Thin Film Reconfigurable Intelligent Surface for Harmonic Beam Steering

TL;DR

This work presents a cost-effective thin-film 1×4 RIS fabricated on a flexible PET substrate via inkjet printing, integrating antennas, switching circuitry, and an MCU without a ground shield to enable independent element control. By modulating each element with baseband signals at a small frequency $f_0$ (here $f_0=313$ Hz), the RIS generates and steers dominant harmonics around the carrier frequency $f_c$ through time-varying reflection coefficients $Γ(t)$, achieving beam steering for the harmonics $f_c\pm f_0$ on both surfaces. Experimental results at $f_c=2.45$ GHz demonstrate steering of the +1st and -1st harmonics with about 9 dB diversity gain and a power consumption of $122$ mW for the controller, validating a practical route toward low-cost RIS-enabled sensing and communication. The approach leverages additive manufacturing and flexible substrates to reduce fabrication complexity and enable rapid deployment, with analysis of limitations due to element coupling and prospects for adaptive calibration and scaling. The work highlights harmonic beam steering as a viable alternative for RIS-aided ISAC applications in compact, low-power platforms.

Abstract

This letter explores an implementation of a novel thin film 1-by-4 reconfigurable intelligent surface (RIS) designed for future communication and sensing scenarios. Utilizing cost-effective inkjet printing methods and additive manufacturing, our approach significantly simplifies the RIS construction process and reduces production costs. The RIS, fabricated on a flexible and lightweight polyethylene terephthalate (PET) substrate, integrates antennas, switching circuitry, and a microcontroller unit (MCU), without a ground shield. This setup enables individual and simultaneous control of each RIS element, manipulating the captured carrier signal by reflecting and refracting its dominant harmonics. Beams of the harmonics can be steered to multiple desired directions at both front and back sides of the surface. Measurement results of the beam steering show that the RIS has the potential to enable RIS-aided communication and sensing applications.

Figures (4)

• Figure 1: RIS. (a) Typical scenarios for sensing. (b) Prototype after additive manufacturing. (c) Schematic and footprint layout.
• Figure 2: Baseband-controlled beam steering. (a) Equivalent circuit of antenna load modulation. (b) Simulation of reflection magnitude and phase of the RIS element. (c) Phased baseband signals. (d) An example of normalized far-field RIS beam pattern with delay profiles.
• Figure 3: Experimental setup.
• Figure 4: Harmonic beam steering measurement results. (a) +1st harmonic $f_{\rm c}+f_0$. (b) -1st harmonic $f_{\rm c}-f_0$.