Fingerprint-Inspired Strain Sensor with Balanced Sensitivity and Strain Range Using Laser-Induced Graphene

Abstract

Sensitivity and strain range are two mutually exclusive features of strain sensors, where a significant improvement in flexibility is usually accompanied by a reduction in sensitivity. The skin of a human fingertip, due to its undulating fingerprint pattern, can easily detect environmental signals and enhances sensitivity without losing elasticity. Inspired by this characteristic, laser-induced graphene (LIG) with a fingerprint structure is prepared in one step on a polyimide (PI) film and transferred into an Ecoflex substrate to assemble resistive strain sensors. Experimentally, the fingerprint-inspired strain sensor exhibits a superfast response time (∼70 ms), balanced sensitivity and strain range (a gauge factor of 191.55 in the 42–50% strain range), and good reliability (>1500 cycles). Self-organized microcracks, initiated in weak mechanical areas, cause prominent resistance changes during reconnection/disconnection but irreversibly fail after excessive stretching. The robust function of fingerprint-inspired sensors is further demonstrated by real-time monitoring of tiny pulses, large body movements, gestures, and voice recognition.

Research Progress on the Preparation and Applications of Laser-Induced Graphene Technology

“…The one-step synthesis of patterned graphene has greatly contributed to the development of smart sensors. Researchers have developed a wide variety of LIG-based sensors or sensor devices with modified LIG materials, such as strain sensors, pressure sensors, temperature sensors, humidity sensors, gas sensors, and biochemical sensors, for monitoring various physical and biochemical signals [ 94 , 95 , 96 , 97 , 98 , 99 ].…”

“…Usually, significant improvements for sensor shape variables are accompanied by a decrease in sensitivity [ 105 , 106 ], therefore, it is a daunting challenge to maintain the balance between sensitivity and strain range of LIG-based strain sensors. Wang et al [ 96 ] investigated a fingerprint-based resistive strain sensor with balanced sensitivity and strain range ( Figure 6 b). The authors used different process parameters to control the high-temperature gradient in the irradiated region and to rationalize the geometry of the LIG lines (e.g., depth, width, and density).…”

“…In addition, this balanced sensitivity and strain sensor could be used to monitor human movement. Take the push-up exercise as an example, a reasonable real-time monitoring of the movement is beneficial for regulating training movements and preventing physical injuries [ 96 ]. Zhu et al [ 107 ] prepared a kind of LIG with high conductivity and good mechanical properties on the surface of polydimethylsiloxane (PDMS) films using a diode laser.…”

“… ( a ) Piezoresistivity and applications of the DLW generated graphitic sensors, adapted with permission from [ 103 ]. ( b ) Performance of the LIG-based strain sensor inspired by the fingerprint, adapted with permission from [ 96 ]. ( c ) Direct laser etching of PDMS films to prepare graphene and characterization of the pressure response, adapted with permission from [ 107 ].…”

Porous graphene foam composite-based dual-mode sensors for underwater temperature and subtle motion detection

“…and L are the lengths before and after stretching. The slope in the curve of the relative resistance change versus the engineering tensile strain gives the sensitivity or gauge factor (GF) of the strain sensor, i.e., GF=(ΔR/R0)/ε [38].…”