Assessment of Human Skin Emissivity using Passive Millimetre-Wave Sensing

Over the past few decades technology in the millimetre wave band has shown a steady and consistent development and increased usage, with a wide variety of devices and system architectures (imaging, non-imaging, radiometers and radars) sensors becoming available. As an imaging sensor, these systems can deliver spatial resolutions of less than the wavelength, which in the millimetre wave band is down to about 1.0 mm. This property enables highly localised measurements to be made of skin which cannot be seen in the visible region of the spectrum. A convenient metric to describe the condition of human skin is the emissivity. Many studies reveal strong correlation between skin dielectric properties, skin thickness, water content and hydration level with age, gender and body site. This study is aiming to assess variation in emissivity between different body sites, age groups and genders over the frequency band (80-100) GHz to obtain a deeper understanding of the signatures of human skin in the millimetre wave frequency band. In this paper a technique to measure the human skin emissivity in vivo is described over the frequency band 80-100 GHz. Emissivity measurements were performed on 60 participants, 35 males and 25 females ranging in age 20-60 years. Results show that emissivity of males higher than that of females. The study also confirm variation trend of emissivity with age for both genders. The results suggest that variation in emissivity over the age is due to variation on skin thickness and water content.