Bosco Fernandes

A portable inductive scanning system for imaging steel-reinforcing bars embedded within concrete

Abstract A novel portable scanning system and inductive sensor that produces images of steel-reinforcing bars embedded within concrete by an inductive principle is described. The sensing element, which comprises a field-compensated receiving coil, detects the magnetic field generated by the steel bars due to eddy currents induced on their surfaces by an excitation coil. The sensor is mounted within a purpose-designed computer-controlled x – y scanner used to collect data within a 400×400 mm 2 area in 18 min, using a scan step of 1 mm along the x -axis and 2 mm along the y -axis. This scanner assembly is fabricated from a unique combination of plastic components to avoid disruption of the magnetic field as signals are acquired. The sensor is translated within the frame using remotely placed stepper motors, and images are generated with a grey-scale resolution of 16 bits/pixel. These images are then enhanced using application-specific image processing techniques developed by the authors. The complete system incorporates fully integrated control, acquisition and processing software, which makes it convenient for on-site use.

Automatic identification of gait events using an instrumented sock

BackgroundTextile-based transducers are an emerging technology in which piezo-resistive properties of materials are used to measure an applied strain. By incorporating these sensors into a sock, this technology offers the potential to detect critical events during the stance phase of the gait cycle. This could prove useful in several applications, such as functional electrical stimulation (FES) systems to assist gait.MethodsWe investigated the output of a knitted resistive strain sensor during walking and sought to determine the degree of similarity between the sensor output and the ankle angle in the sagittal plane. In addition, we investigated whether it would be possible to predict three key gait events, heel strike, heel lift and toe off, with a relatively straight-forward algorithm. This worked by predicting gait events to occur at fixed time offsets from specific peaks in the sensor signal.ResultsOur results showed that, for all subjects, the sensor output exhibited the same general characteristics as the ankle joint angle. However, there were large between-subjects differences in the degree of similarity between the two curves. Despite this variability, it was possible to accurately predict gait events using a simple algorithm. This algorithm displayed high levels of trial-to-trial repeatability.ConclusionsThis study demonstrates the potential of using textile-based transducers in future devices that provide active gait assistance.

A portable system for acquiring and removing motion artefact from ECG signals

A novel electrocardiograph (ECG) signal acquisition and display system is under development. It is designed for patients ranging from the elderly to athletes. The signals are obtained from electrodes integrated into a vest, amplified, digitally processed and transmitted via Bluetooth to a PC with a Labview ® interface. Digital signal processing is performed to remove movement artefact and electromyographic (EMG) noise, which severely distorts signal morphology and complicates clinical diagnosis. Independent component analysis (ICA) is also used to improve the signal quality. The complete system will integrate the electronics into a single module which will be embedded in the vest.

Image reconstruction of steel reinforcing bars in concrete using Fourier-domain interpolation applied to a sparsely populated data set

High-resolution image generation of bars in concrete using a single coil scanning inductive sensor is a time consuming process. This paper presents a method of generating the image using a sparsely populated data set (SPDS), obtained from a reduced number of scan lines, whose use is justifies by an analysis of the sensor spatial frequency response. Three methods are discussed: linear and cubic spline interpolation in the spatial domain, and Fourier interpolation, all of which are applied to an SPDS. Data for the SPDS are provided from a widely spaced scanning regime implemented in both the x and y-axes. Interpolated values are then synthesized to obtain high-resolution images. The Fourier-based method employs zero padding in the spatial frequency domain and inverse Fourier transformation to obtain higher resolution data in the time/spatial domain. In general, the results obtained by the linear interpolation algorithm are unacceptable since they do not represent the point-spread function of the sensor. The results obtained by the cubic spline and Fourier methods are very satisfactory, with the deviation from the results obtained by the standard high-resolution image generation process being very small. However, the cubic spline method is cumbersome to implement, requiring the computation of a large number of unique polynomials. In contrast, the Fourier algorithm is efficient, straightforward to code and yields an ideal band-limited interpolation. Experiments show that this new methodology is faster than the traditional scanning protocol by at least a factor of 10; a large area scan of 0.5 m2 can thus be produced in 12 min, rather than 2 h. In the future, this technique could be applied to widely spaced solid-state arrays, requiring a fraction of a second for image synthesis.

Multiple layer separation and visualisation of inductively scanned images of reinforcing bars in concrete using a polynomial-based separation algorithm

Inductive scanning systems that exploit eddy current effects for imaging steel reinforcing bar mesh within concrete have been developed and reported by the authors in several publications. Images generated in this manner depict the different horizontal and vertical layers of the mesh within a single, 2D plane. Deeper bars appear as much fainter structures than those closer to the surface for two reasons: first, the signals they generate are weaker, and second, the image is linearly normalised with respect to the much stronger signals returned from the upper bars. This makes depth and dimensional analysis of deeper bars a severe problem. Below we describe a new suite of image processing algorithms that enables the original composite image to be visualised as separate, multiple images representing the various bar layers. This technique is termed polynomial-based layer separation (PBLS). The method also makes it possible to perform brightness-compensation of the lower bars and is a precursor to analysis that allows measurement of the diameters, orientations and depths of the bars. This information is critical for civil structures inspection teams. Knowing the spatial location of the bar peak widths in one layer, curve fitting is applied to calculate the baselines of the bars in other layers of the image. For a two-layer image, the peaks in the lower layer are removed leaving an image of the top bars, and vice versa for the bottom bars. Images of steel bar mesh processed using this PBLS system offer significant enhancements to the qualitative and quantitative properties of the original image data, and in tests described below, is significantly more robust than comparable methods of image segmentation.

Inductive and magnetic field inspection systems for rebar visualization and corrosion estimation in reinforced and pre-stressed concrete

Inductive and magnetic field inspection systems are becoming increasing popular for the nondestructive imaging and condition assessment of reinforcing components, such as steel reinforcing bars (rebars) and tendons in reinforced and prestressed concrete structures. In this article, we review the principles of this nascent technology, the research and commercial instruments that are now available, and the directions of future research. Magnetic field imaging technology has in general many potential benefits; it is truly nondestructive and non-invasive, it is non-hazardous, cost-effective and, most important, ignores the concrete matrix in which the reinforcing components are embedded. Most significantly, by analysing the impedance change in an excitation coil, it is also possible to obtain quantitative information (and image data) in relation to regions of corrosion. However, the testing industry has traditionally been reluctant to apply this methodology, for the important reason that the detection range is limited by the rapid attenuation of the magnetic field with increasing distance from the source. This limitation is now being addressed with research into novel coil arrangements, new, more stable and sensitive solid state sensors, and reconstruction algorithms that allow virtual three dimensional reconstruction of embedded components.

Vector extraction from digital images of steel bars produced by an inductive scanning system using a differential gradient method combined with a modified Hough transform

A method of extracting positional information from images of steel bars embedded in concrete using a set of image pre-processing algorithms combined with a modified Hough transform is described. The images are formed using a portable inductive scanning system in which a sensing element detects the magnetic field emanating from the bars. Eddy currents induced on the surfaces of the bars by excitation coils generate these magnetic fields. The results from an edge detection algorithm based on the two-dimensional separable smoothing and local maxima detection are applied to a two-stage Hough transform which locates the major axes of the bars and hence their alignment and number. An effective method of minimising the redundant information in the Hough array is also described. The complete system incorporates fully integrated control, acquisition and processing software, which makes it convenient for on-site use.

An advanced real-time digital signal processing system for linear systems emulation, with special emphasis on network and acoustic response characterization

A fast digital signal processing (DSP) system is described that can perform real-time emulation of a wide variety of linear audio-bandwidth systems and networks, such as reverberant spaces, musical instrument bodies and very high order filter networks. The hardware design is based upon a Motorola DSP56309 operating at 110 million multiplication-accumulations per second and a dual-channel 24 bit codec with a maximum sampling frequency of 192 kHz. High level software has been developed to express complex vector frequency responses as both infinite impulse response (IIR) and finite impulse response (FIR) coefficients, in a form suitable for real-time convolution by the firmware installed in the DSP system memory. An algorithm has also been devised to express IIR filters as equivalent FIR structures, thereby obviating the potential instabilities associated with recursive equations and negating the traditional deficiencies of FIR filters respecting equivalent analogue designs. The speed and dynamic range of the system is such that, when sampling at 48 kHz, the frequency response can be specified to a spectral precision of 22 Hz; when sampling at 10 kHz, this resolution increases to 0.9 Hz. Moreover, it is also possible to control the phase of any frequency band with a theoretical precision of 10−5 degrees in all cases. The system has been applied in the study of analogue filter networks, real-time Hilbert transformation, phase-shift systems and musical instrument body emulation, where it is providing valuable new insights into the understanding of psychoacoustic mechanisms.

Urinary Incontinence: A Vibration Alert System for Detecting Pad Overflow

ABSTRACT A sensor and electronics system is described that monitors the leakage of urine from continence pads into surrounding underwear. Urinary incontinence is involuntary loss of urine and occurs when the bladder muscles contract without warning or the sphincter muscles surrounding the urethra are too weak to prevent leakage. The system comprises a wetness sensor and electronics unit. The sensor is stitched into the underwear and detects overspills of urine from the pad. The electronics unit is attached to the underwear and responds by vibrating, signaling to the wearer that pad has failed. This system has application for individuals who use continence pads in the community, but it could also be used in care homes.

THE APPLICATION OF MAGNETO INDUCTIVE SENSORS FOR NON-DESTRUCTIVE TESTING OF STEEL REINFORCING BARS EMBEDDED WITHIN PRE-STRESSED AND REINFORCED CONCRETE

This paper demonstrates the feasibility of using solid‐state magneto‐inductive probes for detecting and imaging of steel reinforcing bars embedded within pre‐stressed and reinforced concrete. Changes in the inductance of the sensor material are directly proportional to the strength of the measured magnetic field parallel to the sensor. Experimental results obtained by scanning steel bars specimens are presented. General performance characteristics and sensor output limitations are investigated by using different orientations, sensing distance, excitation intensity, bar sizes and geometries.