Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2000-07-14
2002-10-08
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S333000, C324S369000, C175S045000
Reexamination Certificate
active
06462561
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The present invention relates to the nondestructive testing or evaluation of physical properties of materials, more particularly to methods and apparatuses for accomplishing near-field inspection of materials, such as involving utilization of microwave radiation in association with materials such as metallic or composite materials.
Various kinds of near-field microwave inspection have been conducted with respect to various kinds of structures (e.g., composite or metallic structures) having an extended surface area. Generally, a near-field probe (for example, a open-ended rectangular waveguide probe or an open-ended coaxial probe) is used in conventional practice of near-field microwave inspection. Typically, the microwave inspection inherently incorporates or assumes a “standoff distance” or “liftoff” of the near-field probe in relation to the surface area of the material being inspected.
The measurement results are usually sensitive to the changes in this standoff distance. Sometimes a change in the standoff distance is related to variation in surface roughness (or, synonymously expressed, surface height). For instance, in the case of glass reinforced epoxy composites, the change in the standoff distance can be caused by surface roughness/height variations in the composite skin.
It is generally important to distinguish between or among various types of defects. For instance, in the case of a composite laminate, it may be desirable that an internal defect such as a layer-layer disbond be distinguished from a defect on the surface such as related to impact damage. In order to differentiate between or among internal and external defects, the influence of standoff distance variation must somehow be accounted for.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for effectuating near-field microwave nondestructive testing of an object in such a way as to more capably distinguish between internal physical characteristics and external physical characteristics.
The present invention features the neutralization of the effect of surface variation of the object in the context of near-field sensing. Provided by the present invention is a circuit which accounts for standoff distance variation and eliminates its influence from the final inspection system output. The inventive compensatory and equalizing circuit has been designed and successfully tested by the U.S. Navy and Colorado State University in association with open-ended rectangular waveguide probes.
According to typical embodiments of the present invention, the inventive apparatus is used in association with a sensing device which is capable of producing a nonconstant device signal for inspecting an object. The sensing device's nonconstant device signal varies in accordance with the distance of the sensing device from the object. The inventive apparatus comprises means for rendering the sensing device capable of producing a constant device signal at least until reaching said object, wherein the constant device signal is constant regardless of the distance.
According to many inventive embodiments, the inventive means for rendering includes: means for producing a nonconstant counteractive output signal, the nonconstant counteractive signal varying in accordance with the distance; means for modifying the nonconstant device signal so as to become a nonconstant modified device signal which is commensurate with the nonconstant counteractive signal; and, means for combining signals, the means for combining signals including means for combining the nonconstant counteractive signal and the nonconstant modified device signal. The constant device signal is based on the combining of the nonconstant counteractive signal and the nonconstant modified device signal.
According to frequently preferred inventive practice, the inventive means for rendering also includes means for producing a constant offset signal. Thus, the means for combining signals includes means for combining the nonconstant counteractive signal, the nonconstant modified device signal and the constant offset signal. The constant device signal is based on the combining of the nonconstant modified device signal, the nonconstant counteractive signal and the constant offset signal.
In typical inventive practice, the nonconstant device signal, the nonconstant modified device signal and the nonconstant counteractive each vary linearly according to distance. Frequent inventive practice prescribes such linear variation in terms of voltage value. The “constancy” characteristic of both the constant device signal and the the constant offset signal presupposes a nonvarying linearity of each constant signal, freqently manifested in inventive practice as a constancy (i.e., single-valued linearity or invariability) in voltage value. In contrast, the “nonconstancy” characteristic of the nonconstant device signal, the nonconstant modified device signal and the nonconstant counteractive signal entails a varying linearity of each nonconstant signal, frequently manifested in inventive practice as a nonconstancy (i.e., plural-valued linearity or linear variability) in voltage value.
Usually, the nonconstant device signal varies linearly in accordance with the standoff distance; however, the inventive principles are still applicable whether the nonconstant device signal varies linearly or nonlinearly in accordance with the standoff distance. In fact, the present invention can be practiced regardless of whether the nonconstant device signal, the nonconstant modified device signal and the nonconstant counteractive signal vary linearly or nonlinearly according to distance. If, for instance, the initial voltage output varies as a nonlinear function of standoff distance, according to this invention a counterbalancing voltage output can be effected which equally but oppositely varies as a nonlinear function of standoff distance. Similarly, if the initial voltage output varies as a linear function of standoff distance, according to this invention a counterbalancing voltage output can be effected which equally but oppositely varies as a linear function of standoff distance.
Featured by the present invention is the provision of a voltage commensurate with the inspected material's surface roughness, and the addition of such provided voltage to, or the subtraction of such provided voltage from, the voltage detected by the microwave detector. In other words, according to this invention, a voltage is provided which is proportional to the surface roughness and is then added to or subtracted from the voltage detected by the microwave detector; such proportionality of voltage with respect to surface roughness can equivalently be considered to be a proportionality of voltage with respect to standoff distance. In this way, the present invention renders the final output voltage independent of surface roughness variations, which are typically slight but which can manifest diverse degrees and kinds of irregularity.
A near-field microwave device typically produces a voltage output signal which is a linear function of standoff distance. According to the present invention, potentiometer circuitry is provided to produce a voltage output signal which is a linear function of standoff distance, but which is oppositely sloped in comparison with the voltage output signal of the microwave device. Thus, if the microwave device's voltage output linearly increases in accordance with standoff distance, the inventive potentiometer circuitry's voltage output linearly decreases in accordance with standoff distance; on the other hand, if the microwave device's voltage output linearly decreases in accordance with standoff distance, the inventive potentiometer circuitry's voltage
Bigelow Timothy A.
Brown Lawrence M.
Qaddoumi Nasser Nidal
Zoughi Reza
Kaiser Howard
Nguyen Trung Q.
Sherry Michael
The United States of America as represented by the Secretary of
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