Skin-Conformable Flexible and Stretchable Ultrasound Transducer for Wearable Imaging

Ultrasound imaging offers a non-invasive, radiation-free method for visualizing internal tissues and organs, with deep penetration capabilities. This has established it as a crucial tool for physicians in diagnosing internal tissue pathologies and monitoring human conditions. Nonetheless, conventional ultrasound probes are often characterized by their rigidity and bulkiness. Designing a transducer that can seamlessly adapt to the contours and dynamics of soft, curved human skin presents significant technical hurdles. We present a novel flexible and stretchable ultrasound transducer (FSUT) designed for adaptability to large-curvature surfaces while preserving superior imaging quality. Central to this breakthrough is the innovative use of screen-printed silver nanowires (AgNWs) coupled with a composite elastic substrate, together ensuring robust and stable electrical and mechanical connections. Standard tensile and fatigue tests verify its durability. The mechanical, electrical and acoustic properties of FSUTs are characterised using standard methods, with large tensile strains (≥110%), high flexibility (R ≥1.4 mm) and light weight (≤1.58 g) to meet the needs of wearable devices. Center frequency and -6dB bandwidth are approximately 5.3MHz and 66.47%, respectively. Images of the commercial anechoic cyst phantom yielded an axial and lateral resolution (depths of 10 mm to 70 mm) of approximately 0.31mm and 0.46mm, 0.34mm and 0.84mm respectively. The complex curved surface imaging capabilities of FSUT were tested on agar-gelatin-based breast cyst phantoms under different curvatures. Finally, ultrasound images of the thyroid, brachial and carotid arteries were also obtained from volunteer wearing FSUT.