Thinned coding patterns for reflection magnitude control in a multi-functional reconfigurable reflective surface

Reconfigurable intelligent surfaces are distinguished by their ability to enable controlled propagation environments and support multi-functional electromagnetic responses. However, increasing hardware complexity and power consumption remain key challenges for practical, large-scale implementations. This paper investigates spatial-domain magnitude control on an 8 × 8 reconfigurable reflective surface through geometric coding patterns, with analysis conducted at 5.05 GHz and 5.50 GHz. The relationship between reflection magnitude, active element density and spatial distribution is examined across 34 coding patterns. Results show that reflection magnitudes of −6 dB and −10 dB can each be achieved with as few as 12 active elements (19% of the surface) at 5.05 GHz, and that reflection magnitude at 5.50 GHz exhibits a consistent dependence on active element density. In addition, a first-order analytical approximation is introduced to estimate the reflection magnitude of selected patterns, providing reasonable agreement for most cases and capturing the underlying trend for ring-based configurations. The findings demonstrate the feasibility of a thinned coding pattern for multi-functional RIS, with potential for reduced hardware overhead and improved power efficiency at scale.