Optically Transparent and Flexible Radio Frequency Electronics through Printing Technologies

With the advent of the Internet of things, 5G wireless communication, and smart city applications, demand for a new form of radio frequency (RF) electronics has risen, one that can be mounted or integrated on non-conformal objects, is mass manufacturable at lower costs, and is optically transparent to maintain the aesthetics of the environment where deployed. This new breed of electronics can be realized through printing technologies, which are capable of manufacturing diverse designs on flexible substrates via large-scale and high-volume printing techniques at lower costs. However, the major challenge for printed electronics is the preparation of conductive inks with performance comparable to their bulk metal counterparts. This review summarizes the recent developments in printable transparent and conductive materials (TCMs), inks, and methods for optically transparent RF passives. In addition, techniques to enhance the conductivity of the TCMs are presented. Moreover, it covers several design examples of optically transparent RF passives, such as antennas, microwave absorbers, and frequency selective surfaces. Furthermore, many challenges and potential solutions are discussed in terms of the TCMs, inks, and printing technologies needed for the realization of such designs. Finally, some future trends in the area of transparent RF electronics and PE are discussed.