Patent ID: 8829907
Filing Date: 2014-09-09
Classification: G01V

Abstract:
1. An apparatus for estimating a property of an earth formation penetrated by a borehole, the apparatus comprising: a carrier configured to be conveyed through the borehole; a transmitter disposed at the carrier and configured to transmit electromagnetic energy at a first frequency into the formation; a first antenna disposed at the carrier and configured to receive electromagnetic signals from the formation that have characteristics related to the property as a result of the transmitted electromagnetic energy interacting with the formation; an active filter coupled to the antenna and configured to filter electromagnetic signals received by the antenna to let the electromagnetic signals at the first frequency pass for processing to estimate the property; a controller coupled to the transmitter and the filter and configured to direct the transmitter to transmit electromagnetic energy at a second frequency into the formation and to direct the filter to let the received electromagnetic signals at the second frequency pass for processing to estimate the property; wherein: the filter includes an active component configured to amplify the electromagnetic signals passing through the filter; the frequency at which the electromagnetic signals are allowed to pass through the filter is selectable; and the controller is further configured to direct the transmitter to stop transmitting the electromagnetic energy at the first frequency and to direct the filter to stop allowing the received electromagnetic signals at the first frequency to pass.