A Stretchable Wearable Doppler Ultrasound Patch for Continuous Vascular Monitoring

Continuous blood flow monitoring is crucial for the diagnosing and preventing cardiovascular diseases, but existing techniques have several limitations that hinder widespread clinical use, such as invasiveness, operator dependency and lack of continuous measurement. In this paper, we present a wearable ultrasound patch designed for continuous blood flow monitoring. The patch integrates six ultrasonic transducers arranged symmetrically along the central axis. A baseplate with a specific angle (30 degrees) is used to form a 60-degree Doppler incident angle. We have simplified and improved the fabrication process of the serpentine electrodes, avoiding the cumbersome traditional steps such as transfer printing and spin-coating of Cu/PI. The fabricated wearable ultrasound patch exhibits a center frequency of 5.05 MHz, a -6 dB bandwidth of 42.58%, and an elastic stretchability of up to 30%. Based on pulsed-wave (PW) Doppler, it calculates the Doppler frequency shift using a slow-time sampling algorithm. In vitro studies showed an absolute percentage error of 4.1% to 12% for constant flow velocity measurements, with actual flow velocities varying between 20 and 100 cm/s. The mean absolute error (MAE) was 3.56 cm/s, and the mean absolute percentage error (MAPE) was 5.99%. In pulsatile flow experiments, the patch was also able to capture the changing peaks of the velocity waveform, demonstrating its feasibility for continuous blood flow monitoring.