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Interaction of a 2450-MHz Microwave Field with Thermocouples and Thermistors

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McRee · 1973

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In a 2450 MHz microwave field at 100 mW/cm², thermistors gave valid temperature readings with no detectable interaction, while unshielded thermocouples produced erroneous readings.

Plain English Summary

Summary written for general audiences

This 1972 study examined how a 2450 MHz continuous wave microwave field interacts with temperature measurement devices like thermocouples and thermistors, with and without copper braided shielding on the leads. At 100 mW/cm², shielded and unshielded thermistors provided valid measurements with no detectable interaction, while unshielded thermocouples were totally unsatisfactory as detectors and shielding of the leads eliminated most of their problems.

Why This Matters

This is a technical study about measurement equipment, and it bears on microwave research generally. The energy absorbed by a biological specimen is usually measured by thermistors or thermocouples, and erroneous measurements can result when the incoming microwave field interacts with these devices. In a 2450 MHz field at 100 mW/cm², thermistors showed no detectable interaction, while unshielded thermocouples produced randomness and artifacts in the measurements. Shielding the thermocouple leads eliminated most of these problems, although a small amount of interaction was detectable when the leads were parallel to the electric field.

Figures from the Original Paper

Diagrams extracted from the original research document.

chartPage 3 - AI-described figure: Fig. 3: Shielded and unshielded thermistor results.
p. 3 of the original PDF
chartPage 4 - AI-described figure: A graph showing shielded thermocouple results with temperature changes over time.
p. 4 of the original PDF
Cite This Study
McRee (1973). Interaction of a 2450-MHz Microwave Field with Thermocouples and Thermistors.
Show BibTeX
@article{interaction_of_a_2450_mhz_microwave_field_with_thermocouples_and_thermistors_g3801,
  author = {McRee},
  title = {Interaction of a 2450-MHz Microwave Field with Thermocouples and Thermistors},
  year = {1973},
  
  
}
No DOI on file for this study.

Quick Questions About This Study

It depended on the sensor. In a 2450 MHz field at 100 mW/cm², shielded and unshielded thermistors gave valid measurements with no detectable interaction, while unshielded thermocouples were totally unsatisfactory because they interacted with the field.
The study set the power level at the thermocouple or thermistor sensing area to 100 mW/cm² (milliwatts per square centimeter) in a continuous wave 2450 MHz field.
Shielding of the leads eliminated most of the thermocouple problems, although a small amount of interaction was detectable when the leads were parallel to the electric field. Unshielded thermocouples were totally unsatisfactory as detectors.
Thermistors and thermocouples are the usual way to measure the energy absorbed by a biological specimen in microwave experiments. Erroneous measurements may result from interactions of the incoming microwave field with these temperature measuring devices.
Yes, researchers placed thermistors and thermocouples in two different geometric arrangements within the 2450 MHz field to evaluate how positioning affects microwave interference with the temperature sensing devices.