Breaking Through Commercialization Barriers... Kyung Hee University Professor Jin Seonghun's Team Develops 'Flexible Sensor'

Technology Enables Independent Adjustment of Sensitivity and Resistance

Kyung Hee University announced on Wednesday that a research team led by Professor Jin Seonghun of its Department of Information Display had developed an innovative sensor design technology that can independently adjust sensitivity (gauge factor, GF) and baseline resistance ($R_0$), the key performance indicators of flexible strain sensors.

Kyung Hee University Professor Jin Seonghun, who developed a flexible sensor whose sensitivity and resistance can be adjusted independently.

In collaboration with the Korea Polar Research Institute, the team also successfully demonstrated the technology's practical applicability by wirelessly measuring the breathing of large wild animals, including anesthetized tigers and lynxes, in real time. The findings were published in Small, an internationally renowned journal in the fields of nano- and microscience.

Strain sensors, which convert minute mechanical deformations into electrical signals, are key components in wearable devices and smart healthcare monitoring systems. However, conventional flexible strain sensors have a longstanding limitation: when their sensitivity is increased or changed, their baseline resistance, the initial resistance before deformation, also changes in tandem. This has made it difficult to simultaneously achieve the optimal resistance required by signal-processing circuits and the sensitivity desired by users, hindering circuit integration and commercialization.

The team devised a new process in which single-walled carbon nanotubes are spray-coated onto a cracked SU-8/PDMS bilayer substrate. The mechanism uses the "pre-strain" applied to induce cracks in the substrate to control sensitivity, while the "amount of carbon nanotube dispersion sprayed" independently adjusts baseline resistance. By controlling these key characteristics through independent process variables, the team increased the design flexibility for customized sensors.

Performance tests showed that when the amount of carbon nanotube dispersion sprayed was adjusted while pre-strain was held constant, baseline resistance changed by approximately 5.9 times, while sensitivity changed by only about 1.15 times. Conversely, when pre-strain was changed while the spray amount was held constant, sensitivity changed by approximately 4.4 times, while the variation in baseline resistance was kept within a factor of two. The experiments demonstrated that interference with one metric can be minimized when tuning the other.

Using computer simulations, the team also identified the specific operating principle behind the sensor's high sensitivity: conductive pathways in the carbon nanotube network at the crack boundaries connect and break in response to physical deformation. In addition, the team integrated the sensor with a thin-film transistor to build a circuit that converts strain into frequency signals, and successfully demonstrated precise detection of subtle vocal vibrations, pulses, and large movements of the wrist joint. In particular, integrating the sensor with a Bluetooth wireless communication module expanded the scope of its field testing.

In collaboration with the Korea Polar Research Institute, the team attached sensors to a Siberian tiger and a lynx under anesthesia for surgery and wirelessly monitored their breathing rates in real time. The lynx had a breathing rate of 22 to 23 breaths per minute, which matched readings from an existing commercial vital-sign monitor with complete accuracy. In the Siberian tiger, the sensor accurately detected even faint breathing that had slowed dramatically to two to three breaths per minute due to anesthesia. This achievement enabled the precise measurement of biological signals that existing clinical equipment based on electrical signals could not detect.

Professor Jin said, "Through close collaboration with the Korea Polar Research Institute, we verified the technology's outstanding practicality and reliability by measuring the breathing of large wild animals in the field, where conditions are extremely difficult to control. We expect this technology to serve as a key sensor in a wide range of applications, including wearable healthcare devices for humans and remote biomonitoring of wildlife for ecological conservation."

This content was produced with the assistance of AI translation services.