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Sensor for determining the electric properties of a sample

  • US 7,777,504 B2
  • Filed: 10/20/2005
  • Issued: 08/17/2010
  • Est. Priority Date: 11/26/2004
  • Status: Expired due to Fees
First Claim
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1. An apparatus for determining properties of a sample, the apparatus comprising:

  • a first probe having an input, an output and two conductors uncoated with any electrically insulative material, and the first probe having an effective capacitance and an effective resistance;

    a second probe having an input, an output and two conductors coated with an electrically insulative material, and the second probe having an effective capacitance and an effective resistance;

    a pulse generator, for producing square pulses, being connected to the input of the first probe and the input of the second probe, such that the square pulses are produced at the input of the first probe and the second probe, each square pulse having a constant voltage and a period of sufficient duration to allow a voltage across the effective resistance and the effective capacitance of the two conductors of the first probe and the effective resistance and the effective capacitance of the two coated conductors of the second probe to reach steady state;

    a measuring device being connected to the output of the first probe and the output of the second probe and configured to output a representation of the properties of a sample based on the effective resistance and the effective capacitance of the first probe and the second probe; and

    a capacitive element that acts as a simple integrator and a resistive element in series the capacitive element, such that the effective resistance Reff is estimated using formula Reff=[(Vapplied

    V)−

    1]R, and such that the effective capacitance Ceff is estimated using C eff = - ln

    [ V C

    ( t )
    / V max
    ]
    t / R discharge
    ,
    where Vapplied is the voltage of the square pulse, Δ

    V is the steady state voltage of the resistive element R is the resistance of the resistive element, Vc(t) is the voltage response of the capacitive element, Vmax is the voltage of the square pulse less Δ

    V, t is the time required to discharge the capacitor after the square pulse, and Rdischarge=[R·

    Reff/(R+Reff)].

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