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Lee, Hooseok,Chung, Heewon,Kim, Jong-Woong,Lee, Jinseok IEEE 2019 IEEE Sensors Journal Vol. No.
<P>Accurate heart rate estimation from reflectance photoplethysmography (PPG) during intense physical activity is difficult given unpredictable motion artifacts (MAs). Recent research has focused on the removal of MAs in PPG signals by considering acceleration signals as noise references. However, this approach does not always effectively remove MAs, as they can be associated with other noise sources. For instance, finger or hand motion reflects upon the wrist, corrupting the PPG signals, but an accelerometer cannot capture this type of MA. Hence, we propose adding a piezoelectric transducer on the wrist to identify noise originated from finger and hand motion. We first detail the developed wearable device that simultaneously measures PPG, acceleration, and piezoelectric pressure signals from the wrist. Then, the effectiveness of piezoelectric pressure signals for MA removal is verified from PPG signals collected under finger tapping and hand folding/unfolding, and from data of 17 healthy subjects undergoing physical activity. MA removal using both acceleration and piezoelectric pressure signals exhibits a mean absolute error of 1.58 beats per minute (bpm), considerably below the error of 3.75 bpm obtained using only acceleration signals. Therefore, measuring piezoelectric pressure signals on the wrist can improve heart rate estimation by providing more information of MAs corrupting PPG signals.</P>
Numerical simulation of solid liquid interface behavior during continuous strip casting process.
Lee, Changbum,Yoon, Wooyoung,Shin, Seungwon,Lee, Jaewoo,Jang, Bo-Yun,Kim, Joonsoo,Ahn, Youngsoo,Lee, Jinseok American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.5
<P>A new metal-strip-casting process called continuous strip-casting (CSC) has been developed for making thin metal strips. A numerical simulation model to help understand solid-liquid interface behavior during CSC has been developed and used to identify the solidification morphologies of the strips and to determine the optimum processing conditions. In this study, we used a modified level contour reconstruction method (LCRM) and the sharp interface method to modify interface tracking, and performed a simulation analysis of the CSC process. The effects of process parameters such as heat-transfer coefficient and extrusion velocity on the behavior of the solid-liquid interface were estimated and used to improve the apparatus. A Sn (Tin) plate of dimensions 200 x 50 x 1 mm3 was successfully produced by CSC for a heat-transfer coefficient of 104 W/m2 K and an extrusion velocity of 0.2 m/s.</P>
A Low-Power Photoplethysmogram-Based Heart Rate Sensor Using Heartbeat Locked Loop
Lee, Jinseok,Jang, Do-Hun,Park, Sujin,Cho, SeongHwan IEEE 2018 IEEE transactions on biomedical circuits and syste Vol.12 No.6
<P>In this paper, we present an ultralow power heart rate (HR) monitoring photoplethysmography (PPG) sensor using a heartbeat locked loop (HBLL). The HBLL generates a narrow window that turns on the LED and analog-front-end only when a peak is expected in the PPG signal. The prototype PPG sensor implemented in 0.18 <TEX>$\mu$</TEX>m CMOS has an effective duty-cycle of 0.01% and consumes only 43.4 <TEX>$\mu$</TEX>W at a HR of 60 b/m, which is the lowest power consumption compared with previous state-of-the-art PPG sensors. The HR error of the proposed sensor is less than 2.1 b/m for HR below 180 b/m.</P>