Exploring the response of a resistive soot sensor to AC electric excitation

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

Self-Cleaning Micro-Windows for In-Tailpipe Optical Exhaust Gas Measurements

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 \ub0C. 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

Maintaining transparency of a heated MEMs membrane for enabling long-term optical measurements on soot-containing exhaust gas

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 \ub5m up to 2000 \ub5m 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 \ub0C). 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 \ub0C have been achieved without damage to the membrane. Moreover, heating of membranes to ΔT = 40 \ub0C 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

Auto-calibrated capacitive MEMS accelerometer

An electronic calibration technique forcapacitive MEMS accelerometers based on themeasurement of pull-in voltages is described. Acombination of pull-in voltages and resonance frequencymeasurements can be used for the estimation of processinducedvariations in device dimensions from layout anddeviations in material properties from nominal value,which enables auto-calibration. Measurements onfabricated devices confirm the validity of the proposedtechnique and electronic calibration is experimentallydemonstrated

Capacitive MEMS accelerometers testing mechanism for auto-calibration and long-term diagnostics

A test technique for capacitive MEMSaccelerometers and electrostatic micro-actuators based onthe measurement of pull-in voltages is described. Acombination of pull-in voltages and resonance frequencymeasurements can be used for the estimation of processinducedvariations in device dimensions from layout anddeviations in material properties from nominal value,which enables auto-calibration. Preliminary measurementson fabricated devices confirm the validity of the proposedtechnique. Moreover, long-term pull-in measurements haveindicated the suitability of the approach as in-systemdiagnostic tool

SU-8 based waveguide for optrodes

Neural probes can be equipped with light for optogenetics applications. Different approaches are used for delivering light to the tissue: an optical fiber coupled to the probe, a µLED or a waveguide integrated on the probe. Small probe dimensions, adequate optical power for photostimulation and good tissue penetration for in-vivo experiments are critical requirements. Thus, integrating a waveguide is a promising solution. This work shows the design and simulation of a SU-8 based waveguide for integration in a neural probe. The waveguide contains 3 apertures, spaced by 0.5 mm, which will allow the photostimulation of different brain regions simultaneously.ANI supports this work through the Brain-Lighting project by FEDER funds through Portugal 2020, COMPETE 2020 with the reference POCI-01-0247-FEDER-003416. S. B. Goncalves is supported by the Portuguese Foundation for Science and Technology, grant PD/BD/105931/2014, MIT-Portugal program.info:eu-repo/semantics/publishedVersio

CMOS Compatible Fabrication of Mid Infrared Microspectrometers Based on an Array of Metamaterial Absorbers

The design of a mid-infrared micro-spectrometer based on an array of differently tuned narrow-band metamaterial absorbers is presented. The spectral response is tailored by the design of the unit cell. Each spectral band is composed of a thermopile detector with a 300 7180 μm2 Al-based metamaterial absorber fabricated in a CMOS compatible post-process. The challenges in the fabrication of the sub-μm features within the unit cell over a several mm2 absorber area by equipment that is part of the standard infrastructure of a MEMS facility is addressed. The design and fabrication method utilized here for the first time enables the CMOS fabrication of integrated large-area plasmonic components on thermal detectors