Wave-Matter Interaction at mm-Wave Frequencies

The physical concepts underlying the wave-matter interaction, particularly at mm-wave frequencies, are reviewed and discussed in this talk. Health hazard associated with electromagnetic wave exposures are then discussed. These can generally be categorized as ionizing and non-ionizing effects. Health impact of mm-wave exposures belong to the latter, and therefore can be either the direct increase in the body temperature or the indirect overloading of the biological processes responsible for the body thermal regulation. At wavelengths that are much larger than the atomic/molecular scale, a continuous spatial distribution of the electromagnetic wave is an adequate mathematical representation. The wave power-density is described by the Poynting vector, and the power transfer from the wave to the biological substances can be calculated with high precision using the concept of constitutive parameters (conductivity, permittivity, and permeability). These are macroscopic spectral quantities (moving spatial averages), which cannot account for special treatment of specific molecular-scale structures similar to that of, for instance, a DNA strand. mm-Waves and even THz waves belong to this category. In addition, the mm-waves suffer from very strong attenuation inside the human body, so that they cannot penetrate deeper than a few millimeters.