Eamonn Hawe

CO2 monitoring and detection using an integrating sphere as a multipass absorption cell

This paper describes a multipass absorption sensor based on an integrating sphere. The sphere has an internal coating which is highly reflective (over 95%) in the near infrared region and this allows for the detection of CO2 at two regions in the spectrum: 2 µm and 1.57 µm. CO2 was detected around the 2 µm region using a light emitting diode as the emitter and a photodiode as the detector, while detection at the 1.57 µm region took place using a broadband ASE source as the emitter and a miniature spectrometer as a detector. A 2 in diameter (50.8 mm) integrating sphere was used as an absorption gas cell. This paper reports the generation of effective optical path lengths of 114 cm at the 1.57 µm region and 40 cm at the 2 µm region. Experimental results demonstrating the detection of CO2 using a 2 in diameter integrating sphere are presented and simulation results based on larger integrating spheres are also reported. Further simulations conducted in the mid-infrared region suggest the possibility of detecting trace levels of CO2 (less than 200 ppm) using a 2 in diameter integrating sphere.

Hazardous gas detection with an integrating sphere in the near-infrared

This paper describes an optical fibre near infrared Carbon Dioxide sensor. Using an integrating sphere as a test cell, increased path length is achieved due to multiple reflections within the sphere. Carbon dioxide is input into the sphere via an unused optical port. Light from a C + L band ASE source is transmitted through the sphere and any absorption is detected using a near infrared spectrometer. A change in optical intensity was observed at a wavelength of 1.59 um when carbon dioxide was present from which the carbon dioxide concentration can be determined.

Measuring of exhaust gas emissions using absorption spectroscopy

This paper describes an optical fibre sensor for the detection of NOx (NO2 and NO) and CO2 in the exhaust system of a road vehicle. The measurement is based on a free path interaction zone which is interrogated using UV and NIR light guiding optical fibres and collimated lenses. Results are presented in the absorption spectra of the gases in the UV region for the NOx gases and NIR region for CO2. These demonstrate that using this method it is feasible to identify the individual CO2, NO and NO2 species as well as other gases in the exhaust system. Measurement of concentrations to the level of tens parts per million (ppm) have been demonstrated for the NOxx gases.

Gas detection using an integrating sphere as a multipass absorption cell

The reduction of harmful environmental pollutants which can have adverse effects on human health and the development of sensors capable of monitoring low concentrations of these pollutants is a major source of concern for many researchers today. This paper describes a multipass absorption cell used to detect and monitor the presence of several gases in the ultra violet and visible regions. An integrating sphere with a highly reflective internal coating (over 99%) was adapted in order to input and output various gases. Sulphur dioxide was detected in the ultra violet region, ozone in the visible and nitrogen dioxide in both the ultra violet and visible. This paper will report the generation of effective optical path lengths of up to 70 cm using a 5 cm diameter integrating sphere. This results in an optical sensor capable of detecting sulphur dioxide concentrations as low as 10 ppm, nitrogen dioxide concentrations as low as 4 ppm and ozone levels of the order of 500 ppm.

An investigation into the use of an integrating sphere as a gas absorption cell

The experimental results of using a gas sensor based on a spherical absorption gas cell are reported. The integrating sphere has a highly reflective internal coating that causes input light flux to undergo several reflections before exiting the sphere. This results in an optical path length which is several times longer than the diameter of the sphere. Such a sphere may therefore be suitable for use as a multipass absorption cell. For this investigation a 2 inch (50.8 mm) diameter sphere was modified to enable the input and output of several gases, both individually and in mixtures. An optical path length of 70 cm has been demonstrated for ozone at a wavelength of 603 nm, and 55 cm for nitrogen dioxide at 370 nm. A range of measurements of ozone concentrations was taken in the visible range, and nitrogen dioxide in the ultraviolet range. Results are presented for different concentrations of each gas, and the average effective optical path length has been calculated for each of the sensing wavelength ranges. It is reported that this sensor is capable of monitoring 500 ppm (parts per million) of ozone and trace levels of nitrogen dioxide (<10 ppm).

Ozone detection using an integrating sphere as an optical absorption cell

This paper presents a multipass optical absorption cell that is based on a spherical cavity. Ozone concentrations have been detected in the visible region at 603 nm, in the Chappuis band. A 2-inch diameter (50.8 mm) integrating sphere has been modified for use an optical absorption cell. A method of calculating the effective optical path length of the integrating sphere is also presented. It is reported that the effective optical length of the sphere is reduced as the ozone concentration is increased as predicted by the effective path length formula.

UV-based pollutant quantification in automotive exhausts

This paper describes two optical based sensors for the detection and quantification of vehicle exhaust pollutants. The first sensor consists of a single pass absorption cell. Broadband light from a deuterium/halogen source was transmitted through the cell from optical fibre and the resulting absorption is detected using a UV spectrometer which was also fibre coupled. The second approach includes an integrating sphere, which has been adapted for use as a multipass absorption cell. An ultraviolet LED was used as an emitter and a photodiode as the detector. Both were mounted directly on the sphere. The single pass absorption cell has been used to monitor nitric oxide, nitrogen dioxide and sulphur dioxide while the integrating sphere has been used to monitor nitrogen dioxide levels. Concentration levels of 10s of parts per million have been measured for each gas and sensor.

Overview of the OPTO-EMI-SENSE Project: Optical Fibre Sensor Network for Automotive Emission Monitoring

An optical fibre based system has been developed which is capable of monitoring the presence of exhaust gas emissions and measuring their temperature on line in the exhaust system of a modern vehicle. There exists at present no commercial sensor, which is capable of providing online measurements of these exhaust gases as required by European legislation. The design of this sensor using low cost and compact optical components, which make it suitable for operation on board a vehicle, is discussed. The sensor is capable of detecting NO, NO2, SO2 to a minimum detection threshold of 5ppm, CO and HCs to a minimum threshold of 200 ppm, CO2 in the range 300 ppm to 20% and temperature from 0°C to 900°C. Results measured in the exhaust of a modern engine are presented for each of these parameters.

Carbon dioxide detection at 2 μm using an integrating sphere as an optical absorption cell

This paper describes a multipass absorption sensor based on an integrating sphere. The sphere has an internal coating which is highly reflective (over 95%) in the near infrared region and this allows the detection of carbon dioxide (CO2) gas at 2 &mgr;m. CO2 was detected using a light emitting diode as the emitter and a photodiode as the detector. A two inch (50.8 mm) diameter integrating sphere was used as an absorption gas cell. A method of calculating the effective path length of the integrating sphere is also presented. The latter is shown to be dependant on the reflectance of the spheres internal surface, the spheres port fraction and the level of attenuation of the optical signal due to the gas present in the sphere. Effective optical path lengths of 40 cm at the 2 &mgr;m region are reported. Experimental results demonstrating the detection of CO2 using a two inch diameter integrating sphere are presented and these are compared to simulation results based on a CO2 absorption over a 40 cm path length at 2 &mgr;m.