## 1 Introduction  
While 5G [1] is a significant improvement over 4G, 6G (albeit in an early conceptualization stage) is envisioned to take wireless technology to the next level, offering even faster speeds (from 100 Gbps to 1 Tbps) [2], lower latency (as low as 1 \(\upmu\)s) [3], wider coverage (access to remote areas by satellite internet [4]), and more advanced capabilities (combining THz and optical frequencies [5]).  
One of the key challenges in expanding wireless coverage is the limited range of high-frequency radio waves that are used for 5G and 6G. Signal transmission in the THz and millimeter-wavelength ranges experiences significant attenuation and may be entirely obstructed by obstacles present in the propagation environment. To overcome this, one approach being explored is the use of low earth orbit (LEO) satellites [6] to provide global coverage and low-latency connectivity. SpaceX and Amazon are already launching large-scale satellite constellations for internet connectivity with expanded coverage. Alternatively, researchers are exploring new technologies such as \"mirrors\"-based intelligent reflecting surfaces (IRSs) [7, 8], which employ software-controlled mirrors (a host of passive reflecting elements) to reflect and focus radio signals (pencil beam) to a desired direction, thereby enhancing the signal strength and reducing interference, allowing them to penetrate obstacles and extend coverage. These surfaces are usually static and do not have the ability to change their reflection properties.  
To obtain additional capability of dynamically changing reflection properties in response to the wireless environment, the concept of reconfigurable intelligent surface (RIS) was introduced in recent years [9, 10, 11, 12]. RISs can be programmed to change the phase and amplitude of reflected waves, which allows them to actively manipulate the direction and strength of the reflected signals, making them more flexible and adaptable than mirror-based IRSs. The concept of RIS was first introduced in [9], entitled \"Smart radio environments empowered by reconfigurable AI meta-surfaces: an idea whose time has come\", by [PERSON] et al. The paper [9] presents the preliminaries and potential applications of RISs, which are surfaces made of an array of tunable elements that can reconfigure the propagation of electromagnetic waves. Since then, RIS has become an active area of research, and numerous studies have been conducted to investigate its capabilities and potential uses [10; 11; 12; 13; 14]. For most cases, metasurface is utilized as a relay that reflects the signal from the source toward the destination to enhance the signal-to-noise ratio.  
This communication points out the fact that the concept of RIS is arguably not new if being viewed from the angle of liquid crystal reflectarray (LCRA), which has been established for more than two decades [15], and liquid crystal on silicon (LCOS), which has existed even earlier for more than three decades [16; 17], of which people who are dedicated only to the field of microwave engineering might not be fully aware.  
Technically, the main principle and major functionalities are transferable among LCRA, LCOS, and the emerging RIS, but they differ in their operating frequencies and corresponding use cases (illustrated in Figure 1), which will be discussed in Section 2. The main obstacles preventing liquid crystals (LCs) from dominating (or creating) the RIS concept earlier (in another word, to facilitate the conceptualization of RIS for an earlier exposure) are due to the inherent challenges (bottleneck) of LC-based phase-shifting technology, which will be specified in Section 3. This semi-technical review provides a novel perspective on the evolution and potential of RIS technology, leveraging insights from previous LC-based reconfigurability research to inspire new developments in this field.