## 2 Materials and Methods
### Architecture of the Developed Smart Garment
Furthermore, the acquired data are analyzed by the IBM  
Figure 1: Graphical illustration of the deployed monitoring system relying on the proposed wearable device. Cloud Functions service to detect anomalies in the acquired data, in which case, alarm messages are sent to the database of the on-cloud application and a notification to the company's safety manager and the worker. The smart garment also includes signaling devices (e.g., LEDs) and a vibration generator to immediately warn the user when abnormal parameters (e.g., high gas concentrations) are detected. Furthermore, the smart garment is energetically autonomous thanks to an integrated multisource energy harvesting system, enabling the scavenging of energy from sources associated with the human body [42; 43]. Two thin-film flexible photovoltaic cells (model 0.125 W 5 V-45 \(*\) 25, manufactured by Dongguan New Energy Technology Co., Dongguan, Guangdong, China) are positioned on the user's back to convert incoming light energy (solar or artificial) into electrical energy (Figure 3b). These photovoltaic panels are characterized by 1 W maximum power, 1.5 V operating voltage, 1200 mA short-circuit current, 2 V open-circuit voltage, and 197 mm \(\times\) 97 mm \(\times\) 0.8 mm dimensions (Figure 4a). A conditioning section based on the LTC3108 IC (produced by Linear Technology, Milpitas, CA, USA) is employed to scavenge energy from the two photovoltaic panels connected in series (Figure 3b). Through a 1:90 external step-up converter, the LTC3108 IC can be configured as a flyback converter that allows a minimum input voltage of 22 mV. A series of three TEGs (model TEC1-12706, manufactured by Thermonamic inc., Jiangxi, China) is placed on each forearm to scavenge the thermal energy produced by the body to achieve a larger thermal gradient (Figure 4b) [44]; elastic bands maintain contact between the TEGs' hot joints and the skin. The used TEG model has 40 mm \(\times\) 40 mm dimensions, 127 p-n junctions, and a weight of 15 g.  
Figure 2: Top view of the custom microcontroller board integrated into the smart garment. Figure 4: Flexible solar panel (**a**) and TEG device (**b**) integrated into the garment; 3D model (**c**) and photo of realized corrugated piezoelectric transducers for gathering energy from joint motions (placed outside the garment for higher clarity (**d**). Figure 3: Graphical illustration of the multisource energy harvesting section, which shows the connections between the harvesters and conditioning modules integrated into the garment. Front view (**a**) and rear (**b**) views of the designed garment with highlighted the harvesting section. Similarly, two LTC3108-based modules are installed on the garment's sleeves to scavenge energy from the two series of TEGs; all LTC3108 stages are configured to 3.3 V output voltage. Additionally, two flexible piezoelectric harvesters are placed in correspondence to the user's elbows to convert the kinetic energy associated with the limb movements. The piezoelectric harvesters consist of 3D-printed flexible supports with a corrugated profile (160 mm \(\times\) 20 mm \(\times\) 7 mm--at the peak of corrugation), realized using TPU filament (with hardness 80 Shore A), on which is deposited a stack of two PVDF layers (model 3-1004346-0, manufactured by TE Connectivity Measurement Specialities Inc., Schaffhausen, Switzerland) connected in series by means of epoxy glue (Figure 4c,d). The resulting device is highly flexible (also due to its corrugated profile), resilient, and lightweight (10 g), making it unobtrusive to the user's movements. Lastly, a nylon cover was applied to the transducer to protect the surface of the polyvinylidene fluoride (PVDF) layers. For convenience, the two harvesters are fixed to joints by elbow pads for improving the mechanical coupling with the body. Two LTC3588-based modules (manufactured by Linear Technologies Co., Milpitas, CA, USA) are used to scavenge energy from the two piezoelectric harvesters.