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Page 8 of 15 Zhao et al. Soft Sci. 2026, 6, 4

Figure 3. Electrical properties of the respiratory triboelectric sensors. (A) Schematic diagram of the working mechanism; (B) Output
voltages comparison and (C) Signal output curves of sensors with different plasma treatment times under an external pressure of 1 kPa;
(D) Simulation mappings of surface potential distribution during contact-separation process for smooth-surfaced and rough-surfaced
fibers; (E) and (F) Output curves of the respiratory triboelectric sensors under different pressures at a constant frequency of 2 Hz and
under different frequencies at a constant pressure of 1 kPa, respectively; (G) Response and recovery times of the respiratory triboelectric
sensor; (H) Durability test of the respiratory triboelectric sensor under a pressure of 1 kPa. PVDF: Polyvinylidene fluoride.

Electrical properties of triboelectric respiratory sensors
The working mechanism of the respiratory triboelectric sensor is based on the coupling of contact
electrification [Supplementary Figure 10] and electrostatic induction [Supplementary Figure 11] [47-49] . During
inhalation and exhalation, the airflow-induced deformation causes periodic contact and separation between
the epoxy and PVDF fibers [Figure 3A] [50,51] . Upon contact, electrons transfer from the epoxy to the PVDF
due to their difference in electron affinity, creating opposite triboelectric charges on their surfaces. During
separation, the charge redistribution induces a potential difference, driving electrons to flow through the
external circuit. This cyclic process generates alternating electrical signals that correspond to the respiratory
rhythm. Thus, the sensor transduces the mechanical waveform of breathing into time-resolved electrical
signals that can be directly correlated with respiratory metrics.

To optimize sensor performance, the effect of plasma treatment duration on output voltage is investigated to
establish a direct processing-performance relationship. Figure 3B presents a comparative analysis of the
output voltage of triboelectric sensors under a consistent external pressure of 1 kPa for varying plasma
treatment durations. The output voltage increased with plasma treatment time, reaching an optimal point at