I n t h i s paper we discuss the recent advances i n a r e l a t i v e l y new c l a s s o f planar a c o u s t i c dev i c e s employing an a c o u s t i c wave which t r a v e l s j u s t below the surface. These waves a r e r e f e r r e d t o as shallow b u l k a c o u s t i c waves (SBAW's) o r as surface-skimming b u l k waves (SSBW's).I n the l a s t few years t h e r e has been a g r e a t deal o f a c t i v i t y i n t h i s area because o f the inherent advantages which SBAW devices possess over conventional b u l k and s u r f a c e a c o u s t i c wave devices. These devices can be employed as bandpass f i l t e r s and delay l i n e o s c i l l a t o r s , and thus can be incorporated i n t o a v a r i e t y o f s i g n a l processing systems. The mater i a l aspects, e q u i v a l e n t c i r c u i t , energy t r a p p i n g and devices development w i l l be presented i n t h i s overview.
. I n t r o d u c t i o nShallow b u l k a c o u s t i c wave o r surface skimning b u l k wave devices u t i l i z e shear h o r i z o n t a l waves which propagate j u s t below the s u r f a c e o f t h e subs t r a t e . They were f i r s t r e p o r t e d by Yen, e t a l . and Lewis, e t a l . i n 1977.1*2 Since then t h e r e has been a g r e a t deal o f a c t i v i t y i n t h i s area because o f the inherent advantages t h a t they possess over conventional b u l k and surface a c o u s t i c wave devices.3-IB bandpass f i l t e r s and o s c i l l a t o r s , and thus can be incorporated i n t o a v a r i e t y o f s i g n a l processing systems. I n t h i s paper we w i l l discuss the recent advances of t h i s r e l a t i v e l y new c l a s s of planar b u l k a c o u s t i c wave devices. a r e the m a t e r i a l aspects, e q u i v a l e n t c i r c u i t , energy t r a p p i n g and devices development. These devices can be employed as Topics t o be discussed 2. SBAW M a t e r i a l s The important c r i t e r i a uses i n s e l e c t i n g SBAW/SSBW m a t e r i a l s a r e : 1. Large p i e z o e l e c t r i c c o u p l i n g t o shear h o r i z o n t a l wave. 2. Zero o r small p i e z o e l e c t r i c c o u p l i n g t o SAW and o t h e r b u l k waves. 3. Zero o r small beam s t e e r i n g b o t h on the surface and i n t o t h e b u l k . 4. Zero o r small temperature c o e f f i c i e n t o f d e l ay. Using these c r i t e r i a , we have concentrated on w i d e l y used SAW m a t e r i a l s : quartz, b e r l i n i t e , LiNbO and LiTaO 3 ' 3 For s i n g l y r o t a t e d Y-cut q u a r t z and b e r l i n i t e , the above c r i t e r i a a r e s a t i s f i e d w i t h wave propag a t i o n normal t o the X-axis. Here, the SAW and o t h e r b u l k waves c o u p l i n g c o e f f i c i e n t a r e i d e n t ic a l l y zero, so t h a t very spurious f r e e responses a r e obtained. I n a d d i t i o n , the shear h o r i z o n t a l wave s u f f e r s no beam s t e e r i n g on the surface, and f o r two small regions near AT-and BT-crystal, b o t h the temperature c o e f f i c i e n ...
New measurements now permit a comparison to be made with various theories for the propagation characteristics of the strip acoustic surface waveguide in order to determine which theory is the most accurate. These new measurements are presented in the framework of all previously available measurements and theories for the strip waveguide. The ways in which the theories differ are indicated, and recommendations are made as to which theory should be used in which parameter range.
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