All-knitted stretchable dipole antenna: design, fabrication, and effects of yarn alignments on antenna electromagnetic and tensile properties

With the evolution of the Internet of Things, stretchable antennas are playing an increasingly important role in wearable devices and flexible electronics. Typical drawbacks of current stretchable antennas are complex manufacturing processes, inadequate ventilation, and limited flexibility, which negatively impact their comfort and practicality. In this study, an all-knitted stretchable dipole antenna was designed and fabricated. This antenna was breathable and flexible like regular knitted fabric and had a simple manufacturing process. In addition, the effects of two yarn alignment types, namely antenna arms aligned in the course (AaC) and wale (AaW) directions, on antenna electromagnetic properties under tensile stress were investigated. Under unstretched conditions, both antenna AaC and AaW exhibited S11 of less than -10 dB at the operating frequency of 915 MHz, demonstrating good impedance matching performance and omnidirectional radiation characteristics. When stretched along the arm length direction, the frequency variations and strain of antenna AaC and AaW displayed strong linear relationships. Specifically, antenna AaC exhibited a higher sensitivity to the resonant frequency variation induced by strain when compared to antenna AaW. The results suggest that the antenna AaC are a more desirable option to be used as a sensor for human body movement monitoring. This study provides the theoretical basis and experimental foundation for the design and large-scale production of stretchable antennas utilizing textile materials.