Admissibility and Exact Observability of Observation Operators for Micro-Beam Model: Time- and Frequency-Domain Approaches

This study focuses on the exact observability of a non-classical Euler–Bernoulli micro-beam equation. This non-classical model was derived based on the strain gradient elasticity theory, which is intended to explain the phenomenon of size effect at the micron scale. Spectral properties of the corresponding state operator are studied; an asymptotic expression for eigenvalues is calculated, and eigenfunctions are analyzed in order to check the necessary conditions for the exact observability of the system. By examining the eigenfunctions, it is shown that among non-collocated boundary outputs, only measurement of the non-classical moment at the root of the beam yields an admissible observation operator and also defines an exactly observable system. An alternative proof based on the multiplier method, which is commonly employed in the literature on the observability and controllability of infinite dimensional dynamical systems, is presented to provide a comparison between the time- and frequency-domain approaches.