We present a free-space measurement technique for non-destructive
non-contact electrical and dielectric characterization of nano-carbon composites
in the Q-band frequency range of 30 GHz to 50 GHz. The experimental system and
error correction model accurately reconstruct the conductivity of composite
materials that are either thicker than the wave penetration depth, and therefore
exhibit negligible microwave transmission (less than −40 dB), or thinner
than the wave penetration depth and, therefore, exhibit significant microwave
transmission. This error correction model implements a fixed wave propagation
distance between antennas and corrects the complex scattering parameters of the
specimen from two references, an air slab having geometrical propagation length
equal to that of the specimen under test, and a metallic conductor, such as an
aluminum plate. Experimental results were validated by reconstructing the
relative dielectric permittivity of known dielectric materials and then used to
determine the conductivity of nano-carbon composite laminates. This error
correction model can simplify routine characterization of thin conducting
laminates to just one measurement of scattering parameters, making the method
attractive for research, development, and for quality control in the
manufacturing environment.