Table of contents

This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

Large-amplitude internal solitary waves in a stratification comprising a thick, lower, homogeneous layer separated from a thin, upper, homogeneous layer by a broad gradient region are studied using simultaneous measurements of the density and velocity fields. Density field measurements are achieved through synthetic schlieren, operating in an absolute mode to allow efficient and accurate measurements of density in systems with strong curvatures and large perturbations to the density field. The images used for these density measurements are interleaved with images used for particle image velocimetry by phase locking two video cameras (one configured for the density measurements and the other for the velocity measurements) with a computer-driven LCD monitor, allowing the background texture required for synthetic schlieren to be turned off for the particle image velocimetry measurements on the mid-plane of the experimental tank. The simultaneous measurements of both density and velocity fields not only allow greater insight into the internal wave dynamics, but also allow the velocity measurements to be corrected for the normal errors associated with the refractive index variations. As an illustration of the power of this technique, we determine for the first time in an internal solitary wave the spatial structure of the local gradient Richardson number, finding regions where this falls below the limit for linear stability.

A new finite element procedure for the solution of the electromagnetic flow meter weight function is presented. The weight function represents the relative contribution of the fluid velocity at a particular spatial location in the flow cross section to the output signal from the flow meter. The solution of the weight function is important for inferring the velocity profile from measured potential differences within the electromagnetic flow meter. First, a numerical simulation model was constructed with COMSOL Mutiphysics [1]. Next, a study was undertaken to compare the numerical simulation model with Shercliff's [2] analytical solution for the weight function. The finite element methodology was found to be correct for solving the weight function. Based on this result, the numerical simulation model was used to compute the weight function for two flow meter geometries. For both cases the electrodes were located on the internal circumference of the flow pipe and the line joining the electrodes was normal to the imposed magnetic field. In the first case the separation of the electrodes was equal to one pipe diameter but in the second case the electrode separation was less than one pipe diameter. The methodology presented in this paper represents the first stage in the development of an image reconstruction technique which could be used to obtain the liquid velocity profile from boundary voltage measurements obtained in flows with highly skewed velocity distributions.

This study presents a newly developed approach to velocity measurements of moist air in a natural-draught cooling tower (CT). It is based on the cross-correlation of two signals acquired from infrared (IR) light-to-voltage optical sensors. The air flowing through the CT becomes supersaturated in CT packings and thus consists of small water droplets of size 4–12 µm. The same air usually contains droplets resulting from drift, which drags along too small droplets in the spray zone. When the moist-air droplet pattern crosses the beam emitted by IR light-emitting diodes (LEDs), the optical sensors detect a certain signal. The cross-correlation technique gives the time delay of the measured signals. Therefore, by knowing the distance between the sensors, it is possible to calculate the velocity of the moist air. The method has been developed for dynamic velocity measurements of moist air and has achieved a satisfactory precision. The optical velocimeter is a very practical device that makes it possible to carry out measurements on a local basis across the entire plane area of the CT. With the use of simultaneous measurements of velocities and temperatures, the exact location of problems with the packings, nozzles and water distribution system can be thus determined.

An approach to simultaneous measurement of two in-plane displacement components on a specimen by moiré interferometry is performed. In this method, the fringe patterns representing these displacement components are extracted, and the two phases can be analysed from a series of 12 images by adopting simultaneous phase-shifting for both directions. These components can be obtained simultaneously, and the time-varying problem can be analysed using the proposed method. In this paper, an example applied to the thermal deformation of an electronic device is demonstrated and the effectiveness is shown.

Nanoscience promises to transform today's world in the same way that integrated semiconductor devices transformed the world of electronics and computation. In the post-genomic era, the greatest challenge is to make connections between the structures and functions of biomolecules at the nanometre-scale level in order to underpin the understanding of larger scale systems in the fields of human biology and physiology. To achieve this, instruments with new capabilities need to be researched and developed, with particular emphasis on new levels of sensitivity, precision and resolution for biomolecular analysis. This paper describes an instrument able to analyse structures that range from tenths of a nanometre (proteins, DNA) to micron-scale structures (living cells), which can be investigated non-destructively in their normal state and subsequently in chemical- or biochemical-modified conditions. The high-resolution scanning Kelvin nanoprobe (SKN) measures the work-function changes at molecular level, instigated by local charge reconfiguration due to translational motion of mobile charges, dipolar relaxation of bound charges, interfacial polarization and structural and conformational modifications. In addition to detecting surface electrical properties, the instrument offers, in parallel, the surface topographic image, with nanometre resolution. The instrument can also be used to investigate subtle work function/topography variations which occur in, for example, corrosion, contamination, adsorption and desorption of molecules, crystallographic studies, mechanical stress studies, surface photovoltaic studies, material science, biocompatibility studies, microelectronic characterization in semiconductor technology, oxide and thin films, surface processing and treatments, surfaces and interfaces characterization. This paper presents the design and development of the instrument, the basic principles of the method and the challenges involved to achieve nanometric resolution and sub-millivolt sensitivity, for both the topographic imaging of surface micromorphology and surface potential and work-function determination.

We proposed an object size measurement method from noisy scanning electron microscope (SEM) images with shot noise by utilizing the scale space approach. The proposed measurement algorithm consists of six steps: (1) specifying an object to be measured, (2) estimating the noise level, (3) constructing Gaussian and gradient scale spaces, (4) determining a starting scale for edge tracking, (5) edge tracking and (6) object size measurement. For the object size measurement, the model parameters of SEM images are estimated from regions segmented by edge positions at the finest scale. Then the appropriate scale for the object size measurement is automatically selected by estimated model parameters and an optimal scale parameter for smoothing filter in the Canny edge detector. And then, the object size is measured. We applied the algorithm to model SEM images and an SEM image. Though the processing time for our proposed method took about 13 times longer than that of the Canny detector, the range of the probability of extracting true edge positions was extended from 94% in the Canny detector to 80% in our method: the measurable region of the edge tracking was more extensive than that of the Canny detector.

Since its invention, amplitude-modulation tapping-mode atomic force microscopy (AM-AFM) has rapidly developed into a common high-resolution surface characterization tool. However, despite the technical advances, imaging bistability caused by the coexistence of the so-called attractive and repulsive imaging regimes, and potential sample damage in the repulsive regime (often critical in biological and other soft-sample applications) still remain as fundamental barriers which prevent users from consistently obtaining high-quality images. This report proposes a new intermittent-contact AFM imaging concept, frequency- and amplitude-modulation atomic force microscopy (FAM-AFM), which offers the potential to overcome both issues. This imaging method combines existing knowledge from non-contact frequency-modulation atomic force microscopy (FM-AFM) and AM-AFM in a new control scheme involving the use of variable excitation force amplitude and frequency to control the cantilever effective frequency and limit the magnitude of the tip–sample repulsive forces. As in FM-AFM, within the new scheme the cantilever is continuously excited at its (variable) effective frequency so it is not prone to bistability. Control of the repulsive forces is achieved through the adjustment of the excitation force amplitude, so that the effective frequency always remains below the free resonant frequency. Promising results from numerical simulations are presented for single-walled carbon nanotube (SWNT) and silicon tips interacting with a Si(100)-OH surface, and for SWNT tips interacting with the same surface while intermittently forming and breaking covalent bonds, and while experiencing attractive electrostatic interactions.

PZT thin film devices are very competitive when charge signal and force outputs are demanded. A Pb(Zr_0.5Ti_0.5)O₃ thin film with 24 coating layers is deposited by a sol–gel method. An array of three piezoelectric microcantilevers is fabricated using the wet and dry combined bulk micromachining techniques. Each microcantilever has a two-segment top electrode in different dimensions. The actuating and sensing capability of the six segments on the three microcantilevers are measured. It is proved that the proposed piezoelectric microcantilevers have both actuating and sensing functions; different proportion partition results in the diversity of the actuating and sensing capability. At the same location, the longer the piezoelectric segment is, the stronger actuating and sensing capability it has. The maximum actuating sensitivity and sensing sensitivity before poling treatment are 16.7 µN V⁻¹ and 13.44 pC µm⁻¹, respectively, which become about twice as big after poling. We may choose the appropriate microcantilevers to satisfy our purpose on some specific condition where force feedback and object manipulation are needed simultaneously. A hysteresis phenomenon is encountered in the actuating process while not in the sensing process.

The laser profilometry technique can be used to determine the relative chronology or sequence of intersecting lines. With this type of analysis, firstly the questioned document is inspected in any intersecting area that can potentially be sequenced. Subsequently, a cloud of points, representative of the examined area, is obtained. By means of a CAD program, this cloud of points is transformed into a virtual three-dimensional representation of the paper surface. Unfortunately, often the feature characteristics of stroke intersections are comparable with the natural irregularities of the paper surface. In these cases, the virtual representation (with artificial point of view, lights and texture) cannot be impressive. A non-optimal choice of the point of view, lights and texture can lead to wrong interpretations. The problem can be solved by means of a reverse engineering process, realizing a physical replica of the paper surface. The purpose of this work is to show that the technique of reverse engineering can be useful in the line-crossing problems. Besides, it shows that the physical replica has the same informative content as the original data. In other words, the process of reverse engineering does not introduce undesirable features or destroy important characteristics.

The concept of distributed pH measurement was demonstrated at a sensitized region 4 m from the distal end of a 20 m length of plastic optical fibre. The cladding was removed from the fibre over 150 mm and the bare core was exposed to an aqueous solution of methyl red at three values of pH, between 2.89 and 9.70. The optical fibre was interrogated at 648 nm using a Luciol photon counting optical time domain reflectometer, showing the sensing region was attenuated as a function of pH. Least-squares analysis of the traces yielded the linear equation Y = −1.35 pH + 11.4 with a correlation coefficient of −0.96 indicating a high degree of correlation, permitting pH measurement to an estimated ±1.0 pH at the sensing region. Chemical sensing measurements by photon counting OTDR using a standard PCS fibre in aqueous (0.0010 M) and ethanolic (0.000 65 M) solutions of methyl red at 657 nm are also presented. The ingress of methyl red in ethanol was detectable after 2 h and showed reversibility to the pre-doped condition in under 7 min. A case for a silicone resin clad PMMA core hybrid optical fibre as a chemical or pH sensor is presented.

A new method for the calibration of multi-axis, linear and redundant force sensors is presented. This new procedure, named device hyperplane characterization method, is inspired by the shape from motion method for it reduces the burden represented by the need for a huge number of force measurements, typical using least-squares methods, in order to reject errors during the calibration procedure. The proposed technique is an application of the rank theorem and achieves good noise rejection without much time consumption focusing on sensor output measurements, and reducing the effect of disturbances operating the projection of raw output data on the hyperplane to which measurements are ideally compelled to belong in the case of redundant sensors.

Polarization measurements are a powerful tool for better documentation of a variety of liquid and solid particles found in the Earth's atmosphere. Because the solid particles have a non-symmetrical shape, which thereby prevents modelling calculations, it is necessary to build a database of the scattering properties of irregular solid particles in order to interpret the results of remote sensing measurements from aircraft, balloon and satellite. A new laboratory polarization nephelometer was built for this purpose. The particles are levitated by continuous airflow, and are illuminated by a laser at a wavelength of 802 nm. Two avalanche photodiode sensors are used for recording the components of the scattered light perpendicular and parallel to the scattering plane. Detector amplifiers allow light-power detection from a few microwatts down to a few picowatts. Measurements with liquid droplets, made for scattering angles in the 20°–160° range, are in agreement with theoretical calculations, showing that the instrument works well. The first results obtained for irregular solid particles are also presented.

An ultra-violet (UV) rare-gas halide XeCl excimer-Raman laser-based ozone lidar system has been developed and installed at the Indian Institute of Tropical Meteorology (IITM), Pune (18°43'N, 73°51'E, 559 m above mean sea level), India. This system essentially operates in the differential-absorption-lidar (DIAL) mode with laser emission at 308 nm ('on') wavelength as well as reference ('off') wavelength of 353 nm generated by stimulated Raman shifting (SRS) the 308 nm radiation in hydrogen. The receiving system consists of a large diameter telescope tailored with a signal detection and data acquisition/processing system with 5 ns–10.5 ms multi-channel scaler/averager. This paper deals with a brief description of the lidar system developed and discusses the methodology followed for the retrieval of ozone vertical distributions from the lidar back-scattered signals obtained at 'on' and 'off' wavelengths. These initial results are compared with those obtained from a collocated ozonesonde and multi-filter solar radiometer and also with coincident observations from TOMS satellite. They are found to be in fair agreement within the experimental limitations.

A measurement technique to aid decision making and control of a dual-frequency (2 MHz and 2.5 GHz) plasma etch process that is used to manufacture semiconductor devices is described. The technique is based upon the magnitude of the voltage reflection ratios (gamma) of both power sources and the respective gamma values plotted in principal component space on a loading plot. It is shown that the cluster structure and centre coordinate alter as the process proceeds in both time and etch layer. The change in principal component space is used for fault detection and operator decision. Further reduction of the information to a binary code allows the information to be fed into an excursion limit software that controls the plasma tool's operational status.

The regulated level of diesel particulate mass for 2008 light-duty diesel on-road engines will be 0.005 g km⁻¹ in Europe. Measurements by weighing and analysis of this low level of particulate mass based on chemical extraction are costly, time consuming and hazardous because of the use of organic solvents, potentially carcinogenic. An alternative to this analysis is proposed here: a thermal mass analyser that measures the volatile fraction (VOF) as well as the soot fraction of the particulate matter (PM) collected on a cleaned fibre glass filter. This paper evaluates this new thermal mass measurement (TGA) as a possible alternative to the conventional chemical extraction method, and presents the results obtained with both methods when testing a diesel engine fuelled with a reference diesel fuel (REF), a pure biodiesel fuel (B100) and two blends with 30% and 70% v/v biodiesel (B30 and B70, respectively).

The magnetic levitation densimeter is one of the most accurate methods to measure fluid density in a wide range of temperature and pressure. For the existing commercially available densimeter, a relative measurement uncertainty of density is about 0.03%. One of the largest parts of the uncertainty is caused by magnetism of materials around the magnetic coupling in the densimeter, such as a sample fluid under test and a pressure cell. These magnetic effects cause a force transmission error in the magnetic coupling, which is composed of a permanent magnet in the sample fluid and an electromagnet suspended from an electronic balance placed under ambient temperature and pressure. For the existing densimeter, the force transmission error induces an uncertainty of around 0.01% in density. In the present study, the force transmission error is quantitatively investigated by the finite element method (FEM). Reliability of the FEM analysis was confirmed through a comparison with the experimental data measured by using the densimeter established at the National Metrology Institute of Japan (NMIJ). It is found from the FEM results that the density measurement error caused by the force transmission error can be reduced by controlling the permanent magnet at the same vertical position in every measurement state. In addition, the force transmission error linearly changes with the magnetic force acting on the electromagnet when the vertical position of the permanent magnet is constant. On the basis of these FEM results, the authors propose a correction method for the force transmission error by using a dual-sinker type of densimeter.

A new optical diffractometer has been developed and set up at the Physikalisch-Technische Bundesanstalt (PTB). It offers the possibility of high-accuracy calibrations of the lateral period of gratings (pitch) in the micro- and nanometre scale. The measurement principle is based on a modified Littrow configuration, where the incident and the diffracted laser beams are almost collinear. The grating is mounted on a rotary table, and a high-precision rotary encoder is used to measure its angular positions. The profiles of the diffracted laser beams are recorded by means of a line array image detector. To determine the centre positions of the imaged laser beam profiles, different analysis methods can be applied, among others a new correlation method. A variety of laser wavelengths, ranging from 266 nm to 633 nm, can be used. Due to the optional UV wavelength, the smallest measurable pitch is about 150 nm. Depending on the quality of the sample, the measurement uncertainty can be smaller than 10 pm. For two-dimensional gratings the pitch of the two main and the diagonal directions can be measured and thus, also the angle between the two main grating orientations can be determined.

Permittivity monitoring for quality control in fluid-related industrial applications requires difficult procedures and the process control frequently limits the use of traditional sensing technologies. In this paper is reported a combined approach, based on time-domain reflectometry (TDR) and frequency-domain analysis, in order to appropriately improve the measurement of the frequency-dependent dielectric characteristics over a wide range of fluid materials, even when lossy liquids are involved. For this purpose, we have developed a robust algorithm for the time-to-frequency-domain dielectric characterization that suitably compensates the error contribution caused by several effects such as signal dissipation, multiple reflections, impedance mismatching, time-domain truncation and data fitting procedure. In order to assess the combined approach in the time and frequency domain, experimental measurements have been made with both a TDR and vector network analyser (VNA), using the same probe system. Results obtained through the use of such an algorithm on TDR data have been compared with those directly measured in the frequency domain by the VNA, and good agreement has been observed. Substantial improvements are attained in accuracy, high sensitivity and flexibility of the detection method and, most importantly, in the possibility of using low-cost instrumentation directly operating in the time domain.

The paper presents implementation and validation of a method for accurate imaging of three-dimensional surface topographies, developed for AFM metrology but in principle applicable to the whole family of scanning probe microscopes. The method provides correction of the vertical drift, and can be applied to any AFM scanner system, without need for modification of the instrument hardware. Surface correction is performed based on two topographies taken with mutually orthogonal scanning directions. Reconstruction is rapidly achieved through the use of an automatic routine developed for the purpose. The proposed method has been tested by using an optical and a silicon flat and a high precision cylindrical artefact. Examples of successful reconstructions on different samples are also reported within the paper.

This paper presents a new implementation of an optical technique which aims to measure the temporal and spatial evolution of the liquid temperature of a high injection pressure Diesel spray. Measurements are performed using the two-colour laser-induced fluorescence technique in which a temperature-sensitive fluorescent tracer is added to the fuel (ISO 4113 normafluid in the present case) and all the parameters except the temperature (e.g. tracer concentration, incident laser excitation, droplet number density) are eliminated by processing the ratio of the fluorescence intensity measured on two spectral bands. Diesel sprays, issuing from a single-hole injector, are injected at high pressures ranging from 500 to 1500 bar at a frequency of 10 Hz. The signal acquisition is then triggered on the injection cycle to enable the phase-locked monitoring of the liquid phase temperature. Temperature maps of the spray are presented and the influence of the injection pressure on the droplet temperature can be finally inferred from these results.

An experimental procedure based on neural network processing of time-sequence-selected absorbance spectra is described, having the aim of reducing the whole uncertainty of chromium(VI) concentration in water measurements, preventing bias error due to a non-negligible presence of interfering substance, in particular Sn(II). Aspects concerning the instrumentation system, operating steps and data processing procedure are analysed in order to evaluate uncertainty causes and their effects on the whole uncertainty of the methodology, which try to enhance flow injection analysis capabilities, taking into account requirements of method reproducibility and standardization. Chromium solutions in water in the range 0–500 µg l⁻¹, with Sn(II) concentration ranging from 0 to 20 mg l⁻¹, have been analysed by this modified flow injection method. A satisfactory error reduction and a warning when the presence of Sn(II) is detected have been achieved. The effect of pH on the method results is also studied.

A NMR spin–spin (T₂) relaxation technique has been described for determining water distribution changes in human cortical bone tissue. The advantages of using NMR T₂ relaxation techniques for bone water distribution are illustrated. The CPMG T₂ relaxation data can be inverted to T₂ relaxation distribution and this distribution then can be transformed to a pore size distribution with the longer relaxation times corresponding to larger pores. The FID T₂ relaxation data can be inverted to T₂ relaxation distribution and this distribution then can be transformed to bound- and mobile-water distribution with the longest relaxation time corresponding to mobile water and the middle relaxation time corresponding to bound water. The technique is applied to quantify apparent changes in porosity, bound and mobile water in cortical bone. Overall bone porosity is determined using the calibrated NMR fluid volume from the proton relaxation data divided by overall bone volume. The NMR bound and mobile water changes were determined from cortical bone specimens obtained from male and female donors of different ages. Differences in water distribution were found between specimens from male and female donors. Furthermore, the distribution of water within a single specimen was found to be non-homogeneous. Our results show that the ratio of the average bound to mobile water in bone from male donors is higher than in bone from female donors when the bone porosities are similar between male and female groups. We also show that the average bone porosity multiplied by the ratio of bound to mobile water is constant for both male and female bone groups. This parameter may be used as a measure of bone quality describing both porosity and water content, both of which may be important determinants of bone strength and fracture resistance.

A high-resolving, simple and compact electrostatic energy analyser based on a cylindrical bounded field, intended for measurements of parallel flows of charged particles is described. The operation regimes with a second-order focusing mode for several configurations were found, and energy response and energy resolution ability were calculated. It is shown that focusing sharpness and energy resolution increase with the relation of the radius of an outer cylinder to that of an inner one. A combination of high energy resolution ability with high transmission and simple design makes this instrument very promising for a wide range of scientific and technological applications, in particular, for plasma investigations in the laboratory and in space.

The paper presents the application of ultrasonic guided waves for fatigue crack detection in metallic structures. The study involves a simple fatigue test performed to introduce a crack into an aluminium plate. Lamb waves generated by a low-profile, surface-bonded piezoceramic transducer are sensed using a tri-axis, multi-position scanning laser vibrometer. The results demonstrate the potential of laser vibrometry for simple, rapid and robust detection of fatigue cracks in metallic structures. The method could be used in quality inspection and in-service maintenance of metallic structures in aerospace, civil and mechanical engineering industries.

A single bubble was generated and levitated in a high-intensity sound field within a spherical flask excited in its fundamental mode. Under optimum experimental conditions the bubble was observed to emit light in the form of short flashes. This phenomenon is known as single bubble sonoluminescence (SBSL). Using this process, the emitted light from the bubble was monitored when solutions containing fluorescein, quinine and sodium, potassium and copper salts were placed in the cell. The results obtained indicated that reproducible signals related directly to the concentration of the species present in solution could be achieved using single bubble sonoluminescence. The results for the molecular species were compared with those obtained by fluorescence spectroscopy and, in the case of quinine, parallel determinations of concentration in a test solution were performed with consistent results. SBSL signals were also observed to exhibit a linear correlation with the concentration of several trace metal salts introduced to the solution in the measurement cell. However, it was not possible to demonstrate that the SBSL signals were derived from stimulated atomic emission or fluorescence, and it was concluded that the effect may result from an indirect effect involving the bubble excitation mechanism.

The problem of extracting quantified information from physiological and physical indicators of the fatigue level of a vehicle driver is addressed. A chromatic approach has been used for processing the physiological and physical outputs from a driver fatigue monitoring system, the physical indicator being in the form of gyroscopic signals produced by the lateral movements of a vehicle. Some preliminary results are presented which show how the chromatic signatures of the physiological and physical indicators can be used to identify fatigue thresholds and provide a more optimized estimate of tiredness.

We present a variational approach to motion estimation of instationary experimental fluid flows from image sequences. Our approach extends prior work along two directions: (i) the full incompressible Navier–Stokes equation is employed in order to obtain a physically consistent regularization which does not suppress turbulent variations of flow estimates; (ii) regularization along the time axis is employed as well, but formulated in a receding horizon manner in contrast to previous approaches to spatio-temporal regularization. This allows for a recursive on-line (non-batch) implementation of our variational estimation framework. Ground-truth evaluations for simulated turbulent flows demonstrate that due to imposing both physical consistency and temporal coherency, the accuracy of flow estimation compares favourably even with advanced cross-correlation approaches and optical flow approaches based on higher order div–curl regularization.

In the present study, the influence of gas compositional and pressure conditions on thermographic phosphor thermometry was investigated. A heatable pressurized and optical accessible calibration chamber was built to measure the phosphorescence decay time at different temperatures as well as at different partial and absolute pressures. At room temperature, the absolute pressure could be increased to 30 bar. To vary the gas composition, nitrogen, oxygen, carbon dioxide, methane, helium as well as water vapour were used. Three different phosphors were investigated: Mg₄FGeO₆:Mn, La₂O₂S:Eu and Y₂O₃:Eu. Phosphorescence was excited by the third and the fourth harmonics of a pulsed Nd:YAG-laser (355 nm and 266 nm, respectively) and recorded temporally resolved by a photomultiplier. Mg₄FGeO₆:Mn as well as La₂O₂S:Eu were not influenced significantly by varying partial and absolute pressures. In contrast, Y₂O₃:Eu showed a strong sensitivity on the oxygen concentration of the surrounding gas phase as well as irreversible changes in the phosphorescence decay time after increasing the absolute pressure.

The selective catalytic reduction of nitrogen oxides with ammonia (ammonia SCR) and urea (urea SCR), respectively, is a widespread process to clean flue and diesel exhaust gases due to its simplicity and efficiency. The main challenge of the process is to minimize the ammonia emissions downstream of the SCR catalyst. We found that ammonia emissions of >10 ppm can reliably be detected with a simple pH electrode in the presence of CO₂, SO_x, NO_x, and moderately weak organic acids. 10–20 ppm of ammonia in the exhaust gas are sufficient to neutralize the acids and to increase the pH value from 3 to 6. On this basis a continuous measuring method for ammonia was developed, which was used to control the dosage of urea in the SCR process. While keeping the ammonia emissions after the SCR catalyst at 5–30 ppm an average NO_x removal efficiency (DeNO_x) of >95% were achieved at a diesel test rig. The method can also be applied for exhaust gases with higher acid contents, if a basic pre-filter is added adsorbing the acidic exhaust components. Compared to water as absorption solution, more precise ammonia measurements are possible, if a 0.1 M NH₄Cl absorption solution is applied, whose pH value is changing as a Nernst function of the ammonia concentration.

Theoretical analysis of the frequency response of a fine-wire thermocouple probe has been further developed to investigate influences of the difference in physical properties between the two wires composing a butt-welded fine-wire thermocouple. The solution obtained demonstrates complex behaviour of the frequency response of the copper–constantan (type-T) thermocouple whose physical properties differ greatly between the two constitutive wires. It was also shown that, in an air flow, the frequency response is almost uniform in the cross-section of the thermocouple wire, but, in a water flow, it becomes remarkably nonuniform. The present theoretical analysis provides useful information for improving the reliability of fluctuating temperature measurement in high-temperature turbulent flows.

In a previous publication, the authors presented a transient mass flow rate metering technique for pulsating pipe flows and its outstanding performance was demonstrated experimentally for fuel injection nozzles. In the present paper, the application of the mass flow rate metering technique is described for pulsating air flows. The basics of the measuring technique are summarized and the corresponding experimental setup is explained. For verification experiments, a mass flow rate control unit was developed that permits time-varying mass flow rates to be provided proportional to the voltage of an electronic input signal to the unit. The basic ideas of this unit and its performance are summarized. Its application to verify the performance of the developed mass flow rate measuring instrument represents the major part of the paper. Performance tests were carried out for various time variations of mass flow rate pulsations. It is shown that the mass flow rate of the mean flow and that of the pulsating flow can be separated and both can be accurately measured. Comparative measurements show that the mass flow rate measuring technique works very well and reproduces the mass flow rate variations in time imposed by the mass flow rate control unit.

An intercomparison of nanometric lateral scales, which are special one-dimensional (1D) grating standards with sub-hundred-nanometre pitches, among a deep-ultraviolet (DUV) laser diffractometer, a critical dimension scanning electron microscope (CD-SEM) and different types of atomic force microscope (AFM) was performed. The reference value and its expanded uncertainty were provided by the National Metrology Institute of Japan (NMIJ) using an atomic force microscope with differential laser interferometers (DLI-AFM). The consistency of the measurement results obtained using the DUV laser diffractometer, CD-SEM and some AFMs was satisfactory; however, that in the measurement results obtained using other AFMs was unsatisfactory. An improvement in AFM calibration technology using nanometrological standards is required for both AFM manufacturers and AFM users, including metrology institutes.

Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution inside an inhomogeneous distribution by injecting currents at the boundary of a subject and measuring the resulting changes in voltage. A hybrid method is proposed for solving the inverse problem for EIT, which combines the Krylov subspace and the Tikhonov regularization for double levels of regularization to the ill-posed problem. Numerical simulation results using the hybrid method are presented and compared to those from truncated singular value decomposition (TSVD) regularization and the Tikhonov regularization. Experimental results with the hybrid method are also presented, indicating that the hybrid method can reduce the computation time, and improve the resolution of reconstructed images with the regularization parameter automatically chosen by the L-curve method.

Welding has been widely used as a process to join metallic parts. But because of hazardous working conditions, workers tend to avoid this task. Techniques to achieve the automation are the recognition of joint line and process control. A CCD (charge coupled device) camera with a laser stripe was applied to enhance the automatic weld seam tracking in GMAW (gas metal arc welding). The adaptive Hough transformation having an on-line processing ability was used to extract laser stripes and to obtain specific weld points. The three-dimensional information obtained from the vision system made it possible to generate the weld torch path and to obtain information such as the width and depth of the weld line. In this study, a neural network based on the generalized delta rule algorithm was adapted to control the process of GMAW, such as welding speed, arc voltage and wire feeding speed. The width and depth of the weld joint have been selected as neurons in the input layer of the neural-network algorithm. The input variables, the width and depth of the weld joint, are determined by image information. The voltage, weld speed and wire feed rate are represented as the neurons in the output layer. The results of the neural-network learning applied to the welding are as follows: learning ratio 0.5, momentum ratio 0.7, the number of hidden layers 2 and the number of hidden units 8. They have significant influence on the weld quality.

The relative dynamic elasticity modulus is an important evaluation criterion in frost resistance testing of concrete. Generally, in order to validate the decay rules of concrete durability, the measurement of relative dynamic elasticity modulus needs a large number of testing data over time. Therefore, it is often difficult to carry out this test and sometimes it is even not feasible due to cost consideration. In addition, the dynamic relationship between the relative dynamic elasticity modulus and freeze–thaw cycle is very intensive, but so far there is no definite explicit or implicit function to describe it. However, the relative dynamic elasticity modulus of a concrete material can be measured indirectly with the grey prediction model based on a grey system theory that only requires a limited number of discrete data to estimate the behaviour of a dynamic system with uncertain and incomplete information. In this paper, we developed an indirect measurement model of concrete relative dynamic elasticity modulus with the number of freeze–thaw cycles as a leading indicator on the basis of an improved grey prediction model. The improved grey prediction model is established with the Taylor approximation method. We validated the effectiveness of the proposed model by using the relative dynamic elasticity modulus of the concrete material and corresponding experimental data concerning the number of freeze–thaw cycles.

There is no effective method to calibrate the dynamic characteristics of gaseous flow meters. This is because the density of these fluids changes largely with respect to the variation in both pressure and temperature. The present paper describes the development of an unsteady mass flow generator for gases. The generator consists of an isothermal chamber and two spool-type servo valves. The heat transfer area within the isothermal chamber is made sufficiently large by stuffing the copper wool materials to ensure that the essential isothermal conditions are preserved. The calibration of the dynamic characteristics of the gaseous flow meters and the internal flows within such meters are achieved using the generator. Experimental tests reveal that the generator can control oscillatory flows at a frequency of up to 50 Hz with an uncertainty of 5.5%. In addition, the unsteady mass flow generator can generate flows for more than 30 min. Thus, the effectiveness of the generator is demonstrated.

We have developed an innovative ultrasonic transducer system (CHOT) which is optically excited by means of lasers. It can be used both for generation and detection of narrowband ultrasound and provides non-contact (or even remote), couplant-free generation and/or detection. It has also the advantage of being inexpensive to manufacture and the simplicity of its concept makes it ideal for industrial applications. In this study we present results where CHOTs have been used both for excitation and detection of surface acoustic waves. An initial theoretical model is also presented which describes the principle of operation.

The resonance ultrasonic vibrations (RUV) technique is adapted for non-destructive crack detection in full-size silicon wafers for solar cells. The RUV methodology relies on deviation of the frequency response curve of a wafer, ultrasonically stimulated via vacuum coupled piezoelectric transducer, with a periphery crack versus regular non-cracked wafers as detected by a periphery mounted acoustic probe. Crack detection is illustrated on a set of cast wafers. We performed vibration mode identification on square-shaped production-grade Si wafers and confirmed by finite element analyses. The modelling was accomplished for the different modes of the resonance vibrations of a wafer with a periphery crack to assess the sensitivity of the RUV method relative to crack length and crack location.

A Rayleigh light scattering technique to determine ciprofloxacin lactate (CPFL) in drugs by tetraphenylboron sodium (TPB) was developed. Ciprofloxacin lactate was found to bind B(C₆H₅)₄⁻ anion and transformed to CPFL–TPB aggregate which displayed intense Rayleigh scattering light. Effects of factors such as wavelength, acidity, stabilizers and interferents on the RLS of CPFL–TPB were investigated in detail. The RLS intensity of the CPFL–TPB suspension was obtained in acetate buffer (0.50 mol L⁻¹, pH = 4.0). The Rayleigh scattering light intensity at the maximum RLS peak of 408 nm was linear to the concentration of ciprofloxacin lactate in the range of 8.0–20.0 µg mL⁻¹ with a detection limit of 6.0 µg mL⁻¹. Good results were also obtained with the recovery range of 93.68–104.06%. The method was applied to determine ciprofloxacin lactate in injections, eye drops and tablets, showing high sensitivity and accuracy compared with the high performance liquid chromatography method (HPLC) according to Chinese Pharmacopoeia.

Advanced high strength steels are being increasingly used in the automotive industry to reduce weight and improve fuel economy. However, due to increased physical properties and chemistry of high strength steels, it is difficult to directly substitute these materials into production processes currently designed for mild steels. New process parameters and process-related issues must be developed and understood for high strength steels. Among all issues, endurance of the electrode cap is the most important. In this paper, electrode wear characteristics of hot-dipped galvanized dual-phase (DP600) steels and the effect on weld quality are firstly analysed. An electrode displacement curve which can monitor electrode wear was measured by a developing experimental system using a servo gun. A neuro-fuzzy inference system based on the electrode displacement curve is developed for minimizing the effect of a worn electrode on weld quality by adaptively adjusting input variables based on the measured electrode displacement curve when electrode wear occurs. A modified current curve is implemented to reduce the effects of electrode wear on weld quality using a developed neuro-fuzzy system.

The paper presents the application of temperature acquisition systems integrating thermocouples, a thermographic camera and fibre Bragg grating (FBG) sensors in gas metal arc welding (GMAW) process, MIG (metal inert gas) welding type. Efficient procedures to use FBG sensors and thermocouples were developed. The paper presents and compares measurements made in welded plates of aluminium alloy 6082-T6. Tests were performed in both plate surfaces and good agreement between the three techniques was found.

In this paper we present the design of an optical microphone incorporating a distributed feedback fibre-laser sensor. The acoustic frequency response of the device is characterized at low frequencies (up to 250 Hz) and found to deliver a wavelength responsivity of −62 dB re 1 nm Pa⁻¹. Experimental results are compared to a theoretical description of the device that is based upon a mass–spring model.

The effect of heating rate on the thermally stimulated luminescence (TSL) emission due to the temperature lag (TLA) between the TSL material and the heating element has been investigated using Li₂B₄O₇:Cu,Ag,P dosimetric materials. The TLA becomes significant when the material is heated at high heating rates. TSL glow curves of Li₂B₄O₇:Cu,Ag,P material showed two main peaks after β-irradiation. The kinetic parameters, namely activation energy (E) and frequency factor (s) associated with the high temperature main peak of Li₂B₄O₇:Cu,Ag,P were determined using the method of various heating rates (VHR), in which heating rates from 1 to 40 K s⁻¹ were used. It is assumed that non-ideal heat transfer between the heater and the material may cause significant inconsistency of kinetic parameter values obtained with different methods. The effect of TLA on kinetic parameters of the dosimeter was examined.

This paper describes a new measuring system to perform local area magnetization measurements on the surface of a magnetic sample in a pulsed field magnetometer at room temperature. A commercial point pick-up coil is used to detect the induction signal along the radius of samples with cylindrical or disc shapes. The relationship between the induced voltage and the sample geometry is treated and a calibration procedure is proposed to obtain the magnetization values in physical units for the case when the point pick-up coil is at the centre of the sample. The local demagnetizing factor is obtained using the measurement of the local anisotropy field applying the single-point detection (SPD) technique. The measurement of this SPD singularity detected in the transverse reversible susceptibility, using a sample with cubic geometry, is demonstrated for the first time in this type of magnetometer. The application of the system for the investigation of commercial permanent magnets is illustrated, and the advantages and disadvantages are discussed.

A highly sensitive absorption-type nuclear magnetic resonance (NMR) magnetometer capable of measuring low magnetic fields below 1 mT with a NMR sample volume of 3 cm³ is described. It will be used for calibration purposes in an accredited calibration laboratory. The magnetometer uses a direct digital synthesizer for generation of the radio frequency signal, a sampling detector for demodulation of the radio frequency signal and a digital signal processor with an analogue-to-digital converter and a digital-to-analogue converter for signal processing using a lock-in technique with a digital phase sensitive detector. Frequency traceability of the NMR magnetometer reference oscillator is established by means of the long-wave transmitter DCF77.

An experimentally proved method for the automatic correction of drift-distorted surface topography obtained with a scanning probe microscope (SPM) is suggested. Drift-produced distortions are described by linear transformations valid for the case of rather slow changing of the microscope drift velocity. One or two pairs of counter-scanned images (CSIs) of surface topography are used as initial data. To correct distortions, it is required to recognize the same surface feature within each CSI and to determine the feature lateral coordinates. Solving a system of linear equations, the linear transformation coefficients suitable for CSI correction in the lateral and the vertical planes are found. After matching the corrected CSIs, topography averaging is carried out in the overlap area. Recommendations are given that help both estimate the drift correction error and obtain the corrected images where the error does not exceed some preliminarily specified value. Two nonlinear correction approaches based on the linear one are suggested that provide a greater precision of drift elimination. Depending on the scale and the measurement conditions as well as the correction approach applied, the maximal error may be decreased from 8–25% to 0.6–3%, typical mean error within the area of corrected image is 0.07–1.5%. The method developed permits us to recover drift-distorted topography segments/apertures obtained by using feature-oriented scanning. The suggested method may be applied to any instrument of the SPM family.

This paper reports on a technique for fabricating intrinsic fibre Fabry–Perot cavities in fused silica optical fibres. An F₂-excimer laser was used to micromachine parallel walled cavities through the diameter of optical fibres. A custom-designed beam delivery and target alignment system was used to enable the production of high aspect-ratio cavities in fibres. The optical response of the micro-cavities ablated in SMF 28 and SM 800 fibres at suitable energy densities showed Fabry–Perot fringes produced as a result of interference of Fresnel reflections at the cavity wall surfaces. The intrinsic fibre Fabry–Perot cavities were characterized using optical and scanning electron microscopy. Preliminary tests have shown that these intrinsic cavities can be used as strain sensors.

A versatile and portable system based on microsensors for measuring simultaneously pH, oxidation–reduction potential (ORP), conductivity and temperature in samples of environmental interest has been assembled and evaluated. An ion selective field effect transistor (ISFET) for pH measurements and platinum microelectrodes for ORP and conductivity measurements are used within the system. The multi-parametric system includes a commercial temperature sensor and the circuitry for each one of the mentioned sensors which can be exchanged or replaced. A commercial module with a USB interface is used for the acquisition and control of data from a laptop PC. Validation of the whole system has been carried out with standard solutions, providing high device-to-device reproducibility and stable response of all sensors during at least 24 h measured in a standard solution. Analysis of waste water samples with the portable system has been carried out to test its feasibility in environmental applications. Data have been compared with commercial electrodes.

A method is described for measuring small angular movements, some as small as a few tens of a picoradian, and results are presented from two applications. The method uses a linear conducting probe nominally orthogonal to the electric field in a microwave cavity. By pumping the cavity with microwave power large electric fields are generated and the linear probe detects these in a homodyne system with very high sensitivity to the angle between the field and the probe. The first application is a dc investigation of field rotation caused in a lossy waveguide by a ferrite sample and achieves a sensitivity of a few microradians. The second example is the angular rotation of electric fields in a gravitational wave detector which has a target sensitivity of picoradians and operates at 100 MHz.

The method of Ti/TiO₂ photoelectrode preparation using laser-assisted sol–gel is introduced. The prepared TiO₂ film is investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and amperometry, and it illustrates that the TiO₂ film mainly consists of anatase TiO₂ nanoparticles on its surface and exhibits a superior photocatalytic activity when compared with that calcined by oven. The proposed electrode is employed as a sensor for flow injection analysis (FIA) to determine chemical oxygen demand (COD). The measuring principle is based on the photocurrent responses on the electrode, which are proportional to the COD values. The linear range is 50–1000 mg l⁻¹, and the detection limit is 15 mg l⁻¹ (S/N = 3). This method is characterized by short analysis time, simplicity, low environmental impact and long lifetime of the sensor. Additionally, the COD values obtained from the proposed and the conventional method agree well as demonstrated by the significant correlation between the two sets of COD values (R = 0.9961, N = 20).

An image acquisition and storage system without data compression was constructed by combining a personal computer, an external hard disk drive and a charge-coupled device camera (1024 × 768 pixels, monochrome 8 bit/pixel) operating at 30 frame s⁻¹. Test runs indicated the system performance: the storage time, size and speed of 37 min, 55 GB and 25 MB s⁻¹ respectively. The design of the system program was shown and discussed on the basis of the test run results. The constructed system can be applied to various scientific and engineering applications including digital microscopy. The technical information shown in this study is helpful to researchers and engineers in constructing their own system by themselves.