Reflection and absorption of millimeter waves by thin absorbing films

Reflection, transmission, and absorption of mm‐waves by thin absorbing films were determined at two therapeutic frequencies: 42.25 and 53.57 GHz. Thin filter strips saturated with distilled water or an alcohol–water solution were used as absorbing samples of different thicknesses. The dependence of the power reflection coefficient R(d) on film thickness (d) was not monotonic. R(d) passed through a pronounced maximum before reaching its steady‐state level [R(∞)]. Similarly, absorption, A(d), passed two maximums with one minimum between them, before reaching its steady‐state level [A(∞)]. At 42.25 GHz, A(d) was compared with absorption in a semi‐infinite water medium at a depth d. When d