Data-Adaptive Coherent Demodulator for High Dynamics Pulse-Wave Ultrasound Applications

Stefano Ricci,Valentino Meacci

doi:10.3390/electronics7120434

Abstract

Pulse-Wave Doppler (PWD) ultrasound has been applied to the detection of blood flow for a long time; recently the same method was also proven effective in the monitoring of industrial fluids and suspensions flowing in pipes. In a PWD investigation, bursts of ultrasounds at 0.5–10 MHz are periodically transmitted in the medium under test. The received signal is amplified, sampled at tens of MHz, and digitally processed in a Field Programmable Gate Array (FPGA). First processing step is a coherent demodulation. Unfortunately, the weak echoes reflected from the fluid particles are received together with the echoes from the high-reflective pipe walls, whose amplitude can be 30–40 dB higher. This represents a challenge for the input dynamics of the system and the demodulator, which should clearly detect the weak fluid signal while not saturating at the pipe wall components. In this paper, a numerical demodulator architecture is presented capable of auto-tuning its internal dynamics to adapt to the feature of the actual input signal. The proposed demodulator is integrated into a system for the detection of the velocity profile of fluids flowing in pipes. Simulations and experiments with the system connected to a flow-rig show that the data-adaptive demodulator produces a noise reduction of at least of 20 dB with respect to different approaches, and recovers a correct velocity profile even when the input data are sampled at 8 bits only instead of the typical 12–16 bits.

Highlights

The velocity of blood flowing in an artery can be investigated by detecting the Doppler frequency shift that the moving particles produce on the energy pulses of 0.5–10 MHz periodically transmitted in the medium
We present a coherent demodulator designed for high dynamics and suitable to be efficiently integrated into Field Programmable Gate Array (FPGA) [19]
Pulse Wave Signals in Industrial Echo-Doppler Applications and Their Processing In Pulse-Wave Doppler (PWD) measurements a burst of ultrasounds with a central frequency FT is transmitted in the medium to be investigated every Pulse Repetition Interval (PRI) through a suitable transducer [1]

Summary

Introduction

The velocity of blood flowing in an artery can be investigated by detecting the Doppler frequency shift that the moving particles produce on the energy pulses of 0.5–10 MHz periodically transmitted in the medium. This is a technique normally exploited by biomedical echographs for echo-Doppler exams [1]. Modern Pulse-Wave Doppler (PWD) electronics systems (including most of the clinical echographs) are nowadays based on the numerical approach for data processing In these systems, the signal is converted to the digital domain as near as possible to the signal source, i.e., directly at the receiver front-end [2,3,4,5], while the analog conditioning is maintained at a minimum. The echo signal sampled at the same distance from the transducer and from subsequent phase variation that corresponds to the frequency f d described by the Doppler equation [1]: pulses presents a phase variation that corresponds to the frequency fd described by the Doppler v equation [1]:

Methods

Results

Conclusion