Two-dimensional microwave imaging apparatus and methods
First Claim
1. A method of determining electric field properties of an inhomogeneous target, comprising the steps of:
- (A) measuring the electric field external to a boundary that defines the target;
(B) estimating electric property distributions on a coarse mesh discretization of the target; and
(C) computing an electric field on a fine mesh discretization of the target, and at points external to the fine mesh discretization, the fine mesh having finer discretization than the coarse mesh and being overlapping with the coarse mesh.
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Abstract
The invention provides apparatus and methods for determining electric field properties of an inhomogeneous target. The electric property distribution on a coarse mesh discretization of the target is first estimated; and then the electric field on a fine mesh discretization of the target is computed. The fine mesh has finer discretization than the coarse mesh and is overlapping with the coarse mesh. The electric field is then measured at preselected measurement sites within a homogeneous region external to the target. A Jacobian matrix is also calculated which represents a sensitivity calculation relative to a change in the electric field at selected measurement sites due to a perturbation in the electric property distribution on the coarse mesh. A difference vector is formed between the computed electric field and the measured electric field, and an update vector is added to the electrical property distribution as a function of the difference vector and the Jacobian matrix. The electric field is then re-computed based on the updated electric property distribution, which is compared with the measured electric field to produce a least squared error. If this error is not sufficiently small, the steps above, beginning with computing a Jacobian matrix, are repeated until the error is sufficiently small.
183 Citations
32 Claims
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1. A method of determining electric field properties of an inhomogeneous target, comprising the steps of:
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(A) measuring the electric field external to a boundary that defines the target; (B) estimating electric property distributions on a coarse mesh discretization of the target; and (C) computing an electric field on a fine mesh discretization of the target, and at points external to the fine mesh discretization, the fine mesh having finer discretization than the coarse mesh and being overlapping with the coarse mesh. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A system for imaging electrical properties of a target, comprising:
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a chamber for surrounding the target and having an outer core that has substantially homogeneous electrical properties; a plurality of antennas disposed within the core for transmitting and alternately receiving microwave energy within the range of about 300 Mhz to 1100 Mhz, initialization means for estimating the electrical property distribution of the target; e-field computation means for computing an electric field at a fine mesh discretization of the target and at selected locations within the core; e-field measurement means for measuring the electric field within the core; difference vector means for determining a difference vector between the measured and computed electric fields; Jacobian matrix means for forming a Jacobian matrix, each entry of the Jacobian matrix being a sensitivity calculation of the change in electric field at a measurement site due to a perturbation in the electrical property at a discretization node on a coarse mesh; update vector means for determining an update vector as a function of the Jacobian matrix and the difference vector and for updating the electrical property distribution with the update vector; and comparing the measured and computed electric fields as a function of a predetermined metric.
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Specification