Ultrasonic Doppler Signal Detection Based On Generalized S Transform

Ultrasonic Doppler echo signal is a nonlinear and non-stationary signal. Its instantaneous frequency varies over time. Extraction of the instantaneous velocity from Doppler echo signal is of great significance to the analysis of the moving target state. However due to the restrictions of its non-stationary nature, the general signal analysis methods can not provide adequate time-frequency focusing performance. Time-frequency analysis methods can effectively show the signal frequency variation with time, which has some forms, including those methods commonly used such as short-time Fourier transform, Wigner-Ville distribution and wavelet transform. For the problem that those frequency distribution methods can not provide sufficient time-frequency focusing performance, this thesis presents a method to extract the instantaneous velocity in Doppler signal based on generalized S transform. And also computer simulation and experimental verification were made.The following work has been done in this thesis:1、In this thesis, speed of moving object based on the continuous Doppler method was measured, and several time frequency methods in Doppler signal processing were theoretically analyzed. Comparison of time frequency focusing performance of these methods was made, and application of the generalized S transform to extraction of the instantaneous velocity of Doppler signal was introduced.2、In simulation of application of the generalized S transform to Doppler signal, Doppler echo signal was obtained by transmitting ultrasonic to a reciprocating dot, and the computer simulation showed the effectiveness on application of generalized S transform to the extraction of the instantaneous velocity in Doppler signal.3、A reciprocating mechanism has been designed, and a signal acquisition system consisted of FPGA and USB 2.0 chips was constructed. In the experiment, the ultrasound Doppler signal that obtained by receiving probe was acquisited with this system. Then signal data was transferred to PC at real-time, and stored on disk in text format. High-speed data acquisition and transmission functions were achieved, parameters and functions of acquisition system well meet the requirements of Doppler measurement system.4、In experiment of actual measurement of extraction of instantaneous velocity in Doppler signal, generalized S transform was applied to process the acquisited discrete signal to extract the instantaneous frequency in Doppler signal, and the instantaneous velocity of moving target was caculated. The result demonstrated the effectiveness of the application of generalized S transform to extraction of instantaneous velocity of the moving target in Doppler signal.Extraction of instantaneous velocity in Doppler signal is a research direction in medical ultrasonic engineering, this research work is of some practical significance and application value for extraction of instantaneous velocity in ultrasonic Doppler flow signal at high precision.