Low-voltage, ultra-broadband wearable MEMS ultrasound: a frequency-merged, wafer-scale framework for continuous in vivo cardiovascular imaging and monitoring

Continuous, non-invasive monitoring of central hemodynamics is essential for advanced cardiovascular care. Although wearable ultrasound enables deep-tissue sensing, its widespread clinical adoption is limited by the inherent physical trade-off between driving voltage and acoustic bandwidth, alongside the challenges of scaling microelectronic ultrasound devices for medical imaging. Here, we report a wearable, 81.7% broadband piezoelectric micromachined ultrasonic transducer (pMUT) array driven at a low voltage of 5 Vp. To address these bottlenecks, this study introduces two parallel innovations. First, we introduce a novel frequency-merging design, quantified by an equivalent circuit model, to effectively decouple the voltage-bandwidth trade-off. Second, we provide a comprehensive framework directing a scalable silicon-on-insulator wafer-level fabrication process towards fully in vitro and in vivo experimental characterizations for medical imaging. Enabled by these advancements, in vitro characterization demonstrates 0.64 mm axial and 1.27 mm lateral resolutions while maintaining a penetration depth of up to 9 cm in wire phantoms. In vivo, the wearable patch achieves comparable high-fidelity B-mode and M-mode imaging of carotid, brachial, and radial arteries within 4 cm depth to commercial rigid probes. Crucially, the device enables continuous, stable hemodynamic monitoring under limited daily postural activities for up to 9 hours. Inter-subject validation confirms precise blood pressure measurements, with deviations of 2.2 mmHg compared to FDA-approved clinical monitors. Leveraging standard semiconductor batch manufacturing, this work addresses the technical mismatch between low-voltage wearable devices and high-performance ultrasound transduction, creating a feasible development path for highly integrated, mass-producible cardiovascular ultrasound systems-on-chip.