Quick and reliable estimation of BOD load of beverage industrial wastewater by developing BOD biosensor

An amperometric biosensor for determination of biochemical oxygen demand in wastewater has been developed to overcome the time consuming monitoring procedures. The performance and stability of the immobilized membrane have been investigated at 37 °C and pH 6.8. Immobilized microbial membranes maintain their stability and activity after intermittent use for 400 cycles when stored at 4 °C in sodium phosphate buffer pH 6.8. The response time of the BOD sensor was only 90 min, being independent of the concentration, and the lower detection limit was 1 mg/l. The obtained BOD values showed correlation with that of the conventional method for BOD determination (BOD5) with a deviation of ±10%. Moreover, the sensor exhibits good repeatability (3.39–4.45%) and reproducibility (1.85–2.25%). Software was added to upgrade this sensor and to make it a promising candidate for online monitoring.     

Polysilicon nanofilm pressure sensor

Utilizing 80 nm polysilicon nanofilm as piezoresistors, a pressure sensor with high performance is developed. The complete fabrication process is described. The pressure properties of the sensor were measured at the temperature from 0 to 200 °C. For 0.6 MPa full scale pressure, the sensitivity is 23.00 mV/V/MPa at 0 °C and 18.27 mV/V/MPa at 200 °C, the temperature coefficient of sensitivity (TCS) is about −0.098%/ °C without any compensation. The temperature coefficient of offset (TCO) is about −0.017%/ °C. Because of the good piezoresistive and temperature characteristics of polysilicon nanofilm, the pressure sensor demonstrates a better performance.     

Influence of Cs doping in spray deposited SnO2 thin films for LPG sensors

Detection of low concentrations of petroleum gas was achieved using transparent conducting SnO₂ thin films doped with 0–4 wt.% caesium (Cs), deposited by spray pyrolysis technique. The electrical resistance change of the films was evaluated in the presence of LPG upon doping with different concentrations of Cs at different working temperatures in the range 250–400 °C. The investigations showed that the tin oxide thin film doped with 2% Cs with a mean grain size of 18 nm at a deposition temperature of 325 °C showed the maximum sensor response (93.4%). At a deposition temperature of 285 °C, the film doped with 3% Cs with a mean grain size of 20 nm showed a high response of 90.0% consistently. The structural properties of Cs-doped SnO₂ were studied by means of X-ray diffraction (XRD); the preferential orientation of the thin films was found to be along the (3 0 1) directions. The crystallite sizes of the films determined from XRD are found to vary between 15 and 60 nm. The electrical investigations revealed that Cs-doped SnO₂ thin film conductivity in a petroleum gas ambience and subsequently the sensor response depended on the dopant concentration and the deposition temperature of the film. The sensors showed a rapid response at an operating temperature of 345 °C. The long-term stability of the sensors is also reported.     

Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method

ZnO nanopowders were prepared through microwave heating method. ZnO thick film sensors were fabricated by using ZnO nanopowders as sensing materials. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The gas-sensing properties of the sensors based on ZnO nano-materials were investigated. It was found that the sensor based on ZnO nano-materials (low power, 10× 10 min) exhibited very high responses to benzene and toluene when operating at 440 and 370 °C, respectively; but the sensor based on ZnO (low power, 10× 10 min) showed very low responses to benzene and toluene when operating at 205–215 °C. The sensor based on ZnO (low power, 10× 10 min) showed high response and good selectivity to dilute formaldehyde when operating at 210 °C; especially, the response to 0.001 ppm HCHO attained 7.4 when operating at 210 °C.     

Fiber Bragg grating weighing sensor of beam with two parallel holes

Due to the strains of fiber Bragg gratings mounted on the gauge hole of beam with two parallel holes excited by the weight, a fiber Bragg grating weighing sensor is developed. During the double differential operation of the relation shifts of Bragg wavelength of these four mounted gratings, the shifts of Bragg wavelengths caused by the temperature fluctuation and the bending moment caused by the deflection load can be compensated. The loading and unloading experiments indicate that the delay of grating weighing sensor is 0.28%FS, and the repetition is 0.32%FS. Through the least-square algorithm fitting, the load response sensitivity of grating weighing sensor is 9.992 × 10⁻⁶ kg f⁻¹, and the fitting linearity is 0.6%FS. The temperature drift of grating weighing sensor is 0.02%FS/°C at the range of 20–60 °C. The fitting linearity is 1.5%FS under the action of deflection load.     

Solid-state potentiometric SO2 sensor combining NASICON with V2O5-doped TiO2 electrode

A compact tubular sensor based on NASICON (sodium super ionic conductor) and V₂O₅-doped TiO₂ sensing electrode was designed for the detection of SO₂. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al₂O₃ tube; furthermore, a thin layer of V₂O₅-doped TiO₂ with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V₂O₅ doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V₂O₅-doped TiO₂ sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO₂ in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO₂ concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO₂ against NO, NO₂, CH₄, CO, NH₃ and CO₂. Moreover, the sensor had speedy response kinetics to SO₂ too, the 90% response time to 50 ppm SO₂ was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO₂-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.     

Studies on the gas sensing behaviour of nanosized CuNb2O6 towards ammonia, hydrogen and liquefied petroleum gas

Appreciable changes in resistance of polycrystalline nanosized CuNb₂O₆ upon exposure to reducing gases like hydrogen, liquefied petroleum gas (LPG) and ammonia in ambient atmosphere recognize the material as a gas sensor. Nanosized CuNb₂O₆ synthesized by thermal decomposition of an aqueous precursor solution containing copper nitrate, niobium tartrate and tri-ethanol amine (TEA), followed by calcination at 700 °C for 2 h, has been characterized using X-ray diffraction (XRD) study, transmission electron microscopy (TEM), field-emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX) analysis and Brunauer–Emmett–Teller (BET) surface area measurement. The synthesized CuNb₂O₆ exhibits monoclinic structure with crystallite size of 25 nm, average particle size of 25–40 nm and specific surface area of 55 m² g⁻¹.     

Pulsed laser deposited Y-doped BaZrO3 thin films for high temperature humidity sensors

Pulsed laser deposited (PLD) Y-doped BaZrO₃ thin films (BaZr_1-xY_xO_3-y/2, x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures (T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1] and [2]. indicate that bulk Y-doped BaZrO₃ could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO₃ thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films.X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar⁺ etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO₃:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm⁻¹ for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.     

Adhesive bonding with SU-8 in a vacuum for capacitive pressure sensors

This paper describes a method for fabricating capacitive pressure sensors through the use of adhesive bonding with SU-8 in a vacuum. The influence of different parameters on the bonding of structured wafers was investigated. It was found that pre-bake time, pumping time, and the thickness of the crosslink layer are the most important factors for successful bonding. Bonding quality was evaluated by inspection through the transparent glass of the sensor and through the use of an SEM photograph, with 90% of the area successfully bonded and an ultimate yield of 70% of the sensors. The measured bonding strength was 17.15 MPa and 19.6 MPa for wafers bonded in 80 °C and 100 °C, respectively. The pressure–capacitance characteristic test results show that this bonding process is a viable micro electro mechanical systems (MEMS) fabrication technology for cavity sealing in a vacuum.     

Ammonia identification using shear horizontal surface acoustic wave sensor and quantum neural network model

The ammonia detection at room temperature employing a shear horizontal surface acoustic wave (SH-SAW) sensor coated with polyaniline (PANI) film and the recognition of ammonia concentrations in humid environments based on quantum neural network (QNN) have been investigated in this study. Studies were performed in the ranges of 0–67.5% relative humidity and 15–72 ppm ammonia. The frequency shift of SH-SAW was measured to detect the presence of ammonia. The SH-SAW sensor in this study responded to the ammonia gas and could be recovered using dry nitrogen. Detecting at an ammonia concentration of 40.91 ppm in dry environment, the frequency shift was 0.75 ppm and the noise level was 0.08 ppm. In humid environment, the frequency shift increased as the humidity increased. In order to recognize the ammonia in humid environment, the QNN was used as the identifier. From the performance results shown, the neural model we proposed can effectively perform the identification of ammonia in a common ambience and overcome the inference of humidity caused.     

Development of a piezoelectric polymer film sensor for plantar normal and shear stress measurements

We have developed a new sensor prototype for plantar pressure measurements during gait. The mechanical stress at the plantar surface has two components, pressure acting normal to the surface and shear stress acting tangential to the surface. The shear stress can be further divided into anterior–posterior (AP) and medial–lateral (ML) components. The developed sensor simultaneously measures both normal and shear stresses. It utilizes commercial polyvinylidenefluoride (PVDF) material and consists of four separate sensor elements. This paper presents the sensor development and calibration for each force components. A shaker providing dynamic excitation force was used in the calibration. Average sensitivities computed from the results were (12.6 ± 0.8) mV/N for the normal force, (223.9 ± 20.3) mV/N for the AP shear force and (55.2 ± 11.9) mV/N for the ML shear force. A preliminary plantar pressure measurement was also done. The results obtained were promising. However, the sensor developed here is the first prototype. In future, a matrix sensor based on this principle is planned to be constructed.     

Flexible humidity sensor in a sandwich configuration with a hydrophilic porous membrane

We constructed a wearable and flexible humidity sensor (thickness: 80 μm) in a sandwich configuration, with a hydrophilic poly-tetrafluoroethylene membrane placed between two gold deposited layers, using soft-MEMS techniques. The device was used to measure humidity level, via its electrical conductivity, using a multi-frequency LCR-meter at frequencies ranging from 100 Hz to 100 kHz. The device was calibrated at 100 Hz against moist air over the range of 30–85% RH, which includes normal humidity levels in the atmosphere and physiological air such as breath and evaporating sweat. The response sensitivity of the humidity device was extremely high, even for recovery to dry air; for example response time was less than 1 s for a conductivity shift between humid air of 80% RH and dry air of −60 °C dew point. The sensor performance was reproducible over multiple measurements, with a coefficient of variation of 1.77% (n = 5). The sensor was appropriate for physiological applications, and was successfully used in two non-invasive approaches: to monitor breath air at the mouth, and to measure sweat moisture from the nostrils.     

Single-crystalline Te microtubes: Synthesis and NO2 gas sensor application

Tellurium tubular crystals were grown by direct thermal evaporation of tellurium metal in an inert atmosphere on quartz substrates at ambient pressure without employing any catalyst. Tellurium powder was evaporated by heating at 600 °C and was condensed at a substrate temperature of 300–350 °C in the downstream of argon gas at a flow rate of 100 mL/min. The structure and chemical composition of the as-synthesized samples were examined by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-rays microanalysis and micro-Raman spectroscopy. Scanning electron microscopy images and X-ray diffraction patterns showed that the as-synthesized Te had a tubular single-crystalline morphology with a hexagonal cross-section. The Te microtubes were typically 0.5–6 mm long, 30–70 μm in external diameter, and 5–20 μm thick. NO₂ gas-sensing properties of the Te microtubes at room temperature were also investigated. They showed a promising sensitivity and response towards tested gas.     

Characterization of intermediate In/Ag layers of low temperature fluxless solder based wafer bonding for MEMS packaging

Low temperature fluxless solder for wafer bonding has received a lot of attention due to its great potential in hermetic MEMS packaging. Previous research activities mainly deploy solder alloy of eutectic composition to achieve low bonding temperature. We proposed new intermediate bonding layers (IBLs) of rich Ag composition in In–Ag materials systems. In this study, we investigated the intermetallic compounds (IMCs) at the bonding interface with respect to the bonding condition, post-bonding room temperature storage and post-bonding heat treatment. With this IBL, the IMCs of Ag₂In and Ag₉In₄ with high temperature resist to post-bonding process are derived under process condition of wafer bonding at 180 °C, 40 min and subsequent 120–130 °C annealing for 24 h. Low melting temperature IMC phase of AgIn₂ is formed in the interface after long term room temperature storage or 70 °C aging treatment. This low melting temperature IMC phase can be completely converted into high melting temperature IMCs of Ag₂In and Ag₉In₄ after 120 °C additional annealing. Based on our results, we can design the packaging process flow so as to get reliable hermetic packaged MEMS devices by using low temperature fluxless In–Ag wafer bonding.     

Lithium ferrite for gas sensing applications

Microstructure and gas sensing properties of pure and samarium-substituted lithium ferrites, Li_0.5Sm_xFe_2.5−xO₄ (x = 0, 0.05, 0.1 and 0.2), prepared by sol–gel self-combustion were studied. Ethanol, methanol, LPG and ammonia were used as test gases. SEM investigation evidenced that Sm ions induced microstructural changes of the Li ferrite. The finest granulation (about 100 nm) and highest porosity (44%) were observed in Li_0.5Sm_0.2Fe_2.3O₄. The gas response measurements evidenced that it depended on the working temperature and gas type. All ferrites were sensitive to alcohol (ethyl and methyl) and less sensitive to ammonia and LPG. The best responses, over 85%, were obtained at operating temperatures of 340–355 °C to ethanol and methanol vapour.     

Tetrakis(alkylthio)-substituted lutetium bisphthalocyanines for sensing NO2 and O3

In this study, the nitrogen dioxide (NO₂) and ozone (O₃) sensing properties of a series bis[tetrakis(alkylthio) phthalocyaninato] lutetium(III) complexes [(C_nH_2n+1S)₄Pc]₂Lu(III) (n = 6, 10, 16) are investigated as a function of concentration in the temperature range between 25 °C and 150 °C. The concentration ranges were 1–10 ppm for NO₂, and 50 ppb–1 ppm for O₃. The response time and the sensor response to NO₂ are measured for approximately 1 min and 100% ppm⁻¹, respectively, for compound 1 at room temperature. At room temperature, all compounds are in the solid phase. The response time decreases to a few seconds with increasing operation temperature to 150 °C. At this temperature, all compounds are in the liquid crystal phase. The fastest response to oxidizing gases is observed at the liquid crystal phase of the Pcs. It has also been observed that the response time and the sensor response depend on the alkyl chain lengths of the Pcs. The doping effect of oxygen has been determined under high purity nitrogen N₂ flow, after exposure to dry air, at a different period of time and after annealing. It has been found that the conductivities of [(C_nH_2n+1S)₄Pc]₂Lu(III) thin films increased after exposure to dry air and the conduction mechanism also changed from ohmic behavior to space-charge-limited conduction.     

Zeolite based trace humidity sensor for high temperature applications in hydrogen atmosphere

We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (10–110 ppm_V) under harsh conditions, e.g. reducing atmosphere (H₂) and high temperature (up to 600 °C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required.     

Effects of internal electrode composition on the reliability of low-firing PMN–PZT multilayer ceramic actuators

We investigated the effects of internal electrode composition on the reliability of low-firing multilayer ceramic actuators using Ag internal electrodes. Ag–ceramic composite pastes were prepared by adding Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr_0.475,Ti_0.525)O₃ (PMNZT) ceramic powders to a commercial Ag paste at concentrations in the range of 0–60 vol%. PMNZT multilayered laminates were fabricated using tape casting, and then cofired at 925 °C for 10 h. The fatigue behaviors of multilayer actuators with Ag internal electrodes having different PMNZT concentrations were compared by applying a 2 kV/mm ac electric field at 50 °C under a relative humidity of 30%. The failure data were analyzed using Weibull statistics. The addition of PMNZT ceramics enhanced the mean time to failure by reducing the densification mismatch between the piezoelectric ceramic and internal electrode layers during the cofiring process.     

Controlled synthesis and gas-sensing properties of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes

Hollow sea urchin-like α-Fe₂O₃ nanostructures were successfully synthesized by a hydrothermal approach using FeCl₃ and Na₂SO₄ as raw materials, and subsequent annealing in air at 600 °C for 2 h. The hollow sea urchin-like α-Fe₂O₃ nanostructures with the diameters of 2–4.5 μm consist of well-aligned α-Fe₂O₃ nanorods with an average length of about 1 μm growing radially from the centers of the nanostructures, have a hollow interior with a diameter of about 2 μm. α-Fe₂O₃ nanocubes with a diameter of 700–900 nm were directly obtained by a hydrothermal reaction of FeCl₃ at 140 °C for 12 h. The response S_r (S_r = R_a/R_g) of the hollow sea urchin-like α-Fe₂O₃ nanostructures reached 2.4, 7.5, 5.9, 14.0 and 7.5 to 56 ppm ammonia, 32 ppm formaldehyde, 18 ppm triethylamine, 34 ppm acetone, and 42 ppm ethanol, respectively, which was excess twice that of the α-Fe₂O₃ nanocubes and the nanoparticle aggregations. Our results demonstrated that the hollow sea urchin-like α-Fe₂O₃ nanostructures were very promising for gas sensors for the detection of flammable and/or toxic gases with good-sensing characteristics.     

Extracting discriminative information from the Padé-Z-transformed responses of a temperature-modulated chemoresistive sensor for gas recognition

The response patterns of a temperature-modulated chemoresistive gas sensor were transformed to multi-exponential functions which facilitated the extraction of their discriminative features for gas diagnosis. The patterns were generated for air contaminated with different concentrations of various volatile organic compounds by applying a staircase heating voltage waveform to the microheater of a tin oxide-based sensor that modulated its operating temperature in the 50–400 °C range. Padé-Z transform was utilized for the transformation, and a novel heuristic procedure facilitated the extraction of the components of the feature vectors from the transformed data. These vectors were classified by the available techniques. The method differentiated the patterns generated for methanol, ethanol, 1-propanol, 1-butanol, and acetone contaminations in the wide concentration range examined. The method was also used to separately estimate the amount of the discriminative information in various steady state and transient response features; the results are anticipated to help design more elaborate temperature-modulated sensors for gas diagnosis.