RPS S-1 Advisory Note: Compliance of mobile or portable transmitting equipment (100 kHz to 300 GHz)

This Advisory Note sets out the path to evaluate compliance with the requirements of the ARPANSA Standard for Limiting Exposure to Radiofrequency Fields – 100 kHz to 300 GHz (RPS S-1) for mobile or portable transmitting equipment that emits radiofrequency (RF) electromagnetic fields at frequencies between 100 kHz and 300 GHz.

Some mobile or portable transmitting equipment is designed to be used close to the body, for example push-to-talk radio devices or mobile phones. The RF fields produced by these devices may illuminate a small portion of the user’s body in a highly non-uniform spatial distribution. In such situations it may be practicable to determine compliance from a consideration of equipment parameters and conditions of use.

Compliance with the exposure limits is usually demonstrated by measurements or calculation of the RF fields produced by a device.  If the power used by or radiated from the device is sufficiently low, the emitted RF fields will be incapable of producing exposures that exceed the limits of RPS S-1. This inability could be due to limited power available to the antenna, the duty cycle of transmission, or a combination of both. In such circumstances it may be appropriate to provide an exemption from compliance testing.  

The evaluation of mobile or portable transmitting equipment for compliance with RPS S-1 is not required when the nominal mean power output delivered to the antenna does not exceed the Low Power Exclusion (LPE) Level as listed in Table 1 for the appropriate exposure condition. These values have been determined from the Basic Restrictions of RPS S-1 for local specific energy absorption rate (SAR, up to 6 GHz) and local absorbed power density (Sab above 6 GHz).

Table 1. Low Power Exclusion Levels for nominal mean output power averaged over 6 minutes.
Exposure scenario Low Power Exclusion Level at frequency, f
100 kHz ≤ f ≤ 6 GHz 6 GHz< f ≤ 30 GHz 30 GHz < f ≤ 300 GHz
Occupational 100 mW 40 mW 20 mW
General Public 20 mW 8 mW 4 mW

A flow diagram of the compliance process is shown in Figure 1.

Flow diagram of compliance assessment process.
Figure 1. Flow diagram of compliance assessment process.

For the purpose of this advisory note, mean power is, as defined by the ITU Radio Regulations, the average power over an interval of time that is long in comparison with the lowest modulating frequency. An exception to this is for pulse-modulated or intermittent transmissions in which case the mean power is determined as the peak-envelope-power (PEP) multiplied by the duty factor and where for duty factors of less than 5%, mean power is to be taken as 5% of PEP.

Under a restricted set of circumstances, an Alternative Low Power Exclusion (ALPE) Level may be used to assess the nominal mean power output of the device. Note that this approach has only been validated for frequencies in the range 300 MHz to 6 GHz at separations less than 25 mm for antennas with directivity not substantially greater than a half-wave dipole (i.e. 2.1 dBi).

The derivation of the ALPE Level is described in Annex B of the International Standard IEC 62479 (2010). The ALPE Level for a wireless device with a free space antenna bandwidth of BW percent located at a separation distance of s millimeters from the user’s body is defined by:

ALPE Level = exp [ As + Bs2 + C ln ( BW ) + D ].    (1)

The parameters A, B, C and D are third order polynomials of frequency. For compliance with the general public local SAR limit of 2 W/kg averaged over a mass of 10 g the parameters may be calculated using the following formulae:

A = ( -0.4588 f3 + 4.407 f2 – 6.112 f + 2.497 ) / 100    (2)

B = (0.1160 f3 - 1.402 f2 + 3.504 f – 0.4367 ) / 1000    (3)

C = ( -0.1333 f3 + 11.98 f2 – 110.8 f + 301.4 ) / 1000    (4)

D = -0.03540 f3 + 0.5023 f2 – 2.297 f + 6.104    (5)

where f is the frequency in GHz.

For compliance with the occupational local SAR limit of10 W/kg averaged over a mass of 10 g the ALPE Level is equivalent to the general public value (calculated using equations 1 to 5) multiplied by a factor of 5.

Calculation of the ALPE Level may be accomplished using the above formulae or by using the online tools supplied by ARPANSA or the Australian Communications and Media Authority.

Where neither of the test exemption conditions are satisfied, testing or mathematical modelling to demonstrate compliance with the restrictions as specified in RPS S-1 must be undertaken.  Such measurements or calculations should be based on normal use spatial relationships between the equipment and user.

When normal operation of the device entails the antenna being at least 20 cm from the user’s body, compliance may be assessed against the reference levels for the appropriate exposure category as specified in Tables 6 and 7 of RPS S-1.

Otherwise, compliance must be demonstrated against the local SAR restrictions as specified in Table 1 of RPS S-1.

The compliance assessment may be by direct measurement or evaluation in accordance with the recommendations of Australian and New Zealand Standard AS/NZS 2772.2 or other appropriate equivalent standards published by the International Electrotechnical Commission (IEC) or the Institute of Electrical and Electronics Engineers (IEEE).

Where operation of the equipment under unusual or inappropriate conditions is liable to exceed the local SAR restrictions, instructional material must be provided to caution the user against such usage. This should include any requirements regarding minimum separations.

References

AS/NZS 2772.2 (2016) Radiofrequency fields Principles and methods of measurement and computation - 3 kHz to 300 GHz, Standards Australia/Standards New Zealand, Sydney/Wellington Australia/New Zealand.

IEC 62479 (2010) Assessment of the compliance of low-power electronic and electrical equipment with the basic restrictions related to human exposure to electromagnetic fields (10 MHz to 300 GHz), published by the International Electrotechnical Commission, Geneva Switzerland.

RPS S-1 (2020) Radiation Protection Standard for Limiting Exposure to Radiofrequency Fields —100 kHz to 300 GHz, published by the Australian Radiation Protection and Nuclear Safety Agency, Yallambie Australia.