K. Divya

Bio: K. Divya is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Superluminescent diode & Trace gas. The author has an hindex of 1, co-authored 1 publications receiving 18 citations.

Superluminescent Diode-Based Multiple-Gas Sensor for NH $_{\bf 3}$ and H $_{\bf 2}$ O Vapor Monitoring

Abstract: An approach of superluminescent light emitting diode (SLED)-based multiple-gas sensing (NH3 and H2O vapor) is proposed and demonstrated by using an absorption spectroscopy technique for emission monitoring (DeNOx process) applications. Such process normally occurs at temperature range of 250-400°C where significant interference effect due to H2O vapor is expected. Hence, measuring multiple gases and eliminating cross-interference effect is of great importance in sensing trace gases. In this study, an SLED-based sensor with center emission wavelength of 1530-nm region is chosen to measure the concentrations of pure NH3 and H2O vapor by probing its overtone and combination bands present in this region. Detection limit for the NH3 gas accounted in the case of aqua-ammonia (undiluted) is estimated to be 120 ppm ·m. A novel approach of introducing an open-space etalon in the path of the SLED beam is also proposed and demonstrated for adequate isolation from interfering species and improving the detection limit. By using an etalon with a free spectral range of 104 GHz and tuning it to appropriate wavelength, detection limit of about 22 ppm·m is attained for NH3 gas sensing in the presence of H2O vapor.

Fiber laser intracavity absorption spectroscopy for in situ multicomponent gas analysis in the atmosphere and combustion environments

Abstract: Intracavity absorption spectroscopy with a broadband Er3+-doped fiber laser is applied for the measurements of several molecular species revealing quantitative information about the gas concentration, temperature and chemical reactions in flames The spectral range of measurements extends from 6200 cm−1 to 6550 cm−1 with the proper choice of the fiber length and by moving an intracavity lens With a pulsed laser applied in this experiment, the sensitivity to absorption corresponds to an effective absorption path length of 3 km assuming the cavity is completely filled with the sample For a cw laser, the effective absorption path length is estimated to be 50 km Absorption spectra of various molecules such as CO2, CO, H2O, H2S, C2H2 and OH were recorded separately in the cell and/or in low-pressure methane and propane flames The presented measurements demonstrate simultaneous in situ detection of three molecular products of chemical reactions at different flame locations Variation of the relative strengths of OH absorption lines with the temperature enables the estimation of the local flame temperature The sensitivity of this laser does not depend on the broadband cavity losses and it can be used for in situ measurements of absorption spectra in hostile environments such as contaminated samples, flames or combustion engines The presented technique can be applied for various diagnostic purposes, such as in environmental, combustion and plasma research, in medicine and in the determination of stable isotope ratios

UV photo-ionization based asymmetric field differential ion mobility sensor for trace gas detection

Abstract: A high-field Asymmetric Waveform Ion Mobility Spectrometry (FA-IMS) with ultra-violet (UV) photo-ionization source is proposed and demonstrated for measurement of trace amounts of volatile organic compound (VOC) gases. Experimental studies performed with the sensor using a high frequency asymmetrical waveform differential field for detection of acetone, hexane and acetone–hexane mixture in trace concentrations are discussed. The detection limit as estimated for a signal-to-noise ratio of 3 is of the order of 100 ppb for acetone and hexane. Experimental studies clearly show that selective sensing of a gas in a mixture of gases is also possible by appropriate value for the compensation voltage. Numerical Simulation is also performed using two-dimensional fluid-flow equations to estimate the motion of ions in an electric field. The study also demonstrated influence of parameters such as flow velocity, duty-ratio, on compensation voltage for detection of trace VOC gases with asymmetrical high-frequency electric field. Results based on theoretical study are in agreement with the experimental studies.

A fiber laser intracavity absorption spectroscopy (FLICAS) sensor for simultaneous measurement of CO and CO2 concentrations and temperature

Abstract: We report a method for the simultaneous measurement of carbon dioxide (CO2) and carbon monoxide (CO) absolute concentrations and temperature using fiber laser intracavity absorption spectroscopy (FLICAS). FLICAS uses an erbium-doped broadband laser capable of being tuned in the range 6350–6450 cm−1. The range 6390–6410 cm−1, which is emitted by the laser without tuning, allows for simultaneous observation of the CO, CO2, and methane (CH4) spectra. Truly simultaneous observation of these spectra is possible during one laser pulse with duration as short as 3.7 μs. The sensitivity of the CO measurement is about 20 times higher than that of CO2, a feature which is advantageous for several applications. The concentration of CO can be measured with a sensitivity of 400 ppm at room temperature, and this sensitivity can be improved by increasing the generation time. The experiments were performed in a temperature and flow-controlled cell in order to evaluate the accuracy of the concentration and temperature measurements from 296 to 1200 K. The measured spectra of CO and CO2 are well described by the HITRAN database, allowing for accurate and simultaneous determination of CO, CO2 and temperature. The temperature is evaluated using the CO2 spectrum, which includes many “hot” transitions. The CH4 HITRAN data are deficient at high temperatures, so this method only allows for the evaluation of methane concentrations at room temperature.

Monitoring of CO2 and CH4 composition in a biogas matrix from different biomass structures

Abstract: Monitoring of methane (CH4) and carbon dioxide (CO2) in biogas from different feed-stocks using superluminescent diode (SLED) is proposed and demonstrated. The SLED has a broadband spectrum (1540 nm–1640 nm) and this allows for the detection of CO2 at 1570 nm and CH4 at 1600 nm range simultaneously. Experiments were performed on biogas collected from various biomass like food waste, sewage waste and cattle dung. CO2 and CH4 concentration levels were monitored on each source of biogas. The etalon based sensing system provides the opportunity to select absorption lines with a low resolution spectrometer. Further, measurements on CH4 and CO2 concentration changes depending on the food-waste input to the plant are demonstrated.

Off-Resonance Photoacoustic Spectroscopy Technique for Multi-Gas Sensing in Biogas Plants.

Abstract: An off-resonance broadband photoacoustic spectroscopy (PAS) technique with a supercontinuum laser (SCL) in the near-infrared range is demonstrated for biogas measurements with different biomass mat...