NonIntrusive Permittivity Measurement Using Resonant Waveguides

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Non-Intrusive Permittivity Measurement Using
Resonant Waveguides

• Ilker R Capoglu 07/15/2004

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Contents

• Introduction
• Permittivity
• Resonance
• Basic Idea
• Method
• Real Part of the Permittivity
• Imaginary Part of the Permittivity
• Conclusion

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Introduction

• What is the permittivity of a material?

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Permittivity

• Permittivity is generally
• a complex quantity

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Permittivity Resonance

• The resonance phenomenon will be used for
  permittivity measurement
• What is resonance?

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Resonance

• Every structure has intrinsic frequencies.
• Guitar string
• Automobile
• Empire States Building
• Tacoma Narrows Bridge (1940)

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Resonance

• When the external forcing frequency matches any
  of the intrinsic frequencies

Resonance occurs!
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Resonance

• There are two resonance properties

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Basic Idea

• The resonance properties are very sensitive to
  the properties of the surrounding material
• Therefore, they are also sensitive to
  permittivity
• The resonance properties can be used to measure
  the permittivity!

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Method

• A resonant waveguide is used

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Method

• The resonant waveguide has significant
  advantages
• It is non-intrusive.
• It radiates minimally (with high e1).
• It can operate at higher frequencies than the
  coaxial probe does.

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Method

• Basic Idea
• Excite medium I
• Measure resonant properties
• Estimate permittivity in medium II

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Method
Permittivity
It is theoretically possible to

• Measure resonant frequency, and

Measure resonant bandwidth, and
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Real Part of the Permittivity

• Need a relation between resonant frequency and
  real part, e2.

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Real Part of the Permittivity
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Imaginary Part of the Permittivity

• Need a relation between resonant bandwidth and
  imaginary part, e2.

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Imaginary Part of the Permittivity
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Conclusion

• A resonant waveguide was utilized for
  permittivity measurement.
• It was noted that the resonance properties are
  very sensitive to the material properties, hence
  the permittivity.
• Relations were developed between
• the resonant frequency and the real part of the
  permittivity,
• the resonant bandwidth and the imaginary part of
  the permittivity.
• High accuracy was attained in both relations.

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