Recently, low-cost electronics printed on lightweight, flexible and 3D shaped substrates are gaining importance in the markets of wearables and smart packaging. However, printed electronics do not meet the electrical performance of subtractive techniques because the resistivity of metallic printed patterns is still much higher than that of bulk material. To fulfil this need, low-resistive and easy printable inks for high resolution printed electronics techniques are needed. In this work, parameters of silver nanoparticles ink for micro-scale printed electronics technique, Aerosol Jet Printing, are being enhanced. To increase electrical conductivity and enhance printability, surfactants and dispersing agents were used to increase ultrasonic atomisation efficiency, obtain a uniform structure of printed lines, and narrow the width of printed patterns. Electrical measurements show a decrease in resistivity value in samples enhanced by cationic and non-ionic surfactants, by 95%, compared to initially prepared inks. Surfactant additions to silver nanoparticles Aerosol Jet Printing ink show promising features for application in modern electronics.

Gas sensors are widely used in many industrial and home applications. There is therefore continued need to develop novel gas sensor substrates which provide good mechanical and electrical stability, and good flexibility in comparison with the conventional alumina and silicon-based materials. In this paper, we present the experimental results on flexible gas sensors based on the Kapton foil and alumina substrate covered by copper oxide as a gas-sensitive layer. These sensors exhibited good mechanical stability and gas-sensing characteristics. The Kapton-based CuO gas sensors were tested under exposure to acetone in the 0.05-1.25 ppm range (150 °C, 50%RH). The results confirmed that sensors deposited on the flexible substrate such as Kapton can be used in the exhaled breath analyzers dedicated to diabetes biomarker detection or other applications for which the elastic substrate is needed. Graphic Abstract

The Internet of Things is currently one of the fastest-growing branches in electronics. The development of energy storage systems and the miniaturization of dedicated printed circuit boards significantly influence that growth. However, the need for batteries and traditional printed circuit boards still limits devices' minimum size, weight, and cost, narrowing the application area. Energy harvesters and wireless power transfer systems fabricated with printed electronics can significantly reduce such devices' weight, size, and cost. Printed electronics technology provides scalable tools for many electronics applications, shortening the validation time and enabling new low-cost or disposable solutions on lightweight and flexible substrates embedded inside 3D printed structures and directly on device housings. Energy harvesting and wireless power transfer systems in electronic devices can provide enough power to minimize battery capacity and size or even eliminate the need for batteries in low-power applications. This review presents an adaptation of printed electronics technology in the fabrication of radio frequency energy harvesters and wireless power transfer rectennas for IoT applications. Last, perspectives for development towards greater integration with microsystems, transient electronics with ecofriendly materials, adaptation for next-generation telecommunication systems, and 3D structural electronics solutions are briefly discussed.

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