Magnetostrictive composite-fiber Bragg grating (MC-FBG) magnetic field sensor

We report a magnetostrictive composite-fiber Bragg grating (MC-FBG) magnetic field sensor based on the direct coupling of the magnetostrictive strain in an epoxy-bonded Terfenol-D particle pseudo-1-3 MC actuator with a FBG strain sensor. The MC-FBG sensor exhibits a large and fairly linear quasistatic peak wavelength shift of 0.68 nm under an applied magnetic field of 146 kA/m and a wide extrinsic magneto-optical signal frequency range up to at least 60 kHz. These quasistatic and dynamic characteristics, together with the electromagnetic interference immunity, large-scale multiplexing potential and self-reference capability, enable the application of the MC-FBG sensor in distributed magnetic field sensing over long distances.     

Magnetic particle dosing and size separation in a microfluidic channel

Separation of functional magnetic particles or magnetically labeled entities is a key feature for bioanalytical or biomedical applications and therefore also an important component of lab-on-a-chip devices for biological applications. We present a novel integrated microfluidic magnetic bead manipulation device, comprising dosing of magnetic particles, controlled release and subsequent magnetophoretic size separation with high resolution. The system is designed to meet the requirements of specific bioassays, in particular of on-chip agglutination assays for the detection of rare analytes by particle coupling as doublets. Integrated soft-magnetic microtips with different shapes provide the magnetic driving force of the bead manipulation protocol. The magnetic tips that serve as field concentrators of an external electromagnetic field, are positioned in close contact to a microfluidic channel in order to generate high magnetic actuation forces. Mixtures of 1.0 μm and 2.8 μm superparamagnetic beads have been used to characterize the system. Magnetophoretic size separation with high resolution was performed in static conditions and in continuous flow mode. In particular, we could demonstrate the separation of 1.0 μm single beads and doublets in a sample flow.     

Thin film integrated AMR sensor for linear position measurements

A simple anisotropic magnetoresistive (AMR) sensor for linear positioning is designed as integrated bridge structure and implemented based on standard technology processes and rotation of the initial anisotropy axis after the patterning of the resistors. The behavior of the separate resistors is investigated by varying the intensity (0 ± 5 kA/m) and direction (0°, 45°, 90° in respect to the initial anisotropy axis) of the applied magnetic field. The experimental results are compared with data from simulation based on detailed analysis of the energy profile. Good agreement is obtained at assumed declination of 15° between the anisotropy and geometrical axes of the resistors. It is shown that in spite of asymmetries and hysteresis observed at low magnetic fields at higher fields used usually for the purposes of automation the response of the structure is single-valued and stable.     

Magnetically actuated micromechanical tweezers

Two planar actuators with magnetic thin films are used for magnetic tweezers. The planar actuators consisting of a pair of a 75 × 0.8 × 0.3 μm³ silicon oxide beam and a 72 × 13 × 0.3 μm³ silicon oxide plate deposited with a 65 × 4 × 0.1 μm³ Ni magnetic thin film are successfully fabricated and successfully gripped to a single NPC-tw01 cell consisting of Fe₃O₄ magnetic nanoparticles under a vertical magnetic field. The planar actuator bends under an external magnetic field because of the high shape magnetic anisotropy of the Ni magnetic thin film and a highly sensitive microcantilever. NPC-tw01 cells, which are adherent cells, are cultivated in a culture solution. The two planar actuators are placed in water to move and grip a living cell.     

Morphology and magnetic properties of electroplated Co-rich Co-Zn thin films

This work explores the microstructure and magnetic properties of electrodeposited Co-Zn thin films. Using pulse-reverse electroplating technique, Co-rich Co-Zn films are deposited 0.4–1.9 μm thick from aqueous sulfate-based baths at low temperature (55°C). The influence of current density (25–100 mA/cm²) and electrolyte Zn concentration (0–0.28 M) on the microstructure and magnetic properties are investigated. All of the Co-Zn films exhibit higher out-of-plane coercivity, as compared to in-plane. With increasing current density, the out-of-plane coercivity decreases from 50 to 40 kA/m (628–500 Oe). The influence of the Zn concentration in the electrolyte is more pronounced, affecting the grain size, film composition, and magnetic properties. The best magnetic properties were obtained from a bath with 0.21 M Zn and an average current density of 25 mA/cm², resulting in a Co₉₇Zn₃ composition and an out-of-plane coercivity of 92 kA/m (1,160 Oe).     

Acetylene sensor based on Pt/ZnO thick films as prepared by flame spray pyrolysis

ZnO nanoparticles loaded with 0.2-2.0 at.% Pt have been successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate, as precursors dissolved in xylene and their acetylene sensing characteristics have been investigated. The particle properties were analyzed by XRD, BET, TEM, SEM and EDS. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spherical and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5-20 nm in width and 20-40 nm in length. In addition, very fine Pt nanoparticles with diameter of ∼1 nm were uniformly deposited on the surface of ZnO particles. From gas-sensing characterization, acetylene sensing characteristics of ZnO nanoparticles is significantly improved as Pt content increased from 0 to 2  at.%. The 2 at.% Pt loaded ZnO sensing film showed an optimum C₂H₂ response of ∼836 at 1% acetylene concentration and 300 °C operating temperature. A low detection limit of 50 ppm was obtained at 300 °C operating temperature. In addition, Pt loaded ZnO sensing films exhibited good selectivity towards hydrogen, methane and carbon monoxide.     

Magnetic trap effects on nanowire��s dynamics within micro-capillary vessels

The concept of using magnetic nanowires (NWs) as carriers in magnetic drug targeting was largely developed in the last decade. Magnetically controlled and manipulated nanoparticles are gaining more and more ground in various biomedical applications: drug delivery, cancer therapy by magnetic fluid hyperthermia, radiotherapy. In this study, a 2-D mathematical model was developed and implemented to examine the capture of magnetic drug carrier particles within a magnetic trap represented by high magnetic field gradients. The transient dynamics of magnetic NWs under the effect of the blood velocity (v _B) varied from 0.05 up to 1.0 cm/s, magnetic field strength and their initial position within the fluid channel have been analyzed using COMSOL Multiphysics module. The parameters related to the NW with strong influence on the magnetic trap output were systematically modified: magnetic material, cylindrical particle geometry characterized by diameter and length, its initial position related to both fluid flow direction and distance from the channel center. Considering the influence of both hydrodynamic, magnetic forces and torques the magnetic trap’s efficiency was evaluated and phase diagrams were determined for different parameters involved. A considerable number of simulations were made to obtain statistically significant results. These results are commented and discussed in detail.     

Direct numerical simulations of transverse and spanwise magnetic field effects on turbulent flow in a 2:1 aspect ratio rectangular duct

Magnetic fields are used extensively to direct liquid metal flows in material processing. Continuous casting of steel uses different configurations of magnetic fields to optimize turbulent flows in rectangular cross-sections to minimize defects in the solidified steel product. Realizing the importance of a magnetic field on turbulent flows in rectangular cross-sections, the present work is aimed at understanding the effect of a magnetic field on the turbulent metal flow at a nominal bulk Reynolds number of ∼5300 (based upon full duct height) (Re_τ = 170, based upon half duct height) and Hartmann numbers (based upon half duct height) of 0, 6.0 and 8.25 in a 2:1 aspect ratio rectangular duct. Direct numerical simulations in a non-MHD 2:1 aspect ratio duct followed by simulations with transverse and span-wise magnetic fields have been performed with 224 × 120 × 512 cells (∼13.7 million cells). The fractional step method with second order space and time discretization schemes has been used to solve the coupled Navier-Stokes-MHD equations. Instantaneous and time-averaged natures of the flow have been examined through distribution of velocities, various turbulence parameters and budget terms. Spanwise (horizontal) magnetic field reorganizes and suppresses secondary flows more strongly. Turbulence suppression and velocity flattening effects are stronger with transverse (vertical) magnetic field.     

Highly sensitive label-free immunosensor for ochratoxin A based on functionalized magnetic nanoparticles and EIS/SPR detection

A label-free immunosensor for the detection of ochratoxin A (OTA) based on use of magnetic nanoparticles (MNPs) was developed. A gold electrode was modified using bovine serum albumin conjugate with a glutaraldehyde-thiolamine linker, creating a layer that prevents non-specific binding of OTA on gold. The OTA antibodies were attached to MNPs using the carbodiimide chemistry and afterwards were immobilized on the modified gold electrode using a strong magnetic field. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) were used to characterize each step in immunosensor development. The impedance variation due to the specific antibody-OTA interaction was correlated with the OTA concentration in the samples. The increase in electron-transfer resistance values was proportional to the concentration of OTA on a linear range between 0.01 and 5 ng/mL, with a detection limit of 0.01 ng/mL. SPR measurements showed a larger response range (1-50 ng/mL) with a detection limit of 0.94 ng/mL. Analytical results were in accordance with standard ELISA test kit.     

Space approach to the hydro-magnetic flow of a dusty fluid through a porous medium

The technique of the state space approach and the inversion of the Laplace transformation method are applied to the non-dimensional equations of an unsteady laminar free convection flow of an incompressible, viscous, electrically conducting dusty fluid through a porous medium, which is bounded by an infinite vertical plane surface of constant temperature, in the presence of a constant magnetic field. The technique is applied to the thermal shock problem. The inversion of the Laplace transforms is carried out using a numerical approach. The numerical results of the dimensionless temperature, velocity, and induced magnetic and electric field distributions are given and illustrated graphically. The effects of the material’s parameters such as the Grashof number, the Prandtl number, the permeability parameter, the mass concentration of the particle phase, the Alfven velocity, the thermal relaxation time and the relaxation time of the particle phase on the temperature, velocity and the induced magnetic and electric fields are discussed.     

Gas sensors based on anodic tungsten oxide

Nanostructured porous tungsten oxide materials were synthesized by the means of electrochemical etching (anodization) of tungsten foils in aqueous NaF electrolyte. Formation of the sub-micrometer size mesoporous particles has been achieved by infiltrating the pores with water. The obtained colloidal anodic tungsten oxide dispersions have been used to fabricate resistive WO₃ gas sensors by drop casting the sub-micrometer size mesoporous particles between Pt electrodes on Si/SiO₂ substrate followed by calcination at 400 °C in air for 2 h. The synthesized WO₃ films show slightly nonlinear current-voltage characteristics with strong thermally activated carrier transport behavior measured at temperatures between −20 °C and 280 °C. Gas response measurements carried out in CO, H₂, NO and O₂ analytes (concentration from 1 to 640 ppm) in air as well as in Ar buffers (O₂ only in Ar) exhibited a rapid change of sensor conductance for each gas and showed pronounced response towards H₂ and NO in Ar and air, respectively. The response of the sensors was dependent on temperature and yielded highest values between 170 °C and 220 °C.     

Finite difference-based lattice Boltzmann simulation of natural convection heat transfer in a horizontal concentric annulus

In this paper, a finite difference-based lattice BGK model for thermal flows is proposed based on the double-distribution function approach. We applied this model to simulate natural convection heat transfer in a horizontal concentric annulus bounded by two stationary cylinders with different temperatures. Velocity and temperature distributions as well as Nusselt numbers were obtained for the Rayleigh numbers ranging from 2.38 × 10³ to 1.02 × 10⁵ with the Prandtl number around 0.718. It is found that the numerical results are in good agreement with the experimental and numerical results reported in the literature.     

Examination of Au/SnO2 core-shell architecture nanoparticle for low temperature gas sensing applications

Au/SnO₂ core-shell structure nanoparticles (NPs) were synthesized using two methods, microwave and conventional precipitation. In both cases, the size of the Au core was 12-18 nm and the thickness of the SnO₂ shell was 8-12 nm. The particle size of SnO₂ synthesized using the microwave and precipitation method was 3-5 nm and 1-2 nm, respectively. Upon heating to 400-600 °C, both particles maintained their core-shell morphology but the smaller SnO₂ particles prepared using the precipitation method were more sintered. The resistance changes in films of these particles were measured as a function of CO concentration. The Au/SnO₂ particles prepared using the microwave method showed higher sensor response than those prepared using the precipitation method, even providing a significant signal at testing temperatures approaching ambient conditions, thereby affording a new class of material for gas sensing. Both sets of core-shell particles showed higher sensor response than the SnO₂ nanoparticles. The role of the Au core as a catalyst in improving the adsorption and oxidation of CO gas is important for improving the low temperature response. In addition, the maintenance of the size of SnO₂ in the microwave method during sintering contributed to the higher response towards CO sensing.     

Study on design and application of fully automatic miniature surface plasmon resonance concentration analyzer

A fully automatic miniature surface plasmon resonance (SPR) concentration analyzer having high performance and low cost and developed using a Spreeta™ sensor was designed for field applications and concentration analysis. As in the case of Biacore™ instruments, the automatic sampling system of this device can introduce air segments between the sample/regeneration solution and buffer solution in the pipeline, which effectively prevents mixing of the solutions. A temperature sensor (AD 590) and temperature compensation method are used, which make the device insensitive to temperature fluctuations. A real-time data-smoothing algorithm for the SPR detection data is adopted; this can reduce the noise level to 5 × 10⁻⁷ RIU (refractive index units). The noise level of the sensorgram is 3.5% of the original level. Two types of self-prepared sensing chips—SMX-BSA (bovine serum albumin coated with sulfamethoxazole) and SMX-CM5 (carboxymethyl dextran coated with sulfamethoxazole)—are used to analyze the concentrations of sulfamethoxazole (SMX) standard solutions. Each chip's SMX calibration curve is established within the measurement range of 0-2000 ng/ml, and both limits of detection (LOD) are 2 ng/ml. One cycle of assay time is less than 15 min.     

Observed and modelled effects of ice lens formation on passive microwave brightness temperatures over snow covered tundra

Immediately before an April 2007 snow survey and passive microwave radiometer field campaign in the Northwest Territories, Canada, a rain-on-snow event deposited a thin (~ 3 mm) continuous layer of ice on the surface of the snowpack. At eight sites the brightness temperature (T_b) of the undisturbed snow pack was measured with a multi-frequency dual polarization (6.9, 19, 37, and 89 GHz) ground based radiometer system. The ice lens was then carefully removed and the T_bs were measured again. The individual V-pol channels and the 37 V − 19 V difference were largely unaffected by the presence of the ice lens, exhibiting a systematic shift of about 3 K. In comparison, the ice lens had a considerable effect on the H-pol T_b at all frequencies, with a mean difference (ice lens present − ice lens removed) of − 9 K (± 5.3 K) at 6.9 GHz, − 40 K (± 11.3 K) at 19 GHz, − 33 K (± 7.6 K) at 37 GHz, and − 19 K (± 8.0 K) at 89 GHz. The effect of the ice lens on H-pol measurements was also observed with spaceborne data from the Advanced Microwave Scanning Radiometer (AMSR-E) satellite data.Simulations of T_b were produced for each site using a new two layer formulation of the Helsinki University of Technology (HUT) snow emission model. The ice lens was used as the top layer and the underlying snowpack considered as a homogenous second layer. The agreement between observations and simulations was variable, with agreement strongest at 19 GHz. A comparison with simulations produced using the Microwave Emission Model of Layered Snowpacks (MEMLS) suggests HUT model uncertainty is related not to the ice lens, but to difficulties in simulating emission from deep snow. Overall, the observations and simulations suggest H-pol measurements are capable of detecting new ice layers across the tundra snowpack, while V-pol measurements are more appropriate for snow water equivalent (SWE) retrievals due to their relative insensitivity to ice layers.     

Particle mixing and reactive front motions in chaotic but closed shallow flows

A numerical study is presented of wind-induced active mixing and transport processes in closed shallow flows that are able to support chaotic advection. The wind-induced non-linear shallow water flow field is predicted using a quadtree grid based Godunov-type finite volume solver. Particles are tracked by numerically integrating the advection equations using velocity information interpolated from the predicted flow field. In complex oscillating flows, storage of all the necessary velocity information becomes problematical. Instead, we utilize the mean field and the first few dominant unsteady contributions as determined using Singular Value Decomposition. The advected particles are assumed to support autocatalytic reaction defined as A + B → 2B. Wind-induced reactive particle advection is considered in a realistic mine tailings pond with somewhat idealized bed topography. The reactive process reaches a stationary stage where reaction products occupy the whole closed flow domain. However, in the transient stage, particles undergo active advection and trace out filamentary structures that are similar to those in open flows. Because of the impossibility of particle escape and the global fine-scale chaotic mixing, the initial stages of chaotic mixing in closed flows are more efficient than in open flows. The results qualitatively validate a surface reaction theory derived by Károlyi and Tél [Károlyi G, Tél T. Chemical transients in closed chaotic flows: the role of effective dimensions. Phys Rev Lett 2005;95:264501-1-4] for closed systems.     

Influence of high magnetic field on peritectic transformation during solidification of Bi–Mn alloy

The influence of high magnetic fields up to 10 T on the peritectic temperature of Bi–Mn alloys has been investigated experimentally. A method for measuring the peritectic temperature in a gradient magnetic field has been developed by relating the change of magnetic levitation force to the phase transformation due to the change in magnetic susceptibility while the transformation occurs. By measuring the temperature at which the magnetizing force changes abruptly, the phase transformation can be detected. It is shown that along with the increase of magnetic field, the temperature of the peritectic phase transformation BiMn_1.08+ L→BiMn increased significantly, and in a 10 T field the temperature increase was about 20 ^°C. It is found that with the high magnetic field, a split and separation of the BiMn grains in the direction perpendicular to the magnetic field occurred, and its morphology changed from flakes to small blocks. This is attributed to the repulsive force among the peritectic BiMn grains generated by the magnetization during the phase transformation. It seems that the precipitation of ferromagnetic phase results in stress in the grains.     

Nano particulate SnO2 based resistive films as a hydrogen and acetone vapour sensor

SnCl₂ (solution) was spin coated on soda lime glass and Al₂O₃ substrate to obtain nano-particulate tin oxide film, directly by sintering at 550 °C for 40 minutes (min). The surface morphology and crystal structure of the tin oxide films were analyzed using atomic force microscopy (AFM) and X-ray diffraction (XRD). The size of SnO₂ nanostructure was determined from UV-vis and found to be ?3 nm. These films were tested for sensing H₂ concentration of 0.1-1000 ppm at optimized operating temperature of 265 °C. The results showed that sensitivity (R_air/R_gas per ppm) goes on increasing with decreasing concentration of test gas, giving concentration dependent changes. Special studies carried out at low concentration levels (0.1-1 and 1-10 ppm) of H₂, give high sensitivity (200 × 10⁻³/ppm) for lowest concentration (0.1-1 ppm) of H₂. The selectivity for H₂ against relative humidity (RH), CO₂, CO and LPG gases is also good. The sensor, at operating temperature of 200 °C, is showing nearly zero response to 300 ppm of H₂, and offering response to acetone vapour of 11 ppm. Selectivity for acetone against RH% and CO₂ was also studied. These sensors can be used as H₂ sensor at an operating temperature of 265 °C, and as an acetone sensor at the operating temperature of 200 °C.     

Hydrothermal synthesis of hollow ZnSnO3 microspheres and sensing properties toward butane

Hollow ZnSnO₃ microspheres were successfully prepared by hydrothermal method at 160 °C for 12 h. The prepared material was characterized by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and X-ray diffraction measurements (XRD). The average diameter of the hollow ZnSnO₃ microspheres was in the range of 400-600 nm. Compared with solid ZnSnO₃ microspheres structure, the hollow ZnSnO₃ microspheres showed better response (S) to butane. To 500 ppm butane, the sensor response (S) of the hollow ZnSnO₃ microspheres was 5.79 at the optimum operating temperature of 380 °C, and the response and recovery time were 0.3 s and 0.65 s, respectively. The sensitivities of sensors based on this material were linear with the concentration of butane in the range of 100-1000 ppm.     

Influence of combustion parameters on NOx production in an industrial boiler

NO_x formation during the combustion process occurs mainly through the oxidation of nitrogen in the combustion air (thermal NO_x) and through oxidation of nitrogen with the fuel (prompt NO_x). The present study aims to investigate numerically the problem of NO_x pollution using a model furnace of an industrial boiler utilizing fuel gas. The importance of this problem is mainly due to its relation to the pollutants produced by large boiler furnaces used widely in thermal industrial plants. Governing conservation equations of mass, momentum and energy, and equations representing the transport of species concentrations, turbulence, combustion and radiation modeling in addition to NO modeling equations were solved together to present temperature and NO distribution inside the radiation and convection sections of the boiler. The boiler under investigation is a 160 MW, water-tube boiler, gas fired with natural gas and having two vertically aligned burners.The simulation study provided the NO distribution in the combustion chamber and in the exhaust gas at various operating conditions of fuel to air ratio with varying either the fuel or air mass flow rate, inlet air temperature and combustion primary air swirl angle. In particular, the simulation provided more insight on the correlation between the maximum furnace temperature and furnace average temperatures and the thermal NO concentration. The results have shown that the furnace average temperature and NO concentration decrease as the excess air factor λ increases for a given air mass flow rate. When considering a fixed value of mass flow rate of fuel, the results show that increasing λ results in a maximum value of thermal NO concentration at the exit of the boiler at λ = 1.2. As the combustion air temperature increases, furnace temperature increases and the thermal NO concentration increases sharply. The results also show that NO concentration at exit of the boiler exhibits a minimum value at around swirl angle of 45°.