Structural Design for Stretchable Microstrip Antennas.

Wireless technology plays a critical role in the development of flexible and stretchable electronics due to the increasing demand for compactness, portability, and level of comfort. As an important candidate in wireless technology, microstrip antennas have recently been explored for flexible and stretchable electronics. However, the stretchable characteristics of the microstrip antenna typically come at the cost of reduced electrical conductivity and radiation efficiency. By utilizing a soft silicone substrate and the structural design of the conventional metallic materials for both patch and ground plane in the microstrip antennas, we have demonstrated two designs of stretchable microstrip antennas: "meshed microstrip antenna" and "arched microstrip antenna". The former exploits initially wavy structures from patterning, and the latter also uses the deformed wavy structures created from the prestrain strategy. In comparison to their solid microstrip antenna counterpart, the radiation properties of the resulting stretchable microstrip antennas do not change much. Meanwhile, the resonance frequency decreases with the externally applied tensile strain along the feeding direction in the design of the meshed microstrip antenna but increases with the increasing strain in the design of the arched microstrip antenna. The change in the resonance frequency with the externally applied tensile strain in the latter design has a high sensitivity, manifesting a 3.35- and a 1.49-fold increase of sensitivity when compared to those in previous reports that used silver nanowire- or liquid-metal-based stretchable microstrip antennas. Considering the high sensitivity and compliant characteristic of the stretchable microstrip antenna, we have demonstrated an arched microstrip antenna-based strain sensor that is capable of detecting the motion of human wrists with high sensitivity, little hysteresis, and possible wireless communication.