| The electronic detection system based on ultrasonic doppler sensors has beenwidely used in fetal heart detection due to its high safety and stability. Because of thegrowing demand of lower detection signal power applying on human body and thedetectability in earlier fetal heart age, which means a weaker signal needs to betransmitted to detect a smaller fetal heart move, the sensitivity of doppler fetal heartelectronic detection system is becoming a key point in the drastic technologycompetition. The level of sensitivity determines the performance of an ultrasonicdoppler fetal heart detection device at hugest extent.A comprehensive research, including experimental analysis and designimprovements on every module of fetal heart detection circuit system in signal flowsequence, has been done to improve the sensitivity. The key factor in every systemmodule, which affects sensitivity most, has been found out. Solutions to these corresponding factors have also been developed in this thesis. These achievements aremainly reflected in the following four improvements.Configuration of transducer device affects detection signal quality directly on theoriginal stage, optimized configuration has lead to a higher sensitivity; Frequency andimpedance match between receive-transmit circuit and sensors improves the signaltransmission efficiency; In signal processing module, the large amplitude signal withoutfrequency deviation (inutility signal) has a fatal interference on the tiny signal whichhas frequency deviation (wanted signal). Suppression to the inutility signal canefficiently improve sensitivity if amplitude detection circuit is used as demodulationmethod; Application of MCU should be developed to help detection algorithm circuitsolve the misjudgement problem caused by sub-peak of fetal heart signal to makedetection sensitivity higher and more intelligentized. |
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