PVDF piezoelectric ultrasonic transducer converts heart sound vibration signals into weak electrical signals

Heart sound is the shock vibration to the chest wall during the heartbeat. The mechanical vibration of heart sounds can be recorded by instruments such as polyvinylidene fluoride (PVDF) piezoelectric ultrasonic transducer , which is called a phonogram. When detecting simulated human heart sounds, the PVDF piezoelectric sensor first converts the heart sound vibration signal into a weak electrical signal, and the heart sound measurement system passes the weak electrical signal through a two-stage preamplifier, bandpass filter, 50Hz notch filter, and voltage After processing by the lifting circuit, it is sent to the oscilloscope as an output signal. The heart sound waveform is displayed on the oscilloscope and various indicators (including heart rate, amplitude, diastolic and systolic time limit, etc.) are measured, and then compared with the standard value of simulated human heart sound.

There are three methods for the determination of EtCO2: infrared method, mass spectrometer method and colorimetric method. At present, the most commonly used method is infrared method. The CO2 storage tank equipped with the simulator allows the simulation of real EtCO2 detection. After completing the tracheal intubation on the simulator, use the side flow device to draw out part of the exhaled air for EtCO2 measurement. Choose MH-Z19B infrared CO2 monitoring module [Working relative humidity: 0-95%; Measuring range: 0-5000ppm (1ppm=1×10-6); Monitoring accuracy: ±30ppm±3% reading] as the sensor system to obtain weak Electrical signal. The design scheme of the EtCO2 measurement system: the input signal is first passed through a voltage follower to achieve impedance matching, then an appropriate operational amplifier is selected and an amplifier circuit is built, the weak electrical signal of anticorrosive ultrasonic transducer is pre-amplified, and then filtered, second-amplified, and AD converted Then the CO2 waveform is displayed in the upper computer software.

Finally, the detection accuracy of the self-designed EtCO2 measurement system is calibrated with a variety of standard mixed gases of CO2 volume fraction (CO2 volume fraction is 1%-20%, and the balance gas is nitrogen). The CO2 volume fraction detection range of the system is 0~99mmHg (1mmHg=133.322Pa), the error rate is not more than 5%, and the respiratory rate error of 25KHz ultrasonic transducer is not more than 2 times/min.