The generation of acoustic waves in structured nanobeams containing optomechanic cavities is a topic of current interest. In this paper, we study theoretically the efficient conversion of surface acoustic waves (SAW) generated on a substrate by an RF electric signal into the acoustic waves of a nanobeam. First, we demonstrate the possibility of converting the SAW generated on a silicon substrate with a thin piezoelectric AlN layer into the guided mechanical modes of a straight nanobeam with a maximum efficiency of-22.6 dB. This can be achieved by using a set of Inter-Digitated Transducers (IDT) with radial fingers, which provide SAW focusing towards the nanobeam entrance. We analyze the nature of the modes created inside the nanobeam and the conversion efficiency of the SAW into the different modes. Then, we study the interaction of these waves with a one-dimensional (1D) phononic crystal nanobeam containing a cavity. The latter is constituted by an array of holes and stubs and has been proven in our recent works to be very efficient for optomechanic applications. We calculate the transmission properties of the cavity modes and discuss the efficiency of generating the cavity modes from the initial SAW.

We thoroughly investigate the possibility to absorb most (i.e., up to more than 90%) of the incident electro-magnetic radiations in thin multilayered PMMA/graphene structures, thus proposing the technical realization of a device with an operational frequency range in the millimeter-wave domain, i.e., 30 GHz–300 GHz. Our simulations demonstrate the concrete possibility to enhance the field absorption by means of a selective removal and proper micro-pattering within the graphene material, enabling a complete and efficient control of the graphene sheet conductance. This method is applied to design and engineer a class of devices, endowed with a wideband operation capability, showing almost no fluctuations throughout the whole range of mm-wave frequencies.

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