Table of contents

Amorphous materials in the form of ribbons, wires and thin films require special care to be taken in measurements of magnetostriction, the field dependence of elastic moduli and the magnetomechanical coupling factor. Problems arise in these measurements because of the sample geometry and, in some cases, because of the low anisotropy commonly found in amorphous ferromagnetic materials. This paper describes the methods that have been adapted or designed to measure the main magnetomechanical properties of magnetically soft, amorphous alloys of Fe, Co and Ni, in the three forms generally available: ribbons typically 20-50 mu m thick and 1-25 mm wide; wires typically 30-130 mu m in diameter; and films 0.01-10 mu m thick, deposited on substrates 25-250 mu m thick. The methods are described in sufficient detail, supported by numerous references, to enable readers to make a critical choice between them, taking into account such things as the temperature range, sensitivity and geometry. Magnetostriction measurements are classified as direct or indirect. The direct methods covered are the strain gauge, three-terminal and cantilever capacitance dilatometry, optical methods and the tunnelling tip method. Indirect methods include the small-angle magnetization rotation (SAMR) method, susceptibility measurements, the Wiedemann effect and strain-modulated ferromagnetic resonance (SMFMR). The methods described for measuring the field dependence of Young's modulus (the Delta E effect) and magnetomechanical coupling factor k are the resonance-antiresonance method, including the use of the impedance or admittance circle, the vibrating reed method and ultrasonic wave velocity methods. The use of a torsional pendulum for measuring the shear modulus and internal friction is also described.

Laser Doppler velocimetry (LDV) measurements are often made in the presence of transient index of refraction variations which bias the measured velocity. Transient temperature variation (e.g. as found in turbulent combustion or turbulent convective heat transfer situations) is the most common mechanism driving index of refraction changes in systems probed with LDV. The physical phenomena inducing this bias, referred to here as flame-induced velocity bias (FIVB), are outlined. Combustion system velocity RMS biases of 10% are possible. The literature currently lacks a model to predict, and a list of criteria to minimize, FIVB. To fill this need a model is developed to predict the magnitude of FIVB. Predictions are compared to experimental measurements of FIVB in a pool fire to confirm the validity of the model. Specific criteria identified for minimizing the FIVB include maximizing the beam crossing angle magnitude; using a Bragg cell frequency shift to reduce sampling times to less than 1 mu s; using the longest laser wavelength available; orienting beams parallel to index of refraction gradients to minimize the beam incidence angles; and when measuring velocities perpendicular to the main flow direction, orienting the beams such that the main flow is along the bisector of the beam crossing angle. Contrary to intuition, minimizing beam steering displacements by minimizing flame front to probe volume distance may increase the FIVB.

The development of a vision based sensor for measuring, in real time, the size of the weld bead at the top face during automated welding is described. The technique involves the periodic interruption of the arc for a short time duration ( approximately 3 ms), during which an image of the weld pool is captured by a CCD camera. Analysis of the captured image by hardware techniques gives the size of the bead during the time period before the next image is captured. The sensor has been used to control the bead size of a pulsed TIG weld. A desired bead size is requested and control of the weld bead size is achieved by either modifying the magnitude of the arc current or the duration of the time of the arc pulse of the arc current.

A recently reported new technique renders speckle interferometry applicable for measuring high local displacement gradients. This paper reports how the technique is used to detect and quantify damage in fatigued carbon fibre-reinforced plastic laminates via its effect on surface displacements. Moreover, the measured displacement fields are used to verify a finite element damage model. The accuracy of the delamination measurement is confirmed by ultrasonic results.

The local temperature in a micro-area of a film can be measured by a transmission electron microscope. Electrons passing through a film are scattered by thermal diffuse scattering and the intensity of the transmitted beam after an aperture depends on the film temperature. In case of a polycrystalline film, the transmissivity tau relates to the temperature T and the thickness d. The dependence of tau on T and d was measured for evaporated Al films, and the accuracy of temperature measured with tau is estimated at about 5% when an empirical formula is used for the conversion from tau to T. The temperature distribution of an area heated by focused laser pulses was measured and the thermal conductivity of the film was deduced.

The application of gamma -ray attenuation methods to non-intrusive measurement of the solids content in pneumatic flow lines is discussed. An instrument employing a broad single-beam interrogation geometry and a single-element detector with uniform sensitivity profile is described. It is designed primarily for metering pulverized coal, where the solids concentration is typically very low, and also often highly inhomogeneous. A detailed analysis of the factors affecting measurement accuracy is presented, together with results obtained from laboratory tests.

This paper presents a study on the distortion of a 'laser beam analyser' (LBA) output signal. The basic principles of the LBA device were described by Lim and Steen in 1982. This instrument is very useful for characterizing the distribution of power density into a laser beam, and it is now widespread in industrial and research centres. The reasons for the distortion of the analogue output signal of this optoelectronic system are explained, and the correction of such a signal to reconstitute the initial form is shown. This work consists in both a theoretical study on the signal distortion at the output of the device and a study on appropriate corrections. After these corrections, a quantitative analysis is made: through software it is now possible to evaluate accurately the beam physical parameters: diameter, position in space and true energy distribution.

A KrF gain module has been developed for short-pulse off-axis amplification using a new electric charging circuit for efficient and fast pumping and jitter-free operation. Simple UV pre-ionization and a moderate bank voltage of 30 kV are additional features. The amplifier is characterized at three different gap separations (d=28, 55, 75 mm). For d=75 mm, 2.6 J overall energy, 260 mJ momentarily stored energy with a gain window of 13 ns and subnanosecond jitter have been obtained.

We report on a small, all solid state, regenerative ring amplifier designed as a prototype for space application. Features include dual side pumping of a 2 mm*2 mm*10 mm Nd:YAG slab and a triangular ring cavity design, which minimizes the number of optical components. The pump head was fitted with twin single-bar diode arrays consisting of 960 individual stripes, temperature tuned to the Nd:YAG pump bands at 809 nm and capable of operation up to 100 Hz. The single-pass gain of this head was measured at 13% for a pump pulse energy of 18.4 mJ from the diode arrays and the cavity round trip transit time was 3.1 ns. The ring has amplified 170 ps pulses with 10^-13-10^-14 J of energy by a factor of more than about 10⁶ while preserving both the temporal and spatial shape of the pulses. The seeding threshold was about 10^-15 J and a maximum saturated output energy of about 40 mu J was obtained when seeded with pulses greater than 1 pJ. Comparison with modelled performance is also given.

On the basis of the 'sound fluctuation level' concept, a new technique and circuitry for rating environmental sound fluctuations has been developed. The proposed instrument is a properly modified and improved version of a part of a recent microprocessor-based apparatus, which directly measures both mean energy and fluctuation level of noises. The changes made to the previous apparatus concern the physical descriptor of the noise fluctuation level (L_phi ) and are based on preliminary results of physical and subjective tests in the laboratory, carried out in order to optimize the averaging time constants, which have a very important role in measurements involving sound fluctuation assessment.

A new fuel concentration measurement technique, a catalytic hot-wire sonic nozzle probe, is described. This probe was tested in n-pentane/air, n-heptane/air and leadless gasoline/air mixtures. The results obtained show that the probe is very sensitive to fuel concentration even in a rich mixture and has a high reproducibility. It can easily detect an amount of 0.2% mole fraction of gasoline in air. The estimated time response of this probe is less than 400 mu s. The probe is simple in construction and can be used to measure fuel concentration in cases where laser techniques are inappropriate due to optical inaccessibility of a complex experimental set-up such as the combustion chamber of an engine.

Laser Doppler anemometry using the photon correlation method of signal processing has been used to measure a velocity field in which sinusoidal fluctuations generated acoustically are superimposed on a steady flow. A stochastic model has been developed for the form of the correlation function, and it is shown to be consistent with previous models for a steady flow and for sinusoidal fluctuations in an acoustic field. Measurements have been made of the velocity field associated with steady flow in a tube with a superimposed acoustic field, the results were shown to be consistent with the theoretical predictions.

The reliable determination of a plasma electron density structure requires a good knowledge of the errors affecting the employed technique. We have used a technique based on the measurement of the absolute light intensity emitted by travelling plasma structures in plasma focus devices, but it can be easily modified to other geometries and even to stationary plasma structures with time-varying plasma densities. The purpose of this work is to discuss in some detail the errors and limits of this technique. Three separate errors are shown: the minimum size of the density structure that can he resolved, an overall error in the measurements themselves, and an uncertainty in the shape of the density profile.

This paper investigates the influence of quantization on 3D surface characterization by carrying out an analysis of surface parameter changes on a range of real and simulated surfaces. The changes in parameters are calculated as a percentage of the original value. There is also a treatment of the effect of quantization error on visual characterization. The validity of a lot of current practice in surface topography (where 12 bits or more are used in applications involving submillimetre ranges) is confirmed, and limits on that practice established. Recommendations are made as to the number of bits that should be reasonably used in quantization with respect to the surface feature of interest (form, waviness or roughness) and the likely implications of this choice on 3D surface characterization is discussed.

The fabrication of thermoelectric generators using standard MOS thin film technology is described. Process sequences are presented for generators based on both silicon on sapphire and polycrystalline silicon on quartz substrates; the active elements being formed in both cases by ion implantation of alternate n-type and p-type regions. Device performance is evaluated and presented for both types of converter in terms of conversion efficiency and voltage and power outputs as a function of temperature difference. For thermoelements with a carrier concentration of 5*10¹⁹ cm^-3 the overall Seebeck coefficient for a single thermocouple is approximately 500 mu V K^-1 for both silicon on sapphire and silicon on quartz. Extrapolation of results indicates that voltage and current levels suitable for powering a microelectronic circuit (i.e. greater than 1 mu A at 1 V) can be obtained from a chip of dimensions 0.5 cm*1 cm*0.045 cm. The use of polycrystalline silicon on quartz as opposed to silicon on sapphire has been shown to offer two major advantages. Firstly, due to the high thermal resistivity of quartz, the conversion efficiency of the resulting silicon on quartz chip is greater than for the silicon on sapphire case. For a substrate of dimensions 0.5 cm*1 cm*0.045 cm the improvement in device efficiency is almost 50 fold. Secondly, material costs are reduced when polycrystalline silicon on quartz is adopted, whilst, since the actual processing sequences are similar, manufacturing costs will remain approximately the same.

This paper introduces a design of a stratospheric platform pointing system taking into account, as an example, the design of an infrared experiment named ARGO. It shows the design philosophy of both mechanical and electrical parts as well as some software solutions to interface the position sensor (magnetometer) and motor power amplifiers for these gondola azimuth movements. This pointing system controls a single-axis platform (the infrared telescope, in this case, does not require an elevation motion) and may either show the way for other similar stratospheric experiments or be the first step of a higher axis stabilization. It is a two DC torque motor design housed, with a tachometer, in a particular and compact solution named 'pivot'. One motor is devoted to avoiding any disturbance, during stratospheric flight, coming from random rotation of the cruise balloon and the other for any pointing motion needs. The control hardware, fully digital and built around a CPU card, gives this system a high degree of versatility.