A University of Cambridge research team has developed a triaxial force microsensor array using graphene-liquid metal composites, enabling robots to sense force magnitude, direction, slip, and surface roughness at scales rivaling human fingertips. This achievement addresses key limitations in tactile sensing for neuroprosthetics, human-machine interfaces, and dexterous robotics by decoupling normal and tangential forces through multiscale pyramid microstructures.
The device employs anisotropic porous conductive elastomers (APEs) with a hybrid filler of spiky nickel particles, few-layer graphene nanosheets, and eutectic gallium-indium (EGaIn) liquid metal microdroplets. These form a solid-liquid conductive network where LM droplets act as deformable hubs bridged by graphene sheets, cured under magnetic fields to align fillers directionally within an interconnected microporous structure. Pyramid-shaped units, as small as 200 μm across, mimic human epidermal microstructures to concentrate stress at tips, boosting sensitivity while spanning wide force ranges.
It delivers 110 kPa⁻¹ sensitivity over a 500 kPa linear range (R² > 0.998), less than 2° deviation in force direction, and a 0.9 μN detection limit - improving on prior flexible sensors by an order of magnitude in size and resolution. Four electrodes per pyramid enable real-time 3D force vector reconstruction via resistance changes from multiscale deformation.
"Most existing tactile sensors are either too bulky, too fragile, too complex to manufacture or unable to accurately distinguish between normal and tangential forces," said Professor Tawfique Hasan from the Cambridge Graphene Centre, who led the research.
Integrated into grippers, the array supports self-adjusted grasping of unknown objects, detecting slip without prior data and estimating roughness for adaptive control. Microscale versions analyze tiny metal spheres' mass, geometry, and density, suiting microrobots and minimally invasive surgery.
"Our approach shows that bulky mechanical structures or complex optics are not required to achieve high-resolution 3D tactile sensing," said lead author Dr. Guolin Yun. A patent is pending via Cambridge Enterprise, with support from the Royal Society, Henry Royce Institute, and ARIA.
