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Distributed impedance sensor

  • US 7,340,951 B2
  • Filed: 11/04/2005
  • Issued: 03/11/2008
  • Est. Priority Date: 11/04/2005
  • Status: Expired due to Fees
First Claim
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1. An apparatus for measuring at least one parameter of a variable physical structure, comprising:

  • a sensing element placed in proximity to the variable physical structure, the sensing element having a length, the sensing element formed of at least two electrically conductive members, at least two of the conductive members electrically insulated from one another, forming first and second sensing electrodes;

    the sensing element having a sensing capacitance between at least the first and second sensing electrodes, the sensing capacitance approximately distributed along the length of the sensing element;

    a variation in at least one of the measured parameters causing a variation of the sensing capacitance, the variation of the sensing capacitance being representative of the variation in the measured parameter;

    the first sensing electrode forming a first inductance, the second sensing electrode forming a second inductance, the first and second inductances approximately distributed along the length of the sensing element;

    at least two of the sensing electrodes excited with an alternating current at an operating frequency, first and second inductances having first and second inductive reactances, respectively, at the operating frequency, the sensing capacitance having a capacitive reactance at the operating frequency;

    the first inductive reactance being at least ten percent of the capacitive reactance, and the second inductive reactance being at least ten percent of the capacitive reactance.

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