volume | PIER Journals

Abstract

Apractical problem in the reflection method for dielectric constant measurement is the difficulty to ensure the sample is placed exactly at the waveguide flange. Asmall position offset of the dielectric sample will give rise to some errors in calculating the dielectric constant, especially when a thin sample is used. To circumvent this problem, a method to determine the dielectric constant by measuring the transmission coefficient of the thin slab placed in a waveguide has been developed. Slab position offset from the measurement reference plane has no effect on the measurement accuracy. An explicit expression for the dielectric constant is obtained in terms of the transmission coefficient by simplifying the exact solution for transmission through a thin dielectric slab. The method is verified with measurement on Teflon of 0.5-mm thickness. The measured dielectric constant of Teflon shows excellent agreement of both ε' and ε'' with published data. Subsequently, the dielectric constant of a vegetation leaf was measured.

1. Nyfors, E. and P. Vainikainen, Industrial Microwave Sensors, Chapter 2, 1989.

2. Bengtsson, N. E. and P. O. Risman, "Dielectric properties of food at 3 GHz as determined by a cavity perturbation technique II: Measurements on food materials," Journal of Microwave Power, Vol. 6, No. 2, 107-123, 1971. Google Scholar

3. De Loor, G. P. and F. W. Meijboom, "The dielectric constant of foods and other materials with high water contents at microwave frequencies," Journal of Food Technology, Vol. 1, 313-322, 1966. Google Scholar

4. Courtney, W. E., "Analysis and evaluation of a method of measuring the complex permittivity and permeability of microwave insulators," IEEE Trans. Microwave Theory Tech., Vol. MTT-18, No. 8, 476-485, 1970.
doi:10.1109/TMTT.1970.1127271 Google Scholar

5. Qian, C. and W. B. Dou, "Anew approach for measuring permittivity of dielectric materials," Journal Electromagnetic Waves and Applications, Vol. 19, No. 6, 795-810, 2005.
doi:10.1163/1569393054069055 Google Scholar

6. Bindu, G., A. Lonappan, V. Thomas, et al. "Dielectric studies of corn syrup for applications in microwave breast imaging," Progress In Electromagnetics Research, Vol. 59, 175-186, 2006.
doi:10.2528/PIER05072801 Google Scholar

7. Nicholson, A. M. and G. Ross, "Measurement of intrinsic properties of materials by time domain techniques," IEEE Trans. Instrum. Meas., Vol. IM-19, No. 11, 377-382, 1970. Google Scholar

8. Weir, W. B., "Automatic measurements of complex dielectric constant and permeability at microwave frequencies," IEEE Proceedings, Vol. 62, No. 1, 33-36, 1974.

9. Backer, J. and R. Geyer, "Anonlinear least-squares solution with causality constraints applied to transmission line permittivity and permeability determination," IEEE Trans. Instrum. Meas., Vol. 41, No. 10, 646-652, 1992.
doi:10.1109/19.177336 Google Scholar

10. Somlo, P. I., "Acon venient self-checking method for automated microwave measurement of μ and ε," IEEE Trans. Instrum. Meas., Vol. 42, No. 4, 213-216, 1993.
doi:10.1109/19.278551 Google Scholar

11. Szendrenyi, B. B., K. Kazi, and I. Mojzes, "An alternative broadband method for automatic measurement of the complex permeability and permittivity of materials at microwave frequencies," 1988 MTT-S Digest, 743-746, 1988.
doi:10.1109/MWSYM.1988.22138 Google Scholar

12. Chung, B. K., "Acon venient method for complex permittivity measurement of thin materials at microwave frequencies," Journal of Physics D: Applied Physics, Vol. 39, 1926-1931, 2006.
doi:10.1088/0022-3727/39/9/030 Google Scholar

13. Huang, R. F. and D. M. Zhang, "Application of mode matching method to analysis of axisymmetric coaxial discontinuity structures used in permeability and/or permittivity measurement," Progress In Electromagnetics Research, Vol. 67, 205-2302007, 2302.
doi:10.2528/PIER06083103 Google Scholar

14. Stuchly, M. A. and S. S. Stuchly, "Coaxial line reflection methods for measuring dielectric properties of biological substances at radio and microwave frequencies — Areview," IEEE Trans. Instrum. Meas., Vol. IM-29, No. 9, 176-183, 1980. Google Scholar

15. Mosig, J. R., J. C. E. Besson, M. Gex-Fabry, and F. E. Gardiol, "Reflection of an open-ended coaxial line and application to nondestructive measurement of materials," IEEE Trans. Instrum. Meas., Vol. IM-30, No. 3, 46-51, 1981. Google Scholar

16. Misra, D., M. Chabbra, B. R. Epstein, M. Mirotznik, and K. R. Foster, "Noninvasive electrical characterization of materials at microwave frequencies using an open-ended coaxial line: Test of an improved calibration technique," IEEE Trans. Microwave Theory Tech., Vol. 38, No. 1, 8-14, 1990.
doi:10.1109/22.44150 Google Scholar

17. Nyshadham, A., C. L. Sibbald, and S. S. Stuchly, "Permittivity measurements using open-ended sensors and reference liquid calibration — An uncertainty analysis," IEEE Trans. Microwave Theory Tech., Vol. 40, No. 2, 305-314, 1992.
doi:10.1109/22.120103 Google Scholar

18. Chen, G., K. Li, and Z. Ji, "Bilayered dielectric measurement with an open-ended coaxial probe," IEEE Trans. Microwave Theory Tech., Vol. 42, No. 6, 966-971, 1994.
doi:10.1109/22.293564 Google Scholar

19. Trabelsi, S., A.W. Kraszewski, and S. O. Nelson, "Nondestructive microwave characterisation for bulk density and moisture content determination in shelled corn," Meas. Sci. & Technol., Vol. 9, 570-578, 1998.
doi:10.1088/0957-0233/9/4/003 Google Scholar

20. Sarabandi, K. and F. T. Ulaby, "Technique for measuring the dielectric constant of thin materials," IEEE Trans. on Instrum. Meas., Vol. 37, No. 4, 631-636, 1988.
doi:10.1109/19.9828 Google Scholar

21. Agilent Technologies, Network Analysis Applying the 8510 TRL Calibration for Non-Coaxial Measurements, Network Analysis Applying the 8510 TRL Calibration for Non-Coaxial Measurements, 8510, Product Note 8510- 8A, 2001.

22. Ulaby, F. T. and M. A. El-Rayes, "Microwave dielectric spectrum of vegetation-Part II: Dual-dispersion model," IEEE Trans. Geosci. Remote Sensing, Vol. GE-25, 550-557, 1987.
doi:10.1109/TGRS.1987.289833 Google Scholar

Dr. Boon-Kuan Chung