Megahertz magneto-inductive waveguide for electromagnetic energy transmission in radio-frequency identification system

Achieving low-frequency waveguide structures that operate in the low-frequency (LF) band or megahertz range is challenging because of the long wavelengths involved. In this work, we propose a domino-structured magneto-inductive waveguide for electromagnetic energy transmission in radio-frequency identification (RFID) systems at frequencies as low as 13.56 MHz. It is implemented using a metastructure based on a domino-arranged split ring resonator (SRR). Lumped components are introduced into each SRR ring that significantly reduce the ring resonant frequencies. An analytical energy transfer model is proposed based on inductive coupling because almost all the energy is transmitted through the magnetic field. Transmission coefficient measurements were carried out and the experimental results agree well with the energy transfer model. The proposed structure has a wide transmission bandwidth that is typically 30% to 80% of the center frequency. This bandwidth is sufficient to cover the entire 13.56 MHz industry-science-medical (ISM) band and is thus suitable for energy transmission for RFID systems. The waveguide has wide application potential that may be used to extend RFID reader sensing distances or split near-field RFID electromagnetic energies in multi-point applications.