Superior lead-free piezoceramics for wearable multimodal ultrasound imaging arrays.

Medical ultrasound technology provides zero-radiation, non-invasive, high-penetration and high-resolution evaluation of body organs for diagnosing various diseases. However, challenges remain for emerging ultrasonic bioelectronics in terms of novel material exploration, structural flexibility, wearable integration. Here, we present a 64-channel lead-free ultrasound line imaging array transducer developed from biofriendly potassium sodium niobate-based ceramics, which enables wearable multimodal imaging through the incorporation of multilevel material structure engineering and flexible device design. On the materials engineering aspect, the lead-free ceramics exhibits superior piezoelectricity (d33 ~ 630 pC N-1, k33 ~ 0.66) by restoring long range ferroelectric ordering and suppressing excessive polar nanoregions. In terms of device architecture, the miniaturized array integrates 64 lead-free 1-3 piezo-elements on a flexible printed circuit board and a bioadhesive hydrogel layer for acoustic coupling and robust adhesion to the skin, enabling portable, high-precision operation with a center frequency of 8.36 MHz and a -6 dB bandwidth of over 40%. In wearable applications for the human body, this array demonstrates real-time high-resolution vascular imaging, blood flow dynamics, and elastography of muscle dynamics, advancing the next generation of wearable ultrasound technologies.