High Dynamics Adaptive Demodulator for Ultrasound Applications: FPGA Implementation

The modern acquisition and processing systems digitalize the input signal directly at radio-frequency (RF) by using Analog-to-Digital (AD) converters, that works up to several hundreds of MHz, and then process the signal numerically in powerful flexible digital devices like the Field Programmable Gate Arrays (FPGAs). A digital coherent demodulation is the first processing step in several applications. Echo-Doppler ultrasound systems belong to this category. An industrial fluid flowing in a pipe can be investigated by transmitting ultrasound bursts at some MHz in the pipe. Fluid particles produce echoes with a frequency shift (typically some kHz) related to the particle velocity through the Doppler effect. The echoes are sampled at several tens of MHz, and coherent demodulated for detecting the Doppler shift. The demodulator processes the high intensity echoes from the steel pipe's wall together with the weak signal from the fluid, and thus it should feature very high dynamics. In this paper, it is presented an adaptive numerical demodulator integrated in the FPGA of an ultrasound system for flow profile detection. Its performance is tested with synthetic samples and a signal acquired from a pipe. Finally, the flow profile detected in a pipe, calculated by a processing chain that includes the proposed demodulator, is reported.