| Early detection and effective control of hypertension are crucial as it increases the risk of cardiovascular diseases such as heart disease,stroke,kidney disease,and other related conditions.Traditional blood pressure monitoring methods usually require an inflated cuff to be worn on the arm,which is cumbersome and may affect the accuracy of the results.Furthermore,this method cannot provide real-time monitoring of blood pressure.Currently available medical devices for continuous arterial blood pressure monitoring are mostly rigid and bulky,making measurement inconvenient and causing discomfort to the test subject.This paper aims to design a flexible,wearable,and noninvasive blood pressure measurement system based on the principle of ultrasound detection,to achieve a more comfortable,convenient,accurate,and real-time blood pressure monitoring method and to solve the pain points of traditional measurement methods.The paper’s primary focus is on the following research areas:Firstly,the principle of ultrasound measurement of continuous arterial diameter changes in the human body was investigated.The method of repeated pulse emission was used to obtain a set of echo signals reflected from the front and back walls of the artery within one cardiac cycle,thereby calculating the continuous diameter changes of the artery.The attenuation characteristics of ultrasound in human tissue were studied,and the mechanism of the acoustic matching layer to improve the propagation efficiency of ultrasound between different media was obtained.A flexible ultrasound sensor structure based on 1-3 piezoelectric composite material was designed,which includes a 1-3 piezoelectric composite material piezoelectric array layer,a Cu/PI serpentine electrode layer,a bonding layer,and a PDMS flexible substrate layer.A COMSOL finite element simulation model for acoustic multiphysics coupling was used to analyze the acoustic pressure distribution characteristics of 1-3 piezoelectric composite materials with different resonant frequencies,sizes,and the presence or absence of a matching layer.The results showed that when the ultrasound was reflected back from the carotid artery wall and received by the piezoelectric element,the resonant frequency of 5 MHz had an approximately 6.1 d B higher sound pressure level than that of 7.5 MHz.Additionally,considering that a large size is inconvenient for addressing the artery and unfavorable for miniaturization,the element size of 1.5×1.5 mm was chosen,resulting in a sound pressure level of approximately 212 d B at the position of the carotid artery,meeting the requirements for ultrasonic detection.Furthermore,the addition of a matching layer could further increase the sound pressure level by approximately 2 d B.In response to the requirements of pulsed emission and reception for measuring the diameter of human arteries using a flexible piezoelectric array device,an ultrasound detection system was designed.Compared to the traditional method of using sharp pulses to excite the ultrasound probe,a multi-pulse excitation-based ultrasound detection system was designed.The test results for workpiece thickness and fluid velocity showed that the signal-to-noise ratio of the multi-pulse excitation method was improved by 5.7 d B compared to the single-pulse excitation method.Finally,the serpentine electrode layer was fabricated using photolithography-etching method,and the flexible piezoelectric array ultrasonic sensor was successfully fabricated based on the transfer process and PDMS fabrication technology.A model of the relationship between arterial diameter and blood pressure was constructed.By FIR filtering and wavelet transform of the collected echo signals from the arterial walls,the signal-to-noise ratio was improved.The experimental results showed a540% improvement in the signal-to-noise ratio of carotid artery wall echoes. |
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