Loop antenna circuit useful in subterranean tool
First Claim
1. A loop antenna circuit for use in a borehole, comprising:
- a loop antenna disposed to generate, in response to an electromagnetic wave, a pick-up signal on an output node thereof; and
a tuning network coupled to the loop antenna, the tuning network disposed to provide simultaneous tuning at a plurality of interrogation frequencies.
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Accused Products
Abstract
A loop antenna useful, for example, in investigation of earth formations. Embodiments of the invention provide a loop antenna circuit comprising a loop antenna disposed to generate, in response to an electromagnetic wave, a pick-up signal on an output node. Loop antenna circuit further includes a tuning network coupled to the loop antenna. The tuning network is disposed to provide simultaneous tuning at a plurality of interrogation frequencies. Further embodiments include a preamplifier circuit coupled to the loop antenna. The preamplifier circuit is disposed to receive the pick-up signal on an input node and provide a high impedance load to the loop antenna for a first of the plurality of interrogation frequencies to reduce the secondary radiation from the loop antenna to below a predetermined value at the said first interrogation frequency.
81 Citations
41 Claims
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1. A loop antenna circuit for use in a borehole, comprising:
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a loop antenna disposed to generate, in response to an electromagnetic wave, a pick-up signal on an output node thereof; and
a tuning network coupled to the loop antenna, the tuning network disposed to provide simultaneous tuning at a plurality of interrogation frequencies. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A loop antenna circuit for use in a borehole, comprising:
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a loop antenna disposed to generate, in response to an electromagnetic wave, a pick-up signal on an output node thereof, the pick-up signal representative of, for each of a plurality of interrogation frequencies, relative magnitude and relative phase of the electromagnetic wave; and
a tuning network coupled to the loop antenna, the tuning network configured so that a combined source impedance of the loop antenna and the tuning network maximizes the pick-up signal for each of a preselected narrow band of frequencies surrounding each of the plurality of interrogation frequencies, the tuning network further configured so that said combined source impedance attenuates frequencies that are out-of-band. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A tool for measuring attributes of sections of an earth formation surrounding borehole, comprising:
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a housing adapted to be deployed within a borehole;
a transmitter deployed on the housing, the transmitter disposed to selectively generate an electromagnetic wave into the earth formation, the electromagnetic wave including a plurality of interrogation frequency components;
a first receiver loop antenna deployed on the housing, the first receiver loop antenna spaced apart from the first transmitter, the first receiver loop antenna disposed to generate, in response to the electromagnetic wave, a first pick-up signal on an output node thereof, the first pick up signal representative of relative magnitude and relative phase of the electromagnetic wave for each of the plurality of interrogation frequency components; and
a tuning network coupled to the first receiver loop antenna, the tuning network configured so that a combined source impedance of the first receiver loop antenna and the tuning network maximizes the pick-up signal for a preselected narrow band of frequencies surrounding each of the plurality of interrogation frequencies, the tuning network further configured so that said combined source impedance attenuates frequencies that are out-of-band. - View Dependent Claims (26, 27, 28)
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29. A method for processing an electromagnetic wave, comprising:
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(a) receiving, via a receiver loop antenna, an electromagnetic wave having a plurality of interrogation frequency components;
(b) selecting, simultaneously, the plurality of interrogation frequency components of the electromagnetic wave to the exclusion of other frequencies; and
(c) generating a pick-up signal that is representative of the relative magnitude and phase of each of the plurality of interrogation frequency components. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36)
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37. A method for evaluating formations surrounding a borehole, comprising:
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(a) selectively radiating, via a transmitter, an electromagnetic wave including at least a first and second interrogation frequency components;
(b) receiving the electromagnetic wave via a first loop antenna that is spaced apart from the transmitter;
(c) selecting, simultaneously, the first and second of interrogation frequency components as received by the first loop antenna to the exclusion of other frequencies;
(d) receiving the electromagnetic wave via a second loop antenna that is spaced apart from both the transmitter and the first loop antenna; and
(e) selecting, simultaneously, the first and second interrogation frequency components as received by the second loop antenna to the exclusion of other frequencies. - View Dependent Claims (38, 39, 40, 41)
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Specification