Miha Zavrsnik

Fiber-optic microbend sensor structure.

We proposed and experimentally investigated a novel microbend sensor structure. The structure is composed of single-mode leads and multimode sensing fiber. The proposed structure exhibited a level of sensitivity as much as six times higher than that of the classical microbend sensor configuration when the same sensing fiber was used. Additionally, single-mode leads reduce lead noise and allow the use of more-coherent sources. The total loss of the proposed nondeformed structure is near 2 dB when the proper splicing method is used.

Low-frequency acoustic resonance level detector with neural-network classification

Abstract This work presents a new level-detection method. It is based on the acoustic resonance of a waveguide. This method can be successfully implemented for fluid-level detection in industrial plants, where problems of residues, deposits, foams, etc., can be expected. The performance of the detector is additionally improved by the use of neural networks. Neural networks enable the detector to learn from the reference detection cycles; therefore, such a system is flexible and can be easily optimized (trained) for specific operating conditions. The detector has been tested in a highly viscous medium, Styrofoam granulate and under artificially induced residues and deposits in the resonance waveguide.

The use of one-dimensional acoustical gas resonator for fluid level measurements

A new level measurement method based on the one-dimensional (1-D) acoustics gas resonator is presented. The proposed method has been investigated in detail, and experimental gauges have been built and tested under artificially induced residues, foams and deposits. The level measurement method proves to be insensitive under extreme operating conditions, and it can be successfully implemented for fluid level measurements in a variety of industrial conditions. It is an alternative to ultrasonic as well to some other level measurement methods.

Low-frequency acoustic resonance level gauge

Abstract A new level-measurement method is presented. It is based on the acoustic resonance of a waveguide. This method can be successfully implemented for fluid-level measurements in industrial plants, where problems of residues, deposits, foams, etc., can be expected. An experimental gauge has been built and tested under artificially induced residues, foams, deposits, etc. The resonance gauge proves to be insensitive under extreme operating conditions. The proposed method represents an alternative to ultrasonic as well as to some other level-measurement methods.

Theoretical analysis of a quasi-distributed optical sensor system using FMCW for application to trace gas measurement

Abstract We report on the performance of a quasi-distributed sensor system for narrow band absorbers using the frequency-modulated continuous wave (FMCW) method, including signal-to-noise analysis. The sensor units consist of open-path micro-optic cells constructed from GRIN lenses, each of differing lengths. For addressing of the cells interferometric mixing of two signals originating from each cell (from the glass/air interfaces) is employed. Due to the linear frequency ramping of the source, different beat frequencies arise in the output for each cell. The interference patterns of all sensor cells add up at the detector whereby each individual sensing cell is identified by its power spectrum in the frequency domain. We show system performance for narrow band absorbers and the limitations on the number of cells in the system.

Coherence addressing of quasi-distributed absorption sensors by the FMCW method

We report a new addressing mechanism for quasi-distributed absorption sensors based on the frequency modulated continuous wave (FMCW) method. The sensor units consist of open-path microoptic cells constructed from gradient index (GRIN) lenses, each of differing lengths. Coherence addressing of the cells using FMCW is achieved by the interferometric mixing of two signals originating from each cell (from the glass/air interfaces). The time delay between the two reflections, along with the linear frequency ramp of the source, gives rise to beat frequencies in the mixed output which are different for each cell. The connecting fiber length between two successive sensor cells is chosen to be much greater than the coherence length of the source so that the reflections from different cells do not interfere. The interference patterns of all sensor cells add up at the detector whereby each individual sensing cell is identified, by its power spectrum in the frequency domain. We show theoretically and experimentally how individual cells can be addressed and the measured signals obtained by suitable choice of cell length, proper modulation of the source and appropriate signal processing.

POLARIMETRIC TEMPERATURE SENSOR : EXTINCTION RATIO AND SENSING LENGTH EXAMINATION

We theoretically and experimentally investigated the influences of the sensing and lead fiber length, the extinction ratio of the input polarizer, and the coherence properties of the light source on polarimetric temperature measurements. We have shown that there is a possibility to construct a simple and inexpensive fiber optic polarimetric thermometer for absolute temperature measurements by using a low extinction-ratio polarizer and a low-coherence source. An experimental temperature sensor for absolute temperature measurement that works in the range from 20 to 60°C has been produced.

Analysis of quasi-distributed optical sensors combining rf modulation with the FMCW method

We report the theoretical analysis of a quasi-distributed sen- sor system for absorption measurements based on the frequency- modulated continuous wave (FMCW) technique combined with fre- quency modulation spectroscopy (FMS). The laser diode injection current is sawtooth modulated to provide a linear scan of the output over a certain frequency/wavelength range and the output is also externally modulated at radio frequencies. The sensor units consist of a series of open-path micro-optic cells constructed from graded index (GRIN) lenses, each with a unique beat frequency. By arranging for only one sideband of the modulation to be attenuated by the absorption feature, a new signal, proportional to the absorbance, appears in the output spec- trum at a frequency corresponding to the difference between the rf- modulation frequency and the beat frequency of a cell. The method is highly sensitive and applicable to a variety of chemical species with nar- row absorption lines, such as in trace gas analysis. We present the mathematical analysis of the proposed method for single and multiple

Low frequency acoustic resonance level gauge

A new level measurement method is presented. It is based on the acoustic resonance of a one dimensional acoustic gas resonator. The proposed method has been investigated in detail and an experimental gauge has been built and tested under artificially induced residues, foams; deposits, etc. The level measurement method proves to be insensitive under extreme operating conditions and it can be successfully implemented for fluid level measurements in industrial plants, where problems of residues, deposits, foams etc. can be expected. The proposed method represents an alternative to ultrasonic as well to some other level measurement methods.