## 2 Wireless Communication Technologies
#### Smart Wearable Devices
These wearable sensor devices play a crucial role in measuring vital signals such as respiratory rate, temperature, and blood-oxygen levels, which are essential in accurately diagnosing and monitoring COVID-19 [81]. High-performance wearable electrical devices require fibrous material with high strength and considerable stretchability to provide durability and stability. An ultra-thin, robust, and extensible conducting microfibre is constructed for designing fibrous-type mechanical sensors for wearable applications. These sensing devices demonstrated high sensitivity in detecting strains, with a high resolution and a large detection range simultaneously [82]. In [83], researchers evaluated traditional polysomnography measurement tools to study sleep. Some of these tools lack comfort and impose high additional costs. As an alternative, several innovative designs, such as jewellery and body-mounted sensing devices, have been developed as non-invasive options to measure vital signals during sleep. They provide a more comfortable and cost-effective solution for monitoring sleep-related activities and signals [84]. Sleep disorders may be controlled through advanced technologies that make early diagnosis possible [85]. MXenes ink is a highly conductive material [86], as highlighted, and applications have been found in various flexible and stretchable devices. In [87], a highly integrated multipurpose sensor device for intracorporeal applications was proposed. This intracorporeal system incorporated temperature, capacitive-type pressure, and electrochemical-based oxygen sensors onto a single chip, along with their corresponding interface application-specific integrated circuits (ASICs). A low-cost UWB-based landslide monitoring device, named Wi-GIM, was introduced in [88]. This device utilises UWB technology to determine the relative distances between monitoring points and effectively track ground deformations associated with landslides. A novel conformable sensor interface was created in [89]. This sensor was designed to be easily attached and detached from face masks. Smartwatches have become a well-established tool for continuous activity and fitness tracking. Longitudinal tracking using smartwatches is being utilised in clinical applications, including remote monitoring of Parkinson's disease (PD), which is the most prevalent neurodegenerative disease [90]. In [91], researchers investigated biocompatible and biodegradable materials for flexible and stretchable devices without producing any environmental problems. As reported in [92], a laser-engraved wearable sensor was used for the sensitive detection of uric acid and tyrosine in sweat, as shown in Figure 3a. Extensive research has been conducted on intricate measurements, including ECG. For instance, the Apple watch screen has been investigated to detect atrial fibrillation simply through the touch of a finger [93]. Soft polymers have been explored as electrodes and active layers to produce flexible and stretchable electronic devices for wearable applications [94]. Various HMI-based (human-machine interface) vision assistance devices are now possible thanks to advancements in micro-electronics and nanofabrication for wearable and flexible materials. These applications include integrating sensors, circuits,  
Figure 2: Wearable electronic devices (**a**) soft tissue [57], and (**b**) contact lens [74]. and components into a small contact-lens design. Its interaction with apps for displaying information, detecting eye movements, recovering vision, and identifying specific biomarkers in tear fluid is made possible through various smart contact-lens materials, device designs, and componentty [95]. Google's Fitbit-based tracker system examines blood-oxygen levels [96]. Recently, a four-layer sensor device was used for the healthcare system, which is compatible with 5G networks [97]. In another study [98], researchers proposed a sensor network that harnesses 5G-wireless networks for healthcare and safety applications.