## 3 LIG-Based Wearable Systems for Multifunctional and Intelligent HCI
### The Machine Learning-Assisted Dual-Function Acoustic HCI System  
Vocalization and hearing are important ways for people to communicate with the outside world; the ear and throat are natural \"HCI systems\" of humans. Due to its excellent acoustic properties, LIG has been increasingly used in the research of acoustic sensors and actuators [35; 36; 37]. However, it is a challenge to combine the function of \"hearing\" and \"speaking\" and apply it to wearable HCI systems.  
[PERSON] et al. proposed a LIG-based dual-function transducer for human-robot interaction [16]. As shown in Figure 11, the whole system was composed of a LIG artificial ear based on a triboelectric sensor and a LIG artificial mouth based on a thermoacoustic effect actuator. The artificial ear and the artificial mouth were all realized by the same device structure including a PI film with single-sided LIG, a polyethylene (PET) ring spacer, and a PI film with double-sided LIG. The LIG has excellent mechanical, electrical, and thermal properties, making it suitable for multifunctional integration. Furthermore, the whole device has a low-cost advantage (-0.0036 USD) that is suitable for large-scale applications.  
When used as an artificial ear, the microphone based on the triboelectric principle works in contact-separation mode. The LIG layer acts as the electrode and the triboelectric-positive material. When used as an artificial mouth, the speaker uses the thermoacoustic effect to produce sound. The system has a high sensitivity (4500 mV Pa\({}^{-1}\)) and good durability (can work for 1,000,000 cycles and 60 days). With the aid of a convolutional neural network (CNN), the system can reach 99.66% high speech recognition accuracy based on 78,360 speech data collected by the system. Most significantly, based on the high sensitivity of the device and the high performance of the algorithm, the intelligent acoustic system could identify the content, emotion, and speaker information in a sound. To test the system's capabilities for intelligent HCI, the research team applied the wearable system to a robot called \"NANO\". When wearing the intelligent acoustic HCI system, NANO can be woken up and start working when the word \"nano\" is heard. When two subjects greet [PERSON] separately, NANO can use the intelligent analysis function in the HCI system to identify the meaning of their word, who said it, their emotions, and give feedback. For example, when the female subject who felt sad greeted [PERSON] and said she wanted some music, the NANO replied to her through the voice function of the system with the correct name and played light music to improve her mood.  
The presented machine learning-assisted dual-function wearable HCI system showcases a seamless integration of acoustic information recognition, intelligent analysis, and vocal feedback, enabling barrier-free communication between humans and machines. With  
Figure 11: The machine learning-assisted dual-function acoustic HCI system. Reproduced with permission from [16]. Copyright 2022 Wiley.  
its cost-effectiveness, the system holds great potential in revolutionizing the smart HCI interface and in restoring the communication abilities of individuals suffering from voice loss.  
In the next section, on the basis of the acoustic information interaction function, we further introduce the next stage HCI system: realizing action interaction according to the control of voice instruction.