| 1. |
- Ghaderi, Mohammadamir, 1986, et al.
(författare)
-
Self-Cleaning Micro-Windows for In-Tailpipe Optical Exhaust Gas Measurements
- 2020
-
Ingår i: IEEE International Symposium on Industrial Electronics. ; , s. 1104-1108
-
Konferensbidrag (refereegranskat)abstract
- Exhaust gas measurement in the harsh environment of the tailpipe of a combustion engine by optical techniques is a highly robust technique, provided that optical access is maintained in the presence of particulate matter (PM). The considerations are presented for the systematic design of membranes with integrated heaters in SiC-on-Si technology for generating a well-defined lateral temperature profile with peak temperatures above 600 °C. Periodically raising the temperature of the membranes to such a level is demonstrated to keep the surface transparent by oxidation of soot deposits. This paper is about continuous heating of the membrane to a temperature slightly higher than that of the exhaust gas. At such temperatures thermophoretic repulsion of PM allows allows long-term optical measurement in the exhaust without the thermo-mechanical loading by repetitive thermal cycling.
|
|
| 2. |
- Ghaderi, Mohammadamir, 1986, et al.
(författare)
-
Thermally regenerable optical transparent MEMS windows for exhaust gas analysis
- 2020
-
Ingår i: Optics InfoBase Conference Papers.
-
Konferensbidrag (refereegranskat)abstract
- Exhaust gas measurement in the harsh environment of the tailpipe by optical techniques is a highly robust technique, provided that optical access is maintained in the presence of soot. The design, fabrication, and testing of membranes in SiC-on-Si with integrated heaters to serve as a regenerable MEMS optical window into the tailpipe are presented. Membranes at slightly elevated temperatures are demonstrated to keep the surface transparent by thermophoresis, while surface regeneration is achieved at pulsed high temperatures, which allows long-term optical measurement in the exhaust.
|
|
| 3. |
- Middelburg, Luke M., et al.
(författare)
-
Exploring the response of a resistive soot sensor to AC electric excitation
- 2020
-
Ingår i: Journal of Aerosol Science. - : Elsevier BV. - 0021-8502 .- 1879-1964. ; 146
-
Tidskriftsartikel (refereegranskat)abstract
- The resistive particulate matter sensor is a simple device that transduces the presence of soot through impedance change across inter-digital electrodes (IDEs). We investigate the information provided by impedance spectroscopy over the frequency range from 100 Hz to 10 kHz for two purposes. The first is to investigate the opportunities for an improved sensor response to particulate matter (PM), based on the additional information provided by the measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the change in impedance over this frequency range as compared to DC resistance measurement only. Secondly, the origin of the capacitive response of the device is investigated from the perspective that soot on the device is in the form of bendable dendrites that grow in three dimensions. An IDE structure with the housing acting as an additional suspended electrode for introducing a controllable vertical electric field component has been used for this purpose. The formation of dipoles, due to bending of the charged dendrites, is found to be the source of the capacitive response. Simulation of electrostatic soot deposition reinforces dendritic self-assembly mechanisms, driven by charged particle trajectories along electric field lines. Optical microscopy confirms that dendrites growing out of the substrate plane are sensitive to electric and flow forces, bending when force balances are appropriate. We also apply impedance spectroscopy under varying electric field strengths, showing that capacitive response is only observed when conditions are conducive to dendrite bending in response to the applied AC electric fields.
|
|
| 4. |
- Middelburg, Luke M., et al.
(författare)
-
Impedance Spectroscopy for Enhanced Data Collection of Conductometric Soot Sensors
- 2020
-
Ingår i: IEEE International Symposium on Industrial Electronics. ; 2020-June, s. 1099-1103
-
Konferensbidrag (refereegranskat)abstract
- Impedance spectroscopy in the frequency range 100 Hz to 10 kHz has been applied to the Inter-Digitated Electrode (IDE) structure that is conventionally operated as a resistive sensor for the measurement of Particulate Matter (PM). The measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the impedance over this frequency range provides more data on PM as compared to DC resistance measurement only. Experimental validation confirms a more gradual change in capacitance with soot buildup as compared to the sudden reduction of resistance with dendrite formation. The effect of an additional vertical electric field for an increased capacitive sensitivity due to stimulated soot buildup has been experimentally investigated using the electrically conductive flow housing of the IDE structure as an additional suspended electrode.
|
|
| 5. |
- Middelburg, Luke M., et al.
(författare)
-
Maintaining transparency of a heated MEMs membrane for enabling long-term optical measurements on soot-containing exhaust gas
- 2020
-
Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 20:1
-
Tidskriftsartikel (refereegranskat)abstract
- Ensuring optical transparency over a wide spectral range of a window with a view into the tailpipe of the combustion engine, while it is exposed to the harsh environment of sootcontaining exhaust gas, is an essential pre-requisite for introducing optical techniques for long-term monitoring of automotive emissions. Therefore, a regenerable window composed of an optically transparent polysilicon-carbide membrane with a diameter ranging from 100 µm up to 2000 µm has been fabricated in microelectromechanical systems (MEMS) technology. In the first operating mode, window transparency is periodically restored by pulsed heating of the membrane using an integrated resistor for heating to temperatures that result in oxidation of deposited soot (600–700 °C). In the second mode, the membrane is kept transparent by repelling soot particles using thermophoresis. The same integrated resistor is used to yield a temperature gradient by continuous moderate-temperature heating. Realized devices have been subjected to laboratory soot exposure experiments. Membrane temperatures exceeding 500 °C have been achieved without damage to the membrane. Moreover, heating of membranes to ΔT = 40 °C above gas temperature provides sufficient thermophoretic repulsion to prevent particle deposition and maintain transparency at high soot exposure, while non-heated identical membranes on the same die and at the same exposure are heavily contaminated.
|
|
