Fiber optic sensors based on fiber Bragg grating (FBG) technology have the potential to revolutionize the way vital signs of the human body are measured and monitored. By leveraging their unique properties, these sensors can provide accurate and reliable data, thus enhancing the effectiveness of wearable devices. The integration of FBG sensors into different materials not only broadens their application scope but also improves user comfort and device practicality. However, some challenges remain in optimizing the embedding process to ensure sensor performance and durability. This review provides an overview of FBG technology employed for measuring vital signs of the human body reported in the past decade. The focus of the review is on the FBG embedding strategies into different materials, categorized into these three main groups (i.e., 3D printed, textiles, and polymers) and explores the implications of embedding fiber optic sensors in each category. Furthermore, it discusses the potential impact of these embedded sensors on the accuracy, comfort, and practicality of wearable devices designed for monitoring vital signs, highlighting the potential of these sensors to transform the field of health monitoring. Future research directions may include exploring new materials for embedding and refining sensor design further to improve the accuracy and comfort of these wearable devices. Ultimately, the evolution of fiber optic sensors could significantly advance the field of human vital sign monitoring, paving the way for more sophisticated and user-friendly health monitoring systems.

Currently, the use of fiber-optic Bragg gratings in biomedical applications, especially in the field of magnetic resonance imaging (MRI), is becoming popular. In these applications, the fiber Bragg grating (FBG) encapsulation plays a crucial role in terms of the accuracy and reproducibility of the measurements. This paper describes in detail the fabrication method of a prototype FBG sensor, which is realized by encapsulating a Bragg grating between two layers of the MR-compatible material Acrylonitrile Butadiene Styrene (ABS) by 3D printing. The sensor thus created, implemented, for example, on the chest of a human body, enables monitoring of the vital functions of the human body. The paper describes the complete procedure for the creation of the prototype sensor, including strain and temperature dependence, as well as results of long-term experimental measurements against the conventional electrocardiography (ECG) standard. Results based on the objective Bland-Altman (B-A) method confirm that the implemented sensor can be used for reliable monitoring of cardiac activity (>95% based on B-A). Taking into account the single fiber optic cable, its simple implementation, its small size and weight < 5g, the presented sensor represents an interesting alternative to conventional ECG.

This article describes the implementation of an advanced fiber-optic intensity sensor for the comprehensive detection of axles and bogies of rail vehicles in tram transport. The sensor uses the principle of optical fiber bending, where the intensity of transmitted light is modulated due to mechanical stress on the fiber caused by the passage of a tram and the subsequent reversible deformation of the rail. The innovative design of the sensor allows for its easy installation under the rail foot, between the rail and the sleeper, replacing conventional anti-vibration pads, and includes specially designed deformable elements which the optical fiber bends and modulates the transmitted light intensity. During long-term testing (11 months in various weather conditions) conducted in the real tram depot (Ostrava, Czech Republic), 20602 tram passages were secured and analyzed. The sensor demonstrated success in detecting bogies, achieving 100% accuracy with no false positives (FPs) or false negatives (FNs). Axle detection showed an average success rate of 86.1%, with variability among different tram types up to 97.8%. The signal modulation was also subjected to detailed analysis, revealing differences in responses between various tram types, which can be attributed to differences in bogie construction and vehicle weight. Due to its electromagnetic immunity, the implemented fiber-optic sensor offers the potential for more reliable detection and broad application possibilities, including track occupancy monitoring, speed measurement, or determining the direction of travel on single-track lines. With slight optimization, the sensor could also be used to weigh rail vehicles or as an axle counter in railway or light rail transport.

This paper presents a novel fiber-optic temperature sensor based on correlated color temperature (CCT) measurement. The sensor is formed by a homogeneous mixture of polydimethylsiloxane (PDMS) and cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor, applied as a tip on the faces of an optical fiber pair. While YAG:Ce phosphors are commonly used in lighting and white light-emitting diode (WLED) technologies, their use in thermoluminescence and temperature sensing has been only minimally explored. We demonstrate that the temperature of a homogeneous PDMS–YAG:Ce mixture can be directly related to its CCT, and a highly linear dependence on temperature was identified across the studied range. The findings confirm that this CCT-based approach enables both contact and non-contact temperature measurement. The proposed optical sensors operate effectively from −60°C to 220°C (213–493 K), and their resistance to electromagnetic radiation was within a magnetic field range of −2 T to 2 T.