Table of contents

Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal.

The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, in 2005 the Editorial Board decided to present 'Outstanding Paper Awards' in four subject categories: Fluid Mechanics; Measurement Science; Precision Measurements; and Sensors and Sensing Systems.

2005 Award Winners—Fluid Mechanics The Fluid Mechanics working group, chaired by Professor John Foss, was unanimous in its recommendation for the paper authored by J Chen and J Katz (Johns Hopkins University, USA) 'Elimination of peak-locking error in PIV analysis using the correlation mapping method', published in volume 16, issue 8, pp 1605–1618. The essence of the following citation was provided by Board Member Dr Mark Wernet:

The paper of Chen and Katz describes a technique for eliminating the 'peak locking' bias error endemic to estimating the PIV correlation peak location.

Particle image velocimetry (PIV) is used widely in both fundamental and applied fluid mechanics. In essence, a two-dimensional velocity map is extracted from two successive high-resolution images of light scattered by minute tracer particles. The incident light is derived from two laser beams which have been expanded into sheets. A precise time delay is imposed between the two laser light sheets. The cross-correlation of the scattered light intensity within corresponding small interrogation regions in the two images gives the displacement of the particles and hence the local velocity.

Typically, in PIV processing, the correlation peak location is determined by fitting a curve through the correlation peak. This process is known to suffer from a bias error where the estimated displacements are grouped around integer pixel values. Background subtraction can help reduce the tendency for peak locking, but does not completely remove the bias. Other techniques for eliminating the bias are available, but require time-consuming, iterative processing.

The paper of Chen and Katz describes a processing technique that removes this 'peak locking' bias by avoiding the curve fitting process altogether. Instead, the displacement necessary to map the first exposure into the second exposure is determined via a correlation mapping operation. Several example cases using synthetic data and actual PIV data are presented. The new approach is also compatible with the Subregion Image Distortion technique to further improve the quality of the PIV displacement estimates.

2005 Award Winners—Measurement Science The 2005 Measurement Science and Technology Outstanding Paper Award in the Measurement Science category has been awarded to M E Webber, T MacDonald, M B Pushkarsky (Pranalytica, Inc., USA), C K N Patel (UCLA, USA), Y Zhao, N Marcillac and F M Mitloehner (University of California, Davis, USA) for the article 'Agricultural ammonia sensor using diode lasers and photoacoustic spectroscopy', published in volume 16, issue 8, pp 1547–1553.

In making their recommendation the Measurement Science working group chaired by Professor Richard Dewhurst gave the following endorsement:

This paper provides an excellent description of a novel instrumentation system used to detect agricultural ammonia. The sensor system has been designed for use in dusty and humid conditions, and a portable prototype was field-tested on several days over an eight-week period, with encouraging results. In this paper, a short theoretical section is followed by instrumentation details, with a description of the optical system, the electronics, embedded programming and algorithm development. An erbium-doped fibre amplifier was used to enhance the photoacoustic signal by boosting the laser's output power, whilst maintaining the linewidth of the seed laser source. Careful laboratory calibration tests are then described, showing benchmark results of sub-ppm sensitivity, and excellent system linearity up to 100 ppm. The final section describes the condition under which field tests were conducted, and validates the photoacoustic method by cross reference with both a Draeger sensor and an ion chromatograph. Overall, the paper possesses several innovative ideas.

It is a well-structured paper, containing details of the instrumentation and techniques used. It has a careful discussion of the data and its validation, in order to realize the precision demonstrated. It is an innovative system required for a topical need within environmental protection.

2005 Award Winners—Precision Measurement The 2005 Measurement Science and Technology Outstanding Paper Award in the Precision Measurement category has been awarded to Ichiko Misumi, Satoshi Gonda, Qiangxian Huang, Taeho Keem, Tomizo Kurosawa (National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST), Japan), Akihiro Fujii, Nahoko Hisata, Takeshi Yamagishi, Hirohisa Fujimoto (Olympus Corporation, Japan), Ken Enjoji (Olympus Systems Corporation, Japan), Sunao Aya and Hiroaki Sumitani (Mitsubishi Electric Corporation, Japan) for the article 'Sub-hundred nanometre pitch measurements using an AFM with differential laser interferometers for designing usable lateral scales', published in volume 16, issue 10, pp 2080–2090.

In making their recommendation the Precision Measurements working group chaired by Dr Kenichi Fujii gave the following endorsement:

This paper describes a new instrument developed for measuring the pitches of one-dimensional grating standards. In the field of nanotechnology and in the semiconductor industry, reliable one-dimensional grating standards have been solicited for calibrating length measurement in nanometre regions. In the instrument described here, an atomic force microscope (AFM) is combined with differential laser interferometers so that the atomic scale resolution of the AFM is accurately calibrated by optical interferometry, achieving an unprecedented uncertainty of 0.2 nm in measuring the pitches of about 50 nm. The instrument also calibrates the pitches in a wide scanning range. This paper analysed the uncertainty of the measurement in detail, helping to provide users with reliable certified reference materials for one-dimensional grating standards.

2005 Award Winners—Sensors and Sensing Systems The 2005 Measurement Science and Technology Outstanding Paper Award in the Sensors and Sensing Systems category has been awarded to Nicola Bowler and Yongqiang Huang (Iowa State University, USA) for the article 'Electrical conductivity measurement of metal plates using broadband eddy-current and four-point methods', published in volume 16, issue 11, pp 2193–2200.

In making their recommendation the Sensors and Sensing Systems working group chaired by Professor Paul Regtien gave the following endorsement:

The paper addresses two methods to measure the electrical conductivity of metal plates of various materials. In particular for ferromagnetic plates, traditional methods show relatively large measurement uncertainties. In this paper, the origins of these large inaccuracies are studied, and two alternative methods are presented that yield much better accuracies. Both methods—a broadband eddy-current and a four-point contact scheme—are extensively analysed theoretically as well as experimentally. The results are compared with other published data, for plates of brass, stainless steel and spring steel. An uncertainty analysis reveals the superiority of the newly introduced methods in the case of steel. The four-point method has the advantage of being easy to use.

The paper is well-structured, with a good balance between theory and experiments, and a clear presentation of the measurement data and associated uncertainties, both in tables and graphs. The paper concludes with a convincing discussion and outlook for further research. The results are of great value in the field of non-destructive testing.

The Outstanding Paper Awards, comprising a cash honorarium and certificate, will be presented to the authors of the winning papers at suitable venues in the near future.

The Editorial Board would like to congratulate the winning authors and would like to encourage all researchers to think of Measurement Science and Technology as the home for your best submissions.

'Molecular Imaging Technology' focuses on image-based techniques using nanoscale molecules as sensor probes to measure spatial variations of various species (molecular oxygen, singlet oxygen, carbon dioxide, nitric monoxide, etc) and physical properties (pressure, temperature, skin friction, velocity, mechanical stress, etc). This special feature, starting on page 1237, contains selected papers from The International Workshop on Molecular Imaging for Interdisciplinary Research, sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan, which was held at the Sendai Mediatheque, Sendai, Japan, on 8–9 November 2004. The workshop was held as a sequel to the MOSAIC International Workshop that was held in Tokyo in 2003, to summarize the outcome of the 'MOSAIC Project', a five-year interdisciplinary project supported by Techno-Infrastructure Program, the Special Coordination Fund for Promotion of Science Technology to develop molecular sensor technology for aero-thermodynamic research.

The workshop focused on molecular imaging technology and its applications to interdisciplinary research areas. More than 110 people attended this workshop from various research fields such as aerospace engineering, automotive engineering, radiotechnology, fluid dynamics, bio-science/engineering and medical engineering. The purpose of this workshop is to stimulate intermixing of these interdisciplinary fields for further development of molecular sensor and imaging technology. It is our pleasure to publish the seven papers selected from our workshop as a special feature in Measurement and Science Technology. We will be happy if this issue inspires people to explore the future direction of molecular imaging technology for interdisciplinary research.

Overview of frequency domain measurement techniques of the complex permittivity at microwave frequencies is presented. The methods are divided into two categories: resonant and non-resonant ones. In the first category several methods are discussed such as cavity resonator techniques, dielectric resonator techniques, open resonator techniques and resonators for non-destructive testing. The general theory of measurements of different materials in resonant structures is presented showing mathematical background, sources of uncertainties and theoretical and experimental limits. Methods of measurement of anisotropic materials are presented. In the second category, transmission–reflection techniques are overviewed including transmission line cells as well as free-space techniques.

We have shown that energy pooling fluorescence lock provides an effective method for stabilizing a diode laser to a broad, stable atomic reference. We achieved typically a stable lock with a laser linewidth of 1.1 MHz and continuous tunability of ±600 MHz, against the two off-centre peaks fluorescence of 7P_{(3/2, 1/2)} → 6S_1/2 caused by 6P_3/2 + 6P_3/2 → 7P_{(3/2, 1/2)} + 6S_1/2 energy pooling collisions in thermal caesium vapour.

Observation and measurement of a weld pool surface is a key towards the development of next generation intelligent welding machines which can mimic a skilled human welder to a certain extent. However, the bright arc radiation and the specular surface complicate the observation and measurement task. This paper proposes a novel method to turn the difficulty of the specular surface into an advantage by exploiting the difference between propagation of an illumination laser and the arc plasma. The governing law is simply the reflection law which can provide the base for the computation of the weld pool surface. Experimental results verified the effectiveness of the proposed method in acquiring clear images in the presence of the bright arc.

A novel oxygen sensor based on stationary triplet–triplet (T–T) absorption was developed and the stationary absorption change of zinc 5,10,15,20-tetrakis-(pentafluorophenyl)-porphyrin (ZnTFPP) depending on oxygen concentration was investigated. In this technique, a photochemical equilibrium made by two continuous lights, which are S–S excitation and T–T excitation, and the change of equilibrium was monitored as the change of stationary T–T absorption. In this study, ZnTFPP in polystyrene and ZnTFPP immobilizing aluminium oxide were used as a sensor device and the difference between the two devices was clarified by the stationary quenching measurement.

Pressure sensitive paint (PSP) techniques have the capability to be applied to high Knudsen number flows, such as low density gas flows, micro-flows, and so on. In this study, to inspect the feasibility of PSP for measurement of pressure on a solid surface in high Knudsen number flows, the fundamental properties of PSPs are examined, especially in the range of pressure below 130 Pa (about 1 Torr). As a result, it is clarified that the PSP using poly(TMSP) as a binder and using PdOEP or PdTFPP as a luminophore has very high sensitivity to oxygen pressure under low pressure conditions below 130 Pa. Pressure sensitivity to nitrogen monoxide is also examined for the above PSPs, and it is clarified that PdTFPP bound by poly(TMSP) has very high sensitivity while PdOEP has very low sensitivity to nitrogen monoxide. The combination of the PdTFPP-based PSP and NO-LIF technique enables composite measurement of flow field structures and surface pressure in the high-Kn regime.

Organosilane self-assembled monolayers were photodegradated with VUV light of 172 nm in wavelength, using a VUV-exposure system whose proximity gap between photomask and substrate was filled with ambient air and adjustable at intervals of 1 µm. The following knowledge of photodegradation processes was obtained: (1) a larger proximity gap was more favourable for promoting the photochemical reactions and advanced complete photodegradation of the monolayer; (2) such oxidized products as carboxyl groups appeared in irradiation time of several tens of seconds. Moreover, lamination of the second self-assembled monolayer (SAM) against the photodegradated SAM/Si substrate was conducted. It was possible for any permutation of SAMs to laminate the second SAM onto the SAM's surface photodegradated in activated oxygen atmosphere through the reaction between –COOH radicals and –OCH₃ functional groups of organosilane precursors. Also, the conspicuous shift of XPS spectra was observed only in the case of laminating CMPhS-SAM on FAS/Si.

Polystyrene microspheres containing both an oxygen-sensitive platinum porphyrin luminescence and a pressure-insensitive silicon porphyrin luminescence are prepared in high yield. The ratio of these two luminescences responds reversibly in aerodynamic flows over a wide dynamic range of oxygen concentrations, with a response time of <10 ms. These microspheres have been used in a non-intrusive imaging method to potentially obtain the pressure distributions in three-dimensional aerodynamic flows.

A novel measurement approach is described which has been developed to allow both pressure and skin friction measurements at very low speeds in liquid or gaseous environments. This approach, surface stress-sensitive films, S³F, is based on the deformation of an elastic medium and the transformation of this deformation into surface loads (pressure and shear stresses). Measurements in both air and water flows have been made. A comparative analysis of the S³F and PSP techniques for a low-speed air-flow case is presented.

We report improvements to the molecular tagging velocimetry and thermometry (MTV&T) technique for the simultaneous measurement of velocity and temperature fields in fluid flows. A phosphorescent molecule, which can be turned into a long lifetime tracer upon excitation by photons of appropriate wavelength, is used as a tracer for both velocity and temperature measurements. A pulsed laser is used to 'tag' the regions of interest, and those tagged regions are imaged at two successive times within the lifetime of the tracer molecules. The measured Lagrangian displacement of the tagged molecules provides the estimate of the fluid velocity vector. The simultaneous temperature measurement is achieved by taking advantage of the temperature dependence of phosphorescence lifetime, which is estimated from the intensity ratio of the tagged molecules in the two images. In relation to the original molecular tagging thermometry work of Thompson and Maynes (2001 J. Fluid Eng.123 293–302), the improvements reported here are the use of lifetime imaging as a ratiometric method to enhance the robustness and accuracy of temperature measurements and the extension of the technique to simultaneous whole-field planar mapping of velocity and temperature fields. Compared with other simultaneous velocity and temperature measurement techniques such as combined PIV-LIF (Sakakibara et al 1997 Int. J. Heat Mass Transfer40 3163–76, Grissino et al 1999 Proc. 3rd Int. Workshop on Particale Image Velocimetry (Santa Barbara, CA, USA, 16–18 September 1999)) and the DPIV/T technique (Park et al 2001 Exp. Fluids30 327–38), this method accomplishes the same objectives but with a completely molecular-based approach. Because of its molecular nature, issues such as tracking of the flow by the seed particles and the thermal response of the thermal tracer particles are eliminated. In addition, the use of a single molecular tracer and a dual-frame CCD camera provides for a much reduced burden on the instrumentation and experimental set-up. The implementation and application of the new technique are demonstrated by conducting simultaneous velocity and temperature measurements in the wake region of a heated circular cylinder at a Richardson number of 0.36, a value large enough for the buoyancy effects to potentially influence the flow.

The newly designed lifetime imaging system (LIS), which was composed of a multi-gated CCD camera and LED illuminators, has been developed to measure simultaneously pressure and temperature field from luminescent lifetime decay of pressure-sensitive paint (PSP). The new system could reduce the measurement error due to shot noise of a CCD and laser speckle, compared to the previous lifetime imaging system. Optimization of PSP film thickness on white basecoat was also conducted for improving measurement accuracy, and could minimize the measurement error. As a verification test, pressure and temperature images on a simple delta wing were visualized by the newly designed LIS. The quality of the pressure image was considerably improved in comparison with that measured by the previous system. These results indicated that the new LIS was a practical measurement tool to acquire simultaneously pressure and temperature field on an aerodynamic model surface.

The aim of this work is the investigation of the transient electric field radiated by two different commercial generators of electrostatic discharges for various charging voltages. Measurements of the electric field generated by contact electrostatic discharges have been conducted a few centimetres away from the discharge point. In this paper the current transducer, which is used for the measurement of the discharge current, is mounted on a grounded metal plane. It is the first time that measurements of the electric field have been conducted along three different directions in relation to the electrostatic discharge generator. Measurements prove that each generator produces a different transient electric field, which affects the equipment that is tested in a different way. Also, each generator produces a different electric field depending on the orientation of the generator. Finally, comparisons of the electric field for both generators and useful conclusions for the decrease of the electric field are presented.

In order to study the heat and mass transfers between a spray of droplets and the atmosphere in thermal-hydraulics conditions representative of a severe accident in a Pressurized Water Nuclear Reactor, the French Institute for Radioprotection and Nuclear Safety (IRSN) developed the TOSQAN facility. The present paper presents the development and the quantification of an optical diagnostic, global rainbow refractometry, in order to measure falling droplet temperature.

A constant velocity model, a constant acceleration model and a coordinated turn model are used for manoeuvring target. However, high location precision of the target could not be obtained with any one of these models. In this paper, an interacting multiple model particle filter (IMMPF) algorithm is proposed to estimate the target location with several models. Besides similar mixing and interaction to those in a traditional interaction multiple model (IMM) estimator, a standard particle filter runs in every model and the number of particles in every model is fixed. Compared through a target location example, the proposed algorithm is better than the traditional IMM.

The surface profile and dynamic characteristics are some of the important specifications that influence the performance and stability of a MEMS device. Microscopic interferometry is, up to now, the most widely used technique for surface profiles of microstructures, and is also capable of measuring out-of-plane motion of microstructures with stroboscopic illumination. In this paper, a stroboscopic Mirau microscopic interferometer system was developed by integrating some commercially available components and instruments. In order to obtain a lower acquisition time and improve the measurement accuracy and stability of interference phases, an improved Fourier transform method (FTM) for fringe pattern analysis is described. It is necessary to process two interferograms with different phase shifting to achieve reliable phase demodulation in the measurement of surface profile. Out-of-plane motion can be calculated from one interferogram sequence, in which only one interferogram per motion phase is collected. Experimental studies of the measurement of a microcantilever surface profile and out-of-plane motion are described, and the measurement results are compared with that of a five-step phase-shifting method. It is demonstrated that stroboscopic microscopic interferometry based on a FTM can be used to determine the static and dynamic characteristics of microstructures.

Sound velocity changes of unpolarized polycrystalline BaTiO₃, in the diamond anvil cell (DAC) up to 6.8 GPa, across the tetragonal to cubic phase transition at room temperature (RT) have been detected by a photoacoustic technique. The light absorption before, during, and after the structural phase transformation shows changes. This is very clear using a photoacoustic method where a pulsed laser is used as a standard source of ultrasound. The phase transition is recognized by a profile generated through sequence values of the temporal peak positions acquired from sequential measurements of the pulsed photoacoustic signal (PA) obtained for each pressure applied. The results are in agreement with those obtained by high-pressure Raman spectroscopy carried out under similar conditions. In both techniques a 4:1 methanol–ethanol mixture was used as a pressure transmitting medium, and the pressure was calibrated using the ruby fluorescence technique.

A miniaturized nanoindenter system has been designed and fabricated to carry out localized in situ deformation studies in a high resolution transmission electron microscope (TEM). The coarse positioning is carried out with the help of small inertial drives so that the whole system could fit into the specimen holder of the JEOL 2010 microscope. The fine positioning is achieved with a piezoelectric tube and the force is measured with the help of a four bar flexible hinge spring element. The ability of the system to correlate the force–distance data with the events observed in TEM is demonstrated.

The paper describes a system for the determination of the size-of-source effect (SSE) of radiation thermometers with the direct reading of temperature, which form the majority of commercial radiation thermometers. Optics in every radiation thermometer (RT) gathers radiation from a larger area than is defined by the nominal target size. Thus, a measured temperature is more or less dependent on available target area. Every radiation thermometer suffers from the SSE. We developed a system, based on a water-cooled holder, for measuring the SSE by a direct method. The system could be placed in front of any blackbody. Manufacturing of such a system was relatively easy and could be important for users of commercial radiation thermometers because the majority of those thermometers have direct reading of temperature. We measured the SSE characteristics by the direct method for a radiation thermometer with a linearized signal and direct reading of temperature. The results of the SSE were analysed for the direct method without correction of the background radiation and with correction of the background radiation. Knowledge about the SSE characteristic of a radiation thermometer is one of the key elements for correct temperature measurement.

We describe miniature all-optical pressure sensors, fabricated by wafer etching techniques, less than 1 mm² in overall cross-section with rise times in the µs regime and pressure ranges typically 900 kPa (9 bar). Their performance is suitable for experimental studies of the pressure–time history for test models exposed to shocks initiated by an explosive charge. The small size and fast response of the sensors promises higher quality data than has been previously available from conventional electrical sensors, with potential improvements to numerical models of blast effects. Results from blast tests are presented in which up to six sensors were multiplexed, embedded within test models in a range of orientations relative to the shock front.

Two optical fibre anemometers, one based on a Mach–Zehnder interferometer (OFIA) and another a novel laser-optical fibre Bragg grating sensor (FBGA) have been constructed to measure the speed of the convective air flow generated in the point-plane gap of a negative corona discharge in atmospheric air. In both configurations the sensing section of the optical fibre anemometers is subjected to controlled, repetitive bursts of infrared radiation from a CO₂ laser and the combination of localized heating and convective cooling by the corona wind results in an optical signal that is directly calibrated to the speed of the wind. Both the OFIA and FBGA successfully measured the speed of the corona wind in the discharge gap, with wind speeds ranging from 0 to 0.7 m s⁻¹ observed at different locations in the discharge gap. However, the FBGA, due primarily to the ability to average sensor response over many measurements, exhibited an order of magnitude higher sensitivity than the OFIA (Δv ≈ 4 × 10⁻³ m s⁻¹ compared to 3 × 10⁻² m s⁻¹). Both sensors yielded measurements of wind speed that were an order of magnitude lower than similar measurements using laser Doppler anemometry (LDA), indicating that the seed particles introduced as part of the LDA system are providing false reading of wind speed due to acceleration by the gap electric field.

The dynamic (time resolved) PIV (particle imaging velocimetry) measurement technique was applied to high-speed gas flow in a narrow channel with an obstacle. The boundary layer was visualized with a high-speed APX RS camera and an Nd:YLF high repetition double-pulse laser. Nitrogen gas seeded with oil particles using Laskine nozzle flows through a 10 × 10 mm² square channel with Reynolds numbers of 11 000 and 34 000. Although a sufficient quantity of images was difficult to capture for the Re = 34 000 flow to visualize the vortex evolution in time for the time resolved analysis of the boundary layer, large scale structures of turbulence at the edge of the thin plate are clearly visualized in the temporal domain. Fluctuation transfer velocities in the boundary layer were measured employing the whole field two-point velocity correlation. It is proposed that dynamic PIV can open a way of measuring the fluctuation transfer velocities in the whole flow target area simultaneously for high-speed turbulent flows even in small scales.

A microscope objective designed for air medium has been used under non-design optical conditions to focus an exciting laser beam on sub-micron fluorescent particles with the emitted fluorescence received through a glass layer with a mismatched refractive index. The diffraction pattern with several clear interference fringes generated from the fluorescence emitted from a fluorescent particle changed with the particle's position along the optical axis. A scalar diffraction model developed by Gibson and Lanni (1991 J. Opt. Soc. Am. A 8 1601–13) was used to predict the diffraction patterns for various aberration conditions and to analyse the effects of the coherence properties of the fluorescence on the details of the diffraction pattern. The particle position along the optical axis, i.e. its defocus distance, could be determined based on the characteristic sizes of the particle's diffraction pattern to track the particle in three dimensions.

Much attention has been paid to the optical design of a birefringent lens and analysis of its polarization aberration due to its essential application in bifocal interferometric microscopes. To investigate a practical way of designing a birefringent lens with large separation between the two foci, a novel concept named 'pseudo-chromatic aberration' is proposed, which results from the difference of refractive indices between the ordinary and extraordinary rays when they pass through the birefringent lens. As the concept is similar to normal chromatic aberration, the existing primary aberration theory to design a thin cemented lens can also be adopted on the design of a birefringent lens. A table of primary structure of cemented doublet birefringent lenses is consequently obtained. Different combinations of three kinds of birefringent crystals and optical glasses can satisfy various requirements. A concrete example of a birefringent lens with the compactness factor γ of 0.25 is given using the glass of SF2 and calcite.

In this paper we describe a machine vision system for automatic optical quality inspection of light emitting diodes (LEDs). The proposed system is capable of measuring the intensity, mean colour, colour variation, divergence of the optical axis from the mechanical one and viewing angle of the emitted light. These optical properties are obtained by analysing the image of the light projected on a screen. A detailed analysis of the repeatability and thermal stability of the system was performed. The obtained results show that the proposed system is a powerful tool for automatic sorting of LEDs as it is capable of measuring the above-mentioned optical properties with high repeatability.

The aim of this work was the classification of milk samples with the use of Support Vector Machine networks. An electronic tongue, based on a sensor array of miniaturized solid-state potentiometric electrodes, was used for measurements of milk originating from various dairies (i.e. various brands) and with different fat content. The sensors were mounted into the measurement flow-cell developed at Warsaw University of Technology. Their signals were input to the Support Vector Machine neural network without a pre-processing stage. The results of the classification of milk by trademark and by fat content proved the proposed system to be very efficient.

In this paper, we describe a new, simple and fast photothermal method for characterizing the quality of natural gas used as automobile fuel. The method consists essentially in measuring the thermal properties of a sequence of natural gas diluted in nitrogen with a photothermal gas analyser time especially designed for this purpose. It is shown that the proposed method is capable of measuring the thermal properties with an accuracy of 3%. It is also shown that the proposed method is capable of detecting traces of H₂S greater than 7.8 mg m⁻³ in the natural gas. This good accuracy, together with its fast response and portability, suggests it as a simple routine, local, checking device for natural gas quality assurance at retailers' stations.

The novel design of a flexible guarded capacitor which conforms to a core sample's cylindrical surface is presented. The proposed device allows non-destructive measurements of hard rock samples produced by diamond drilling, and has numerous advantages over previous methods. No material is lost to sample preparation and a detailed characterization of the entire core, including inclusions and transitions between rock types, may be performed. A detailed methodology for the rapid and cost-effective construction of a robust capacitor is given. Guidelines for its operation to achieve repeatable and accurate measurements of the complex dielectric constant of samples of varying homogeneity in the 1–25 MHz frequency range are presented.

A new method for the production of four-component (element or compound) combinatorial thin films is presented. The combinatorial thin film consists of nine continuous four-component regions producing planes in quaternary composition space. The method allows for the coverage of large continuous regions of quaternary or pseudoquaternary systems. The magnetron sputtering deposition method is mechanically simple and uses existing infrastructure. New software for the visualization of quaternary data is also presented. This software allows the straightforward identification of composition-dependent properties such as x-ray diffraction intensities. The new production method and software are demonstrated with a four-element combinatorial thin film containing Si, Sn, Co and C.

A new electrically calibrated calorimetric system to measure heat capacities of solids has been designed and tested by determining the heat capacity of sapphire and benzoic acid in the temperature range 298–393 K. Comparison of the obtained results with recommended adiabatic calorimetry data showed that the maximum and average absolute deviations were 3.3% and 1.6%, respectively. The technique provides a convenient alternative to routine heat capacity determinations by DSC, since the experiments are faster and, in general, the results have better accuracy. In addition, the sample cells can be kept under argon or nitrogen atmosphere thus enabling the study of air sensitive compounds.

In this paper, we describe an ultrasonic inspection system used for detection of surface defects in food cans. The system operates in the pulse–echo mode and analyses the 220 kHz ultrasonic signal backscattered by the object. The classification of samples into valid or defective is achieved with χ² statistics and the k nearest neighbour method, applied to features computed from the envelope of the ultrasonic echo. The performance of the system is demonstrated empirically in detection of the presence of the pull tab on the removable lid of easy-open food cans, in a production line. It is found that three factors limit the performance of the classification: the misalignment of the samples, their separation of the ultrasonic transducer, and the vibration of the conveyor belt. When these factors are controlled, classification success rates between 94% and 99% are achieved.

Optical beam deflection detection is one of the main techniques used to detect the vibrating amplitude of dynamic mode atomic force microscope cantilevers. Due to the limitations of optical beam deflection detection systems and cantilevers, light leakage of the incident laser beam around the cantilevers can occur. An interference effect between the reflected beam from the cantilever and some scattered light from the specimen surface occurs, and an interference error in the probe tip–specimen approaching curve arises from this effect. In this paper, the interference effect in a dynamic atomic force microscope is analysed and observed in different conditions, and the micro-profile measurement error caused by the optical interference is deduced and calculated mathematically. The influence of the interference effect on a grating pattern measurement is then simulated.

A lead resistance compensation technique for remote variable resistive sensors has been proposed here. The main objective of this technique is that the measurements for remote variable resistive sensors must be insensitive to connecting lead resistance or compensate for it. Theoretical predictions are supported by experimental results. It is quite conveniently adaptable in industry.

The tile-based phase unwrapping method employs an algorithm for finding the minimum spanning tree (MST) in each tile. We first examine the properties of a tile's representation from a graph theory viewpoint, observing that it is possible to make use of a more efficient class of MST algorithms. We then describe a novel linear time algorithm which reduces the size of the MST problem by half at the least, and solves it completely at best. We also show how this algorithm can be applied to a tile using a sliding window technique. Finally, we show how the reduction algorithm can be combined with any other standard MST algorithm to achieve a more efficient hybrid, using Prim's algorithm for empirical comparison and noting that the reduction algorithm takes only 0.1% of the time taken by the overall hybrid.

The ability to determine the centre position of a localized temperature change within a chirped fibre Bragg grating (CFBG) has been investigated as a function of grating strength. The intragrating sensor is based on the analysis of reflected power spectra arising from a CFBG. The technique uses a discrete Fourier transform (FFT) in which the measured spectrum of the CFBG due to a localized temperature change (heat source) was simulated using a FFT grating design model. The model operated on the reference spectrum and hypothesis temperature distributions, T(z), to generate a spectrum of a CFBG subjected to a hypothesis temperature disturbance. The simulated spectrum was fitted to the measured spectrum using a three-parameter automatic disturbance function fitting algorithm operating on position, width and amplitude of temperature change. RMS deviations to within 0.03 mm of applied values of position have been obtained.

Wear plays an important role in the game of tennis as it affects both ball performance and player perceived ball quality. Visual appearance can be used in ball differentiation, but has so far been limited to subjective assessments used to estimate ball wear and performance characteristics. A metric for ball surface condition will allow performance and perception data from varied testing set-ups to be objectively compared and analysed. A versatile new method of assessing surface roughness using digital imaging has been developed to allow the quantitative assessment of tennis ball condition. This metric allows manufacturers and researchers to predict ball performance and player perception from worn ball samples, developing acceptable wear limits. In the successful implementation of this metric, several key factors, including lighting, image thresholding, algorithm implementation and camera specifications, were identified to aid future alternative implementations.

A new technique of three-dimensional hybrid stereoscopic particle image velocimetry (3D hybrid SPIV) for measuring a volumetric spatial distribution of three-dimensional velocity is presented in this paper. The accuracy and uncertainty of this technique are examined by numerical tests. The 3D hybrid SPIV has been found to be able to measure major features of velocity field involving a vortex with turbulence in a shear flow. This technique is used for measuring an instantaneous three-dimensional flow structure under breaking waves. The formation of the three-dimensional vortex structures involving roller and longitudinal vortices in breaking waves is investigated in this study.

In this paper we describe an experimental technique for imaging defects in carbon composite structures non-invasively using ultra-high input impedance electric potential (displacement current) sensors. We suggest that with suitable two-dimensional arrays of these sensors it should prove practicable to image in real time, and in situ, large scale carbon composite structures such as aircraft wing and tail surfaces.

Fibre optic Bragg gratings (FBGs) written in normal and reduced diameter high birefringence (HiBi) fibres are studied. Chemical etching is used to reduce the diameter of fibres while the optical properties of the FBG spectrum are measured. The results obtained agree qualitatively with the stress enhanced chemical etching. The birefringence of the fibre is determined as a function of the diameter. Optical characterization of the FBG under transverse strain and temperature is also performed. The results obtained show the feasibility of the simultaneous measurement of those parameters with a HiBi FBG sensor.

In this paper, we propose an interferometric approach for visualizing and measuring the quasi-static strain experienced by fibre Bragg grating sensors. The method makes use of a simple bi-polished silicon sample acting like an etalon tuneable filter. The Bragg wavelength shift can be evaluated by analysing the overall interferometric signal achieved by tuning the etalon tuneable filter angularly. A fast Fourier transform method is applied for phase retrieval. The choice of the silicon sample is determined by the low-cost and well-developed silicon technology and fabrication, the easy design and tuneability of the spectral response, and the possibility of integrating on the same sample also the circuitry for electronic control. The principle of operation of this method is described and results obtained by employing such a configuration are reported.

Recently, a novel optical method, coherent gradient sensing (CGS), has been widely used in the study of deformation near crack tips under quasi-static and dynamic conditions, which can produce high contrast fringes and provide some degree of control on the sensitivity of measurement during experiment. It involves a simple optical set-up and is relatively insensitive to vibrations and rigid body motions. Like other interferometries, such as electronic speckle pattern interferometry, moiré method, etc, the accuracy of the fringe order in the CGS interference image will deeply influence the precision of experimental study. But because of the different optical principle, the fringe order of CGS cannot be obtained through the phase-shift technology. In this paper, a modified CGS method is introduced and analysed, which can accurately obtain the fringe order of a random position in the CGS interference image. The modified CGS method needs two original CGS optical set-ups, and can be used in static and dynamic conditions, which requires no complicated image processing techniques. Static fracture experiments on mode-I crack in homogeneous materials show that this modified method can evidently improve the measurement precision of the CGS method.

On-line roughness measurement of a surface with one-dimensional manufacturing marks is difficult to implement. For example, a contact stylus-type inspection method often does not perform very well or fails without any prior knowledge of the mark distribution on the surface. In this paper, we propose an on-line surface roughness measurement method based on laser light scattering, which is very effective for roughness measurement of one-dimensional manufacturing surfaces. The surface roughness is obtained from the spatial distribution of the scattered light intensity. The measurement setup has a very simple configuration, which consists of a CCD sensor, a collimated diode laser and an expander. The orientation of the spatial distribution of the scattered light intensity from the surface, which depends on the surface orientation, is detected by the CCD sensor, and then the mark direction can be readily determined from image processing. After that the root-mean-square (RMS) height of the surface roughness is extracted by means of image processing of the scattered light distribution in the direction parallel to the manufacturing mark, rather than in the direction perpendicular to the mark which is often followed by other measurement probes. The experimental tests show that the non-contact method has great potential for on-line surface roughness measurement.

Rainbow schlieren deflectometry was integrated with a high-speed digital imaging system to quantify the scalar flow structure of flames at a high temporal resolution. The schlieren image data were processed to determine the temperature field across the whole field assuming chemical equilibrium in the flame. First, shapes of steady hydrogen jet diffusion flames estimated from the schlieren technique were compared with those obtained by direct visualization. Next, the schlieren technique was applied to flame experiments at a jet exit Reynolds number of 300, which produced periodic oscillations or flame flicker. Rainbow schlieren images taken at acquisition rates of 30, 60, 125, 250, 500 and 1000 frames per second were analysed to construct the instantaneous temperature distributions across the whole field, the vortex convection velocity profiles, and the mean and root-mean-square temperature profiles. Results demonstrate that high-speed rainbow schlieren deflectometry is effective in quantitatively describing the transient flow structure of unsteady flames.

On-line identification of flow regimes is important in two-phase flow because hydrodynamics and adequate operation of multiphase systems are highly dependent on the flow pattern. This work describes the application of an artificial neural network (ANN) to process the signals measured by a conductivity probe and classify them into their corresponding flow regimes. Experiments were performed in an adiabatic air–water upward two-phase flow rig. Some statistical parameters of the cumulative probability density functions (CPDF) of the bubble chord length were used as the inputs to the ANN. Different ANN configurations were evaluated to optimize the characteristics that best suit the specific ANN application. The results demonstrate good agreement with the visual flow map identification, even for reduced temporal conductivity signals.

In this paper, a method for real-time fault detection and isolation is presented, which has been tested successfully for unmanned aerial vehicles. In this method, two parity vectors are constructed to achieve the fault detection and isolation. In addition, the maximum likelihood estimate is used to estimate and correct the fault vector. Simulation results show that not only can the faulty system be detected accurately in time by this method, but also the fault can be repaired efficiently. Thus, the fault tolerance of the integrated system is improved remarkably by this method.

This paper describes a new and practical method to estimate the size of a crack on a rotating beam in a laboratory setting. The paper consists of selecting and validating a sensor and a measurement variable, devising a signal processing method for crack size estimation and carrying out experimental validations. The study employed a microphone to measure the pressure wave excited by the vibration of the rotating beam, validated the microphone signal, utilized chirp z-transform to extract the first and second vibration mode frequencies and established a diagnostic neural network to map the frequencies to crack size. Four fatigue tests were conducted to initiate and then propagate a crack. Microphone outputs and crack sizes were periodically recorded during the four tests. Data of test no. 1 were used to calibrate the neural net and data of the other three tests were used for testing. The experimental results show that the proposed approach can provide reasonably good estimates of the crack size using the indirectly excited acoustic signal.

The quality of measurements depends directly on the quality of the measurement system model. With this concern, novel hybrid modelling techniques have been formulated for model performance enhancement. Air-gauge focus system sensor modelling has been accomplished by theoretical and empirical data integration. These modelling techniques combine a priori knowledge in theoretical model elaboration, and to attain the enhanced levels of adequacy, accuracy and precision they approximate the exact unknown model, simultaneously by available theoretical and appropriate polynomial empirical functions. For such a hybrid model the solution of two approaches by means of linear transformation and successive linear and nonlinear transformations have been developed. The validations of elaborated air-gauge sensor models revealed that sensor hybrid model solving by successive linear and nonlinear transformations permits us to attain minimum discrepancy with empirical evidence for the whole region of interest for model predictor variables.

In this paper, we present the fundamental characteristics of a novel dual-colour optical fibre surface plasmon resonance (SPR) sensor for a portable low-cost sensing system. The principle of the proposed SPR sensor is based on the differential reflectance method. Light from two light-emitting diodes (LEDs), which are flashing alternately with different wavelengths, is fed to a sensor via two optical couplers. The reflected light is detected by a photodiode. Changes of reflectance at two wavelengths are proportional to the refractive index change of the medium of interest. Taking the difference in reflectance at two wavelengths improves the sensitivity almost twofold. Measuring ethanol solutions with different refractive indices reveals that the sensor has a linear response to the refractive index change from 1.333 to 1.3616. By measuring the stability in the time response we estimate that the limit of detection (LOD) of the refractive index is 5.2 × 10⁻⁴.

Surface waves on liquids act as a dynamical phase grating for incident light. In this paper, we revisit the classical method of probing such waves (wavelengths of the order of mm) as well as inherent properties of liquids and liquid films on liquids, using optical diffraction. A combination of simulation and experiment is proposed to trace out the surface wave profiles in various situations (e.g. for one or more vertical, slightly immersed, electrically driven exciters). Subsequently, the surface tension and the spatial damping coefficient (related to viscosity) of a variety of liquids are measured carefully in order to gauge the efficiency of measuring liquid properties using this optical probe. The final set of results deal with liquid films where dispersion relations, surface and interface modes, interfacial tension and related issues are investigated in some detail, both theoretically and experimentally. On the whole, our observations and analysis seem to support the claim that this simple, low cost apparatus is capable of providing a wealth of information on liquids and liquid surface waves in a non-destructive way.

Earth magnetic field mapping from planetary orbiting satellites requires a spacecraft magnetic field environment control program combined with the deployment of the magnetic sensors on a boom in order to reduce the measurement error caused by the local spacecraft field. Magnetic mapping missions (Magsat, Oersted, CHAMP, SAC-C MMP and the planned ESA Swarm project) carry a vector magnetometer and an absolute scalar magnetometer for in-flight calibration of the vector magnetometer scale values and for monitoring of the inter-axes angles and offsets over time intervals from months to years. This is done by comparing the two magnetometer outputs for several days and for as many different external field directions and amplitudes in the satellite frame as available. The vector and the scalar sensor may be placed of the order of 2 m apart and at the end of an about 10 m long boom counted from the spacecraft centre-of-gravity. In line with the classical dual vector sensors technique for monitoring the spacecraft magnetic field, this paper proposes and demonstrates that a similar combined scalar/vector gradiometry technique is feasible by using the measurements from the boom-mounted scalar and vector sensors onboard the Oersted satellite. For Oersted, a large difference between the pre-flight determined spacecraft magnetic field and the in-flight estimate exists causing some concern about the general applicability of the dual sensors technique.

An impedance method for the periodic 'in situ' diagnostics of the solid electrolyte/liquid-metal electrode interface during the lifespan of yttria-stabilized zirconia (YSZ) based sensors measuring oxygen partial pressure in melts was developed. Polarization effects on the YSZ, resulting from the corrosive measuring environment (molten alkaline metals), may be interpreted as a blocking reaction layer on the electrolyte/liquid-metal electrode interface. The proposed impedance method allows information to be obtained about the level of polarization of the YSZ/liquid-metal electrode interface that is characterized by a second semi-arc of a hodograph of impedance. The second semi-arc represents the parameters of polarization resistance (R_f) and capacitance of the double electrical layer on the interface YSZ/liquid metal (C_D). Analysis of the impedance method on the single crystal zirconia sensor measuring dissolved oxygen in molten lead at temperatures of 380–480 °C revealed that this sensor, with a Bi–Bi₂O₃ reference electrode, showed a negligible level of polarization effects on the electrode/electrolyte interface at temperatures as low as 380 °C. The results of the present work may be applicable for the diagnostics of oxygen sensors with more complicated applications, such as in the measurement of oxygen activity in lead–bismuth, sodium or lithium heat carriers in liquid-metal nuclear facilities.

The amount fraction of oxygen in oxygen–nitrogen gas mixtures has been measured with a relative uncertainty of ±0.02% within the range 100–1000 mmol mol⁻¹. The method employed uses an auto-null 'dumbbell' type paramagnetic oxygen sensor, which has high resolution (10 µmol mol⁻¹) and excellent linearity. The sensor is used to compare the sample gas mixture with pure oxygen and nitrogen gases, which compensates for drift and pressure change, and avoids the uncertainty from using bottled calibration gas mixtures. The method was verified by measuring primary standard gas mixtures at the National Physical Laboratory. To the authors knowledge the uncertainty achieved is better than any other analytical instrument, within the specified range.

This paper brings together considerations of gas leak behaviour and leak detector design and use, with a view to improving the detection of low-pressure natural gas leaks. An atmospheric boundary layer wind tunnel has been used to study ground-based releases of methane at full scale over distances of up to 3 m, under controlled conditions. These scales are relevant to the detection of natural gas leaks from mains and services using hand-portable gas detectors. The mean spatial distribution of the leaking gas plume was determined and used to test and fit a Gaussian dispersion model. This was used for subsequent analysis with respect to the ability of gas leak detectors to confirm and locate a leak. For ground-based leaks, gas concentrations drop rapidly with height such that instruments should ideally sample the air from within 100 mm of ground level. The rapid dilution of gas with distance from the source means that instruments with lower limits of detection, ideally of a few parts per million, have much improved ability to detect a leak from greater distances downwind. Finally, observations showed the variable temporal nature of the gas and the potential for confusion when sampling gas at a single point in time and space.

In this paper, a multifibre optic sensor is developed to measure the thickness of the liquid film located between a moving bubble and an inclined surface. The sensor takes into account the presence of a second interface independently of its distance from the solid surface. In the first part of the paper, a mathematical model is developed to simulate the behaviour of several configurations of the fibre optic sensor in order to determine the best configuration of the sensor. In the second part, the calibration setup is presented and described in detail. In the last part of the paper, the method is validated. The results showed that the applicability range of the sensor is from 125 µm to 1400 µm. In the operating range, the accuracy of the sensor is around 5%.

The demanding task of monitoring the spatial position of vertex detectors used in high energy physics experiments performed in particle accelerators requires sensors able to measure linear displacements with high resolution under strong magnetic and radio frequency fields. Due to the severe environmental conditions, traditional electric transducers are hindered from working satisfactorily. This paper describes the development of a packaged opto-mechanical sensor which can overcome these problems. The principle of operation relies on the measurement of the tangential strains of a CFRP Ω-shaped elastic element by means of an optical in-fibre Bragg grating (FBG): its design allows us to measure linear displacements with high accuracy and extended linear range. The sensor is self-compensated in temperature in order to take into account wavelength shifts due to apparent strains and to increase its intrinsic accuracy. The latter has been evaluated by calibration performed in the laboratory to be within ±3 pm, corresponding to ±13 µm, which is close to the resolution of the interrogation system used to detect the FBG reflected wavelength shift.

Matrix cracking damage is a generic type of damage that develops under load in the off-axis plies of laminated composites and is generally the precursor of more serious damage mechanisms, particularly delamination. Hence, it is important to identify and if possible locate this type of damage. Chirped fibre Bragg grating sensors have been embedded in a transparent glass fibre reinforced plastic crossply laminate and changes to the reflected spectra as a consequence of crack development have been studied. An approximately sinusoidal variation of the intensity of the reflected spectrum occurs at the position of the crack, enabling both crack development and crack position to be identified. A simulation of a reflected spectrum, incorporating a stress transfer model to predict the strains and an optical model to predict the reflected spectrum, is in reasonable agreement with the experimental results.

Developments in digital image correlation in the last two decades have made it a popular and effective tool for full-field displacement and strain measurements in experimental mechanics. In digital image correlation, the use of the sub-pixel registration algorithm is regarded as the key technique to improve accuracy. Different types of sub-pixel registration algorithms have been developed. However, little quantitative research has been carried out to compare their performances. This paper investigates three types of the most commonly used sub-pixel displacement registration algorithms in terms of the registration accuracy and the computational efficiency using computer-simulated speckle images. A detailed examination of the performances of each algorithm reveals that the iterative spatial domain cross-correlation algorithm (Newton–Raphson method) is more accurate, but much slower than other algorithms, and is recommended for use in these applications.

Photosensitive optical media of the types that are used in real-time holography generally exhibit both photorefractive and photochromic response. The parameters that characterize each of these types of response can be extracted by detailed quantitative analysis of four-wave mixing experiments in the Raman–Nath regime. This principle has been tested using reactive eyeglass lenses. The techniques of Fourier optics have been applied to the analysis of diffraction from amplitude/phase gratings produced in the photochromic glass by laser illumination. Dithering of a laser-induced fringe pattern produces a combination of two-wave and four-wave mixing that can be analysed in terms of amplitudes proportional to products of Bessel functions of different orders. The incident and diffracted beams are predicted, and observed, to be modulated at the dither frequency and its harmonics. The small dither amplitudes that were employed, made possible by use of a phase-sensitive detection technique, allowed Bessel function expansions to be truncated after only a few terms for the purpose of parameter estimation. The technique has allowed the very small refractive index change associated with dispersion of the photo-induced absorption in silver halide doped photochromic glass to be measured for the first time.

In thermoelastic stress analysis, an infrared detector is used to obtain the small temperature change resulting from the thermoelastic effect. The output from the detector, known as the thermoelastic signal, is dependent on both the surface stresses and the surface temperature of the component under investigation. For quantitative thermoelastic stress analysis, it is important that the response resulting from changes in the surface temperature is decoupled from the response resulting from the stress changes. In this paper, a means of decoupling the response is presented that involves making corrections for increases in surface temperature so that the thermoelastic signal is dependent only on the stresses. The underlying theory is presented and a correction factor is developed using an experimental approach. A methodology for applying the correction factor to full-field data is provided. The methodology is validated through a number of case studies and applied to a composite component subject to fatigue damage initiated at a central hole.