Time and space resolution of bulk acoustic waves generated concomitantly with Rayleigh surface waves by an interdigital transducer

摘要

Surface acoustic waves (SAW) and unwanted bulk acoustic waves (BAW) are radiated simultaneously from an interdigital transducer in commonly used SAW crystal substrates. This is a report of tracking BAW groups in their initial passages through a crystal. Directly radiated BAW phase fronts are time resolved via tone burst drive and photomultiplier scan of diffraction patterns produced by a 6328‐Å laser probe interacting with the BAW. Laser tracking of the paths of the energy radiation shows sharply defined BAW beams in 9.5×9.5×26‐mm specimens. Identity of modes, radiation angles, measured counterclockwise from the backward SAW path, and the approximate amplitudes, measured relative to the SAW or to the main BAW lobe are as follows: (a) In Y‐cut Z‐propagating (PPG) LiNbO3 there are (i) equal longitudinal lobes (LL) at 37 ° and at 81 ° with relative amplitudes (RA) ≪0.04; (ii) Y‐Z shear lobes (SL) at 28 °, 54 °, 114 °, and 162 ° with RA’s of 0.12, 0.12, 0.15, and 0.35. (b) In X‐cut Z‐PPG LiNbO3 there are (i) a LL at 40 ° with RA ≪0.04; (ii) X‐Z SL at 24 °, 28 °, and 71 ° with RA’s of 0.35, 0.10, and 0.10; and (iii) a tangential SL at 32 ° with RA of 0.08. (c) In X‐cut Y‐PPG quartz there are LL at 54 ° and at 90 °; RA’s are 0.15 and 0.3. (d) In ST‐cut quartz there are (i) a LL at 26 ° with RA=0.10; (ii) Y′‐X SL at 10 °, 21 °, and 27 °, with RA’s of 0.15, 0.40, and 0.15. (e) In [111]‐cut [11¯0]‐PPG BGO there LL at 53 ° and 90 °; RA’s are 1.0 and 0.9. (f) In [1¯1¯2]‐cut [111-n]‐PPG BGO there are LL at 87 °, 108 °, and 143 ° with RA’s of 0.6, 1.0, and 0.4. In (b) – (e) there is mirror image radiation in the fourth quadrant. The most surprising result here is the presence of broadside radiation. An adequate theoretical explanation is not yet available.