Self-aligned 0-level sealing of MEMS devices by a two layer thin film reflow process

Many micro electromechanical systems (MEMS) require a vacuum or controlled atmosphere encapsulation in order to ensure either a good performance or an acceptable lifetime of operation. Two approaches for wafer-scale zero-level packaging exist. The most popular approach is based on wafer bonding. Alternatively, encapsulation can be done by the fabrication and sealing of perforated surface micromachined membranes. In this paper, a sealing method is proposed for zero-level packaging using a thin film reflow technique. This sealing method can be done at arbitrary ambient and pressure. Also, it is self-aligned and it can be used for sealing openings directly above the MEMS device. It thus allows for a smaller die area for the sealing ring reducing in this way the device dimensions and costs. The sealing method has been demonstrated with reflowed aluminium, germanium, and boron phosphorous silica glass. This allows for conducting as well as non-conducting sealing layers and for a variety of allowable thermal budgets. The proposed technique is therefore very versatile

Multiscale and multispectral characterization of mineralogy with the ExoMars 2020 rover remote sensing payload

This work was supported by the UK Space Agency (ST/P001297/1 and ST/P001394/1). Cousins also acknowledges the Royal Society of Edinburgh for funding.In 2020, the European Space Agency and Roscosmos will launch the ExoMars rover, with the scientific objective to detect evidence of life within the martian surface via the deployment of a 2 meter drill. The ExoMars Pasteur payload contains several imaging and spectroscopic instruments key to this objective: the Panoramic Camera (PanCam), Infrared Spectrometer for ExoMars (ISEM), and Close‐UP Imager (CLUPI). These instruments are able to collect data at a variety of spatial (sub‐mm to decimeter) and spectral (3.3 to 120 nm) resolutions across the 440 to 3300 nm wavelength range and collectively will form a picture of the geological and morphological characteristics of the surface terrain surrounding the rover. We deployed emulators of this instrument suite at terrestrial analog sites that formed in a range of aqueous environments to test their ability to detect and characterize science targets. We find that the emulator suite is able to effectively detect, characterize, and refine the compositions of multiple targets at working distances spanning from 2‐18 m. We report on: (i) the detection of hydrothermal alteration minerals including Fe‐smectites and gypsum from basaltic substrates, (ii) the detection of late‐stage diagenetic gypsum veins embedded in exposures of sedimentary mudstone, (iii) multispectral evidence of compositional differences detected from fossiliferous mudstones, and (iv) approaches to cross‐referencing multi‐scale and multi‐resolution data. These findings aid in the development of data products and analysis toolkits in advance of the ExoMars rover mission.Publisher PDFPeer reviewe

UV luminescence characterisation of organics in Mars-analogue substrates

This project was supported by a Leverhulme Trust Research Project Grant (RPG-2015-071). C Cousins also wishes to acknowledge funding by the Royal Society of Edinburgh.Detection of organic matter is one of the core objectives of future Mars exploration. The ability to probe rocks, soils, and other geological substrates for organic targets is a high priority for in situ investigation, sample caching, and sample return. UV luminescence – the emission of visible light following UV irradiation – is a tool that is beginning to be harnessed for planetary exploration. We conducted  UV photoluminescence analyses of (i) Mars analogue sediments doped with polyaromatic hydrocarbons (PAHs; <15 ppm), (ii) carbonaceous CM chondrites and terrestrial kerogen (Type IV), and (iii) synthetic salt crystals doped with PAHs (2 ppm). We show that that detection of PAHs is possible within synthetic and natural gypsum, and synthetic halite. These substrates show the most apparent spectral modifications, suggesting that the most transparent minerals are more conducive to UV photoluminescence detection of trapped organic matter. Iron oxide, ubiquitously present on Mars surface, hampers but does not completely quench the UV luminescence emission. Finally, the maturity of organic carbonaceous material influences the luminescence response, resulting in a reduced signal for UV excitation wavelengths down to 225 nm. This study demonstrates the utility of UV luminescence spectroscopy for the analysis of mixed organic-inorganic materials applicable to Mars exploration.PostprintPeer reviewe

Low frequency acoustic and ultrasound waves to characterise layered media

Poor penetration and excessive absorption of high frequencies limit spectroscopic approaches using fast rise pulses for inspecting many engineered structures. So, this study focused on the alternative application of low frequency acoustic and ultrasound waves for the characterisation of challenging structures in airborne and waterborne environments. A simple, transfer matrix model approach was developed for the simulation of 1D sound propagation through layered media that comprise many engineered structures. This model was used to test the feasibility of using sound waves for non-destructive characterisation of an articulated lorry transported trailer and offshore foundation infrastructure. The targets were not in contact with the sound sensors and incorporated highly attenuating layers with acoustic contrasts to the surrounding medium that result in over 90% reflection of incident wave pressure. In both cases, resonances controlled by the thicknesses and interval velocities of component layers modulated sound reflection from, and transmission through the whole structure. These effects were observed as local maxima and minima in the spectra of the transmission and reflection coefficients. These spectral coefficients also determined the modulation to the temporal envelope of a linear frequency modulated pulse used to insonify the targets. In the acoustic study, which comprised only theoretical modelling, discrimination of differing cargo widths and between solid versus empty cargo trailers was possible using the transmission coefficient. In the ultrasound study, which comprised theoretical modelling and experimental testing, discrimination of differing steel and concrete substructure thicknesses and also of gaps between them was possible using the reflection coefficient. The model outcomes indicated while an acoustic system would require around 90–100 dB of dynamic range, an ultrasound system would only require around 40 dB to be effective

Ultrasonic testing of laboratory samples representing monopile wind turbine foundations

Wind energy turbines and offshore hydrocarbon platforms rely on injected concrete grout to support and transfer loads between steel substructures. Deterioration of this grout under large operational stresses can lead to a loss of bonding, the formation of gaps, crushing and the loss of grout from the annulus between the steel substructures. In this paper, the integrity of the grout between two steel panels is experimentally tested using a low-frequency ultrasound backscatter method[1]. The experimental results and modelled outcomes[1] are compared for grout condition classes, including: good condition, gaps between the grout and either steel panel and the complete absence of grout. Pearson correlation coefficients of over 83% are observed when comparing the notch magnitudes and the frequencies on the modelled and experimental reflectance spectra of the front and rear gap, as well as missing grout conditions. Kolmogorov-Smirnov (K-S) similarity tests on the modelled and experimental notch magnitudes indicate a 20% significance on the rear gap and front gap spectra and a 10% significance on the missing grout spectra. The significance of these tests supports the potential application of backscattered low-frequency ultrasound for grout condition inspection. However, development of automated condition recognition algorithms, based on either spectral characteristics or time-localised spectral features of the backscatter, is required to make routine inspection commercially viable

Remote detection of past habitability at Mars-analogue hydrothermal alteration terrains using an ExoMars Panoramic Camera emulator

JKH is funded by a Birkbeck University of London Graduate Teaching Assistantship. CRC is funded by a Royal Society of Edinburgh Personal Research Fellowship co-funded by Marie Curie Actions. The Aberystwyth research leading to these results has been funded by the UK Space Agency, ExoMars Panoramic Camera (PanCam) Grant Nos. ST/G003114/1, ST/I002758/1, STL001454/1, and the UK Space Agency CREST2 PanCam-2020 research Grant No. ST/L00500X/1. Additional Aberystwyth funding has come from The European Community’s Seventh Framework Programme (FP7/2007-2013), Grant Agreement Nos. 21881 PRoVisG, 241523 PRoViScout, and Grant Agreement No. 312377 PRoViDE. PMG is funded by a UK Space Agency Aurora Fellowship (grants ST/J005215/1 and ST/L00254X/1).A major scientific goal of the European Space Agency’s ExoMars 2018 rover is to identify evidence of life within the martian rock record. Key to this objective is the remote detection of geological substrates that are indicative of past habitable environments, which will rely on visual (stereo wide-angle, and high resolution images) and multispectral (440–1000 nm) data produced by the Panoramic Camera (PanCam) instrument. We deployed a PanCam emulator at four hydrothermal sites in the Námafjall volcanic region of Iceland, a Mars-analogue hydrothermal alteration terrain. At these sites, sustained acidic–neutral aqueous interaction with basaltic substrates (crystalline and sedimentary) has produced phyllosilicate, ferric oxide, and sulfate-rich alteration soils, and secondary mineral deposits including gypsum veins and zeolite amygdales. PanCam emulator datasets from these sites were complemented with (i) NERC Airborne Research and Survey Facility aerial hyperspectral images of the study area; (ii) in situ reflectance spectroscopy (400–1000 nm) of PanCam spectral targets; (iii) laboratory X-ray Diffraction, and (iv) laboratory VNIR (350–2500 nm) spectroscopy of target samples to identify their bulk mineralogy and spectral properties. The mineral assemblages and palaeoenvironments characterised here are analogous to neutral–acidic alteration terrains on Mars, such as at Mawrth Vallis and Gusev Crater. Combined multispectral and High Resolution Camera datasets were found to be effective at capturing features of astrobiological importance, such as secondary gypsum and zeolite mineral veins, and phyllosilicate-rich substrates. Our field observations with the PanCam emulator also uncovered stray light problems which are most significant in the NIR wavelengths and investigations are being undertaken to ensure that the flight model PanCam cameras are not similarly affected.Publisher PDFPeer reviewe

Cosmological parameters from SDSS and WMAP

We measure cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a ``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1 sigma constraints on the Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt figures available at http://www.hep.upenn.edu/~max/sdsspars.htm

Metal enrichment processes

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

The PanCam Instrument for the ExoMars Rover

The scientific objectives of the ExoMars rover are designed to answer several key questions in the search for life on Mars. In particular, the unique subsurface drill will address some of these, such as the possible existence and stability of subsurface organics. PanCam will establish the surface geological and morphological context for the mission, working in collaboration with other context instruments. Here, we describe the PanCam scientific objectives in geology, atmospheric science, and 3-D vision. We discuss the design of PanCam, which includes a stereo pair of Wide Angle Cameras (WACs), each of which has an 11-position filter wheel and a High Resolution Camera (HRC) for high-resolution investigations of rock texture at a distance. The cameras and electronics are housed in an optical bench that provides the mechanical interface to the rover mast and a planetary protection barrier. The electronic interface is via the PanCam Interface Unit (PIU), and power conditioning is via a DC-DC converter. PanCam also includes a calibration target mounted on the rover deck for radiometric calibration, fiducial markers for geometric calibration, and a rover inspection mirror.publishersversionPeer reviewe