Method Using Bilinear Transformation for Measurement of Impedance Parameters of a Multielement Two-Terminal Network

This paper presents a method for the identification of the impedance parameters of objects, which can be modeled by two-terminal networks. The method uses the properties of bilinear transformation, which allows presentation of object impedance as a function of each parameter of the equivalent circuit of the object. Inverse bilinear transformation allows the determination of the value of each parameter on the basis of impedance measurement at a single frequency. The measurement frequency is selected for each identified element (on the basis of the minimal relative sensitivity of the identified element to changes of other elements), so the number of measurement frequencies is equal to the number of elements to be identified. This makes it possible to shorten the identification time when compared with the traditional identification method based on the impedance spectrum fitting method (complex nonlinear least squares). When the object model and the order of component values are known, the developed method fully assures conditions that allow an implementation in low-cost portable diagnostic instruments.