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.