This blog shows how to enable support for expression input in the Fields Calculator for HFSS and Maxwell. Introduced as a beta feature in the 2025 R1 release, this capability allows users to work with both stack and algebraic input modes when building expressions. In the following example, we calculate the capacitance of a simple parallel plate structure using each method and compare the results with the solution data.
1. Enabling Expression Input in the Fields Calculator
To enable this feature, go to Tools > Options > General Options, and under General > Desktop Configuration, click the Beta Options button.
In the Beta Options window, check the box for HFSS/Maxwell Support Expression Input in Fields Calculator. Once enabled, you will be able to switch between the traditional stack-based method and the algebraic method.
2. Calculating Capacitance Using the Fields Calculator
In this example, we calculate the capacitance of parallel plates using both the stack-based and algebraic methods in the Fields Calculator.
After running the simulation, you can find the capacitance value in the results under Solution Data, which in this case is approximately 14.941 pF.
To verify this result, we use the Fields Calculator. The capacitance formula is:
C = (ε₀ · εᵣ · A) / d
where ε₀ is the permittivity of free space, εr is the relative permittivity of the dielectric material between the plates, A is the area of the plates, and d is the distance separating them.
As shown below, the Fields Calculator returns a capacitance value of approximately 14.941 pF, which matches the simulation results.
The Fields Calculator automatically converts the expression as you switch between the stack-based and algebraic methods.
The video below walks through this example in detail, and the model is included in the downloadable resources.
Downloadable Resources
Capacitance Calculation
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