## 3 LIG-Based Wearable Systems for Multifunctional and Intelligent HCI
### Electrooculography and Tactile Perception Collaborated 3D HCI System  
Traditional HCI systems have limitations in their ability to perform well in multi-scene applications or 3D interactive experiences as they rely on a single type of device or signal.  
To address this issue, [PERSON] et al. proposed an electrooculography (EOG) and tactile perception collaborated wearable HCI system that could realize accurate and convenient interaction in three dimensions [13]. As shown in Figure 10, the system consisted of two parts: the EOG interaction module and the tactile array module. Both LIG-based modules were made by transferring a laser-induced sensor pattern from the PI substrate onto a flexible and stretchable medical PU (polyurethane) adhesive film. The difference was that the EOG module used the LIG layer as the electrode and was in direct contact with the skin. The system, therefore, adopted a single-sided structure that was not encapsulated, while the capacitive 4 \(\times\) 4 tactile array module consisted of two LIG-PU films stacked together in the same direction: one layer of PU film served as the encapsulation while the other was used as a dielectric layer. The resulting ultra-thin and soft PU substrate (45 \(\upmu\)m) could be closely attached to the human skin for high-quality signal acquisition and comfortable wear.  
Through four EOG electrodes around the eyes, the system could recognize nine kinds of eye movements including normal blinking, looking up/down, looking right/left, closed down/up, and up/down blinking. In addition, an intelligent algorithm was designed to train and classify these nine kinds of eye movement with high accuracy and efficiency to realize eight kinds of control using movement direction including stop, move forward/backward, move left/right, move left front/right front, and move left back/right back. The EOG module combined with the intelligent algorithm could realize machine control in a two-dimensional plane (X-Y direction). Furthermore, for HCI in 3D space, a tactile array is needed to realize control in the Z direction. Based on 16 tactile sensing units, the tactile array could realize multi-point tactile perception and sliding perception. By using the tactile array to realize the perception of different sliding trajectories and the perception of pressing at different points, complex and precise motion control can be realized.  
In conclusion, the EOG module can realize easy and fast 2D interaction and the tactile module can realize accurate and complex movement control, when working together, the whole wearable system can realize fast, accurate, and convenient HCI in 3D space. On one hand, this system has important application values in the field of 3D HCI such as in unmanned aerial vehicle (UVA) control. On the other hand, this 3D HCI system can free  
Figure 10: The EOG and tactile perception collaborated 3D HCI system. Reproduced with permission from [13]. Copyright 2022 American Chemical Society.  
people's hands compared with traditional handheld VR devices, which means that this kind of system can have a wider range of applications in the metaverse. However, this research mainly focused on the control function of the wearer-centered HCI system. In the next section, we will introduce a human-like system, which realizes the voice interaction between the wearer and the robot by endowing the HCI system with listening and speaking functions.