Design of an Embedded System for Ultrasonic Beamforming: From Power Electronics to Control Algorithms

This thesis presents the design, implementation, and experimental characterization of a 32-channel ultrasonic phased array system for controlled acoustic streaming generation in air. The work is motivated by the long-term objective of investigating acoustic streaming as an active flow control mechanism for aerodynamic drag reduction on heavy vehicles. The system was developed through three prototyping stages, culminating in a 32-channel planar matrix. Each channel features a full H-bridge power stage driven by a gate driver with adaptive dead-time, a symmetric impedance matching network, and a logic inverter for complementary signal generation. The firmware, running on an STM32 microcontroller, utilizes a bit-banging architecture with a 32-step look-up table to provide independent phase control across all channels with an 11.25-degree resolution. The ultrasonic transducers were characterized to identify an optimal operating frequency of 41.75 kHz. A comparison between two-level and three-level PWM modulation confirmed that square-wave excitation maximizes acoustic output. Various hardware challenges, including gate drive anomalies and Miller plateau effects, were successfully diagnosed and resolved during the iterative design process. Consuming 13 W at a 30 V supply, the complete system successfully generated observable acoustic streaming: a directed airflow capable of deflecting lightweight materials, with qualitative evidence of beam steerability through electronic phase control. While the current streaming velocity is below the requirements for full-scale aerodynamic drag reduction, the system establishes a functional hardware platform for future quantitative fluid-dynamic characterizations. With a total development cost of approximately 800 euros and a per-channel cost below 10 euros, this work demonstrates that multichannel ultrasonic beamforming systems can be realized affordably using commercial off-the-shelf components.