Gas sensors are fundamental for continuous online monitoring of volatile organic compounds. Gas sensors based on semiconductor materials have demonstrated to be highly competitive, but are generally ...made of expensive materials and operate at high temperatures, which are drawbacks of these technologies. Herein is described a novel ethanol sensor for room temperature (25 °C) measurements based on hematite (α‑Fe
O
)/silver nanoparticles. The AgNPs were shown to increase the oxide semiconductor charge carrier density, but especially to enhance the ethanol adsorption rate boosting the selectivity and sensitivity, thus allowing quantification of ethanol vapor in 2-35 mg L
range with an excellent linear relationship. In addition, the α-Fe
O
/Ag 3.0 wt% nanocomposite is cheap, and easy to make and process, imparting high perspectives for real applications in breath analyzers and/or sensors in food and beverage industries. This work contributes to the advance of gas sensing at ambient temperature as a competitive alternative for quantification of conventional volatile organic compounds.
This paper presents a developed methodology for the detection of bovine milk adulteration by applying electrical impedance measurements. This parameter allows characterizing samples of raw and ...ultrahigh temperature milk, adulterated with different proportions of drinking water, deionized water, hydrogen peroxide (H 2 O 2 ), sodium hydroxide (NaOH), and formaldehyde (CH 2 O). The samples were electrically analyzed by applying the electrical impedance spectroscopy measurements and a dedicated microcontroller system, developed for this application. In both cases, the measures allowed classifying the milk quantitatively, enabling the development of real-time monitoring systems for fraud detection in milk composition. A classification of the results is proposed through a k-nearest neighbors algorithm that allows to quantitatively qualify the samples of pure and adulterated milk.
Water is the most valuable natural resource. To preserve this good, several water monitoring systems for pipe networks have been proposed. However, there is a lack of research on the development of ...high-frequency electromagnetic sensors for this task. This study proposes a non-destructive technique to locate carrying water polyvinyl chloride pipes using a microstrip patch antenna. An experimental apparatus was mounted and the resonant frequency and Q factor of the antenna were measured for different relative positions between the sensor and the pipe filled with water. To detect the pipe position, experimental data were trained and tested by applying an approach based on support vector machines. The best results were from using a simple linear kernel, which allowed 100% accuracy using a 30% fraction of data used for holdout validation.
The research on new materials, fabrication processes, and characterization methods aims at obtaining sensors with low cost, high sensibility, and possibility of integration with electronic circuits. ...Recently, several works have focused on the development of gas sensors based on nanomaterials deposited on insulating platforms due to the remarkable sensing properties of such materials and simple device fabrication methods. However, the interference of such insulating platforms in the sensing properties of a miniaturized sensor becomes non-negligible depending on the dimensions, the type and amount of material, and the gas species analyzed. Thus, this paper proposes the use of interdigital aluminum microelectrodes patterned on a glass substrate to evaluate the influence of adsorption and desorption mechanisms of humidity and volatile organic compounds on this insulating surface. By analyzing the electrical conduction changes when the device is exposed to the mentioned vapors, we demonstrate that this influence is quite significant, as the electrical resistance of the glass insulating platform presented pronounced and fast resistance variation with repeatability and low drift. In addition, the selectivity among the experimented gas species was achieved by applying principal component analysis and supervised linear discriminant analysis classification methodologies, obtaining a success rate of 94% by using a cross-validation technique. The results show that the sensing properties of insulating platforms must be considered in some situations because they can affect the response of sensors based on nanomaterials deposited on insulating substrates.
Vanadium pentoxide xerogels (VXG) incorporating
meso(3- and 4-pyridyl)porphyrin cobalt(III) species coordinated to four Ru(bipy)
2Cl
+ complexes were employed as gas sensing materials capable of ...detecting small amounts of water in commercial ethanol and fuel supplies. According to their X-ray diffraction data, the original VXG lamellar framework was maintained in the nanocomposite material, but the interlamellar distance increased from 11.7 to 15.2
Å, reflecting the intercalation of the porphyrin species into the vanadium pentoxide matrix. The films generated by direct deposition of the nanocomposite aqueous suspensions exhibited good electrical and electrochemical performance for application in resistive sensors. The analysis of water in ethanol and fuels was carried out successfully using an especially designed electric setup incorporating a laminar gas flow chamber and interdigitated gold electrodes coated with the nanocomposites.
•A FE device characterization system based on emission image mapping is proposed.•The system associates images with current to characterize FE devices during a trial.•Real-time 3D graphs and ...histograms are examples of field emission analyses proposed.•The system evaluates individual emitters according to their emission characteristics.•Qualitative and quantitative information about FE device performance are extracted.
Field Emission devices (FE) have been proposed as efficient electron sources for several applications such as electron microscopy and vacuum sensors. Evidently, characterization methods applied during development phase of FE devices are crucial to evaluate aspects related with their working stability, homogeneity, and efficiency. However, the traditional methods provide only overall information about such characteristics, which difficult to improve the performance of these devices and their integration with electronics. To overcome this problem, this work presents an alternative system to characterize FE devices through electron emission imaging in real-time. The proposed system acquires I-V features of FE devices, while a video camera captures the emission image from a phosphor screen. Virtual instrumentation based on LabVIEW manages the whole system including measurement instruments, image capture, and data processing. As a result, histograms, 3D maps, and other FE analyses provide information about emitting characteristics of selected regions of interest. The main contribution of this work is to offer an important tool for the analyses of electron emission, by the association of captured images with the localized emission current. The extracted information from our system can efficiently support the characterization and the development of FE devices.
Vanadium pentoxide xerogel films deposited onto gold microelectrodes were micropatterned by thermally induced conversion into crystalline α-V 2 O 5 , using optical lithography written at the focus of ...a confocal Raman microscope. The laser scribing process improved the electric contact and promoted the n-doping of the film with V IV ions. In this way, a field effect transistor like device was constructed and successfully applied as humidity sensor, where the combined lithographic design and the application of a negative back gate field (V G = -10.0 V) boosted the source-drain current by a hundred times, leading to a large gain in sensitivity.
Didactic platforms, used in real-time digital signal processing courses, are generally dedicated digital signal processors or field-programmable gate arrays. These devices are expensive and difficult ...to program, preventing their widespread use in signal processing courses. On the other hand, the new technology of digital signal controllers, microcontrollers with floating point and mathematical operations, can reduce the cost of dedicated platforms for real-time digital signal processors, facilitating the development of digital signal processors projects and educational applications, such as teaching adaptive filters. Here, we present a low-cost didactic platform for developing real-time adaptive filters using the digital signal processors hardware based on the ARM Cortex-M7 processor. We present the theoretical aspects of the least mean squares and normalized least mean squares algorithms and an experimental script to help students learn real-time adaptive filters. We also describe the platform structure and the performance measurement, in terms of mean square error, signal-to-noise ratio, and computational efficiency. Finally, we present a brief discussion on the use of this platform in classes and the improvement in the student engagement and attendance.
This paper presents a relatively simple method to fabricate field-emitter arrays from silicon substrates. These devices are obtained from silicon micromachining by means of the HI-PS technique - a ...combination of hydrogen ion implantation and porous silicon used as sacrificial layer. Also, a new process sequence is proposed and implemented to fabricate self-aligned integrated field-emission devices based on this technique. Electrical characteristics of the microtips obtained show good agreement with the Fowler-Nordheim theory, which are suitable for the proposed application.
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