Exposure data include SAR (W/kg) (Table I-1, Table I-5), chamber field strength (V/m) (Tables I2 and I6), and E- and H-field measurements (V/m) (Table I-3, Table I-4, Table I-7, Table I-8). For the medium and high dose GSM chambers, where a second E-field probe was used, the H-field measurements were converted from E-field measurements (E-field divided by 377). Fields were measured continuously throughout the study and measurements were automatically recorded approximately every 20 seconds. For every 20-second interval, the SAR was calculated based on the average H- and/or E-field data. The data presented for each exposure parameter include the mean and standard deviation [expressed in decibels (dB), W/kg, or V/m]; the total number of measurements recorded during the identified period of exposure (>44,000 calculated SAR per month and more than 1.1 million over the course of the 2-year study); the lowest (min) and highest (max) measurement recorded during the given exposure period; the number of measurements that were within the acceptable range; and the ratio of all measurements within range. The data reported for SAR also include the range of animal body weights (g) over the indicated time period of exposure, as well as the selected target SAR for each group. The data reported for field strengths (chamber, E-field, and H-field) include the target range of the field required to maintain appropriate SAR exposures. The minimum and maximum exposure values reported represent a single recorded measurement over the 2-year exposure period. The SAR and chamber-field in the sham and exposure chambers were within the target ranges (defined as ± 2 dB) for >99.85% of recorded measurements over the course of the 2-year study; ≥99.70% of E-field and H-field exposures in the sham and exposure chambers were within the target ranges for all but one chamber (97.35% within range).

The dB is a mathematical transformation of a number or numerical ratio using base 10 logarithms. Multiplication of ratios is transformed into addition of dBs; raising a number to a power is transformed into multiplication of dBs.

In general, dB(power) = 10 × log(R), and dB(field) = 20 × log(R). The formulas differ by a factor of two because power or SAR varies as the square of the fields. For SAR (in watts/kg), the decibel formula is calculated as:

SAR(dB) = 10 × log(SAR_M/SAR_T)

where SAR_M is the measured value and SAR_T is the target value, and

–2 dB = 10 × log(SARL/SART), where SARL (low) = SART × 10–0.2

+2 dB = 10 × log(SARH/SART), where SARH (high) = SART × 100.2

On this basis, the ± 2 dB range specified by NTP translates to the following ranges for each SAR used in the 2-year study:

Target SAR (W/kg): Acceptable SAR Range (W/kg; ± 2 dB)

2.5: 1.58 to 3.96

5: 3.15 to 7.92

10: 6.31 to 15.85