Fig. 4. Fiber-based, noncontact respiratory moisture sensors.

(A) Schematic showing a single-layer fiber wearable breath sensor attached to a disposable mask. (B) Commercial humidity sensor versus the iFP PEDOT:PSS fiber array in response to a single breath and continuous fast breathing (C). (D) Schematic showing a portable trilayer fiber sensor attached onto the front camera of a cell phone and a single-layer fiber sensor positioned above the nose. (E) Zoomed-in schematic of the fiber layer arrangement of the trilayer fiber sensor. PVDF, polyvinylidene difluoride. (F) Photo of the mouth area in the “no face covering.” (F₁) Normalized fiber resistance change (ΔR/R₀) of long exhale breath and cough (F₂), with the inset showing cough sound detected by the middle piezoelectric fiber layer. (G) Photo showing a surgical mask wearer, with fiber sensor recordings during long exhale (G₁) and cough (G₂). (H) Photo of a respiratory mask wearer, with fiber sensor recordings during long exhale (H₁) and cough (H₂). It is to note that photos of (F), (G), and (H) were all captured by the phone camera through the trilayer fiber sensor (Photo credit: Wenyu Wang, University of Cambridge).