Fig. 7: Human respiratory monitoring.

a Photograph showing the humidity sensor in a mask worn by a volunteer. b Capacitance response curve during breathing (four cycles). c Respiratory monitoring results for four randomly selected volunteers. d Responses of the sensor to the different respiratory modes. e Respiratory response curves recorded for 12 months from the same device. f Flow chart for the respiratory state recognition algorithm based on machine learning. g Classification test confusion matrix with 400 groups of the dataset during recognition of four different respiratory states. The color bar represents the sizes of the predicted numbers