Coherently Assisted Wireless Power Transfer Through Poorly Transparent Barriers

TL;DR

Barriers that reflect RF energy hamper wireless power transfer; the paper proposes coherently assisted WPT, where a phase-locked auxiliary wave from the receiver coherently controls barrier scattering to suppress back-reflection. In the lossless two-port limit, the transmitter-to-receiver efficiency can reach unity and the optimal routing yields $\Sigma_{max}=|t|^2+|r_{22}|^2$ with $s_1^-=0$, while in lossy barriers positive net delivery $P_{net}^{(2)}$ remains achievable. Analytical and full-wave demonstrations on a Fabry-Pérot slab and on a barely transparent perforated metasurface show near-unity transmission and large enhancement factors (up to about 100) without altering the barrier. The framework connects to time-reversal and programmable metasurface concepts and suggests barrier-agnostic power delivery in shielded or enclosed environments, with extensions to multi-channel barriers via wavefront control.

Abstract

Poorly transparent barriers (e.g., reinforced walls, shielding panels, metallic or high-contrast dielectrics) strongly reflect incident radiation, limiting wireless power transfer (WPT) unless the barrier is structurally modified to support a narrowband transparency window. Here we introduce a barrier-agnostic alternative based on coherent scattering control: a phase-locked auxiliary wave is launched from the receiver side with an amplitude and phase chosen from the measured complex scattering parameters of the barrier. In a two-port (single-channel-per-side) description, we derive closed-form conditions for (i) canceling back-reflection toward the transmitter and (ii) maximizing the net extracted power at the receiver side. In the lossless limit these conditions imply unit transmitter-to-receiver efficiency (all transmitter power is routed to the receiver side) even when the barrier is nearly opaque under one-sided illumination. We validate the concept using (1) an analytically solvable high-index Fabry--Pérot slab and (2) a numerically simulated perforated PEC metasurface exhibiting vanishing one-sided transmission; in both cases, coherent assistance yields near-unity transmission and large enhancement factors. We further analyze dissipative barriers using a receiver-side energy-balance metric, showing that substantial net delivery can persist well into the lossy regime. The approach is closely related to coherent perfect absorption and time-reversal ideas in wave physics, but targets \emph{reflectionless delivery through barriers} without modifying the obstacle itself.

Figures (4)

• Figure 1: Concept. Conventional WPT through a highly reflective barrier suffers strong back-reflection and poor transmission. In coherently assisted WPT, a phase-locked auxiliary wave is launched from the receiver side and tuned in amplitude and phase using the barrier's complex scattering parameters. In the lossless two-port limit, coherent assistance can cancel reflection toward the transmitter and route all transmitter power to the receiver side (unit transmitter-to-receiver efficiency). In lossy barriers, coherent assistance cannot eliminate dissipation but can still strongly increase the net received power.
• Figure 2: Fabry--Pérot slab barrier. (a) One-sided reflection $R$ and transmission $T$ for a dielectric slab ($\varepsilon_r=100$, $L=405nm$): transfer-matrix theory (solid) and full-wave simulation (markers). (b) Fractional routing metric $\Sigma$ [Eq. \ref{['eq:Sigma_a_phi']}] versus auxiliary amplitude $a$ (horizontal) and phase $\varphi$ (vertical); star marks a near-$\Sigma=1$ operating point. (c) Enhancement $B=\Sigma/|t|^2$ and transmitter-side reflected power under coherent assistance; the optimized point yields large $B$ while suppressing reflection. (d) Field magnitude snapshots (normalized) for one-sided (top) and two-sided coherently assisted excitation (bottom), illustrating the transition from a standing-wave to a reflectionless-through state.
• Figure 3: Lossy barrier. Receiver-side net extracted power $P_{\mathrm{net}}^{(2)}=|s_2^-|^2-|s_2^+|^2$ for a dielectric slab with $\varepsilon_r=100+\mathrm{i}\,\mathrm{Loss}$, plotted versus loss and auxiliary amplitude $a$ (phase held near the lossless optimum). The dashed curve indicates $P_{\mathrm{net}}^{(2)}=0$; below it the receiver extracts net power from the transmitter despite dissipation. The star marks the lossless operating point used in Fig. \ref{['fig:fig3']}.
• Figure 4: Perforated PEC metasurface barrier. (a) One-sided reflection and transmission show nearly perfect reflection across the band. (b) $\Sigma(a,\varphi)$ computed from Eq. \ref{['eq:Sigma_a_phi']} at $k_0 D=0.165$; star indicates an operating point with $\Sigma\approx 1$. (c) Under coherent assistance, effective transmission approaches unity and reflection is suppressed, yielding large enhancement $B$ relative to the vanishing one-sided transmission. (d) Representative field magnitude maps comparing one-sided and coherently assisted excitation, illustrating reflection suppression and forward delivery.