Soft and Ultra-Thin Wearable Tactile Interface with Electrical Impedance Tomography for High Spatiotemporal Resolution

Wearable tactile mapping devices, a burgeoning area in human-computer interaction, have gained significant attraction due to their wide range of applications. These include interfaces for virtual reality and gaming devices, haptic feedback systems, and artificial skin for medical and robotic applications. Tactile sensors, as a cornerstone of this technology, must achieve high spatiotemporal resolution while maintaining soft mechanical properties to replicate the human sense of touch accurately. This is paramount in creating seamless and immersive user experiences, whether it's in navigating virtual environments or enabling prosthetic devices to mimic real tactile feedback. However, the development of these sensors presents distinct challenges. Current high resolution tactile sensing technologies predominantly rely on inorganic material-based sensors, which, despite offering high spatial resolution and reliability, pose significant limitations. They are inherently brittle and ill-suited to accommodate mechanical deformation, a critical attribute for wearable sensors meant to conform to human skin. On the other hand, soft materials, characterized by a low Young's modulus, are mechanically desirable for wearable tactile systems as they can conform to varied and changing surfaces. However, the fabrication processes for these materials tend to deviate from conventional microelectronics manufacturing techniques. This divergence often results in less sophisticated device structures, hindering the development of advanced and intricate tactile sensing systems.<br/><br/>To overcome these limitations, we propose an ultra-thin tactile sensor offering single-cell based multi-channel array functionality via the application of electrical impedance tomography (EIT). The sensor's stretchable sensing area consists of an elastomeric substrate and encapsulation, alongside a conductive functional layer comprising multi-wall carbon nanotube (MWCNT) layers. With a thickness of just 50 microns, this low-modulus, highly stretchable sensor can conformably adhere to human skin, maintaining robust functionality under applied force and mechanical deformation. The EIT computational analysis method allows our single-cell device to operate as a multi-channel array by reconstructing high-resolution conductivity changes within the broad sensing area. Piezoresistive effect-induced conductivity changes in the MWCNT-based conductive layer occur when external forces are applied, causing mechanical deformation, bending, and stretching. These changes can be mapped by EIT measurements using surrounding electrodes, achieving high-resolution detection of force applications. This EIT-based soft tactile interface can differentiate external pressures down to a 1mm scale, and vertical deformation of a few hundred micrometres. We validated our tactile sensor's functionality through two real-time applications: a wearable drone controller and a handwriting recognition interface. Our work illustrates the potential of applying EIT to soft, ultra-thin elastomeric devices for the development of high-performance wearable tactile sensing systems. These systems could find potential applications in healthcare, robotics, and human-machine interfaces, paving the way for more advanced tactile sensors in the future.