Prof. Richard C. Bailey Profile

Prof. Richard C. Bailey

at Univ of Toronto

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Proceedings Article | 16 May 2006 Paper

Spectral representation: a core aspect of modelling the response characteristics of time-domain EMI mine detectors

G. West, R. Bailey

Proceedings Volume 6217, 621702 (2006) https://doi.org/10.1117/12.665898

KEYWORDS: Sensors, Electromagnetic coupling, Data modeling, Magnetism, Modeling, Mining, Inductance, Transmitters, Receivers, Ferromagnetics

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Most modern EMI mine detectors can detect the very small conductive and/or ferromagnetic parts of typical mines with relative ease. However, they also respond significantly to certain soils that contain lossy ferromagnetic minerals. In some special environments such as ocean beaches, conductivity of the host soil may also cause a response. Characterizing and modelling both the various target response mechanisms and the EMI detectors quantitatively would be relatively straightforward if it were not for the fact that most modern EMI detectors operate in time domain and use different current waveforms and time gates to observe response. Furthermore, much of the information about targets and interferences and even instrumental spectral limitations is observational rather than analytical data. In this paper, we put forward a spectral representation method that can be incorporated into both EMI data gathering and instrument modelling and which facilitates efficient quantitative simulation of arbitrary time- domain detection systems. The methodology and examples of its use are presented. Pure induction response from the ground is modelled with a sum-over-N-elements transfer function in which the kernel elements are single pole, pure damping responses which are log-spaced over the spectral range of interest. Instrument transfer functions can be described with a standard sparse pole and zero representation (located anywhere in the damped frequency half plane), if required. Model fitting techniques employing generalized inversion controls are used to go back and forth between frequency and time domain and the set of model parameters.

Proceedings Article | 16 May 2006 Paper

Characterizing mine detector performance over difficult soils

R. Bailey, G. West

Proceedings Volume 6217, 62170P (2006) https://doi.org/10.1117/12.665858

KEYWORDS: Transmitters, Receivers, Magnetism, MATLAB, Sensors, Target detection, Soil science, Electromagnetic coupling, Free space, Electromagnetism

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A variety of metal detectors are available for the detection of buried metallic targets in general and for humanitarian demining in particular. No one detector is optimal in all environments: variations in soil conductivity, and more importantly, frequency dependent soil magnetic susceptibility can favor one design over another. The use of computer modeling for assessing different designs is straightforward in principle, at least to first order, but still difficult in practice. The Geophysics Lab of the University of Toronto is attempting to address this problem in two ways. The first is by assembling the required computational algorithms to do this into a single simulation code with a straightforward GUI, intended to be public domain as a MATLAB code. The second, the subject of a companion paper in this conference, is by making measurements of the electromagnetic properties of difficult soils, and finding semi-analytic representations of these responses suitable for modeling purposes. The final version of the code, when completed, is to handle single or multiple transmitter and receiver coils of circular or polygonal shape, general transmitter current waveforms, arbitrary transmitter orientations and survey paths, small targets with frequency-dependent anisotropic responses (permitting both magnetic and inductive responses to be calculated), embedded in multi-layered half spaces with both conductivity and frequency-dependent susceptibility (so-called "difficult soils"). The current state of the simulation code and examples of its use will be described in this paper.

Proceedings Article | 10 June 2005 Paper

An instrument for measuring complex magnetic susceptibility of soils

Gordon West, Richard Bailey

Proceedings Volume 5794, (2005) https://doi.org/10.1117/12.602992

KEYWORDS: Magnetism, Transmitters, Sensors, Receivers, Electromagnetic coupling, Spectroscopy, Mining, Metals, Soil science, Land mines

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To improve the success of electromagnetic induction (EMI) metal detectors in identifying anti-personnel land mines buried in slightly ferromagnetic natural soils, we need to know what range of soil physical properties must be dealt with. We have therefore built a laboratory instrument for measuring complex magnetic susceptibility in inch-sized samples over a frequency range from 100 Hz to ~ 70 kHz with errors of a few percent of the sample susceptibility in a sample of ~1 milli-SIU volume susceptibility, (i.e. ~30 micro-SIU). The instrument is a symmetrical, six coil, induction spectrometer. A pair of transmitter coils in Helmholtz configuration generates a uniform magnetic field over the sample region. The magnetic moment induced in the sample is detected (mainly) by a pair of receiver coils which are closer to the sample than the transmitter pair and also (nearly) in Helmholtz configuration, so as to provide uniform sensitivity over the whole sample region. The coupling of the main receiver pair to the transmitter pair is annulled with a second pair of coils (called the reference receiver pair) situated outside the transmitter pair. The transmitter coils are energized with a wideband current. Data acquisition is by a PC computer with a 192 kHz, 24 bit, 2 channel sound card using software in written in MatLab. Although our instrument is still a prototype and its design continues to evolve, we have measured susceptibility spectra of some samples from de-mining projects in areas where false alarms are a problem and have found dispersive susceptibilities.

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