Recent Advances in Broad-Band VHF and UHF Transmission Line Methods for Moisture Content and Dielectric Constant Measurement

Recent advances in VHF and UHF transmission line methods for determining either the complex permittivity or moisture content of bulky or film-like materials, or the thickness of film-like materials are discussed. These methods include TDR, CW phase, and |S21| transmission methods and employ a time-domain reflectometer (TDR), a vector voltmeter, and a network analyzer, respectively. Each technique involves monitoring the change of the transmission line parameters of a balanced open line, or of an unbalanced coaxial transmission line, when loaded with the material under test. Particular attention is given to the frequency range 10 to 1000 MHz and to broad-band methods. Experimental results are presented for several common materials, viz. concrete, asphalt, Plexiglas, moist paper, and moist soil.