Acoustic wave devices

DETAILED DESCRIPTION FIGS.
1A and 1B are perspective and top views, respectively, of a variable delay line 10 which includes electrode structure in accordance with a feature of the invention.
Delay line 10 is comprised of a body of crystalline material 11 in which acoustic waves will propagate.
A conventional surface acoustic wave (SAW) transducer 12 is disposed on the surface of body 11.
Electrical signals to be delayed are received by transducer 12 on input lead 12a.
The transducer converts same to acoustic energy, which propagates through body 11 to output SAW transducer 13 along a path which is substantially parallel to delay line axis 15.
The latter converts the acoustic energy back to electrical form on output lead 13a.
Conventional SAW absorbers 14 disposed at each end of body 11 absorb acoustic wave energy which would otherwise be reflected internally within the device and distort the signals being delayed.
The crystalline material of body 11 is of a type in which regions, or domains, of at least two distinct crystal orientations, interfacing at a so-called domain wall, can coexist stably within the body.
Body 11 is illustratively comprised of three domains--11A, 11B and 11C--with the a crystal axis aligned with device axis 15 in domains 11A and 11C and the b crystal axis aligned with the device axis in domain 11B.
Domains 11A and 11B interface at domain wall 16; domains 11B and 11C interface at domain wall 17.
Walls 16 and 17 are the planes demarcating the regions of different crystal axis orientation.
The orientation of domain walls 16 and 17 with respect to the crystal axes is a characteristic of the crystalline material selected for body 11 and cannot be varied.
Surface acoustic waves propagate along the a axis of the crystalline material at (illustratively) a slower speed than they propagate along the b axis.
Thus, the total delay .
tau.
for surface acoustic waves propagating from transducer 12 to transducer 13 is given by .
tau.
= (l - x)/v.
sub.
a + x/v.
sub.
b (1) where l is the distance between transducers 12 and 13, x is the distance (measured along the device axis) between domain walls 16 and 17, and v