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1 共横抑制技术仪器利用超声多普勒效应,检测出妊娠期胎畜心音和血流音,以此作为判断妊娠的依据。多普勒效应最基本的特征是接收信号频率的改变。所以,多普勒信号提取的主要手段就是将这种由于血流运动而产生的频率改变量检测出来。值得指出的是接收器上所接收到的信号并不单纯是一个具有频偏的调频信号。因为发射压电晶片和接收压电晶片靠得很近,发射信号总是有一部分经过电和声直接耦合到接收压电片上,假设发射压电片上发出Asinωt的超声波,接收压电片接收到运动着的血流中红血球的反射波为Bsin(ω_0+ω_0)t,其中ω_0为多普勒频移,而由发射压电片直接耦合过来的信号为Csinω_0t,如果忽略不计初相位,则接
A total cross-suppression technology Instrument using ultrasound Doppler effect, detection of fetal heart rate during pregnancy and blood flow sound, as a basis for the determination of pregnancy. The most basic feature of the Doppler effect is the change in the frequency of the received signal. Therefore, the main means of Doppler signal extraction is to detect the frequency change caused by blood flow. It is worth pointing out that the signal received on the receiver is not simply a frequency modulated signal with frequency offset. Because the transmitting piezoelectric wafer and the receiving piezoelectric wafer are in close proximity, a part of the transmitted signal is always directly coupled to the receiving piezoelectric film through electrical and acoustic sound. Assuming that the transmitting piezoelectric chip emits Asinωt ultrasonic waves, the receiving piezoelectric film receives the motion The reflected wave of the red blood cells in the blood flow is Bsin (ω_0 + ω_0) t, where ω_0 is the Doppler frequency shift, and the signal directly coupled by the transmitting piezoelectric film is Csinω_0t. If neglecting the incipient phase, then