In-Duk Hwang

Multiple diagnosis based on photoplethysmography: hematocrit, SpO2, pulse, and respiration

Photo-plethysmography measures pulsatile blood flow in real-time and non-invasively. One of widely known applications of PPG is the measurement of saturated oxygen in arterial blood(SpO2). In our work, using several wavelengths more than those used in a pulse oximeter, an algorithm and instrument have been developed to measure hematocrit, saturated oxygen, pulse and respiratory rates simultaneously. To predict hematocrit, a dedicated algorithm is developed based on scattering of RBC and a protocol for detecting outlier signals is used to increase accuracy and reliability. Digital filtering techniques are used to extract respiratory rate signals. Utilization of wavelengths under 1000nm and a multi-wavelength LED array chip and digital-oriented electronics enable us to make a compact device. Our preliminary clinical trials show that the achieved percent errors are ±8.2% for hematocrit when tested with 594 persons, R2 for SpO2 fitting is 0.99985 when tested with a Bi-Tek pulse oximeter simulator and the SpO2 error for in vivo test is ±2.5% over the range of 75~100%. The error of pulse rates is less than ±5%. We obtained a positive predictive value of 96% for respiratory rates in qualitative analysis.

High-density magneto-optical disk suitable for short wavelength recording

High density magneto-optical recording was realized with the combination of a compact green laser and a very sensitive NdTbFeCo/TbFeCo MO disk for the wavelength of 532 nm. This media has a high Kerr rotation angle at 532 nm and maintains a stable recording domain. With an objective lens of 0.6 NA, CNR of 48 dB and jitter of 3.0 nsec by mark edge recording was obtained for a mark length of 0.45 micrometers (0.34 micrometers /bit) at a writing power of 4.5 mW.