Detailing their findings in the Applied Physics Letters under the title "Flexible and wearable 3D graphene sensor with 141 KHz frequency signal response capability", the researchers explain that since the band gap of graphene dynamically changes upon mechanical deformation, changes in its resistance can be monitored, making for an effective strain sensor.
They synthesized the three-dimensional graphene foam (3D GF) by CVD on a nickel (Ni) foam used as a template, with ethanol as the carbon source. After the formation of graphene over the nickel foam (at 900ºC), the cooled Ni/graphene composite was immersed in hydrochloric acid to remove the metal, leaving a highly porous and flexible 3D GF.
The researchers then wired the 200µm-thin 3D GF before embedding it into PDMS to obtain a rugged flexible and stretchable sensor.
In their experiments, they characterized the response of various GF/PDMS composites under acoustic stimulus (affixing the sensor to one branch of a tuning fork), or attaching it to a piezoelectric ceramic transducer for high frequency tests.
The paper reports a clear linear response from audio frequencies, including frequencies up to 141KHz in the ultrasound range, noting that to date, no other flexible force sensors were able to detect signals in the KHz range.
Thanks to the wide bandwidth of 3D GF/PDMS sensors, the researchers expect such sensors to become an integral part of interactive wearable devices or artificial prosthetics, providing an e-skin capable of perceiving seismic waves, ultrasonic waves, shock waves, and transient pressures.