  Inductive wireless power transfer (WPT) systems can be effectively described
as non-Hermitian systems using the coupled-mode theory. In these systems,
parity-time (PT) symmetric states facilitate efficient power transfer.
Traditionally, passive resonators have been used as relay devices in such
systems to extend transmission distance; however, this approach may induce
additional eigenstates with broken PT symmetry, particularly when specific
spatial arrangements of the relay resonators, dependent on the positions of the
transmitting (Tx) and receiving (Rx) resonators, are not maintained. This
limitation hampers applications like free positioning WPT. To address this
challenge, we introduce a multibody WPT system employing metamaterial
controlled PT symmetry, which circumvents the constraints of physical
arrangement. We utilize inverse design to configure the metamaterial, targeting
a specific resonance mode that controls the effective coupling coefficients.
Our approach ensures that a PT-symmetric state emerges when these coefficients,
relating to the metamaterial and both the Tx and Rx resonators, are balanced.
We confirm the stability of this state in a strong coupling regime, both
theoretically and experimentally. Our experiments demonstrate the formation of
PT-symmetric states governed by the metamaterial's resonant mode, achievable
even with varying sizes and positions of the Tx and Rx in relation to the
metamaterial. Moreover, we show that the PT symmetric state is attainable with
different spatial configurations of the Rx resonator. This finding underscores
our system's potential for free-positioning WPT, significantly broadening its
applicability.
