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Sensors, Volume 7, Issue 2 (February 2007), Pages 157-221

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Research

Open AccessArticle A Modified Adaptive Stochastic Resonance for Detecting Faint Signal in Sensors
Sensors 2007, 7(2), 157-165; doi:10.3390/s7020157
Received: 16 July 2006 / Accepted: 5 February 2007 / Published: 15 February 2007
Cited by 5 | PDF Full-text (134 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, an approach is presented to detect faint signals with strong noises in sensors by stochastic resonance (SR). We adopt the power spectrum as the evaluation tool of SR, which can be obtained by the fast Fourier transform (FFT). Furthermore, [...] Read more.
In this paper, an approach is presented to detect faint signals with strong noises in sensors by stochastic resonance (SR). We adopt the power spectrum as the evaluation tool of SR, which can be obtained by the fast Fourier transform (FFT). Furthermore, we introduce the adaptive filtering scheme to realize signal processing automatically. The key of the scheme is how to adjust the barrier height to satisfy the optimal condition of SR in the presence of any input. For the given input signal, we present an operable procedure to execute the adjustment scheme. An example utilizing one audio sensor to detect the fault information from the power supply is given. Simulation results show that th Full article
(This article belongs to the Special Issue Intelligent Sensors)
Open AccessArticle A Novel Type of Tri-Colour Light-Emitting-Diode-Based Spectrometric Detector for Low-Budget Flow-Injection Analysis
Sensors 2007, 7(2), 166-184; doi:10.3390/s7020166
Received: 31 July 2006 / Accepted: 13 February 2007 / Published: 23 February 2007
Cited by 8 | PDF Full-text (227 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we describe a low-cost spectrometric detector that can be easily assembled in a laboratory for less than €80 with a minimal number of optical components and which has proved sensitive and flexible enough for real-life applications. The starting point [...] Read more.
In this paper we describe a low-cost spectrometric detector that can be easily assembled in a laboratory for less than €80 with a minimal number of optical components and which has proved sensitive and flexible enough for real-life applications. The starting point for the idea to construct this small, compact low-cost spectrometric detector was the decision to use a tri-colour light-emitting diode (LED) of the red-green-blue (RGB) type as a light source with the objective of achieving some flexibility in the selection of the wavelength (430 nm, 565 nm, 625 nm) but avoiding the use of optical fibres. Due to the dislocation of the emitters of the different coloured light, the tri-colour LED-based detector required an optical geometry that differs from those that are described in literature. The proposed novel geometry, with a coil-type glass flow-through cell with up to four ascending turns, proved useful and fit for the purpose. The simplicity of the device means it requires a minimal number of optical components, i.e., only a tri-colour LED and a photoresistor. In order to make a flow-injection analysis (FIA) with the spectrometric detector even more accessible for those with a limited budget, we additionally describe a low-cost simplified syringe-pump- based FIA set-up (€625), the assembling of which requires no more than basic technical facilities. We used such a set-up to test the performance of the proposed spectrometric detector for flow-injection analyses. The tests proved its suitability for real-life applications. The design procedures are also described. Full article
(This article belongs to the Special Issue Sensors in Flow Analysis)
Open AccessArticle Influence of Thickness on Ethanol Sensing Characteristics of Doctor-bladed Thick Film from Flame-made ZnO Nanoparticles
Sensors 2007, 7(2), 185-201; doi:10.3390/s7020185
Received: 21 February 2007 / Accepted: 27 February 2007 / Published: 28 February 2007
Cited by 38 | PDF Full-text (566 KB) | HTML Full-text | XML Full-text
Abstract
ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zincnaphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particleproperties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced bymixing the particles into an organic paste composed of [...] Read more.
ZnO nanoparticles were produced by flame spray pyrolysis (FSP) using zincnaphthenate as a precursor dissolved in toluene/acetonitrile (80/20 vol%). The particleproperties were analyzed by XRD, BET, and HR-TEM. The sensing films were produced bymixing the particles into an organic paste composed of terpineol and ethyl cellulose as avehicle binder and were fabricated by doctor-blade technique with various thicknesses (5,10, 15 μm). The morphology of the sensing films was analyzed by SEM and EDS analyses.The gas sensing characteristics to ethanol (25-250 ppm) were evaluated as a function of filmthickness at 400°C in dry air. The relationship between thickness and ethanol sensingcharacteristics of ZnO thick film on Al2O3 substrate interdigitated with Au electrodes wereinvestigated. The effects of film thickness, as well as the cracking phenomenon, though,many cracks were observed for thicker sensing films. Crack widths increased withincreasing film thickness. The film thickness, cracking and ethanol concentration havesignificant effect on the sensing characteristics. The sensing characteristics with variousthicknesses were compared, showing the tendency of the sensitivity to ethanol decreasedwith increasing film thickness and response time. The relationship between gas sensingproperties and film thickness was discussed on the basis of diffusively and reactivity of thegases inside the oxide films. The thinnest sensing film (5 μm) showed the highest sensitivityand the fastest response time (within seconds). Full article
Open AccessArticle Home-made Detection Device for a Mixture of Ethanol and Acetone
Sensors 2007, 7(2), 202-213; doi:10.3390/s7020202
Received: 22 January 2007 / Accepted: 27 February 2007 / Published: 28 February 2007
Cited by 2 | PDF Full-text (142 KB) | HTML Full-text | XML Full-text
Abstract
A device for the detection and determination of ethanol and acetone wasconstructed, consisting of a packed column, a chamber with a sensor head, 2 dc powersupplies, a multimeter and a computer. A commercially available TGS 822 detector head(Figaro Company Limited) was used [...] Read more.
A device for the detection and determination of ethanol and acetone wasconstructed, consisting of a packed column, a chamber with a sensor head, 2 dc powersupplies, a multimeter and a computer. A commercially available TGS 822 detector head(Figaro Company Limited) was used as the sensor head. The TGS 822 detector consists of aSnO2 thick film deposited on the surface of an alumina ceramic tube which contains aheating element inside. An analytical column was coupled with the setup to enhance theseparation of ethanol and acetone before they reached the sensor head. Optimum systemconditions for detection of ethanol and acetone were achieved by varying the flow rate of thecarrier gas, voltage of the heating coil (VH), voltage of the circuit sensor (VC), loadresistance of the circuit sensor (RL) and the injector port temperature. The flow of the carriergas was 15 mL/min; the circuit conditions were VH = 5.5 V, VC = 20 V, RL = 68 k ; and theinjection port temperature was 150°C. Under these conditions the retention times (tR) forethanol and acetone were 1.95 and 0.57 minutes, respectively. Calibration graphs wereobtained for ethanol and acetone over the concentration range of 10 to 160 mg/L. The limitsof detection (LOD) for ethanol and acetone were 9.25 mg/L and 4.41 mg/L respectively. Full article
Open AccessArticle DNA Optical Detection Based on Porous Silicon Technology: from Biosensors to Biochips
Sensors 2007, 7(2), 214-221; doi:10.3390/s7020214
Received: 15 February 2007 / Revised: 26 February 1995 / Accepted: 1 January 2007 / Published: 28 February 2007
Cited by 49 | PDF Full-text (130 KB) | HTML Full-text | XML Full-text
Abstract
A photochemical functionalization process which passivates the porous silicon surface of optical biosensors has been optimized as a function of the thickness and the porosity of the devices. The surface modification has been characterized by contact angle measurements. Fluorescence measurements have been [...] Read more.
A photochemical functionalization process which passivates the porous silicon surface of optical biosensors has been optimized as a function of the thickness and the porosity of the devices. The surface modification has been characterized by contact angle measurements. Fluorescence measurements have been used to investigate the stability of the DNA single strands bound to the nanostructured material. A dose-response curve for an optical label-free biosensor in the 6-80 μM range has been realized. Full article

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