Dielectric Properties of lce
A laboratory study of the dielectric behaviour of single crystals of ice from a temperate glacier and ice cores from the Greenland ice cap is described. A field investigation of the properties of snow on Axel Heiberg Island (Arctic Canada) is discussed. The permittivity of ice in the HF and VHF rang...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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University of Cambridge
1970
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| Online Access: | https://www.repository.cam.ac.uk/handle/1810/280152 https://doi.org/10.17863/CAM.27518 |
| Summary: | A laboratory study of the dielectric behaviour of single crystals of ice from a temperate glacier and ice cores from the Greenland ice cap is described. A field investigation of the properties of snow on Axel Heiberg Island (Arctic Canada) is discussed. The permittivity of ice in the HF and VHF range is deduced to be 3.20 + 0.07 at -40°c and a small temperature coefficient is found, consistent with theoretical ideas. The temperate glacier ice has a low dielectric loss: the same as the lowest loss single crystals grown in the laboratory. The absence of impurity spectra and dislocation spectra is due to the lengthy process of strain annealling in temperate glaciers. Measurements of dielectric loss in Greenland ice and in Axel Heiberg snow confirm earlier data and, by studying the results of fourelectrode resistivity surveys of glaciers, it is concluded that the measurements are typical of many natural ice mass,es. The solubility limit for impurities within the ice grain is responsible for the behaviour. Near the melting point however, other effects occur, attributable to impurities which remain in the grain boundaries. It is possible that these results do not apply to the centre of large ice sheets, where sea salt impurity concentrations are lower than the solubility limit, or to strongly deformed cold ice. The electrical behaviour of artificially doped ices is shown to be related to the behaviour of Greenland ice cores. Further evidence of the effect of impurities is found from literature reviews: of the dielectric behaviour of sea ice and of the DC resistivity of glaciers. The theory of heterogeneous dielectrics is also reviewed and the results are used -to interpret the observed relaxation spectrum of snow. The free ice-air surfaces in snow have no effect on the audio frequency relaxation spectrum. Digitisation of this thesis was sponsored by Arcadia Fund, a charitable fund of Lisbet Rausing and Peter Baldwin. |
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