Table of contents

Signatures of the first three modes of stress wave propagation in a Hopkinson bar, given by the Pochhammer-Chree solution a century ago, are derived from a set of recent experiments. The data suggest that, at frequencies at which multiple theoretical modes are possible, the mode with the fastest group velocity dominates the propagation. The Gaussian-windowed Fourier transform technique is used to obtain time-dependent Fourier coefficients from a measured signal. The transformed signal is displayed in a gray scale plot of the power spectra of the Fourier coefficients as a function of time and frequency. This plot shows clear evidence of the theoretical modes. A new dispersion curve for stress wave propagation in bars is derived from the transformed data. The new dispersion curve, used in the DISBAS code (a bar gauge deconvolution technique that uses dispersed basis functions), gives a highly resolved stress wave.

This paper describes the design of an involute spur gear inspection system in which measurements are made using a video camera and image analysis software. The measurement accuracy possible using low-cost CCTV cameras is investigated, and the possible sources of error identified. It is concluded that the measurement accuracy is comparable to that of current methods for tolerance inspection of spur gears and the low cost and ease of use make image analysis measurement systems an attractive alternative.

Fluidic flowmeters, based on oscillating jet devices, have been investigated for use in the metering of domestic water and gas. Both applications specify a large flow range, which, when combined with pressure-loss limitations, results in a very demanding minimum flow rate requirement. It is demonstrated that the minimum measurable flow rate is governed principally by a combination of minimum operating Reynolds number and meter aspect ratio (profile depth compared with nozzle width). For two meter designs, experiments are reported, which show that there is an optimum aspect ratio, resulting in a minimum measurable flow for each design. It is concluded that fluidic domestic water metering is an attainable objective but domestic gas metering is unlikely to be achieved by a fluidic device alone.

A new technique for measuring the thermal conductivity of metallic materials during liquid/solid phase transformation is proposed and applied to the determination of the thermal diffusivity and thermal conductivity of Wood's metal (Bi, 48%; Pb, 26%; Cd, 13%; Sn, 13%) at the melting point. The technique incorporates measurements in two sequences: (1) during a one-dimensional propagation of the phase transition interface, and (2) during a quasi-equilibrium state where the interface is stationary. The position of the interface is determined from measurement of the electrical resistance over the specimen including the interface. The resistance over time obtained during the melting/freezing processes enables the determination of the speed of the solid-liquid interface. The thermal diffusivity and conductivity at the interface can be evaluated from the speed of the interface, temperature gradients normal to the interface, and thermal properties. The mean value of the thermal conductivity at the transition temperature, was found to be 32.9 Wm^-1 degrees C^-1 and 22.4 Wm^-1 degrees C^-1 for the solid and the liquid phases respectively. Independent measurements of the electrical resistance gave the ratio of the resistivity of the solid and the melt equal to 1.51. A Lorenz number is evaluated to be about twice the theoretical value for a metal. A brief discussion of a tentative separation of the electronic and the lattice component of the thermal conductivity is made.

A transient technique for the determination of absorptance, alpha , and emittance, epsilon , of materials is presented. The technique is based on the sample heating and cooling histories obtained from a simple enclosure with a window and no vacuum. An array of four spatially placed type-T thermocouples are used as temperature sensors with an automated microcomputer interface using a multiplexed analogue-to-digital converter. The average sample temperature is obtained from the four readings. The heat balance equations are solved analytically to obtain these parameters. Results obtained for commercial copper and aluminium samples using a 60 W tungsten-halogen lamp are discussed.

Mechanical vibration is investigated experimentally to evaluate electromagnetic forces on non-magnetic and ferromagnetic thin plates in the impulsive magnetic field. In addition to a Lorentz force due to eddy currents, a drag force is created by magnetization in the ferromagnetic plate. The electromagnetic forces are evaluated from the peak deflection of a cantilevered acrylic beam holding the test piece. Dependence of the forces on the excitation coil current is discussed based on the experimental results.

A new method suitable for the single core fluxgate magnetometer has been proposed. The method makes use of the coupling property of odd and even harmonics generated by the self-product of the induced voltage during the magnetization of ferromagnetic material by an external field superposed on the AC driving magnetic field. The power difference between the two half-periods of magnetization was expressed by the coupling of odd and even harmonics, which is proportional to the external field under the condition that H_ext<<H_AC and H_AC is constant, where H_ext and H_AC are the external magnetic field and AC driving field amplitude respectively.

A novel method for designing at gradient coil using a genetic algorithm is presented; the ease of construction of the set is implicitly incorporated into the optimization process. A z gradient set designed for human brain imaging in which the coil length and diameter are similar is found to have improved linearity compared with the standard Maxwell pair design.

The influence of multiple reflections on the measured and calculated values of the phase retardance is considered. Resultant interference fringes are distinguished as participating in so-called comparative and cross reference interference of terms respectively with equal and different number of reflections. The named cross reference interference of terms with the unequal number of reflection results in irregular measurement noise. Interference of beams with limited coherence length results in an increase of the retardance by auxiliary passes of light reflected by retarder surfaces. Calculations are presented for both coherent and incoherent light beams and retarders with reflective and coated surfaces. Comparisons between estimated and measured magnitudes of phase retardance are made over a wide spectral range and a variety of surface reflectances.

To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of signals derived from optical back reflection, and optical transmission, through the interferometer. Theoretical analysis and experimental results have demonstrated that the new scheme has a higher sensitivity than those described previously. Sensitivity enhancements between 2 and 17 times can be expected. Depending on mirror reflectivity, the frequency response is approximately flat in the range of 10 MHz and above, limited only by the free spectral range of the interferometer device.

A new design of a simple and inexpensive optical cell of variable thickness for absorption coefficient measurements in highly absorbing liquids is presented. The cell, which can be also used with highly corrosive samples and up to temperatures of 300 degrees C, is suitable for measurements from the near infrared up to near ultraviolet. As an example, the absorption spectrum of liquid iodine measured over six decades is reported.

An optical column for a scanning positron microprobe is described. A beam of variable energy from 1 to 30 keV and a spot diameter of 1 mu m, that can be scanned over an area of 0.6*0.6 mm² is formed using electron optical elements that are already well known but rarely used in an optical column. The idea allows the construction of a sample chamber free of material and electric fields in a hemisphere above the sample with a radius of some 100 mm or more. The absence of diaphragms and the comfortable inner diameter of the lenses used makes it possible to work with a beam of comparatively large diameter and aperture. This is necessary because of the low intensity of the positron sources available, which makes a system with a very high transmission essential. Although the idea was created for a positron microprobe, other applications, such as with a retarding field analyser introduced into the sample chamber, are conceivable.

A simple instrument is described for the coincidence measurement of two near-zero energy (threshold) electrons, which can be used for the study of double-photo-ionization processes. The threshold electrons are collected by means of the penetrating field technique and the coincidence measurements are performed using a single detector (channel plates). The application of time-of-flight techniques leads to much improved spectral resolution and yields information on the double-photo-ionization process.

An X-ray interface continuous tracking device was developed, which enables continuous tracking of interface motion in crystalline solids. The device utilizes X-ray diffraction rather than optical methods to determine a boundary position and allows one to determine the velocity of migration at any moment of the experiment. The device was particularly designed to investigate grain boundary migration. The measurable velocity ranges from 1 to 1000 mu m s^-1 with a temporal resolution of about five measurements per second.

Absolute single-particle detection efficiencies of a microchannel plate (MCP) detector were determined by photo-ionization of atoms or molecules. The ionized heavy particles were detected in coincidence with the resulting electrons. This method allows the determination of detection efficiencies without a knowledge of the absolute event rates. We obtained the detection efficiencies for the ions H₂⁺, D₂⁺, HD⁺, H⁺, D⁺ and Ar⁺ in the impact energy range 0-5 keV. The detection efficiencies saturate above 3 keV and reach generally 41%. This value seems to reflect mainly the physically effective area of the MCP.

A fast ion detector based on secondary electron emission from an aluminium surface is described. The secondary electrons are accelerated by 1.2 kV and detected by two microchannel plates in cascade configuration. Applying channel plates to the secondary electrons leads to the same detector efficiency as with the channeltron but at a much higher counting rate. The efficiency of the detector for 150 keV protons was measured as a counting rate of 0.8 at 1 MHz.

An optical fibre based, speckle shearing interferometer for out-of-plane time-averaged vibration analysis is described. The technique uses a highly birefringent optical fibre to illuminate a test object with equal intensities of light guided by the orthogonal polarization eigenstates of the fibre. Phase modulation between the sheared images is readily achieved, without mechanical movement of components, by sinusoidally strain modulating the relative phase of the polarization states in the fibre. A Wollaston prism is used to obtain two sheared images with adjustable shear.

A practical device is described, which implements a scanning scheme by which a solid-state dye laser sample, tranversely pumped, is rotated to a new position every few shots, thereby avoiding early degradation. Two different dyes are tested; the proton-transfer dye 5(6)-allyloxycarbonyl-2-(5'-fluoro-2'-hydroxyphenyl) benzimidazole co-polymerized with methyl methacrylate and Rhodamine 6G dissolved in a co-polymer 1:1 by volume of 2-hydroxyethyl methacrylate and methyl methacrylate. Pumping was by means of a N₂ laser at 337 nm using full laser output. It is demonstrated that laser power falls by less than 70% after 5500 shots at a repetition rate of 2 Hz for the proton-transfer dye and by less than 6% after 150000 shots at 10 Hz for Rhodamine 6G.

The injection-locking of laser diodes with adjustable frequency difference of the order of 1 GHz with respect to the frequency of a master laser is demonstrated. Each slave laser frequency can be individually switched between up to five discrete values simply by changing its operation current. The presented scheme does not need any RF servo loop or optical filters in the locking path of the slave diodes.

We describe a simple device that may be employed as a compact and quick calibrator for measurements of respiratory impedance. The real and imaginary parts of the complex impedance of the calibrator are computed as a function of frequency from the theory of sound propagation along a cylindrical duct; a table is set up for the usual operational range 0-50 Hz. Theoretical predictions have been tested experimentally by forcing almost sinusoidal waves through the device by a mechanical piston. The calibrator has been used to confirm that experimental results based on the forced oscillation technique may significantly depend on the type and model of the commercial pressure sensor employed.

The NO₂ gas-sensing characteristics of chemiresistors in the form of multilayered Langmuir-Blodgett (LB) films of copper tetra-4-tert-butyl phthalocyanine (CUTTBPC) molecules deposited on quartz substrates with pre-deposited platinum interdigitated electrodes have been investigated. Response and recovery times, tau _res and tau _rec, respectively are estimated for different gas concentrations from a model based upon kinematics of adsorption and desorption of NO₂ gas molecules by CUTTBPC films. It is found that recovery times are longer than response times irrespective of gas concentration. For a given film thickness, the adsorption probabilities increase while the desorption probabilities decrease, with increasing concentrations. On the basis of the analysis of the results obtained, LB films of CUTTBPC molecules are believed to be a suitable material for disposable NO₂ gas sensors.

Traditional quality measurement systems in the petroleum-related industry are complex in structure and difficult to maintain. A measurement system for high-sensitivity and accurate permittivity measurements has been built in order to investigate dielectric spectroscopy as a basis for an easier-to-maintain system, which can replace some of the traditional instrumentation systems. The permittivity measurement system has been designed and tested for low-permittivity and low-loss fluids in the frequency range from 1 kHz to 5 GHz. In the lower part of the frequency range impedance measurements are used, and in the higher range reflection coefficient measurements are employed. The characteristics of the measurement cells are optimized to give high sensitivity. High-accuracy permittivity measurements are obtained by calibration with several known fluids. Temperature control and careful experimental routines ensure good repeatability. Estimated overall uncertainty and presented measurement results on low-permittivity and low-loss oils and reference fluids confirm the performance of the system.

The design of an apparatus for a single-fibre de-bonding test for fibre-reinforced polymer systems is presented. The apparatus is specially designed to perform the microbead de-bonding process. It can be assembled from common commercially available parts. The detailed procedures of preparation and measurement of the glass fibre/epoxy samples as well as the operation of the de-bonding apparatus are described in this paper. The results presented show that the effects of different fibre surface treatments on interfacial shear strength for the glass fibre/epoxy system can be determined using this apparatus.

The application of a micro-lens array for optical inspection of large-scale windows is proposed for on-line operation. With a micro-lens array, the planarity of laminated windows can be inspected. Another technique, based on the use of a computer-generated hologram, was studied in order to facilitate the inspection of small-scale deformations in security windows.

The thermal wave interferometry (TWI) technique is investigated as a means of measuring the thermal and optical properties of plasma-sprayed coatings. Results obtained from a range of ceramic coatings on metallic substrates are presented with a methodology for estimation of the accuracy of the technique. The factors that determine the accuracy of the technique are discussed.

This paper discusses the operating principles of a digital propagation delay time meter based on the heterodyne technique. It is composed of two independent oscillators, two mixers, phase detector, two counters, a digital-to-analogue converter and microcomputer. The meter is used for propagation delay time measurement through CMOS and TTL combinational logic circuits. An accuracy of 1% and a resolution of the order of 10 ps in the frequency range of interest (up to 12 MHz) have been achieved.

Stresses and strains in the mid-plane of a pulsed magnet are analytically calculated by solving the system of equations describing the displacement in each layer of the coil. Nonlinear stress-strain characteristics and the propagation of plastic deformation are taken into account by sub-dividing each layer of the coil in the radial direction and changing the elastic-plastic matrix at each transition point. The effects of pre-stressing during winding and thermal stresses are calculated and discussed. Two coils that have been tested up to 60-70 T fields are described as examples. It is shown that, under some conditions, elastic-plastic cycling leads to a stable state, whereas in others this results in runaway deformation that leads to coil destruction after a few cycles.

A four-electrode capacitance-to-period converter designed for capacitance measurements of bilayer lipid membranes is described. The capacitance measurement consists of cyclically charging and discharging the measured capacitance with a constant current, regarding its absolute value. The voltage of the studied capacitor is triangularly shaped. The cycle duration is proportional to the input capacitance. Capacitance measurement with a four-electrode system makes it possible to reduce considerably the errors caused by electrode and electrolyte impedance. It is possible to use high-resistance microelectrodes. The system makes it possible to measure the capacitance at an imposed polarization potential; the voltage oscillates about that value during the measurement. This makes it possible to measure the membrane capacitance as a function of polarization potential. An example is cited of using the capacitance-to-period converter in a computer-controlled measuring system.

The use of four-electrode systems in the studies of electric phenomena occurring in membranes makes it possible to reduce errors caused by electrode and electrolyte resistance. A four-electrode potentiostat-galvanostat is described in this paper. It allows for electric measurements of membranes in controlled potential and current conditions or measurements of transmembrane potential. The method of selection of the operation mode of the system is described.

The theoretical performance of an optical instrument can be greatly reduced in practice by the effect of manufacturing errors on the quality of its optical system. This design note describes the development and testing of software that can be used to desensitize optical systems during the design process, by incorporating suitable code into a damped least-squares optimization program.

We describe a polarity inverter for power DC inductive loads, such as electromagnets, which avoids switching with non-zero current, thus protecting power supplies and loads against damage. The inverter can be driven by a logic signal and the total cost is around 100 US$.

An analytic formula for the exit position and transit time of an electron traversing a hemispherical electrostatic analyser is presented. Exit position and transit time dispersions with electron energy are computed and plotted for an actual analyser.

The Mims cavity is an effective sample resonator for pulsed ESR at low temperature because of its low quality factor and high filling factor. Its size, however, is inherently linked to the waveguide dimensions of the frequency band of operation, and the operation of such a conventional unit below X-band is therefore impractical because the entire structure must reside within a helium cryostat (Dewar flask). A modified version of the Mims cavity is described that is based on ridged waveguide transmission line feeds while retaining the lambda /2 resonant strip. The modified transitions reduce the cavity dimensions to 4 cm*4 cm, thereby greatly facilitating compatibility with a liquid helium immersion Dewar flask while extending the operating frequency range downwards to 4.75 GHz.

A simple ultrasonic displacement measurement system is described, based on a phase-sensitive detection principle. A low-frequency ultrasonic transducer, operating in continuous-wave mode, is used to transmit a 44.2 kHz acoustic wave to the target body. The reflected signal is detected by a matched transducer and the phase difference between the transmitted and received signal is found in real time. Tests show that the system is capable of detecting displacement with an accuracy of +or-5.3 mu m, with targets situated over 2 m from the transducers.

Based on the fact that a piezoelectric element does not consume any substantial active power we have designed an inexpensive multichannel amplifier to drive a piezo-tube actuator of a home made long-range scanning tunneling microscope (STM). The design is based on optocouplers working in their linear characteristic regime where they provide current, sourced from arrays of small-signal transistors, over a high potential difference. With this amplifier and a five section 90 mm long piezotube, a so called 'pocket size' STM, has been modified to scan a maximum area of 56 mu m*56 mu m. We demonstrate the mid-range (a few micrometres) performance of this new STM by imaging a gold replica of a holographic grating. Images of the magnetic fringing fields at the bit tracks of a hard disk acquired in the tunneling stabilized magnetic force microscope mode of the STM are presented to demonstrate the maximum scanning range (56 mu m*56 mu m) capabilities of the instrument.

Two plates of different birefringent materials with properly chosen thicknesses can be combined to produce an achromatic retarder. An inexpensive design for such an achromatic retarder using quartz and mica is described.