EEG Electrode Caps Can Reduce SAR Induced in the Head by GSM900 Mobile Phones

Abstract

This paper investigates the influence of EEG electrode caps on specific absorption rate (SAR) in the head from a GSM900 mobile phone (217-Hz modulation, peak power output 2 W). SAR measurements were recorded in an anthropomorphic phantom using a precision robotic system. Peak 10 g average SAR in the whole head and in just the temporal region was compared for three phantom arrangements; no cap, 64-electrode "ElectroCap," and 64-electrode "Quick-Cap". Relative to the "no cap" arrangement, the Electro-Cap and Quick-Cap caused a peak SAR (10 g) reduction of 14% and 18% respectively in both the whole head and in the temporal region. Additional computational modeling confirmed that SAR (10 g) is reduced by the presence of electrode leads and that the extent of the effect varies according to the orientation of the leads with respect to the radiofrequency (RF) source. The modeling also indicated that the nonconductive shell between the electrodes and simulated head material does not significantly alter the electrode lead shielding effect. The observed SAR reductions are not likely to be sufficiently large to have accounted for null EEG findings in the past but should nonetheless be noted in studies aiming to measure and report human brain activity under similar exposure conditions. Abstract-This paper investigates the influence of EEG electrode caps on specific absorption rate (SAR) in the head from a GSM900 mobile phone (217-Hz modulation, peak power output 2 W). SAR measurements were recorded in an anthropomorphic phantom using a precision robotic system. Peak 10 g average SAR in the whole head and in just the temporal region was compared for three phantom arrangements; no cap, 64-electrode "Electro-Cap," and 64-electrode "Quick-Cap". Relative to the "no cap" arrangement, the Electro-Cap and Quick-Cap caused a peak SAR (10 g) reduction of 14% and 18% respectively in both the whole head and in the temporal region. Additional computational modeling confirmed that SAR (10 g) is reduced by the presence of electrode leads and that the extent of the effect varies according to the orientation of the leads with respect to the radiofrequency (RF) source. The modeling also indicated that the nonconductive shell between the electrodes and simulated head material does not significantly alter the electrode lead shielding effect. The observed SAR reductions are not likely to be sufficiently large to have accounted for null EEG findings in the past but should nonetheless be noted in studies aiming to measure and report human brain activity under similar exposure conditions.

Pulse modulated radiofrequency exposure influences cognitive performance

“…Generally, EEG electrode leads have been found to produce a shielding effect, reducing the SAR in head regions close to the antenna and also where the maximum value is obtained. The reduction in SAR tends to be less than 20% (Murbach et al, 2014, Hamblin et al, 2007. These findings indicate that electrode configurations do not act like an antenna, and therefore do not enhance SAR.…”

“…These findings indicate that electrode configurations do not act like an antenna, and therefore do not enhance SAR. Furthermore, as the reductions have been found to be less than 20%, electrode configurations are also not thought to greatly attenuate SAR to the point where results are influenced (Murbach et al, 2014, Hamblin et al, 2007.…”

Specific Absorption Rate Analysis of Heterogeneous Head Models with EEG Electrodes/Leads at 7T MRI

“…We have modeled 32 electrodes and leads, a configuration currently used in many laboratories for EEG-MRI recordings. The results of this study cannot be directly extrapolated to different number of electrodes, because the presence of more leads may increase the interaction with the EM field, with resulting SAR in the head that could be higher or lower, depending on the geometry, the shielding effect of the EEG leads [Hamblin 2007] and the frequency considered [Angelone 2004]. …”

“…The interactions of the EEG leads and RF coils will induce changes in the EM field inside the head (i.e., "shielding effect" of the EEG leads) [Hamblin 2007] and local SAR enhancement at the interface between electrodes and skin [Armenean 2004, Yeung 2002 Table 1) determines an electric field enhancement at the interface between leads and head surface (i.e., epidermis). This observation is in line with theoretical models [Guy 1975] and physical evidence of reports of burns due to "antenna-effect" of leads [Dempsey 2001].…”

“…Figure 4 shows the effect of metallic leads with the head. The superposition of the electric field radiated from the RF coil and field scattered by the leads resulted in an increase of the field near the leads and on the skin, and in a reduction of the field at the center of the head ("shielding effect of the EEG leads") [Hamblin 2007]. There was a peak of induced currents on the skin, near the leads.…”