Wireless microwave based moisture sensors for hardwood drying kilns

This goal of this project was to develop a prototype microwave based moisture sensor system to be used in a hardwood dry kiln. The individual moisture sensors are battery powered and will communicate with the host kiln control system via spread spectrum wireless communications. To the present we have developed 2 separate designs of launcher/receiver systems working at 4.5 GHz to 6 GHz that give a linear response to moisture content (MC) over a range of 90% MC to 6% MC. These sensors allow us to make a swept frequency transmission measurement through a small area of a board. We have developed electronic circuit boards that provide the microwave excitation and read and store the microwave signal returned through the wood. We are currently testing the "second generation" prototype electronics to go into the kiln mated with these launchers to produce a prototype MC measurement system design to be tested in kilns. We are able to obtain the same MC accuracy with our small circuit boards as we did with the laboratory network analyzer. We are proceeding to a 3^rd generation micro-circuit design that will provide gains in reliability and lower the eventual commercialization cost.