Chemical Controlled Dissolution of LGS Samples: Comparison with Quartz and GaPO4
Though the use of LGS family crystals for filtering applications is now well known, we present here one of the best way to realize antimesa structures working at higher frequencies than a few tens of MHz. Generally, this kind of realizations requires dissolution depths higher than 100 mum. Consequently, the rough surface state does not remain constant: it becomes smoother or its roughness parameter can increase drastically. For that, we have compared the chemical dissolution of the crystal in four different etchants (HCl, HNO3, H3PO4 and NH4F.HF) for three crystal orientations: X-, Y-and Z-cuts (in LGS, Y-cut is similar to the AT-cut in quartz crystal). The parameters chosen to compare the efficiency of our selected solvents are the dissolution rate and the average roughness Ra. Furthermore, we have worked at 2 different temperatures: 60 and 80degC. The experiences show firstly that a X-cut plate is etched in HCl rapidly, compared to the Z-cut and so reveal the anisotropy of the material structure. Secondly, we observe that the dissolution rate of LGS in HCl solution is 8 to 10 times higher than in other solvents, at a given temperature. Unfortunately, it tends to reveal deep dissolution figures on the surface. From this set of experiments, we conclude that the best compromise is obtained with the ammonium bifluorure solvent which allows us to obtain a smoother surface state than initially.
Numerical and experimental investigation SAW in langasite
The present paper contains the complete numerical investigation of surface acoustics waves in langasite. The results are comprehensive contour-map and three-dimensional loci for velocity (Vo,Vm), beam steering (/spl theta//sup 1/), electromechanical coupling factor (K/sup 2/), first and second temperature derivatives of delay times (TCD1, TCD2). Optimal cuts for multimode resonators (TCD1=0), for bandpass filter (K/sup 2/=0.54%) and for sensors (TCD1=32.82 ppm//spl deg/C) are determined. The rotated Z+25/spl deg/ cut has large K/sup 2/=0.26% and TCD1=0 at the room temperature. The surface transverse wave that propagates over this cut in X+90/spl deg/ exists only at the metalized surface.
The Italian Renaissance: Culture and Society in Italy
In this newly revised edition of his widely acclaimed work, Peter Burke presents a social and cultural history of the Italian Renaissance. He discusses the social and political institutions that existed in Italy during the fifteenth and sixteenth centuries, and he analyzes the ways of thinking and seeing that characterized this period of extraordinary artistic creativity. Developing a distinctive approach, the author is concerned not only with the finished works of Michelangelo, Raphael, Leonardo da Vinci, and others, but also with the social background, patterns of recruitment, and means of subsistence of this "cultural elite." He thus makes a major contribution both to our understanding of the Italian Renaissance and to our comprehension of the complex relations between culture and society. An excellent social history of the lives and culture of the artists and artisans which made it possible for the arts to flourish.