Accurate double transmission measurement concepts for the permittivity determination in pneumatic conveying tubes with microwaves

In this contribution, two measurement concepts for the determination of volume fractions in multi phase flows are presented. Essential requirements for the proper functionality of double transmission measurement concepts, such as the feed side reflection suppression, are presented. The first measuring method uses a two state modulator which allows a high accurate feed side reflection suppression. The second measuring method makes use of a transpolarizing reflector which improves measuring speed and decreases setup complexity. In order to verify the introduced measuring methods, various electromagnetic field simulations and measurements on a borosilicate glass tube are presented and discussed in detail.