Design Of Pre-circuit For Fetal Heart Probe Based On Doppler Principle

Ultrasound Doppler fetal heart rate detection technology uses Doppler principle,which couples the ultrasonic probe to the abdomen of pregnant women to send ultrasound.The fetal heart rate signal is obtained by receiving the frequency shift signal of fetal heart reflex and processing the back-end signal circuit.Both fetal heart rate monitors used in obstetrics departments of hospitals and home multi-fetal heart rate monitors used by ordinary pregnant women adopt this technology.By examining the fetal heart rate,we can objectively reflect the state of the fetus in the maternal body,and timely discover pregnancy hypertension,fetal malposition,umbilical cord around the neck,intrauterine hypoxia and so on.Although there is a certain scale of application of Doppler technology in testing fetal heart rate on the market,most of the products are of uneven quality,so the recognition degree of fetal heart rate measured is not high.When the fetal heart beat is weak,it is easy to lead to the inaccurate value of fetal heart rate detected,so it can not reflect the status of the fetus in the mother objectively.The accuracy of fetal heart rate monitoring results is mainly determined by the performance of the fetal heart rate monitoring probe.There are not many studies on the improvement of Doppler probe performance in the field of fetal heart rate monitoring,and few optimization schemes are summarized.Therefore,it is of great significance for the industry to study the technology of Doppler fetal heart rate signal extraction and improve the performance of fetal heart rate probe.After the performance of the probe is improved,on the one hand,it can help doctors and pregnant women to find the fetal heart rate more easily and accurately,on the other hand,it can make the probe detect more weak fetal heart rate beat,and the detected gestational age is earlier.For this reason,this paper mainly does the following work:1.The design principles of CW Doppler probe and PWD probe are discussed.For two types of probes,a high-performance pre circuit design scheme is proposed.In addition,the influence of probe performance on each design detail is discussed in modules,including front-end transducer tuning and matching,signal sending circuit design,echo receiving circuit design,signal modulation and demodulation,Butterworth high-order filter channel design,pulse wave probe timing generation program design accurate to instruction period,etc.2.Several innovations that have been verified by many experiments are summarized: for the angle design of the continuous wave probe transducer,the derivation process is given in this paper,and the size of the angle is calculated,which can fully meet the clinical application.For the thickness design of probe transition layer,the derivation process is also given in this paper,and the thickness of full transmission is obtained.In addition,this paper also gives the anti-interference measures in the transducer processing technology,the preventive measures for the squeal phenomenon of the fetal heart apparatus loudspeaker caused by the self excitation of the continuous wave probe signal flow circuit,the board layer planning,device layout,sensitive circuit processing,etc.in the PCB layout process,all of which have clear engineering application value.In this paper,two kinds of probe performance test methods are proposed,one of which is to obtain the lowest driving voltage that can stably distinguish the simulated heart rate value of the fluctuation of the target by adjusting the voltage of the driving target,so as to compare the advantages and disadvantages of different manufacturers and different design schemes.Another method is to read the signal voltage amplitude and noise voltage amplitude through the oscilloscope to calculate the signal-to-noise ratio of the probe when the constant signal source is input.