## 2 Wireless Communication Technologies
#### Smart Wearable Devices  
The global phenomenon of population aging, coupled with concerns surrounding family planning and its impact on birth rates, has led to significant implications for the socio-economic healthcare system. The cost of medicine, medical devices, and hospital care continues to rise. To address these challenges, wearable biosensors have emerged as non-invasive smart gadgets that enable continuous real-time patient monitoring. These technologies serve as effective tools for disease management, promoting healthier behaviours, and facilitating early identification of risk factors, diagnosis, and treatment [55; 56]. Sensing electronic devices attached to soft tissue and worn as skin patches have recently been developed to establish a new interface for monitoring applications, as shown in Figure 2a [57]. Skin patches, when placed discrerely beneath clothing, can capture highly precise data without being influenced by human movement. These patches are capable of accurately monitoring vital signals like temperature, tension, sweat, and heart rate when affixed to the surface of the skin [58]. Sweat holds significant importance as a crucial bodily fluid due to its composition of essential elements such as electrolytes, small chemicals, and proteins. In recent years, the development of sweat-analysis devices has enabled the detection of various components present in sweat. These devices utilise sensing techniques to conduct a comprehensive analysis of sweat composition [59]. It is crucial to monitor changes in skin temperature during the initial phases of diagnosis and treatment [60]. Recently, a group of researchers developed a flexible stress-monitoring patch with a small area of skin contact. This is an important factor since it reduces the effects of the patch on the human body. In [61], it is reported that a group of scientists created a photonic crystal for non-invasive glucose monitoring of tear fluid made of colloidal particles dissolved in the hydrogel in a face-centre cubic structure. Tear fluid had 100 mol/L or more of glucose, which was detected by photonic-based glucose-sensing materials. The detection threshold for tear fluid was 1 mol/L. A mouthguard, which uses built-in wireless electronics to test salivary uric acid, is a recent addition to wearable devices in WBAN systems [62]. In another research investigation, a mouthguard was used to monitor and detect salivary glucose [63]. To measure blood pressure (BP) without a cuff, a portable patch sensor with an adjustable flexible piezo-resistive sensor (FPS), as well as epidermal ECG sensors, has been created [64]. Numerous studies have investigated wearable flexible and fluidic devices used to measure vital signals [65]. Wearable devices have found applications beyond human health and well-being, extending to animal health in the field of pet care and animal husbandry, etc [66]. Autonomously functioning wearable sensor systems have the capability to integrate point-of-care functionality with mobile connectivity. These systems comprise a combination of active and passive components, as well as sensing devices. These autonomously functioning wearable sensor systems support ongoing evaluation for disease prevention, early reduction of health risk factors, and maintenance of optimal, lifetime health quality [66; 67]. However, modern wearable devices perform high-quality measurements as compared to conventional medical devices. The first-generation wearables predominantly focused on biophysical devices designed to monitor and track metrics related to physical activity, such as heart rate and body temperature. These devices were integrated with various wearables such as watches, shoes, and headphones [68]. The initial wave of wearables gained widespread adoption, leading to a shift in focus toward second-generation devices. The second-generation wearables encompass non-invasive or minimally invasive biochemical and multi-functional designs.