SAR compliance in Australia

The possibility of harmful effects of EMR has forced regulators to introduce SAR measurement standards for mobile and portable transmitting devices.

Regulations protecting people from exposure to harmful levels of RF electromagnetic radiation (EMR), also known as electromagnetic energy (EME), have been in force in Australia since 1990. The EMR regulations set limits for the specific absorption rate (SAR) of virtually all consumer RF transmitting devices. This article will discuss the Australian EMR regulations and the SAR measurement methodologies prescribed for the compliance testing of a range of wireless transmitting devices used in close proximity to the human body.

Introduction

There has recently been a proliferation of mobile and portable transmitter (MPT) devices that are used in close proximity to the human body. To ensure the protection of the public and workers from exposure to RF EMR, most countries have enforced regulations and standards to limit the exposure of persons to RF fields from MPT devices that have an integral antenna.

To legally market MPT devices in Australia, suppliers must comply with the provisions of the Australian Communications and Media Authority (ACMA) regulations on EMR and specific absorption rate (SAR). The ACMA has mandated the Radiocommunications (Electro-magnetic Radiation Human Exposure) Standard 2014, known as the EMR Standard.

This regulation has mandated the exposure limits prescribed by the human exposure standard published by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).

The RF human exposure evaluation methods differentiate between portable and mobile devices according to their proximity to exposed persons. Current methods of measurement are intended for devices used at the ear or devices used near other parts of the body. When MPT devices are used at a distance exceeding 20 cm from the human body and operate over the range 100 kHz to 300 GHz, the exposure levels can be evaluated with respect to electric or magnetic field strength limits. These limits are often referred to as Reference Levels and measurement is generally straightforward using conventional RF field meters or assessed by computation techniques.

When the antenna of an MPT device is less than 20 cm from the human body, measurement with a conventional EMR meter is not suitable because of the difficulty in trying to measure field levels in the extreme near field of a radiating antenna. The perturbation of the radiating fields caused by the close proximity of the human body adds further unacceptable measurement errors.

At distances closer than 20 cm, only SAR measurements may be used to determine compliance with the ARPANSA and ACMA requirements. The ARPANSA standard prescribes the limits and the criteria to be used to determine the appropriate evaluation method, ie, SAR or Reference Levels.

SAR limits, regulations and standards

SAR is a measure of the rate at which RF energy is absorbed per unit mass of human tissue (W/kg or mW/g). Australian and European human exposure standards have adopted the ICNIRP recommendations, which set SAR spatial peak limits of 2 W/kg measured in a 10 g cube of tissue for devices used near the head or body. The Federal Communications Commission (FCC) in the USA specifies SAR spatial peak limits of 1.6 W/kg measured in a 1 g cube of tissue. MPT devices are evaluated for SAR using the standard IEEE1528 while other devices are evaluated using Specific FCC published procedures known as FCC KDBs.

The SAR measurement methodologies for Australia are given in EN62209-1 (devices used at the ear) and EN 62209-2 (devices used at the body).

Influences on measured SAR

SAR is a measure of the rate of energy absorption per unit mass of tissue at a specific location in the tissue medium.

σ = conductivity of the tissue (S/m)

ρ = mass density of the tissue (kg/m³)

E = rms electric field strength (V/m)

For most handheld transmitters, the antenna radiates within 1–2 cm of the user’s head/body. Even at low power levels, relatively high field strengths would be expected near the antenna. The actual field strength is highly dependent on the location, orientation and electromagnetic characteristics of adjacent objects, including the user’s body. The RF energy is scattered and attenuated as it propagates through the body tissues. To account for near-field energy coupling effects, portable transmitters are evaluated with realistic head and body models (phantoms).

Current SAR measurement standards

The scope of both parts of current SAR measurement standard EN 62209 is limited to devices used up to a frequency range of 6 GHz.

The recently published IEC/EN 62209-1:2016, applicable for devices used at the ear over the frequency range 300 MHz to 6 GHz, has been adopted in Europe and Australia. No current harmonised standards exist for frequencies above 6 GHz; however, work on this is currently underway in international standards bodies. The latest standards also cater for concurrent exposures from multiple transmitters.

SAR evaluation criteria

Evaluation of an MPT device for compliance against the ARPANSA limits is determined by its specific characteristics eg, frequency, power and duty cycle as well as the intended operating positions and proximity relative to the human body. The scope of the ACMA EMR Standard 2014 applies in the range 100 kHz to 100 GHz while the SAR requirements are currently limited to the range 150 MHz to 5.8 GHz. The criteria and evaluation methods are summarised in Table 1.

User position	Applicable frequency range	ARPANSA/ACMA evaluation method
>20 cm from human body	100 kHz to 100 GHz	Power density or field strength reference level measurements — EMR meter or computation per AS/NZS 2772.2
20 cm or less from human body, >20 mW	150 MHz to 5800 MHz	SAR measurement if more than 20 mW — EN62209-2
Close proximity to human ear, >20 mW	300 MHz to 6000 MHz	SAR measurements at the ear, mobile/portable phones — EN62209-1
Less than 20 cm from human body	100 kHz to 100 GHz	If less than 20 mW — deemed to comply without testing

Table 1: ACMA EMR Standard 2014 Evaluation Criteria.

When the RF transmitter power is less than 20 mW averaged over 6 minutes, it is virtually impossible for the device to exceed the ARPANSA basic restrictions so it is deemed to comply without testing. This is referred to as the ‘non-evaluation criteria’.

For devices used within 20 cm of the human body, and the RF transmitter exceeds 20 mW average, compliance can only be determined by means of SAR measurements. The power threshold is 100 mW for aware user devices. Note that this is not consistent with USA (FCC) and Canada (ISED) requirements.

Devices used at the ear

In Australia, the EMR Standard 2014 accepts test method EN62209-1 for SAR measurements on mobile phones and similar devices and operating in the range 300 MHz to 6 GHz. The test report (from an accredited SAR test laboratory) must include the specific test data and other relevant information.

The Specific Anthropomorphic Mannequin (SAM) is specified for devices used at the ear and is called up by the published standards.

The SAM head phantom is based on the selected dimensions of a large anthropomorphic database of males and has specified dimensions and dielectric properties.

Test sample configuration

A mobile phone is tested against the SAM phantom in the positions that are precisely defined in the standard. The phone is set for centre frequency channel at maximum transmit power and the SAR measured in both ‘tilt’ and ‘cheek’ positions on the left and right sides of the head. The position of highest SAR on each side of the head is then tested for the upper and lower frequencies of the band. If the mobile phone has a retractable antenna, all of the tests described above are performed with the antenna extended and retracted.

The entire process is repeated for each transmitting band and each operating mode that is likely to result in higher SAR. Typical modes include GSM, 3G and 4G, and Wi-Fi. Simultaneous activation of different operating modes such as IEEE802.11a/b/g WLAN and Bluetooth functions is necessary if consistent with normal use. Configuring the mobile phone for normal operation in each operating mode can present a major challenge for the test engineer. Generally, it is not possible without sophisticated base station simulators and controllers.

Devices not used at the ear

The EMR Standard 2014 requires compliance for MPT devices operating over the range 100 kHz to 100 GHz. SAR measurements are specified over the range 150 MHz to 5.8 GHz. Compliance by means of SAR computation is currently excluded. An important difference between the FCC and ACMA methods is that ACMA SAR spatial peak limit is 2 W/kg averaged over a 10 g tissue mass compared with the FCC spatial peak limit of 1.6 W/kg averaged over a 1 g tissue mass.

Devices covered by the ACMA EMR Standard 2014 include mobile phones (belt clip position), PTT transmitters, body-worn transmitters, WLAN transmitters in laptop computers and generally all transmitting devices used within 20 cm of the human body that transmit RF power exceeding the ARPANSA threshold levels per the criteria of Table 1. The scope includes hi-tech clothing, wrist-worn cellular devices and body-worn IoT devices, to name a few.

Body phantoms for devices not used at the ear

A body phantom (also known as a flat phantom or box phantom) is specified for devices not used at the ear. The body phantom must be constructed from low-loss dielectric material with specified dimensions. The length and width of the flat phantom must be at least twice the corresponding dimensions of the device under test, including its antenna. The tissue simulating liquid is based on the average dielectric values of muscle tissue and must be a depth of 15.0 cm.

Test sample configuration

The body-worn position is simulated by placing the MPT device against the flat phantom and SAR is measured for each frequency band for the upper, middle and lower frequencies. Devices having an operating bandwidth of less than 10 MHz need only be tested at the centre frequency. A total of three SAR scans is usually sufficient for body-worn devices if the highest operating duty factor is used.

The effect of different operating modes, battery types and other accessories must be investigated. Battery droop or RF power drift must be factored into the final SAR result. Accessories such as headsets and microphones should be connected as per normal use and positioned against the flat phantom.

The ACMA setup for multimode devices differs from the FCC method. Special tests are described for devices where the difference between the highest output of a low-output mode and the lowest output of the high-output mode exceed 2.0 dB.

Tissue simulating liquid

The dielectric properties of the brain and muscle tissue simulating liquids are provided in the standards. The tissue dielectric values for the centre frequency of the transmission band should be within 5% of the target value. Linear interpolation should be used for other frequencies. The dielectric properties for muscle tissue simulating liquid are given by current FCC and ACMA standards and are provided in IEC 62209-1 and IIEC 62209-2. It is important to note that there are differences between these standards and IEEE1528 (used for FCC testing).

Laptop and tablet portable computers

EN62209-2 prescribes the methodology for SAR testing of laptop/tablet PCs. The location of the antenna determines whether or not SAR evaluation is required. Is it on the bottom? Along the front? On the lid? Can it operate with the lid closed? The highest measured SAR levels generally correspond to the location of the antennas and their proximity to the body. When the laptop PC is used in what is considered a ‘typical’ use position and the antenna is located at less than 20 cm from the any part of the human body, then SAR evaluation is necessary.

Lap-held position: This position simulates a laptop/tablet PC used on a person’s lap. The bottom side of the laptop is pressed against a flat phantom.

Arm-held (interactive display) position: If a tablet PC has display-mounted antennas and an interactive screen display then this test configuration may be applicable. The face of the tablet screen is pressed against the flat phantom.

Edge position: SAR evaluation is required when antennas are located along the edges of the screen surround as normal use is within 20 cm of the human body.

Other positions: All typical use positions must be considered including the ‘back of lid’ position.

WLAN/Wi-Fi devices

WLAN/Wi-Fi transmitters installed in laptop computers or handheld devices must be assessed in a host device. Each operating mode must be assessed and device modulation, power output and duty cycles must be taken into account. The intent is to ensure that the worst-case SAR is determined. Some personal portable computers use three bands eg, 2.45 GHz, 5.2 GHz and 5.8 GHz and some also include the Bluetooth function. If each WLAN module has an antenna then the cumulative (worst-case) SAR levels should be determined.

Using pre-approved transmitter modules does not guarantee compliance because it is not known how the original module was configured for the original compliance test. In some cases, different antennas are used, or different modules using different modes may operate simultaneously.

Two-way radios (PTT)/portable phones

PTT two-way radios and portable phones operating in the range 150 MHz to 5.8 GHz require SAR evaluation for the face and body positions, both simulated with a flat phantom.

Belt-clip position: The MPT device is placed underneath a flat phantom and suspended until the belt clip touches the phantom. If the device incorporates a headphone socket then it is a requirement to test with the hands-free earpiece/microphone connected.

Face position: The device is placed 2.5 cm from the phantom.

Conclusion

The Australian SAR regulatory and approval requirements have been explained. The scope of the current harmonised SAR measurement standards includes all devices that transmit more than 20 mW and are used in close proximity to the body. The possibility of harmful effects of EMR has forced the regulators to introduce SAR measurement standards. Work is currently underway in international standards bodies and it is expected that internationally harmonised SAR testing methods and procedures will soon be available to cater for 5G devices.

References:

Radiocommunications (Electromagnetic Radiation – Human Exposure) Standard 2014; Australian Communications Authority regulation, first gazetted 1 March 2003 under section 162 Radiocommunications Act 1992.

Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) Radiation Protection Series 3 - Radiation Protection Standard for Maximum Exposure Levels to Radiofrequency Fields — 3 kHz to 300 GHz.

International commission on Non-Ionising Radiation Protection (1998), Guidelines for limiting exposure in time varying electric, magnetic and electromagnetic fields (up to 300 GHz). Health Physics 74, 494-522.

IEEE 1528 Recommended Practice for Determining the Peak Spatial-Average Specific Absorption Rate (SAR) in the Human Body Due to Wireless Communications Devices: Experimental Techniques.

FCC OET Bulletin 65, Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields. SUPPLEMENT C Edition 01-01 to OET BULLETIN 65 Edition 97-01.

EN50361: 2001: Basic Standard for the measurement of specific Absorption Rate related to human exposure to electromagnetic fields from mobile phones (300 MHz to 3 GHz).

IEC 62209-1: Human exposure to radio frequency fields from hand-held and body-mounted wireless communication devices — Human models, instrumentation, and procedures — Part 1: Procedure to determine the specific absorption rate (SAR) for hand-held devices used in close proximity to the ear (frequency range of 300 MHz to 6 GHz).

IEC 62209-2: Human exposure to radio frequency fields from hand-held and body-mounted wireless communication devices — Human models, instrumentation, and procedures — Part 2: Procedure to determine the Specific Absorption Rate (SAR) in the head and body for 30 MHz to 6 GHz Handheld and Body-Mounted Devices used in close proximity to the Body.