In this paper, we analyze the effect of different underground materials on very-low and low frequency magnetic fields used in the contexts of magneto-inductive localization and communication applications, respectively. We calculate the attenuation that these magnetic fields are subject to while passing through most common rocks and minerals. Knowing the attenuation properties is crucial in the design of underground magnetoinductive communication systems. In addition, we provide means to predict the distortions in the magnetic field that impair localization systems. The proposed work offers basic design guidelines for communication and localization systems in terms of channel path-loss, operation frequencies and bandwidth. For the sake of the reproducibility of the results, we provide the raw data and processing source code to be used by the two research communities.

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Ferrous and highly conductive materials distort lowfrequency magnetic fields and can significantly increase magnetoinductive positioning errors. In this work, we use image theory in order to formulate an analytical channel model for the magnetic field of a quasi-static magnetic dipole positioned above a perfectly conducting half-space. The proposed model can be used to compensate for the distorting effects that metallic reinforcement bars (rebars) within the floor impose on the magnetic field of a magneto-inductive transmitter node in an indoor, single-story environment. Good agreement is observed between the analytical solution and numerical solutions obtained from 3-D finite element simulations. Experimental results indicate that the image theory model shows improvement over the free space dipole model in estimating position in the distorted environment, typically reducing positioning errors by 22% in 90% of the cases and 26% in 40% of the cases. No prior information on the geometry of the metallic distorters was available, making this essentially a "blind" technique.

We derive a two parameter multi-exponential model to describe the frequency spectrum of Barkhausen noise in bulk steel under high excitation rates and applied tensile stress. We show how the amplitude and shape of the frequency spectrum depend on two directly measurable quantities, Barkhausen voltage and effective magnetic permeability, respectively, and how these change with stress. By incorporating frequency and depth dependence components into our model, we provide a framework for identifying stress variations along depth, which can be used for the purposes of non-destructive characterization. KeywordsBarkhausen effects, Domain walls, Emission spectra, Elasticity, Random Noise Disciplines Electromagnetics and Photonics CommentsThe following article appeared in Journal of Applied Physics 115 (2014) We derive a two parameter multi-exponential model to describe the frequency spectrum of Barkhausen noise in bulk steel under high excitation rates and applied tensile stress. We show how the amplitude and shape of the frequency spectrum depend on two directly measurable quantities, Barkhausen voltage and effective magnetic permeability, respectively, and how these change with stress. By incorporating frequency and depth dependence components into our model, we provide a framework for identifying stress variations along depth, which can be used for the purposes of nondestructive characterization. V C 2014 AIP Publishing LLC. [http://dx

The effects of design parameters for optimizing the performance of sensors for magneticBarkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration. KeywordsBarkhausen effects, Magnetic field sensors, Coils, Magnetic materials, Magnetic fields Disciplines Electromagnetics and Photonics CommentsThe following article appeared in Journal of Applied Physics 115 (2014) The effects of design parameters for optimizing the performance of sensors for magnetic Barkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration. V C 2014 AIP Publishing LLC.[http://dx