Electronically Controllable Impedance for Tuning of Active Metamaterials

In recent years, passive metamaterials consisting of a geometrical arrangement of $LCR$ -resonator-type base units are proposed for the shielding of magnetic stray fields at low- and medium-frequencies. The screening factor of such passive metamaterial shields can be deteriorated by component value tolerances and variations with temperature and/or by aging. These issues can be overcome with an active metamaterial assembled by an array of engineered active base units. Each base unit contains an $LCR$ -resonator and a control unit called Electronically Controllable Impedance (ECI). The ECI consists of a four-quadrant power converter with integrated measurement and control units for emulating an arbitrary impedance and is used to tune the $LCR$ resonator such that the base unit exhibits an ideally purely electric inductive or capacitive behavior when excited by an external field. Thereby, each single $LCR$ -resonator’s resonant frequency is tuned to be close to the excitation frequency and the resonator’s quality factor $Q$ is optimally adjusted. This paper shows different realizations of an ECI and proposes an ECI control algorithm to tune the resonant frequency and to adjust the quality factor $Q$ of the resonators. Furthermore, experimental verifications of the ECI concept employing a linear power amplifier are provided.