Air-Filled Circular Cross Sectional Cavity for Microwave Non-Destructive Testing

Dielectric sheet perturbation to the dominant TE111 mode resonant frequency of a circular cavity is studied and presented in this paper. The dielectric sheet, placed at the middle of the airfilled cavity, introduces discontinuities and disturbs the configuration of electromagnetic fields in the cavity. For fixed dimensions of cavity and fixed thickness of the loading dielectric, the dominant resonant frequency varies quite linearly with the permittivity of the dielectric. This quasi-linear relationship is plotted using Maple software and verified using 3D electromagnetic simulations. Two probes are used in the simulation for wave excitation into and from the cavity. The best length of probe is found to be 3 mm, giving the closest resonant frequency to the one calculated using Maple. A total of fourteen different dielectrics of permittivity ranging from 1 to 12.9 are tested one by one in the simulation. The works show very close agreement between the results from Maple and the simulation. A constant difference of 0.04 GHz is found between the resonant frequencies collected during simulation and the ones from Maple. The success of this project may lead to the possibility of using the middle loaded cavity at TE111 mode as a microwave non-destructive testing of solid materials.

Authors:

• Mohd Tarmizi Ali
• Mohd Khairul Mohd Salleh
• Md. Mahfudz Md. Zan

Keywords:

• Middle-loaded cavity
• dielectric sheet perturbation.

References:

[1] T. Itoh, "A New Method for Measuring Properties of Dielectric
Materials Using a Microstrip Cavity", (Short Papers), IEEE Trans. On
Microwave Theory and Tehcniques, May 1974.
[2] S. Genraud, S. Verdeyme, P. Guillon, "Design and realization of a four
pole elliptic microwave filter using low dielectric loaded cavities", 1997
IEEE MTT-S Digest.
[3] H. E. Stinehelfer Sr., "Ridge waveguide resonant cavity for measuring
dielectric constants", Patent Gazette, 3,384,814, May 21, 1968.
[4] S. Ivkovic, B. Milovanovic, A. Atanaskovic, V. Tasic, "Automatization
of permittivity measuring using microwave cylindrical cavity",
TELSIKS, October 1999.
[5] B. Milovanovic, A. Atanaskovic, V. Tasic, "A simple method for
permittivity measurement using microwave resonant cavity",
Microwaves and Radar, 1998. MIKON '98., 12th International
Conference, Volume 3, 20-22 May 1998 Page(s):705 - 709 vol.3.
[6] Atanaskovic, A.; Tasic, V.; Ivkovic, S., "Automatization of the complex
dielectric constant measurement", Telecommunications in Modern
Satellite, Cable and Broadcasting Service, 2001. TELSIKS 2001. 5th
International Conference, Volume 2, 19-21 Sept. 2001 Page(s):691 -
694 vol.2.
[7] Janezic, M.D.; Grosvenor, J.H. "Improved technique for measuring
permittivity of thin dielectrics with a cylindrical resonant cavity",
Instrumentation and Measurement Technology Conference, 1991.
IMTC-91. Conference Record., 8th IEEE, 14-16 May 1991 Page(s):580
- 584.
[8] Afsar, M.N.; Hanyi Ding; Tourshan, K., "A new 60 GHz open-resonator
technique for precision permittivity and loss-tangent measurement",
Instrumentation and Measurement, IEEE Transactions, Volume 48,
Issue 2, April 1999 Page(s):626 - 630.
[9] Afsar, M.N.; Hanyi Ding, "A new open resonator method for the
measurement of dielectric permittivity and loss tangent of low absorbing
materials at 60 GHz", Infrared and Millimeter Waves, 2000. Conference
Digest. 2000 25th International Conference, 12-15 Sept. 2000
Page(s):403 - 404.
[10] Raveendranath, U.; Bijukumar, S.; Mathew, K.T, "Broadband coaxial
cavity resonator for complex permittivity measurements of liquids",
Instrumentation and Measurement, IEEE Transactions, Volume 49,
Issue 6, Dec. 2000 Page(s):1305 - 1312.
[11] U. Raveendranath, J, Jacob, K. T. Mathew, "Complex permittivity
measurement of liquids with coaxial cavity resonators using a
perturbation technique", Electronics Letters, 23rd May 1996 Vol. 32 No.
11.
[12] Keam, R.; Green, A.D, "Measurement of complex dielectric permittivity
at microwave frequencies using a cylindrical cavity", Electronics
Letters, Volume 31, Issue 3, 2 Feb. 1995 Page(s):212 - 214.
[13] Linfeng Chen; Ong, C.K.; Tan, B.T.G, "Cavity perturbation technique
for the measurement of permittivity tensor of uniaxially anisotropic
dielectrics", Instrumentation and Measurement, IEEE Transactions,
Volume 48, Issue 6, Dec. 1999 Page(s):1023 - 1030.
[14] Janezic, M.D.; Grosvenor, J.H., "Improved technique for measuring
permittivity of thin dielectrics with a cylindrical resonant cavity",
Instrumentation and Measurement Technology Conference, 1991.
IMTC-91. Conference Record., 8th IEEE, 14-16 May 1991 Page(s):580
- 584.
[15] Mrityunjay Santra and K. U. Limaye, "Estimation of complex
permittivity of arbitrary shape and size dielectric samples using cavity
measurement technique at microwave frequencies", IEEE Transactions
on Microwave Theory and Techniques, Vol. 53, No. 2, February 2005.
[16] M. K. Mohd Salleh et. al, "Effect Of Varied Probe Length On The
Resonant Frequency Of A Circular Cross-Sectional Cavity", Conference
on Scientific & Social Research (CSSR) 2003D.
[17] Moraud, S.; Verdeyme, S.; Guillon, P.; Ulian, P.; Theron, B., "A new
planar type dielectric resonator for microwave filtering", Microwave
Symposium Digest, 1998 IEEE MTT-S International, Volume 3, 7-12
June 1998 Page(s):1307 - 1314 vol.3.
[18] Zhang, G.; Nakaoka, S.; Kobayashi, Y., "Millimeter wave measurements
of temperature dependence of complex permittivity of dielectric plates
by the cavity resonance method", Microwave Conference Proceedings,
1997. APMC '97, 1997 Asia-Pacific, Volume 3, 2-5 Dec. 1997
Page(s):913 - 916 vol.3.
[19] Kent, G., "Non-destructive permittivity measurement of substrates",
Precision Electromagnetic Measurements, 1994. Digest, 1994
Conference, 27 June-1 July 1994 Page(s):352 - 353.