“…Recently, several non-classical theories such as couple stress theory (Mindlin and Tiersten, 1962), modified couple stress theory (Yang et al, 2002), strain gradient theory (Mindlin, 1964), nonlocal elasticity theory (Eringen, 1972), and nonlocal strain gradient theory (Lim et al, 2015) try to capture the size effect in the structures. The scientific literature includes many papers based on different non-classical theories on the mechanical analysis of micro-and nano-sized structures such as micro/nanorod (Bahrami, 2017b), micro/nanobeam ( While there are many papers in the literature regarding the effects of thickness and small scale on the frequency ratio of nanobeams and nanoplates using Eringen's nonlocal theory, unfortunately, most papers presented the thickness effect on the frequency ratio for fully simply supported cases due to simplicity of the calculation in this case (Aghababaei and Reddy, 2009;Aydogdu, 2009;Bahrami and Teimourian, 2016;Daneshmehr et al, 2015;Eltaher et al, 2012;Natarajan et al, 2012;Rahmani and Pedram, 2014;Reddy, 2007;Thai, 2012). As a result, the true effect of the thickness to length ratio on the frequency ratio of nanobeams and nanoplates was not captured and reported at all.…”