Table of contents

The frequency change of an electrochemical quartz crystal microbalance (EQMB) is a function of both the rigid and the viscous masses coupled to its surface. The viscoelastic properties of the contacting medium define the mechanical loss of the vibrating quartz, which is characterized by the resistance R' in the equivalent electrical circuit. A new driver circuit for the EQMB is described. It permits monitoring of in situ changes of the resonant frequency f_s and of the quartz crystal equivalent resistance R'. Thus this set-up allows one to distinguish between the rigid and viscous masses. Results obtained in different media with a prototype are discussed.

A new instrument to measure the Wobbe index of natural gas has been developed and tested. The instrument detects the residual oxygen content of the flue gases after a known amount of gas is burned with a known amount of air. This residual oxygen content is a measure for the Wobbe index. The instrument has a fast response and a low noise level which makes it suitable for use in burner control systems. The measurement is hardly affected by external influences so an expensive conditioned room will not be required.

A measurement technique for simultaneously obtaining the size, velocity and temperature of particles entrained in thermal plasma jets is described. Particle size and velocity are obtained from a combination laser sizing system and laser Doppler velocimeter (LDV). The particle temperature is determined by two-colour pyrometry and the data rate is a measure of relative particle number density. Since particle size, velocity and temperature are measured simultaneously, cold, solid particles or unmelts are identified and their relative number density can be quantified. Typical data are presented.

A method of phase angle control is analysed which uses the charge flowing through the gradient coil as the feedback signal in a closed loop system. A reduced influence of current transients and amplifier linearity upon the control accuracy is obtained due to integral feedback.

To establish the relationship between measured refractivity and gas concentration, a measurement system has been developed which can precisely determine the absolute refractive indices of medical vapours and gases at a wavelength of 633 nm. The refractive index of chloroform vapour has been measured over the respective pressure and temperature ranges of 1 to 9 kPa and 15 to 40 degrees C with an uncertainty of better than +or-8 parts in 10⁸. The specific refraction and the second virial coefficient of chloroform have also been derived.

A novel optical fibre system, for out-of-plane vibration analysis, comprising the complementary techniques of laser velocimetry and electronic speckle pattern interferometry, is described. The laser velocimeter (LV) and the electronic speckle pattern interferometer (ESPI) share a common reference arm and phase modulator. The LV locks to the motion of a point on the vibrating surface and since the ESPI and LV share a common reference arm, automatic heterodyning of the time-averaged ESPI fringes is achieved. The experimental results are described.

A microstrip quarter wavelength ( lambda _g/4) resonator in conjunction with a small probe is used to resolve objects with characteristic dimensions as small as a thousandth of the wavelength ( lambda _g/1000). The characteristic length for the decay of the evanescent waves at the tip of the probe was measured to be approximately 100-150 mu m at a microwave frequency of 1 GHz ( lambda _free approximately=30 cm). The authors applied this technique to map microwave conductivity of metallic lines on glass and printed circuit boards and to investigate conductivity variations across a silicon wafer. It was possible to detect holes in printed circuit boards that were covered with solder and were not detectable otherwise.

A pulsed Nd-YAG laser beam is used to produce a transient refractive index gradient in air adjoining the plane surface of the sample material. This refractive index gradient is probed by a continuous He-Ne laser beam propagating parallel to the sample surface. The observed deflection signals produced by the probe beam exhibit drastic variations when the pump laser energy density crosses the damage threshold for the sample. The measurements are used to estimate the damage threshold for a few polymer samples. The present values are found to be in good agreement with those determined by other methods.

A novel design of a tunable prism filter using two dense flint prisms for eliminating laser plasma lines in a Raman spectrometer is presented. Angular dispersion, beam diameter of the laser beam and divergence of the plasma radiation are considered to select the optimal configuration. A remarkable feature of the filter is its high transmission efficiency. The performance of the filter is compared with that of commercial tunable grating filters.

A simple in-fibre technique for the measurement of small frequency separations is described. A sinusoidal frequency modulation, applied to the source, is converted into phase modulation of an optical carrier, thereby enabling measurement of the frequency modulation amplitude. The source must be continuously tunable, which makes the technique particularly suitable for measurement of frequency shifts produced by injection current modulation of solid state lasers. The technique is demonstrated by incorporation into an electronic speckle pattern interferometer (ESPI) surface contouring system.

A novel optical fibre sensor has been developed for on-line monitoring of oil quality within industrial equipment. The monitoring is based on chromatic modulation because of the inherent self-referencing demonstrated by this technique. The sensor is shown to exhibit long-term stability and is capable of operating up to a temperature of 120 degrees C. Several industrial oils have been examined using the sensor, and typical modulation depths of 20% were obtained with resolution in the range of 0.1%. This is sufficient to record some interesting physical and chemical changes related to the reaction kinetics of oil degradation. The sensor is also capable of detecting oil leaks within a system since it can distinguish between the chromaticities of oil and air.

A fibre optic digital speckle pattern interferometer is reported for mural painting diagnostics. As a result, the influence of flaws and cracks on fringe patterns, characterizing the displacement fields of mural paintings, has been visualized in real time also in an outdoor environment. Preliminary tests establish that this method, by its flexibility and compactness, allows one to overcome some drawbacks of existing conventional arrangements in non-destructive testing of artworks.

A high-speed, high-resolution, digital computer-based interrogation system for particle image velocimetry (PIV) has been developed. It utilizes advanced parallel array processing technology to achieve computational speeds comparable to those of current supercomputers, and high-resolution image acquisition equipment to achieve the data input rates necessary for high-speed analysis of PIV images. Advanced cross correlation techniques are incorporated into the algorithm, which take advantage of the high-speed capabilities and improve the quality of the measurements. The architecture, algorithms, and performance characteristics of the system are described.

The impedance analysis technique has been used to measure the complex permittivity and conductivity of highly conductive perfluoropolyether microemulsions. The cell construction details, calibration procedure and data analysis procedure are reported. Examples of dielectric analysis on perfluoropolyether microemulsions are given.

A compact multiplexed sensor fluxgate magnetometer capable of displaying the X, Y and Z components as well as the intensity, inclination and declination of a magnetic field is described. Control of the switching sequence, the arithmetic and the display is effected with a microprocessor-based unit. The instrument works on rechargeable batteries with 8 h continuous operation between charges and weighs about 2 kg.

A paper dealing with parameters' errors of a least-squares determined curve was published by G.C. Cecchi (1991). A.H. Kalantar (1992) correctly pointed out that the results quoted by Cecchi for the variance estimates of a straight-line fit do not agree with those previously reported by other authors. Nevertheless, for straight-line fits the formalism discussed by Cecchi is essentially correct. In the present communication, complete agreement between results is achieved after some detailed calculations.