UWB time domain transmission sensor for free-space moisture measurements

This paper presents an UWB time domain transmission system for free-space moisture measurements. The system is capable of transmitting UWB signals having a bandwidth of several gigahertz which illuminate the samples. The size of the samples is in the range of some of the transmitted wavelengths and is smaller than the antennas' footprints. The scattered pulses are collected by an array of receiving antennas. The received signals can be sampled instantaneously with just one receiving channel and a special combiner, which adds a time shift to each antenna path in order to separate the signals in time. Multivariate calibration is applied in order to develop a statistical model for the moisture content of the samples. An accuracy for the determination of the moisture content of 0.61% is achieved while the range of moisture is varied from 1.7% to 20%.