Printed bidirectional stretch antenna sensor

This paper presents an antenna-based bidirectional stretch sensor for real-time wireless sensing applications. The proposed design utilizes an antenna structure with two orthogonal dipole elements operating at different frequency bands to independently sense strain in two perpendicular directions. One pair of elements is configured to operate at 2.4 GHz, while the other operate at 5GHz. The antenna is fabricated using direct ink writing (DIW) with stretchable silver ink on a flexible thermoplastic polyurethane (TPU) substrate, enabling the mechanical flexibility required for stretch sensing. Under applied stress, the antenna's physical dimensions change, leading to a shift in its resonant frequency. This frequency shift is observed to be linearly correlated with the applied strain along either axis (x-axis or y-axis). Experimental results show that for stretch levels ranging from 0 % to 10 % of the original dimensions, the resonant frequency shifts by approximately 6 % in the x-axis direction and 7 % in the y-axis direction, respectively. The proposed design demonstrates potential for applications requiring simultaneous stretch sensing and wireless communication using the same antenna structure.