Table of contents

This issue of Measurement Science and Technology (MST) contains three papers presented at the second international symposium on Standard Materials and Metrology for Nanotechnology (SMAM-2), held in the Akihabara Convention Hall in Tokyo, Japan, on 25 and 26 May 2006.

The SMAM symposium aims to emphasize the importance of standard materials and metrology (SM/M) for the development of nanotechnology, which is expected to be the most promising driving force for the development of advanced industrial science/technology in various fields. New fabrication processes based on nanotechnology will become really powerful when the processes are reproducible and reliable. The SM/M that have been developed for use in nano-scale characterization are therefore the key tools for the establishment of reliability in the areas of information, environment and biotechnology, where the application of nanotechnology is essential for their development.

The symposium had four sessions featuring the most important issues in the field of SM/M: (I) Nanotechnology Standardization, (II) SM/M for Nano-particles and Nano-pores, (III) SM/M for Nanostructure Evaluation, (IV) SM/M for Thin-film Characterization. A total of 29 papers had been submitted to the SMAM-2 Publishing Committee and six papers were tentatively selected by the committee to forward to the MST editors for publication in this journal. The three papers published in this issue are epoch-making in that they present new methods and knowledge for the standard materials and metrology especially developed for nanotechnology. We hope the papers will show readers how important standard materials and metrology are for the development of nanotechnology.

We appreciate very much the important contribution of those who refereed the manuscripts and we particularly want to thank the MST staff for helping in publishing this special feature. Finally we expect SMAM-3 to be held two years after SMAM-2 and we hope to attract many more participants and papers and to publish a further special feature in MST.

Shingo Ichimura Chairman of the Organizing Committee of SMAM-2

The National Institute of Advanced Industrial Science and Technology (AIST), National Metrology Institute of Japan (NMIJ) developed nanometric lateral scales (design pitch: 25 nm) consisting of a GaAs/InGaP superlattice (multilayer) for atomic force microscope (AFM) and scanning electron microscope (SEM) calibration. The pitch of the fabricated nanometric lateral scales was measured using our AFM with a differential laser interferometer (DLI-AFM) and the uncertainty in the pitch measurements was evaluated. The average pitch and its expanded uncertainty (k = 2) were 25.39 nm and 0.43 nm, respectively. The quality of the developed scales was high enough to make them a suitable candidate for CRMs. On the basis of the obtained results in this technical study, the fabrication procedure and layout of the nanometric lateral scales will be optimized for the future distribution of these scales.

A new method for the vertical scale calibration in step height measurement has been established using a multiple delta-layer film. The vertical scale of a stylus profilometer can be traceable to the length unit by the certified film thickness in a multiple delta-layer. A Si/Ge multiple delta-layer film with six Si layers separated by Ge delta-layers was developed. The total thickness and delta-layer spacing were certified by high resolution transmission electron microscopy. Six craters with different depth were formed on the Si/Ge multiple delta-layer film by ion beam sputtering via SIMS depth profiling. The depths of the craters can be determined from the certified depth of the delta-layer and direct measurements using a stylus profilometer calibrated by a step-height standard. The vertical scale of a stylus profilometer can be calibrated by the slope and the offset of the measured crater depth fitted as a function of the certified nominal thickness.

The scanning electron microscope (SEM) and transmission electron microscope (TEM) are very powerful tools for the nanoscale characterization of materials. To make the best use of these capabilities, it is necessary to understand the nature of the uncertainties in the measurement process and to allow for errors during the data capture and data analysis stages of the measurement. By using replicated measurements and statistical analyses, it is possible to address repeatability and reproducibility issues and to assign a precision to the measurements. In general it is much harder to address accuracy issues in the experiment because some of the errors are systematic and non-statistical in nature and in almost all cases the true value of the measurand is unknown. In this work computer simulations are used to understand systematic errors and accuracy concerns in dimensional and chemical metrology in both the SEM and TEM. Multislice high-resolution TEM (HRTEM) simulations are used to produce synthetic cross-section micrographs of SiO₂ gate dielectrics on Si substrates. These synthetic images are processed in the same manner as experimental images to extract a film thickness value from the micrographs. The absolute error in the dielectric film thickness measurement is determined by comparing this 'measured' value with the known, true thickness intrinsic to the sample's structural model used for simulation. This process allows the accuracy of the measurement process to be assessed for a given set of microscope, sample, environmental, data capture and data processing parameters. Statistical design of experiment methods is used to screen the influence of variables including beam tilt, along-beam thickness, dielectric thickness, defocus, astigmatism and vibration on the accuracy. The most important main effects are beam tilt, defocus and vibration, and the most significant two-term interactions are (beam tilt–defocus) and (defocus–vibration). Three-dimensional Monte Carlo simulations in Java and Jython are used to simulate the electron transport and x-ray generation of energy-dispersive x-ray (XEDS) experiments in the SEM. This code permits the simulation of synthetic hyperspectral XEDS datasets from complex, chemically heterogeneous nanostructures. Analysis of these datasets reveals the effects of self-absorption, thickness and beam broadening due to multiple scattering on the accuracy of chemical measurements in the SEM and TEM. A synthetic XEDS datacube from a four-phase Raney nickel sample is presented. While the effects mentioned above degrade both TEM-based and SEM-based measurements, their magnitude is larger and more easily visualized in the SEM because of lower beam energies and thicker samples.

A system has been constructed for measurement of the gas concentration in a binary gas mixture and of the total flow rate of the gas mixture, using a venturi flowmeter and a laminar flowmeter. The flow rate and air concentration in tested gas mixtures, consisting of air and carbon dioxide or helium, are measured. The results are compared with reference values and the obtained results are found to be similar to those obtained using existing flowmeters and concentration meters. The response of the system to the flow rate and the mixing ratio change is tested. The flow rate change response is approximately equivalent to existing flowmeters, and the concentration change response is better than for existing meters.

The vortex signal is greatly disturbed by noises from external interference when the meter works at low flow rate, which results in a limited measuring range for the flowmeter. In order to solve the problem, a new signal processing method based on the Hilbert–Huang transform (HHT) is proposed. With its good performance on local adaptability and time–frequency analysis, noises are removed by the empirical mode decomposition (EMD) and the residue components are analysed by the Hilbert transform; then instantaneous frequency distributions are achieved. When the probability density of a certain frequency component exceeds 5%, the sifting process will be terminated. Subsequently, the vortex frequency can be calculated from the last residue component. Experimental studies were carried out to compare the improved method with the classic method FFT at low flow rate. A better linearity and lower limit of measurement are achieved by the proposed method.

Although much work on modelling the drift of fiber optic gyroscope (FOG) in the quiescent case has been done, little attention is paid to eliminate the influence of the uncertain gyroscope drift in the maneuvering case. In this paper, a novel adaptive mechanism based on double transitive factors is highlighted, which is implemented in two stages. In the first stage one adaptive factor is investigated, and then the productions of the stage, the suboptimal estimated state vector and its suboptimal covariance matrix are passed to the second stage, where the other adaptive factor is derived, and then the modified covariance matrix of measurement noise is passed to the first stage; consequently the optimal estimation may be achieved based on the recursive mechanism. As demonstrated in the testing of a specific type of FOG, the proposed method, compared with the other scheme in this paper, greatly reduces the influence of insufficient kinematic model and stochastic error, thus improving the measurement accuracy of FOG in the maneuvering case.

Crossed electron-molecular beam experiments featuring skimmed nozzle beams may be used to study electron interactions with species such as radicals, excited molecules and biomolecules. A new technique for placing measured cross sections on an absolute scale is reported, as the traditional relative flow method used for effusive molecular beams does not apply to skimmed supersonic jet beams. Absolute cross sections for Ar and CF₄, using this new procedure, are measured and compared to previous effusive beam results as a proof of concept.

To evaluate the potential of a ground-penetrating radar for leak detection of water pipes, well-controlled experiments allowing flexibility of the involved parameters are necessary. To accomplish this purpose, a laboratory scaled-down model of the radar under leak conditions is proposed here. The laboratory system consisted of a dry sand tank, a pipe and a simulated zone of leakage adjacent to the pipe. The size and burial depth of the pipe were scaled down to about 1/6 of the real world condition. An equivalent leakage model was employed using an acrylic plastic box filled with methanol. A support for the model was provided by acrylic plastic plates and tubes with dry sand filling. The electrical properties of the equivalent leakage and support were verified by measuring their complex permittivities. B-scan radar images were displayed by background removal and neighbouring difference of raw data. For three cases of leaky pipes, the images showed the superimposition of nearly symmetric and inverted hyperbolas produced by non-leaky pipes and the blurring effects caused by the leakage. Thereafter, diffraction tomography was also applied to B-scan images to improve resolution of the pipe and leakage zone.

The central role of modern experimental analysis is to help complete, through measurement and testing, the construction of a fully specified analytical model such as a finite-element model. In this paper, we demonstrate our approach on a rubber model undergoing large deflections. The inverse problem has two stages. The first is the parameter identification that determines properties such as material constants. The second involves the force identification for determining unknown loads. We formulate both inverse problems using the sensitivity response method (SRM). The advantage of the SRM is that it utilizes commercial FE programs and therefore there is essentially no restriction on the range of problems to which it can be applied. Experimental results using image data of the deformed model will be presented.

We have developed a full-field solid-state range imaging system capable of capturing range and intensity data simultaneously for every pixel in a scene with sub-millimetre range precision. The system is based on indirect time-of-flight measurements by heterodyning intensity-modulated illumination with a gain modulation intensified digital video camera. Sub-millimetre precision to beyond 5 m and 2 mm precision out to 12 m has been achieved. In this paper, we describe the new sub-millimetre class range imaging system in detail, and review the important aspects that have been instrumental in achieving high precision ranging. We also present the results of performance characterization experiments and a method of resolving the range ambiguity problem associated with homodyne and heterodyne ranging systems.

To resolve the computational complexity of computer vision algorithms, one of the solutions is to perform some low-level image processing on the sensor focal plane. It becomes a smart sensor device called a retina. This concept makes vision systems more compact. It increases performance thanks to the reduction of the data flow exchanges with external circuits. This paper presents a comparison between two different vision system architectures. The first one involves a smart sensor including analogue processors allowing on-chip image processing. An external microprocessor is used to control the on-chip dataflow and integrated operators. The second system implements a logarithmic CMOS/APS sensor interfaced to the same microprocessor, in which all computations are carried out. We have designed two vision systems as proof of concept. The comparison is related to image processing time.

The transformer diagnostic methods are systematically being improved and extended due to growing requirements for reliability of power systems in terms of uninterrupted power supply and avoidance of blackouts. Those methods are also driven by longer lifetime of transformers and demand for reduction of transmission and distribution costs. Hence, the detection of winding faults in transformers, both in exploitation or during transportation is an important aspect of power transformer failure prevention. The frequency response analysis method (FRA), more and more frequently used in electric power engineering, has been applied for investigations and signature analysis based on the admittance and transfer function. The paper presents a novel approach to the identification of typical transformer winding problems such as axial or radial movements or turn-to-turn faults. The proposed transfer function discrimination (TFD) criteria are based on the derived transfer function ratios, manifesting higher sensitivity.

The aim of this paper is to demonstrate an alternative method of measurement to be used in determining the minimum thickness of insulation on electrical and telecommunications conductors that are circular in section. As such, a critical analysis of the standard that is usually used in this type of measurement is undertaken and a new error-free methodology is proposed. The problem is reduced to obtaining the minimum separation between the two interior, eccentric circumferences. The method proposed indirectly determines this separation from four measurements between tangents to each circumference, two on the X-axis and two on the Y-axis, positioning the test piece to be measured in any position and taking any origin of coordinates at random. As such, errors derived from the skill of the operator are avoided, as the test piece can be positioned in any direction without the need to determine the thinnest section visually. This method does not involve increasing the uncertainty and is carried out using the same measuring instruments that the standard indicates (a microscope or profile projector).

Electrical impedance tomography (EIT) is an imaging method that estimates conductivity distribution inside a body. In EIT, images are obtained by applying a sequence of low intensity electrical currents through electrodes attached to the body. Although in EIT there are serious difficulties to obtain a high-quality conductivity image, for medical applications this technology is safer and cheaper than other tomography techniques. The EIT deals with an inverse problem in which given the measured voltages on electrodes and a finite element (FE) model, it estimates the conductivity distribution, which are parameters of the FE model. In this work, the topology optimization method is applied as a reconstruction algorithm to obtain absolute images in EIT. It is an optimization method that has been applied successfully to structural mechanical applications and consists of systematically finding a conductivity distribution (or material distribution) in the domain that minimizes the difference between measured voltages and voltages calculated by using a computational model. This algorithm combines the finite element method and sequential linear programming (SLP) to solve the inverse problem of EIT. The SLP allows us to easily apply some regularization schemes based on included constraints in the topology optimization problem. Constraints based on image tuning control and weighted distance interpolation (WDI) are proposed, while a material model is applied to ensure the relaxation of the optimization problem. A new formulation to analytically perform the sensitivity analysis is proposed, using Maxwell's reciprocity theorem. To illustrate, the implemented algorithm is applied to obtain conductivity image distributions of some 2D examples using numerical and experimental data.

Measurements of the dielectric (or impedance) properties of cells can be used as a general characterization and diagnostic tool. In this paper, we describe a novel impedance spectroscopy technique for the analysis of single biological cells in suspension. The technique uses maximum length sequences (MLS) for periodic excitation signal in a microfluidic impedance cytometer. The method allows multi-frequency single cell impedance measurements to be made in a short time period (ms). Spectral information is obtained in the frequency domain by applying a fast M-sequence transform (FMT) and fast Fourier transform (FFT) to the time domain response. Theoretically, the impedance is determined from the transfer function of the system when the MLS is a current excitation. The order of the MLS and sampling rate of A/D conversion are two factors that determine the bandwidth and spectral accuracy of the technique. Experimentally, the applicability of the technique is demonstrated by characterizing the impedance spectrum of red blood cells (RBCs) in a microfluidic cytometer. The impedance is measured within 1 ms at 512 discrete frequencies, evenly distributed in the range from 976.56 Hz to 500 kHz. The measured spectrum shows good agreement with simulations.

Complex permittivity measurement of low permittivity thin films is necessary to understand the fundamental properties and to implement these materials in devices. A new technique has been developed employing split-post dielectric resonators at operating frequencies of 10 GHz and 20 GHz to measure relative permittivity and loss tangent of low permittivity materials, respectively. The results have been confirmed by comparing the measurements with those of thick films fabricated on a quartz substrate. This paper substantiates the validity of performing non-destructive measurements of the complex permittivity of thin polymer films which was not previously possible with the split-post dielectric resonator technique. A detailed error analysis of the measurement procedure is also reported in this paper.

An on-line roboticized apparatus, including an optical biosensing film with an automatic flow sampling system, has been developed for biochemical oxygen demand (BOD) determination of seawater. The sensing film employed in the apparatus consisted of an organically modified silicate (ORMOSIL) film embedded with tri(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) perchlorate. Three species of microorganism cultivated from seawater were immobilized in an ORMOSIL-polyvinyl alcohol matrix. Possible factors affecting BOD determination were studied, including sampling frequency, temperature, pH and sodium chloride concentration. Based on measurements of the linear fluctuant coefficients and the reproducibility of its response to seawater, the BOD apparatus showed the advantages of high veracity and short response time. Generally, the linear fluctuant coefficient (R²) in the BOD range 0.2–40 mg l⁻¹ was 0.9945 when using a glucose/glutamate (GGA) BOD standard solution. A reproducible response for the BOD sensing film of within ±2.8% could be obtained in the 2 mg l⁻¹ GGA solution. The BOD apparatus was applied to the BOD determination of seawater, and the values estimated by this biosensing apparatus correlated well with those determined by the conventional 5 day BOD (BOD₅) test.

Quantitative ultrasound (QUS) techniques have recently been widely applied for the characterization of tissues. For example, they can be used for the quantification of Achilles tendon properties based on the broadband ultrasound attenuation (BUA) and the speed of sound (SOS) when the ultrasound wave passes through the tissues. This study is to develop an integrated system to investigate the properties of Achilles tendons using QUS images from UBIS 5000 (DMS, Montpellier, France) and B-mode ultrasound images from HDI 5000 (ATL, Ultramark, USA). Subjects including young (32 females and 17 males; mean age: 23.7 ± 2.0) and middle-aged groups (8 female and 8 males; mean age: 47.3 ± 8.5 s) were recruited and tested for this study. Only subjects who did not exercise regularly and had no record of tendon injury were studied. The results show that the BUA is significantly higher for the young group (45.2 ± 1.6 dB MHz⁻¹) than the middle-age group (40.5 ± 1.9 dB MHz⁻¹), while the SOS is significantly lower for the young (1601.9 ± 11.2 ms⁻¹) compared to the middle-aged (1624.1 ± 8.7 m s⁻¹). On the other hand, the thicknesses of Achilles tendons for both groups (young: 4.31 ± 0.23 mm; middle age: 4.24 ± 0.23 mm) are very similar. For one patient who had an Achilles tendon lengthening (ATL) surgery, the thickness of the Achilles tendon increased from 4 mm to 4.33 mm after the surgery. In addition, the BUA increased by about 7.2% while the SOS decreased by about 0.6%. In conclusion, noninvasive ultrasonic assessment of Achilles tendons is useful for assisting clinical diagnosis and for the evaluation of a therapeutic regimen.

Sleepiness correlates with sleep-related accidents, but convenient tests for sleepiness monitoring are scarce. The posturographic test is a method to assess balance, and this paper describes one phase of the development of a posturographic sleepiness monitoring method. We investigated the relationship between trial length and accuracy of the posturographic time-awake (TA) estimate. Twenty-one healthy adults were kept awake for 32 h and their balance was recorded, 16 times with 30 s trials, as a function of TA. The balance was analysed with regards to fractal dimension, most common sway amplitude and time interval for open-loop stance control. While a 30 s trial allows estimating the TA of individual subjects with better than 5 h accuracy, repeating the analysis using shorter trial lengths showed that 18 s sufficed to achieve the targeted 5 h accuracy. Moreover, it was found that with increasing TA, the posturographic parameters estimated the subjects' TA more accurately.

Two-phase flow modelling is strongly dependent on flow patterns. For the purpose of objective flow pattern identification, a capacitance sensor was developed for horizontal two-phase flow in small diameter tubes. Finite element simulations were made during design to study the effect of vapour distribution, wall thickness and electrode angle. A test rig was constructed and a series of experiments was done with horizontal air–water flow in a 9 mm tube. The sensor test results are presented in time, amplitude and frequency domain. Flow regime characterization with the capacitance measurements is clearly possible.

The conformation and dynamics of double-stranded DNA molecules in cross-slots with equal arm length are examined with the use of fluorescent labeled λ-DNA at 1.2 ⩽ De ⩽ 4.1. The stretching and diffusing of individual DNA molecules in the flow was visualized/recorded with confocal laser scanning microscopy (CLSM). The onset of coil–stretch transition of DNA molecules in the elongational flow was determined at the microscale. Time-dependent velocity distribution with a mean velocity of 50 µm s⁻¹ for DNA molecules was observed by using FluoSpheres, carboylate-modified microspheres over a time period of 1.12 s. The effect of channel geometry (corner and outlet regions) and the solution viscosity (1.9 cP and 9.5 cP) on the conformation and diffusion are also studied and discussed. We report the maximum and the distribution of the fractional extension of DNA molecules, and show that the maximum fractional extension may be up to 0.64 at De = 4.1, and at a strain of 1.8 there is a corresponding stretching force of about 200 pN.

Can current experimental techniques and analytical procedures produce x-ray absorption fine structure (XAFS) which is independent of the beam line or synchrotron used? We investigate the consequence upon XAFS interpretation of typical systematic errors, including determination of the edge energy, detector response and synchrotron bandwidth. Using the highest accuracy data set of the mass-attenuation coefficient collected so far, we consider a series of systematic effects in the analyses of both the near-edge and extended energy regions of the spectrum. We investigate whether conclusions derived from an experiment using a given analytical procedure are consistent when performed on different synchrotron beam lines. We find that the effectiveness of common XAFS analysis is limited by experimental and data reduction techniques, particularly relating to determinations of photon energy. By correcting for all major systematic errors in XAFS data, one can determine bond lengths more robustly and with greater accuracy.

This paper is on automated visual inspection of tablets that may, in contrast to manual tablet sorting, provide objective and reproducible tablet quality assurance. Visual inspection of the ever-increasing numbers of produced imprinted tablets, regulatory enforced for unambiguous identification of active ingredients and dosage strength of each tablet, is especially demanding. The problem becomes more tractable by incorporating some a priori knowledge of the imprint shape and/or appearance. For this purpose, we consider two alternative automated tablet defect detection methods. The geometrical method, incorporating geometrical a priori knowledge of the imprint shape, enables specific inspection of the imprinted and non-imprinted tablet surface, while the statistical method exploits statistical a priori knowledge of tablet surface appearance, derived from a training image database. The two methods were evaluated on a large tablet image database, consisting of 3445 images of four types of imprinted tablets, with and without typical production defects. A 'gold standard' for testing the performances of the two inspection methods was established by manually classifying the tablets into good and five defective classes. The results, obtained by ROC (receiver operating characteristics) analysis, indicate that the statistical method yields better defect detection sensitivity and specificity than the geometrical method. Both presented image analysis methods are quite general and promising tools for automated visual inspection of imprinted pharmaceutical tablets.

A Michelson-based fibre optic low-coherence interferometric quasi-distributed sensing system is proposed, permitting absolute length measurement in the sensor array. The main part of the sensing system is a fibre optic 3×3 star coupler. The architecture of the fibre optic sensor can easily be realized as a linear sensor array, twin sensor arrays or a loop sensor array. The proposed sensing scheme will be useful for the measurement of strain distribution. An important application could be deformation sensing in smart structures. Experimentally, a six-sensor array has been demonstrated.

A fibre optic multiple-pass surface plasmon resonance (SPR) sensor coupled with a field-assist capability for detecting extremely low concentrations of charged particles is demonstrated for the first time. The field-assist feature forces charged particles/molecules to the SPR surface, increasing the local concentration for detection and thus the sensitivity by an additional factor of about 100. A 10 pM concentration of 47 nm diameter polystyrene (PS) latex beads and 2 µM concentration of salt dissolved in DI water were detected within a few seconds. The equivalent index resolution for atomic size corresponding to ionized chlorine in salt is 2.6 × 10⁻⁸. This technique should offer the potential for the sensitive and fast detection of analytes in a solution.

A general analysis of an inserted long-period grating in an air-clad photonic crystal fiber for temperature and strain measurement is presented. The temperature and strain can be detected simultaneously by using an artificial neural network. A simulation study was carried out with the data set generated by using theoretical strain and temperature sensitivities of the long-period gratings. It indicates that the maximum temperature error is 0.04 °C in the temperature range from 35 °C to 120 °C. At the same time, the maximum strain error is 2.7 µε in the strain range from 0 to 3000 µε.

An imaging fibre bundle is incorporated into a full-field imaging optical coherence tomography system, with the aim of eliminating the mechanical scanning currently required at the probe tip in endoscopic systems. Each fibre within the imaging bundle addresses a Fizeau interferometer formed between the bundle end and the sample, a configuration which ensures down-lead insensitivity of the probe fibres, preventing variations in sensitivity due to polarization changes in the many thousand constituent fibres. The technique allows acquisition of information across a planar region with single-shot measurement, in the form of a 2D image detected using a digital CCD camera. Depth scanning components are now confined within a processing interferometer external to the completely passive endoscopic probe. The technique has been evaluated in our laboratory for test samples, and images acquired using the bundle-based system are presented. Data are displayed either as en-face scans, parallel to the sample surface, or as slices through the depth of the sample, with a spatial resolution of about 30 µm. The minimum detectable reflectivity at present is estimated to be about 10⁻³, which is satisfactory for many inorganic samples. Methods of improving the signal-to-noise ratio for imaging of lower reflectivity samples are discussed.

A high performance rotational EIT (REIT) system capable of producing better quality EIT images is developed by expanding the independent measurements. In this system, electrodes are attached to a rotational phantom tank which is driven by a microstepping motor. The measurement site of the electrode pairs can be precisely changed. We increase the independent measurements by moving electrodes from the original location to a subsequent location. Increasing the number of independent measurements enhances the resolution of the impedance image and improves the quality arising from the ill-posed condition. The experimental results clearly show the improvement of the REIT image. It is believed that this improvement will provide help in the field of electrical impedance tomography.

We describe how an acousto-optic tunable filter can be used to both demultiplex the signals from multiple fibre Bragg grating sensors and simultaneously provide wide bandwidth signal demodulation in a system using interferometric wavelength shift detection. In an experimental demonstration, the approach provided a noise limited strain resolution of 24.9 nε Hz^−1/2 at 15 Hz.

High-intensity light from a laser pulse can produce laser-induced breakdown in a liquid followed by a shock wave and the growth of a cavitation bubble. When the bubble reaches its maximum radius, the pressure of the surrounding liquid causes it to collapse; this results in bubble oscillations. The cavitation bubble's oscillations and the corresponding shock waves were measured from the deflections of a laser beam. These deflections were detected using a fast quadrant photodiode, built into the optical probe. The precise relative-positioning system and the small diameter of the beam's waist made it possible to detect and analyse the signals from the shock wave and the cavitation bubble. Here, we have demonstrated that a method based on a beam-deflection probe can be used to measure the fast phenomena that follow immediately after laser-induced breakdown as well as the whole dynamics of the bubble oscillations, which corresponds to a three-orders-of-magnitude larger time scale.

Construction of a regression function of order m in an n-space entails optimized choice of a set of points at which probing will take place. The choice is regarded as optimal if it yields a minimized determinant for the correlation matrix of the regression function coefficients or, equivalently, a maximized determinant for the information matrix. In as much as this task involves cumbersome sets of nonlinear equations with multiple unknowns, several recommendations are offered on the disposition pattern of the points. The search solution is illustrated by the examples of a circle, a triangle and a sphere.

An improved ambiguity function method (AFM) for GPS attitude determination is presented. The new algorithm is a combination of an analytical resolution and the AFM. The first part of the algorithm is capable of reducing the search integer space by solving a dual nonlinear coupled equation, while the second resolves the adaptive function within the analytical solutions space. Static and kinematic experiments are performed to demonstrate the feasibility of the new algorithm in terms of accuracy, reliability and computation load. Comparisons to traditional algorithm and other measurement tools are given.

We describe the effect of polyethylene glycol (PEG) addition to the precursor solution on the humidity sensing properties of a TiO₂ thin film. Thin films of TiO₂ were prepared by sol–gel and spin coating techniques. An increase in humidity sensitivity has been observed after the addition of PEG. This increase in sensitivity is due to smaller crystallites and pores created during the combustion of the polymer. The response and recovery time of the sensor were about 10 and 176 s, respectively. An equivalent circuit has been proposed and fitted well with the experimental data. We demonstrate that a controlled amount of polymer addition leads to the sensor being highly sensitive in the lower humidity (<40% RH) region.

Low-concentration formaldehyde (HCHO) together with ethanol/toluene/acetone/α-pinene (as an interference gas of HCHO) is detected with a micro gas sensor array, composed of eight tin oxide (SnO₂) thin film gas sensors with Au, Cu, Pt or Pd metal catalysts. The characteristics of the multi-dimensional signals from the eight sensors are evaluated. A multilayer neural network with an error backpropagation (BP) learning algorithm, plus the principal component analysis (PCA) technique, is implemented to recognize these indoor volatile organic compounds (VOC). The results show that the micro gas sensor array, plus the multilayer neural network, is very effective in recognizing 0.06 ppm HCHO in single gas component and in binary gas mixtures, toluene/ethanol/α-pinene with small relative error.

Miniature temperature fixed-point industrial platinum resistance thermometers (IPRTs) have been constructed to investigate the feasibility of a self-testable IPRT integrated with a mercury or indium fixed-point cell. The miniature cell was constructed from stainless steel with a combined small PRT sensor element inside it, and was contained within an IPRT protection tube. The reproducibilities of the freezing and melting temperatures measured using the mercury miniature cell were ±0.08 °C and ±0.63 °C, respectively. In the case of indium, only the melting temperature was taken into account, and its reproducibility was ±0.01 °C. The performance of both miniature fixed-point IPRTs was good enough to keep track of the long-term stability of the IPRTs in the order of 0.1 °C.

This paper reports on a bimorph impedance transducer (BIT) which can measure multi-directional translational and rotational impedances in multi-directions. Translational and rotational four-pole models are constructed to describe the dynamic behavior of the transducer. Derived from these models, calibration functions are defined and numerically determined under various boundary conditions. Taking advantage of these functions, point translational and rotational impedance of a structure can be easily and accurately determined by measuring the excitation electrical signals applied to the transducer. To verify the effectiveness of the transducer, a two-dimensional plate is utilized as a test structure. The point impedances of the plate in all its three active degrees of freedom (DOFs) are numerically obtained by the BIT. Through comparing the impedances obtained via BIT with the verification results, it is concluded that the newly designed transducer is accurate in measuring both translational and rotational frequency response functions (FRFs).

A microcontroller-based current electrometer built from LOG112 and C8051F006 system-on-a-chip has been developed for measuring current flowing through a MOS (metal–oxide–semiconductor) device. The Fluke 5100B series calibrator and a computer have been used to calibrate the electrometer. In order to examine the performance of the electrometer, Al|SrTiO₃|Si and BS250 MOSFET-based MOS devices have been employed as devices under test and the Keithley 617 Programmable Electrometer has been applied as a reference. It has been found that the currents measured by the Keithley 617 Programmable Electrometer were reproduced very well by the developed electrometer.

The Fukunaga–Koontz transform (FKT) has been proposed for many years. It can be used to solve two-pattern classification problems successfully. However, there are few researchers who have definitely extended FKT to kernel FKT (KFKT). In this paper, we first complete this task. Then a method based on KFKT is developed to detect infrared small targets. KFKT is a supervised learning algorithm. How to construct training sets is very important. For automatically detecting targets, the synthetic target images and real background images are used to train KFKT. Because KFKT can represent the higher order statistical properties of images, we expect better detection performance of KFKT than that of FKT. The well-devised experiments verify that KFKT outperforms FKT in detecting infrared small targets.

A new approach to studying thermo-acoustically driven heat release fluctuations has been developed. By performing a phase correlation of the pulsation signal for each instant in time in post-processing, a number of advantages over the usual online processing technique are obtained: many frequencies can be analysed from the same data set allowing faster recording and introducing fewer errors than performing the phase correlation online. The method does not require complicated trigger and delay line setups and is most flexible. As an example of this technique, two different pulsation modes of a swirl combustor are resolved from only 300 chemiluminescence images. Further use of this method for a wide variety of applications is indicated.

The water vapour permeability of textile fabrics is a critical determinant of wearer comfort. Existing test methods are either time consuming or require large amounts of material. A new test apparatus was developed for characterizing the water vapour permeability of fabrics. An aluminium cylinder covered with waterproof and vapour permeable PTFE laminate is used for generating water vapour source on one side of the sample. A dry nitrogen sweep gas stream is used to carry water vapour away. The calculation of the rate of water vapour transmission across the fabric is based on the measurement of the relative humidity of the outgoing nitrogen stream. This new measuring apparatus offers a short test time and calls for a small sample size. The comparison measurements show that the test results correlated well with those obtained from ISO 11092 and ASTM E96. Therefore, this test method provides a new technique to accurately and precisely characterize the water vapour transport properties of fabrics.

Ball bearings with defects can cause catastrophic machine element failure. The technique of detection using visual features provides a rapid means of inspection, although it reveals only surface defects. Nevertheless, the specular nature of the bearing surface makes it difficult to design illumination that produces high quality images for analysis using this method. In this work, a technique that uses ring light for illumination is demonstrated to be able to clearly reveal surface defects such as spalling and waviness in ball bearings.

We present a compact extended cavity laser (ECL) system based on a high-power laser diode optimized for maximum efficiency of the Rb optical pumping process. The system represents the crucial part of the HpXe (hyperpolarized xenon) production process. We concentrated on the ECL system optimization—linewidth matching and frequency stabilization—for the optical pumping process. We show that the intensity of optical feedback in the ECL laser influences linewidth and output power and it is possible to find an optimum value for the highest power spectral density coinciding with the absorption line of desire. At the optimum emission linewidth was reduced approximately ten times with only half of the total optical power loss.