A modified tri-plate transmission line structure for the characterisation of liquid dielectrics

In this paper, a modified tri-plate transmission line structure is described for the characterization of O/W (oil in water) emulsions and other liquid dielectrics. It mainly consists of a tri-plate structure with the liquid to be tested filled into slots which are symmetrically placed between the centre conductor and the outer conductors of the tri-plate, the remaining cross section of which consists of Plexiglas. This test structure is used in conjunction with a PC based measurement system, into which mathematical models of the modified tri-plate structure have been implemented, linking measured resonance frequencies to the dielectric properties of the emulsion/liquid partially filling the cross-section. Particularly, a quasi-static model and a full-wave mode matching analysis have been implemented and tested. From the dielectric data extracted together with simple calibration data, the oil content of O/W emulsions can be directly derived without conventional chemical analysis techniques.