New graphene sensors make for better brain-machine interface
The development of a cutting-edge graphene sensor has led to the creation of an interface that is able to accurately control a robot using thought alone. The development has positive implications not only for healthcare but for a range of other industries.
Brain-machine interfaces (BMIs) allow a person to operate a device using their brainwaves. As hands-free and voice-free interfaces, BMIs hold great potential for use in robotics, bionic prosthetics, and self-driving cars.
A BMI is ordinarily made up of three modules: an external sensory stimulus, a sensing interface, and a unit that processes neural signals. Of the three, the sensing interface is crucial because it detects electrical activity generated by the brain's outermost layer, the cerebral cortex, which is responsible for higher-level processes, including motor function.
But it's the visual cortex, the part of the cerebral cortex that receives and processes information sent from the eyes, which is key to BMIs that rely on visual stimuli. The visual cortex is situated at the very back of the brain, in the occipital lobe.
Brainwaves are registered via implantable or wearable sensors, such as electroencephalography (EEG) electrodes. The problem with using EEG electrodes and other non-invasive biosensors on the back of the head is that it is an area typically covered with hair.
Wet sensors rely on the use of conductive gel on the scalp and hair, but that can cause the sensors to move when the individual does. Dry sensors can be used as an alternative, but they, too, have challenges; they are less conductive than wet sensors, and, given the rounded shape of the head, they can run into difficulties maintaining adequate contact.
Researchers from the University of Technology Sydney (UTS) have addressed these issues by developing a dry biosensor containing graphene, a one-atom-thick layer of carbon atoms arranged in a hexagonal lattice that is 1,000 times thinner than a human hair and 200 times stronger than steel.
Graphene is an optimal material for creating dry biosensors, given its thinness and high electrical conductivity. It’s also resistant to corrosion and the effects of sweat, making it perfect for use on the head.
The researchers found that combining graphene with silicon produced a more robust dry sensor. The graphene layer on the sensors they developed is less than a nanometer thick.
“By using cutting-edge graphene material, combined with silicon, we were able to overcome issues of corrosion, durability and skin contact resistance, to develop the wearable dry sensors,” said Francesca Iacopi, corresponding author of the study.
The researchers experimented with different sensor patterning, including squares, hexagons, pillars and dots, and found that the hexagon-patterned sensors yielded the lowest on-skin impedance. They then tested their new sensor using a BMI.
The hexagon-patterned sensors are placed over the scalp at the back of the head to detect brainwaves from the visual cortex and the user wears an augmented reality (AR) lens displaying white squares. By concentrating on a particular square, brainwaves are created that are picked up by the biosensor. A decoder then translates that signal into a command.
“Our technology can issue at least nine commands in two seconds," said Chin-Teng Lin, co-author of the study. "This means we have nine different kinds of commands and the operator can select one from those nine within that time period.”
Australian Army soldiers performed a real-world test of the graphene-sensor BMI, using it to control a four-legged robotic dog. The device allowed the robot to be commanded hands-free, with up to 94% accuracy.
“The hands-free, voice-free technology works outside laboratory settings, anytime, anywhere,” Iacopi said. “It makes interfaces such as consoles, keyboards, touchscreens and hand-gesture recognition redundant.”
However, the researchers don’t consider this to be the final iteration of their design. Further research and testing are needed to strike a balance between the total available graphene area, the ability to accommodate the presence of hair, and the ability to maintain sensor contact with the scalp.
But it’s a promising step toward the development of technology that could be of great benefit to people with disabilities in operating a wheelchair or prosthetic, as well as having broader application in the fields of advanced manufacturing, defense, and aerospace.
The study was published in the journal ACS Applied Nano Materials.
Source: University of Technology Sydney