Design and Implementation of a CMUT Ultrasound Front-End PCB for a Wearable Ultrasound Demonstrator

Abstract

Wearable ultrasound could enable continuous, non-invasive monitoring of physiological signals outside clinical environments, but it depends on flexible transducer arrays that conform to the body. When such an array bends, the positions of its elements shift, which degrades measurement accuracy unless the deformation is corrected. The wider project addresses this with a concept demonstrator that uses dedicated shape sensing sensors to estimate the geometry of the array. This thesis covers one of the demonstrator's three subsystems, namely the ultrasound front-end that excites the transducers, receives the echoes, digitises them, and transfers them to a computer. The front-end was built as a circuit board which is driven by a programmable logic device. The transmit path combines a three-level high-voltage pulser which provides a configurable bipolar excitation up to plus or minus twenty volts with a selectable cycle count, frequency, and polarity, with a high-voltage switch that routes the pulse to a chosen transducer element. The receive path converts the received echo current to a voltage in a low-noise transimpedance stage, amplifies it differentially, filters it, and digitises it, after which the controller stores the samples and returns them over a serial link. Validation measurements confirmed operation stage by stage. The pulser produced the specified excitation, every switch channel could be selected reliably with low on-resistance, the receive chain met its measured gain and signal quality targets, the converter captured a full-scale input without distortion, and the controller completed a full acquisition within its timing budget. With the transducers connected, the front-end successfully performed pulse-echo measurements, and reflections were captured for both CMUTs, confirming that the complete transmit-receive path operates as intended. Finally, the front-end was integrated with the other two subsystems, demonstrating a complete and functional demonstrator. The front-end is therefore validated as a complete pulse-echo front-end.