This study focus on the analysis of various plastic samples using the portable MEMS-FTIR spectrometer in both transmission and diffuse reflection modes operating at two resolutions of 10 nm and 16 nm. The analysis focuses on the mid-infrared region spanning from 2000 nm to 4600 nm. Many plastic samples have been differentiated such as Nylon, Polypropylene, Polystyrene, Acrylonitrile butadiene styrene, and colored High-Density Polyethylene. The results shows that transmission module is efficient for clear plastic samples sorting and diffused reflection module is efficient for opaque plastic samples sorting. The findings position the MEMS-FTIR spectrometer as a portable, cost-effective, and accurate solution for plastic analysis tasks, demonstrating versatility and potential advantages over traditional methods in the specified MIR range.
Diffused reflectance infrared spectroscopy is well known as a compact, low-cost, and efficient handheld spectrometers. One of the spectrometer’s most important optical parameters is the effective collected spot profile from diffuse reflection samples not the simple illumination spot which determines the analyzed sample portion defining the spatial resolution. In this work, we present a novel method for characterizing the spot size based on the Knife-Edge technique. A sharp high scattering material such as PTFE is displaced into the spectrometer optical interface on a 1-dimensional moving stage while capturing the power at each step. Then by differentiating this cumulative power, the intensity spot profile is obtained and fitted to a Gaussian profile where the spot size is defined as the diameter that contains 90% of the reflected power. MEMS FT-IR spectrometers with different spot sizes measured as a demonstration of the technique. Moreover, this method quantifies different other parameters such as Goodness of Fit, spot lateral shift in addition to spot shape wavelength dependence that may occurs due to any non-ideality in the spectrometer system.
The conventional methods used for the diagnostics of viral infection are either expensive and time-consuming or not accurate enough and dependent on consumable reagents. In the presence of pandemics, a fast and reagent-free solution is needed for mass screening. Recently, the diagnosis of viral infections using infrared spectroscopy has been reported as a fast and low-cost method. In this work a fast and low-cost solution for corona viral detection using infrared spectroscopy based on a compact micro-electro-mechanical systems (MEMS) device and artificial intelligence (AI) suitable for mass deployment is presented. Among the different variants of the corona virus that can infect people, 229E is used in this study due to its low pathogeny. The MEMS ATR-FTIR device employs a 6 reflections ZnSe crystal interface working in the spectral range of 2200-7000 cm-1. The virus was propagated and maintained in a medium for long enough time then cell supernatant was collected and centrifuged. The supernatant was then transferred and titrated using plaque titration assay. Positive virus samples were prepared with a concentration of 105 PFU/mL. Positive and negative control samples were applied on the crystal surface, dried using a heating lamp and the spectrum was captured. Principal component analysis and logistic regression were used as simple AI techniques. A sensitivity of about 90 % and a specificity of about 80 % were obtained demonstrating the potential detection of the virus based on the MEMS FTIR device.
In this work, we present a MEMS-based ATR FTIR spectrometer operating in the wavelength range of 1.8 μm to 6.8 μm. The core engine of the spectrometer is a monolithically integrated scanning Michelson interferometer on a silicon chip. The ATR crystal is illuminated with an IR source and the output light of the crystal is free-space coupled to the MEMS interferometer using micro-optics reflective mirrors and the modulated light from the interferometer is then coupled to an MCT photodetector. The recorded SNR of the spectrometer is about 1000:1 in 10 seconds measurement time with a spectral resolution of 66 cm-1. The spectra of different liquid samples were obtained and the effect of the ATR crystal refractive index on the absorption depth was investigated, showing good agreement with the theoretical model. The proposed miniaturized ATR MEMS spectrometer opens the door for various applications in oil analysis, food safety and health care among others.
Infrared portable spectral sensors are greatly required for rapid and simultaneous analysis of material composition; triggering new applications in the domain of on-site spectroscopy. At the same time, miniaturization of Fourier transform infrared (FTIR) spectrometers based on the silicon technology has been proven to be one of the most promising approaches for wide spectral range applications. In this work, we present a fiber-free MEMS FTIR spectrometer working in the wavelength range of 1.8 μm to 6.8 μm (5500-1470 cm-1). The spectrometer is based on the use of a monolithically integrated scanning Michelson interferometer, assembled with external reflecting micro-optical part, which is responsible for light coupling to and from the MEMS chip. The measured signal-to-noise ratio of the spectrometer is larger than 5000:1 with a spectral resolution of 66 cm-1. The experimental results of measuring the transmission of a polystyrene reference calibration film show four absorption peaks in the Mid Infra-Red (MIR) range at 3.27, 3.5, 5.15, 6.24 μm in close agreement with theoretical predictions.
Air pollution is used to refer to the release of pollutants into the air, where these pollutants are harmful to the human health and our planet. The main source of these pollutants comes from energy production and consumption that release Volatile Organic Compounds (VOCs) such as BTEX and Aldehydes group. Real time monitoring of these VOCs in factories, stations, homes and in the street is important for analysis of the pollution sources fingerprint and for alerting, when exceeding the harmful limits. In this work we report the use of a MEMS FTIR spectrometer in the mid-infrared for this purpose. The spectrometer works in the wavelength range of 1.6 μm - 4.9 μm with a resolution down to 33 cm-1. This covers the absorption spectrum of water vapour, BTEX, Aldehydes and CO2 around 2.65 μm, 3.27 μm, 3.6 μm and 4.3 μm, respectively. The spectra of Toluene with different concentrations are measured, using a multipass gas cell with a physical length of 50 cm and an optical path length of 20 m, showing excellent sensor linearity. The minimum concentration measured is 350 ppb limited by the interference of the side lobes of the strong absorption of water vapour, which can be overcome in the future by humidity compensation. The SNR is measured and found to be 5000:1, corresponding to a detection limit of about 90 ppb. The achieved results open the door for a compact and low-cost solution targeting air pollution monitoring.
In this work we report the modelling of the emissivity of micromachined black silicon structure based on treating the black silicon as an array of cone-shaped textured silicon structure. The geometrical ray optics is used to calculate the reflection and transmission coefficient for each ray hitting the silicon surface with a certain incidence angle. The coherence length is assumed to be much smaller than the travelled distance by the rays such that their contribution is summed incoherently. The validity of the geometrical optics holds since the modeled structure dimensions are much larger than the wavelength. The model is applied on experimental data reported in the literature for black silicon structure fabricated using femtosecond laser pulses. The height of the structure is in the order of 20 μm, the cone angle is about 20 degrees and silicon doping level is about 1019 cm-3. The model results are compared to the measured emissivity in the wavelength range of 500 nm to 2000 nm good matching within 0.5 % to 5 % is obtained for smaller to longer wavelengths, respectively.
Portable and handheld spectrometers are being developed and commercialized in the late few years leveraging the rapidly-progressing technology and triggering new markets in the field of on-site spectroscopic analysis. Although handheld devices were commercialized for the near-infrared spectroscopy (NIRS), their size and cost stand as an obstacle against the deployment of the spectrometer as spectral sensing components needed for the smart phone industry and the IoT applications. In this work we report a chip-sized microelectromechanical system (MEMS)-based FTIR spectrometer. The core optical engine of the solution is built using a passive-alignment integration technique for a selfaligned MEMS chip; self-aligned microoptics and a single detector in a tiny package sized about 1 cm3. The MEMS chip is a monolithic, high-throughput scanning Michelson interferometer fabricated using deep reactive ion etching technology of silicon-on-insulator substrate. The micro-optical part is used for conditioning the input/output light to/from the MEMS and for further light direction to the detector. Thanks to the all-reflective design of the conditioning microoptics, the performance is free of chromatic aberration. Complemented by the excellent transmission properties of the silicon in the infrared region, the integrated solution allows very wide spectral range of operation. The reported sensor’s spectral resolution is about 33 cm-1 and working in the range of 1270 nm to 2700 nm; upper limited by the extended InGaAs detector. The presented solution provides a low cost, low power, tiny size, wide wavelength range NIR spectral sensor that can be manufactured with extremely high volumes. All these features promise the compatibility of this technology with the forthcoming demand of smart portable and IoT devices.
Micromachined infrared sources are enabling component for interferometric and spectroscopic sensors. Their compact size and low cost transform bulky instruments to the sensor scale, which is needed for a wide range of applications in the conventional and unconventional environments. The silicon micromachined sources should be engineered to have good emissivity across a large wavelength range because the intrinsic emissivity of silicon is low. This optimization was reported in literature by either the deposition of black metal at the surface of an emitter or the use of deep phonic crystal cavities, which complicates the fabrication technology and results in sharp dip lines in the spectral emissivity, respectively. In this work we report a micromachined infrared radiation source based on a heater on the top of black silicon structure for the first time in the literature, up to the authors’ knowledge. The temperature of the device is characterized versus the applied voltage and the radiated spectrum is captured in the 1300 nm to 2500 nm spectral range; limited by the spectrum analysis instrument. The reported source opens the doors for completely integrated MEMS spectral sensors onchip.
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