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The investigation into a novel thick film material, a combination of MnO, ZnO and Fe 2 O 3 , is documented for humidity sensing applications. To date, no other accounts using this combination for humidity sensing have been reported in the literature. Different paste preparations have been investigated in full, including the effect of increasing polymer content for the polymer samples, and the effect of different firing profiles for the cermet samples. RuO 2 has been considered as a method for improving the conductivity of the samples. DC and AC conduction studies have been carried out on different polymer and cermet pastes. From the AC conduction studies, it is confirmed that electronic tunnelling is the dominant conduction mechanism. From the DC conduction studies, space charge limited conduction has been observed. A large number of sensor samples have been manufactured and tested. The fabrication and characterization of three typical sensor samples is presented and discussed in this paper, sample 1: vacuum-fired cermet sensor, sample 2: air-fired cermet sensor and sample 3: 10:1 polymer sensor. The sensor pattern consists of an interdigitated conductor on top of which a 30μm thick sensing layer is printed using screen-printing technology. The thermal effect of the sensors is quite low, ranging from a minimum of 0.0037%/ o C (sample 1) to a maximum of 0.0085%/ o C (sample 3). In comparison, the measured humidity sensitivity values are much higher, ranging from 0.0356%/RH% (sample 1) to 1.697%/RH% (sample 2). All the samples exhibit a low drift over a 1 year span, low hysteresis, high linearity and reasonably fast response times.
In this report, we fabricated and characterized a high frequency transducer with lead-free piezoelectric thick film, 0.948(K 0.5 Na 0.5 )NbO 3 –0.052LiSbO 3 , formed on a platinized silicon substrate by aerosol-deposition. X-ray diffraction analysis and scanning electron microscopy revealed that the film had well-crystallized perovskite structure and was dense and crack-free microstructure. The film showed the dielectric constant of 766 at 1kHz and the remnant polarization of 13.2μC/cm 2 . The film was used to fabricate a high frequency needle transducer with an aperture size of ∼200μm. The center frequency of the transducer was 197MHz and the −6dB bandwidth was 50% which was comparable to the PZT-based transducers. A 6-μm tungsten wire phantom was imaged to assess the −6dB axial and lateral resolution of the transducer, which were found to be 12 and 66μm, respectively.
Novel glass electrodes for the determination of cations with reversible internal solid contact are introduced. They are based on a semiconducting zinc oxide layer with a maximum thickness of 1 µm in contact with ion selective glasses on one side and with a metal layer on the other side. The metal oxide layer is thereby generated either by ultrasonic spray pyrolysis from zinc acetate solution, by electrochemical deposition from zinc nitrate solution or by spin coating from a dispersion of ZnO in an organic binder. A following activation in a palladium chloride solution allows the chemical reductive deposition of NiP as electronic conductor. Dipping-type and flow through electrodes as well as planar glass electrodes in thick film technology fabricated in the above-mentioned method are described. In this case gold electrodes are applied by screen printing on isolated steel substrates. The zinc oxide layers, created in different manners, are covered afterwards with cation selective glasses in thick film technology. They cause a stabilisation of the half-cell potentials of the all solid state indicator electrodes proved by suitable measurements.
In order to meet future NOx emission standards for commercial vehicles, so called urea selective catalytic reduction (SCR) systems will be introduced. In the SCR converter ammonia serves as a reducing agent for selective NOx reduction. An ammonia exhaust gas sensor is required to optimize the injected amount of urea and to assure that no ammonia emissions occur. This paper reports on the development of a selective thick film ammonia sensor that can meet the requirements for applications in automotive exhaust gas. Main topic is the development of the functional gas sensitive film. Zeolites were successfully investigated as selective functional materials for this kind of sensors. It is shown, that the type of the zeolite, its module, the working temperature and the working frequency determine sensitivity and selectivity of the sensor. From the most promising zeolite material—zeolite H-ZSM5 with a module of 140, sensors were manufactured and tested in engine test benches. It could be shown, that this kind of sensors is a useful tool to control an ammonia-SCR system and to detect ammonia slip.
We are presenting here a new approach to gas sensor, using the electromagnetic (e.m) properties variation of some sensitive materials in the presence of gas at ultrahigh frequencies (ca. 1 GHz). The chemical sensor basically consists of a microwave resonator to which a sensitive coating is added. The e.m perturbation can be seen through a frequency variation measurement when the sensor serves as feedback element in an oscillator chain. After the development of a narrow-band-pass filter, a permittivity variation study is done, thanks to an e.m simulator HP-MDS. Then a humidity sensor is designed and tested. A good sensitivity as well as a great reversibility are obtained.
Tungstated-zirconia has been tested as a functional material for a selective ammonia gas sensor. The sensor has been found to respond consistently and rapidly to changes in concentration of ammonia in the oxygen rich and moist gas mixture at 673K. The sensor showed negligible cross-sensitivity to propene, CO, and NO. From characterizations of tungstated-zirconia by XRD, Raman, UV–vis, high-resolution TEM, and ammonia-TPD, it was found that subnano-sized polytungstate clusters are uniformly supported on the zirconia surface, and the strong acid sites derived from the polytungstate clusters are suggested to effectively work as selective adsorption sites for ammonia. The fabricated ammonia sensor utilizing tungstated-zirconia is expected to be useful for controlling the injection amount of ammonia in urea-SCR systems.
Exhaust gas recirculation (EGR) is an effective means to reduce NO x emissions of internal combustion engines without increasing fuel consumption. Up to now, only complex procedures to determine the exhaust gas recirculation rate are available. Here, a novel sensor device is suggested that measures directly at one position and with only one single sensor device the concentration of a tracer gas at the intake manifold and at the exhaust gas recirculation entry point. The tracer gas (e.g. CO 2 or NO) is formed during combustion and is only in a negligible concentration present in the fresh air. A solid ion conducting membrane constitutes the core of the sensor device and separates both gas atmospheres. The sensor voltage depends Nernst-like on the exhaust gas recirculation rate. Two types of sensors, one comprising a NO + –β″-Al 2 O 3 solid electrolyte membrane and one using a KNO 2 -covered Na + –β″-Al 2 O 3 membrane showed a slope in the semilogarithmic plot almost as expected from theory for a single electron process. It was shown that the sensor output voltage is not dependent on the air-to-fuel ratio. Further research should address solid oxygen ion conducting membranes using a double side mixed potential principle.
In this paper Cu2O nanoparticles were prepared and used for the construction of novel electrochemical voltammetric biosensor for the simultaneous detection of adenine and guanine. Cu2O nanoparticles were synthesized via simple wet chemical route, where glucose was used as a reductant. The nanoparticles were characterized by SEM and XRD analysis, which showed the presence of spherical aggregations with diameter of 1000nm. These nanoparticles were successfully used for fabrication of spray-coated and screen-printed working electrodes on alumina substrate for the electrochemical detection of purine bases. We observed that Cu(I) reacts with adenine to form insoluble complex that accumulates on the electrode surface and causes the decrease of current response. In the case of guanine, we did not observed any significant decrease of current response which is probably caused by adsorption of guanine on the electrode surface.
In pellistor gas sensors, the heat exhaust produced by the catalytic combustion of reducing gases increases the temperature of the device. A typical pellistor consists of a platinum wire supported in an alumina bead impregnated with a finely dispersed noble metal like palladium. The platinum wire serves as heater of the bead to its operating temperature and as a thermometer. In reality, the temperature measured by the resistance of the Pt wire is compared to that of a reference element which has a similar structure but without any catalytic activity. No selectivity of such a device has to be expected since the catalytic combustion of any combustible gas will lead to a temperature increase of the device. In order to try to achieve selectivity to methane, we have in a first step exploited the differential activity of palladium and platinum by using two screen-printed pellistors, one based on Pd and the other on Pt. At around 400°C, all reducing gases including methane are oxidized by Pd whereas Pt oxidized all gases except methane. In order to extend the recognition process to combustible gases other than methane, that is to propane, and ethanol vapour, a small array of four pellistors with various percentages of Pd and Pt has been elaborated with thick film technology, which is very valuable for realizing series of similar sensors, required in arrays. The four microcalorimetric sensors are exposed to various gases and various concentration values. A recognition of methane, propane, and ethanol is obtained by neural network techniques. The network consists of three layers: an input layer; a hidden layer; and an output layer which permits gas identification. Back-propagation is used as the learning algorithm. In this case, the selectivity of the system is demonstrated.
An amperometric glucose biosensor strip based on a three electrodes (counter, reference and working) planar configuration was fabricated using thick film technology. Glucose oxidase (GOD) was immobilized in the bulk of a graphite-epoxy composite paste. This paste was used to screen-print the working electrode on a glass fibre board. The integration on the same support of pseudo-reference electrode was obtained by screen printing a commercial silver-epoxy paste, and subsequent electrochemical chlorinization in KCl 1 M at +1 V (SCE). Finally, the counter electrode was integrated using the same technique by depositing a graphite-epoxy composite paste, taking into account the counter/working electrode area ratio. Response characteristics of a glucose biosensor strip based on this transducer are similar to those of previously reported one electrode configuration glucose biosensor constructed using the same biocomposite material [Galan-Vidal and Munoz, Sens. Actuators B 45 (1997) 55-62].
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Electrochemistry has superior properties respect to the other measurement systems because of the rapid, simple and sensitive characteristics. For all these reasons, electrochemical sensors are playing a key role in many scientific sectors.Planar electrochemical sensors present many advantages respect to the three-dimensional devices, but this technology requires the use of specialty chemicals to meet the new functional requirements of planarization and miniaturization. In this paper, some production techniques and procedures to obtain planar electrochemical sensors are reported, together with their applications.
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Content accesss denied pH Monitoring: a review
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Glass pH electrodes are being utilized for the measurement of pH values using liquid internal reference systems, which had been introduced on principle nearly hundred years ago and are still existing. To avoid several drawbacks in the practical usage of these kinds of chemical sensors, every effort has been made to develop an all-solid-state electrode with properties that are comparable to those of the conventional glass electrode. Metal oxide electrodes like RuO2 or IrO x are a low-priced alternative. Different concepts for substituting the conventional (aqueous) reference system by solid systems and also for changing the classical bulb shape design to a planar structured one have been proposed. A suitable reference system can be achieved by means of modification of classic reference electrodes by employing a new type of mixed conducting oxides. Both metal oxide and glass electrodes can be screen-printed on substrate materials like ceramics and plastics etc. to get miniaturized all-solid-state electrodes. pH sensors based on field effect transistors (FET) become more important. However, up to now an equivalent FET compatible reference electrode is not available.
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