Sensing property of piezoelectric filter material and its application in masks

In the field of labor protection, the real-time monitoring of workers’ physical health status has received a lot of attention. Because breathing contains a lot of physiological information, the development of wearable devices with sensing functions for monitoring the wearer’s respiratory status has become a research hotspot. Traditional commercial respiratory monitoring devices are expensive, bulky, and not easy to be carried, limiting their use in front-line production sites, such as high dust mass concentration mines’ operating environments. In view of this situation, based on the piezoelectric properties of polyvinylidene fluoride (PVDF), a flexible PVDF nanofiber membrane with sensing properties was prepared using electrospinning technology. The high permeability carbon fiber felt and PVDF nanofiber membrane were designed as a sandwich structure. The sensing module was embedded in the mask. The sensor module converted the mechanical energy generated by the respiratory airflow into electrical energy. Through the collection and analysis of electrical signal data, the real-time monitoring of respiratory intensity and respiratory frequency was completed. The results show that the piezoelectric signals generated by the mask embedded with the sensing module are significantly different under different breathing states. Under the three breathing states of low intensity (15 L/min), medium intensity (50 L/min) and high intensity (85 L/min), the output piezoelectric voltage peaks are 300, 700 and 1 100 mV, respectively, and the frequency of voltage peaks is 18, 16 and 14 times/min, respectively. Therefore, based on the analysis of the peak voltage and its frequency of the piezoelectric signal, the real-time monitoring of respiratory parameters such as the wearer's respiratory intensity and respiratory frequency can be realized. In addition, the piezoelectric properties of PVDF nanofiber membranes were determined to be related to the content of β-phase crystals by XRD, FT-IR, TG and other analysis methods, which provided a basis for further improving the piezoelectric properties of PVDF nanofiber membranes. The developed mask with sensing function can be used for the real-time respiratory monitoring of mine workers’ working conditions, and the feedback to managers when workers’ working conditions are abnormal to facilitate some timely treatment measures.