Principles of the radiofrequency and microwave characterization of materials



according to the proprietes of your materials


Free-space characterization test bench: paraxial beam



Listing of the team publication
Permeability tensor of magnetized ferrites



Description
This method allows a broad-band measurement of the complex permittivity and permeability of solid and isotropic materials. The samples to be tested are either rectangular plates or thin films plated out onto a rectangular holder.

Principle
This method is based on the determination of the distribution parameters, Sij, of a microstrip line that contains the material to be tested.  These Sij parameters are measured using a vector network analyzer. The rectangle-shaped sample consists in either a plate or a thin film. The method is original because the sample is directly placed onto the line substrate without needing to fully fill in the cross-section of the cell. This results in a simple and reproducible measurement procedure.

Analysis of measured data
The analysis of measured data, that is the determination of e* and µ* from Sij requires to associate an optimization program (inverse problem) to the electromagnetic analysis of the cell (direct problem) as follows:

  • The underlying approach in the direct problem is the one that, in the spectrum range of concern,  allows one to take into account several propagation modes in the calculation.
  • The inverse problem is solved using a numerical optimization process based on the Raphson-Newton method.

Results

  • Frequency range used: 300 kHz - 15 GHz (network analyzers HP 8753ES and HP8510B).
  • Type of material tested: dielectric, ferrimagnetic and ferrocomposite materials with  mean to high losses, i.e. tan d > 10-3.
  • Accuracy: relative errors < 5%.
  • Network analyzer calibration: SOLT up to 8 GHz and TRL up to 15 GHz.
  • Thickness of the tested samples:  from several tens of micrometers to several millimeters.

Permittivity and permeability of a referency dielectric.

Comments
The above method was used to characterize several types of dielectrics and ferrites; then, the comparison of these experimental results with those reported in the literature confirmed the validity of the obtained data (figure). When the sample thickness is greater than 500 µm, the relative error on permittivity is less than 5% in 2 and 4 mm, the relative error on permittivity is less than 5%, whereas the one on permeability is below 2%. This method was designed and developed within the framework of a DRET contract (French Defense Department) and was the subject of several papers in peer-reviewed publications [1-3].


1. P. Queffelec, Ph. Gelin, J. Gieraltowski and J. Loaec, "A microstrip device for the broad-band simultaneous measurement of complex permeability and permittivity", IEEE Transactions on Magnetics, Vol. 30, No. 2, pp. 224-231, March 1994.

2. P. Quéffélec and Ph. Gelin, "Influence of higher order modes on the measurements of magnetic and dielectric materials using a microstrip discontinuity", IEEE Transactions on Microwave Theory and Techniques, Vol. 44, No. 6, pp. 816-824, June 1996.

3. P. Quéffélec, M. Le Floc'h and Ph. Gelin, "Broad band characterization of magnetic and dielectric thin films using a microstrip line", IEEE Transactions on Instrumentation and Measurement, Vol. 47, No. 4, pp. 956-963, August 1998.