GB1516400A - Elastic waves device for memorizing information - Google Patents

Abstract

1516400 Electro-acoustic memorizing devices THOMSON-CSF 5 Nov 1975 [8 Nov 1974] 45974/75 Heading H3U In a memory device, acoustic waves corresponding to the information to be memorized are emitted by a transducer on a substrate and a first electromagnetic pulse is then applied to the substrate to produce a time-independent spatial pattern which is then fixed; the pattern is subsequently read by applying to the substrate a second electromagnetic pulse which interacts with the pattern to produce second acoustic waves which propagate back to the transducer. A plurality of independently-operating transducers may be provided. A surface wave device, Fig. 1, comprises interdigital transducers 5 on a piezoelectric substrate I and an electrical charge pattern is fixed by a composite layer 4 employing ferroelectric or magnetoelastic phenomena, or employing the modification of charge carrier population in a semiconductor. Alternatively the pattern may be memorized by the substrate itself. The electromagnetic pulses are applied by electrodes 2, 3. On their way back to the transducer the second acoustic waves may be "re-frozen" by a third acoustic wave, and subsequently again "unfrozen" by a fourth acoustic wave. To avoid interference between the signals corresponding to the different transducers 5, the transducers may have non-rectilinear teeth (Fig. 4 not shown). Similarly in a bulk wave device, Fig. 6, transducer 50 may be irregularly shaped, i.e. non-planar; in this embodiment a three-dimensional pattern is produced by applying an electromagnetic pulse to electrodes 20, 30.