Selection of materials for multilayered structures to be used in packageless sensors
Recently a multilayered structure with a low-velocity layer sandwiched between two high-velocity materials, one of which also works as a supporting substrate and another one as a coat isolating the wave from the influence of undesired external factors, was suggested for application in packageless sensors [1,2]. The thickness of a middle piezoelectric layer must be sufficient to confine the wave within this layer. The suggested combinations of materials included ZnO or GaN as a waveguiding layer, sapphire or diamond as a supporting substrate and Al2O3 (alumina) or AlN as a coating. In the present work, two previously reported structures were analyzed and compared to find the selection criterion for optimal combination of materials enabling high coupling of the useful mode and suppression of parasitic modes.
A universal technique for analysis of acoustic waves in periodic grating sandwiched between multi-layered structures and its application to different types of waves
A numerical technique, which combines FEM analysis of electrode area with matrix formalism applied to spectral domain analysis (SDA) of eigen modes in multi-layered substrate and multi-layered dielectric upper half-space, is described as an efficient tool of investigating the wave characteristics in periodic metal grating sandwiched between two multi-layered half-spaces, with arbitrary thickness of each layer. The universal character of the developed technique is illustrated by few examples of its application to different types of structure providing propagation of common SAW, boundary waves at interface, plate modes, normal modes in a thin film deposited over the grating etc. The transformation between the waves with continuously increasing film thicknesses can be observed.
Heritage Languages: In the 'Wild' and in the Classroom
Heritage speakers are people raised in a home where one language is spoken who subsequently switch to another dominant language. The version of the home language that they have not completely acquired – heritage language – has only recently been given the attention it deserves from linguists and language instructors. Despite the appearance of great variation among heritage speakers, they fall along a continuum based upon the speakers’ distance from the baseline language. Such a continuum-based model enables researchers and instructors to classify heritage speakers more accurately and readily. This article discusses the results of research on lower-proficiency speakers, identifying recurrent features of heritage languages in phonology, morphology, and syntax. Preliminary results indicate that different heritage languages share a number of structural similarities; this finding is important for the understanding of general processes involved in language acquisition. The article also presents implications of the main findings for language education and identifies areas needing further study.