A Novel Approach for Precise Motion Artefact Detection in Photoplethysmograph Signal Processing based on Dark Photocurrent

PPG signal is a useful tool for quick and critical diagnosis related to cardiovascular output via wearable or portable devices. Its drawback is unreliable during non-stationary states due to occurrences of frequency overlap of the desired and motion artifact signals. The accelerometer is usually used to reflect the motion artifact when the adaptive noise cancellation technique is implemented to address this obstacle, but it failed to predict the value of real induced noise accurately. In this work, we investigate a new concept that is capable of providing the entire motion artifact separately by recruiting twin photodetectors to formulate the influential signals. The main function of photo-detector (MPD) is to generate the corrupted PPG signal. While the second photo-detector (CPD) that covered up from the light effect, will be used to reflect the corruption effect that exists in both sources simultaneously by counting the generated dark photocurrent (GDPC). To validate the GDPC approach, experiments were executed to analyze the response of two methods during steady and motion state. Results showed resemblance responses for both methods regarding the’ amplitude fluctuations and high positive correlations in the time domain. Furthermore, the FFT peak plots in frequency domain indicated the potential of CPD to reflect all fundamental frequencies caused by motion, unlike the acceleration approach. Therefore, the proposed concept is a sure-fire method to obtain precise measurements at a lower cost.光电容积脉搏波（PPG）信号是一种可借助可穿戴或便携式设备，实现与心输出量相关的快速关键诊断的实用工具。其缺陷在于，当处于非稳态时，由于目标信号与运动伪影（motion artifact）出现频率重叠，会导致检测结果不可靠。在采用自适应噪声抵消（Adaptive Noise Cancellation）技术解决该问题时，通常会借助加速度计（accelerometer）来表征运动伪影，但该方法无法准确预测实际感应噪声的数值。本研究提出了一种全新方案，可通过双光电探测器（twin photodetectors）生成表征运动伪影的有效信号，从而单独提取完整的运动伪影。主光电探测器（Main Photo-detector, MPD）的核心功能是生成含噪PPG信号；而第二个光电探测器（Secondary Photo-detector, CPD）被遮蔽以隔绝光照，其将通过检测生成的暗光电流（Dark Photocurrent, GDPC），来反映同时存在于两个信号源中的噪声干扰效应。为验证该暗光电流方法的有效性，本研究开展了实验，以分析两种方法在稳态与运动状态下的响应表现。实验结果显示，两种方法在时域的振幅波动与高度正相关性方面表现相似。此外，频域的快速傅里叶变换（Fast Fourier Transform, FFT）峰值图谱表明，相较于加速度计方法，CPD能够完整反映运动引发的所有基频成分。因此，本研究提出的方案是一种能够以更低成本实现精准测量的切实可行方法。