Thick Sensors Research Articles

CO Sensing Performance of Porous Thick Film Nasicon-Based Solid Electrolyte Gas Sensors

We have reported the CO sensing properties of sintered disk-type NASICON(Na3Zr2Si2PO12)-based solid electrolyte gas sensors equipped with a metal oxide (MO)-added Pt sensing electrode (SE, Pt(nMO) (n: MO additive amount in wt%)) and a pristine Pt or another metal oxide (M’O)-added Pt counter electrode (CE, Pt or Pt(nM’O)) on the same side of the disk [1, 2]. The outstanding CO sensing characteristics of these NASICON-based sensors are 1) no reference atmosphere necessary (both SE and CE can be exposed to the same atmosphere, leading to a simple sensor structure), 2) capable of operation at room temperature and also at temperatures below the freezing point, 3) improvement of CO selectivity against H2 in humid environment at room temperature operation, whereas CO response decreased slightly, 4) CO response based on the mixed potential theory, etc. To realize a further simple manufacturing process of sensor elements and also excellent CO sensing properties, the present study was directed to establishing the optimum fabrication conditions of porous thick film NASICON-based solid electrolyte CO gas sensors. Pt paste (Tanaka Corp., TR-7907) mixed with 15 wt% of a metal oxide (Pt(15MO)) and pristine Pt paste were applied in a rectangular shape (1 × 4 mm) with a distance of 4 mm on the same surface of a quadrate alumina substrate (10 × 10 mm), then the same past was used to attach a Pt lead wire to each electrode, followed by drying at 100°C for 10 min in air. Thereafter, NASICON paste was applied on the alumina substrate equipped with a pair of the electrodes and dried at 100°C for 1 h, followed by calcination in the temperature range of 700 to 900°C for 0.5 h in air. The thickness of porous NASICON thick films fabricated was ca. 1 mm. The sensor thus fabricated is denoted as Pt(15MO)/Pt-T, where T represents the calcination temperature. Response properties to 300 ppm CO balanced with dry air of as-fabricated sensors and those subjected to the following aging treatment, heating at 400°C for 1 h in dry air and then exposure to 3,000 ppm CO balanced with air at 400°C for 0.5 h, were measured at 30°C and −10°C. The sensor subjected to the aging treatment is referred to as Pt(15MO)/Pt-Ta. The metal oxides tested were Bi2O3, Cr2O3 and CeO2. The electromotive force (E, mV) of the sensors was measured with a digital electrometer as a sensing signal. The magnitude of CO gas response was defined as a difference in E measured between in 300 ppm CO balanced with air and in base air. Figures 1 and 2 show CO response transients of Pt(15Bi2O3)/Pt-T and Pt(15Bi2O3)/Pt-Ta at 30°C. Even for porous thick film sensors, we could obtain CO response abilities as those observed for sintered disk-type sensors [1, 2]. When Bi2O3 was used as an additive to SE, the aging treatment improved sensing stability, enhanced CO response and shortened the response and recovery time, especially for the sensor calcined at 700°C. CO response properties were also much improved by the aging treatment in the case of the Cr2O3 addition, but were deteriorated in the case of the CeO2 addition. Similar aging effects were also observed at the operation of −10°C, whereas the excellent CO response properties were observed at different calcination temperature values. Another notable feature is the shift in E to a positive direction upon exposure to CO for both the Bi2O3 and Cr2O3 additions, irrespective of the calcination and operating temperatures, but to a negative direction for the Pt(15CeO3)/Pt-T sensors. The detailed CO sensing performance of these sensors will be delivered in my presentation.Reference[1] H. Takeda, T. Ueda, K. Kamada, K. Matsuo, T. Hyodo, Y. Shimizu, CO-sensing properties of a NASICON-based gas sensor attached with Pt mixed with Bi2O3 as a sensing electrode, Electrochimica Acta, 155, 8−15 (2015).[2] T. Ueda, H. Takeda, K. Kamada, T. Hyodo, Y. Shimizu, Enhanced CO response of NASICON-based gas sensors using oxide-added Pt sensing electrode at low temperature operation, Electrochemistry, 85(4), 174−178 (2017). Figure 1

Emerging waste-free non-destructive system based on molecular sensors originating from novel europium complexes for in-situ determination of polymer coating thickness

Herein, novel europium(III) complex derivatives dedicated to polymer chemistry applications as molecular sensors have been reported. The following are among them tris(4,4,4-trifluoro-1-phenylbutane-1,3-dione)europium(III) (BTA) and tris(4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dione)europium(III)] (NTA). To obtain the relevant europium complexes, they were coordinated with the corresponding ligands, e.g., 4-phenyl-2,6-bis(2-pyridyl)pyridine (PPP), 2,2′-bipyridine (Bpy), 2-(2-pyridyl)-1,3-benzothiazole (PBT) and 2-(2-pyridyl)imidazo[1,2-a]pyridine (PIP). The application of these compounds as luminescent sensors to monitor the kinetics of cationic photopolymerisation of monomers has been investigated along with the determination of optical properties. Ultimately, the possibility of employing europium(III) complexes as thickness sensors for polymer coatings resulting from the free radical photopolymerisation of trimethylolpropane triacrylate was measured using Fluorescence Probe Technology developing a zero-waste, non-destructive method for in-situ determination of polymer coating thickness.

Temperature effects on clustering in TPX3-Si pixel detectors

The performance of a Timepix3 (TPX3) detector equipped with a 500 μm thick silicon sensor was evaluated while in vacuum and subjected to temperature variations. Proton beam measurements were performed at the Tandem Van de Graaff accelerator of the University of Montreal to determine the effect of sensor temperature on cluster parameters as well as measured energy. It was observed that temperature had a negative effect on the reconstructed energy obtained from the conventional calibration technique. The sizes of registered proton clusters increased as the sensor was heated up, indicating greater charge drift, resulting in additional charge sharing between neighbouring pixels.

Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors—The Influence of Humidity

Polycrystalline NiO thick film-based gas sensors have been exposed to different test gas atmospheres at 250 °C and measured via simultaneous electrical resistance and work function investigations. Accordingly, we decoupled different features manifested toward the potential changes, i.e., work function, band-bending, and electron affinity. The experimental results have shown that the presence of moisture induces an unusual behavior toward carbon monoxide (CO) detection by considering different surface adsorption sites. On this basis, we derived an appropriate detection mechanism capable of explaining the lack of moisture influence over the CO detection with NiO-sensitive materials. As such, CO might have both chemical and dipolar interactions with pre-adsorbed or lattice oxygen species, thus canceling out the effect of moisture. Additionally, morphology, structure, and surface chemistry were addressed, and the results have been linked to the sensing properties envisaging the role played by the porous quasispherical–hollow structures and surface hydration.

Effect on Neural Pattern Classifier for Intelligent Gas Sensor by Increasing Number of Hidden Layer

Abstract: Neural networks are used to solve complex problem viz., speech and image recognition, pattern recognition (Pattern classification), computer vision etc. Pattern classification by using Back Propagation algorithm for an intelligent gas sensor application is presented. The classifier is trained using published data of thick film tin oxide sensor array. Its superior classification and learning performance is demonstrated for discrimination of alcohols and alcoholic beverages by increasing number of hidden layer. The new model proposed in this article give steep and monotone learning curve and better classification efficiency. Keywords: Neural Network classifier, Back Propagation Algorithm, system error, classification efficiency, learning curve

Experimental Investigation of AdBlue Film Formation in a Generic SCR Test Bench and Numerical Analysis Using LES

In this work, an experimental investigation of AdBlue film formation in a generic selective catalytic reduction (SCR) exhaust gas test bench is presented. AdBlue is injected into a generic SCR test bench resulting in liquid film formation on the lower wall of the channel. The thickness of this liquid film is measured using a film thickness sensor based on absorption spectroscopy. Simultaneously, the wall temperature at the measurement point is monitored, which allows for examining correlations between the evolution of the film thickness and the temperature of the wetted wall. The velocity of the airflow in the channel and the initial wall temperature are varied in the experiments. Correspondingly, the measurements are performed during different thermodynamic regimes, including liquid film deposition and boiling. Repeated measurements have also shown that the film thicknesses are reproducible with a standard deviation of 3.4 %. LES-based numerical simulations are compared to the experimental results of the film thickness during the early injection stage. Finally, a numerical analysis is performed to analyze the AdBlue droplet impingement and subsequent film-formation dynamics.

Distributed Algorithms for Multiple Path Backbone Discovery in Thick Linear Sensor Networks

Continued advancements in microprocessors, electronics, and communication technology have led to the design and development of sensing devices with increased functionalities, smaller sizes, larger processing, storage, and communication capabilities, and decreased cost. A large number of these sensor nodes are used in many environmental, infrastructure, commercial, and military monitoring applications. Due to the linearity of a good number of the monitored structures such as oil, gas, and water pipelines, borders, rivers, and roads, the wireless sensor networks (WSNs) that are used to monitor them have a linear topology. This type of WSN is called a linear sensor network (LSN). In this paper, two distributed algorithms for topology discovery in thick LSNs are presented: the linear backbone discovery algorithm (LBD) and the linear backbone discovery algorithm with x backbone paths (LBDx). Both of them try to construct a linear backbone for efficient routing in LSNs. However, the LBD algorithm has the objective of minimizing the number of messages used during the backbone discovery process. On the other hand, the LBDx algorithm focuses on reducing the number of hops of the data messages transmitted from the nodes to the sink. LBD and LBDx exhibit good properties and efficient performance, which are confirmed by extensive simulations.

Multi-energy reconstructions, central electron temperature measurements, and early detection of the birth and growth of runaway electrons using a versatile soft x-ray pinhole camera at MST.

A multi-energy soft x-ray pinhole camera has been designed, built, and deployed at the Madison Symmetric Torus to aid the study of particle and thermal transport, as well as MHD stability physics. This novel imaging diagnostic technique employs a pixelated x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel. The detector of choice is a PILATUS3 100K with a 450 μm thick silicon sensor and nearly 100 000 pixels sensitive to photon energies between 1.6 and 30 keV. An ensemble of cubic spline smoothing functions has been applied to the line-integrated data for each time-frame and energy-range, obtaining a reduced standard-deviation when compared to that dominated by photon-noise. The multi-energy local emissivity profiles are obtained from a 1D matrix-based Abel-inversion procedure. Central values of Te can be obtained by modeling the slope of the continuum radiation from ratios of the inverted radial emissivity profiles over multiple energy ranges with no a priori assumptions of plasma profiles, magnetic field reconstruction constraints, high-density limitations, or need of shot-to-shot reproducibility. In tokamak plasmas, a novel application has recently been tested for early detection, 1D imaging, and study of the birth, exponential growth, and saturation of runaway electrons at energies comparable to 100 × Te,0; thus, early results are also presented.

Highly sensitive thick diaphragm-based surface acoustic wave pressure sensor

Diaphragm-based Surface acoustic wave (SAW) pressure sensors are of great interest to fulfill high-pressure sensing requirements in industrial and commercial applications. These sensors are developed with a thick diaphragm, can endure considerable pressure but adversely result in low sensitivity and affect device accuracy. The trade-off between diaphragm thickness and sensitivity is the major problem in designing pressure sensors for high-pressure sensing ranges. This work proposed a highly sensitive pressure sensor design based on one port SAW resonator with AlN/Mo/SOI multilayer structure. The sensor utilizes a 50 μm thick rectangular diaphragm and has been fabricated with simple microfabrication techniques, making it cost-effective and easy to implement in pressure sensing equipment. Finite element analysis (FEA) has been performed for analyzing diaphragm to locate IDTs based on bending, uniformity of stress distribution and induced strain type. The developed sensor exhibits good performance characteristics, including high sensitivity (up to 129.17 ppm/MPa), wide pressure sensing range (up to 2 MPa), and good repeatability with linear behavior for applied pressure range. Additionally, this work has presented a novel approach to enhance pressure sensitivity based on increased velocity without compromising sensing range. The obtained sensitivity has been enhanced up to 228.46 ppm/MPa by modifying the primarily developed sensor design such that the SAW propagation direction becomes parallel to the induced strain direction. With the proposed novel concept, the sensitivity has been significantly improved by 76.87 % compared to the primarily developed sensor. Besides improved sensitivity, the modified sensor also shows the best repeatability and linearity. All these performance characteristics pave the way to make this design a good choice for high-pressure sensing applications.

Acoustic-pressure sensor array system for cardiac-sound acquisition

This paper presents a cardiac-sound-detection system based on an acoustic-pressure sensor array. The traditional cardiac-sound probe has the disadvantages of high cost and thick structure, which makes embedding difficult. Therefore, a methodology for cardiac-sound detection, comprising a sound-pressure sensor array, is proposed to achieve a low cost, very thin, and wearable cardiac-sound probe, which can be embedded in furniture or clothes for long-term heart sound monitoring. By introducing several miniature electret-condenser-microphone-based acoustic-pressure sensors, a sensor array for picking up cardiac sound was designed. The data-processing platform comprised a field-programmable gate array and microcontroller unit. Furthermore, a series of de-noising methods including oversampling, finite impulse response digital filtering, and digital extraction were used, thereby facilitating accurate cardiac-sound signal identification. Test results showed that the average Root Mean Square amplitude of the noise after processing was more than 3 dB lower than that of the signal obtained from a single sensor in the array. The signal-to-noise ratio improved more than 7 dB after processing. Furthermore, actual cardiac sounds were acquired and compared using the proposed sensor array and the dedicated cardiac-sound sensor. The proposed 4 mm thick sensor array could effectively acquire S1- and S2-segments of cardiac sound. The proposed system demonstrates the potential for use in the development of wearable cardiac-sound monitoring systems.

Response of electrical film thickness sensors to waves in the liquid film

The electrical liquid film thickness (LFT) sensor developed at ETH Zurich is applied to study wavy annular flows. The LFT sensor consists of a matrix of electrodes put flush to the surface of the wall at which the liquid film of interest is present. The conductance between transmitter and receiver electrodes is sampled and converted into a film thickness using a calibration function obtained for a flat liquid film without waves. Due to limited lateral resolution and non-linear sensor response, waves are characterized with measuring errors, which depend on the wave height, length and angle of attack. The paper presents the result of potential field simulations of waves passing over the sensor surface. The wave parameters obtained from the simulated sensor signals are compared to the input. The results are used to quantify the uncertainty of dynamic film thickness measurements. The obtained detailed information on the sensor response allows a better interpretation of experimental results.

Charge Sharing and Charge Loss in High-Flux Capable Pixelated CdZnTe Detectors.

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field.

Bulk factor characterization of heated debulked autoclave and out-of-autoclave carbon fibre prepregs

Tow impregnation during cure causes change in the laminate thickness, thus bulk factor, which causes variation in prepreg air permeability and large thickness deviations around corners. A noncontact eddy current thickness sensor monitored the laminate thickness throughout debulk and cure in an oven. Bulk factor values averaged to 1.1 for materials intended for autoclave use and 1.2 for out-of-autoclave, where a lower number is ideal for complex geometries. A heated debulk (HD) at around 48 °C for 2 h resulted in similar bulk factor values as a 16-h room temperature debulk (RTD), suggesting that this shorter cycle can be used as a replacement, resulting in a 26–71% cycle time reduction. For these thick sixteen ply laminates, up to six percent and five percent pore area can be expected of laminates processed RTD and HD, respectively. The highest short beam strength was achieved by a plain weave material intended for out-of-autoclave processing and lowest pore area was achieved by a 5-harness material intended for autoclave processing.

Development of a label-free ATP image sensor for analyzing spatiotemporal patterns of ATP release from biological tissues

Abstract We investigated the output characteristics of a label-free, 37.3 μm pitch, 128 × 128 pixel adenosine-5'-triphosphate (ATP) image sensor, in which different thicknesses of ATP-degrading enzyme apyrase were deposited using the poly-ion complex (PIC) method. ATP was detected based on the changes in the concentration of hydrogen ions (H+) generated by enzymatic reactions. Enzyme films of different thicknesses were formed on the surface of the sensor by controlling the volumes of the PIC solution. A reduction in the enzyme film thickness (0.2 μm thickness), improved the sensitivity of the ATP sensor, and a clear image than that obtained with a sensor with a thicker film (2.3 μm thickness) was obtained. Additionally, the detection limit for the 0.2-μm-thick sensor was as low as 10 μM, whereas that of the 2.3-μm thick sensor was 100 μM. To examine ATP release from biological tissues, we placed a mouse hippocampal slice on the sensor with the 0.2-μm-thick film and electrically stimulated the nerve fiber (i.e., the Schaffer collateral). The neuronal stimulation evoked significant changes in the output signals of the hippocampal slice but not in the sensor area which was not in contact with tissue. An elevation in the output signal was initiated at the stimulated site with a maximum increment of 5 mV, and the signal traveled along the neuronal fibers. By reducing the film thickness, we successfully developed a high-sensitivity label-free ATPo image sensor with a high spatiotemporal resolution, which allows imaging of endogenous ATPo released from the hippocampus.

Quantifying the performance of a hybrid pixel detector with GaAs:Cr sensor for transmission electron microscopy

Hybrid pixel detectors (HPDs) have been shown to be highly effective for diffraction-based and time-resolved studies in transmission electron microscopy, but their performance is limited by the fact that high-energy electrons scatter over long distances in their thick Si sensors. An advantage of HPDs compared to monolithic active pixel sensors is that their sensors do not need to be fabricated from Si. We have compared the performance of the Medipix3 HPD with a Si sensor and a GaAs:Cr sensor using primary electrons in the energy range of 60–300 keV. We describe the measurement and calculation of the detectors’ modulation transfer function (MTF) and detective quantum efficiency (DQE), which show that the performance of the GaAs:Cr device is markedly superior to that of the Si device for high-energy electrons.

Direct conversion X-ray sensing nature of bismuth (III) iodide thick films

In this work, Bismuth (III) iodide (BiI3) thick film-based direct conversion X-ray sensor was fabricated for low-dose (mGy) X-ray detection since it exhibits high attenuation against 70 keV X-ray photon energy that is about 4.70 cm2/g. Prior to the device fabrication, commercial BiI3 powder was characterized for their phase, morphology, and optical properties. Nanocrystalline BiI3 film with ~211 µm thickness was coated on wet-etch-derived interdigitated electrode by the glass rod sliding technique using Poly(vinylidene fluoride co-hexafluoropropylene) as a binder. The photocurrent induced under the illumination of X-ray was measured for four different doses 7.97, 5.05, 2.56, and 1.28 mGy, then the observed photocurrent characteristics were applied to estimate sensitivity of the device and it was found to be 0.053, 0.045, 0.037, and 0.030 nC/mGy cm3, respectively. The response rate of our sensor was found to be linear with the exposed X-ray doses and it offers the applicability of BiI3 thick film in the direct conversion X-ray sensor fabrication for real-time applications.

Methane Sensitivity of Alpha-Fe2O3 Obtained from Pechini Combustion Synthesis using Different Organic Fuels

Phase-pure alpha-iron-oxide (α-Fe2O3) nano-powders were obtained via Pechini gel-combustion using iron nitrates as an oxidant and different organic compounds (L-alanine, glycine, citric acid, oxalic acid, tartaric acid and urea) as fuels. The complex precursors isolated before the system's combustion were characterized by thermal analysis (TGA). After combustion, the as-synthesized powders were calcined at 600°C to obtain the α-Fe2O3 phase and eliminate the residual carbon. The powders prepared using different fuels were characterized using x-ray diffraction and field emission scanning electron microscopy. n-type gas sensitivity of thick film resistive sensors fabricated by using α-Fe2O3 powders was investigated in detail and it was observed that amongst the different fuels, citric acid-derived α-Fe2O3 is methane selective at 120°C operating temperature, examined in the presence of other similar types of resistive gas analyses of the same concentrations.

Free-standing, thin-film sensors for the trace detection of explosives

In a world focused on the development of cybersecurity, many densely populated areas and transportation hubs are still susceptible to terrorist attacks via improvised explosive devices (IEDs). These devices frequently employ a combination of peroxide based explosives as well as nitramines, nitrates, and nitroaromatics. Detection of these explosives can be challenging due to varying chemical composition and the extremely low vapor pressures exhibited by some explosive compounds. No electronic trace detection system currently exists that is capable of continuously monitoring both peroxide based explosives and certain nitrogen based explosives, or their precursors, in the vapor phase. Recently, we developed a thermodynamic sensor that can detect a multitude of explosives in the vapor phase at the parts-per-trillion (ppt) level. The sensors rely on the catalytic decomposition of the explosive and specific oxidation–reduction reactions between the energetic molecule and metal oxide catalyst; i.e. the heat effects associated with catalytic decomposition and redox reactions between the decomposition products and catalyst are measured. Improved sensor response and selectivity were achieved by fabricating free-standing, ultrathin film (1 µm thick) microheater sensors for this purpose. The fabrication method used here relies on the interdiffusion mechanics between a copper (Cu) adhesion layer and the palladium (Pd) microheater sensor. A detailed description of the fabrication process to produce a free-standing 1 µm thick sensor is presented.

Thickness sensor for drying paints using THz spectroscopy.

Optical terahertz technology has, despite its exciting properties, such as transparency of visibly opaque materials, 30 years after its technological breakthrough, not found a widespread application with societal relevance. Main causes are its maturity and costs. If, however, the uniqueness of both THz radiation and time-domain spectroscopy is used to close a technological gap in the right market sector, we here show that successful applications are in reach. We have chosen the automotive industry, where the optimization of coatings applied in the paint shop is of longstanding concern for this most expensive unit of the car production line. Here we report on the development of a THz-based sensor system. We study the light-matter interaction of drying polymer coatings and use advanced novel signal processing algorithms to determine the state of matter of drying paints. This very first sensor system for the inspection of wet coatings that accurately predicts the eventual dry thickness without requiring paint-type calibration. Industrial robustness is guaranteed by a bespoke optical beam design. Our sensor demonstrator outperforms state-of-the-art thickness sensors applied on dry coatings by a factor three and is expected to become a game changer for the paint shop, where today's scrap rates worldwide are as high as one car body per minute.

A highly sensitive cobalt chromite thick film based trace acetone sensor with fast response and recovery times for the detection of diabetes from exhaled breath

Acetone is known as the breath biomarker of diabetes. In this paper we have reported on a highly sensitive, stable cobalt chromite (CoCr2O4) thick film-based trace acetone sensor with quick response and recovery times promising for the detection of diabetes from exhaled breath. CoCr2O4 nanoparticles were prepared by a cost-effective and easy sol-gel method. The as prepared nanoparticles were well characterized by sophisticated characterization techniques, such as, XRD, FESEM. TEM, HRTEM, XPS, and BET. Further these nanoparticles were exploited to fabricate a Taguchi type chemoresistive sensor using a customized drop coater. The developed sensor was characterized by I–V measurement. The developed sensor exhibited high p-type response towards 1 ppm of acetone vapor (~3.81 folds), and appreciable resolution between 1 ppm, 2 ppm (response = ~4.82 folds), and 5 ppm (response = ~6.64 folds) acetone vapor at 300 °C. Further, the sensor exhibited fast response and recovery times of ~1.65 s and ~62 s, respectively. Also, the response of the sensor to 1 ppm acetone vapor is appreciably higher than that of 0.2 ppm ethanol, 0.25 ppm ammonia vapor, and saturated moisture. Finally, the sensor is stable for at least 6 months and exhibits repeatable measurements.