Reconfigurable Metasurface for Near-Field Efficient Wireless Power Transfer System

doi:10.12142/ZTECOM.202603009

Abstract

Abstract:

Wireless power transfer (WPT) offers a promising solution for powering distributed devices in smart cities, significantly simplifying system complexity and accelerating urban automation. In traditional WPT systems, far-field schemes are costly, energy-intensive, and inefficient, while near-field transmission offers higher efficiency but suffers from limited distance. To address the limited transmission distance of near-field WPT, this paper derives an electromagnetic model for WPT using reflective metasurfaces and presents the design of a high-performance 3-bit reconfigurable intelligent surface (RIS). Based on theoretical models, we investigate the effects of phase quantization and array size on focusing efficiency. Simulation results guide the subsequent fabrication of the RIS prototype. Experimental measurements on the fabricated prototype validate the beam-focusing effect and evaluate the overall WPT efficiency.

Key words: reconfigurable intelligent surface, near-field beam focusing, wireless power transfer

Wang Yunfeng, Xu Zhiyu, Zhang Hongtao. Reconfigurable Metasurface for Near-Field Efficient Wireless Power Transfer System[J]. ZTE Communications, 2026, 24(3): 70-81.

Figures/Tables 17

Figure 1 Application scenarios of RIS in a WPT system

Figure 2 Schematic diagram of phase compensation for reflective focusing metasurfaces

Figure 3 Electric field distribution of the metasurface focal area

Figure 4 Phase compensation and normalized electric-field distributions: (a) non-quantized compensation phase distribution; (b) 1-bit quantization; (c) 2-bit quantization; (d) 3-bit quantization; (e) 4-bit quantization; (f) non-quantized electric-field distribution (reference)

Figure 5 Normalized electric field distribution of different array sizes and focus distances: (a) 10 × 10 array at (0, 0, 1 m); (b) 10 × 10 array at (0, 0, 5 m); (c) 20 × 20 array at (0, 0, 1 m); (d) 20 × 20 array at (0, 0, 5 m); (e) 40 × 40 array at (0, 0, 1 m); (f) 40 × 40 array at (0, 0, 5 m)

Figure 6 Design diagram of the unit

Table 1 Geometric parameters and material properties of the unit design

Geometric Parameters	Element dimensions and thickness	D = 25 mm	h₁= 4 mm
	Element dimensions and thickness	h₂ = 0.2 mm	h_pp= 0.1 mm
	Patch parameters	w₁ = 0.9 mm	l₁= 2.985 mm
	Patch parameters	w₂ = 0.5 mm	l₂= 15 mm
	Via dimensions	d₁ = 0.6 mm	d₂ = 1.6 mm
Material Properties	Dielectric substrate	F4B material (with a relative permittivity of 2.65 and a loss tangent of 0.001 5)
Material Properties	Adhesive material	Prepreg material (with a relative permittivity of 2.5 and a loss tangent of 0.004)

Figure 7 Equivalent circuit of the varactor diode, modeled as a series RLC circuit

Figure 8 S11 phase curves for different capacitance values

Figure 9 S11 amplitude curves for different capacitance values

Table 2. 3 -bit encoding correspondence table

Encoded Value	Bias Voltage/V	Capacitance/pF	Resistance/Ω	Inductance/nH	Phase/deg
000	9.60	0.150	0.88	0.02	124.41
001	4.56	0.330	0.88	0.02	79.64
010	4.08	0.368	0.88	0.02	33.85
011	3.70	0.376	0.88	0.02	-7.42
100	3.32	0.408	0.88	0.02	-62.63
101	2.94	0.430	0.88	0.02	-110.79
110	2.12	0.460	0.88	0.02	-157.71
111	0	0.950	0.88	0.02	-190.30

Figure 10 Phase compensation (left) and focusing effect (right) of the array

Figure 11 WPT efficiency versus distance for near-field focus beam and high-gain beam

Figure 12 Fabricated 3-bit RIS: (a) front view; (b) back view

Figure 13 Near-field measurement setup for focal spots in the anechoic chamber

Figure 14 Measured normalized electric field distributions with focusing distance (represented as z) set to 1 m (left column) and 3 m (right column): (a) focusing position at (0, 0, z) m; (b) focusing position at (-0.1, -0.1, z) m

Figure 15 Measurement setup for WPT efficiency: (a) anechoic chamber setup; (b) Rx antenna

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