The increasing interest in innovative solutions for health and physiological monitoring has recently fostered the development of smaller biomedical devices. These devices are capable of recording an increasingly large number of biosignals simultaneously, while maximizing the user’s comfort. In this study, we have designed and realized a novel wearable multisensor ring-shaped probe that enables synchronous, real-time acquisition of photoplethysmographic (PPG) and galvanic skin response (GSR) signals. The device integrates both the PPG and GSR sensors onto a single probe that can be easily placed on the finger, thereby minimizing the device footprint and overall size. The system enables the extraction of various physiological indices, including heart rate (HR) and its variability, oxygen saturation (SpO₂), and GSR levels, as well as their dynamic changes over time, to facilitate the detection of different physiological states, e.g., rest and stress. After a preliminary SpO₂ calibration procedure, measurements have been carried out in laboratory on healthy subjects to demonstrate the feasibility of using our system to detect rapid changes in HR, skin conductance, and SpO₂ across various physiological conditions (i.e., rest, sudden stress-like situation and breath holding). The early findings encourage the use of the device in daily-life conditions for real-time monitoring of different physiological states.

Wearable health devices (WHDs) are rapidly gaining ground in the biomedical field due to their ability to monitor the individual physiological state in everyday life scenarios, while providing a comfortable wear experience. This study introduces a novel wearable biomedical device capable of synchronously acquiring electrocardiographic (ECG), photoplethysmographic (PPG), galvanic skin response (GSR) and motion signals. The device has been specifically designed to be worn on a finger, enabling the acquisition of all biosignals directly on the fingertips, offering the significant advantage of being very comfortable and easy to be employed by the users. The simultaneous acquisition of different biosignals allows the extraction of important physiological indices, such as heart rate (HR) and its variability (HRV), pulse arrival time (PAT), GSR level, blood oxygenation level (SpO₂), and respiratory rate, as well as motion detection, enabling the assessment of physiological states, together with the detection of potential physical and mental stress conditions. Preliminary measurements have been conducted on healthy subjects using a measurement protocol consisting of resting states (i.e., SUPINE and SIT) alternated with physiological stress conditions (i.e., STAND and WALK). Statistical analyses have been carried out among the distributions of the physiological indices extracted in time, frequency, and information domains, evaluated under different physiological conditions. The results of our analyses demonstrate the capability of the device to detect changes between rest and stress conditions, thereby encouraging its use for assessing individuals’ physiological state. Furthermore, the possibility of performing synchronous acquisitions of PPG and ECG signals has allowed us to compare HRV and pulse rate variability (PRV) indices, so as to corroborate the reliability of PRV analysis under stationary physical conditions. Finally, the study confirms the already known limitations of wearable devices during physical activities, suggesting the use of algorithms for motion artifact correction.

In recent years, the importance of flexible and textile electronics in the field of wearable devices has continuously increased, as they are expected to replace conventional wires that exhibit limited resistance to the mechanical stress occurring in on-body applications. Wearable health devices (WHDs) can provide physiological information about various body parts and employ distributed sensor networks. Among the sensors typically integrated within WHDs, those based on the I²C communication protocol are very common and exploit signals transmitted at frequencies up to hundreds of kilohertz. Therefore, robust communication is required to guarantee a proper transmission of the signal at those frequencies. In this context, we have realized embroidered conductive threads exhibiting a lower resistance, appositely designed to replace conventional wires in a microcontroller-based wearable device employing I²C sensors. A commercial conductive thread (silver coated polyamide) was used to embroider the conductive lines on to cotton fabric. Preliminary measurements were performed to characterize the response of these materials to signals typically operated within the I²C communication protocol at different path lengths. Resistive measurements have also been performed to stimulate different environmental conditions, that is, temperature, the effect of sweating, and repeated washing cycles, also apply mechanical stress, i.e. twisting, with promising results that validate our conductive paths for digital signal communication.

This work investigates innovative technologies for DEMOnstration power plant (DEMO) Fast Discharge Units (FDUs), in comparison with traditional temperature-dependent discharge resistors. The protection system for the DEMO Toroidal Field (TF) superconducting magnets is designed to respond to a quench, which is a rapid transition from the superconducting state to normal conduction, or other faults. This system helps prevent severe damage to the TF magnets, which can experience significant thermal and voltage stresses during a quench, due to the intervention of the FDUs. These stresses can damage the insulation and compromise the magnet's integrity. FDUs play a crucial role in rapidly discharging the magnetic energy stored in the magnets. Silicon Carbide (SiC) varistors within the FDU, with their nonlinear behavior, can significantly reduce the voltage peak across the TF magnet at fast discharge with respect to normal resistors. In the high current configuration, the DEMO TF magnet system is composed of 16 TF coils, with: a total inductance of 22.56 H, an operating current of 105 kA and a total magnetic energy stored of about 124 GJ. Maximum voltage limits for TF coils are 6 kV terminal-to-terminal and 3 kV terminal-to-ground. Performance of technologies are compared considering voltage and hotspot temperature.

This paper investigates the feasibility and technical advantages of utilizing silicon carbide (SiC) varistors for the energy extraction systems of the toroidal field coils (TFC) in case of a quench in the present European DEMO fusion reactor design. Varistors offer a non-linear voltage-current response that provides faster discharge times and voltage limiting behavior compared to traditional linear resistors. Using the Metrosil 9000 series varistors as a baseline, comprehensive discharge simulations were conducted for both 8 and 16 Fast Discharge Unit configurations. The study integrates electrical transient simulations to assess clamping voltages and advanced thermal modeling to evaluate the corresponding stress on the superconducting cables. Specifically, the quench propagation and the hotspot temperature evolution were investigated using both conservative adiabatic calculations and detailed transient thermal-hydraulic modeling (via the 4 C code). Results indicate that, in normal operation mode, while voltage limits are successfully managed, the Joule integral limit is currently exceeded. Consequently, the thermal-hydraulic analysis reveals that jacket hotspot temperatures surpass the 150 K acceptance limit with varistor-based discharges, inducing higher thermal stresses than traditional resistors. This highlights a dual requirement: the need for varistor material optimizations in the case of DEMO TFCs–specifically targeting a lower non-linearity parameter ( β < 0.3 )— , in order to fully realize the benefits of SiC varistors for high-energy fusion applications, and a potential reassessment of the conductor design, in terms of both copper stabilizer amount and cross-section geometry, to improve current sharing during the discharge and conductor stability against small disturbances.