SAR Testing

RFI Ltd was established in 1997 it now has offices located both in Europe and North America where it is recognised as one of the major EMC compliance and conformance specialists. Over the past 13 years RFI has been providing EMC consultancy, services and solutions for a range of electrical and electronic equipment and system manufacturers around the globe.

The new facility, recently opened in Thatcham provides development and testing services for GSM 900, DCS1800 and PCS 1900 cellular terminals. The test facilities include two Rohde & Schwarz TS 8916B system simulators, as shown in Pic 1, two Orga SIM simulators and an Anite SuperSAT+.

At the Ewhurst Park Basingstoke site there are sufficient test and assessment resources coupled with the engineering experience to conduct the complete range of emissions and immunity tests on anything from mains borne to microwave equipment. With UKAS accreditation the organisation is able to supply its customers with anything from an initial conformance consultancy to an entire turnkey compliance solution.

In addition RFI's UKAS schedule provides total coverage for full compliance testing off site. This can include site evaluation surveys assessing radiation hazards and localised interference problems.

In keeping with its commitment to accommodate changing trends and to embrace new technologies the company applied for and has received associate membership of the Bluetooth SIG (Special Interest Group) and is in the forefront of development with a program of appropriate conformance services. In addition it has applied for BQB (Bluetooth Qualification Body) status for two members of its Regulatory and Technical Support Services Group.

More recently, the R&TTE directive specified that all handheld or body-mounted mobile telecoms equipment must be evaluated against a radiation standard. This standard examines the consequences of exposure to radiation from extensive use of mobile telephone handset terminals and other radiating devices and sets basic restrictions for the Specific Absorption Rate (SAR) of RF energy by the human body. In addition attention by the media and concerns voiced by some scientific bodies have contributed to a growing level of concern for safety among today's ever increasing number of phone users. Based on this the company took the decision to extend its capability to encompass SAR testing. Thus it was that in August of this year the existing range of compliance test facilities was complemented with a DASY3 professional SAR test system from Schmid & Partner Engineering AG of Switzerland. This places RFI among the very few independent European organisations offering a SAR testing facility in accordance with international standards.

Jozef Lomako the senior engineer responsible for SAR measurements at Ewhurst Park has been involved with this discipline for five years. He explained that SAR is a method of measuring the amount of energy resulting from electromagnetic radiation that is absorbed per unit mass in a biological substance, the level of absorption being a function of the conductivity and density of the substance. The example in question concerns that radio frequency energy resulting from use of a handset or similar device which may be absorbed and converted to heat in a human head.

The DASY3 testing facility at RFI comprises a generic twin phantom containing brain equivalent material, a computer controlled high precision robotic arm, a very precisely positioned near field probe and probe alignment sensor. See Pic 2. The generic twin Phantom is designed to provide an accessible and reproducible physical model of a human head. This consists of a suitably shaped open receptacle which is filled with a fluid carefully prepared to replicate the dielectric equivalent of the human brain. It was not flattering to discover that this consisted of mostly a sugar solution.

The test is conducted by placing the active radiating device, in this case the mobile phone handset to be evaluated, beneath the phantom. The robot then immerses the probe in the fluid and precisely positions it at those vertical and horizontal points of maximum electromagnetic field. The results thus measured are software interpolated to provide the relevant SAR value in a 1g or 10g mass. The standard SAR unit relates RF energy absorbed per unit mass in Watts/Kg.

For more information please contact Helen Redpath:
Tel: 01256 855408, e-mail: helen.redpath@rfi-wireless.com
or visit the Web site http://www.rfi-wireless.com

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