Reflection and absorption of millimeter waves by thin absorbing films

Area of Science:

• Physics
• Electromagnetism
• Materials Science

Background:

• Millimeter waves (mm-waves) are increasingly used in medical applications.
• Understanding their interaction with biological tissues is crucial for therapeutic and diagnostic purposes.
• Thin absorbing layers exhibit unique electromagnetic properties not seen in bulk materials.

Purpose of the Study:

• To investigate the reflection, transmission, and absorption of mm-waves by thin absorbing films at therapeutic frequencies.
• To determine the impact of film thickness on these electromagnetic properties.
• To compare the behavior of thin films with semi-infinite media and validate theoretical models.

Main Methods:

• Experimental determination of mm-wave reflection, transmission, and absorption coefficients for thin water and alcohol-water films.
• Varying film thickness (d) at 42.25 GHz and 53.57 GHz.
• Applying Fresnel equations to model the observed phenomena and extract material properties.

Main Results:

• Reflection and absorption coefficients showed non-monotonic dependence on film thickness, with pronounced maxima.
• Absorption in thin films significantly exceeded that in semi-infinite media at comparable thicknesses.
• Fresnel equations accurately described the experimental data, enabling determination of refractive index, dielectric constant, and penetration depth.

Conclusions:

• The interaction of mm-waves with thin absorbing layers differs significantly from semi-infinite media due to multiple internal reflections.
• Accurate modeling of mm-wave behavior in thin biological samples and phantoms requires consideration of these thin-film effects.
• The study provides essential data for optimizing mm-wave applications in medicine and other fields.