An Ultrathin Wearable Ultrasound Patch Having Four PMUT Chips in a T-Shaped Layout for Bladder Volume Monitoring

This article uses the piezoelectric micromachined ultrasonic transducer (PMUT) to verify the feasibility of ultrathin structures in wearable urine volume detection devices. The properties of PMUT allow it to operate without a backing layer or impedance matching, offering a unique advantage in miniaturization. It is fixed to the reinforced flexible printed circuit (FPC) through wire-bonding, then encapsulated in solid silicone, keeping the overall thickness within 1 mm, making it more comfortable to wear without significantly affecting performance. Arranging four chips in a T-shaped configuration and simultaneously activating them to acquire positional information are obtained in practical verification. Ellipses are fit in the XY and XZ planes using coordinates from three chips (middle, left, and right) and two chips (middle and top), respectively, combined with the distance between the bladder’s walls. These data were used to construct an ellipsoid to estimate volume, followed by linearization of the output data. Incremental water injection into a pig bladder resulted in a nonlinear error of 3.78%, demonstrating the system’s effectiveness for long-term wearable monitoring of bladder dysfunction.