Table of contents

By means of a multi-channel detection system, broadband microwave radiation, up to at least 12 GHz, has been measured from a simple solid-dielectric switch closing a circuit charged to 10 kV. The spectrum of the radiated electric field has been measured up to 7 GHz by means of a high-bandwidth antenna coupled to a fast digitizing oscilloscope. The detected radiation could prove to be an interesting topic of study for solid-state physicists, as many questions remain unanswered.

We present a miniaturized, low-cost optical method for detection of in-plane speckle translation. The speckles are produced by illumination of a non-specular target surface with coherent light from a vertical cavity surface emitting laser. The scattered light propagates through free space to the sensor inlet. At the inlet speckle translation appears due to both translation and rotation of the target. The sensor is based on a micro-lenticular array and a spherical lens, which implement a narrow spatial band-pass filter. The spatial filter acts on the intensity distribution of the translating speckle pattern. The presented free-space propagation design provides a sensor that in principle operates within a large range of working distances, and with a low susceptibility to variations in working distance. The relation between the precision of the sensor and the decorrelation length for speckle translation at the sensor inlet is studied. Configured as a free-space propagation sensor, and in this case operating with a low power laser source, the pitch of the lens array is required to be in the order of a few tens of micrometres. Therefore, limitations due to diffraction and aberrations due to the high numerical aperture of the lenslets have been studied.

A proper adjustment of the translation portion of pixel shifts for the multi-pass, nine-point (9P), central difference image correction (CDIC) method is found to be effective for further reducing the evaluation errors of digital particle image velocimetry recordings. In the improved central difference image correction scheme, the translation portion of pixel shifts is adjusted between the mean value of particle image displacements (initially introduced for the 9P method) and the particle image displacement at the centre (initially suggested for the four-point method) of the interrogation window, so that the evaluation errors of the iterated evaluation may converge to a lower level than both the initially introduced nine- and four-point methods. Based on a 50% overlap of interrogation windows, five possible algorithms to determine the pixel translation shift of the central difference image correction are discussed. Tests with synthetic particle image velocimetry recording pairs of simulated periodic flows demonstrate that the evaluation error of the 9P-central difference image correction method can be reduced to less than half of its initially introduced level, and it is obviously lower than that of the four-point method suggested by Wereley and Gui (2001 4th Int. Symp. on Particle Image Velocimetry (Göttingen, Germany, 17–19 Sept.); 2003 Exp. Fluids34 42–51). Simulations and real image tests indicate that the error distribution and the peak-locking effect of the central difference image correction method have a two-pixel period.

This paper reports a new technique of micro-resolution particle image velocimetry (PIV). To investigate transient phenomena in a microfluidic device, a high-speed micro-PIV technique was developed by combining a high-speed camera and a continuous wave (CW) laser. The technique was applied to a micro counter-current flow, consisting of water and butyl acetate. The velocity fields of water in the micro counter-current flow were visualized for a time resolution of 500 µs and a spatial resolution of 2.2 × 2.2 µm². Using the micro-PIV technique, the vortex-like motions of fluorescent particles around the water–butyl acetate interface were captured clearly.

An optical method for measuring the frictional force acting between general materials is proposed. In the method, the frictional force is measured as the inertial force acting on a mass. A pneumatic linear bearing is used to realize a linear motion with sufficiently small friction acting on the mass, i.e., the moving part of the linear bearing. The inertial force acting on the mass is calculated from the velocity of the mass, and the velocity is determined highly accurately by means of measuring the Doppler shift frequency of the laser light beam reflecting on the mass using an optical interferometer. The performance of the proposed method is demonstrated by means of measuring the frictional force acting between a model car and a metal plate.

This paper reports on mass sensing with 33 nm thick single-crystalline cantilevers by a double-beam laser Doppler vibrometer. The resonant frequency of an oscillating thin cantilever beam is very sensitive to a loaded mass. However, the drift of the resonance, due to gas adsorption and mechanical instability, limits the minimum detectable mass in general. Two cantilevers for sensing and its reference will compensate their influences. Two cantilevers were made to self-oscillate by electrostatic actuation at different resonant frequencies. A 10 pg sample (a particle of organosilicon monomer) was mounted at the end of one cantilever, and thermogravimetry of the sample using the two cantilevers was demonstrated. The cantilevers were heated up by a heater in vacuum, and the change in mass was detected from the change in resonant frequency. The exact temperature change can be estimated from the change in resonant frequency of one cantilever as a reference. The derivative of the frequency change, corresponding to desorbed mass, clearly shows a peak of mass desorption at about 270 °C.

We show that the noise and spurious signals over the entire input frequency response of a binary digital divider contribute with equal weight to the output signal. Similar results are also obtained using non-binary digital dividers. We present a simple model that allows one to understand the mechanisms that produce these aliasing effects. Only filters at the input or intermediate stages of division can reduce these effects in digital dividers. We also show that direct-digital-synthesis, where the output of a counter is used to drive a shift register and a digital-to-analogue converter to produce a sinewave output, is largely free from these effects.

Porphyrins play key roles in natural energy conversion systems, including photosynthesis and oxygen transport. Because of their chemical stability, unique optical properties and synthetic versatility, porphyrins are well suited as chemical sensors. One successful application is the use of platinum porphyrin (PtP) in pressure-sensitive paint (PSP). Oxygen in the film quenches luminescence, and oxygen pressure was initially monitored by measuring the ratio of I(wind-off)/I(wind-on). But this ratio is compromised if there is model motion and if the paint layer is inhomogeneous. Furthermore it requires careful monitoring and placement of light sources. Moreover, this method is seriously affected by temperature. The errors caused by model motion and temperature sensitivity are eliminated or greatly reduced using dual luminophor paint. This paper illustrates a successful application of a dual luminophor PSP in auto model testing. The PSP is made from an oxygen sensitive luminophor, Pt tetra(pentafluorophenyl)-porpholactone, which provides I_sen, and Mg tetra(pentafluorophenyl)porphine, which provides temperature-sensitive paint (TSP) as the pressure-independent reference. The ratio PSP/TSP in the FIB polymer produced ideal PSP measurements with a very low-temperature dependence of −0.1% °C⁻¹.

This paper presents a new mechatronic approach of using infrared thermography combined with image processing for the quality control of a laser sealing process for food containers. The suggested approach uses an online infrared system to assess the heat distribution within the container seal in order to guarantee the integrity of the process. Visual image processing is then used for quality assurance to guarantee optimum sealing. The results described in this paper show examples of the capability of the condition monitoring system to detect faults in the sealing process. The results found indicate that the suggested approach could form an effective quality control and assurance system.

Pulsed microchip lasers have become useful in a broad area of applications due to their robustness and low cost. The pulse widths of these lasers are typically from tens of picoseconds to a few nanoseconds, a range that has proved to be either difficult or costly to characterize by currently available instrumentation. As a cost-effective and sufficient solution for microchip laser characterization an autocorrelator was built. This long-arm (400 mm) intensity autocorrelator was designed to be easy to align and tolerant to non-idealities of the mechanical scanning process. Standard measurements were fully automated.

The atomic force microscope (AFM) is a powerful tool for measuring surface roughness on the nanometre scale. This paper numerically analyses the factors affecting roughness evaluation of the surface measured by AFM. Parameters of both tip and sample are considered such as tip radius, surface autocorrelation length, standard deviation of original rough surface and its height distribution. The rough surface is generated using a 2D digital filter and the Fourier analysis method with controlled autocorrelation function and height distribution. The AFM image is simulated by mathematical morphology. For a given tip radius, a surface with high standard deviation and low correlation length causes a large error in determining roughness by AFM. We also show that the effect of tip radius on roughness exhibits two different trends depending on the surface skewness. For a normally distributed surface with near zero skewness and a rough surface with negative skewness, the root mean square (RMS) roughness decreases monotonically as tip radius increases. For a surface with large positive skewness, the RMS roughness tends to increase initially and then decrease with increasing tip radius.

Digital particle imaging velocimetry (DPIV) is a high resolution, high accuracy, planar velocimetry technique, which provides valuable instantaneous velocity information in aeropropulsion test facilities. DPIV is capable of providing three-component flow field measurements using a two-camera, stereo viewing configuration. Doppler global velocimetry (DGV) is another planar velocimetry technique which is also capable of providing three-component flow field measurements, but requires three detector systems that must be located at oblique angles from the measurement plane. The three-dimensional (3D) configurations of either technique require multiple (DGV) or at least large (stereo PIV) optical access ports in the facility in which the measurements are being conducted. In some test facilities, only limited optical access is available (either a single viewing window or small optical access port), which prohibits the implementation of either technique for three-component flow measurements. A hybrid measurement technique is described, called planar particle image Doppler velocimetry (PPIDV), which combines elements from both the DPIV and DGV techniques into a single detection system. The resulting system is capable of measuring all three components of velocity across a planar region of a flow field through a single optical access port. An error analysis is performed which reveals an optimal configuration for the DGV portion of the measurement system. Measurements of a rotating wheel are used to verify the integrity of the technique. Then simultaneous measurements of a nozzle flow are obtained using both a stereo viewing DPIV system and the PPIDV system.

A method is devised for true three-dimensional (3D) particle sizing in two-phase systems. Based on a ray-optics approximation of the Mie scattering theory for spherical particles, and under given assumptions, the principle is applicable to intensity data from scatterers within arbitrary interrogation volumes. It requires knowledge of the particle 3D location and intensity, and of the spatial distribution of the incident light intensity throughout the measurement volume. The new methodology is particularly suited for Lagrangian measurements: we demonstrate its use with the defocusing digital particle image velocimetry technique, a 3D measurement technique that provides the location, intensity and velocity of particles in large volume domains. We provide a method to characterize the volumetric distribution of the incident illumination and we assess experimentally the size measurement uncertainty.

A new method for traceable measurement of micro-roughness by using a newly developed metrological large range scanning force microscope (LR-SFM) is described. The LR-SFM has an Abbe error free design and direct interferometric position measurement capability, and is capable of measuring samples in a volume of 25 mm × 25 mm × 5 mm along x, y and z axes. The instrumentation and several important design concepts are introduced in this paper. Measurement results of a plane glass and a micro-roughness standard have illustrated that the instrument has a low noise level of R_a = 0.58 nm and good measurement repeatability. Furthermore, a group of comparison measurements on a micro-roughness standard have been carried out between the LR-SFM and a stylus profiler. The obtained roughness values from both instruments are in excellent agreement with each other. This LR-SFM overcomes the difficulty that roughness values measured by conventional SFMs cannot be compared to stylus profilers or interference microscopes, mainly due to the fact that conventional SFMs do not have the required scanning range of ISO standardized evaluation methods.

In automatic data acquisition, a sample is generally made up of several instrumental readings. A series of readings is generally reduced to a single value by simple methods, such as averaging. However, outlying values can affect the series. The paper introduces an algorithm, named 'sequence-analysis outlier data rejection' (SAODR), which takes into account one of the most common problems affecting the measurand during the acquisition, i.e. a nonlinear drift with embedded sequences of outliers due to pulse-noise peaks. The algorithm uses a time-ordering procedure and the 'distances' between successive readings. The frequent case of constant sampling rate is discussed. The reported tests show the results obtained with Fortran 77 and MATLAB® implementations of the algorithm. A rejection efficiency higher than 99% was obtained.

Inertial navigation system (INS) and global position system (GPS) technologies have been widely utilized in many positioning and navigation applications. Each system has its own unique characteristics and limitations. Therefore, the integration of the two systems offers a number of advantages and overcomes each system's inadequacies. INS/GPS integration is usually implemented using Kalman filters. However, Kalman filters perform adequately only under certain predefined dynamic models and suffer from several problems related to observability and immunity to noise effects. An INS/GPS integration method based on artificial neural networks (ANNs) to fuse INS measurements and differential global positioning system (DGPS) measurements has been recently suggested. Although able to provide high performance INS/DGPS integration with accurate prediction of position components during GPS outages, the conventional methods of updating the ANN weights limit the real-time capabilities. This paper offers a new weight updating criterion to improve the limitation of traditional weight updating methods with the utilization of two different architectures; the position update architecture and position and velocity update architecture.

Linear birefringence is one of the most important parameters of optical (fibre-optic) current-sensing heads, which can obviously affect the performance of optical current sensors. Therefore, it is of great importance to measure the linear birefringence inside the optical current-sensing head to enhance the properties of sensors. A novel method to measure the linear birefringence inside bulk glass current-sensing heads is reported in this paper, which gives a theoretical analysis of the principle, the measurement uncertainty analysis—using the Jones matrix as a mathematical tool—and an applied example. This method overcomes the shortcomings of the two methods reported before which cannot uniquely determine the value of the linear birefringence or introduce large measurement uncertainty. The experimental result shows that this method can certainly enhance the measurement precision.

The frequency response analysis method is more and more frequently used as a diagnostic tool for investigation of electrical device windings. The method is being used for identification of dislocations and deformations of transformer windings. This paper presents a novel application regarding possibilities of the frequency response analysis method in electrical machine windings. Of special importance is the early detection of winding failures in electrical machines, both during the manufacturing process and in operation. The results of investigations of winding faults in electrical machines of different construction are presented in this paper. The influence of turn-to-turn faults between adjacent winding wires on the admittance waveform was investigated.

A miniature laser-Doppler velocimeter (LDV) system was developed to make simultaneous three-velocity-component measurements. The probe has been tested in a zero-pressure gradient two-dimensional turbulent boundary layer and the results agree well with earlier data and several DNS data sets. The overall size of the probe is 23.3 mm × 8.7 mm × 90.6 mm and measurement spatial resolution is 50 µm. The probe volume can be traversed 32 mm vertically. The lightweight and compact design of the LDV probe head allows the probe head to be embedded inside models and machinery for three-dimensional turbulent flow measurements where larger probes are unusable.

A study of the sources of variability in particle size measurements using a dilution minitunnel and a scanning mobility particle sizer (SMPS) has been conducted in order to obtain a comprehensive and repeatable methodology that can be used for measuring the particle size distribution of the exhaust aerosol emitted by a heavy duty diesel engine. The paper includes three experimental phases: an experimental analysis of the SMPS operating parameters' influence; an evaluation of the effect of dilution conditions, such as the dilution ratio and the dilution residence time; and a study of the influence of sampling factors, such as measurement stabilization and the effect of exhaust system pre-conditioning. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a measurement methodology of low uncertainty that could be applied to a further study concerning the effect of engine operating parameters on the exhaust particle size distribution.

With the shrinkage of integrated circuit devices, direct process control is expected to improve productivity by monitoring the process in real time. A vacuum rapid thermal processing system is described in detail for microelectronic applications. It has features of rapid thermal processing, UV assisted processing, chemical vapour deposition, O₃ processing and in situ process/sample characterization. The in situ process/sample characterization includes infrared spectroscopy, ellipsometry, goniometry and residual gas analyser. These techniques enable the probing of film properties, interfaces, film thickness, surface contact angles and gas phase chemistry. The system is capable of various microelectronic processes such as gate dielectrics formation, ozone surface oxidation, low k dielectric formation and chemical vapour deposition. An exemplary application of the system is demonstrated in Si oxidation.

A two-dimensional axisymmetric parametric model was developed to calculate the vector value of the small force between the electrodes of a cylindrical capacitor with a given voltage, which is called an electrostatic force balance and studied to establish a force standard traceable to the SI in the range from µN to nN. The reasons for developing this model are (1) to optimize the design of the electrostatic force balance and (2) to improve the accuracy of the force standard. NIST will check this model by calculating the forces with mechanical forces of their prototype electrostatic force balance loaded with deadweights of several mg.

Electrical impedance tomography (EIT) is a relatively new imaging modality in which the internal impedivity distribution is reconstructed based on the known sets of injected currents and measured voltages on the surface of the object. In this paper, an effective EIT imaging scheme is presented for on-line monitoring of the time-varying resistivity distribution inside the object based on the interacting multiple model (IMM) algorithm. The inverse problem is treated as a nonlinear state estimation problem and time-varying resistivity (state) is estimated on-line with the aid of the IMM algorithm. In doing so, multiple kinematic models are employed as the state evolution model to reduce the modelling uncertainty. Computer simulations are provided to illustrate the reconstruction performance of the proposed algorithm.

We present a total-variation-based image reconstruction algorithm for electrical capacitance tomography. This is a nonlinear iterative algorithm designed to minimize both the data error and the total variation of the permittivity, with iterations updated by the projected Gauss–Newton steps. We present numerical examples to illustrate the effectiveness of the algorithm in reconstructing permittivity images from both noise-free and noisy capacitance data.

Plastic optical fibre sensors offer remarkable ease of handling, and recent research has shown their potential as a low-cost sensor for damage detection and structural health monitoring applications. This paper presents details of a novel extrinsic polymer-based optical fibre sensor and the results of a series of mechanical tests conducted to assess its potential for structural health monitoring. The intensity-based optical fibre sensor proposed in this study relies on the modulation of light intensity as a function of a physical parameter (typically strain) as a means to monitor the response of the host structure to an applied load. Initially, the paper will reveal the design of the sensor and provide an outline of the sensor fabrication procedure followed by a brief description of its basic measurement principle. Two types of sensor design (fluid type and air type) will be evaluated in terms of their strain sensitivity, linearity and signal repeatability. Results from a series of quasi-static tensile tests conducted on an aluminium specimen with four surface-attached optical fibre sensors showed that these sensors offer excellent linear strain response over the range of the applied load. A comparison of the strain response of these sensors highlights the significant improvement in strain sensitivity of the liquid-filled-type sensor over the air-filled-type sensor. The specimens were also loaded repeatedly over a number of cycles and the findings exhibited a high degree of repeatability in all the sensors. Free vibration tests based on a cantilever beam configuration (where the optical fibre sensor was surface bonded) were also conducted to assess the dynamic response of the sensor. The results demonstrate excellent agreement with electrical strain gauge readings. An impulse-type loading test was also performed to assess the ability of the POF sensor to detect the various modes of vibration. The results of the sensor were compared and validated by a collocated piezofilm sensor highlighting the potential of the POF sensor in detecting the various eigen-frequencies of the vibration. Finally, preliminary results of a loading–unloading test of the same sensor design encased within a metal tube will be presented. The results obtained were encouraging offering the possibilities of employing the proposed device as an embedded sensor for damage detection in concrete beams.

In optical interferometry, calibration of phase shift is an important aspect of phase-shifting algorithms. A windowed Fourier transform approach is proposed which enables calibration of phase shift from the 'good' parts of two fringe patterns.

A low-loss monolithic sapphire has been developed for use as a novel transducer via the interaction between the electrical and mechanical resonances, with the intent of measuring the standard quantum limit in a macroscopic mass. This work has investigated the transductance mechanism due to the interaction between electrical and mechanical resonances in a low-loss electrical and acoustic resonator, which operates in the regime where parametric interactions dominate. High electrical and mechanical quality factors (Q-factors) are obtained at low temperatures (4.2 K) using high purity sapphire and single loop suspension vibration isolation. In deriving the displacement sensitivity of the monolithic sapphire transducer (MST), the acoustic mode shape and electromagnetic field distribution must be taken into account rather than the use of a simple mass–spring model. With the aid of this model we determine for the first time the strain-induced coefficient of permittivity for sapphire, both perpendicular and parallel to the c-axis. By comparison with other work, it has been determined that changes in the dielectric constant due to strain are approximately eight times smaller than changes caused by thermal expansion.

In a laser Doppler interferometer, besides the probe and reference beams, a third coherent light wave, caused by spurious reflection, may hit the detector. Interference effects between regular and unwanted waves, which are dependent on the actual intensity ratios, contribute to the generation of the electrical output signal. A mathematical analysis predicts the appearance of ripple and spikes riding on the demodulated signal due to distorted modulation of the Doppler signal. These effects are verified by experiments, demonstrating the dependence of distortions on given optical conditions.

Microcontrollers with embedded timers can directly measure resistive and capacitive sensors by determining the charging or discharging time of an RC circuit that includes the sensor. This time-to-digital conversion is affected by the quantization of the timer and the trigger noise, which limit the resolution to an effective number of bits (ENOB). This paper analyses the standard uncertainty and the ENOB of that time-to-digital conversion. When interfacing resistive sensors and the capacitor C is small, quantization effects predominate over trigger noise effects, and ENOB increases for increasing C. But, for capacitor values larger than a given C, trigger noise effects predominate and the ENOB remains constant regardless of C. Therefore, an optimal time constant yields the best speed–ENOB trade-off. This type of sensor interface was implemented by using an AVR microcontroller with an embedded 16-bit timer connected to a resistor simulating a Pt1000-type temperature sensor. The experimental results agree with the theoretical predictions. If the time was determined from a single observation, the optimal time constant was about 2–3 ms and the ENOB was about 11.5 b, which corresponds to a 0.22 Ω resolution. By averaging ten observations, that resolution improved to 13.5 b (0.05 Ω).

It may be quite difficult to find analytical solutions for some simple circuits containing a thermistor element. Iterative numerical procedures may also yield impractical or complicated operations including convergence problems. Often, it is not necessary to obtain a complete solution for the dynamic thermistor equation, but rather search for a steady-state response for a thermistor element. Here, circuit simulation algorithms such as SPICE can be helpful. In this study, an electrical equivalent circuit model for the steady-state NTC thermistor current–voltage characteristics at different ambient temperatures is proposed. The model includes a number of electrical equivalent circuit components (namely, diode, resistor and current source) for a piecewise-linear approximation to the current–voltage characteristic curve of an NTC thermistor. Once the electrical parameters of the loaded (self-heated) thermistor are computed at a given ambient temperature using this proposed model, then one may easily find its working (body) temperature. The performance of the method is demonstrated using a practical example. Advantages as well as limitations of the model are also discussed.

Micro-traces of water in gases have been determined by using a combination of a conversion reactor column and a high sensitivity hydrogen gas sensor (abbreviated here to CRHS-GC). A special purge installation was designed to clean the system with dried and purified liquid nitrogen. Micro-traces of water in gases first were introduced into the reactor column. The column was prepared by filling with a mixture of lithium and aluminium hydride (LiAlH₄) and glass fibre in a vacuum box, where the water present reacted with LiAlH₄ at about 60 °C. Hydrogen was released and determined by the hydrogen gas sensor, which was calibrated by a series of standard micro-trace hydrogen mixture gases. The experimental results showed that this method can be used to determine micro-traces of water in gases quickly, accurately and at a low cost. Only about 2–5 litres of sample were needed during each analysis. The method developed does not have the shortcoming of direct determination of micro-traces of water in gases that is caused by the absence of appropriate traceable calibration gases.