The advancement of printed flexible electronics technology empowers the RFID tags with a simple fabrication process and innovative features such as flexibility, stretchability, and wearability. Flexible RFID tags based on...

Flexible antennas based on the printed flexible electronic technology are of great interest for important applications in wireless communication systems due to their distinctive features over traditional rigid-based antennas. The ultrawideband (UWB), notch characteristics, and bending capabilities of such antennas are crucial for flexible and wearable applications. Currently, only a few are focused on the printed flexible electronics technology with printable ink materials for UWB antenna applications. In addition, flexible UWB antennas with triple-notch characteristics and good bending performance are rarely reported. Thus, there is a need to make advances in this area. Here, we describe the application of a printable silver nanoparticlebased ink for rapidly fabricating an antenna with bendable and triple-notch characteristics designed for UWB communication systems. The ink, composed of monodisperse silver nanoparticles, isopropanol, and ethyl glycol, can easily produce favorable conductive patterns at a sintering temperature below 130 °C after inkjet printing. The antenna is designed on a flexible polyethylene terephthalate (PET) substrate and has a moderate size of 27 mm × 38 mm × 0.12 mm. It operates at a frequency range of 1.9−10.75 GHz, which covers the desired UWB frequency band. By loading a "U"-like slot and two "C"-like slots on the radiating patch, band rejections were generated at 3.2−3.8, 5.3−6.2, and 7.8−8.5 GHz, shielding the interference from world interoperability for microwave access, wireless local area networks, and X uplink bands. The bending results show that the antenna retains good UWB and triple-notch performance even after bending along the Y-or X-axis for different degrees. An antenna prototype was finally fabricated by inkjet printing of the silver nano ink on the PET substrate, exhibiting the desired notch characteristics and excellent bendability. The fabricated antenna prototype proved the feasibility of use as a flexible device at an ultrawide frequency band. The research provides a design guide for flexible antennas with notch features toward flexible and wearable electronics.

Advancement of printed flexible electronics provides electronic devices with a facile manufacturing process and some innovative characteristics such as bendability and flexibility. The exploitation of functional ink materials is a critical challenge for printed flexible electronics. Silver-based particle-free inks have drawn widespread research interest because of their merits in terms of synthesis, flexibility, and low-temperature processing. Although the fact that various kinds of silver precursors have been employed to formulate silver particle-free inks, they are still not ideal owing to concerns with stability, the synthetic process, and conductivity. On the other hand, as a major component, the type of silver precursors has a significant effect on the performance of the formulated ink and the associated film. Therefore, it is essential to develop silver precursors with desirable properties and study the influence of their types on the ink performance. In this paper, three dibasic silver carboxylates with increasing alkyl carbon chain length were synthesized. Their chemical composition, thermal behavior, and morphologies were investigated in detail. Silver malonate was found to have a relatively low thermal decomposition temperature, excellent stability, and the capacity to be synthesized at room temperature, making it appropriate for ink synthesis. Then, a silver malonate (AgMa) ink was formulated, where the thermal decomposition behavior, the evolution process of the microstructure of the film, and the influence of the length of the alkyl carbon chain on the ink were explored. By utilizing silver oxalate as a co-precursor, the performance of the AgMa ink was effectively enhanced. The research provides a facile and cost-effective way for controlling the decomposition process, film morphology, and electrical performance of silver ink, only by using specially designed mixed silver dicarboxylates as precursors.