ALLPCB
Background
Breakthroughs in sensor performance can enable new applications in bionic robotics, prosthetics, and wearable health monitoring. In medical monitoring, a temperature sensitivity of about 100 millikelvin (mK) is required to detect body temperature changes caused by injury, infection, or intense exercise. Monitoring subtler thermophysiological changes from balance disorders, stress, or sleep deprivation requires higher sensitivity. To mimic human thermal touch, artificial skin must match or exceed human skin sensitivity (about 20 mK). At millikelvin sensitivity levels, artificial skin could even surpass human skin, approaching the thermal detection capabilities of animals such as snakes (3 mK) and sharks (1 mK) for thermal radiation and thermal trails.
Sensor Concept and Working Mechanism
A research team at Jilin University developed an ultra-high-sensitivity flexible temperature sensor for high-precision body temperature monitoring and biomimetic thermoperception. The device is based on the thermal sensing mechanism of human skin and employs an asymmetrical polymer bilayer (APB). The sensing principle uses thermally induced cation cross-membrane migration in the APB to achieve ultrahigh temperature sensitivity for detecting minute temperature changes. Because of this mechanism, increasing temperature shifts the sensor's electrical behavior from a nonionic polymer type toward an ion-conductive polymer type. This change in conduction mechanism produces an orders-of-magnitude change in resistance over a small temperature range.
Temperature Sensing Performance
The study examined key factors affecting the temperature sensitivity of the asymmetrical polymer bilayer. The temperature response of the sensor first increases and then decreases with the thickness of the nonionic conductive polymer layer, which is attributed to a raised ion migration energy barrier as that layer becomes thicker. The APB sensor exhibits Arrhenius behavior over the 10–60 °C range; fitting yields good linearity (R2 > 0.99) and a high thermal activation parameter (B = 10128 K) . Compared with previously reported flexible temperature sensors, the APB sensor demonstrates ultrahigh temperature sensitivity (1.42 mK) and a large temperature coefficient of resistance (11.25%/°C), along with good cycling stability.
Application: Material Recognition with a Robotic Hand
Analogous to how human skin judges material by touch, the APB sensor enables a robotic hand to recognize object materials. Due to the sensor's sensitivity, it captures the heat exchange process when a biomimetic robotic hand at 37 °C contacts an object. Contact with materials of different thermal conductivity produces measurement curves with distinct maximum slope values. Using the maximum slope as a feature, data from nine different materials were collected by having the robotic hand grip each material 100 times. Features were split into training and validation sets using five-fold cross-validation, and classification learning algorithms were applied for machine learning. The system distinguished objects of identical shape but different materials with 99.9% accuracy. Integrating the APB temperature sensor into artificial skin increases the dimensionality of tactile sensing for robotic hands and supports more lifelike tactile functions.
