The Importance of Sample Preparation

Proper sample preparation is the first step to accurate measurements

Both methods, the resonator method and the S-parameter method, require the sample to be machined to fit the fixture. Since the size of the sample is used to calculate the permittivity and permeability, measurement errors in the sample size directly affect the measured values of permittivity and permeability. Therefore, in order to evaluate material properties accurately, it is necessary to know the size accurately. Ideally, the cross-sectional area of a rod-shaped sample should be uniform, and the thickness of a plate-shaped sample should be uniform.

Material preparation for cavity resonators

It is basic to machine the sample into a rod shape. The recommended size is shown below. In the case of anisotropic samples, the difference in permittivity due to anisotropy can be evaluated by changing the direction of sample extraction.

Recommended size for cavity resonator
Resonator W×D (mm) L (mm)
1-5.8 GHz 1.5 × 1.5 80
10 GHz 60

Material preparation overview for Split Cylinder

The sample needs to be processed into a plate. The characteristics of the material and the measurement frequency determine the appropriate thickness and size.


We recommend about 100μm. The chart shows the approximate maximum thickness that can be measured with the split cylinder resonators. The larger the permittivity and the higher the frequency, the thinner the sample needs to be. If the loss is more than about 0.01, a thinner sample may be required. On the other hand, it should be noted that the thinner the sample (e.g. 10μm), the more noticeable the error in thickness measurement becomes, and consequently the larger the error in permittivity measurement becomes. For details, please contact us.

calculate max thickness of sample

maximum thickness


Recommended sample size
Resonator Short side (mm) Long side (mm)
10 GHz 62 75
20-80 GHz 34 45

Material Preparation Overview for Fabry-Perot Resonator

The sample needs to be processed into a squere plate. The characteristics of the material and the measurement frequency determine the appropriate thickness and size.


Recommended sample size
Resonator Size
E/W/D/G/Jband 50 mm square
Broadband 65 mm square


The appropriate thickness depends on the dielectric properties and the resonator used, but 100 µm is a good rule of thumb. The higher the frequency and the higher the dielectric constant, the thinner the sample needs to be. The relationship between the sample thickness, dielectric constant, and frequency band is shown in the charts below. Note that a sample with high loss (tanδ>0.01 is a rough guide) requires an even thinner sample.

How to use the chart

  • Samples within the white area of the chart can be measured at all frequency points.
  • Samples within the black area of the chart (including the thick black line) cannot be measured.
  • Samples within the gray area of the chart will have erratic measurements in some parts of the band.
    Disturbance in measurements Disturbance in measurements

Chart: Sample thickness and dielectric constant

Broadband Low(25-55GHz) 
Max sample thickness
Broadband High(55-110GHz) 
Max sample thickness
E-band (60-90GHz) 
Max sample thickness
W-band (75-110GHz)
Max sample thickness
D-band (110-170 GHz) 
Max sample thickness
G-band (140-220 GHz)
Max sample thickness
J-band (220-330 GHz) 
Max sample thickness

Material preparation overview for free space method

It is necessary to process the sample into a plate shape. The recommended size varies depending on the measurement frequency and the permittivity/permeability of the material.


One quarter wavelength is optimal. (It is necessary to take into account the wavelength shortening 1/√ (relative permittivity / relative permeability) in the sample.) If the sample gets thicker, the error due to multiple reflection inside the sample can get significant. This is especially noticeable in magnetic permeability measurement.


A diameter of 6 wavelengths or more is recommended. A diameter of 60 mm or more makes it easier to fix to the fixture.