## 3 Wireless Body Area Network (WBAN)
### Sensors for pulse rate  
Pulse rate sensors, also known as heart rate sensors, are devices used to measure an individual's heart rate or pulse rate. They are commonly used in fitness trackers, smartwatches, and medical devices. There are many pulse rate sensors; however, photoplethysmography (PPG) is a common technique. PPG sensors detect changes in blood volume using light. Its operation mechanism depends on emitting light, usually green or red, into the user's skin or fingertip. Blood vessels in the skin or fingertip absorb some of the emitted light while the remaining light is reflected to the sensor [40]. As the heart beats, blood flow changes, causing variations in the absorption and reflection of light. The sensor detects these changes. The detected light variations are converted into electrical signals and then processed to determine the heart rate. The processed data can be displayed on a \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Commercial** & **Structure** & & **Technical Specification** & **Biological Measurement** \\ \hline  & & & (a) & Connectivity & \\  & & & 1. & Wi-Fi & 1. & Examines breathing rate. \\  & & & (IEEE 802.11a/b/g/n) & 2. & Skin temperature changes \\  & 1. & Optical heart rate sensor & 2. + 5 GHz & 3. & Measures SpO2. \\  & 2. & Skin temperature sensor & 2. & Bluetooth & 4. & Sleep phases. \\  & 3. & Three-axis accelerometer & 3. & NFC & 5. & Sleep quality. \\ Fitbit & 4. & Infrared and & 4. & LTE & 6. & Tracks body activities. \\ Versa & & red-light sensors & 5. & GLONASS & 7. & Tracks calories burned. \\
[37] & 5. & Microphone & (b) & Display & 8. & Measures health stress, \\  & 6. & GPS & 1. & Size: 1.58 inches & & emotions, and \\  & 7. & Vibration motor & 2. & Resolution: 336 \(\times\) 336 pixels & & breathing exercises. \\  & 8. & Altimeter sensor & (c) & Power & 9. & Heart rate, resting \\  & & & 1. & Li-Ion 420 mAh & & heart rate, and cardiovascular fitness. \\  & & & (d) & Processor & & \\  & & & & ARM Cortex M4F & & \\ \hline  & & & (a) & Connectivity & & \\  & 1. & Accelerometer & 1. & Bluetooth & & \\  & 2. & Altimeter & 2. & LTE & & \\ Withings & 3. & ECG with 3 electrodes & (b) & Display & 1. & Records ECG readings \\
[38] & 4. & Microphone & 1. & 13.8 mm PMOLED & & \\  & 5. & GPS & (c) & Power & & \\  & & & 1. & Li-Ion 420 mAh & & \\ \hline  & & & (a) & Connectivity & & \\  & & & 1. & Bluetooth 5.0 & & \\  & 1. & Accelerometer & 2. & NFC & & \\  & 2. & Digital MEMS & (b) & Display & & \\  & & microphone & 1. & AMOLED color touchscreen & 1. & Monitors the health \\ Xiaomi & 3. & Gyroscope & 2. & Size: 1.1 inches & & of women. \\ Mi Smart Band 5 & 4. & SpO2 sensor & 3. & Resolution: 126 \(\times\) 294 (450 nits) & 2. & Monitors sleep (deep \\
[39] & 5. & GPS & 4. & Glass with 2.5D reinforcement and & & sleep, light sleep, REM \\  & 6. & Heart rate sensor & & AF coating & 3. & Monitors heart rate. \\  & 7. & Barometer & (c) & Power & 4. & Tracks stress. \\  & 8. & Proximity sensor & 1. & 125 mAh & & \\  & & & 2. & 14-day battery life & & \\  & & & (d) & Processor & & \\  & & & (Dialog DA14697) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._screen or transmitted to a connected device for further analysis or tracking of the user's pulse rate [41]. It Is significant to mention that various pulse rate sensors may vary on this basic method. Some more advanced sensors employ additional technologies, such as the electrocardiogram (ECG), for more precise measurements. The different types of market-available heart rate sensors are introduced as follows [40; 41; 42]. 1. Optical sensor: It uses light to detect changes in blood volume. A light-emitting diode (LED) and a photodetector measure the reflected light. When blood flow increases during each heartbeat, the amount of light reflected in the sensor changes, allowing the pulse rate to be calculated. 2. Piezoelectric sensor: It uses piezoelectric materials that generate voltage when subjected to mechanical pressure or vibration.