APPARATUS FOR MICROWAVE NDT OF DIELECTRIC MATERIALS BY MULTI FREQUENCY METHODS
Oleg O. Drobakhin, Valentine F. Borulko, and Vladimir A. Karlov Department of Radiophysics, Dniepropetrovsk State University 72 Gagarin Street, Dniepropetrovsk-10, 320625, Ukraine
Keywords: NDT, Dielectric structure, Microwave, Algorithm, MULTI FREQUENCY
ABSTRACT
The estimation of multilayered dielectric structure (MDS) parameters is induced by some engineering applications for instance in aircraft and rocket industries. The constancy of every layer parameters is admitted. The problem is to estimate values of dielectric constant and thickness d of every layer simultaneously with only one-side access, thus only reflection coefficient (RC) can be measured. Microwaves have advantages for NDT of composite MDS due to their great penetration power. NDT of radar and antenna covers, materials absorbing microwaves demands usage of microwaves only. Sometimes materials with small permittivity such as foams, which have equal 1.05 - 1.20 must be tested. Simultaneousness of every layer parameter estimation induces application of MULTI FREQUENCY methods. But interpretation of results in time domain can be carried out more simply as in time-domain location, thus spectral analysis of frequency results is need. These facts demand to measure complex RC by vector reflectometer. The peculiarity of NDT is positioning MDS not in a waveguide but in free space. The parameters of interfaces of the layers can be obtained in the same way as waveguide discontinuity ones. Six-port conception usage is one of common decisions in this case but it has limitations due to a number of calibrations and a number of calibrating standards. Simplicity of scalar reflectometer application is very attractive. A distribution of interfaces of layers and their parameter estimates can be found by spectral analysis of data obtained by use of comparison reflectometer [1] measuring sum of reference reflection and reflection of the MDS under test. REFERENCE
D. L. Hollway "The comparison reflectometer" IEEE Trans. Microwave Theory and Techniques, Vol. 15, No. 4, pp 250-259, 1967.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 3, pages 1559 - 1562 Publisher:Ashgate Publishing Company
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