SAR Associated with the Use of Hands Free Kits (HFKs) for GSM Cellphones

The document Sar_Associated_with_the_Use_of_Hands_Free provides an in-depth analysis of Specific Absorption Rate (SAR) levels associated with the use of Hands-Free Kits (HFKs) for GSM mobile telephones. Below is a summary of the findings and conclusions:

Key Findings:

1. SAR Levels and Hands-Free Kits:
   • SAR levels within the head are generally lower when using HFKs compared to using mobile phones directly against the head.
   • The peak 10g average SAR values measured in a phantom head were reduced when phones were used with HFKs.
2. Factors Influencing SAR Levels:
   • Strong Factors:
     • HFK Layout Relative to the Phone: Optimal positioning of the HFK significantly reduces SAR levels.
     • Proximity of the HFK to Other Body Parts: SAR levels increase if the HFK cable runs close to the torso.
   • Moderate Factors:
     • Proximity to the Head: This becomes more significant at higher frequencies due to shorter wavelengths.
   • Weak Factors:
     • Specific HFK type, although it affects the location of the SAR peak.
     • Frequency band changes, as differences in coupling efficiency can offset changes in power.
3. Optimal Configuration:
   • When the HFK cable is positioned away from the body (e.g., “tabletop” configuration), SAR levels are minimized.
   • Ferrite beads placed along the HFK cable can further reduce SAR by mitigating induced currents.
4. Measurement Observations:
   • SAR and induced currents were assessed using human subjects and phantom models in anechoic chambers. Measurements showed consistency across different setups.
   • Configurations where the HFK cable was taped to the body (“Body Close”) resulted in higher SAR levels compared to free-standing configurations.
5. Frequency Bands:
   • SAR at 1750 MHz was generally lower than at 888 MHz, partly due to a 3dB reduction in power at higher frequencies.

Recommendations:

1. Ferrite Bead Usage:
   • Ferrite beads should be installed on HFK cables, at least 15 cm from the earpiece, to minimize SAR levels effectively.
2. Public Safety:
   • Awareness about optimal HFK usage is crucial. Misuse or suboptimal configurations can increase SAR levels instead of reducing them.
3. Standards and Testing:
   • Standardized testing for SAR in HFK-phone combinations should be developed, focusing on realistic worst-case configurations.

Conclusion:

This study confirms that using HFKs can significantly reduce SAR levels in the head when compared to direct phone usage. However, the effectiveness depends on the HFK’s layout, the user’s positioning, and the frequency band. Adopting optimal configurations and additional safeguards, such as ferrite beads, can further enhance safety.

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