Electronic skin creates vivid touch experience for VR

A research team led by the City University of Hong Kong (CityU) has developed an advanced wireless haptic interface system, called WeTac, worn on the hand, which has soft, ultrathin features, and collects personalised tactile sensation data to provide a vivid touch experience in the metaverse. The system has application potential in gaming, sports and skills training, social activities, and remote robotic controls.

Dr Yu Xinge, Associate Professor in the Department of Biomedical Engineering at CityU, said that touch feedback has great potential, along with visual and audial information, in virtual reality (VR). “We kept trying to make the haptic interface thinner, softer, more compact and wireless, so that it could be freely used on the hand, like a second skin,” Yu said.

Together with Professor Li Wenjung, Chair Professor in the Department of Mechanical Engineering, Dr Wang Lidai, Associate Professor in the Department of Biomedical Engineering and other collaborators, Yu’s team developed WeTac, an ultra-flexible, wireless, integrated skin VR system. The research findings were published in the scientific journal Nature Machine Intelligence.

Existing haptic gloves rely mostly on bulky pumps and air ducts, powered and controlled through a bunch of cords and cables, which hinder the immersive experience of VR and augmented reality (AR) users. The WeTac overcomes these shortcomings with a soft, ultrathin, skin-integrated wireless electrotactile system. The system comprises two parts: a miniaturised soft driver unit, attached to the forearm as a control panel, and hydrogel-based electrode hand patch as a haptic interface.

The entire driver unit weighs 19.2 g and is small (5 x 5 x 2.1 mm) enough to be mounted on the arm. It uses Bluetooth low energy (BLE) wireless communication and a small rechargeable lithium-ion battery. The hand patch is 220 µm to 1 mm thick, with electrodes on the palm. It exhibits great flexibility and provides effective feedback on various poses and gestures. According to Yu, electrotactile stimulation is a good method to provide effective virtual touch for users. “However, as individuals have different sensitivities, the same feedback strength might be felt differently in different users’ hands. So we need to customise the feedback parameters accordingly to provide a universal tool for all users to eliminate another major bottleneck in the current haptic technology,” Yu said.

Image caption: The wireless skin-integrated electrotactile system comprises two parts: a soft driver unit (right) attached to the forearm, and the hand patch (left). Image credit: Dr Yu Xinge’s research group / City University of Hong Kong.

The ultra-soft feature of WeTac allows the threshold currents to be mapped for individual users to determine the optimised parameters for each part of the hand. Based on the personalised threshold data, electrotactile feedback can be delivered to any part of the hand on demand in a proper intensity range to avoid causing pain or being too weak to be felt. In this way, virtual tactile information, including spatial and temporal sequences, can be reproduced over the whole hand. The WeTac patches are worn on the hands to provide programmable spatio-temporal feedback patterns, with 32 electrotactile stimulation pixels on the palm instead of the fingertips only. The average centre-to-centre distance between the electrodes is about 13 mm, providing wide coverage over the whole hand.

The device has built-in safety measures to protect users from electric shock, and the temperature of the device is maintained in a range of 27 to 35.5°C to avoid causing any thermal discomfort during continuous operation. WeTac has been successfully integrated into VR and AR scenarios, and synchronised with robotic hands through BLE communication. With the miniature size, wearable and wireless format, and sensitivity-oriented feedback strategy, WeTac makes tactile feedback in the hand easier and more user-friendly. Users can feel virtual objects in different scenarios, such as grasping a tennis ball in sports training, touching a cactus, or feeling a mouse running on the hand in social activities, virtual gaming, etc.

Image caption: In an AR scenario, a virtual mouse hops forwards and rests briefly on each point of the hand. The hand patch, with hydrogel-based electrodes, has 32 electrotactile stimulation pixels on the palm side, allowing the threshold currents to be easily mapped for different users. Image credit: Dr Yu Xinge’s research group / City University of Hong Kong.

“We believe that this is a powerful tool for providing virtual touching, and is inspiring for the development of the metaverse, human–machine interface (HMI), and other fields,” Yu said.

Top image caption: Dr Yu Xinge (centre) and his research team at City University of Hong Kong, including Zhou Jingkun (right), Wu Mengge (left) and Yao Kuanming, developed the “WeTac” system. Image credit: City University of Hong Kong.