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Electronic phase comparison apparatus for the remote measurement of layer thickness

  • US 4,075,555 A
  • Filed: 03/25/1977
  • Issued: 02/21/1978
  • Est. Priority Date: 03/25/1977
  • Status: Expired due to Term
First Claim
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1. Apparatus for the remote measurement of the thickness of n layers in a dielectric target where n ≧

  • 1, comprising;

    transmitter means having n + 1 single frequency channels for directing n + 1 related frequency signals to the target; and

    receiver means for receiving the n + 1 signals from the target, said receiver means including first means for converting the signals to a common frequency and second means for comparing the phase of pairs of the converted signals for determining the thicknesses l of the n layers as a function of the phase differences where l <

    λ

    /4, λ

    being the shortest wavelength of the difference frequency between the related n + 1 signals.

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