Using nanoresonators with robust chaos as hardware random number generators.

In this paper, we investigate theoretically the potential of a nanoelectromechanical suspended beam resonator excited by two-external frequencies as a hardware random number generator. This system exhibits robust chaos, which is usually required for practical applications of chaos. Taking advantage of the robust chaotic oscillations, we consider the beam position as a possible random variable and perform tests to check its randomness. The beam position collected at fixed time intervals is used to create a set of values that is a candidate for a random sequence of numbers. To determine how close to a random sequence this set is, we perform several known statistical tests of randomness. The performance of the random sequence in the simulation of two relevant physical problems, the random walk and the Ising model, is also investigated. An excellent overall performance of the system as a random number generator is obtained.

Prediction of robust chaos in micro and nanoresonators under two-frequency excitation.

Robust chaos in a dynamical system is characterized by the persistence of the chaotic attractor with changes in the system parameters and is generally required in practical applications based upon physical sources of chaos. However, for applications that rely upon continuous time chaotic signals, there are now very few alternatives of dynamical systems with robust chaos that could be used. In this context, it is important to find a new dynamical system and, particularly, new physical systems that present robust chaos. In this work, we show through simulations that a relevant physical system, suspended beam micro and nanoelectromechanical resonators, can present robust chaos when excited by two distinct frequencies. To demonstrate the existence of robust chaos in the system, we perform an extensive numerical analysis, showing that the attractor is unique and changes smoothly in a large region of the relevant physical parameter space. We find that the robustness of the chaotic dynamics depends crucially on the dissipation, which must be sufficiently small. When the dissipation is small, we find a large range of frequencies, frequency ratios, and applied voltages where robust chaos is observed. These findings turn these systems into viable and strong candidates for practical applications since the chaotic dynamics becomes quite insensitive to fabrication tolerances, changes in the physical parameters induced by the environment, and aging.

Rigorous analysis of Casimir and van der Waals forces on a silicon nano-optomechanical device actuated by optical forces.

Nano-optomechanical devices have enabled a lot of interesting scientific and technological applications. However, due to their nanoscale dimensions, they are vulnerable to the action of Casimir and van der Waals (dispersion) forces. This work presents a rigorous analysis of the dispersion forces on a nano-optomechanical device based on a silicon waveguide and a silicon dioxide substrate, surrounded by air and driven by optical forces. The dispersion forces are calculated using a modified Lifshitz theory with experimental optical data and validated by means of a rigorous 3D FDTD simulation. The mechanical nonlinearity of the nanowaveguide is taken into account and validated using a 3D FEM simulation. The results show that it is possible to attain a no pull-in critical point due to only the optical forces; however, the dispersion forces usually impose a pull-in critical point to the device and establish a minimal initial gap between the waveguide and the substrate. Furthermore, it is shown that the geometric nonlinearity effect may be exploited in order to avoid or minimize the pull-in and, therefore, the device collapse.