Permittivity - Measurement

Measurement

The dielectric constant of a material can be found by a variety of static electrical measurements. The complex permittivity is evaluated over a wide range of frequencies by using different variants of dielectric spectroscopy, covering nearly 21 orders of magnitude from 10−6 to 1015 Hz. Also, by using cryostats and ovens, the dielectric properties of a medium can be characterized over an array of temperatures. In order to study systems for such diverse excitation fields, a number of measurement setups are used, each adequate for a special frequency range.

Various microwave measurement techniques are outlined in Chen et al.. Typical errors for the Hakki-Coleman method employing a puck of material between conducting planes are about 0.3%.

• Low-frequency time domain measurements (10−6-103 Hz)
• Low-frequency frequency domain measurements (10−5-106 Hz)
• Reflective coaxial methods (106-1010 Hz)
• Transmission coaxial method (108-1011 Hz)
• Quasi-optical methods (109-1010 Hz)
• Terahertz time-domain spectroscopy (1011-1013 Hz)
• Fourier-transform methods (1011-1015 Hz)

At infrared and optical frequencies, a common technique is ellipsometry. Dual polarisation interferometry is also used to measure the complex refractive index for very thin films at optical frequencies.