Cost-efficient speckle interferometry with plastic optical fiber for unobtrusive monitoring of human vital signs

Abstract

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 ± 437.3 ms for the heartbeat and respiration are obtained, respectively.

Reflection-based fiber specklegram sensor

“…These first sensors using bulky assemblies and signal processing was very extensive and laborious. However, during last years, technological advances allow to have affordable laser diodes and small CCD cameras [7][8][9][10]. Furthermore, computation technology have also been improved, making possible real time measurements.…”

Fiber-optic sensors for monitoring patient physiological parameters: a review of applicable technologies and relevance to use during magnetic resonance imaging procedures

“…[73][74][75] Speckle patterns can be observed in the laser light output of coherently illumined multimode fibers (MMFs), as shown in Fig. 5.…”

“…[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75] Body movements caused by the function of the lungs and heart cause phase changes between signals (sensing and reference) and could be identified as a series of time-variable interference patterns. Thus far, in research on the acquisition of physiological signals, fiber-optic interferometers have been tested in their most popular configurations, i.e., Michelson, Mach-Zehnder, and Sagnac interferometers.…”

Low-cost fiber specklegram sensor for noncontact continuous patient monitoring

“…9 Since that test, similar experiments have been carried out in different institutions. 10,11 In this work, different speckle-based optical-fiber sensors are employed to detect and measure heart rate (HR) and motion of patients lying on a bed. The proposed devices are able to measure HR and motion without direct contact with people's skin, even when lying in different positions.…”

“…By analyzing variations within speckle patterns, different perturbations applied to the medium (e.g., optical fiber) can be detected, among them vibration, 14 displacement, 15 angular alignment, 16 strain, 17,18 and even vital signs. [9][10][11] An approximated relation between the perturbations and the variations of speckle patterns can be directly obtained to get information regarding the applied perturbation, simplifying the final model. Indeed, there is a model 14 that determines the relation between the speckle pattern variation and the perturbation to be measured.…”