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A single-material dual-mode sensor developed by researchers at Nanjing Tech University, Tsinghua University, and Tohoku University operates natively in both air and underwater environments without requiring waterproof encapsulation, according to findings published in Nano-Micro Letters. Led by Peng-an Zong and Heng Liu, the team engineered a pyramid-interface-structured $text{Bi}_2text{Se}_3$ layer on flexible carbon paper that decouples temperature and pressure measurements without cross-interference.
Pyramid-Interface Engineering Eliminates Waterproof Coatings
Traditional amphibious sensors rely on heterogeneous composites like PDMS/carbon nanotube sponges that suffer from baseline drift and interfacial delamination when water infiltrates the structure. While organic hydrophobic coatings such as polyimide are often applied, they require complex processing, lower corrosion resistance, and dampen signal transmission. To solve this, the research collaboration synthesized a pyramid-interface-structured $text{Bi}_2text{Se}_3$ layer that combines intrinsic hydrophobicity, piezoresistive sensitivity, and high thermoelectric performance.
According to the published study, the material is created via pulsed electrochemical deposition of $text{Bi}_2text{Se}_3$ onto flexible carbon paper, followed by thermal annealing at 300°C. Finite-element modeling and density functional theory calculations show the pyramid microstructure stems from optimized nucleation kinetics at a deposition potential of −0.02 V. This specific geometry establishes a stable Cassie–Baxter state with a water contact angle of 143.7°, which minimizes solid-liquid contact and allows water droplets to roll off efficiently.
Pro Tip: When designing sensors for dual aquatic and atmospheric deployment, prioritizing single-material architectures with intrinsic hydrophobic geometry prevents the signal attenuation typically caused by secondary waterproof encapsulation layers.
Performance Metrics and Signal Decoupling
The optimized $text{Bi}_2text{Se}_3$ film on carbon paper delivers a power factor of 106.0 $mutext{W}text{ m}^{-1}text{K}^{-2}$, representing a nine-fold increase compared to bare carbon paper, alongside an electrical conductivity of 779.3 $text{S}text{ cm}^{-1}$ and a Seebeck coefficient of −36.9 $mutext{V}text{ K}^{-1}$. The stacked $text{Bi}_2text{Se}_3$/carbon paper multilayer assembly uses the Seebeck effect for voltage-based temperature detection and piezoresistive interlayer contact modulation for resistance-based pressure detection.
Data from the research team indicate the sensor achieves a temperature response time of 0.9 seconds and a pressure sensitivity of 0.94% $text{kPa}^{-1}$, with a detection range spanning from 0.1 kPa to 100 kPa. Crucially, the device maintains complete signal decoupling in both air and underwater settings. Pressure adjustments do not alter temperature sensitivity, and thermal shifts do not interfere with the pressure response.
Environmental durability tests show the sensor maintains over 62 dB electromagnetic interference shielding effectiveness across the X-band, which equates to greater than 99.9% attenuation. Furthermore, the device demonstrates stable operation following 1,000 bending cycles, 100 immersion cycles, direct flame exposure for 200 seconds without ignition, and continuous deployment in a 5 wt% $text{NaCl}$ solution at 60°C for 100 hours.
Amphibious Applications in Robotics and Wearables
Practical demonstrations of the sensor highlight its utility in diverse operational environments. Integrated into a smart mask, the device tracks real-time respiratory rates, successfully differentiating between sitting at 17.09 breaths per minute, standing at 18.75 breaths per minute, and squatting at 26.67 breaths per minute. A 3×3 underwater sensor array facilitates touch-encoded word recognition for terms like “age,” “bed,” and “hic” while mapping thermal and mechanical stimuli simultaneously.
Did You Know? The pyramid-shaped microstructure’s sloped facets induce a stress-concentration effect, causing the interlayer contact area to vary nonlinearly with applied pressure to ensure high sensitivity over a broad detection range.
The sensor also monitors human joint articulation, capturing subtle facial expressions on moist skin and finger, wrist, and elbow movements to support emotion-aware diving assistants and underwater communication. When mounted on a robotic fish, the sensor recorded stable periodic signal output during tail-flapping propulsion over a 200-second test window.
Frequently Asked Questions
How does the sensor detect temperature and pressure simultaneously?
The sensor utilizes a stacked $text{Bi}_2text{Se}_3$/carbon paper multilayer design where temperature is measured via the Seebeck effect (generating a voltage signal) and pressure is detected through piezoresistive interlayer contact modulation (generating a resistance signal).
What prevents water from interfering with underwater signal transmission?
The electrochemically constructed pyramid interface creates a stable Cassie–Baxter state with a water contact angle of 143.7°, providing intrinsic hydrophobicity that eliminates the need for external waterproof coatings.
What are the primary use cases for this amphibious technology?
Potential applications include marine exploration, environmental monitoring, smart respiratory masks, underwater human-machine interfaces, and motion-tracking sensors for soft underwater robotics.
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