Design of solid broadband human tissue simulant materials

The basis of a quantitative design process for solid broadband human tissue simulant materials is described. It is shown that the complex permittivity spectra of human tissue is not well represented by simple effective media theory (equivalent to using a single Debye-type dielectric relaxation), but that it can be represented by a percolative response. A solid two-layer spherical phantom with material properties representative of human head tissue over the frequency range 1 MHz to 10 GHz has been designed and tested. Such a simple phantom geometry was selected to assist, through validation, the development of related electromagnetic computer models. The dielectric properties of the simulant materials were tailored using appropriate quantities of a conducting filler dispersed in an insulating thermosetting plastic matrix. The two materials exhibit both a dielectric constant and an AC conductivity comparable (to first approximation) to that of human grey matter and fat. The phantom was constructed by injection moulding. The uniformity of the electromagnetic properties throughout the phantom and their temperature dependence were both assessed using broadband dielectric spectroscopy.