Steady-state analysis of self-heated thermistors using finite elements

Area of Science:

• Biomedical Engineering
• Thermal Analysis
• Materials Science

Background:

• Accurate measurement of biological tissue thermal conductivity is crucial for various medical applications, including thermal therapy and cryosurgery.
• Existing methods often rely on analytical models with simplifying assumptions about thermistor probe geometry and heat generation patterns.
• The validity of these assumptions in real-world scenarios, particularly with complex probe shapes and non-uniform heating, requires rigorous investigation.

Purpose of the Study:

• To numerically validate the thermal assumptions underpinning an analytical model for tissue thermal conductivity measurement using a thermistor probe.
• To assess the accuracy of a derived linear relationship between thermistor temperature rise, power input, and tissue thermal conductivity under realistic conditions.

Main Methods:

• Employed finite element methods (FEM) to simulate steady-state temperature profiles generated by thermistor probes.
• Utilized realistic thermistor geometries (prolate spheroid with a passive shell) and non-uniform internal heat generation patterns in the simulations.
• Compared FEM results against the predictions of an analytical model based on simplified assumptions (spherical bead, uniform heating).

Main Results:

• FEM simulations generated accurate temperature profiles for the complex thermistor probe model.
• The study found that the empirical linear relationship between thermistor temperature rise and electrical power input remains valid.
• This validity holds even when simplifying assumptions regarding thermistor shape and heat distribution are significantly relaxed.

Conclusions:

• The finite element analysis confirms the robustness of the analytical model for determining tissue thermal conductivity.
• The validated linear relationship provides a reliable basis for experimental thermal conductivity measurements in biological tissues.
• This research enhances confidence in using thermistor-based methods for precise thermal property assessment in biomedical contexts.