Online proceedings - EDA Publishing Association

24-26 September 2008, Rome, ItalyThe behavior of the higher gap observed in the band certain frequency range, the opening of the gaps results fromstructure of Fig. 1a has been studied as a function of the the crossing of the normal acoustic branches with almost flatgeometrical parameters h, e and β, along the high symmetry bands, which is similar to the case of locally resonantaxes ΓX and ΓM of the irreducible BZ (Fig. 5).materials.In Fig. 5, we fix the values of the filling fraction β=0.564 We have also studied the evolution of the gaps with theand the thickness of the plate (e=0.2µm) while increasing the thickness of the plate e, keeping constant h=2.7µm andheight of the dots from h=0.6µm to h=2.7µm. For h=0.6µm β=56.4% (Fig. 6a). Increasing e from 0.1µm to 1.0µm, we(Fig.5a), we note the existence of three gaps. The lowest one observe a slow variation of the central frequency of the gap.[0.5193, 0.5717GHz], discussed in the previous section, In addition, most of the gaps close for e>1µm, due to manycloses for h>1.0µm. Besides, the band structure exhibits two new dispersion branches moving downwards. The evolutionhigher gaps respectively in the frequency ranges [1.560, of the gaps with the filling factor has also been investigated.1.887GHz] and [2.092, 2.328GHz]. When increasing h to When increasing a from 1.0µm (Fig. 5c) to 1.4µm (Fig. 6b)1.5µm (Figs. 5b) and then to 2.7µm (Figs. 5c), the central with the same h and e, several branches move downwardsfrequencies of these gaps move downwards together with the from the high frequency region and progressively fill thedispersion curves, whereas new absolute band gaps appear at higher gaps; at the same time, the lowest remaining gapshigher frequencies. It is interesting to remark that, up to a keep their central frequencies almost preserved.2.5(a) h=0.6µm2.5(b) h=1.5µm2.5(c) h=2.7µm2.02.02.0frequency (GHz)1.51.0frequency (GHz)1.51.0frequency (GHz)1.51.00.50.50.50.0MΓreduced wavevectorX0.0MΓreduced wavevectorX0.0MΓreduced wavevectorXFig.5. Evolution of the band structure for different values of the height of the dots: (a) h=0.6µm, (b) h=1.5µm and (c) h=2.7µm. The other geometrical parametersare e=0.2µm and β=56.4%.©EDA Publishing/THERMINIC 2008 166ISBN: 978-2-35500-008-9