A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.T. Manabe was with the Institute for Telecommunication Sciences, NTIA-DoC, on leave from the Radio Research Laboratory, Ministry of Posts and Telecommunications, Koganei, Tokyo 184. He is now with ATR Optical and Radio Communications Research Laboratories, Seika-cho, Soraku-gun, Kyoto 619-02, Japan.