General Loss Model
This loss model includes the metalization surface resistance quantities Rdc and Rrf as described in the Rdc/Rrf Metal Model section. It adds metalization reactance, composed of the Surface Reactance (Xdc), and the Surface Inductance (Ls). Xdc is specified, in Ohms/square (by default) and uses a constant reactance value versus frequency. Ls is specified in the pH/square and models the reactance as linearly proportional to frequency.
Superconductor physics leads to traces that have both a magnetic inductance and a kinetic inductance (Lk). The magnetic inductance of all conductors is captured in the EM analysis for all metal types. The General Model Ls setting can be used to include the additional kinetic inductance found in superconductors. The value of LK is based on several variables, and it is best to work with the group fabricating your device for a precise value for your application. The superconductor field is constantly changing, so reviewing the latest literature may also be useful to determine an appropriate Lk value.
Tip: All the values in the general model may be specified using equations that can be a function of frequency or other constants such as temperature. Therefore, any complex surface impedance may be modeled by using a combination of Rdc, Xdc, and/or Ls, and these values may be a function of frequency.
One approximation for using the General Model for superconductors is given below, where the kinetic inductance is a function of temperature:
The equation for the kinetic inductance is from Shen, Z.Y., "High-Temperature Superconducting Microwave Circuits," Boston, 1994, Artech House and there are certain assumptions. Please review the condition cited in the book to determine if this equation is appropriate for your application.
Please see the Sonnet's Superconductor References web page for additional superconductor references.