An SOx (x = 2, 3) sensor using ?-alumina/Na2SO4 couple

A solid-state sensor for SOx (x = 2, 3) species has been designed using ?-alumina as the solid electrolyte and Na2SO4 as the auxiliary electrode. The measured e.m.f. of the cell Pt, O?2 + SO?2 + SO?3|Na2SO4short parallel?-aluminashort parallelNa2SO4|SO?3 + SO?2 + O?2, PT in the temperature range 700 K to 1150 K agrees well with values calculated using the Nernst equation. The sodium sulphate acts both as a protective covering, preventing direct access of the gaseous SOx species to the ?-alumina electrolyte, and as an auxiliary electrode, converting chemical potentials of SOx species and O2 into an equivalent sodium potential. The open-circuit e.m.f. varies non-linearly with temperature for fixed composition of inlet gas mixtures containing SO2, O2 and Ar. The response time (t0.99) of the cell varies between 1.9 ks at 750 K and 0.06 ks at 1100 K. The e.m.f. response is faster when the partial pressure of SOx at the electrode is increased than when it is decreased.

Redundancy resolution using tractrix -- Simulations and Experiments

Hyper-redundant robots are characterized by the presence of a large number of actuated joints, many more than the number required to perform a given task. These robots have been proposed and used for many applications involving avoiding obstacles or, in general, to provide enhanced dexterity in performing tasks. Making effective use of the extra degrees of freedom or resolution of redundancy has been an extensive topic of research and several methods have been proposed in literature. In this paper, we compare three known methods and show that an algorithm based on a classical curve called the tractrix leads to a more 'natural' motion of the hyper-redundant robot, with the displacements diminishing from the end-effector to the fixed base. In addition, since the actuators nearer the base 'see' a greater inertia due to the links farther away, smaller motion of the actuators nearer the base results in better motion of the end-effector as compared to other two approaches. We present simulation and experimental results performed on a prototype eight link planar hyper-redundant manipulator.

Ring Resonators and Micro Fluidics: Novel Design for Drug/Disease Detection

MEMS systems are technologically developed from integrated circuit industry to create miniature sensors and actuators. Originally these semiconductor processes and materials were used to build electrical and mechanical systems, but expanded to include biological, optical fluidic magnetic and other systems 12]. Here a novel approach is suggested where in two different fields are integrated via moems, micro fluidics and ring resonators. It is well known at any preliminary stage of disease onset, many physiological changes occur in the body fluids like saliva, blood, urine etc. The drawback till now was that current calibrations are not sensitive enough to detect the minor physiological changes. This is overcome using optical detector techniques 1]. The basic concepts of ring resonators, with slight variations can be used for optical detection of these minute disease markers. A well known fact of ring resonators is that a change in refractive index will trigger a shift in the resonant wavelength 5]. The trigger for the wavelength shift in the case discussed will be the presence of disease agents. To trap the disease agents specific antibody has to be used (e. g. BSA).

Piezoelectrically stimulated dielectric dispersion in KAP single crystals

The frequency response of the dielectric constant (epsilon(r)), the loss tangent (tan delta) and impedance Z of potassium acid phthalate (KAP) single crystals, monitored along the polar axis, exhibit strong resonances in the frequency range 50-200 kHz, depending on the dimensions of the sample. The observed resonance effect, which is strongly dependent on the geometric shape and size of the sample, is attributed to its piezoelectric nature. The resonance peak positions have been monitored as a function of both temperature and uniaxial pressure. The stiffness coefficient (C), computed based on the resonance data, is found to decrease with increasing temperature and increase with increasing pressure. The electro-mechanical coupling coefficient (k), obtained by resonance-anti-resonance method, has also been found to increase with rise in temperature. The epsilon(r) behaviour along the polar axis, as a function of temperature is consistent with that of k. The preliminary results on the influence, of partial replacement of K+ ions in the KAP crystal by Cs+ and Li+ ions, on the observed piezoelectric resonance effects are also included.

A portable battery-operated chip thermocycler based on induction heating

A microchip thermocycler, fabricated from silicon and Pyrex #7740 glass, is described. Usual resistive heating has been replaced by induction heating, leading to much simpler fabrication steps. Heating and cooling rates of 6.5 and 4.2 degreesC/s, respectively have been achieved, by optimising the heater dimensions and heating frequency (similar to200 kHz). Four devices are mounted on a heater, resulting in low power consumption (similar to 1.4 W per device on the average). Using simple on-off electronic temperature control, a temperature stability within -0.2 degreesC is achieved. Features such as induction heating, good temperature control, battery operation, and low power consumption make the device suitable for portable applications, particularly in polymerase chain reaction (PCR) systems. (C) 2002 Elsevier Science B.V. All rights reserved.

FE analysis of piezo-laminate composites under thermal loads

A shear flexible 4-noded finite element formulation, having five mechanical degrees of freedom per node, is presented for modeling the dynamic as well as the static thermal response of laminated composites containing distributed piezoelectric layers. This element has been developed to have one electrical degree of freedom per piezoelectric layer. The mass, stiffness and thermo-electro-mechanical coupling effects on the actuator and sensor layers have been considered. Numerical studies have been conducted to investigate both the sensory and active responses on piezoelectric composite beam and plate structures. It is. concluded that both the thermal and pyroelectric effects are important and need to be considered in the precision distributed control of intelligent structures.

Towards the concept of hydrodynamic cavitation control

A careful study of the existing literature available in the field of cavitation reveals the potential of ultrasonics as a tool for controlling and, if possible, eliminating certain types of hydrodynamic cavitation through the manipulation of nuclei size present in a flow. A glass venturi is taken to be an ideal device to study the cavitation phenomenon at its throat and its potential control. A piezoelectric transducer, driven at the crystal resonant frequency, is used to generate an acoustic pressure field and is termed an �ultrasonic nuclei manipulator (UNM)�. Electrolysis bubbles serve as artificial nuclei to produce travelling bubble cavitation at the venturi throat in the absence of a UNM but this cavitation is completely eliminated when a UNM is operative. This is made possible because the nuclei, which pass through the acoustic field first, cavitate, collapse violently and perhaps fragment and go into dissolution before reaching the venturi throat. Thus, the potential nuclei for travelling bubble cavitation at the venturi throat seem to be systematically destroyed through acoustic cavitation near the UNM. From the solution to the bubble dynamics equation, it has been shown that the potential energy of a bubble at its maximum radius due to an acoustic field is negligible compared to that for the hydrodynamic field. Hence, even though the control of hydrodynamic macro cavitation achieved in this way is at the expense of acoustic micro cavitation, it can still be considered to be a significant gain. These are some of the first results in this direction.

Radiation resistance of PFN and PNM-PT relaxor ferroelectrics

The relaxor ferroelectric compositions Pb(Fe1/2Nb1/2)O-3 (PEN) and [Pb(Mg1/3Nb2/3)O-3](0.8)-[PbTiO3](0.2) (PMN-PT) are studied for their radiation response to the high energy heavy ions (50 MeV Li3+, fluence 1 X 10(13)-1 X 10(14) ions/cm(2)) in terms of their structural, dielectric and piezoelectric properties. There was no change in the crystallinity of both the compositions after irradiation as seen from the XRD. The PEN composition did not show much change in the dielectric constant but the value of T-m decreased by 8degreesC. The PMN-PT composition showed an increase in the dielectric constant with increase in the irradiation fluence from 1 x 10(13) to 1 X 10(14) ions/cm(2) with no change in the value of T-m. The piezoelectric coefficient decreased in both the samples after irradiation. Among the compositions studied, PEN is observed to be more radiation resistant to changes in structural and dielectric properties than PM-PT. (C) 2003 Elsevier Ltd. All rights reserved.

Visualizing lone pairs in compounds containing heavier congeners of the carbon and nitrogen group elements

In this mini-review, I discuss some recent work on the stereochemistry and bonding of lone pairs of electrons in divalent compounds of the heavier carbon group elements (SnII, PbII) and in trivalent compounds of the heavier nitrogen group elements (BiIII). Recently developed methods that permit the real-space visualization of bonding patterns on the basis of density functional calculations of electronic structure, reveal details of the nature of s electron lone pairs in compounds of the heavier main group elements – their stereochemistry and their inertness (or lack thereof). An examination of tetragonal P4/nmm SnO, a-PbO and BiOF, and cubic Fm3m PbS provides a segue into perovskite phases of technological significance, including ferroelectric PbTiO3 and antiferroelectric/piezoelectric PbZrO3, in both of which the lone pairs on Pb atoms play a pivotal rôle.

Lamb wave based identification and parameter estimation of corrosion in metallic plate structure using a circular PWAS array

A circular array of Piezoelectric Wafer Active Sensor (PWAS) has been employed to detect surface damages like corrosion using lamb waves. The array consists of a number of small PWASs of 10 mm diameter and 1 mm thickness. The advantage of a circular array is its compact arrangement and large area of coverage for monitoring with small area of physical access. Growth of corrosion is monitored in a laboratory-scale set-up using the PWAS array and the nature of reflected and transmitted Lamb wave patterns due to corrosion is investigated. The wavelet time-frequency maps of the sensor signals are employed and a damage index is plotted against the damage parameters and varying frequency of the actuation signal (a windowed sine signal). The variation of wavelet coefficient for different growth of corrosion is studied. Wavelet coefficient as function of time gives an insight into the effect of corrosion in time-frequency scale. We present here a method to eliminate the time scale effect which helps in identifying easily the signature of damage in the measured signals. The proposed method becomes useful in determining the approximate location of the corrosion with respect to the location of three neighboring sensors in the circular array. A cumulative damage index is computed for varying damage sizes and the results appear promising.

Health Monitoring Of Composite Structures Based On Acoustic Wave Sensing Using Fiber Optic Sensors

Structural Health Monitoring has gained wide acceptance in the recent past as a means to monitor a structure and provide an early warning of an unsafe condition using real-time data. Utilization of structurally integrated, distributed sensors to monitor the health of a structure through accurate interpretation of sensor signals and real-time data processing can greatly reduce the inspection burden. The rapid improvement of the Fiber Optic Sensor technology for strain, vibration, ultrasonic and acoustic emission measurements in recent times makes it feasible alternative to the traditional strain gauges, PVDF and conventional Piezoelectric sensors used for Non Destructive Evaluation (NDE) and Structural Health Monitoring (SHM). Optical fiber-based sensors offer advantages over conventional strain gauges, and PZT devices in terms of size, ease of embedment, immunity from electromagnetic interference (EMI) and potential for multiplexing a number of sensors. The objective of this paper is to demonstrate the acoustic wave sensing using Extrinsic Fabry-Perot Interferometric (EFPI) sensor on a GFRP composite laminates. For this purpose experiments have been carried out initially for strain measurement with Fiber Optic Sensors on GFRP laminates with intentionally introduced holes of different sizes as defects. The results obtained from these experiments are presented in this paper. Numerical modeling has been carried out to obtain the relationship between the defect size and strain.

Ethanol sensing using CuO/MWNT thin film

Copper (II) oxide (CuO)/multiwall carbon nanotube (MWNT) thin film based ethanol-sensors were fabricated by dispersing CVD-prepared MWNTs in varying concentration over DC magnetron sputtered-CuO films. The responses of these sensors as a function of MWNT concentrations and temperatures were measured, and compared. The sensing response was the maximum at an operating temperature near 400 degrees C for all the samples irrespective of the MWNTs dispersed over them. At optimum operating temperature (T(opt)) of 407 +/- 1 degrees C, the response is linear for 100-700 ppm range and tends to saturate at higher concentrations. In comparison with bare CuO sample, the response of CuO/MWNT sensing films increased up to 50% in the linear range. The response improvement for 2500 ppm of ethanol was up to 90% compared to bare CuO sample. In addition, the sensing response time also reduced to around 23% for lowest ethanol concentration at T(opt). However, a decrease in the sensor response was observed on films with very high concentrations of MWNTs. (C) 2011 Elsevier B.V. All rights reserved.

Optimal location of centre of gravity for swashplateless helicopter UAV and MAV

To investigate the use of centre of gravity location on reducing cyclic pitch control for helicopter UAV's (unmanned air vehicles) and MAV's (micro air vehicles). Low cyclic pitch is a necessity to implement the swashplateless rotor concept using trailing edge flaps or active twist using current generation low authority piezoceramic actuators. Design/methodology/approach – An aeroelastic analysis of the helicopter rotor with elastic blades is used to perform parametric and sensitivity studies of the effects of longitudinal and lateral center of gravity (cg) movements on the main rotor cyclic pitch. An optimization approach is then used to find cg locations which reduce the cyclic pitch at a given forward speed. Findings – It is found that the longitudinal cyclic pitch and lateral cyclic pitch can be driven to zero at a given forward speed by shifting the cg forward and to the port side, respectively. There also exist pairs of numbers for the longitudinal and lateral cg locations which drive both the cyclic pitch components to zero at a given forward speed. Based on these results, a compromise optimal cg location is obtained such that the cyclic pitch is bounded within ±5° for a BO105 helicopter rotor. Originality/value – The reduction in the cyclic pitch due to helicopter cg location is found to significantly reduce the maximum magnitudes of the control angles in flight, facilitating the swashplateless rotor concept. In addition, the existence of cg locations which drive the cyclic pitches to zero allows for the use of active cg movement as a way to replace the cyclic pitch control for helicopter MAV's.

Structural Health Monitoring (SHM) Using Strain Gauges, PVDF Film and Fiber Bragg Grating (FBG) Sensors: A Comparative Study

The term Structural Health Monitoring has gained wide acceptance in the recent pastas a means to monitor a structure and provide an early warning of an unsafe conditionusing real-time data. Utilization of structurally integrated, distributed sensors tomonitor the health of a structure through accurate interpretation of sensor signals andreal-time data processing can greatly reduce the inspection burden. The rapidimprovement of the Fiber Bragg Grating sensor technology for strain, vibration andacoustic emission measurements in recent times make them a feasible alternatives tothe traditional strain gauges transducers and conventional Piezoelectric sensors usedfor Non Destructive Evaluation (NDE) and Structural Health Monitoring (SHM).Optical fiber-based sensors offers advantages over conventional strain gauges, PVDFfilm and PZT devices in terms of size, ease of embedment, immunity fromelectromagnetic interference(EMI) and potential for multiplexing a number ofsensors. The objective of this paper is to demonstrate the feasibility of Fiber BraggGrating sensor and compare its utility with the conventional strain gauges and PVDFfilm sensors. For this purpose experiments are being carried out in the laboratory on acomposite wing of a mini air vehicle (MAV). In this paper, the results obtained fromthese preliminary experiments are discussed.

Benchmark Control Problem for Highway Bridge based on FLC

Fuzzy logic control (FLC) systems have been applied as an effective control system in various fields, including vibration control of structures. The advantage of this approach is its inherent robustness and ability to handle non‐linearities and uncertainties in structural behavior and loading. The study evaluates the three‐dimensional benchmark control problem for a seismically excited highway bridge using an ANFIS driven hydraulic actuators. An ANN based training strategy that considers both velocity and acceleration feedback together with a fuzzy logic rule base is developed. Present study needs only 4 accelerometers and 4 fuzzy rule bases to determine the control force, instead of 8 accelerometers and 4 displacement transducers used in the benchmark study problem. The results obtained are better than that obtained from the benchmark control algorithm.