1. A system for determining characteristics of a multi-material object comprising: a measurement unit to obtain a measured electrical signal set from electrodes surrounding the multi-material object; and a processing circuitry configured to perform steps of: determining an electric element matrix representing the multi-material object based on the measured electrical signal set; pre-multiplying the electric element matrix with a first mathematical transformation matrix to obtain a first transformed electric element matrix; post-multiplying the first transformed electric element matrix with a second mathematical transformation matrix to obtain a second transformed electric element matrix; and determining the characteristics of the multi-material object based on the second transformed electric element matrix, wherein the characteristics of the multi-material object comprise compositions and distributions of different materials within the multi-material object.