Kirigami Integrated Yagi-Uda Antenna for Strain Sensing in Biomedical Applications

This paper presents a low-profile flexible microstrip Yagi- Uda array antenna with strain sensing capability assisted by a Kirigami structure and design. The Yagi-Uda array was integrated on a PET substrate with a thickness of
$100\mu{\mathrm{m}}$
, demonstrating strain-induced changes in the antenna's resonant frequency and impedance bandwidth. Operating based on the concept of mutual impedance, displacing the director elements of the antenna by an applied force (i.e., strain), affects the mutual coupling of array elements, and consequently impacts the antenna parameters. The unstrained antenna operated at 5.32 GHz, showing a 1.7% fractional bandwidth with a measured estimated gain of 5.86 dBi. For variations in the range of 3–7 cm from the initial length, equivalent to 27-63% strain, the observed shift in the resonant frequency was
$140\sim 4$
MHz, respectively. This antenna array with both communication and strain-sensing capabilities is a proof of concept for multi-functional, wearable/flexible microwave devices in biomedical applications.