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Zhao et al. Soft Sci. 2026, 6, 4 Page 5 of 15

Figure 1. Design and preparation of respiratory monitoring system. (A) Schematic diagram of respiratory monitoring and oxygen supply
between pilots and ground control platform; (B) Schematic diagram of periodic respiration waveform with feature extraction and artifact
identification, including time, depth, energy, and frequency; (C) Fabrication process of triboelectric fibers; (D) (ⅰ) Digital image (Scale bar:
2 mm) and (ⅱ) SEM image (Scale bar: 2 μm) of triboelectric fibers; (E) Pilot mask integrated with triboelectric sensors; (F) Schematic
illustration of the machine learning-assisted respiratory monitoring system. SEM: Scanning electron microscope; PVDF: polyvinylidene
fluoride; VCC: voltage common collector; STM32: STMicroelectronics Microcontroller 32-bit; ADC: analog-to-digital converter; DMA:
direct memory access; USART: universal synchronous asynchronous receiver transmitter; GND: ground; MCU: microcontroller unit.

RESULTS AND DISCUSSION
Design and fabrication of the respiratory monitoring system
To address the needs of extreme scenarios, the sensor system is designed in a form that can be placed inside
the breathing mask to enable real-time, non-invasive monitoring of respiratory parameters. This
configuration enables unobtrusive placement within standard respiratory protection gear, allowing
continuous monitoring without impeding the wearer. Figure 1A demonstrates a potential application
involving a high-altitude fighter pilot equipped with a sensor-integrated oxygen mask that continuously
monitors respiratory patterns and transmits data to a ground station. It captures periodic respiratory
waveforms while extracting key features and identifying artifacts for respiratory assessment, as schematically
illustrated in Figure 1B. When the system detects respiratory abnormalities, the monitoring system can
trigger an alarm promptly to assist the command center in quickly adjusting the oxygen supply strategy and
ensuring pilot safety. Thus, fast detection and clear alarms are essential to timely interventions in
mission-critical environments. Such mission-critical operation demands exceptional sensitivity and robust
performance under dynamic motion and low-pressure conditions.

The core sensing element is composed of plasma-treated triboelectric fibers fabricated through a multi-step