A fractal interpretation of the dielectric response of animal tissues

Dissado, L.A.

doi:10.1088/0031-9155/35/11/005

Cited by 65 publications

(46 citation statements)

References 37 publications

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“…The tissue conductivities in the model were assigned the mean value from multiple compiled references; skin at 0.465 S/m, bone at 0.010 S/m, CSF at 1.654 S/m, gray matter at 0.276 S/ m, and white matter at 0.126 S/m (Crille et al 1922;Oswald 1937;Lepeschkin 1951;Freygang and Landau 1955;Ranck 1963;Radvan-Ziemnowicz et al 1964;Hasted 1973;Geddes 1987;De Mercato and Garcia Sanchez 1992;Gabriel and Gabriel 1996;Akhtari et al 2002;Kammer et al 2004); thus, each individual tetrahedron of the FEM was assigned the conductivity corresponding to its tissue type. Tissue permittivities were also assigned values reflective of trends in the literature (see Table 1) (Pethig and Kell 1987;Dissado 1990;Foster and Schwan 1996;Gabriel and Gabriel 1996;Hart et al 1996). The source was modeled as a figure-of-eight copper coil with two 3.5 cm radius windings made of a single turn of 7 mm radius copper wire.…”

Section: Mri Guided Finite Element Head Modelmentioning

confidence: 99%

Transcranial magnetic stimulation and brain atrophy: a computer-based human brain model study

et al. 2008

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This paper is aimed at exploring the effect of cortical brain atrophy on the currents induced by transcranial magnetic stimulation (TMS). We compared the currents induced by various TMS conditions on several different MRI derived finite element head models of brain atrophy, incorporating both decreasing cortical volume and widened sulci. The current densities induced in the cortex were dependent upon the degree and type of cortical atrophy and were altered in magnitude, location, and orientation when compared to healthy head models. Predictive models of the degree of current density attenuation as a function of the scalp-to-cortex distance were analyzed, concluding that those which ignore the electromagnetic field-tissue interactions lead to inaccurate conclusions. Ultimately, the precise site and population of neural elements stimulated by TMS in an atrophic brain cannot be predicted based on healthy head models which ignore the effects of the altered cortex on the stimulating currents. Clinical applications of TMS should be carefully considered in light of these findings.

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Section: Mri Guided Finite Element Head Modelmentioning

confidence: 99%

Transcranial magnetic stimulation and brain atrophy: a computer-based human brain model study

et al. 2008

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“…This type of response was termed anomalous low frequency dispersion (LFD) by Jonscher [9] since it commonly appears as the lowest frequency dispersion process observed, however the theoretical q-dc mechanism of Dissado and Hill [7] is not restricted to such low frequency for its operation [10] as it depends upon the speed of the charge carriers on restricted paths. The q-dc mechanism exhibits a characteristic (or threshold) frequency ω c that defines the cross-over between a high frequency range where charge carriers are bound together as dipoles giving only a weak dispersion, and a low frequency range where the charge carriers become free to move along the restricted paths.…”

Section: Dielectric Response Models Of Oil-paper Insulationmentioning

confidence: 99%

Charge transport in thermally aged paper impregnated with natural ester oil

Abdelmalik

Dodd

Dissado

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link ABSTRACTSamples of a dried composite oil-paper system were thermally aged in the laboratory under N 2 in a sealed container and analysed using their dielectric response. The contributing loss processes were separated using an equivalent circuit model containing constant high frequency capacitances, dc-conductances, a dispersive capacitance, and a low frequency quasi-dc (q-dc) dispersion process as circuit elements. This low frequency dispersion in oil-paper samples is a bulk property of the system that is often mistaken for a dc conduction process when only the imaginary capacitance or acconductance is measured. The Dissado-Hill response function is proposed for the frequency dependence of the dispersive capacitance in the mid-frequency range rather than the Debye function because its cluster concepts correlate with the sample morphology of a matrix of oil-filled cavities. The quasi-dc dispersion is assigned to the transport of mobile charges between charge-clusters associated with locally connected oil filled cavities, which is a process that can be represented on a global scale by the form of hierarchical circuit system that leads to constant phase angle responses, and is here modelled by the Dissado-Hill q-dc function. It was found that the two dispersions moved together to higher frequency with thermal ageing of the composite material. The characteristic frequency common to the dispersions had an activation energy that decreased with thermal ageing, whereas their amplitude increased. This behaviour is discussed in terms of possible changes to the oil-paper composite caused by the ageing process.

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“…According to Nivikov et al [226], this type of hierarchical relaxation process should lead to a CC or HN relaxation behaviour. However, more details about the microscopic geometry of pressboard insulation are required to confirm whether this type of relaxation exists in the frequency band of our interest (10 -4 -10 3 Hz) [227].…”

Section: Loss Peak Behaviourmentioning

confidence: 98%

“…He has identified that [227], most of the biological systems are composed of self-similar hierarchal structures on average such that small structural units with their own dielectric responses are embedded in larger units which are themselves embedded in even larger units [227]. The dielectric susceptibility of such material can be characterised by a series of fractional power law similar to eq (6.4).…”

Section: Universal Relaxation Lawmentioning

confidence: 99%

“…In the case of the q-dc process, ωc denotes the rate of charge escape from the cluster and charge transfer to nearby clusters through weakly conducting connections (bonds of a percolation model matrix) [227]. It is accepted that the principal charge transportation mechanism in cellulose is the proton hopping along a percolation network of water molecules and CHOH groups in cellulose polymer.…”

Section: Through Modelling Of Fds Datamentioning

confidence: 99%

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Condition monitoring of biodegradable oil filled transformer

Mudiyanselage¹,

Bandara²

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Natural and synthetic ester insulating oils have higher fire points and excellent biodegradable characteristics. Therefore, in order to reduce the adverse environmental impact and to improve the fire safety of transformers, there is an increasing demand for natural and synthetic ester insulating liquids as a transformer insulating oil. However, present understanding on ageing behaviour of ester oil-paper composite insulation system and knowledge on application of existing condition monitoring tools for ester based insulation systems are inadequate. This impedes the cost effective and reliable field applications of ester insulating oils, particularly application of natural esters. To reduce this knowledge gap, series of controlled ageing experiments are performed in this research project to provide a better and comprehensive understanding on ageing behaviour of ester oil-paper insulation systems. Furthermore, applicability of existing chemical and electrical based condition monitoring techniques for ester oil-paper insulation systems is systematically investigated in this research project.In this thesis, ageing behaviour of dry pressboard insulation in mineral and three different ester insulating oils under simulated transformer operating environment is investigated. Moreover, the ageing behaviour of natural ester-pressboard composite insulation in moisture rich environment is also compared with that of mineral oil-pressboard system. Degree of polymerisation of pressboard samples measured at different ageing interval is used in this research to determine the ageing condition of pressboard. Moreover, applicability of oil related diagnostic parameters such as concentration of dissolved furanic compounds, acidity value, Dielectric Dissipation Factor (DDF), viscosity and colour to assess the degree of degradation of both ester and mineral insulating oils is thoroughly investigated in this research project. The potential of FTIR (Fourier Transform Infrared spectroscopy) techniques for characterising the degree of degradation of paper insulation is also discussed in this thesis. In addition, this thesis concentrates on characterisation of the charge dynamic in insulating oil through modelling of their dielectric responses.The comparison of gassing behaviour of ester and mineral insulating oils under two different low temperature faults and low energy electric discharge condition is also presented in this thesis.Dissolved Gas Analysis (DGA) results presented in this thesis depicts that faults gases detected in ester and mineral oil samples subjected to a similar fault are akin in type but quantitatively different. The quantity of fault gases produced in two different natural ester oils is also dissimilar.For example, soy-based natural ester produces a large quantity of ethane (C2H6) under low temperature overheating condition than sunflower oil based natural ester. Therefore, this research project investigates the applicability of well-established DGA interpretation schemes namely Duval II | P a g e triangle, IE...

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A fractal interpretation of the dielectric response of animal tissues

Cited by 65 publications

References 37 publications

Transcranial magnetic stimulation and brain atrophy: a computer-based human brain model study

Transcranial magnetic stimulation and brain atrophy: a computer-based human brain model study

Charge transport in thermally aged paper impregnated with natural ester oil

Condition monitoring of biodegradable oil filled transformer

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