Patent Document ID: 5521515
Application ID: 08394108
Patent Status: 1

Claim One:
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.