  The envisioned sixth-generation (6G) of wireless networks will involve an
intelligent integration of communications and computing, thereby meeting the
urgent demands of diverse applications. To realize the concept of the smart
radio environment, reconfigurable intelligent surfaces (RISs) are a promising
technology for offering programmable propagation of impinging electromagnetic
signals via external control. However, the purely reflective nature of
conventional RISs induces significant challenges in supporting
computation-based applications, e.g., wave-based calculation and signal
processing. To fulfil future communication and computing requirements, new
materials are needed to complement the existing technologies of metasurfaces,
enabling further diversification of electronics and their applications. In this
event, we introduce the concept of reconfigurable intelligent computational
surface (RICS), which is composed of two reconfigurable multifunctional layers:
the `reconfigurable beamforming layer' which is responsible for tunable signal
reflection, absorption, and refraction, and the `intelligence computation
layer' that concentrates on metamaterials-based computing. By exploring the
recent trends on computational metamaterials, RICSs have the potential to make
joint communication and computation a reality. We further demonstrate two
typical applications of RICSs for performing wireless spectrum sensing and
secrecy signal processing. Future research challenges arising from the design
and operation of RICSs are finally highlighted.
