Table of contents

Various examples are presented to illustrate the interdisciplinary nature of chemical sensor research at the Linkoping Institute of Technology. At least three goals were followed-developing basic knowledge, developing new sensor ideas, and helping industry to solve specific sensor problems. Among examples presented are: the anaesthetic gas monitor called EMMA; a gas concentrator and separator for use in measuring very small quantities of halogenated hydrocarbons; H₂-sensitive Pd-MOS structures for use in leak detection of buried cables and medical diagnostics.

A review of attempts which have been made to produce in vivo images of the spatial distribution of tissue resistivity is given. The collection systems for in vivo images and the methods for the reconstruction of such images are discussed. Some of the problems that remain to be solved for applied tomography are identified.

By simulating various contact geometries with evaporated gold Schottky pads on epitaxial GaAs, an optimised design for the mercury probe has been obtained. This involves a circular reverse biased contact surrounded by a concentric forward biased ring, whose area is as large as possible.

The precision of hyperfine field determinations by Mossbauer spectroscopy can be improved by carrying out measurements on absorbers comprising both the sample to be studied and an internal standard, e.g. an Fe foil. The improvement brought about by this method is illustrated by measurements on a series of aluminous hematites. Use of an Fe foil as internal standard reduced the standard deviation of hyperfine fields determined for the antiferromagnetic phase of hematites at 4.2K from 1.6 to less than 0.4 kOe. The improved precision allowed the assessment of the degree of aluminium substitution from these measurements-which was not possible from the uncorrected data-to about +or-1%.

Equipment for photon correlation spectroscopy (PCS) measurements in the heterodyne mode, using a mixing technique for the scattered and reference beam outside the scattering cell, has been developed, starting from a commercial apparatus for PCS measurements in the homodyne mode. It is also possible to switch from heterodyne to homodyne measurement without changing the sample in the scattering cell. Experimental results using a suspension of polystyrene latex particles are shown to demonstrate that with this equipment correct heterodyne correlation functions can be determined.

A novel modification of stroboscopic illumination was used to give an unambiguous record of the direction of the flow in an otherwise conventional visualisation of a complex three-dimensional air-flow. In this particular experiment, the flow was seeded with small soap bubbles which were viewed by scattered light. Each flash of light was split into two periods of unequal length, separated by a short extinction, thereby marking the direction of flow on the photographs. The technique allows a more complete determination of the velocity field than can be obtained by the usual stroboscopic method.

A simple technique has been used to investigate the linearity of response of Kodak 10101 EUV film at low exposure levels. Radiation at lambda approximately 18.2 nm from a laser produced plasma and at lambda approximately 17 nm from a Garton flash tube were used in separate experiments to study the response for ns and mu s exposure times. This film responds linearly up to film densities of 0.45 D above fog. The technique is generally applicable to films recording spectra from the X-ray to VUV regions.

The dielectric properties of nitrocellulose/nitroglycerine propellants have been examined. The authors demonstrate the analysis of the data using a microcomputer, with particular reference to obtaining epsilon ₀, epsilon _infinity , and the distribution parameters alpha and beta as defined in the Havriliak-Negami formula.

It is demonstrated that stimulated Raman scattering (SRS) continuum from an optical fibre may conveniently be used as the monitor light source in flash-photolysis experiments. The construction of a transient absorption spectrometer and its performance are described. The SRS continuum is intense enough for a single-shot recording of a transient spectrum. The power requirement is quite modest. An advantage of this approach is that no fast (and expensive) detection system is necessary. The apparent difficulty arising from the rather large shot-to-shot function of the SRS spectrum is eliminated by a double-beam arrangement using a pair of diode arrays as detectors.

Reports the effect of composition and sheet resistance on the gauge factor and temperature coefficient of resistance of thin Cr-SiO cermet films. The films were deposited onto smooth glass microscope slides using both flash evaporation and RF sputtering. The measured gauge factor and temperature coefficient of resistance is shown to increase with decreasing chromium content. A monatonic relationship between the measured gauge factor and temperature coefficient of resistance is established. The composition of the deposition films has been analysed as a function of depth using Auger electron spectroscopy. The composition of the deposited films is shown to consist of chromium, elemental silicon, silicon oxide of differing stoichiometry together with other oxides formed during deposition.

A doubly preionised ArF excimer laser is described using a pulse forming network (PFN) with an LC-inversion circuit totally enclosed inside the laser volume. The high potential difference across the capacitors uniformly preionises the laser gas and arcing is prevented by carefully shaping the metal surfaces inside the laser. By applying normal preionisation techniques the main discharge runs in a stable mode. The output energy of the laser from a volume of 65 cm³ was 50 mJ at a charging voltage of 25 kV and the performance of the laser with the pre-ionisation technique is compared with the performance of two other excimer lasers without the use of this technique. A circuit model indicates that good preionisation results in better impedance matching between the PFN and the laser plasma.

The design of an AC potential drop (ACPD) system for monitoring crack length in fracture specimens is outlined. The amplified voltage across a cracked specimen is compared with that across a reference specimen by employing a dual-slope analogue to digital convertor in the radiometric mode. The resultant digital output provides an accurate measure of the crack length. Because of the strong skin effect in steel even at relatively low frequencies, the output varies linearly with crack length. Although the output is insensitive to variations in specimen current and temperature, it is affected by the position of the sensing and current leads and by the presence of ferromagnetic materials in the vicinity of the specimen. In the case of steel, whilst the ACPD output is increased by crack growth it is decreased by tensile stress and plasticity in the specimen. The competition between the two opposing effects enables the ACPD to detect initiation of crack extension even when crack growth is accompanied by large scale plasticity.

A technique is presented to determine the complex permittivity epsilon = epsilon '-j epsilon " by means of a coaxial line set-up for transmission coefficient measurement within the frequency range of 1 to 1000 MHz. A highly sensitive broad-band vectorvoltmeter and dielectric sample cells of the cut-off variety enable precise measurements in a comparatively short time and ease of handling. The cells are designed for the investigation of weakly as well as highly polar liquid dielectrics. The relative error of the real part epsilon ' of the complex permittivity typically amounts to 1-2% and the absolute error of the dielectric loss angle up to 0.3 degrees .

The resistance-temperature characteristics and self-heating of three ceramic-encapsulated rhodium-iron alloy resistance thermometers have been studied below 80K. The stability of the thermometers at 20K on repeated thermal cycling between 20 and 288K proved to be excellent (+or-25 mu Omega over 20 cycles). Small changes in resistance (up to 0.6 m Omega ) were noted on physical handling of the thermometers.

A device for remoulding tip-shaped field emitters is presented. It is described in the context of field electron emission, but many of its basic principles will apply to field ion emission as well. The system consists of two high tension cascades providing positive and negative high voltage, a device generating DC (constant or intermittent) for resistively heating the emitter, the microcomputer system and some additional protection circuits. First tests of the remoulding system in a simple field electron emission assembly are reported. A novel type of remoulding method is presented where the emitter is switched to field electron emission operation between heating pulses. This allows a better and faster control of the remoulding process. The normally desirable emission pattern consisting of only one single bright spot could be produced conveniently and quickly. Future possibilities for improving the system in terms of automating the remoulding process are discussed.

A description is given of a vibrating capacitor probe that is UHV compatible, bakeable to 350 degrees C, and capable of movement in three dimensions for scanning measurements of the potential of specimen surfaces, such as on freshly cleaved NaCl single crystals. A novel pulse method of capacitor drive greatly reduces electromagnetic pick-up and enables reliable measurements to be made on poorly conducting specimen surfaces. Calibration curves show that probe output is a linear function of specimen surface potential for values up to 10 V, with a probe sensitivity of 4 mV over a specimen temperature range varying from room temperature to 450 degrees C. Evaluation of probe performance shows that freedom from random spurious signals makes the probe well suited for the purpose for which it was designed.

A published method for estimating the thermal conductivity of powders, using an electrically-heated copper probe embedded in the sample, has been tried successfully on pyrotechnic compositions of antimony and potassium permanganate with various fuel/oxidant ratios. An alternative method for mathematical analysis of results is suggested. The thermal conductivity results obtained have been compared with predictions from several models of heat transfer in granular materials. These predictions have also been compared with published results for the tungsten/potassium dichromate pyrotechnic system.

A compact apparatus designed for accurate thermal conductivity measurements in the range 10 W.m^-1 K^-1 to 380 W.m^-1 K^-1 from 50 degrees C to 500 degrees C is described. It operates on the linear heat-flow principle using bar-shaped specimens clamped between guarded heater-unit and a water-cooled heat-sink, surface heat losses being minimised by a system of heat shields and allowed for in the evaluation of the conductivity using a simple analytical approach. The performance of the apparatus is illustrated in terms of the results obtained on stainless steel, electrolytic iron and tungsten certified reference materials supplied by the National Bureau of Standards (USA). Agreement between the measured and certified values is better than +or-3.1% throughout the above temperature range.

Theoretical and experimental investigation of the frequency response of fine-wire thermocouples is presented for the case of heated airflows (300K<T<800K) and for 0.5 m s^-1<U<8 m s^-1. The influence of temperature on the thermocouple transfer function has been studied through the variation of physical properties of surrounding gas and thermocouple material. Dynamic calibration has been carried out by using an 'external heating technique'. This study provides evidence that, over the velocity and temperature ranges considered, the transfer function depends on thermocouple geometry (r_w and r_b/r_w) as well as on characteristics of the flow (velocity and temperature).

Studying amorphous ferromagnetic ribbons, a system for helical stress annealing has been performed. The angular deformation against the time at constant applied torque, torsional creep, and the relaxation curves can be obtained. The helical induced magnetic anisotropy is also measured. During the annealing processes the magnetic behaviour can be observed for an annealing temperature below the Curie temperature. The M_z against H_z and M_z against H_y (inverse Wiedemann effect) hysteresis loops are measured.

The impact dynamics of a high strain rate compression test are analyzed and shown to give strain data in good agreement with those obtained by direct observation using high speed photography. The analysis can be used either as a curve fitting procedure for the photographic data or as an independent technique.