This study presents a hybrid fabrication process for LED matrix on flexible multilayer printed circuit boards (PCBs). To prepare for the flexible PCB, a roll-to-roll screen printing process was developed to create a core circuit board by printing on both sides of the flexible substrate. From the core PCB, the lamination and etching processes are then used to form four layers in total. By using the proposed method, we successfully implemented the passive LED matrix display. This approach could be used for other applications that require flexible and multilayer circuits.

Evaporation characteristics of a droplet on the surface of a transparent heater depend on the surface wettability.

Due to the increasing use of polypropylene-based nonwoven dust masks and air filters, environmental problems that occur due to the plastic pollution resulting from the disposal of these materials have also increased. Hence, an eco-friendly air filter based on PVA nanofibers (NFs) was fabricated by electrospinning on a nonwoven fabric, and its performance was evaluated as a filter capable of blocking or capturing particulate matter. The quality factor of the optimized PVA NF-based air filter was found to be 0.010606 Pa⁻¹, which is lower than that of a HEPA filter (0.015394 Pa⁻¹), but higher than that of a cabin air filter (0.010517 Pa⁻¹) and a dust mask (0.009102 Pa⁻¹). The contamination level of the PVA NF-based filter was analyzed by optical and structural analyses of the filter surface. Finally, the filter was soaked in water to selectively remove the contaminated PVA NF layer, and the remaining nonwoven fabric was able to be reused to make the filter.

To develop high-performance de- or anti-frosting/icing devices based on transparent heaters, it is necessary to study the evaporation-rate control of droplets on heater surfaces. However, almost no research has been done on the evaporation-rate control of liquid droplets on transparent heaters. In this study, we investigate the evaporation characteristics of water droplets on transparent heater surfaces and determine that they depend upon the surface wettability, by modifying which, the complete evaporation time can be controlled. In addition, we study the defrosting and deicing performances through the surface wettability, by placing the flexible transparent heater on a webcam. The obtained results can be used as fundamental data for the transparent defrosting and deicing systems of closed-circuit television (CCTV) camera lenses, smart windows, vehicle backup cameras, aircraft windows, and sensor applications.