Sensors and Systems for Wearable Environmental Monitoring Toward IoT-Enabled Applications: A Review
The rapid urbanization has led to the deterioration of the air quality, worsened the climatic conditions, and increased environmental nuisance. Exposure to this environmental pollution has adverse health effects, leading to escalations in healthcare costs and even high death rate. Apart from the individual health issues, the demand for air quality data is growing immensely for various application scenarios like traffic management, domestic condition monitoring, energy management, decisions on protection measures against climate change, and industrial processes optimization. It makes the monitoring of environmental parameters imperative.
The conventional systems of monitoring environmental quality set up with sophisticated devices, and the skilled workforce don’t work for an individual. It is here where the latest developments in wearable environmental monitoring systems (WEMS) come to serve at an individual level to monitor the micro-climate and gather the individual’s environmental data. Wearable devices may potentially be used in various applications that can improve human living quality.
The data from this WEMS should get collected at some server. Hence it demands a sensor network which has three major parts; the wearable sensor node, wireless network, and micro-power manager. The WEMS widely uses resistive and electrochemical type sensing technologies. Bluetooth, BLE, and Wi-Fi are the commonly used communication technologies for establishing the wireless network between several such nodesin WEMS.
The development and advancement in low-power wireless communications, low form factor electronic devices, and progressive acceleration of computing capability of low-cost microcontrollers have promoted the emergence of the Internet of Things (IoT) in every sphere of today’s life.
WEMS has been developed as Wrist, Lanyard, Smart Clothing Based, Printable, Flexible Wearable Devices. The wearable IoT devices are light enough to be worn as jewellery, helmet, textiles, eyewear, belt, or lanyard. It has made it possible to measure an individual’s surrounding environmental data even when on the move. It collects some environmental data at a regular interval. It transmits the data to a gateway for local storage and a remote server for further processing and visualization.
The WEMS functions by transmitting data between wearable to a coordinator. From the coordinator, the data gets transferred to the internet cloud. In the former case, wearable sensor nodes usually form a wireless sensor network with a basic topological configuration (e.g., star topology) to transmit the data to a coordinator. Bluetooth is the most widely used wireless communication standard employed for data transmission between wearable and coordinators, followed by Wi-Fi and ZigBee. From the coordinator to the internet cloud, generally, long-range wireless communication standards transmit data. There are various available wireless communication standards like WLAN, 4G, LTE, UMTS, Wi-Fi, or WiMAX.
WEMS is programmed to uses the MOS-based heating technique to measure environmental pollutants, ambient temperature, and humidity. RN4020 Bluetooth module from Microchip is attached to transmit the collected data from the wearable to a smartphone or a gateway, followed by the transmission to the internet cloud. A 3.7 V and 240 mA Li-Pol battery is used to supply power to the system.
For short-range communication, Chirp Spread Spectrum (CSS) based nanoLOC technology is used, which has an accuracy of 2m for indoors and 1m for outdoors. For long-range communication, long-range wide area network (LoRaWAN) technology is used. It is suitable for applications that need to transmit data over long distances with lower data rates and transmission frequency.
WEMS turns out to become more applicable to real-life situations. The most critical issues include the efficient implementation of sensor miniaturization and integration, sensor calibration and normalization, real-time localization, and tracking, especially for indoor and appropriate data analytics and security.