Title: Measuring the complex permittivity tensor of uniaxial biological materials with coplanar waveguide transmission line Authors
Submitted to: Microwave and Wireless Components Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 31, 2014
Publication Date: N/A
Interpretive Summary: Dielectric properties, or permittivities, of materials are electrical characteristics that determine how they interact with electric fields. For example, these properties determine how rapidly the material will heat in a microwave oven. The dielectric properties of agricultural and food materials are also often correlated with quality characteristics of such materials. When useful correlations are found, permittivities of agricultural products can be useful for rapid sensing of the quality of such materials with electrical instruments designed for that purpose. Permittivities of some materials are anisotropic. That is, the value of the permittivitiy may depend upon the orientation of the material when it is subjected to the electric field. Thus, it is useful to know whether or not a material is anisotropic. This requires a technique for measuring the permittivity tensor, which provides the components of the permittivity, or dielectric properties, in two dimensions. This paper describes the use of a coplanar waveguide sensor, which is a transmission line formed on the surface of a plane printed-circuit board. In this case, two small transmission lines of different length on the printed-circuit board were used for the necessary measurements. The theory underlying the permittivity measurement technique is described in the paper, and results are presented for anisotropic permittivity measurements on four chicken breast samples and one beef sirloin tip sample. These results, illustrated in an elliptical pattern, are useful in judging the degree of anisotropy present in the permittivity. The new technique will be helpful in ongoing research to evaluate the usefulness of dielectric properties in sensing the quality of meat samples. Successful use of the principle may lead to rapid, nondestructive measurements for meat samples, which would be of benefit to processors, marketers and consumers.
Technical Abstract: A simple and accurate technique is described for measuring the uniaxial permittivity tensor of biological materials with a coplanar waveguide transmission-line configuration. Permittivity tensor results are presented for several chicken and beef fresh meat samples at 2.45 GHz.