Design Of Flexible Piezoelectric Film Sensor And Its Application In Continuous Blood Pressure Measurement

In recent years,cardiovascular diseases have attracted more and more attention from the public.Hypertension,as a common type of cardiovascular diseases,poses a serious threat to human health.However,due to the"white coat effect"and the existence of hidden hypertension people,intermittent blood pressure measurement cannot fully represent the real state of human blood pressure.Therefore,it is important to study how to achieve continuous monitoring of blood pressure in daily life.In this paper,we propose a flexible wearable piezoelectric sensor based on P（VDF-TRFE）,and then combined it with a photoplethysmography pulse wave sensor to further propose a continuous monitoring of blood pressure based on a two-way pulse wave conduction time.Firstly,the following research was made in the preparation and design of piezoelectric sensors:on the basis of the original laboratory equipment,a set of horizontal high-voltage electrospinning equipment with controllable temperature and humidity was developed and improved to prepare P（VDF-Tr FE）piezoelectric films.Based on this device,P（VDF-Tr FE）thin films containing different concentrations of barium titanate under at different ambient relative humidity were spun.The morphological structure of the nanofibers of the film was observed by scanning electron microscopy.It was found that with the increase of humidity,the surface of the fibers gradually became uneven and the average diameter increased.In addition,the XRD diffraction pattern of the thin film was determined by XRD diffractometer,and it was found that theαphase andβphase crystals co-existed in P（VDF-Tr FE）powder,and with the increase of barium titanate concentration,part of theαphase was converted intoβphase.Furthermore,the piezoelectric response output test of the prepared film was carried out by the excitation equipment,and it was found that the piezoelectric output of the composite piezoelectric film with a humidity of65%and a concentration of 1wt%Ba Ti O₃ reached the maximum,and the average peak-to-peak voltage could reach 26.8V.The film was encapsulated as the base to prepare the piezoelectric sensor.The sensor’s sensitivity and amplitude-frequency characteristics were evaluated.It was found that the sensor has the best output at the frequency of 10Hz,and it only takes 1.1 milliseconds from sensing the force acting on the film to generating the maximum piezoelectric response output,indicating that the sensor is sensitive.Secondly,the following research is made in the acquisition and processing of pulse signals:a two-way pulse wave signal acquisition system is built,which consists of a terminal sensor,a charge amplifier,an NI data acquisition card and a LABVIEW software platform,in which the terminal sensor includes a piezoelectric sensor placed in the radial artery to measure pulse signal and a PPG sensor to measure PPG signal at the abdomen of the ipsilateral index finger.The pulse signal collected by the piezoelectric sensor is connected to the acquisition channel of the data acquisition card through the charge amplifier,and the PPG sensor is directly connected to the data acquisition card,and the acquisition card transmits the dual pulse wave signals to the LABVIEW software platform by USB connection.For the saved pulse wave signal,the wavelet transform threshold denoising algorithm is adopted on the MATLAB platform for filtering processing,and then the feature extraction of three pulse wave parameters is extracted:Pulse transit time,heart rate and K value.Finally,the following research was made for blood pressure prediction:due to the particularity of pulse wave signal measurement points,the matching blood pressure database could not be found,so the pulse and blood pressure data were collected by themselves.The data of 30 healthy volunteers were collected,filtered and feature-extracted,and then a linear regression model and a support vector regression model were constructed for blood pressure prediction,and the prediction results of both models met the AAMI standard.