An apparatus for presenting a sample comprising a plurality of sample particles to a scanning field defined by a sensor device, the apparatus comprising: a first rotating surface configured to rotate about a central axis in a first direction; a second rotating surface, characterized in that the second rotating surface is disposed radially inward from the first rotating surface and configured to rotate about the central axis in a second direction opposite the first direction, the second rotating surface comprising an inner wall member extending substantially vertically from a radially-inward edge of the second rotating surface; and by: a dividing member fixedly disposed radially between the first rotating surface and the second rotating surface, the dividing member having an entrance end and an exit end, the dividing member being configured to cooperate with the second rotating surface and the inner wall member thereof to define a scanning chamber configured to contain at least a portion of the scanning field of the sensor device; an entrance gate disposed adjacent to the entrance end of the dividing member, the entrance gate disposed substantially vertically with respect to the first rotating surface and configured for directing the sample from the first rotating surface to the second rotating surface and into the scanning chamber; and an exit gate disposed adjacent to the exit end of the dividing member, the exit gate disposed substantially vertically with respect to the second rotating surface and configured for directing the sample from the second rotating surface to the first rotating surface and out of the scanning chamber, such that the plurality of sample particles of the sample are reoriented relative to the scanning field defined by the sensor device as the sample is directed into and out of the scanning chamber. a first rotating surface configured to rotate about a central axis in a first direction; a second rotating surface, characterized in that the second rotating surface is disposed radially inward from the first rotating surface and configured to rotate about the central axis in a second direction opposite the first direction, the second rotating surface comprising an inner wall member extending substantially vertically from a radially-inward edge of the second rotating surface; and by: a dividing member fixedly disposed radially between the first rotating surface and the second rotating surface, the dividing member having an entrance end and an exit end, the dividing member being configured to cooperate with the second rotating surface and the inner wall member thereof to define a scanning chamber configured to contain at least a portion of the scanning field of the sensor device; an entrance gate disposed adjacent to the entrance end of the dividing member, the entrance gate disposed substantially vertically with respect to the first rotating surface and configured for directing the sample from the first rotating surface to the second rotating surface and into the scanning chamber; and an exit gate disposed adjacent to the exit end of the dividing member, the exit gate disposed substantially vertically with respect to the second rotating surface and configured for directing the sample from the second rotating surface to the first rotating surface and out of the scanning chamber, such that the plurality of sample particles of the sample are reoriented relative to the scanning field defined by the sensor device as the sample is directed into and out of the scanning chamber. a dividing member fixedly disposed radially between the first rotating surface and the second rotating surface, the dividing member having an entrance end and an exit end, the dividing member being configured to cooperate with the second rotating surface and the inner wall member thereof to define a scanning chamber configured to contain at least a portion of the scanning field of the sensor device; an entrance gate disposed adjacent to the entrance end of the dividing member, the entrance gate disposed substantially vertically with respect to the first rotating surface and configured for directing the sample from the first rotating surface to the second rotating surface and into the scanning chamber; and an exit gate disposed adjacent to the exit end of the dividing member, the exit gate disposed substantially vertically with respect to the second rotating surface and configured for directing the sample from the second rotating surface to the first rotating surface and out of the scanning chamber, such that the plurality of sample particles of the sample are reoriented relative to the scanning field defined by the sensor device as the sample is directed into and out of the scanning chamber.