Implementação e avaliação de um sistema reconfigurável de excitação convencional e chirp codificada pela técnica PWM para atividades de pesquisa do ultrassom

Abstract

Reconfigurable systems based on Field-Programmable Gate Arrays (FPGAs) have been proposed to compose the Arbitrary Waveform Generator (AWG) module to meet the need for new excitation methods in ultrasound research activities. This work presents the implementation and evaluation of an open, flexible, and reconfigurable single-channel Pulse-Echo AWG system based on the MD2131 chip for the generation of complex excitation waveforms using Pulse Width Modulation (PWM) modulation technique. The system allows the generation of Conventional Sinusoidal Excitation (CSE) and Coded Chirp Excitation (CCE) and consists of a Graphical User Interface (GUI) for waveform simulation, hardware control, and acquisition of raw ultrasound echoes, an FPGA kit, and a dedicated transmission/reception front-end board. Synthesized PWM signals from GUI simulations are transferred via a USB interface to the FPGA, which controls the AWG. In addition to the MD2131, the dedicated board features a reception front-end circuit with the 12-bit resolution 80 MSPS analog-to-digital converter ADS6123. System characterization and performance tests were conducted with RC loads and single-element ultrasound transducers with central frequencies of 1.6 MHz and 5 MHz. In the reception stage, the full width at half maximum (FWHM) and relative distance of targets were evaluated using a general-purpose commercial phantom with a 1.6 MHz transducer. Phase adjustment and amplitude apodization control functionalities yielded central frequencies of 5.03 ± 0.04 MHz with an RC load and 4.80 ± 0.03 MHz with a 5 MHz transducer using a CSE pulse with a duration of 3 cycles and Hanning windowing. The maximum amplitudes of the generated waveforms were 166 V and 55 V for RC load and 5 MHz transducer, respectively. Experimental results for CSE and CCE with the RC load and transducers, as well as the system’s evaluation for raw data capture from phantom to a depth of 15 cm, confirm that the proposed system is suitable for future research in optimizing spatial resolution and image quality in ultrasound applications for medical and industrial instrumentation.