Wireless devices have become a part of our everyday life, from mobile phones, to wireless speakers, to your smart watch. These pieces of technology are commonplace in our modern-day existence, with reminders, notifications, and automated tasks, it seems odd to note that even after 47 years since the first cell phone, there are still some health risks associated with wireless technology.
But what are these health risks? At the frequencies at which most of these devices operate, the known health effects center around tissue heating, the measurement for this effect is known as Specific Absorption Rate (SAR). As part of worldwide efforts to regulate consumer health and safety aspects, many authorities now require products that are placed on the market to meet SAR limits. As new wireless devices hit the market every day, SAR is therefore becoming a fast-growing requirement for companies that make such products.

US Regulations

The basis for US requirements are ANSI/IEEE C95.1 and ANSI/IEEE C95.3 which establish exposure limits. These standards are reflected in the current FCC requirements found in 47 CFR §2.1091 and 2.1093 and OET 65 Supplement C 01:01. Under the FCC’s rules, the following types of devices are subject to routine environmental evaluation for RF exposure prior to equipment authorization or use:

● Fixed, mobile and portable transmitting devices that operate in the Cellular Radiotelephone, Personal Communications (PCS), Satellite Communications, General Wireless Communications, Wireless Communications, Maritime (ship earth stations only) and Specialized Mobile Radio Service authorized, respectively, under Part 22 (Subpart H), Part 24, Part 25, Part 26, Part 27, Part 80, and Part 90 of the FCC rules.
● Portable devices operating in the Wireless Medical Telemetry Service (WMTS) and the Medical Implant Communications Service (MICS), authorized under Subparts H and I of Part 95 of the FCC Rules.
● Unlicensed PCS, U-NII and millimeter wave devices authorized under Part 15 of the FCC Rules.
All other mobile and portable devices are excluded from routine environmental evaluation for RF exposure.
SAR & SAR Limits
Specific absorption rate or SAR is the time derivative of the incremental energy (dW) absorbed by or dissipated in an incremental mass (dm) contained in a volume (dV) of a given density (ρ):

 SAR should be considered an “absorbed dose rate” and is related to electric fields at a point by:

 Where: σ = conductivity of the tissue (S/m)

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

 Ε = rms electric field strength (V/m)

SAR can also be a calculated rate of temperature rise at a given point for commercial testing of radiating devices, electric field measurements are normally used.
The limits, which apply in general for mobile telephones and similar apparatus, are drawn directly from the applicable source documents: ANSI/IEEE C95.1 for the US and ICNIRP for Europe and most of the rest of the world. Two limits are used: a lower value for exposure averaged over the whole body and a higher value which is applicable to local exposure to parts of the body (e.g. the head). This partial-body SAR is averaged over a volume of tissue defined as a tissue volume in the shape of a cube (see Table1).

SAR Test Standards

The IEEE and IEC standards (IEEE1528 and IEC62209) are similarly structured or harmonized with only minor variations in emphasis between them. The following shows the general format of this new work.

● Scope, normative references, and definitions

● Measurement system specifications

● Phantoms

● Measurement probe and equipment

● Scanning system

● Protocol for SAR assessment

● Preparation

● Measurement procedure

● Post-processing

● Uncertainty assessment

● Measurement reporting requirement

The most important aspects are the requirements for the accuracy and performance of the test system and the method of carrying out the measurements. An innovation in each of these standards is an explicit and detailed requirement for performing an assessment of the measurement uncertainty budget and a limit on the maximum allowable uncertainty. This places requirements both on the equipment and on the laboratory’s procedures.

The SAR Measurement System

According to IEC 62209 Para 5.1: “The test shall be performed using a miniature probe that is automatically positioned to measure the internal E-field distribution in a phantom model representing the human head exposed to the electromagnetic fields produced by wireless devices. From the measured E-field values, the SAR distribution and the maximum mass averaged SAR value shall be calculated.”

In our lab we have state of the art SAR Measurement System DASY6 (see Figure 1).

DASY6 is flexible, high-precision near-field scanner equipped with advanced software for performing any near-field scan in arbitrary volumes in free-space or any dielectric media.

DASY6 is optimized for accelerated SAR compliance testing according to IEC 62209-1, IEC 62209-2, IEEE 1528, CE, and FCC regulations. Time saving and increased reliability are realized with:

  • An integrated expert system for test time reduction based on a continuously updated ruleset for worldwide regulatory SAR tests and test reduction requirements.
  • An intelligent and optimized selection of testing points with speed – maximized robot movements.
  • Automated call handling with base-station simulators and automated verification of the applied calibration parameters.

The key features of DASY6 are: support of specific phantoms that enables testing of any body part; integration of time averaged SAR measurement procedure to facilitate testing of devices that can control the transmitted averaged power over time.