Gas sensors usually exhibit lack of selectivity, require frequent calibration, exhibit drift of the response and a lot of factors, such as humidity or ambient temperature, influence their performance. Different approaches can be used to overcome this shortcomings. Building arrays of different sensors and usage of pattern recognition methods to analyze responses of elements in array is a popular approach. In this paper the approach of using a single sensor and special measurement techniques will be presented. Instead of increasing the number of sensors an additional information, needed to improve the properties of the sensor, is obtained from the response signal of a single sensor.
A periodic temperature modulation using sinusoidal heater voltage was applied to a commercial SnO2 semiconductor gas sensor. Resulting resistance response of the sensor was analyzed using a feature extraction method based on Fast Fourier Transformation (FFT). The amplitudes of the higher harmonics of the FFT from the dynamic nonlinear responses of measured gas were further utilized as an input for Artificial Neuron Network (ANN). Determination of the concentration of chlorine was performed. Moreover, this work evaluates the sensor performance upon sinusoidal temperature modulation.
KEYWORDS: Gas sensors, Feature extraction, Sensors, Electronics, Modulation, Gases, Temperature metrology, Statistical analysis, Data analysis, Data acquisition
Gas analyzers based on gas sensors are the devices which enable recognition of various kinds of volatile compounds. They have continuously been developed and investigated for over three decades, however there are still limitations which slow down the implementation of those devices in many applications. For example, the main drawbacks are the lack of selectivity, sensitivity and long term stability of those devices caused by the drift of utilized sensors. This implies the necessity of investigations not only in the field of development of gas sensors construction, but also the development of measurement procedures or methods of analysis of sensor responses which compensate the limitations of sensors devices. One of the fields of investigations covers the dynamic measurements of sensors or sensor-arrays response with the utilization of flow modulation techniques. Different gas delivery patterns enable the possibility of extraction of unique features which improves the stability and selectivity of gas detecting systems. In this article three utilized flow modulation techniques are presented, together with the proposition of the evaluation method of their usefulness and robustness in environmental pollutants detecting systems. The results of dynamic measurements of an commercially available TGS sensor array in the presence of nitrogen dioxide and ammonia are shown.
The practical application of human nose for fragrance recognition is severely limited by the fact that our sense of smell is subjective and gets tired easily. Consequently, there is considerable need for an instrument that can be a substitution of the human sense of smell. Electronic nose devices from the mid 1980s are used in growing number of applications. They comprise an array of several electrochemical gas sensors with partial specificity and a pattern recognition algorithms. Most of such systems, however, is only used for qualitative measurements. In this article usage of such system in quantitative determination of gas concentration is demonstrated. Electronic nose consist of a sensor array with eight commercially available Taguchi type gas sensor. Performance of three different pattern recognition algorithms is compared, namely artificial neural network, partial least squares regression and support vector machine regression. The electronic nose is used for ammonia and nitrogen dioxide concentration determination.
Recent increasing demand for new eco-friendly materials and for low cost fabrication process for use in optical sensors field, raise concern about alternative materials for this application. We have designed two glass-ceramics compositions from the quaternary ROAl2O3- SiO2-B2O3(R=Ba) alkali-earth aluminum silicate system, labeled B72 and B69, with high refractive index (>1.6), large values of Abbe number (94.0 and 53.0, respectively), and free of lead and arsenic. We present an analysis and discussion of experimental optical properties, thermal and thermo-chemical stability along with important properties such as transition temperature (Tg), onset of crystallization (Tx) as well transport properties as ionic conductivity behavior in the quaternary glass-ceramic system containing boron for use as optical sensors. Complex Impedance Spectra (Bode Plot) and Potentiodynamic Polarization curves (Tafel plots) measurements were carried out in the temperature range of 600 to 850°C. The most probable conductivity mechanism is a thermally activated process of mobile ions overcoming a potential barrier (EA), according to the Arrhenius regime. Here we report that charge transfer is caused by the flux of electrons, in the region of elevated temperatures (>700°C), and is affected by immiscibility of crystals, nucleation and growth type, that causes phase separation. We found conductivity (σ) values from 10-9 to 10-5 S/cm at temperatures between 700 and 850°C. Our results highlight a need for research on ion mobility in the glassy network above the transition range, and the effect cause by metastable immiscibility in the alkaline-earth glasses are exposed. The two glass compositions B72 and B69 can be tailored by proper use as glassy optical sensor.
One of the types of gas sensors used for detection and identification of toxic-air pollutant is an electro-catalytic gas sensor. The electro-catalytic sensors are working in cyclic voltammetry mode, enable detection of various gases. Their response are in the form of I-V curves which contain information about the type and the concentration of measured volatile compound. However, additional analysis is required to provide the efficient recognition of the target gas. Multivariate data analysis and pattern recognition methods are proven to be useful tool for such application, but further investigations on the improvement of the sensor’s responses processing are required. In this article the method for extraction of the parameters from the electro-catalytic sensor responses is presented. Extracted features enable the significant reduction of data dimension without the loss of the efficiency of recognition of four volatile air-pollutant, namely nitrogen dioxide, ammonia, hydrogen sulfide and sulfur dioxide.
Results of impedance measurements of humidity sensors with epoxy resins containig quarternary ammonium salts are presented in this paper. The humidity sensitive membranes were prepared from polyethyleneimine (PEI). PEI was cross-linked using 1,4-butanediol diglycidyl ether (BDDGE) and glycidyl trimethyl ammonium chloride (GTMAC) was added as a humidity sensitive epoxy monomer.
Electrocatalytic sensors belong to a relatively new group of solid state electrochemical gas sensors. Its working principle is based on electric current acquisition, while voltage ramp is applied to the sensor. The current-voltage plot has unique shape, which depends on surrounding gas type and its concentration. Response of the electrocatalytic gas sensor contains significantly more information in comparison with typical amperometric or potentiometric one. Methods of sensors response analysis, which was employed so far, did not fully utilize this feature. Moreover, shape of sensor response, in case of some gases or mixtures, is hard to be interpreted with traditional techniques. In this work more advanced methods to analyze electrocatalytic gas sensor response, which are based on explorative and confirmative techniques as well as artificial neural network, are presented.
In this paper preparation method of nano-porous alumina based humidity sensors is presented. Investigation of relation between technological process parameters, sensor's porous layer structure and electric parameters is main aim of this study. Surface morphology was investigated by scanning electron microscopy. Impedance spectroscopy was used to identify electrical parameters of the sensor.
The effect of humidity influence on characteristics of a ceramic sensor with a porous dielectric Al2O3 layer is presented. Influence of chosen electrolytic process parameters on electrical properties of the sensor is shown. The experimental data of two groups of sensors are interpreted using two, known from literature, electric equivalent circuits.
Construction and properties of electrocatalytic gas sensor based on samarium-doped ceria solid electrolyte are described. Electrocatalytic sensors form a new group of gas sensor, which employ kinetics of controlled chemical reaction. Measurements in mixtures of synthetic air and nitrogen dioxide are shown. Current-voltage response has unique shape, which depends on NO2 concentration. Influence of voltage sweep rate and temperature on sensor characteristics is reported. The constructed sensor can be used for nitrogen dioxide monitoring.
In the present paper, results of computer simulation of cyclic voltammetry applied to electrocatalytic solid state sensor are presented. The computer software developed by D.Gosser is based on explicit finite difference method. The software is devoted for the simulation of cyclic voltammetry experiments in liquid electrochemistry. However the software is based on general electrochemical rules and may be used for simulation of experiments in solid state electrochemistry. The electrocatalytic sensor does not have a reference electrode and therefore it is necessary to employ virtual reference electrode into the model of the sensor. Data obtained from simulation are similar to measurement one what confirms correctness of assumed sensing mechanism.
In the paper the amperometric properties of polymer humidity sensor based on polythyleneimine are presented. Usually properties of this sensor are examined by means of impedance spectroscopy. The new approach is proposed. It is shown that the current flow in the investigated sensor is a result of the electrode reaction at the anode. The quasi-static diffusion current is a linear function (in the log-lin scale) of relative humidity, so this sensor can be used as an amperometric. An equivalent circuit, containing the elements representing diffusion effect, has been proposed. The shape of impedance plots show diffusion related process.
The results of impedance measurements of thin film polymer humidity sensors are presented in this paper. The sensors were made of chemically modified polyethyleneimine, spread on alumina substrate with comb type gold electrodes. Electrical properties of the sensors are strongly dependent on relative humidity (RH). The influence of the selected cross-linking agents on the properties, measuring range, and technology of preparation of the sensors is discussed.
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