Investigation of lubricating grease using terahertz transmission spectroscopy

A nondestructive and contactless screening method for selected lubricating grease stored in common plastic box has been examined using the terahertz (THz) time-domain spectroscopy. The THz wave has been transmitted through the commercially available lubricating grease in polystyrene filters. Greases have unique spectral features in the THz range, and the differences in the absorption coefficient and the refractive indices, which reflect the ingredients of organic compounds, suggested that the THz spectroscopy can be used to characterize the type and consistency of lubricating grease.