Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2002-03-19
2004-08-10
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S607000, C324S658000
Reexamination Certificate
active
06774643
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to determining a state of a dielectric material by determining a similarity or dissimilarity between: (a) a derived set of impedance values obtained from signals output by a capacitor having the dielectric material therein, and (b) one or more predetermined sets of impedance values, each such set indicative of a possible state for the dielectric material. In particular, each of the derived and predetermined sets has impedance values for a common plurality of electrical frequencies used to excite the capacitor. Each of the sets is presumed to correspond to a time interval that is sufficiently short so that the dielectric material is expected to remain in substantially the same state during the time interval.
BACKGROUND OF THE INVENTION
In many circumstances the quality of material(s), and/or the evaluation of a process of manufacturing material(s) can be determined by the unique responses of the material(s) to electrical currents flowing therethrough. In particular, electrical impedances of such a material(s) may be used to identify changes and/or differences in the dielectric of the material(s). Thus, during a manufacturing process, the monitoring of dielectric changes of a manufactured item has been used to determine whether the manufacturing process is producing items having desired characteristics. For example, in U.S. Pat. No. 5,219,498 by Keller et al., composite materials having fibers impregnated with polymeric matrices are cured or thermoformed in a heating system. While the composite material is curing, capacitance and conductance samplings are taken, over an extended time, and the shape or geometric characteristics of the curve(s) generated by the samples (e.g., topographical features) are used to determine whether the curing process is progressing as expected, or whether appropriate modifications to the process need to be timely introduced for yielding a high quality product from the curing process. For example, a rule base is used to identify such geometric curve characteristics. In particular, the Keller patent attempts to identify geometric curve characteristics such as peaks, valleys, flats, rises and falls, and if identified, then those geometric characteristics are used to determine the state or condition of the dielectric material. Accordingly, complex pattern matching techniques can be required to identify such geometric curve characteristics. Additionally, sampling frequency adjustments can be required to detect such relative curve characteristics. For example, the time sale can be critical in the Keller patent since it is concerned with, e.g., rates of change and whether such changes are negative or positive, or changing between negative and positive. Thus, substantial time and/or computational resources can be expended in determining a similarity between actual and desired geometric curve characteristics.
In many contexts, however, it is desirable to determine the state of a dielectric material by directly comparing capacitive and/or conductive response values to corresponding reference capacitive and/or conductive values for one or more electrical frequencies. Moreover, it is desirable to determine state capacitive and conductance (i.e., impedance) information regarding a dielectric material in substantially real-time and/or with reduced computational capabilities. Furthermore, it is desirable to determine such state information without concern for timing adjustments needed for matching geometric characteristics determined over an extended time period. Thus, it would be desirable to have a simpler, more efficient and substantially non-time scale dependent system for using dielectric related values of a material to thereby determine a state or condition of the material, and in particular, for a material whose condition needs to be determined in substantially real-time.
SUMMARY OF THE INVENTION
The present invention is a method and system for identifying a condition or state of a dielectric material (such as an, item of manufacture, or substance) by analyzing a “signature” of impedance related values for the dielectric material, wherein the values are derived from impedances of a range of one or more electrical frequencies applied to the dielectric material, and subsequently the values are compared to one or more sets of reference values. For example, such dielectric materials may include vulcanizates, resins, lubricating fluids, water, medical solutes, pharmaceuticals, and bulk chemicals such as isocyanates, polyurethanes, formaldahydes, epoxies, and phenolics that may be evaluated with the present invention for thereby: (a) changing a production process, (b) determining a contaminant level of such a dielectric material, or (c) identifying that a desired characteristic exists in the dielectric material.
The present invention determines such an impedance signature as a collection of discrete conductivity and capacitance values for each of a plurality of frequencies, wherein each of the values is obtained substantially simultaneously from a dielectric material being analyzed. Accordingly, the resulting impedance signature is similar to a “barcode”, in that, for each frequency applied to the dielectric material, at least one of a conductivity and a capacitance (i.e., impedance) related value is obtained. Accordingly, for determining a state or condition of the dielectric material, the barcode analogy for such impedance signatures may be even further strengthened by representing each of the impedance related values as a value on a common predetermined impedance scale. Moreover, the resulting aggregate collection of impedance related values are compared to one or more predetermined such impedance barcodes having corresponding conductivity/capacitance related values for the same frequencies, wherein each such predetermined impedance barcode includes or identifies impedance related values indicative of a corresponding possible condition or state of the dielectric material. Thus, an impedance barcode obtained from the dielectric material may be compared with one or more of the predetermined impedance barcodes for determining similarities and/or differences between the barcodes. Thus, instead of determining a condition of a dielectric material by identifying and comparing geometric characteristics (e.g., peaks, valleys, rises, falls, etc.) of a curve obtained from pairs of points (t, imp), where imp is an impedance value and t is a corresponding sampling time, the present invention compares, for each of one or more of electrical frequencies: (a) one or more corresponding values, v, related to actual impedance responses obtained from the dielectric material being assayed with (b) one or more corresponding predetermined or designated impedance values V
r
that serve as reference values. Note, that unless otherwise stated, the terms “predetermined impedance value” and “designated impedance value” will be used interchangeably. The meaning intended by both terms is the combination of their meanings; i.e., a predetermined or designated impedance value that serves as a reference value for comparing with a derived impedance value for the same frequency.
More generally, an apparatus embodying the present invention can be characterized as having the following components (1.1) through (1.5) following:
(1.1) a repository for storing, for each of one or more predetermined possible states for a dielectric material, a corresponding set of designated impedance related values for the dielectric material, wherein for each of a plurality of electrical frequencies, one of said designated impedance related values is provided in said corresponding set, such that said designated impedance related values of said set are collectively indicative of the predetermined possible state of the dielectric material;
(1.2) a capacitor having first and second spaced apart capacitor plates and a dielectric material therebetween;
(1.3) a signal generator and a load resistor electrically connected in series to said first capacitor plate for exci
Le N.
Sheridan & Ross P.C.
Signature Control Systems
Teresinski John
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