Design of a 13.56 MHz segmented Helmholtz coil for RF exposure testing of biologics to simulated RFID readers

Abstract

The design methodology of a large 13.56 MHz Helmholtz coil with central magnetic field strength of H0 = 5.0 amperes/m is described. This apparatus is for use in protocol testing evaluating any thermal or non-thermal effects on blood and blood product samples that might be caused by long-term exposure to the fields produced by the 13.56 MHz RFID reader antennas. The Helmholtz coil was initially constructed as one continuous inductor; however, stray capacitance prevented it from resonating above 10.17 MHz. It was then successfully reconstructed as a four-segment Helmholtz coil by following methods used in designing Helmholtz coils for use in magnetic resonance imaging. Complete design, construction and testing details of the segmented Helmholtz coil and its RF drive system are given both to enable duplication and as a design guide for similar large Helmholtz coils. Occupational safety recommendations are made to enable safe operation. An application to blood products RF safety testing is discussed.