  This paper addresses the hardware structure of Reconfigurable Intelligent
Surfaces (RIS) and presents a comprehensive overview of RIS design, considering
both unit design and prototype systems. It commences by tracing the
evolutionary trajectory of RIS, originating from static cell-structured
hypersurfaces. The article conducts a meticulous examination from the
standpoint of adaptability, elucidating the diverse array of unit structures
and design philosophies that underlie existing RIS frameworks. Following this,
the study systematically categorizes and synthesizes channel modeling research
for RIS-facilitated wireless communication, leveraging both physical insights
and statistical data. Additionally, the article provides a detailed exposition
of current RIS experimental setups and their corresponding empirical findings,
delving into the attributes of prototype design and system functionalities.
Moreover, this work introduces an in-house developed RIS prototype. The
prototype undergoes rigorous empirical evaluation, encompassing multi-hop RIS
signal amplification, image reconstruction, and real-world indoor signal
coverage experiments. The empirical results robustly affirm the efficacy of RIS
in effectively mitigating signal coverage blind spots and enabling radio wave
imaging. With RIS-enhanced augmentation, the average indoor signal gain
surpasses 8 dB.
