STANDARDS AND COMPLIANCE TESTING P. Bernardi Department of Electronic Engineering - University of Rome "La Sapienza"

Contents  Exposure assessment  Review and comparison  Radio base stations  Cellular phones  INTRODUCTION  STANDARDS  COMPLIANCE TESTING  THE CEPHOS PROJECT

Exposure assessment - relevant parameters Electromagnetic field source EMISSIONEXPOSUREABSORPTION Environment Human

The Mobile Cellular Phone System Radio Base Station Two different exposure conditions Cellular Phone

Standard for safe human exposure to RF fields In the frequency range from 30 MHz to a few GHz the basic parameter is the Specific Absorption Rate (SAR): Restrictions on the effects of exposure are based on established health effects and are termed basic restrictions. Protection against adverse health effects requires that the basic restrictions are not exceeded (ICNIRP, 1998). (W/kg) On the whole body:

Basic limits The SAR WB of 4 W/kg has been established as a reasonable value for adverse effect threshold. Using a safety factor of 50 for the exposure of general population, the limit of 0.08 W/kg is obtained. To avoid excessive hot spots, a limit for the spatial peak SAR is also established.

Established SAR related effects BRAIN  T > 4.5 °C Neuron thermal damage EYE  T > °C Cataract of the lens SKIN  T > °C Thermal damage WHOLE BODY  T > 1 °C Various physiological effects The most widely accepted effect of RF exposure is a heating effect. Threshold temperature increase for some effects:

Comparison of basic limits ANSI (1g) CENELEC (10g) FCC (1g) ICNIRP (10g) General public SAR wb SAR peak (W/kg) Using an averaging cube of 10 g instead of 1 g of tissue mass can reduce the spatially averaged SAR value by a factor of about two, at higher frequencies

Derived or secondary limits (Reference levels) Represent a practical approximation of the incident plane wave power density flux needed to produce the whole-body- averaged SAR of 0.08 W/kg. They are defined in terms of external electric field, magnetic field, and incident power density

Basic restrictions and reference levels While compliance with all reference levels will ensure compliance with basic restriction it does not necessarily follow that if measured values are higher than reference levels, the basic restrictions are exceeded. In this case a more detailed analysis is necessary to assess compliance with basic restrictions (ICNIRP, 1998)

Comparison of reference levels General public

Safety standards conclusions While there is almost general consensus on the limit on SAR as averaged over the whole body, differences are present among the limits on spatial SAR and on the derived reference levels. This renders compliance testing for new devices more complicated

Compliance with standards Compliance testing consists in checking that the field exposure from MTE is below reference levels OR SAR absorbed in body is below the basic limits

Radio Base station Exposure in free space E max => reference level

Urban scenario Exposure in complex environment

Radio Base station Exposure levels in urban environment E rms [V/m] rooftop (A) balcony (b)street (C) f = MHz P irr = 30 WG = 14.7 dBi E rms [V/m] (cm)

Cellular phones We can differentiate between portable and mobile devices according to their proximity to the exposed person (FCC, 1996). Portable devices are defined as devices designed to be used with any part of their radiating structure in direct contact with, or within 20 cm from, the body of the user. Mobile devices are defined as transmitting devices designed to be used in definite locations with radiating structures maintained 20 cm or more from the body of the user or nearby persons. For handheld cellular phones, (portable devices) compliance testing must be done only with reference to the basic limits on SAR

Procedures to demonstrate compliance of CPs with basic restrictions General requirements: the method should ensure that the assessed SAR do not underestimate the exposure of possible users; the CP should be tested at the highest power at the central transmitting band frequency; test procedures should give reproducible results

Compliance methods Compliance with the basic restrictions can be done: theoretically: computational simulation procedures; experimentally: measurement simulation procedures. In case of numerical compliance testing, at least one position of the CP (the intended use position) should be verified by measurements (CENELEC, ES 1998)

Intended use position (CENELEC, ES 1998) The intended use position: is established by fully extending the CP antenna; provides good acoustic coupling Tests shall be done at least in the intended use position REFERENCE LINE LINE CONNECTING AUDITORY CANAL OPENINGS REFERENCE PLANE

Computational simulation procedures Numerical method (e.g. FDTD) Dielectric characteristics ,  Source Maxwell’s equations SAR peak basic limits

Open problems Phantom model –head shape, tissue distribution, tissue parameters –effect of the hand –metallic accessories and environmental effects a worst case can be defined? Uncertainty of the evaluation techniques

Measurement simulation procedures Requirements: to know with great precision the measurement points (rapid spatial variations); accurately evaluate the SAR close to the surface; software for data processing & measurement control. Phantom Automatic scanning system E-field probe Power delivering system Data processing SAR peak basic limits Total power

Open problems Phantom model –shape and size; heterogeneous or not –dielectric properties –ear simulation –modeling the hand worst case scenario? calibration procedure Uncertainty of the measurement set-up –probe isotropy, linearity, sensibility –spatial resolution –phone and probe positioning

The CEPHOS project Purpose:  development of a data-base on relevant literature  design and study of canonical situations of exposure  development of numerical and experimental phantoms  assessment of the human exposure in actual situations Activities: to assess a rational basis for a compliance procedure of cellular phones with standards

CEPHOS working groups Work undertaken: exposure assessment & uncertainty of numerical simulations: CNET, National Technical Univ. of Athens, Univ. of Ancona, Univ. of Bradford, Univ. of Rome La Sapienza exposure assessment & uncertainty of experimental set-ups: Alcatel, CSELT, ENEA, NPL, Univ. of Bordeaux, Univ. of Bristol definition of a testing procedure: Univ. of Rome La Sapienza, Alcatel, CNET, CSELT, National Technical Univ. of Athens, Univ. of Bradford CEPHOS consortium is made up of 6 universities, 4 research laboratories and 4 industries.

Conclusions In the recent years significant progress in the area of exposure assessment of cellular phone systems has been done; the precision of experimental and numerical techniques has been greatly improved. However: a universally accepted compliance procedure (numerical and experimental) is still lacking; improvements are still necessary to assess the exposure in complex environments (both for radio base stations and hand-held phones).