An automated SAR measurement system for compliance testing of personal wireless devices

An automated specific absorption rate (SAR) measurement system has been dev eloped for compliance testing of personal wireless devices. Unlike other sy stems, this system uses a model with a lossy ear-shaped protrusion and the accuracy of this experimental setup has been checked by comparing the peak 1-g SAR's for ten cellular telephones, five each at 835 and 1900 MHz, with the results obtained using a 15-tissue anatomically based model with the fi nite-difference time-domain (FDTD) numerical electromagnetic technique. The SAR measurement system uses a three-dimensional (3-D) stepper motor to mov e a Narda Model 8021 E-field probe to measure the SAR distribution inside a head-shaped tissue-simulant phantom near the radiating device. The head an d neck part of the model with an ear-shaped protrusion of 3 mm thickness is made of a lossy outer shell of 5-7 mm thickness of epoxy laced with KCl so lution. The phantom is filled with appropriate frequency-specific fluids wi th measured electrical properties (dielectric constant and conductivity) th at are close to the average for gray and white matters of the brain at the center frequencies of interest (835 and 1900 MHz). The implantable E-field probe is calibrated using the FDTD-calculated SAR variations for a slab mod el at two commonly used frequencies, 835 and 1900 MHz and is checked to hav e good isotropic characteristics (+/-0.23 dB) and a nide dynamic range (0.0 1-10 W/kg). The system is validated using a 223-mm-diameter sphere model. P eak 1-g SAR's for ten telephones using different antennas are within +/-1 d B bf those obtained using the FDTD numerical method for the anatomical mode l of the head and neck region.