Browse Prior Art Database

COAXIAL WAVEGUIDE FOR DIELECTRIC CONSTANT AND CONDUCTIVITY MEASUREMENTS

IP.com Disclosure Number: IPCOM000008513D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-19
Document File: 5 page(s) / 204K

Publishing Venue

Motorola

Related People

Danny McCoy: AUTHOR [+2]

Abstract

The purpose of this paper is to introduce an improved device over existing equipment for measurement of dielectric constant and conductivity of solutions utilized in simulation of human tissue or mixtures. Advantages of this device include high accuracy and repeatability combined with easy disassembly for cleaning and superior signal to noise ratio.

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Page 1 of 5

MOTOROLA Technical Developments

COAXIAL WAVEGUIDE FORDIELECTRIC CONSTANT

AND CONDUCTIVITY MEASUREMENTS

end of a probe before insertion into a mixture for measurement. After the mixture is probed, relative parameters are calculated. This method has the advantage of frequency sweeping and also probing non flowable substances such as tissue. Problems with this type of approach is that it uses reflection data at a highly sensitive single boundary location. In addition, the user has to be especially careful with the maintenance of the probe tip where fring- ing field data is used during calibration. Sir bubbles or other matter which is not microscopically homo- geneous throughout the probe tip region will cause erroneous data.

SLIDING PROBE OUTPUT

WAVPGIJllX FTI.LETI WlTH MlXTl TRE

I 4 SLOT ___.-____.--.___.--__________

by Danny McCoy and Maurice Ballen

  The purpose of this paper is to introduce an improved device over existing equipment for measurement of dielectric constant and conductivity of solutions utilized in simulation of human tissue or mixtures. Advantages of this device include high accuracy and repeatability combined with easy disassembly for cleaning and superior signal to noise ratio.

  Two common techniques for measuring mix- tures are the slotted line technique (Figure la) and the open ended coaxial line technique (Figure lb). The open ended coaxial line method is based upon determination of the total fringe capacitance at the

--- .-----__.----____---____________________------~------~------~~------~--~------

Fig. la Slotted Line Technique

L1 Mofar~la. 1°C. IYYi

168 December 1997

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Page 2 of 5

MOTOROLA Technical Developments

TO ANALYZER

GROUND PLANE COMMONLY USED

PROBE AT FRINGING END

(INSERT INTO MIXTURE) )

Fig. 1 b Open Ended Coaxial Line

  The slotted line technique of measurement is used to determine electrical parameters differently from the open ended coaxial cable method. A filled coaxial waveguide is used along with relatively simple and well accepted propagation theory rather than diffraction type theory associated with fring- ing. Waveguide lengths of one foot or more when used with relatively lossy mixtures prevent large amplitude reflected waves from adding to the incident waves of interest and thus standing waves are minimized even at low frequencies. (Reflected waves from the end of the guide can be taken into account but for practical purposes a long wave guide can cause enough attenuation of reflections so as the guide can be considered infinitely long or at least significantly long). This slotted line approach is based upon multiple sampling of amplitude and phase data at different locations throughout the medium of interest rather than at a single probe/mixture boundary. Plotted data of amplitude and phase versus distance along the guide should form straight line curves. This gives beneficial

visual support of verification that propagation data is cre...