Gunhee Lee1,Jingoo Lee2,Taewi Kim2,Inyong Park1,Sang Bok Kim1,Dae Hoon Park1,Bangwoo Han1
Korea Institute of Machinery and Materials1,Ajou University2
Gunhee Lee1,Jingoo Lee2,Taewi Kim2,Inyong Park1,Sang Bok Kim1,Dae Hoon Park1,Bangwoo Han1
Korea Institute of Machinery and Materials1,Ajou University2
Among the various wearable devices for monitoring various human bio-signals (e.g., human motion monitoring, health care monitoring) being developed, the strain sensor is one of the representatives means for measuring mechanical bio-signals. In order to effectively utilize the strain sensor as a wearable monitoring device, it should satisfy high sensitivity, long-term durability, fast response characteristics, and high flexibility. However, it remains a challenge to accurately detect deformations caused by small stresses with high sensitivity due to the stiffness of the sensor itself. In general, the strain sensor expresses the sensitivity as the magnitude of the signal change with respect to the strain. In the case of soft objects such as human skin, even if an ultra-sensitive strain sensor is used, it cannot detect the deformation properly because the deformation of the skin cannot deform the sensor if the sensor itself is too stiff. To solve this problem, strain sensors made of low-modulus materials can be used, but these generally have low sensitivity and high hysteresis, making accurate measurements difficult. Herein, we proposed a buckled crack-based sensor consisting of thin metal films and polymer-based substrates to deal with these abovementioned problems. The crack-based sensor with a buckling structure sensitively responds to skin deformation and has a strain range of up to 80%. The buckled crack-based sensor possesses high sensitivity (gauge factor (GF) ≈ 250), long-term stability (>10,000 cycles), and low mechanical stiffness during stretching. As the human health monitoring system application, the buckled crack-based sensor successfully demonstrated to measure human respiration rate and depth, as well as the volume of inhalation and exhalation.