Detection of ultrasonic doppler signal and estimation of its mean frequency and variance초음파 도플러 신호의 검출 및 평균 주파수와 분산의 측정

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A new Doppler system using second-order sampling is proposed. To reduce the hardware complexity and to eliminate the balancing problem between in-phase and quadrature-phase signal channels in conventional systems, the proposed system uses a single signal channel. This system can be used in a multigate or 2-dimensional Doppler system and implemented in a full digital system. We analyze the effect of second-order sampling on estimating the mean frequency of the Doppler signal. In order to reduce the sampling frequency of analogue-to-digital converter, it is possible to obtain the Doppler signal by sampling the radio frequency echo signal with the low frequency of $4f_0$/5 or $4f_0$/9 instead of $4f_0$, where $f_0$ is the center frequency of the transmitted signal. The computer simulation and experiments show that if the narrowband signal is transmitted as is usual in the Doppler system, the error of the mean frequency estimates due to the low sampling frequency is negligible. In order to estimate the mean frequency and variance of the diagnostic ultrasound Doppler signal in the presence of clutter noise, a new estimator using a second-order autoregressive (AR) model, called AR estimator, is proposed. In the proposed method, the sampled signal which contains information of both the Doppler signal and clutter is described by the second-order AR model with two poles. The mean frequency and variance of a unidirectional Doppler signal can be estimated, respectively, from the phase and the magnitude of the pole with larger phase among the two poles. It turns out that if the clutter is not completely rejected, all conventional estimations including the autocorrelation (AC) estimator result in erroneous estimations for the mean frequency and variance of the Doppler signal, whereas the AR estimator gives an accurate estimation. In the absence of clutter, however, the performances of both the AC and AR estimators are similar. If the blood flows in both directions ...
Advisors
Ra, Jong-BeomresearcherPark, Song-Bairesearcher나종범researcher박송배researcher
Description
한국과학기술원 : 전기 및 전자공학과,
Publisher
한국과학기술원
Issue Date
1990
Identifier
61534/325007 / 000855216
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 전기 및 전자공학과, 1990.8, [ v, 113 p. ]

URI
http://hdl.handle.net/10203/36127
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=61534&flag=dissertation
Appears in Collection
EE-Theses_Ph.D.(박사논문)
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