Frequency scanning capaciflector for capacitively determining the material properties
First Claim
1. Apparatus for capacitively determining the material composition of an object being approached, comprising:
- a capacitive type sensor including a sensor element and at least one shield member located between said object and a reference potential surface, said shield member being of a size substantially larger than said sensor element for reducing the parasitic capacitance between said sensor element and said reference potential surface;
signal generating means for generating a signal varied in frequency over a predetermined frequency range;
circuit means for commonly coupling said signal generator means to said sensor element and said shield member;
means coupled at least to said sensor element for detecting a capacitance vs. frequency characteristic of the capacitance between said sensor element and said object over said frequency range;
means for storing a plurality of capacitance vs. frequency characteristics, each of said characteristics being a respective characteristic of a plurality of different constituent materials; and
means for comparing the detected capacitance vs. frequency characteristic of the capacitance between said sensor element and said object against said plurality of capacitance vs. frequency characteristics for matching and thereby identifying the constituent material of said object.
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Abstract
A capaciflector sensor system scanned in frequency is used to detect the permittivity of the material of an object being sensed. A capaciflector sensor element, coupled to current-measuring voltage follower circuitry, is driven by a frequency swept oscillator and generates an output which corresponds to capacity as a function of the input frequency. This swept frequency information is fed into apparatus e.g. a digital computer for comparing the shape of the capacitance vs. frequency curve against characteristic capacitor vs. frequency curves for a variety of different materials which are stored, for example, in a digital memory of the computer or a database. Using a technique of pattern matching, a determination is made as to the identification of the material. Also, when desirable, the distance between the sensor and the object can be determined.
75 Citations
20 Claims
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1. Apparatus for capacitively determining the material composition of an object being approached, comprising:
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a capacitive type sensor including a sensor element and at least one shield member located between said object and a reference potential surface, said shield member being of a size substantially larger than said sensor element for reducing the parasitic capacitance between said sensor element and said reference potential surface; signal generating means for generating a signal varied in frequency over a predetermined frequency range; circuit means for commonly coupling said signal generator means to said sensor element and said shield member; means coupled at least to said sensor element for detecting a capacitance vs. frequency characteristic of the capacitance between said sensor element and said object over said frequency range; means for storing a plurality of capacitance vs. frequency characteristics, each of said characteristics being a respective characteristic of a plurality of different constituent materials; and means for comparing the detected capacitance vs. frequency characteristic of the capacitance between said sensor element and said object against said plurality of capacitance vs. frequency characteristics for matching and thereby identifying the constituent material of said object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for capacitively determining the material composition of an object, comprising the steps of:
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generating a signal swept in frequency over a predetermined frequency range; coupling said signal swept in frequency to a sensor element and to a shield member of a capaciflector type sensor located between said object and a reference potential surface; detecting a capacitance vs. frequency characteristic of the capacitance between said sensor element and said object over said frequency range; storing a plurality of capacitance vs. frequency characteristics of a plurality of different object materials; and comparing and matching the capacitance vs. frequency characteristic of the capacitance between said sensor element and said object against said plurality of stored capacitance vs. frequency characteristics for identifying the constituent material of said object. - View Dependent Claims (17, 18, 19, 20)
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Specification