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For the electromagnetic eddy current (EC) testing, various methods have been proposed for reducing the lift-off error on the measurement of samples. In this article, instead of eliminating the measurement error caused by the lift-off effect, an algorithm has been proposed to directly measure the lift-off distance between the sensor and nonmagnetic conductive plates. The algorithm is based on a sample-independent inductance (SII) feature. That is, under high working frequencies, the inductance is found to be sensitive to the lift-off distance and independent of the test piece under an optimal single high working frequency (43.87 kHz). Furthermore, the predicted lift-off distance is used for the thickness prediction of the nonmagnetic conductive samples using an iterative method. Considering the EC skin depth, the thickness prediction is operated under a single lower frequency (0.20 kHz). As the inductance has different sensitivities to the lift-off and thickness, the prediction error of the sample thickness is different from that of the lift-off distance. From the experiments on three different nonmagnetic samples—aluminum, copper, and brass, the maximum prediction error of the lift-off distance and sample thickness is 1.1 mm and 5.42%, respectively, at the lift-off of 12.0 mm.

For the electromagnetic eddy current testing, various methods have been proposed for reducing the lift-off error on the measurement of samples. In this paper, instead of eliminating the measurement error caused by the lift-off effect, an algorithm has been proposed to directly measure the lift-off distance between the sensor and non-magnetic conductive plates. The algorithm is based on a sample-independent inductance (SII) feature. That is, under high working frequencies, the inductance is found sensitive to the lift-off distance and independent of the test piece under an optimal single high working frequency (43.87 kHz). Furthermore, the predicted lift-off distance is used for the thickness prediction of the non-magnetic conductive samples using an iterative method. Considering the eddy current skin depth, the thickness prediction is operated under a single lower frequency (0.20 kHz). As the inductance has different sensitivities to the lift-off and thickness, the prediction error of the sample thickness is different from that of the lift-off distance. From the experiments on three different nonmagnetic samples – aluminium, copper, and brass, the maximum prediction error of the lift-off distance and sample thickness is 1.1 mm and 5.42 % respectively at the lift-off of 12.0 mm.

We present a rigorous model for the overall band structure calculation using the perturbative k &middot, p approach for arbitrary layered cubic zincblende semiconductor nanostructures. This approach, first pioneered by Kohn and Luttinger, is faster than atomistic ab initio approaches and provides sufficiently accurate information for optoelectronic processes near high symmetry points in semiconductor crystals. k &middot, p Hamiltonians are discretized and diagonalized using a finite element method (FEM) with smoothed mesh near interface edges and different high order Lagrange/Hermite basis functions, hence enabling accurate determination of bound states and related quantities with a small number of elements. Such properties make the model more efficient than other numerical models that are usually used. Moreover, an energy-dependent effective mass non-parabolic model suitable for large gap materials is also included, which offers fast and reasonably accurate results without the need to solve the full multi-band Hamiltonian. Finally, the tools are validated on three semiconductor nanostructures: (1) the bound energies of a finite quantum well using the energy-dependent effective mass non-parabolic model, (2) the InAs bulk band structure, and (3) the electronic band structure for the absorber region of photodetectors based on a type-II InAs/GaSb superlattice at room temperature. The tools are shown to work on simple and sophisticated designs and the results show very good agreement with recently published experimental works.

This paper presents a performance evaluation of intercell interference and packets collision in scalable Low Power Wide Area Networks (LPWANs). The collision problem is one of the most critical challenges in LPWANs because it can substantially affect network performance and reliability. The paper also offers a rigorous and flexible mathematical model for the ALOHA-based random access protocol with the support of multiple groups of devices and multiple message copies. The analysis is based on the worst-case scenario of message collision, which calculates the message lost ratio (MLR) by assuming that even a weak overlap between two packets in the time-frequency domain leads to the loss of both. Simulations of Weightless-N and Sigfox LPWAN technologies using a variable number of devices, message copies, payload, transmission time, and channels offer some fresh insights into the LPWANs performance. For example, increasing the number message copies reduces the MLR but only up to a certain number of connected devices. After which, the redundancy in packet transmission is no longer beneficial.

In this paper, we present the results of a failure analysis done on new heat exchanger tubes, which shows loss of thickness during a EC inspection to stablish a prior loss of thickness base line aiming guarantee fitness for service during its working life. The root cause analysis indicates that there is intergranular corrosion due a differential concentration caused by seawater evaporation inside the tubes during the ship transit from the port of origin in China to the destination port in Brazil. The intergranular corrosion depth showed by root cause failure analysis is smaller than that showed by EC inspection. We attribute the EC inspection results deviation to a tube magnetisation due to mechanical stress and to a secondary phase due to an incomplete solubilisation after tube conforming and welding. Traditionally, these tubes are visually inspected and deemed acceptable but our conclusions reveal that eddy current testing is capable of detecting some corrosion anomalies which makes the tubes unfit for service.

A simulator was developed for modeling and designing multiple quantum wells structures such as quantum well infrared photodetectors and quantum cascade laser, based on a single-electron effective mass Schrodinger equation. It employs box integration finite differences and transfer matrix approaches to find energies of bound and scattering states in the structures. The graphical user interface allows the user to vary easily design parameters including effective mass, layer thickness and number of layers as well as simulation parameters in order to optimize the structure for different device applications and functionality. Three simulation examples were performed on: three coupled quantum wells structure, two-color asymmetric quantum well infrared photodetector structure and on a quantum cascade laser design. The results show an accuracy which is comparable to more complicated simulations.

Training to qualify as a manual ultrasonic inspector takes a long time and costs a considerable amount of money. We developed a virtual training environment using an innovative dead-reckoning optical sensor that yields translational position which offers additional information to operators and examiners alike. The training environment contains a library of test scenarios, shows surface coverage, measures the time of inspection, indicates detected defects and provides a performance score. Our test-bed trial results using a pool of Ultrasonic Test (UT) qualified and unqualified participants on two virtual training blocks that contain 2 flaws each reveal 100% detection and an accuracy of 5 mm in locating defects in more than 50% of the measured defect locations.

There are different techniques used by Machine- to-machine (M2M) communications technologies to mitigate collision problem and data loss. One of these techniques is Frequency Hopping (FH), which is used by Weightless-N technology with a special random channel selection algorithm. In such a system, the probability of a message collision mainly depends on the randomisation algorithm used to access channels. This paper provides a novel randomisation algorithm for the channel selection process of the Weightless-N system. The new proposed algorithm is based on a uniform randomization distribution and called a Uniform Randomisation Channel Selection Technique (URCST). This new algorithm provides a better system performance and lower probability of collision. In addition, it is faster and easier than the Mersenne Twister algorithm.

Slender boiler tubes are subject to localised swelling when they are expose to excessive heat. The latter is due to the formation of an oxide layer, which acts as an insulation barrier. This excessive heat can lead to microstructural changes in the material that would reduce the mechanical strength and would eventually lead to critical and catastrophic failure. Detecting such creep damage remains a formidable challenge for boiler operators. It involves a costly process of shutting down the plant, performing electromagnetic and ultrasonic non-destructive inspection, repairing or replacing damaged tubes and finally restarting the plant to resume its service. This research explores through a model developed using a finite element computer simulation platform the thermal behaviour of slender tubes under constant temperature exceeding 723 \K. Our simulation results demonstrate that hematite layers up to 15 \μm thickness inside the tubes do not act as insulation. They clearly show the process of long term overheating on the outside of boiler tubes which in turn leads to initiation of flaws.

The first demonstration of a directly modulated microring laser array is presented for on-off keyed, wavelength- division- multiplexed fiber-optic data transmission. GaInAsP-InP microring resonators oscillating at separate wavelengths in the 1.5-μm band are vertically coupled to a common passive waveguide bus, which is fabricated on the reverse side of the InP membrane. Two microrings defined with radii for a wavelength channel separation of 6 nm have been assessed for both individual and simultaneous operation. Negligible power penalty (2 per microring on a common passive bus allows a highly scalable solution for short-reach wavelength-multiplexed links.

A highly compact and scalable microring-laser-based optical-add multiplexer is presented for wavelength division multiplexed bus networks. The output of a 40 mu m-radius microring laser is vertically coupled to a passive waveguide bus and the chip is subsequently mounted in a butterfly package with fibre pigtailing at both input and output. In the first such experiment with a microring-based module, a wavelength channel is added into a wavelength multiplexed fibre-optic link with negligible power penalty. Successful transmission of a 2 lambda x 2.5 Gbit/s signal over 25 km is demonstrated for a 0.9 nm channel spacing.

Near-field ultrasonic response (50-2000 kHz) of an underwater 1-3 piezocomposite transducer is experimentally investigated using a polarimetric polarization maintaining fiber sensor. Measured outputs from our sensor and a reference hydrophone are observed to be comparable.