WO1993000591A1 - Mesure des proprietes dielectriques de materiaux - Google Patents

Mesure des proprietes dielectriques de materiaux Download PDF

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Publication number
WO1993000591A1
WO1993000591A1 PCT/GB1992/001160 GB9201160W WO9300591A1 WO 1993000591 A1 WO1993000591 A1 WO 1993000591A1 GB 9201160 W GB9201160 W GB 9201160W WO 9300591 A1 WO9300591 A1 WO 9300591A1
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WO
WIPO (PCT)
Prior art keywords
conductivity
adjacent
contact
complex permittivity
change
Prior art date
Application number
PCT/GB1992/001160
Other languages
English (en)
Inventor
Alan William Preece
Reginald Harry Johnson
Original Assignee
The University Of Bristol
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The University Of Bristol filed Critical The University Of Bristol
Priority to EP92913403A priority Critical patent/EP0591335A1/fr
Publication of WO1993000591A1 publication Critical patent/WO1993000591A1/fr
Priority to GB9325689A priority patent/GB2272777A/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
    • G01R27/2617—Measuring dielectric properties, e.g. constants
    • G01R27/2623—Measuring-systems or electronic circuits

Definitions

  • the present invention relates to measuring dielectric properties of materials, that is the permittivity and conductivity, at radio and microwave frequencies.
  • dielectric properties of a material have been measured using a sample of the material prepared for insertion in, for example, a coaxial line or resonant cavity and observing changes in transmission or reflection characteristics.
  • An alternative method uses an open-ended coaxial line in contact with the material whose properties are to be measured, an automatic network analyser being used to measure the complex impedance thus presented to the coaxial line (see IEE Electronics Letters, 15 February 1990, Vol. 24, No.4, pp 234-235, S Jenkins and A W Preece; and J. Phys. E: Sci. Instrum. 22 (1989), pp 757-770, J P Grant, et al).
  • Such a method requires knowing the geometry of the open-ended coaxial line and is particularly suitable for liquids.
  • apparatus for measuring the complex permittivity and conductivity, or a change in the complex permittivity and conductivity, of a dielectric material
  • the apparatus comprising: a structure which can be made to resonate at a radio or microwave frequency when in contact with or adjacent a dielectric material;
  • first means for providing a first indication, related to a change in resonant frequency of said structure when the latter is in contact with or adjacent said material as compared with a reference resonant frequency when not in contact with or adjacent said material;
  • second means for providing a second indication, related to the return loss when said structure is in contact with or adjacent said material, whereby the complex permittivity and conductivity, or a change in the complex permittivity and conductivity, of said material can be calculated using said first and second indications.
  • a method of measuring the complex permittivity and conductivity, or a change in the complex permittivity and conductivity, of a dielectric material comprising:
  • Fig. 1 is an equivalent circuit diagram of an example of a resonant structure for apparatus according to the present invention
  • Fig. 2 is a graph of return loss against frequency of an example of such a structure
  • Fig. 3 is a circuit diagram of apparatus for measuring return loss for apparatus according to the present invention.
  • Fig. 4 is a diagram of one example of a resonant structure for apparatus according to the present invention, in the form of a resonant open-ended coaxial line;
  • Fig. 5 is a diagram of another example of a resonant structure for apparatus according to the present invention, in the form of a closed resonant structure.
  • a structure 1 is made to resonate by a microwave or radio source 2, being coupled to the latter by a coupling having a coupling reactance X c .
  • the structure 1 is equivalent to an inductance L, a capacitance C and losses represented by a resistance R.
  • a material whose dielectric properties are to be monitored is placed in contact with, or adjacent, the resonant structure 1, so inducing additional reactance X x and resistance R x .
  • the resonant frequency and Q-factor are changed by an amount which is a function of the dielectric properties of the material.
  • the change in resonant frequency can be measured, or the original resonant frequency restored by suitable modification of the resonant structure, for example by changing a dimension or varying a reactance.
  • the behaviour of the resonant structure 1 can be calibrated using liquids or other material having accurately known dielectric properties.
  • absolute measurement of complex permittivity can be made.
  • the reactance of L and C in parallel in the equivalent circuit in Fig. 1 is X
  • the impedance Z, looking into X c will be a pure resistance.
  • This impedance can be made any value, such as 50 ohm, by adjusting X c with consequent change in resonant frequency.
  • the reflection coefficient r is 0.001
  • the return loss is -60dB
  • Fig. 2 shows an example of return loss as a function of frequency.
  • Z x F(Z, X x , X c , R x )
  • Source 2 is a fixed frequency power source of 1 to 20mW and excites the resonant structure 1 through a directional coupler 3 (10 to 20dB) having good isolation, and a matching section 4. Any reflected signal passes into a calibrated attenuator 5 (0 to 60dB), an RF amplifier 6 (30 - 50dB gain), a detector 7 and a signal lever meter 8, reference numeral 9 designating a matched load. With the resonant structure 1 first replaced by a well-matched load, the matching section 4 is adjusted for minimum reflected signal.
  • This matched load is then replaced by a short-circuit and the output of the detector 7 adjusted to a reference level by suitable setting of the power of source 2, gain of amplifier 6 and calibrated attenuator 5. Adjustment of the resonant structure 1 for resonance is by minimising the detected signal, and the return loss obtained from the difference in calibrated attenuator setting required to restore the signal to the reference level obtained with the short circuit. More sophisticated systems using isolators, mixers, modulated sub-carriers and linear detectors can be alternatives.
  • the system illustrated in Fig. 3 is suitable for measuring a lightly damped resonance, so that the resonant structure 1 must not be tightly coupled to a lossy dielectric. Otherwise a frequency swept source is desirable for accurately determining resonance.
  • resonant structure 1 is a coaxial structure which comprises metallic tubes 11 and 12 providing two outer sections of a coaxial line of which the inner conductor is a continuous conductor 10 terminated by a sliding short-circuit 13 for tuning the structure.
  • the latter is excited (e.g. at 500 MHz) through a coupling capacitance which is formed between the inner conductor 10 and the inner conductor of a coaxial input 14. Suitable means of fine adjustment of this capacitance is provided by changing the spacing between the inner conductors.
  • a coupling section 15 of the coaxial line is terminated by an open-end 16 of the structure 1 and the inner conductor 10 is held in place by dielectric spacers 17 and 18.
  • Dielectric spacer 17 has dimensions to minimise reflections at interfaces.
  • a flange 19 of metallic tube 11 terminating the coaxial line enables the open-end impedance to be accurately calculated. If the coaxial line section 15 is exactly half a wavelength, the impedance at the open-end 16 is exactly transferred to a coupling plane 20 in a section 21 which joins tubes 11 and 12 and receives the input 14, and resonance occurs when the sliding short-circuit 13 adjusts the length of the coaxial line to be the appropriate amount less than one quarter wavelength. If the coaxial line section 15 is not half a wavelength, but its length is accurately known, then the impedance at the coupling plane 20 is changed but can be calculated.
  • the structure 1 is made to resonate when radiating into air and with the coupling capacitance adjusted by adjusting input 14 for the minimum necessary to obtain a measurable response on an automatic network analyser.
  • the impedance transferred to the coupling plane 20 from the open-and short-circuit ends must now be equal.
  • the coupling capacitance is now increased until the input impedance at input 14 is matched to the network analyser (usually 50 ohm) and the return loss is about 60dB.
  • the short-circuit length of the line must be readjusted and this change allows the coupling capacitance to be calculated.
  • the open-end 16 is now placed in contact with or adjacent material with unknown dielectric properties and resonance at the measurement frequency is restored by adjustment of the short-circuit length of the coaxial line by sliding the short-circuit 13, the return loss also being measured.
  • Fig. 5 shows another resonant structure 1, which includes an inductance formed by a generally U-shaped, flat high conductivity strip 30, the ends of the U being coupled together by a capacitance formed by a plurality of conductive plates 31. Movement of a conductive disc 32 adjusts the capacitance between additional conductive half-plates 33 attached to the ends of the U-shaped conductive strip 30 in order to tune the resonant frequency. An insulating bush 34 isolates disc 32 from a micrometer assembly 35. Excitation of this resonant circuit is provided by a coaxial input 36 through the capacitance between a conductive plate 37 and one side of the U-shaped conductive strip 30.
  • Fine adjustment of this coupling capacitance is provided by a suitable screw assembly 38 insulated from the conductive plate 37 by an insulating bush 39.
  • the base of the U-shaped conductive strip 30 is secured by suitable means to a low-loss dielectric end cap 40 in such a way that the base of the U is uniformly covered by a relatively thin layer 41 of low-loss dielectric.
  • the end cap 40 is made re-entrant for attachment to a screening container 42. It is important that end cap 40 should insulate the outside of the lower part of the screening container 42 to prevent contact with a liquid dielectric.
  • the thickness of the dielectric layer 41 is chosen to suit the range of values of permittivity and conductivity to be measured. For example, if the conductivity to be measured is high, then damping of the resonant structure must be limited by providing sufficient thickness of the dielectric layer 41 to allow resonant frequency and return loss to be accurately measured.
  • the structure of Fig. 5 may be used with the measuring system shown in Fig. 3.
  • the coupling capacitance between plate 37 and strip 30 is adjusted to match a 50 ohm input for resonance when radiating into air and the desired operating frequency set by adjustment of micrometer assembly 35.
  • the structure is then applied in contact with or adjacent dielectrics having known characteristics of the order of those to be measured, and calibration of the relationship between permittivity and conductivity and micrometer movement and return loss respectively is established.
  • the resonant structure can be coupled to the source and treated like a resonant cavity where calibration can be used to obtain the coefficients in the equations relating e and ⁇ to frequency change and Q- factor (see Waldron, R A, 1969, "Theory of Electric Waves", van Nostrand Reinhold, London). No accurately prepared material samples are required.
  • applicators such as are mentioned in the introduction are insensitive to load, i.e. resonant frequency is not be much affected by small changes in proximity to load or minor load changes.
  • return loss should remain >10dB, i.e. standing wave ratio ⁇ 2 or reflection coefficient ⁇ 03; whereas the resonant structures according to Figs. 4 and 5 are responsive to load, with relatively large changes in resonant frequency and return loss.
  • the resonant structure of Fig. 5 should have a relatively large inductance and small capacitance to make it sensitive to the proximity of a lossy dielectric.
  • Such applicators as are mentioned in the introduction have relatively small inductance and high capacitance to reduce the effect of adjacent lossy material.
  • one feature of these applicators is that they are intended to become mis ⁇ matched when radiating into air, i.e. become unloaded, and consequently they radiate inefficiently into air and this is intended as a safety feature.
  • the ratio of inductance to capacitance of structures according to Figs. 4 and 5 cannot be increased too much because of losses in the conductor which limit the Q-factor at ⁇ tainable. Conversely, the ratio cannot be made too low, because the circuit becomes difficult to drive.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

Appareil mesurant la constante diélectrique et la conductivité complexes d'un matériau diélectrique, ou une variation de celles-ci. Il comporte: une structure (1) que l'on peut faire résonner en radiofréquence ou en hyperfréquence lorsqu'elle se trouve en contact avec un matériau diélectrique, ou à proximité de celui-ci; un premier dispositif (4) fournissant une première indication associée à une variation de la fréquence de résonance de ladite structure lorsque cette dernière se trouve en contact avec ledit matériau, ou à proximité de celui-ci, et cela par rapport à une fréquence de résonance de référence lorsque ladite structure ne se trouve ni en contact avec ledit matériau, ni à proximité de celui-ci; ainsi qu'un second dispositif (5, 6, 7, 8) fournissant une seconde indication associée à l'affaiblissement d'équilibrage lorsque ladite structure se trouve en contact avec ledit matériau, ou à proximité de celui-ci, la constante diélectrique et la conductivité complexes dudit matériau, ou une variation de celles-ci, pouvant ainsi être calculées sur la base desdites première et seconde indications.
PCT/GB1992/001160 1991-06-28 1992-06-26 Mesure des proprietes dielectriques de materiaux WO1993000591A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP92913403A EP0591335A1 (fr) 1991-06-28 1992-06-26 Mesure des proprietes dielectriques de materiaux
GB9325689A GB2272777A (en) 1991-06-28 1993-12-15 Measuring dielectric properties of materials

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9114044.2 1991-06-28
GB919114044A GB9114044D0 (en) 1991-06-28 1991-06-28 Measuring dielectric properties of materials

Publications (1)

Publication Number Publication Date
WO1993000591A1 true WO1993000591A1 (fr) 1993-01-07

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EP (1) EP0591335A1 (fr)
AU (1) AU2195692A (fr)
GB (2) GB9114044D0 (fr)
WO (1) WO1993000591A1 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6518777B2 (en) * 1999-12-20 2003-02-11 Murata Manufacturing Co., Ltd. Method and apparatus for measuring insulation resistance
EP2446233A2 (fr) * 2009-06-26 2012-05-02 Schrader Electronics Ltd. Appareil de détection de niveau et de qualité de liquide, systèmes et procédés utilisant la propagation d ondes de champ électromagnétique
WO2014006391A1 (fr) * 2012-07-04 2014-01-09 Sparq Wireless Solutions Pte Ltd Procédés et appareil de détection
WO2015121365A1 (fr) * 2014-02-14 2015-08-20 Fmc Kongsgerg Subsea As Système et procédé pour mesure d'écoulement à phases multiples
CN106324360A (zh) * 2015-06-19 2017-01-11 深圳光启高等理工研究院 用于介电参数的测量系统及测量方法
CN114113789A (zh) * 2021-11-25 2022-03-01 天津大学 一种高频下测量金属薄膜电导率的装置及方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2221213A1 (de) * 1972-04-29 1973-11-15 Licentia Gmbh Verfahren zum bestimmen der dielektrizitaetskonstanten eines probekoerpers
DE2255861B2 (de) * 1971-11-16 1980-12-11 Fisons Ltd., London Vorrichtung zum Nachweis des Vorhandenseins dielektrischer Eigenschaften oder zum Nachweis einer Änderung dielektrischer Eigenschaften von Körpern unter Verwendung einer Hochfrequenzspannungsquelle

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2255861B2 (de) * 1971-11-16 1980-12-11 Fisons Ltd., London Vorrichtung zum Nachweis des Vorhandenseins dielektrischer Eigenschaften oder zum Nachweis einer Änderung dielektrischer Eigenschaften von Körpern unter Verwendung einer Hochfrequenzspannungsquelle
DE2221213A1 (de) * 1972-04-29 1973-11-15 Licentia Gmbh Verfahren zum bestimmen der dielektrizitaetskonstanten eines probekoerpers

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6518777B2 (en) * 1999-12-20 2003-02-11 Murata Manufacturing Co., Ltd. Method and apparatus for measuring insulation resistance
EP2446233A2 (fr) * 2009-06-26 2012-05-02 Schrader Electronics Ltd. Appareil de détection de niveau et de qualité de liquide, systèmes et procédés utilisant la propagation d ondes de champ électromagnétique
WO2014006391A1 (fr) * 2012-07-04 2014-01-09 Sparq Wireless Solutions Pte Ltd Procédés et appareil de détection
WO2015121365A1 (fr) * 2014-02-14 2015-08-20 Fmc Kongsgerg Subsea As Système et procédé pour mesure d'écoulement à phases multiples
US9939418B2 (en) 2014-02-14 2018-04-10 Fmc Kongsberg Subsea As System and method for multiphase flow measurements
CN106324360A (zh) * 2015-06-19 2017-01-11 深圳光启高等理工研究院 用于介电参数的测量系统及测量方法
CN106324360B (zh) * 2015-06-19 2023-10-31 深圳光启高等理工研究院 用于介电参数的测量系统及测量方法
CN114113789A (zh) * 2021-11-25 2022-03-01 天津大学 一种高频下测量金属薄膜电导率的装置及方法
CN114113789B (zh) * 2021-11-25 2023-07-21 天津大学 一种高频下测量金属薄膜电导率的装置及方法

Also Published As

Publication number Publication date
AU2195692A (en) 1993-01-25
EP0591335A1 (fr) 1994-04-13
GB2272777A (en) 1994-05-25
GB9114044D0 (en) 1991-08-14
GB9325689D0 (en) 1994-03-02

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