A cost-efficient plastic optical fiber (POF) system for unobtrusive monitoring of human vital signs is presented. The system is based on speckle interferometry. A laser diode is butt-coupled to the POF whose exit face projects speckle patterns onto a linear optical sensor array. Sequences of acquired speckle images are transformed into one-dimensional signals by using the phase-shifting method. The signals are analyzed by band-pass filtering and a Morlet-wavelet-based multiresolutional approach for the detection of cardiac and respiratory activities, respectively. The system is tested with 10 healthy nonhospitalized persons, lying supine on a mattress with the embedded POF. Experimental results are assessed statistically: precisions of 98.8%±1.5% and 97.9%±2.3%, sensitivities of 99.4%±0.6% and 95.3%±3%, and mean delays between interferometric detections and corresponding referential signals of 116.6±55.5 and 1299.2±437.3ms for the heartbeat and respiration are obtained, respectively.
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