Real-time frequency-domain combined temperature and oxygen sensor using a single optical fiber
The combined excited state phosphorescence lifetimes of alexandrite and platinum tetraphenylporphyrin Pt(TPP) were used to remotely monitor temperature and oxygen concentration simultaneously using a single-optical-fiber probe. Temperature and oxygen concentration were successfully monitored in the physiological range from 15-45°C and 0-50% O2 with precisions of 0.24°C and 0.15% O2, and accuracies of 0.28°C, 0.2% O2. The dual-parameter sensor comprised a 500 μm cubic alexandrite crystal bound to the distal end of a 750 μm diameter plastic optical fiber core which was circumferentially coated with a 1 cm length of Pt(TPP). Sensor luminescence was excited using pulsed super bright blue LED light, and a frequency-domain representation of the time-domain phosphorescence decay was obtained by using fast Fourier transform algorithms. At least four log-spaced harmonic phases were averaged before decoding the two lifetimes of the temperature and oxygen phosphorescent sensors. A component of zero lifetime has introduced to account for the excitation backscatter leakage. Linear and second order empirical polynomials were employed to compute the temperatures and oxygen concentrations from the inverse lifetimes. The system drift was 0.24°C for the temperature measurement and 0.59% for the oxygen concentration measurement over 30 hours of continuous operation. The instrumentation and methods allow for 6-s update times and 90-s full response times.