conditions. Initial successes could be seen, especially in the areas of health care and the economic sector. So far, electrification has had no influence on the area of education. While the connections for the main infrastructure have been institutionally supported, the system-related electricity price of €1.30/kWh has proven to be a major obstacle for private households. This is far too high for widespread use compared to incomes. The article thus focuses on the observation that full socio-economic development through electrification can only succeed if local people can afford it. Possibilities to solve this problem are analysed. Since the energy is generated on the basis of renewable resources, the analysis focuses on the use of mechanisms of the emissions trading system (ETS). The aim is to generate revenue through the sale of certified emission reductions (CERs) for the saved CO 2 emissions and thus reduce the electricity price. A reference scenario of conventional energy production forms the basis for discussion of the effectiveness of the Clean Development Mechanism (CDM) and the Carbon Initiative for Development (Ci-Dev). In addition, the approach of a monthly free quota of electricity, the free basic electricity initiative (FBE), is included in the evaluation. Graphical abstract

Water is an essential resource required for various human activities such as drinking, cooking, growing food, and personal hygiene. As a key infrastructure of public services, access to clean and safe drinking water is an essential factor for local socio-economic development. Despite various national and international efforts, water supply is often not guaranteed, especially in rural areas of Africa. Although many water resources are theoretically available in these areas, bodies of water are often contaminated with dangerous pathogens and pollutants. As a result, people, often women and children, have to travel long distances to collect water from taps and are exposed to dangers such as physical violence and accidents on their way. In this article, we present a socio-economic case study for rural development. We describe a drinking water treatment plant with an annual capacity of 10,950 m3 on Kibumba Island in Lake Victoria (Tanzania). The plant is operated by a photovoltaic mini-grid system with second-life lithium-ion battery storage. We describe the planning, the installation, and the start of operation of the water treatment system. In addition, we estimate the water prices achievable with the proposed system and compare it to existing sources of drinking water on Kibumba Island. Assuming a useful life of 15 years, the installed drinking water system is cost-neutral for the community at a cost price of 0.70 EUR/m3, 22% less than any other source of clean water on Kibumba Island. Access to safe and clean drinking water is a major step forward for the local population. We investigate the socio-economic added value using social and economic key indicators like health, education, and income. Hence, this approach may serve as a role model for community-owned drinking water systems in sub-Saharan Africa.

Lithium ion batteries play an increasing role in everyday life, giving power to handheld devices or being used in stationary storage solutions. Especially for medium or large scale solutions, the latter application confines a huge amount of energy within a small volume; however, increasing the hazard potential far above the common level. Furthermore, as the safety hazards of lithium ion cells have been known for years, impressively shown by several burning cars or laptops, the need for a further enhancement of the safety of these systems is rising. This manuscript presents measurements of the gas emission from lithium ion batteries in case of a malfunction for different scenarios, showing a large variety of species with mostly toxic to highly toxic properties. The measurements were carried out using a combination of gas chromatography-mass spectrometry (GC-MS), quadrupole mass spectrometry (QMS), photoacoustic spectroscopy, and chemical analysis. It is shown that the inflammation of a cell can be overcome, also preventing a cascading effect to neighboring cells, but giving rise to worse toxic gas emission. Furthermore, a filtration concept is presented that decreases the concentration of the emitted components significantly and promises filtration below immediately dangerous to life or health (IDLH) equivalent levels.