ASTM D7449 Measurement of Relative Complex Permittivity and Relative Magnetic Permeability of solid materials at Microwave frequencies using Coaxial Airline.

Scope:

The ASTM D7449 test method determines the relative complex permittivity (relative dielectric constant and loss) and relative magnetic permeability of isotropic, reciprocal (non-gyromagnetic) solid materials. This method can be used to test permittivity only if the material is non-magnetic. The values of complex permittivity and permeability at working frequencies must be known when doing design calculations for radio frequency (RF), microwave, and millimeter-wave components. This test procedure helps assess materials used in continuous manufacturing or small experimental batches for electromagnetic applications. Employ this method to concurrently determine complex permittivity and permeability or just complex permittivity (in non-magnetic materials).

Test Procedure:

The test method ASTM D7449 is carried out as follows: 

• A carefully machined test specimen is placed in a coaxial airline and connected to a calibrated network analyzer, which measures the S-parameters of the transmission line with the specimen. A specified data-reduction algorithm is then used to calculate permittivity and permeability. Error corrections make up for the air gaps between the specimen and the transmission line conductor surfaces. Also, check to ensure the calibration of the inversion algorithm and that phase correction was properly applied. 
• Measure and record the dimensions of the specimen with a micrometer or other precision instrument. Insert the unknown specimen into the Port 1 side of the specimen holder. Ensure the sample’s front surface is flush with the Port 1 reference plane. Record how the specimen fits (loose, snug, tight, loose at first, then tight, and so forth). This subjective observation helps to determine the specimen’s dimensional qualities. Tighten the coaxial airline connectors with the proper torque wrench. 
• Ensure that the feed cables’ position is identical to when the calibration was done to minimize phase errors from cable movement. Measure the scattering parameters of the specimen holder containing the specimen. The necessary scattering parameters depend on the calculation procedure to determine intrinsic properties. If 1 h or more has elapsed since the calibration, renew the calibration and reverify with the known verification specimen. 
• This will account for temperature changes in the waveguide fixture, which induce phase variations. As described in the section on calculation, calculate the intrinsic properties of the specimen from the measured scattering parameters.

Specimen Size:

The size of the specimen dimension is limited by test frequency, intrinsic specimen electromagnetism properties, and the algorithm request.

Data:

The Data stated in SI units or inch-pound units are considered standard. No other units of measurement are included in this standard.

Conclusion:

This test method, ASTM D7449, covers a procedure for determining relative complex permittivity (relative dielectric constant and loss) and relative magnetic permeability of isotropic, reciprocal (non-gyromagnetic) solid materials. This method can be used to test permittivity only if the material is non-magnetic.