A reflective terahertz (THz) system has been under development for imaging and monitoring of skin hydration, and
through consideration of attenuation, scattering, spatial resolution and measurement of sensitivity, the frequency band
0.4 - 0.7 THz has been determined optimal for operation. THz, typically defined as the frequency range between 0.1-10
THz, has been proposed for skin hydration imaging and monitoring primarily due to being non-ionizing radiation and
highly sensitivity to water concentrations. While it is important to maximize measurement sensitivity to changes in water
concentration, the optimal operational frequency band must simultaneously minimize the scattering from the targets (i.e.
skin) and attenuation, as well as maximize the spatial resolution. In terms of atmospheric attenuation, from 0.4 to 1 THz,
there are broad absorption lines at 556 GHz and 750 GHz, and large transmission windows centered at 500, 650, and 870
GHz. Scattering of the energy reflected from skin was show, using modeling, that as the frequency increased there was a
considerable decrease in the power fraction reflected in the specular direction. For measurement sensitivity, it was
shown that a change in reflectivity per change in water volume at 100 GHz was nearly an order of magnitude higher at 1
THz. Finally, as should be expected, higher frequencies were better for spatial resolution. In consideration of the above
criteria, the motivation for using the 0.4-0.7 THz band will be presented as well as an overview the developed THz pulse
reflective imaging system for imaging of skin hydration.