Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1998-12-30
2001-01-09
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S642000
Reexamination Certificate
active
06172510
ABSTRACT:
BACKGROUND OF THE INVENTION
The detection and evaluation of structural flaws by non-destructive use of radiation is generally known in the art, including use of microwave radiation exhibiting certain advantages over other forms of radiation such as x-ray, ultrasound and thermography radiation. Such uses of microwave radiation include emission and reflection of the radiation after interaction with the targeted material for detecting the presence or absence of a defect therein. Microwave radiation types of defect detection systems heretofore involved one or more antennas for emission of the radiation and reception of reflective radiation. Some of the advantages over the use of other forms of radiation include, avoiding use of a couplant and heat diffusion means, increasing depth of detection and avoiding the provision of radiation hazard prevention. It is therefore an important object of the present invention to enlarge evaluation of structural flaws by the advantageous use of microwave radiation as disclosed in connection with the embodiment covered in the aforementioned prior copending parent application, Ser. No. 08/798,683 now U.S. Pat. No. 5,859,535. According to the disclosure in such prior copending parent application, detection location and sizing of an internal defect in a thick non-metallic material or composite is achieved by isolating in time reflections of microwave radiation from external surfaces using Fourier transformation of frequency domain data applied in a straight forward manner.
SUMMARY OF THE INVENTION
In accordance with the present invention, microwave radiation is both transmitted from and received by one antenna positioned and orientated to transmit and receive microwave energy along an oblique angle from the surface normal of a targeted material at a focus location from which reflected radiation originates in order to identify and evaluate defects from measurement of the microwave radiation. Evaluation of structural flaws is thereby achieved through calculations based on readings of radiation measurement data with respect to a single radiation path, pursuant to techniques constituting an extension of the approach set forth in the aforementioned prior copending parent application, wherein reflection from a defect is not completely separated in time with respect to reflection originating from some interfaces in the material structure being targeted. By use of gating techniques, generally known in the art, the data on reflections from boundaries or interfaces are excluded from data on reflections originating from targeted defects of interest in accordance with the present invention. The new approach or technique of the present invention involves utilization of frequency domain response from either an internal thin layer or an external surface of the targeted structure after a reverse Fourier transformation is applied to the time domain for return of gated reflection to the frequency domain. Such new technique is based on the defect induced changes in the resonances of the material layer in question in the frequency domain. This new approach is also applicable to cases wherein the signals originated from material interfaces near the defect are not completely excluded from the defect signal by time gating.
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Forrest John
Metjahic Safet
Nguyen Vincent Q.
Shuster Jacob
The United Sates of America as represented by the Secretary of t
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