Table of contents

An overview of fibre-optic interferometry based sensing is given, particularly as it applies to high-performance sensing applications. The operation of a fibre-optic interferometer as a sensor is reviewed. The sensitivity limitations of a fibre-optic sensor are derived, and the system impact of multiplexing many sensors together is explored. A review of the development of the fibre-optic acoustic transducer is presented, as well as system applications and future trends in fibre-optic interferometric sensing.

The magnetocaloric effect and the order of magnetic transition in La(Fe_0.88Al_0.12)₁₃C_x interstitial compounds have been investigated by means of magnetic measurements and Mössbauer spectroscopy. With increasing carbon content from x = 0.2 to 0.6, the maximum magnetic entropy change decreases from 9.6 to 8.3 J kg⁻¹ K⁻¹ under an external field of 5 T, which is comparable with that of pure Gd metal. Analyses of magnetic measurements and Mössbauer results indicate there is a weakly first order magnetic transition between ferromagnetic and paramagnetic (F–P) states at T_C for x = 0.2. Increasing the carbon content drives the F–P transition towards second order, which is the main reason why the magnetic entropy change decreases with increasing carbon content.

The effect of production method on the chemical and magnetic stability of a range of cobalt nanoparticles formed in polysiloxane copolymer micelles was studied. The nanoparticles were suspended in polydimethylsiloxane (PDMS) carrier fluids and are prototypes for use in biomedical applications. Three families of particles were investigated: cobalt particles in triblock copolymer micelles and silica-coated cobalt particles where the silica coating is formed either in toluene or PDMS carrier fluid. The silica coating effectively protects the cobalt particles from ongoing oxidation, with little change in the saturation magnetization of the particles observed over time and only a small shift in the centre of the field-cooled hysteresis loop observed. Temperature-dependent magnetization measurements show that the silica-coated particles have superparamagnetic blocking temperatures of 100–130 K compared with the non-silica-coated particles, which do not reach their characteristic blocking temperature below the melting point of the frozen fluids. This result is interpreted as a smaller magnetic core size in the silica-coated particles. The zero-field-cooled temperature-dependent magnetization of the silica-coated particles has two apparent superparamagnetic blocking temperatures, with a second, lower blocking temperature of approximately 15 K. This second apparent blocking temperature may be due to unreacted cobalt clusters in the suspensions or, alternatively, due to surface states on the nanoscale cobalt particles. The prototype silica-coated cobalt particles show promise for potential biomedical applications.

We present a theory for predicting fluid ejection for microfluidic systems that utilize the squeeze-film effect as the dominant pressure generation mechanism. We derive the equations of motion for such systems taking into account both viscous and inertial effects. The dominant viscous term is due to the squeeze-film effect, in which a thin layer of incompressible viscous fluid is 'squeezed' between a moving piston and an orifice plate. We apply Reynolds lubrication theory and derive an analytical expression for the squeeze-film pressure distribution, taking into account both flow through the orifice and restricted flow around the piston. The dominant inertial effects are due to the acceleration of fluid between the piston and the orifice plate, through the orifice, and around the piston. We derive an analytical expression for an effective fluid mass that accounts for these effects. We use these expressions in the equations of motion and obtain a theoretical model for predicting the behaviour of squeeze-film dominated microfluidic fluid ejectors. We demonstrate the theory via application to a practical device.

The effects of Er³⁺ concentration in ZrO₂ on the red (680 nm) and green (545 nm) upconversion emission from Er³⁺ under near infrared radiation (NIR) excitation (at both 1438 and 962 nm) are presented. For the highest Er³⁺ concentration used, the red band is almost quenched under VIS (489 nm) excitation, whereas it is enhanced under NIR excitation. Such a difference between photoluminescence and upconversion is explained taking into account the concentration dependent cross-relaxation process (²H_11/2 + ⁴I_15/2) → (⁴I_9/2 + ⁴I_13/2). Experimental results suggest that two- and three-photon upconversion processes are taking place under 962 nm and 1438 nm excitation, respectively.

Light emission in the UV and visible (blue) range (330–440 nm) generated by an IR image converter and the possibility of locally increasing the gas discharge light emission for a given photosensitivity of a planar GaAs semiconductor photocathode were studied. The use of metallic patched concentrators with an area of S = 5 × 10⁻⁴ cm² and a density of 400 cm⁻² and an IR light to excite the photocathode of the system leads to a fivefold increase in the gas discharge light intensity. In a system with metallic patched concentrators, the local density of gas-discharge light exceeds the density of uniform gas-discharge light in an IR image converter by the same factor by which the working area of the photocathode exceeds the total area of the current concentrators. Moreover, the use of metallic patched concentrators prolongs the working time of the photocathode. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap, which changed the discharge from the Townsend to the glow type.

Electrical breakdown of cold (room temperature) metal-halide arc lamps typically occurs through the fill of a rare gas (at a pressure of tens of Torrs) and the vapour produced by the metal donor. Restarting a warm lamp is often made difficult by the high pressure of the metal and metal-halide vapours. To reliably start cold lamps with a minimum voltage and a minimum sputtering of the electrodes, and to restart warm lamps that have a high pressure of the metal and metal-halide vapours, auxiliary sources of ionization are often used. As a point of departure for the study of these processes, measurements of formative breakdown times were made in a cylindrical discharge tube resembling a compact polycrystalline alumina envelope metal-halide lamp. Breakdown times were measured for Ar/Xe gas mixtures at total pressures of 10–90 Torr and biases up to 2 kV applied to a 1.6 cm gap. The data provide a knowledge base for a companion computational investigation. We found that breakdown times generally decreased with small admixtures of Xe in Ar (5–15%) and increased with larger admixtures. We attribute these trends to the changing shape of the tail of the electron energy distribution.

The breakdown phase of the startup of metal halide lamps is typically through a cold fill of a rare gas and the ambient vapour pressure of a dose of metals. The dynamics of the breakdown stage are of interest for improving the efficiency and lifetime of lamps. A computational investigation of the breakdown of Ar/Xe mixtures in an idealized lamp geometry was performed using global and two-dimensional (2-d) models to provide insight into the lamp ignition processes and to facilitate comparison with experiments. The experimental trends for breakdown for pressures of 10–90 Torr were qualitatively captured with the global model. Quantitative agreement required accounting for the temporal and spatial plasma dynamics included in the 2-d model. Small fractions of Xe in Ar were found to decrease the breakdown time as the ionization rates increased due to the lower ionization potential of xenon, while the electron energy distribution was not significantly affected. With higher Xe fractions the electron temperature in the ionization front decreased due to there being larger momentum transfer and inelastic losses to the Xe, and as a result the breakdown times increased. The compression of voltage ahead of the ionization front produced large electric fields at the cathode that enabled significant contributions to ionization by secondary electrons.

Self-organizing 'neck' type instabilities in capillary discharges are believed to be responsible for the population inversion in vacuum ultraviolet (VUV) spectral region. Selective population of the lasing levels originates as a result of charge–exchange recombination of the hot plasma ions during their flow from 'necks' into the cold surrounding gas. We propose a new approach of the 'induced neck' exploiting the axially inhomogeneous shock wave, generated in a capillary with a special wall profile and with high discharge current time derivative (about 10¹² A s⁻¹). A series of experiments with argon filling of the profiled capillary tube were performed. Time resolved pinhole VUV images of the discharge volume demonstrate the presence of the hot and compressed plasma objects on the discharge axes. All of them reproducibly appear at the same time and strictly on the axis of the capillary, in accordance with the wall structure. The VUV spectra, emitted by the compressed plasma, indicate a rather high electron temperature (50–100 eV), which must be sufficient for the production of hot plasma outflow.

This paper presents a theoretical model for describing globular transfer in gas metal arc welding. The heat and mass transfer in the electrode, arc plasma and molten pool are considered in one unified model. Using the volume of fluid method, the transport phenomena are dynamically studied in the following processes: droplet formation and detachment, droplet flight in arc plasma, impingement of droplets on the molten pool and solidification after the arc extinguishes. The simulation of heat and mass transfer in the arc plasma considers the developing surface profile of the electrode and molten pool and also the effect of the flying droplet inside the arc plasma. Furthermore, the heat inputs to the electrode and the molten pool result from the simulation of the arc plasma. In addition, a He–Ne laser in conjunction with the shadow-graphing technique is used to observe the metal-transfer process. The theoretical predictions and experimental results are shown to be in good agreement.

Breakdown at atmospheric pressure in a nitrogen discharge is examined using analytic calculations and numerical solutions of the fluid equations and the Boltzmann equation. The fully analytic capacitor model is set up by dividing the discharge 'capacitor' into N small capacitors and letting them break down one at a time. The fluid model uses transport parameters found from the kinetic model, but it gives the best agreement with the kinetic model when it is made to conserve the mean kinetic energy, κ, when the parameters in the model are expressed in term of κ rather than of the electric field, E, and when the fluid model uses a mesh similar to that required for the kinetic model. The 'local' and 'non-local' behaviours of the breakdown in the discharge are examined. In long discharges, we see that the density at any point tends to saturate when the electric field is shielded out, and in this limit the density agrees well with the analytic N-capacitor model, which embodies the same principle of energy conservation as governs the saturation of density in the fluid model.

Classical fracture mechanics applied to a viscoelastic material states that the critical stress-intensity factor at which the crack propagates depends on the instantaneous elastic modulus of the solid, and provides no mechanism for a speed dependence of the apparent surface energy. This suggests that any speed dependence must be because surface energy itself is speed-dependant. Schapery (1975) has explained how by using the Barenblatt concept of fracture mechanics, involving surface forces instead of surface energy alone, a dependence of the apparent surface energy on the crack speed is found. Here, Schapery's principles are applied to the particular case of a Maugis–Dugdale surface force law and a three-element viscoelastic solid to find the complete dependence of the apparent surface energy, both in fracture and in crack healing, on the crack velocity. To a good approximation, the apparent surface energy in crack healing is the reciprocal of the energy for fracture. Simple approximate equations relating the crack speed to the stress-intensity factor are given.

The dispersion relation for surface and bulk plasmons in a two-component optical semiconductor superlattice (2COSSL) arranged in periodic fashion is derived in the non-retardation limit using the one-dimensional transfer matrix method. Detailed calculations are presented for a [(GaAS/Al_0.3Ga_0.7AS)/glass] geometry, treating one of the alternating layers as frequency dependent and the other as frequency independent, and for a [(GaSb/InAS)/SiO₂] geometry, treating both the layers as frequency dependent. An extension of this theory has been carried out in a three-component optical semiconductor superlattice (3COSSL). Spectral properties of bulk plasmons are demonstrated for the 3COSSL in symmetrical (air/GaSb/air) and unsymmetrical (air/GaSb/SiO₂) geometries. It is indicated that a three-component periodic multilayered system is a better option for designing optical devices such as optical filters, filter-polarizers, monochromators and etlons.

The influence of C₆₀ on fluorescence spectra, UV–visible spectra and photoconductivity of polymethylphenylsilane (PMPS) has been studied. The results show that the photoconductivity of PMPS doped with C₆₀ increases by one order of magnitude. The fluorescence and UV–visible analyses indicate that an intermolecular charge-transfer complex of PMPS and C₆₀ may be formed. Compared with C₆₀-doped PMPS, the C₆₀-linked PMPS displays higher photoconductivity than expected, which may come from the intramolecular charge-transfer process.

A series of Co thin films have been evaporated onto Si(100) and glass substrates. The Co thickness, t_Co, ranges from 50 to 195 nm. The structural and magnetic properties have been investigated by x-ray diffraction, hysteresis curves, Brillouin light scattering and magnetic force microscopy (MFM) techniques. The Co thin films are found to be polycrystalline with (0001) texture. There is an increase of the grain size with increasing film thickness. The coercive fields range from values as low as 2 Oe in thinner films to the highest values, 2500 Oe, in 195 nm thick Co/Si films. The magnetocrystalline anisotropy field H_a decreases as the thickness increases; surface and stress induced anisotropies seem to contribute to the value of H_a. MFM images reveal a well-defined stripe pattern for thicker Co/Si samples. Such domains are not observed in the case of the thinner films. These so-called weak-stripe domains appear in magnetic films with a low or intermediate perpendicular anisotropy. Similar behaviour was observed in Co/glass samples, in addition, cross-tie walls were seen in thinner ones.

Structural refinement and Raman spectroscopy were used to obtain structural information for Bi_3.25La_0.75Ti₃O₁₂, including site preference of La atoms, cation distribution, cation occupancy and lattice parameters. Structural refinement was carried out for three cation disorder models. The best structural refinement result was obtained assuming that, of the three possible substitutions, La atoms substitute Bi atoms only in the perovskite Bi₂Ti₃O₁₀ unit. The final weighted R-factor, R_wp, and the goodness-of-fit indicator, S (=R_wp/R_e), were 4.81% and 1.56%, respectively. The results of Raman spectroscopy provided evidence for the cation disorder model. The band originating from the Bi atoms in the Bi₂O₂ layer did not show significant changes while the vibrational modes assigned to the Bi atoms in the perovskite units moved to high frequencies due to the substitution of La atoms. The final lattice parameters obtained from the refinement were a = 5.4238(1) Å, b = 5.4169(2) Å and c = 32.9002(2) Å. The β angle was 90.09°.

In this work the effect of hydrogen addition on the physical properties and the sputtering efficiency of an radio-frequency (rf) (13.56 MHz) Ar plasma was investigated. The discharges in Ar–H₂ were used to sputter-deposit carbon films from a graphite cathode, with a hydrogen concentration in the feed gas ranging from 0 to 100% (the useful range for film growth was however limited to 0–85%). The physical plasma parameters were determined using a Langmuir probe, which, coupled with a chemical modelling of the ion–molecule and electron–molecule reactions in gas phase, enabled us to define the energy flux conditions at the cathode. The results show that hydrogen exerts a positive effect on the film deposition rate at the lowest end of the hydrogen concentration range, an enhancing deposition effect correlated with a high density of ArH⁺ ions in the plasma and a high energy flux carried by the ions to the cathode. Nonetheless, an analysis of the processes at the cathode indicates that the sputtering mechanism was essentially physical in the low [H₂] range (3–20%) but that a chemical assistance of the process should be considered too for the remaining [H₂] range. Besides, even in the physical sputtering regime, the target material removal occurred with a reactive sputtering mechanism, which implies a chemical modification of the target surface layers and surface binding energy.

Neutron image plates (NIPs) have found widespread application as neutron detectors for single-crystal and powder diffraction, small-angle scattering and tomography. After neutron exposure, the image plate can be read out by scanning with a laser. Commercially available NIPs consist of a powder mixture of BaFBr : Eu²⁺ and Gd₂O₃ dispersed in a polymer matrix and supported by a flexible polymer sheet. Since BaFBr : Eu²⁺ is an excellent x-ray storage phosphor, these NIPs are particularly sensitive to γ-radiation, which is always present as a background radiation in neutron experiments. In this work we present results on NIPs consisting of KCl : Eu²⁺ and LiF that were fabricated into ceramic image plates in which the alkali halides act as a self-supporting matrix without the necessity for using a polymeric binder. An advantage of this type of NIP is the significantly reduced γ-sensitivity. However, the much lower neutron absorption cross section of LiF compared with Gd₂O₃ demands a thicker image plate for obtaining comparable neutron absorption. The greater thickness of the NIP inevitably leads to a loss in spatial resolution of the image plate. However, this reduction in resolution can be restricted by a novel image plate concept in which a ceramic structure with square cells (referred to as a 'honeycomb') is embedded in the NIP, resulting in a pixelated image plate. In such a NIP the read-out light is confined to the particular illuminated pixel, decoupling the spatial resolution from the optical properties of the image plate material and morphology. In this work, a comparison of experimentally determined and simulated spatial resolutions of pixelated and unstructured image plates for a fixed read-out laser intensity is presented, as well as simulations of the properties of these NIPs at higher laser powers.

For safe handling and storage of munitions it is necessary to assess the response of energetic materials. In this work, a method to determine the unreacted Hugoniot of a plastic bonded explosive (PBX) using commercial manganin pressure transducers is described. The Hugoniot for the PBX has been measured using single stage gas guns. The unreacted Hugoniot states determined have been measured under ambient conditions, and the results are compared with work upon a sugar based mock PBX of a similar composition. Comments are made on the ease of calculating the response of the composite based upon knowledge of the individual phases.

By exploiting tapping mode atomic force microscopy, the moisture-induced degradation mechanisms of ITO (indium tin oxide)-coated glass/CuPc (copper phthalocyanine)/NPB (N, N'-di(naphthalene-1-yl)-N, N'-diphthalbenzidine)/Alq₃ (tris(8-hydroxyquinoline) aluminium)-based organic light-emitting diodes without cathode were investigated. It is found that three types of degradation mechanisms are associated with moisture-exposed Alq₃ films, when the device is exposed to moisture, namely, hydration of Alq₃, crystallization of Alq₃ and reaction of the Alq₃ complex with H₂O. Crystallization of the NPB layer of ITO/CuPc/NPB was observed on exposure to moisture, and de-wetting simultaneously takes place at the interface of CuPc/NPB. Indium and/or oxygen may diffuse from ITO into the organic layers. These observations provide a clear picture of the moisture-induced degradation mechanisms of the ITO/CuPc/NPB/Alq₃-based OLEDs.