  This work peruses a simultaneous transmitting and reflecting reconfigurable
intelligent surface (STAR-RIS) based wireless system wherein untrusted energy
harvesting nodes wiretap the legitimate signal. The achievable secrecy rate and
the harvested energy for multicast communication are computed as functions of
STAR-RIS transmission and reflection coefficients (TARCs). Thus, to maximize
the secrecy rate while satisfying the minimum required harvested energies, the
non-convex optimization problem is investigated. By using the Dinkelbach
transformation and semi-definite relaxation technique, the optimization problem
is transformed into a convex problem. Eventually, the numerical results are
reported to specify the effects of the size of the STAR-RIS and optimizing its
TARCs elements on magnifying the secrecy rate-energy harvesting region.
