Electrospinning Machine| A flexible temperature sensor with ultrafast response speed and high stability achieved by improving substrate thermal conductivity and radiative cooling

The rapid advancement of flexible electronics and materials has driven significant progress in wearable technology, including implantable devices, electronic skin (e-skin), and physiological signal monitoring. Various wearable devices enable long-term, continuous tracking of human activity and health in daily life. Among these, temperature sensors are particularly crucial as they detect body-emitted heat to infer internal temperature and health status. However, traditional rigid temperature sensors, typically made from bulky metals or semiconductors, suffer from inherent limitations that hinder real-world applications. Their inability to conform to the body’s complex contours leads to unreliable thermal contact and inaccurate readings, especially during dynamic movement. Thus, developing flexible temperature sensors is imperative.

To address this, this study employs breathable nanofibers as a platform, integrating highly thermally conductive aligned boron nitride nanosheets (BNNS) and temperature-sensitive polyaniline (PANI)/graphene (G) to create a sensor with rapid response, high sensitivity, excellent stability, and body heat management capabilities—paving a new path for practical temperature sensing.

Recently, a collaborative effort between Dr. Wang Peng from Ji University, Professor Fu Xiuli, and Professor Meng Chuizhou from Zhejiang Sci-Tech University has developed a flexible temperature sensor using electrospun nanofibers as the substrate. By incorporating aligned BNNS to enhance thermal conductivity, adding PANI/G for high sensitivity, and covering with TPU/SiO₂ nanofibers to improve stability, they successfully created a sensor suitable for long-term human monitoring, respiratory monitoring, and battery temperature measurement.

This research, titled "A flexible temperature sensor with ultrafast response speed and high stability achieved by improving substrate thermal conductivity and radiative cooling," was published in Advanced Functional Materials. The paper's first author is Dr. Sun Guifen from the School of Mechanical Engineering at Hebei University of Technology.

The flexible temperature sensor utilizes breathable electrospun nanofibers as its core platform, consisting of four distinct layers from bottom to top:

1. TPU/BNNS nanofiber layer (enhances thermal conductivity)

2. PVA/graphene (G) interdigitated electrodes (connects to the sensing layer)

3. PVA/G/PANI linear sensing layer (temperature detection)

4. TPU/SiO₂ nanofiber layer (protection and radiative cooling) (Fig. 1).

The sensor exhibits exceptional breathability (>600 mm s⁻¹) and moisture permeability (>480 g m⁻² day⁻¹), ensuring comfort during prolonged wear. Additionally, the combination of TPU/SiO₂ and TPU/BNNS nanofibers provides superior thermal management, reducing body temperature by over 15°C in outdoor environments compared to conventional clothing.

To validate its applications, the sensor was tested for long-term human temperature monitoring under various conditions, respiratory monitoring in different states, and battery temperature tracking during charge/discharge cycles. With its rapid response, high stability, and high sensitivity, this temperature sensor lays a solid foundation for the future development of smart health-monitoring hardware.

Fig. 1: Sensor design and performance. (a) Schematic: Four layers—TPU/SiO₂ (top, radiative cooling), PVA/G/PANI (sensing), PVA/G electrodes, TPU/BNNS (bottom, thermal conduction). (b) SEM of sensitive layer: Graphene (G) and PANI act as "temperature switches," with resistance increasing as temperature rises; PVA bonds the layer to the substrate. (c–d) Breathability (>600 mm/s) and thermal conductivity (BNNS alignment creates "thermal highways"). (d) Simulation: BNNS-enhanced substrate (0.76 W m⁻¹ K⁻¹) conducts heat 4× faster than pure TPU (0.18 W m⁻¹ K⁻¹). (e) Thermal conductivity comparison. (f) Response time: BNNS-based sensor responds in 0.32 s, 3× faster than pure TPU. (g) Benchmarking against prior work. (h) Cooling: Sensor surface is 4.5°C below ambient temperature outdoors, while cotton is 5.8°C above. (i) Performance across environments.

Fig. 2: Thermal conductivity and response speed. (a–b) Heat transfer mechanisms. (c) BNNS increases in-plane thermal conductivity from 0.70 to 8.12 W m⁻¹ K⁻¹. (d) Comparison with literature. (e–f) Radiative cooling with varying BNNS content. (g) Response time drops from 1.2 s to 0.32 s as BNNS increases to 40%. (h–i) Thicker substrates reduce thermal conductivity and slow response.

Fig. 3: Radiative cooling tests. (a–b) Outdoor setup. (c) TPU/SiO₂ reflects 92% sunlight and emits 96% infrared. (d) Skin temperature: 23.8°C under sensor vs. 35.8°C under cotton after 1-hour sun exposure. (e) Comparison with PI film. (f–g) Commercial sensors show 45.8% signal noise vs. 12% for this sensor.

Fig. 4: Performance validation. (a) Test setup. (b) Sensitivity: 0.077°C⁻¹ at 20–55°C. (c–d) Stable over 10 cycles and 1500 s. (e–f) Cyclic and step tests. (g) Hydrophobicity (143.5° contact angle). (h–i) Humidity resistance. (j–k) Breathability (>600 mm/s, comparable to fabric). (l) Biocompatibility: No skin irritation after 10-day wear.

Fig. 5: Applications. (a) System diagram. (b) Respiratory monitoring. (c) Human activity tracking. (d) Battery temperature monitoring.

In this study, the authors developed a rapid-response and highly stable temperature sensor using breathable TPU/SiO₂ and TPU/BNNS nanofiber platforms. The sensor consists of four functional components: a TPU/BNNS nanofiber layer for enhanced thermal conductivity, PVA/G interdigitated electrodes connecting the linear sensing layer, a six-layer linear PVA/G/PANI structure for temperature detection, and a TPU/SiO₂ nanofiber layer that improves both sensing stability and human thermal management performance.

Benefiting from its optimized structural design and material composition, the fabricated temperature sensor demonstrates exceptional performance characteristics: ultrafast response speed (0.32 s response time and 0.98 s recovery time), high stability, and superior sensitivity (0.077°C⁻¹ in the 20-55°C range and 0.009°C⁻¹ in the 55-95°C range). The nanofiber architecture provides outstanding breathability (>600 mm s⁻¹) and moisture permeability (>480 g m⁻² day⁻¹), significantly improving long-term wearing comfort.

Furthermore, the incorporation of TPU/SiO₂ and TPU/BNNS nanofibers endows the sensor with remarkable thermal management capabilities, achieving over 15°C reduction in human body temperature compared to conventional clothing in outdoor environments. For practical validation, the sensor was successfully employed in various applications including long-term human temperature monitoring under different environmental conditions, respiratory status detection, and battery temperature measurement during charge/discharge cycles.

The sensor's rapid response capability enables accurate material identification when integrated with machine learning systems. With its combination of ultrafast response, exceptional stability and sensitivity, and superior thermal management performance, this temperature sensor demonstrates broad application prospects in telemedicine diagnostics, electronic skin technologies, biomimetic sensors, and other advanced fields.

Paper link: https://doi.org/10.1002/adfm.202512296