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%.