Researchers tested the laser radiation process for future motion detection, tactile sensing and health monitoring devices.
Graphene is a semiconductor material of choice in various applications of flexible electronic devices due to its superior pliability and high conductivity. Several substances can be converted into carbon to create graphene through laser radiation. The laser-induced graphene (LIG) can have specific properties determined by the original material.
Researchers from Pennsylvania State University have tested this process and published their results in SCIENCE CHINA Technological Sciences. They published two studies, which they believe, can inform research and development of future motion detection, tactile sensing and health monitoring devices.
For testing, researchers irradiated polyimide through laser scanning. They varied the power, scanning speed, number of passes and density of scanning lines.
“We wanted to look at how different parameters of the laser processing process create different nanostructures,” Huanyu “Larry” Cheng, Dorothy Quiggle Career Development Professor in Penn State’s Department of Engineering Science and Mechanics (ESM), said. “Varying the power allowed us to create LIG either in a fiber or foam structure.”
The researchers observed that the power levels from 7.2 watts to 9 watts changed the LIG formation pattern from foam to bundles of small fibers. The bundles grew larger in diameter with increased laser power, while higher power promoted the web-like growth of a fiber network. This fibrous network showed better electrical conductivity than the foam. And according to Cheng, the network can open possibilities for sensing devices.
“In general, this is a conductive framework we can use to construct other components,” Cheng said. “As long as the fiber is conductive, we can use it as a scaffold and do a lot of subsequent modifications on the surface to enable a number of sensors, such as a glucose sensor on the skin or an infection detector for wounds.”
Using this study as a foundation, researchers designed, fabricated and validated a flexible LIG pressure sensor. This work was published in SCIENCE CHINA Technological Sciences.
“Pressure sensors are very important,” Cheng said. “We can use them not only in households and manufacturing but also on the skin surface to measure lots of signals from the human body, like the pulse. They can also be used at the human-machine interface to enhance performance of prosthetic limbs or monitor their attachment points.”
The team tested two designs. The first design consists of a sandwiched thin LIG foam layer between two polyimide layers containing copper electrodes. The LIG generates electricity when pressure is applied. Researchers report that the voids in the foam reduced the number of pathways for electricity to travel, making it easier to localize the pressure source, and appeared to improve sensitivity to delicate touches.
This first design can detect bending and stretching hand movements, as well as heartbeats when attached to the back of the hand or the finger.
The second design involves nanoparticles into the LIG foam. The tiny spheres of a semiconductor molybdenum disulfide enhanced the foam’s sensitivity and resistance to physical forces. According to the researchers, this design showed nearly identical performance before and after nearly 10,000 uses.
Cheng says that both these methods were cost-effective and allowed for simple data acquisition.