Progress in Thick Film Testing Technology
To address the strict dimensional requirements for materials in current permeability testing, this study improves the permeability test fixture by applying the principle of the inductance measurement method. A specialized fixture for testing thick film materials within the frequency range of 0.1GHz~0.6GHz is developed, with the test error controlled within ±20%.
The widely used test fixture based on the inductance measurement method operates on the principle that it functions as a single-turn inductor when short-circuited. The permeability of the material under test is derived by measuring the change in inductance of the fixture before and after inserting the material. However, this method requires the test material to be in a toroidal shape, making it impossible to measure the low-frequency permeability of small-sized materials.
Starting from the fixture design principle, a fitted empirical formula is obtained through simulation and actual measurements. The permeability test fixture suitable for thick film materials is improved by adjusting the length, width, and height of the strip line's metal conductor. The S11 parameter graph of the empty fixture in the range of 0.1GHz~1GHz shows that the S11 values are far from the resonance point, and practical tests have been conducted to verify its performance.
As shown in Figure 4, a comparison between the calculated results from the empirical formula and the actual measured data of the real and imaginary parts of permeability for samples with different thicknesses reveals that the absolute error of the imaginary part of permeability is within 20% except for a few frequency points. Based on the comprehensive results of the real and imaginary parts of permeability, this method is applicable for permeability measurement in the frequency range of 0.1GHz~0.6GHz.
