In this paper, we present a novel fiber optic ultrasonic sensing system to conduct a 2D temperature field monitoring. The fiber optic ultrasonic sensing system was used as an ultrasonic pyrometer to measure the temperature field. The ultrasonic pyrometer was based on the thermal dependence of the speed of sound in air. The speed of a sound wave traveling in a medium was proportional to the medium’s temperature. A fiber optic ultrasonic generator and a microphone were used as the ultrasonic signal generator and receiver, respectively. A carbon blackPolydimethylsiloxane (PDMS) material was utilized as the photoacoustic material for the fiber optic ultrasonic generator. A test was performed outside of a lab furnace, the testing area temperature range was from 26°C to 70°C. A 2D temperature field was mapped. The 2D temperature field map matched with the reference thermocouple results. This system could lead to the development of a new generation temperature sensor for temperature field monitoring in coalfired boilers or exhaust gas temperature monitoring for turbine engines.
This paper presents a novel fiber optic ultrasonic sensing system to measure high temperature in the air. Traveling velocity of sound in a medium is proportional to medium’s temperature. The fiber optic ultrasonic sensing system was applied to measure the change of sound velocity. A fiber optic ultrasonic generator and a Fabry-Perot fiber sensor were used as the signal generator and receiver, respectively. A carbon black- Polydimethylsiloxane (PDMS) material was utilized as the photoacoustic material for the fiber optic ultrasonic generator. A water cooling system was applied to cool down the photoacoustic material. A test was performed at lab furnace environment (up to 700 ℃). The sensing system survived 700℃. It successfully detect the ultrasonic signal and got the temperature measurements. The test results agreed with the reference sensor data. The paper validated the high temperature measurement capability of the novel fiber optic ultrasonic sensing system. The fiber optic ultrasonic sensing system could have broad applications. One example is that it could serve as acoustic pyrometers for 3D temperature distribution reconstruction in an industrial combustion facility
KEYWORDS: Sensing systems, Acoustics, Code division multiplexing, Combustion, Energy efficiency, Optical fibers, Algorithms, Sensors, Signal to noise ratio, Optical components, Temperature metrology, Signal detection, Multiplexing
3D temperature field reconstruction is of practical interest to the power, transportation and aviation industries and it also
opens up opportunities for real time control or optimization of high temperature fluid or combustion process. In our
paper, a new distributed optical fiber sensing system consisting of a series of elements will be used to generate and
receive acoustic signals. This system is the first active temperature field sensing system that features the advantages of
the optical fiber sensors (distributed sensing capability) and the acoustic sensors (non-contact measurement). Signals
along multiple paths will be measured simultaneously enabled by a code division multiple access (CDMA) technique.
Then a proposed Gaussian Radial Basis Functions (GRBF)-based approach can approximate the temperature field as a
finite summation of space-dependent basis functions and time-dependent coefficients. The travel time of the acoustic
signals depends on the temperature of the media. On this basis, the Gaussian functions are integrated along a number of
paths which are determined by the number and distribution of sensors. The inversion problem to estimate the unknown
parameters of the Gaussian functions can be solved with the measured times-of-flight (ToF) of acoustic waves and the
length of propagation paths using the recursive least square method (RLS). The simulation results show an
approximation error less than 2% in 2D and 5% in 3D respectively. It demonstrates the availability and efficiency of our
proposed 3D temperature field reconstruction mechanism.
Ultrasonic temperature measurements have been developed and widely applied in non-contact temperature tests in many industries. However, using optical fibers to build ultrasound generators are novel. This paper reports this new fiber optic ultrasonic system based on the generator of gold nanoparticles/polydimethylsiloxane (PDMS) composites. The optical acoustic system was designed to test the change of temperature on the aluminum plate and the temperature of the torch in the air. This paper explores the relationship between the ultrasonic transmission and the change of temperature. From the experimental results, the trend of ultrasonic speed was different in the aluminum plate and air with the change of temperature. Since the system can measure the average temperature of the transmission path, it will have significant influence on simulating the temperature distribution.
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