Electromagnetic detection of an embedded dielectric region within an ambient dielectric region

• US 6,064,903 A
• Filed: 12/28/1998
• Issued: 05/16/2000
• Est. Priority Date: 12/29/1997
• Status: Expired due to Fees

• Current Assignee: Spectra Research, Inc.
• Original Assignee: Spectra Research, Inc.
• Inventors: Pasala, Krishna Murthy, Riechers, Ronald George
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US09/221,337
• Time in Patent Office: 505 Days
• Field of Search: 600/407, 600/430, 324/637, 324/638, 324/629, 324/633, 324/642
• US Class Current: 600/407
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/0507 using microwaves or terahertz waves
• CPC Class Codes: G06F 2218/22 Source localisation; Inverse modelling

Abstract

A system for and method of electromagnetically detecting an embedded dielectric region within a target object are provided. The method includes the steps of: (i) selecting a target object including a plurality of discrete scattering mediums, wherein the plurality of discrete scattering mediums include the embedded dielectric region and an adjacent dielectric region, and wherein the plurality of discrete scattering mediums define at least one dielectric interface between the embedded dielectric region and the adjacent dielectric region; (ii) directing electromagnetic radiation at the target object, wherein the electromagnetic radiation is characterized by a diagnostic frequency that is varied incrementally over a diagnostic frequency band; (iii) detecting electromagnetic radiation reflected by the target object over the predetermined frequency band such that there are M measurements of a reflected electromagnetic signal at frequencies f₁, f₂, . . . , f_N, where M represents a number of scattering mediums within the target object and where N represents a number of diagnostic frequencies within the diagnostic frequency band; (iv) constructing a correlation matrix representative of the reflected signal, wherein the correlation matrix comprises a number of signal eigenvectors and a number of noise eigenvectors; (v) decorrelating the correlation matrix by dividing the reflected signal according to frequency sub-bands within the diagnostic frequency band, wherein adjacent bands of the frequency sub-bands overlap, forming a series of iterated correlation matrices using signal eigenvectors and noise eigenvectors from each of the overlapping frequency sub-bands, forming a decorrelated matrix by averaging the iterated correlation matrices, wherein the decorrelated matrix comprises a finite group of signal eigenvectors and a finite group of noise eigenvectors; and (vi) constructing a scattering signature of the target object from the finite group of signal eigenvectors, wherein the scattering signature is indicative of the properties of the embedded dielectric region and the adjacent dielectric region.

Claims

1. A method of electromagnetically detecting an embedded dielectric region within a target object comprising the steps of:

selecting a target object including a plurality of discrete scattering mediums, wherein said plurality of discrete scattering mediums include said embedded dielectric region and an adjacent dielectric region, and wherein said plurality of discrete scattering mediums define at least one dielectric interface between said embedded dielectric region and said adjacent dielectric region;

directing electromagnetic radiation at said target object, wherein said electromagnetic radiation is characterized by a diagnostic frequency that is varied incrementally over a diagnostic frequency band;

detecting electromagnetic radiation reflected by said target object over said predetermined frequency band such that there are M measurements of a reflected electromagnetic signal at frequencies f₁, f₂, . . . , f_N, where M represents a number of scattering mediums within said target object and where N represents a number of diagnostic frequencies within said diagnostic frequency band;

constructing a correlation matrix representative of said reflected signal, wherein said correlation matrix comprises a number of signal eigenvectors and a number of noise eigenvectors;

decorrelating said correlation matrix by

dividing said reflected signal according to frequency sub-bands within said diagnostic frequency band, wherein adjacent bands of said frequency sub-bands overlap,

forming a series of iterated correlation matrices using signal eigenvectors and noise eigenvectors from each of said overlapping frequency sub-bands,

forming a decorrelated matrix by averaging said iterated correlation matrices, wherein said decorrelated matrix comprises a finite group of signal eigenvectors and a finite group of noise eigenvectors; and

constructing a scattering signature of said target object from said finite group of signal eigenvectors, wherein said scattering signature is indicative of the properties of said embedded dielectric region and said adjacent dielectric region.

2. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said step of constructing said scattering signature incorporates the step of determining a frequency dependent scattering spectrum of selected ones of said discrete scattering mediums.

3. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said scattering signature comprises a signal plot across said diagnostic frequency band.

4. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said reflected electromagnetic signal comprises a real component and an imaginary component, and wherein said scattering signature comprises a plot of said real component across said diagnostic frequency band.

5. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said reflected electromagnetic signal comprises a real component and an imaginary component, and wherein said scattering signature comprises a plot of said imaginary component across said diagnostic frequency band.

6. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said scattering signature comprises a plot of the amplitude of said reflected electromagnetic signal across said diagnostic frequency band.

7. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said method further comprises the step of substantially removing portions of said reflected signal corresponding to predetermined known scatterers, whereby signal portions of interest tend to dominate the construction of said scattering signature.

8. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 7 wherein said portions of said reflected signal corresponding to predetermined known scatterers are substantially removed by constraining the noise eigenvectors to be orthogonal to the signal eigenvectors of known scatterers.

9. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said method further comprises the step of removing portions of said reflected signal corresponding to background scatterers, whereby signal portions of interest tend to dominate the construction of said scattering signature.

10. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 further comprising the steps of:

estimating said number of signal eigenvectors within said reflected signal; and

verifying said number of signal eigenvectors within said reflected signal by plotting an eigenvalue spectrum of said correlation matrix and identifying a set of substantially equal eigenvalues.

11. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein each frequency sub-band differs from an adjacent frequency sub-band in that their respective frequency ranges are incremented relative to one another by an amount equal to the incremental variation of said diagnostic frequency.

12. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said diagnostic frequency band extends from about 0.5 GHz to about 20.0 GHz.

13. A method of electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 1 wherein said diagnostic frequency band extends from about 0.5 GHz to about 6.0 Ghz.

14. A system for electromagnetically detecting an embedded dielectric region within a target object, wherein the target object includes a plurality of discrete scattering mediums, wherein said plurality of discrete scattering mediums include said embedded dielectric region and an adjacent dielectric region, and wherein said plurality of discrete scattering mediums define at least one dielectric interface between said embedded dielectric region and said adjacent dielectric region, said system comprising:

an electromagnetic radiation source configured to direct electromagnetic radiation at said target object, wherein said electromagnetic radiation is characterized by a diagnostic frequency that is varied incrementally over a diagnostic frequency band;

an electromagnetic radiation detector configured to detect electromagnetic radiation reflected by said target object over said predetermined frequency band such that there are M measurements of a reflected electromagnetic signal at frequencies f₁, f₂, . . . , f_N, where M represents a number of scattering mediums within said target object and where N represents a number of diagnostic frequencies within said diagnostic frequency band; and

a data processor configured to

construct a correlation matrix representative of said reflected signal, wherein said correlation matrix comprises a number of signal eigenvectors and a number of noise eigenvectors,

decorrelate said correlation matrix by

dividing said reflected signal according to frequency sub-bands within said diagnostic frequency band, wherein adjacent bands of said frequency sub-bands overlap,

forming a series of iterated correlation matrices using signal eigenvectors and noise eigenvectors from each of said overlapping frequency sub-bands, and

forming a decorrelated matrix by averaging said iterated correlation matrices, wherein said decorrelated matrix comprises a finite group of signal eigenvectors and a finite group of noise eigenvectors; and

construct a scattering signature of said target object from said finite group of signal eigenvectors, wherein said scattering signature is indicative of the properties of said embedded dielectric region and said adjacent dielectric region.

15. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 further comprising a frequency spectrum plotter in communication with said data processor, wherein said data processor is operative to cause said frequency spectrum plotter to display said scattering signature as a frequency dependent scattering spectrum of selected ones of said discrete scattering mediums.

16. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 15 wherein said scattering signature comprises a signal plot across said diagnostic frequency band.

17. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 15 wherein said reflected electromagnetic signal comprises a real component and an imaginary component, and wherein said scattering signature comprises a plot of said real component across said diagnostic frequency band.

18. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 15 wherein said reflected electromagnetic signal comprises a real component and an imaginary component, and wherein said scattering signature comprises a plot of said imaginary component across said diagnostic frequency band.

19. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 15 wherein said scattering signature comprises a plot of the amplitude of said reflected electromagnetic signal across said diagnostic frequency band.

20. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 wherein said data processor is further configured to substantially remove portions of said reflected signal corresponding to predetermined known scatterers, whereby signal portions of interest tend to dominate the construction of said scattering signature.

21. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 20 wherein said data processor is further configured to substantially remove portions of said reflected signal corresponding to predetermined known scatterers by constraining the noise eigenvectors to be orthogonal to the signal eigenvectors of known scatterers.

22. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 20 wherein said data processor is further configured to substantially remove said portions of said reflected signal corresponding to background scatterers, whereby signal portions of interest tend to dominate the construction of said scattering signature.

23. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 wherein said data processor is further configured to:

input an estimate of said number of signal eigenvectors within said reflected signal; and

enable verification of said number of signal eigenvectors within said reflected signal by generating a plot of an eigenvalue spectrum of said correlation matrix.

24. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 wherein said data processor is further configured to select each frequency sub-band such that it differs from an adjacent frequency sub-band in that their respective frequency ranges are incremented relative to one another by an amount equal to the incremental variation of said diagnostic frequency.

25. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 wherein said electromagnetic radiation source is configured to generate said diagnostic frequency band such that it extends from about 0.5 GHz to about 20.0 GHz.

26. A system for electromagnetically detecting an embedded dielectric region within a target object as claimed in claim 14 wherein said electromagnetic radiation source is configured to generate said diagnostic frequency band such that it extends from about 0.5 GHz to about 6.0 GHz.