Papers by Keyword: Chemical Sensors

Abstract: There were made and tested three types of polymer and nanographite composites: 1) Ethylene vinyl acetate copolymer (EVA) as matrix and extra-conductive highly structured carbon black (EHSCB) as conductive filler; 2) EVA matrix and carbon nanotubes (CNT) as filler; 3) EVA matrix and as filler are used optimal combination of two kind of conductive filler, EHSCB and CNT. Volatile organic compound vapour sensor-effect is tested for all composite types.

Abstract: In recent years, there has been significant progress in a number of sensing technologies related to on-body measurements, such as platforms for monitoring respiration, heart rate, location and movement. In these cases, the sensing element (s) are based on highly effective transducers that are increasingly integrated into garments such that they are becoming innocuous to the user. In contrast, the area of on-body chemical sensing remains highly under-developed. In this paper, we will address the significant challenges that are inhibiting the practical realisation of reliable chemical sensors and biosensors capable of generating accurate data in real time.

Abstract: Electrodes with submicron gaps are desired for achieving high amplication redoxcycling sensors. In this contribution we report the use of electrodeposition of gold in order todecrease the inter-electrode spacing at interdigitated electrodes. Using this method submicronspacings can be obtained without expensive techniques such as e-beam lithography or focusedion beam milling. Initially, gold interdigitated electrodes with a nger spacing of 2.5 m wererealized by lift-o processing. Using a commercial gold sulphite bath (ECF64D) and 100 mscurrent pulses of -1.78 A, these gold electrodes were plated with an additional gold layer. Asa result, the inter- electrode spacing, as measured using atomic force microscopy and conven-tional microscopy, was reduced to 0.6 m. The achieved gap spacing is limited by electrodeimperfections resulting from the lift-o process. At these imperfections the electrodes becomeshorted. Additional experiments with wet etched electrodes are expected to yield smaller gapspacings

Abstract: The objective of this paper is to present simulation results of the Thickness Shear Mode (TSM) resonator based on quartz using finite element simulation method. 3D model of quartz resonator and simulations were completed using finite element method in CoventorWare software suite for design and simulation of MEMS devices. Different techniques for simulation of adsorption effect on selective layer were studied: influence of change in mass of the sensitive layer and influence of change in density of the sensitive layer. Analyses of resonant modes were performed for both cases and displacement profiles in selected modes were determined for the resonator under study. Impedance and phase characteristics were calculated and measured for clean sample and sample with selective layer coated. The adsorption model calculates the frequency shift in basic resonant frequency with adsorbed amount of sensed gas. The simulation results were used in design of gas sensors for dangerous substances detection.

Abstract: Uniform MoO₃ nanobelts were synthesized through a fast and simple hydrothermal route without any other agents. The hydrothermal reaction was performed at 180 °C for 12 h using a HNO₃ aqueous solution as the solvent. The phases and microstructures were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the sample obtained was an orthorhombic MoO₃ phase, and had a belt-like morphology with lengths of 510 μm and apparent widths of about 220 nm. The MoO₃ nanobelts obtained were used as the sensing materials to fabricate chemical sensors for detection of some volatile organic compounds (VOCs) (including ethanol, methanol, isopropanol, acetone, methanal, and benzene). The gas-sensing results indicated that the sensor of the α-MoO₃ nanobelts has enhanced ethanol-sensing performance, e.g., with the highest sensitivity of S_r =144 for 500 ppm ethanol vapor operating at 300 °C.

Abstract: The nanofiber optic evanescent field sensor based on a changed cladding part as a sensor presented numerically. The influences of numerical opening, core radius of the fiber, the wavelength is effected on the light source and the submicron fiber on the sensors are promise to studied in this work. The results pointed out the sensitivity of the sensor increases when the numerical opening of the fiber is increases and the core radius is decreases. The NA of the fiber affects the sensitivity of the sensor. In the uniform core fiber, the increase in the NA increases the sensitivity of the sensor. Therefore, one should choose a fiber with high NA for the design of an evanescent-wave-absorption sensor if the core of the sensing segment uniform in diameter, so that the increase in the penetration depth or number of ray reflections or both, increases the evanescent absorption field and hence the sensitivity of the sensors. Keywords: fiber optic sensor, chemical sensors, biosensors, nanofiber optic.

Abstract: Chemocapacitors are polymer coated Interdigital electrodes (IDE) where the transducer mechanism relies on the permittivity changes and swelling of the coating polymer (sensitive layer), usually in a form of a thin film, when exposed to an volatile organic compound (VOC). Despite several synthetic and natural polymers have already been produced by electrospinning, there have been fewer studies on rubbery polymers with low glass transition temperature (e.g. Poly(dimethyl siloxane) – PDMS). In this work we produce PDMS:PMMA 3:1 nanofiber (NF) layers by electrospinnig to be used as chemical sensitive layers on IDE chemocapacitors. The results show an enhanced response from the sensors with NFs with respect with sensors prepared with the same sensitive layers in the form of a homogeneous film.

Abstract: In this paper, measurement method for the refractive index of chemical substances based on fiber Bragg grating (FBG) sensor was proposed. The relation between Bragg wavelength shift and surrounding refractive index (SRI) was analyzed theoretically and experimentally. The SRI sensitivity of the chemical sensor could be enhanced by reducing the cladding thickness of the FBG using hydrofluoric acid (HF) solution etching process. The experimental results indicated that the variation of Bragg wavelength increased as the SRI increased. In the low SRI region, the relationship between the Bragg wavelength shift and the change of the SRI was approximately linear.

Abstract: Inorganic frameworks obtained by the sol-gel route can be templated by a molecular imprinting (MIP) approach to generate functional cavities. Such MIP ceramics show highly appreaciable properties for chemical sensor applications, because they are inherently chemically and thermally robust. In combination with mass-sensitive devices (e.g. quartz crystal micro balance – QCM, surface transverse wave oscillator - STW), they yield highly selective and sensitive chemical sensors. Gas phase measurements with volatile organic compounds (VOCs) e.g. lead to sensitivities below 1 ppm. Sensitivity can be tuned by the sol-gel-precursor: when hydrolysing more bulky alkoxides, this leads to enhanced sensitivity by increasing porosity as a consequence of slower solvent evaporation. By adding products of oxidative oil degradation to the sol-gel mixture, we succeeded in generating sensors for degradation processes in these complex matrices. This allows parallelly monitoring both the chemical state of oil and changes in viscosity. Sensitivity is enhanced according to the Sauerbrey equation by going from 10 MHz QCM transducers to higher frequencies either by etching the quartz substrates and so reducing the resonator thickness or by applying STWs.