DocumentCode :
760993
Title :
Real time frequency domain fiberoptic temperature sensor
Author :
Alcala, J. Ricardo ; Liao, Shih-Chu ; Zheng, Jielin
Author_Institution :
Dept. of Biomed. Eng., Case Western Reserve Univ., Cleveland, OH, USA
Volume :
42
Issue :
5
fYear :
1995
fDate :
5/1/1995 12:00:00 AM
Firstpage :
471
Lastpage :
476
Abstract :
The excited state phosphorescence lifetime of alexandrite crystals is used to monitor temperature in the physiological range from 15-45°C with precision and accuracy of 0.2°C. A 500-μm cubic alexandrite crystal bounded to the distal end of an optical fiber of similar core dimensions is excited with pulsed Ne-He laser light. This apparatus uses a sampler for data acquisition and frequency domain methods for data fitting. The instrument amplifies the AC components of the detector output and band limits the signal to 12.5 kHz. The fundamental frequency of the excitation is set to 195.13 Hz to obtain 64 harmonics. This band limited signal is sampled and averaged over few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. Five to 50 values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited state lifetimes from subpicowatt luminescent signals in plastic optical fibers. A least squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation seen by the photodetector leaking through optical interference filters. The phosphorescence lifetimes measured reproducibly to about three parts in a thousand are used to monitor physiological temperature. Temperatures are computed employing empirical polynomials. The system drift is negligible over 15 h of continuous operation. The instrumentation and methods allow 1.3-s update times and 30-s full response times
Keywords :
biomedical equipment; biomedical measurement; fibre optic sensors; laser applications in medicine; phosphorescence; temperature sensors; 1.3 s; 12.5 kHz; 15 h; 15 to 45 C; 195.13 Hz; 30 s; 500 mum; Ne-He; cubic alexandrite crystal; detector output AC components; empirical polynomials; excited state phosphorescence lifetime; frequency domain data representation; least squares fit; optical interference filters; photodetector leaking; physiological range temperature monitoring; plastic optical fibers; real-time frequency domain fiberoptic temperature sensor; signal band-limiting; subpicowatt luminescent signals; system drift; Biomedical monitoring; Frequency domain analysis; Instruments; Laser excitation; Optical fiber sensors; Optical fibers; Phosphorescence; Power harmonic filters; Temperature measurement; Temperature sensors;
fLanguage :
English
Journal_Title :
Biomedical Engineering, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9294
Type :
jour
DOI :
10.1109/10.376151
Filename :
376151
Link To Document :
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