On the measurement errors in SAR supervision introduced by directional couplers

Area of Science:

• Electromagnetics
• Radio Frequency Engineering
• Biomedical Engineering

Background:

• Online Specific Absorption Rate (SAR) supervision is crucial for monitoring electromagnetic field exposure.
• Directional couplers are commonly used in SAR measurement systems but can introduce calculation errors.
• Quantifying these errors is essential for ensuring accurate SAR supervision.

Purpose of the Study:

• To develop a mathematical framework for determining calculation errors in online SAR supervision due to directional couplers.
• To establish a method for calculating a safety factor to mitigate these inaccuracies.
• To assess the impact of directional coupler performance on SAR calculation accuracy.

Main Methods:

• A novel mathematical framework was developed to represent measurement errors as virtual observation points (VOPs).
• An optimization process was used to compare VOPs and calculate the maximum SAR underestimation.
• The framework was validated by applying it to five different radio frequency (RF) arrays.

Main Results:

• SAR calculation error is highly sensitive to the directional coupler's reference plane position and array S-parameters.
• Achieving less than 5% error necessitates directional couplers with directivity exceeding 40 dB for the studied arrays.
• The findings highlight the critical role of coupler directivity in accurate SAR measurements.

Conclusions:

• The proposed framework offers a robust method for quantifying directional coupler-induced errors in online SAR supervision.
• It enables the calculation of a safety factor to ensure reliable SAR measurements.
• The framework's adaptability allows for its application to various measurement types beyond SAR supervision.