A Stretchable and Wearable Ultrasonic Transducer Array for Bladder Volume Monitoring Application

Monitoring bladder volume is an essential application for patients with voiding dysfunction. Current wearable ultrasonic bladder monitors are rigid, bulky, and cannot conform to human skin. This study presents a stretchable and wearable ultrasonic transducer array that can both conform to non-planar skin surfaces and continuously monitor bladder volume. The wearable transducer array mainly consists of
$4\times4$
piezoelectric transducer elements, stretchable serpentine-based electrodes for electrical interconnection, electrically conductive adhesive as both matching and backing layers, and silicone elastomer for encapsulation. The transducer array has a center frequency of 3.9 MHz, −6 dB acoustic bandwidth of 57.6%, and up to 40% elastic stretchability. The volume of balloon-bladder phantom was estimated by a least square ellipsoid fitting method. With the true volume of balloon-bladder phantoms ranging from 10 to 405 mL, the proposed transducer array has a mean absolute percentage error (MAPE) of 9.4%, a mean absolute error (MAE) of 11.9 mL, and a coefficient of determination of 0.975, which demonstrates the capability of the proposed stretchable and wearable ultrasonic transducer array for bladder volume monitoring application.