Abstract: Aspects of the technology described herein relate to an apparatus including an ultrasound-on-a-chip device configured to be bound to a user's wrist. The ultrasound-on-a-chip device may include a two-dimensional array of ultrasonic transducers. The transducers may be capacitive micromachined ultrasonic transducers (CMUTs) and may be configured to emit ultrasound waves having a frequency between approximately 5-20 MHz. A coupling strip may be coupled to the ultrasound-on-a-chip device to reduce the air gap between the ultrasound-on-a-chip device and the user's wrist. The ultrasound-on-a-chip device may be waterproof and may be able to perform both transverse and longitudinal ultrasound scanning without being rotated. The ultrasound-on-a-chip device may be configured to calculate pulse wave velocity through a blood vessel in a user's wrist.