Electrical characterization of differential stretchable transmission line

The rise of wearable computing and biomedical technologies demands development of flexible and stretchable interconnects. This paper presents the design and characterization of differential stretchable transmission line. The transmission line is embedded in the low cost Polyurethane thin film which has excellent stretchablility and flexibility, and the copper pattern is optimized as a zigzag shape to allow stretch maintaining the mechanical reliability. The electrical characteristics were measured as the line stretches by using 4-port network analyzer with house made calibration kits. Especially, the measurement was made without common ground connections between near-end and far-end VNA ports and differential characteristics are successfully extracted. Measured differential mode characteristic impedance is 94-Ω at the normal length and slightly increased as the line stretches due to the deformation of the line. The insertion loss is 0.035dB/mm at 1-GHz from the beginning and slightly reduced as the line stretches. It is shown that the line can be elongated up to 25% guaranteeing the electrical and mechanical reliability.