Analysis and measurement of rapidly attenuating fields around magnetic multipoles in low-frequency band

It is known that the attenuation rate of fields around multipoles becomes larger as the order of the multipoles increases. We experimentally confirmed that a magnetic quadru-pole and octapole composed of coil antennas can create low-frequency magnetic fields attenuating at the rate of 80 and 100 dB/decade, respectively. We also obtained approximate equations that represent the fields around the quadrupole and octapole in simple forms. The rapid attenuation of the low-frequency magnetic fields can provide identification areas with well-defined boundaries, which will be needed in order to build reliable radio-frequency identification systems for communication with things and mobile/wearable devices.