2014-08-222014-08-222006-01-17BARBOSA, Antônio Vinícius Corrêa. Avaliação de métodos eletromagnéticos aplicando campos polarizados e focalizados. 2006. 80 f. Tese (Doutorado) - Universidade Federal do Pará, Centro de Geociências, Belém, 2006. Curso de Pós-Graduação em Geofísica.https://repositorio.ufpa.br/handle/2011/5468In the near surface investigations employing advanced electromagnetic induction methods, the low induction number – LIN targets produce very low anomalies which are difficult to interpret. To overcome this difficulty, in this thesis I have studied the applicability of the Polarized Focused Electromagnetic – POLFOCEM fields as a primary inductive source. The horizontal end vertical E.M. field polarizations are obtained by the vectorial combinations of the fields due to the coil pairs in the central region between them; and the focalization occurs in this region at a depth 0.25 of the spacing between the transmitting coils – L. Therefore, maximum coupling can be obtained by selecting the field polarizations depending upon the geometry of the target and focusing the magnetic flux on it by varying L; consequently producing higher anomalies. This study has been realized by computing anomalies employing the Finite Element Technique for 2.5D problem. In all these numerical experiments a comparative qualitative and quantitative study has been done between the POLFOCEM anomalies and the conventional system anomalies where only one transmitter is used (dipole-dipole system). The POLFOCEM system anomalies, wherein both transmitters T1 and T2 are energized simultaneously, correspond to the sum of the anomalies produced by the T1-R and R- T2 dipoles independently; obeying in this way the linearity the electromagnetic fields. These numerical experiments have been carried out for a bidimensional prismatic model in a resistive half-space at three different inclinations and using radio frequencies. The asymmetrical anomalies obtained in a conventional coil system become symmetrical in POLFOCEM system, and have their amplitudes reduced in relation to that of the conventional system. On the other hand conventional anomalies, symmetrical or asymmetrical, become anti-symmetrical in POLFOCEM, and have their amplitude increased. As a consequence, the Argand diagrams of LIN targets for conventional coil system suffer respectively anticlockwise or clockwise rotation for POLFOCEM system. The experiments, to verify the quality in identifying the two nearby targets, shows that the conventional system is superior in relation to the POLFOCEM system.porAcesso AbertoProspecção - Métodos geofísicosMétodo eletromagnéticoAnomaliasModelagem numéricaMétodo dos elementos finitosTeseCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOFISICA::GEOFISICA APLICADA