Investigation of different graphite morphologies for microwave absorption at X and Ku-band frequency range

The different graphite morphologies, like graphite intercalation compound (GIC), expanded graphite (EG), and exfoliated graphite (ExfG), were investigated as microwave absorbing materials (MAMs). The modification of the GIC was carried out in two independent parts, consisting of heat treatment and subsequent ultrasound agitation, forming the EG and ExfG, respectively. The surface morphology and structural characterization were investigated using the scanning electron microscope and Raman spectroscopy. Electromagnetic characterization was performed with a vector network analyzer and rectangular waveguide in the frequency range from 8.2 to 12.4 GHz (X-band) and from 12.4 to 18 GHz (Ku-band). The effects of different graphite morphologies and thickness of the composite were analyzed on the electromagnetic properties. The results of the reflection loss show that the samples affect the performance of the MAMs. The EG sample presents an excellent attenuation of around - 22.5 dB (approximate to 99 microwave attenuation) for 2 mm thickness samples within the X-band frequency range. This behavior can be attributed to the expanded and interconnected structure of the EG, which has a large surface area and connectivity between the structures within the composite. Thus, it was found that EG is the best graphite structure for application in microwave absorber of broadband. The GIC and ExfG exhibited poor performance of microwave absorption (above - 10 dB).