Table of contents

Describes a capacitive displacement sensor using the spatial sampling principle. A first experimental prototype has been manufactured. Measurements show that this prototype achieves a resolution of 1 mu m and an accuracy of 3 mu m over a displacement of 150 mm. The linear displacement range can be as large as several metres. The prototype confirms low sensitivity to both alignment inaccuracies and external influences like dust and electromagnetic disturbances.

In a measurement system with intelligent, distributed sensor processes, complementary observations from different sensors need to be combined with each other. For this purpose, the authors introduce a concept where the sensor uses its input data to form an opinion, in the form of a fuzzy membership, on hypotheses regarding the state of the environment. These local opinions are then combined into a global opinion. This paper focuses on developing measures of distance between fuzzy opinions. These may be used to cluster opinions into groups prior to fusing them.

A modified computer-controlled high-temperature X-ray diffractometer with good stability and an upper temperature limit of more than 2300 K is described. a critical test of the system, determining the thermal expansion of Pt, Ni and AlN, showed close agreement with dilatometric and literature data. Lattice thermal expansion data of CrB₂ and TiB₂ up to 2100 K were also determined.

A method of obtaining phase fringe patterns of improved quality using electronic speckle pattern interferometry (ESPI) is complemented by new equations governing the displacement sensitivity if asymmetric illumination is used. The techniques are experimentally verified. The accuracy of the method for determination of highly localized strain fields is demonstrated by comparing the measurements with the results of a finite-element model. The potential of the improved method in the field of fracture mechanics is outlined.

An interferometric dilatometer has been designed for determination of thermo-optic coefficients of millimetric nonlinear optical (NLO) materials. The apparatus is a combination of a modified Mach-Zehnder arrangement for dilation measurements and a Fizeau technique for determination of changes in optical length. Its configuration allows measurements under known conditions of applied electric field. Analysis of the linear thermal expansion coefficient alpha _b of a triglycine sulphate (TGS) single crystal around its second-order phase transition is used to evaluate the sensitivity of the interferometer, and measurements performed on a LiNbO₃ single crystal exhibit step-like variations of changes in optical length from 20 degrees C to 122 degrees C. These experiments show that an accuracy better than 1*10^-6 K^-1 is achievable for both dilation and thermo-optic coefficients with this dilatometer, provided that they are not highly temperature-dependent and are under the condition of suitably controlled applied electric field.

Yttrium aluminium garnet scintillators coupled to photo-diode arrays (YAG/PDA) are used extensively in parallel electron energy loss spectrometers (PEELS). The use of uniform illumination spectra acquired with the electron beam spread over a YAG/PDA has been shown to be inadequate for determining the response of YAG/PDA detectors to electrons. The electron response of a YAG/PDA detector depends on the specific operating conditions of both spectrometer and electron microscope and should be determined under the same experimental conditions as used for collecting the spectra for analysis. The response of a YAG/PDA can be conveniently measured by translating the electron beam, with no specimen intercepting the beam, across the detector while acquiring a long-integration-time spectrum. This technique was used to examine the effect on YAG/PDA response of changes in spectrometer energy resolution and entrance aperture size for a particular spectrometer. The technique was also used to examine the effects of incomplete charge collection in the PDA. YAG/PDAS are also shown to exhibit nonlinear response to electron intensity and a phenomenological correction factor is determined for one set of microscope and spectrometer operating conditions. The cause of ripple observed in spectra collected at the highest resolution of the PEELS, while the electron beam was being translated across the YAG/PDA, was investigated and was determined to be due to low level electromagnetic noise deflecting the electron beam across the detector.

A novel model is presented for estimation of the secondary electron intensity distribution in linewidth measurements using scanning electron microscopes (SEMS). A cylindrical envelope projection model is proposed for both steep and gentle slants, such that the secondary electron emission area is defined by the surface included by a cylindrical volume rather than the spheroids of conventional models. Predictions from the model have been experimentally verified and the model may be confidently used for the measurement of topological specimen features.

A simple, low-cost Q-switching technique, based on a rotating mirror, is described. When applied to an alexandrite laser the rotation speeds are so low (typically <2000 rpm) that almost any small motor can be employed without paying particular attention to balancing. Optimum design features and performance were investigated both experimentally and theoretically for a room-temperature laser running in single-mode or multimode. Predictions, based on a rate-equation model, are provided to allow optimum design of systems using different rod lengths, pumping powers, temperatures or wavelengths.

A correlation method for accurate measurement of ultrafast optical pulses of femtosecond resolution is presented. It uses a lock-in amplifier and a variable mixing method of reference frequencies in a Michelson interferometer. The read-out system consists of an X-Y plotter or a computer monitor. This technique does not require high-speed photodetectors but is sufficiently sensitive to plot femtosecond pulses at low optical power level (about 10 mu W average power). The measurement of 320 fs FWHM light pulses from an actively mode-locked semiconductor laser and a contrast ratio of 80 were demonstrated. The resolution of this technique is believed to be a few femtoseconds.

A non-contact, optical fibre-based vibrometer is described with output in the form of a set of spatial fringes. The fringe system is sampled at three different phases using a non-multiplexed linear detector array. No source frequency modulation is necessary, allowing convenient use of a wide variety of lasers, and surface motion is measured free from directional ambiguity. Fringe interpolation and multiple-fringe unwrapping are effected using a digital fringe processor. With a received power of 4 nW, a minimum noise-equivalent phase sensitivity of 150 mu Rad Hz^-1/2 is demonstrated.

A novel concept for a digital rotary displacement sensor is presented. Broadband light issuing from the encoder input fibre is focused on a 9 bit Gray coded dis. Rays emerging from the disc under Littrow conditions are diffracted back to the input fibre by a grating. The output spectrum is encoded as a function of the disc's angular position. The theoretical prediction of the sensor's performance is developed and compared with experimental results. A prototype with a resolution of 0.7 degrees and a nonoperating range of 360 degrees has been successfully tested.

A simple and easily calibrated thin film thickness monitor involving optical fibre components is described. Film thickness was determined by monitoring the return power via a 2*2 directional coupler arrangement. This optical fibre monitor was used to calibrate a conventional quartz crystal microbalance.

The design and construction of a novel cryogenic cell which may be used to carry out photoacoustic measurements on either opaque or transparent samples are described. The design allows any temperature to be employed within 0.5 K. Results for graphite test samples show the expected inverse frequency dependence of the photoacoustic signal, increase in signal with decreasing temperature and resonance effects at low temperature.

The authors report on measurements of the dynamic range and the spatial resolution in streaked mode for a Kentech 2* magnifying XUV/X-ray streak camera. The Balmer- alpha line at 18.2 nm from a laser-produced carbon plasma, attenuated by a thin-film copper step wedge, is used to generate the input photon flux or varying intensity on the 0.5 mm*20 mm CsI photocathode. For X-ray pulse durations between 400 ps and 4.0 ns the dynamic range is found to vary between 180 and 2*10⁴ with a spatial resolution along the photocathode of 7 lp/mm. Calibration of the streak rates in combination with a proximity focused image intensifier completes the characterization.

Initial film growth in electroless deposition has been investigated nondestructively by measuring the variation in transmissivity of He-Ne laser light. A specific correlation has been observed between the results of the transmissivity measurement and the structures and magnetic properties of deposited films.

Biomagnetic measurements have been made since 1963. Since then measurement devices have been developed with increasing sensitivity. When performing biomagnetic investigations, one hs to choose between an expensive high-performance shielding and a cheaper but sophisticated and more noisy gradiometer technique. Combined methods of shielding and gradiometers are difficult because of the distortion of the field homogeneity due to shielding material. Nevertheless, combined means of weak shielding and balanced gradiometers can be satisfactory compromise with adequate signal-to-noise ratio and reasonable expense. In the Ragnar Granit Institute at Tampere University of Technology a shielding chamber consisting of thick aluminium walls has been used. For this study a DS SQUID system with a well-balanced second-order gradiometer was developed to improve the signal-to-noise ratio. The results of this work are presented.

A nonlinear transmission line (NLTL) is used to speed up the risetime of high voltage (>1 kV) pulses. The theory of the NLTL is reviewed and practical implementations and limitations are discussed. An NLTL is used to generate a 1.5 kV pulse with a risetime of 500 ps. A discussion of generating pulses with amplitudes greater than 3.5 kV and risetimes less than 200 ps, is presented.

A variant of the broadline, solid state, gradient echo imaging technique which uses repetitive small flip angle pulses to overcome bandwidth limitations and which is analogous to FLASH liquid state magnetic resonance imaging is described. The improvements in image quality which can be obtained are demonstrated by one-dimensional profiles of a rubber phantom obtained with an echo time of only 80 mu s.