Reflective Measurement Of Water Concentration Using Millimeter Wave Illumination

Terahertz (THz) and millimeter wave (mmW) sensing have shown the potential to become valuable medical imaging tools because of their sensitivity to water and their safe, non-ionizing photon energies. Using the high dielectric constant of water in these frequency bands, reflection-mode mmW sensing systems can be employed to measure water content in target materials with high sensitivity. This sensitivity may lead to the development of clinically useful systems to measure the hydration state of biological targets. Such measurements may be useful for fast and convenient diagnosis of conditions whose symptoms can be characterized by changes in tissue water concentration such as skin burns, dehydration, or chemical exposure. This system employs a 100 GHz Gunn diode source and pyroelectric detector to perform point reflectivity measurements of a wetted cellulose towel as it dries on a mass balance. A noise-limited sensitivity to water concentration differences (Noise Equivalent Water Concentration Difference) of less than 0.074% by mass was measured in a sample drying between 70% and 80% water concentration. This sensitivity may be sufficient to identify disease-related water concentration changes in skin, cornea, and liver tissues and may lead to clinical tools to assess diseases such as skin burns, liver cirrhosis, and corneal dystrophy and graft rejection.