Measuring Moisture in Bauxite with Microwaves

Abstract

AbstractMoisture measurement in bauxite ore as it is being offloaded from a ship is a challenge that was brought to a European Study Group with Industry at the University of Limerick in 2017. A refinery asked the Study Group to confirm if it is possible to calculate the moisture content once every second, by passing microwaves through the ore as it is being offloaded at about 2 m/s. The microwaves experience a phase shift and signal attenuation, depending on the amount of moisture present. We review the theory of microwave transmission through a polarising medium, and we present and study the data produced by the microwave analyser. We explore the consequences of the method for measuring phase change, and the effects of noise on the phase shifts observed. We provide an algorithm for lifting the measured phase shifts from their restricted range to an unlimited range for the true phase shift. Concurrent measurements of ore height are central to the lifting algorithm. We note the effect of interference on the attenuation seen in data.KeywordsMicrowavesMoistureBauxiteLifting algorithmContinuous measurement