Spectroscopic evaluation of epidermis-equivalent phantom in terahertz-frequency region

The complex refractive index and reflectance of an epidermis-equivalent phantom were evaluated in the terahertz-frequency region. The complex refractive indices of the epidermis and the epidermis-equivalent phantom, made using ultrapure water, mineral oil, glycerin fatty acid ester, and agar, were measured using a terahertz time-domain spectrometer. The complex refractive indices of the epidermis and the epidermis-equivalent phantom were in agreement. However, their mean reflectances had a difference of approximately 3%. The difference disappeared on adding surface roughness to the epidermis-equivalent phantom. Thus, we found that roughness of the surface of the epidermis-equivalent phantom was required to ensure a match of the reflectance of the phantom with that of the epidermis at frequencies from 0.2 THz to 0.6 THz.