# Flexible Wearable Heart Rate Monitoring System and Low-Power Design: A Review
## 7 Summary and Outlook
When the heart rate variability (HRV) index is detected to be within a stable range, it automatically reduces the data acquisition frequency from 256 Hz to 64 Hz, while proactively increasing the sampling frequency and activating an early warning mechanism at the onset of abnormal HRV fluctuations. Clinical trials have verified that this intelligent regulation strategy can reduce system power consumption by over 45% without affecting the extraction of key physiological features. More notably, the innovative model of hardware-algorithm co-design--customizing specialized accelerators with systolic arrays [148] for the computational characteristics of Wavelet Transform denoising algorithms--can shorten the algorithm execution time from 120 ms on traditional CPUs to 15 ms while reducing power consumption by 70%. This \"tailor-made\" design philosophy is becoming the core technical path to break through power consumption bottlenecks. From the perspective of the ultimate form of technological evolution, future flexible wearable systems are expected to achieve breakthrough progress in the field of fully flexible devices: all electronic components, including resistors, capacitors, inductors, flexible thin-film transistors (TFTs) and so on, are projected to be manufactured with a micrometer-scale thickness. This will completely eliminate rigid components (such as the hard substrates of traditional silicon-based chips and metal pins), ultimately forming a fully bendable, stretchable, and even foldable \"fully flexible system\" [149; 150]. However, the development of fully flexible wearable systems is not without challenges and still faces numerous obstacles.Here, explanations will be made with components such as resistors, capacitors, inductors, TFTs and so on. At the material level, existing flexible materials have obvious drawbacks. The temperature resistance of flexible substrates (such as PDMS and PI) needs to be improved, which causes the resistance stability of flexible resistors and the dielectric properties of capacitors to be easily affected in high and low temperature environments. According to the properties of basic circuit components in the literature [151], it is assumed that the magnetic permeability of inductors and the switching characteristics of TFTs will also change. In addition, the compatibility between these flexible substrates and electronic materials is poor [152]. When combined with the conductive layers of flexible resistors and the dielectric layers of flexible capacitors, interface issues are likely to occur, leading to a decline in device performance. It is reasonably inferred that problems may also arise when flexible substrates are combined with flexible inductors or TFTs. At the manufacturing process level, high-difficulty manufacturing technologies have become a bottleneck hindering the development of fully flexible wearable systems. Technologies such as the alignment of gate-source-drain electrodes for TFTs with micrometer-level thickness are still immature and cannot meet the requirements of high-performance devices [153]; meanwhile, the lead welding of flexible resistors and the magnetic core packaging of inductors have extremely high precision requirements, and any deviation may affect the normal operation of the devices. According to the literature [154], it can be reasonably inferred that the stacking alignment of capacitors and the multi-layer wiring of TFTs also have equally high precision requirements. At the level of performance reliability, the stability of fully flexible structures faces severe challenges. Currently, the degradation mechanisms such as resistance drift of resistors, capacitance attenuation of capacitors, and threshold voltage shift of TFTs under repeated bending and stretching conditions in fully flexible structures are still unclear. According to the literature [155], it is reasonably inferred that other components, such as the Q-value reduction of inductors, may also occur; in addition, the packaging technology of fully flexible systems also needs innovation.