Ultra‐Sensitive and Highly Stretchable Strain Sensors for Monitoring of Human Physiology

Abstract

The flexible strain sensors have potential applications in advanced electronics, health monitoring systems, wearable sensors, robotics, and human-machine interfaces. The development of highly sensitive, stretchable, and durable strain sensors is a challenging task for researchers. However, the sensors with a detection range from large strain to minute deflection are imperative for human-interactive applications. This work has demonstrated a facile method of sensor fabrication, which use reduced graphene oxide (rGO) as sensing material and silicone sealant as a flexible substrate. Few-layer rGO is synthesized by electrochemical exfoliation of pencil lead. The fabricated sensors have a gauge factor higher than 4000 and durability longer than 1600 cycles at 100% strain. At the same time, developed strain sensors exhibit detection capability over a wide range of strain (0-120%), which is an essential requirement of wearable sensors. To the best of the authors' knowledge, fewer works have reported strain sensors that have ultra-high gauge factor (≥4000) in combination with high stretchability (>100%). Utilizing the ultra-sensitivity and sub-second response time of the rGO-sealants, these wearable sensors are used to monitor physical activities, heartbeats, and finger touches.

IoT-Enabled Stretchable Piezoresistive Sensor for Real-Time Monitoring of Fruit Growth and Human Physiology

“…A study of the diffraction peak position corresponding to the (002) plane is crucial to identifying graphite and graphene. Figure a exhibits the (002) plane diffraction peak of graphite at 2θ values of 30.97°, whereas exfoliated graphite shows the same peak at 2θ values of 25°, indicating a distinct characteristic peak of graphene. ,, Bragg’s equation was used to calculate spacings between the atomic layers, which were found to be 0.33 nm for the graphite rod (powder) and 0.35 nm for synthesized graphene. , …”

“…Figure 2a exhibits the (002) plane diffraction peak of graphite at 2θ values of 30.97°, whereas exfoliated graphite shows the same peak at 2θ values of 25°, indicating a distinct characteristic peak of graphene. 23,37,38 Bragg's equation was used to calculate spacings between the atomic layers, which were found to be 0.33 nm for the graphite rod (powder) and 0.35 nm for synthesized graphene. 23,39 Raman spectroscopy is a standard method for analyzing the quality of carbon-based materials.…”

“…23,37,38 Bragg's equation was used to calculate spacings between the atomic layers, which were found to be 0.33 nm for the graphite rod (powder) and 0.35 nm for synthesized graphene. 23,39 Raman spectroscopy is a standard method for analyzing the quality of carbon-based materials. It is particularly effective in distinguishing between ordered and disordered crystal structures of the materials.…”

“…The lower I D / I G value observed for the synthesized graphene implies the removal of oxide groups and the restoration of the sp 2 carbon bond. 23,40 The Raman 2D peak is important in differentiating graphene from graphite due to its distinct characteristics. 37,41−44 In this case, the intense 2D peak of graphene compared to the minor 2D peak of graphite rod confirms the exfoliation of graphene layers.…”

Demonstration of miniaturized LIG electrodes for temperature and ECG sensing using a femtosecond laser

“…One of the critical aspects of wearable sensors is the development of miniaturized, flexible, and highly sensitive sensing elements that can be seamlessly integrated into various form factors without compromising user comfort or signal quality 7 . Traditional methods for sensor fabrication, such as photolithography and screen printing, can be timeconsuming, costly, and may involve the use of hazardous chemicals 8 . Therefore, there is a growing demand for more efficient and environmentally friendly fabrication techniques for wearable sensors.…”