# Laser Synthesized Graphene and Its Applications
## 3 Applications of Laser Synthesized Graphene
### Strain Sensing  
Strain sensors generally exploit a variation of the electrical properties of a material upon deformation of the material itself. These are generally evaluated by the gauge factor (GF), defined as \(\frac{\mathrm{a}\hbar/\mathrm{f}_{\mathrm{g}}}{\varepsilon}\), where \(\varepsilon\) is the applied strain (\(\Delta\)L/L\({}_{0}\)). LRG has been demonstrated as a strain sensor by [PERSON] et al. [59]. Here, rGO was obtained by DVD LightScribe process on a PET substrate. The authors showed the operation of a low GF system (0.11), with a linear relationship between R/R\({}_{0}\) and the strain, suitable for high deformations, where rGO was formed as a film, as well as high GF system (9.49) formed by an rGO microribbon, suitable for very small deformations [59]. The former shows repeatable operation at least up to 150 cycles, while the latter fails after 35 cycles.  
A strain sensor based on an LIG stripe obtained from PI was demonstrated by [PERSON] et al. [60]. Here, while the system showed robust repeatability at least up to 1000 cycles, the relationship between R/R\({}_{0}\) and the strain is logarithmic, and the GF is thus not constant. This is attributed to a very high resistance change at strains closer to 100%. While the authors admit that this might require more complex circuitry in a real-life system, they propose that the system is promising for human body applications where high strain sensing is critical, and demonstrate this by applying the sensor to a hand glove and measuring electrical properties during hand motion (Figure 11a) [60]. A similar application was demonstrated in Ref. [61] where graphene was obtained within a polydimethylsiloxane (PDMS) matrix and tested against different parts of the body, including facial muscles for facial expression and fingers and biceps for body movement. An LIG pattern on PI was transfer-printed onto a fiberglass composite, allowing in situ structural health monitoring of components, with no need for external bonding [62]. Here, the system shows a strain gauge between 0.5 and 1.3 and is able to detect both dynamic and quasi-static strain [62]. [PERSON] et al. went a step further and demonstrated heart beat detection using LIG from PI (Figure 11c) [63]. [PERSON] et al. went even further and developed a system, based on porous LIG made from PI, that is able to detect electrophysiological processes that produce signals commonly known as electroencephalogram (EEG), electrocardiogram (ECG), and electromyogram (EMG) (Figure 11b) [64].  
Figure 10: Electrical response of an LRG system under exposure to drops of different liquids. Reproduced with permission from Ref. [58]. Copyright 2019, Elsevier.  
Overall, strain sensing has been extensively studied, especially for LIG, and a number of real-life applications have been demonstrated as proof of concept, mainly in the healthcare field. Thus, with appropriate scaling up of the production, such systems may potentially be ready to compete in the market with existing devices.  
Somehow related to strain sensing is sound sensing, as an \"artificial throat\" was demonstrated by [PERSON] et al. as a device that can both produce and detect sound [65]. Indeed, as the device, made from LIG, is exposed to AC voltage, the material produces sound waves generated by expansion of air, induced by the periodic joule heating. On the other hand, under a low bias voltage, the device can detect the vibrations of throat cords through a resistance change, if applied on a human tester throat [65]. In the latter case the device can distinguish different sounds such as humming, coughing, screaming, as well as movements such as swallowing and nodding, acting in this case as a strain sensing device.