Experimental Validation of Non-Invasive SAR Evaluation from Measurements and Numerically Assisted Post Processing

Faster Specific absorption rate (SAR) techniques have been an area of interest since the beginning of compliance measurements for radiating devices. Since the arrival of 4G and specially moving towards 5G and future communication standards, a reliable and accurate fast SAR technique has become crucial. The purpose is to reduce the measurement time ensuring the applicability to different scenarios, frequencies, and beams directions. In this paper, a fast SAR technique is presented based on Over The Air (OTA) measurements combined with post processing and numerical simulations. A test case based on a simple dipole antenna is presented here. The SAR is measured using a standard compliant system and compared with values obtained from, i) the full-wave simulations, and ii) CW measurements and numerical simulations. The results show a good agreement within a 1.5dB uncertainty range, and thus validates this fast SAR measurement approach which could help reduce the testing time during R&D and pre-compliance phase of the product development.

I. Introduction

Compliance testing for radiating devices is regulated by the IEC / IEEE standard 62209-1528 covering the 4MHz – 10GHz frequency range [1] and follows the ICNIRP (International commission on non-ionizing radiation protection) guidelines [2]. A typical testing mechanism is based on scalar E-field measurements using a robotic arm, inside a phantom representing a part of the human body, filled with a liquid representing the human tissue (Figure 2). The radiating device is placed below the phantom and a maximum E-field spot is searched inside the phantom using the E-field probe. Once this maximum point is found, E-field is measured around it inside a cube (at discrete points) which represents 1g or 10g of human tissue. The SAR is then computed form this E-field data according to the procedure outlined in the standard [1]. However, this evaluation is valid only for a given frequency / modulation, and a given device orientation / separation distance respect to the phantom. With the accumulation of multiple technologies inside the everyday user equipment (smart phones, tablets, small cells, wearables, etc.), and the arrival of beamforming for 5G and future networks, the number of scenarios in which to evaluate the SAR has risen exponentially over the last few years. A typical modern smart phone has the possibility to radiate in 2G, 3G, 4G / LTE, 5G, Wi-Fi frequency bands covering a frequency band from 400 MHz up to 6GHz (and potentially up to 10GHz with the new Wi-Fi bands). As of today, there are more than 80 frequency bands identified by the 3GPP [3]. This is a big challenge for SAR evaluation of modern communicating devices by the regulatory bodies, R&D facilities, and device manufacturers.