Low compression smart clothing for respiratory rate monitoring using a bending angle sensor based on double-layer capacitance

Fig. 1. Bending angle sensor based on double-layer capacitance. Structure of the bending angle sensor, featuring five conductive layers separated by nonconductive layers. The dimensions of the sensor are 600 mm × 20 mm (length (L) × width (W))

Fig. 2. Illustration of bending angle and capacitance variation. (a) The entirety of conductive sheets and (b) Enlarged view of the micro-interval section

Fig. 3. Illustration of smart clothing equipped with a bending angle sensor based on double-layer capacitance

Fig. 4. Schematic illustrating the bending angle sensor based on double-layer capacitance responding to changes in body shape owing to breathing. The solid line represents the body shape at exhalation, and the dashed line represents the expanded body shape at inhalation. The bending angle of the sensor changes accordingly from θC to θE

Fig. 5. Illustration of experimental setup and measurement block diagram. (a) An example of measurement in the sitting posture. Pressure meter and air bag are used only initially and removed before the respiratory rate measurement. (b) Measurement block diagram for respiratory rate monitoring, featuring the bending angle sensor based on double-layer capacitance coupled with a CV converter

Fig. 6. Measured respiration signal and respiratory rate. (a) Sensor output for rib cage (upper) and abdomen (lower). (b) Ensemble waveform of rib cage and abdomen. The amplitude of breathing was 2.3 ± 0.6 (mean ± SD). (c) Ventilation reading using a spirometer. (d) Respiratory rate calculated from sensor output. (e) Respiratory rate derived from the ventilation rate

Fig. 7. Comparison of respiratory rate measurements between smart clothing and a spirometer in sitting, supine, and lateral postures. (a) Comparison in the sitting position and Bland–Altman plot for the sitting position. (b) Comparison in the supine position and Bland–Altman plot for the supine position. (c) Comparison in the lateral position and Bland–Altman plot for the lateral position

Fig. 8. Limit of agreement (LOA) versus compression pressure (a) and mean amplitude of breathing (b). Each scatter point in both figures is the mean value for the sitting, supine, and lateral positions