Transfer matrix method for precise determination of thicknesses in a 150-ply polyethylene composite material

The multilayer structure of an ultra-high molecular weight polyethylene composite material was investigated in the terahertz (THz) spectral range by means of time domain spectroscopy (TDS) technique. Such structures consist of many alternating layers of fibres (~150), each being perpendicular to the other and each having a thickness of about 50 mm. A transfer matrix method (TMM) and a time-domain fitting procedure were used to determine thicknesses of all layers of the composite material with high accuracy.