Alain Ferber

Sensitive and Selective Photo Acoustic Gas Sensor Suitable for High Volume Manufacturing

Sensitive and selective gas measurements are crucial for a large variety of applications. This paper describes the manufacturing and characterisation of a photo acoustic gas sensor system. The system is based on a pressure sensor element with a sensitivity of 10 muV/V/Pa. 12 prototypes for measuring CO2 have been characterised. Detection limits ranging from 92 ppm to below 6 ppm CO2 were obtained, depending on the measurement time and photo acoustic cell design. No cross-sensitivity towards CO, CH4, or humidity could be observed in any of the sensors. The temperature drift of the uncompensated raw signal of two sensor designs was below 117 ppm CO2 in the range from 25degC to 50degC.

Magnetic Field Exposure Assessment in Electric Vehicles

This article describes a study of magnetic field exposure in electric vehicles (EVs). The magnetic field inside eight different EVs (including battery, hybrid, plug-in hybrid, and fuel cell types) with different motor technologies (brushed direct current, permanent magnet synchronous, and induction) were measured at frequencies up to 10 MHz. Three vehicles with conventional powertrains were also investigated for comparison. The measurement protocol and the results of the measurement campaign are described, and various magnetic field sources are identified. As the measurements show a complex broadband frequency spectrum, an exposure calculation was performed using the ICNIRP “weighted peak” approach. Results for the measured EVs showed that the exposure reached 20% of the ICNIRP 2010 reference levels for general public exposure near to the battery and in the vicinity of the feet during vehicle start-up, but was less than 2% at head height for the front passenger position. Maximum exposures of the order of 10% of the ICNIRP 2010 reference levels were obtained for the cars with conventional powertrains.

A Photoacoustic Gas Sensing Silicon Microsystem

A miniature photoacoustic (PA) gas sensing module has been made using silicon microsystem technology to make two key components: 1) A high-speed infrared emitter (IRE) with a diamond-like carbon thin film resistor on a silicon micromachined diaphragm as support structure. 2) A silicon micromachined microphone to sense the photoacoustic signal. The IRE is manufactured by Patinor Coating by a proprietary process, while the silicon microphone is manufactured in a multi-project wafer (MPW) foundry service called NORMIC, with SensoNor as the foundry. The silicon microphone was designed by SINTEF. The complete module also consists of analog and digital system with control logic, signal conditioning and interface electronics. A patented scheme with the target gas as a selective filter is giving high selectivity. Preliminary test and evaluation of a prototype for carbon dioxide monitoring show that the principle to achieve high selectivity is working. A resolution better than 0.5 ppm and an accuracy around 10 ppm have be achieved, with a potential towards better than 5 ppm, provided the relative high thermal drifts are compensated.

Sensitive and Selective Photoacoustic Gas Sensor Suitable for High-Volume Manufacturing

Sensitive and selective gas measurements are crucial for a large variety of applications. This paper describes the manufacturing and characterization of a photoacoustic gas sensor system. The system is based on a pressure sensor element with a sensitivity of 10 muV/V/Pa. To demonstrate and evaluate the concept, 12 prototypes for measuring CO2 have been manufactured and characterized. Detection limits ranging from 92 ppm to below 6 ppm CO2 were obtained with a path length of 10 cm, depending on the measurement time and photoacoustic cell design. Measurements showed no cross-sensitivity towards CO, CH4, or humidity in any of the sensors. The temperature drift of the uncompensated raw signal of two sensor designs was below 117 ppm CO2 in the range from 25degC to 50degC.

Validation of Online Monitoring of PFC by QCL with FTIR Spectroscopy

Monitoring of perfluorocarbon (PFC) evolution from aluminium smelting is gaining attention, not only because of their high greenhouse gas potentials but also due to process optimization purposes. Conventionally, PFC monitoring has been conducted by extractive sampling and subsequent analysis by fourier transform infrared (FTIR) spectroscopy. With FTIR, the quantification can be performed by IR spectral features specific for PFC. The downside is a requirement of gas scrubbing to remove HF detrimental to the instrument as well as relatively poor gas dynamics due to the large internal gas volume of the instrument. With emerging quantum cascade laser (QCL) technology, online monitoring can now be conducted with duct mounted lasers with calcium fluoride optical windows. However, due to a strong spectral overlap of CF4 and other gas constituents present in the process (e.g. methane), the QCL instruments currently suffer from some cross-interference. In this work, QCL single cell PFC monitoring has been validated by simultaneous monitoring with FTIR.

Evaluation of Gas Composition from Laboratory Scale Electrolysis Experiments with Anodes of Different Sulphur Content

With the anticipated decrease in available anode raw materials, future anodes are expected to contain higher levels of impurities. Currently the implications of this are being investigated through evaluation of electrochemical performance of anodes and the environmental aspects through gas evolution studies. In this work, four experiments of aluminum smelting have been conducted with anodes of varying sulphur content. The aim of this work was to evaluate the speciation of sulphur in the off-gas. It was found that COS is the main sulphur species in the inert argon furnace atmosphere. The gas composition was further evaluated as a function of set anode voltages in potentiostatic mode. The significance levels of gas composition were evaluated through repeated experiments. As an FTIR multicomponent analyzer was used, less commonly discussed gaseous constituents such as CH4 and HCl were evaluated with respect to given impurity levels in the anode.

In‐Situ Gas Monitoring by Emission Spectroscopy

Off-gas monitoring of experimental reactors give little information about intermediate reaction products and reflect chemical equilibria at reduced gas temperatures. A reactor design with optical access was designed and tested in order to be able to qualify and quantify gaseous species from their emission spectra. By use of a sequence of sapphire, UV fused silica and IR transparent sapphire and CaF2 windows and lenses optical access to a hot, maximum 1800 °C, reaction zone was gained. A cooled area behind the reaction zone was used as a background in order to avoid signal saturation from reactor walls. In addition to molecular emission spectra, atomic emission lines are used to characterize stable gas constituents and radicals. The setup has been designed for the study of methane dehydrogenation experiments in order to investigate the carbon activity of reduction of oxide with methane, but has also been used to monitor gaseous silicon suboxide.

Monitoring of Continuous PFC Formation in Small to Moderate Size Aluminium Electrolysis Cells

The existence of continuous or non-anode effect formed perfluorocarbons (PFC) has been documented for larger size aluminium electrolysis cells. It has been proposed that less uniformity in dissolved alumina for larger cells may elevate individual anode overvoltage sufficiently to produce PFC. Continuous PFC was monitored after the dry scrubber on a train of 28 cells at a Norwegian smelter. For this work a fourier-transform infrared spectrometer was used. Equipped with a mercury cadmium telluride detector and retrofitted with a 35 m / 11 L measurement cell it was possible to get the detection limit down in the low ppb range needed for this study.