# Flexible Wearable Heart Rate Monitoring System and Low-Power Design: A Review
## 2 Overview of Flexible Wearable Heart Rate Monitoring Systems
### Definition of Flexible Wearable Heart Rate Monitoring Systems  
In this paper, the flexible wearable heart rate monitoring system is composed of four modules: the heart rate signal acquisition module, the heart rate signal preprocessing module, the heart rate signal computation module, and the heart rate signal transmission and output module, as shown in Figure 1, each with its specific function. Meanwhile, this subsection also introduces the technical principles of the flexible wearable heart rate monitoring system. \begin{table}
\begin{tabular}{p{71.1 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Comparison Dimensions** & **Reference [12]** & **Reference [30]** & **This Paper** \\ \hline \multirow{3}{*}{Core topic} & Analysis and summary of flexible wearable systems for cardiac physiological monitoring. & The Latest Progress and Applications of Flexible Wearable systems in Intelligent Health Monitoring. & Low-power Design of Flexible Wearable Heart Rate Monitoring System. \\ \cline{2-4}  & Merely mentioning the low-power requirements without elaborating on specific optimization strategies. & Merely mentioning low-power-related directions such as self-power supply and material optimization in the ’Future Outlook’ section. & Low-Power Design of Acquisition, Preprocessing, Computation, and Transmission Modules from Three Dimensions: Hardware, Algorithms, and Hardware— Algorithm Collaboration. \\ \hline \hline \end{tabular}
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Table 1: Comparison between this paper and the existing literature on flexible wearable heart rate monitoring systems. The heart rate signal acquisition module primarily employs flexible sensors or signal acquisition circuits to capture cardiac signals for the system [41], such as ECG and PPG signals. During the acquisition process, intelligent algorithms dynamically optimize the sampling rate of these flexible components to ensure optimal data capture. However, the raw signals often contain noise, artifacts, and baseline drift [49]. Consequently, the preprocessing module [43] utilizes filtering circuits and adaptive algorithms to denoise, remove artifacts, and amplify the signals [50], enhancing signal strength. The preprocessed signals are then transmitted to the computation module, which leverages microprocessors [46] and neural network algorithms to perform tasks including heart rate feature detection, heart rate variability (HRV) analysis, and arrhythmia detection [51]. Finally, the processed data is transmitted via low-power Bluetooth (BLE) [48], Wi-Fi, or other wireless protocols to mobile devices or cloud platforms for further analysis and visualization. The modularity of flexible wearable heart rate monitoring systems offers multiple advantages: First, in terms of hardware, it enables layered integration of flexible materials  
Figure 1: **(a)** Flexible electrodes with sensors [41], under CC BY 4.0, copyright 2020, Springer Nature. **(b)** Flexible ECG sensor [42], under CC BY 4.0, copyright 2023, Wiley Online Library. **(c)** Flexible organic differential amplifiers, reproduced with permission [43], copyright 2019, Springer Nature. **(d)** Band-pass filter circuits, reproduced with permission [44], copyright 2023, Elsevier. **(e)** The BioAIP processor, reproduced with permission [45], copyright 2023, IEEE. **(f)** A flexible chip, reproduced with permission [46], copyright 2024, Nature. **(g)** A BLE module [47], under CC BY 4.0, copyright 2019, IEICE TRANSACTIONS on Information and Systems. **(h)** A BLE protocol stack, reproduced with permission [48], copyright 2023, Elsevier. and functional components [52], allowing tight adherence to the human body's contours to significantly enhance wearing comfort. Independent power consumption control also extends system battery life. Second, the signal processing flow is more professional--layered filtering and dynamic calibration mechanisms [53] can boost the Signal-to-Noise Ratio to over 35 dB, effectively addressing interference issues like motion artifacts.